title:
The Dynamics of Non-Crystalline Silica: Insight from Molecular Dynamics
  Computer Simulations

abstract:
  Using a large scale molecular dynamics computer simulation we investigate the
dynamics of a supercooled melt of SiO_2. We find that with increasing
temperature the temperature dependence of the diffusion constants crosses over
from an Arrhenius-law, with activation energies close to the experimental
values, to a power-law dependence. We show that this crossover is related to
the fact that at low temperatures the dynamics of the ions is dominated by
hopping processes, whereas at high temperatures it shows the continuous
flow-like motion proposed by the ideal version of mode-coupling theory (MCT).
Finally we show that at low temperatures the dynamics of the system in the
beta-relaxation regime obeys the factorization property, in agreement with MCT.


title: Holon Pair Condensation and Phase Diagram of High T_c Cuprates

abstract:
  A possibility of holon (boson) pair condensation is explored for hole doped
high T_c cuprates, by using the U(1) slave-boson representation of the t-J
Hamiltonian with the inclusion of hole-hole repulsion. A phase diagram of the
hole doped high T_c cuprates is deduced by allowing both the holon pairing and
spinon pairing. It is shown that the spin gap size remains nearly unchanged
below the holon pair condensation temperature. We find that the s-wave holon
pairing under the condition of d-wave singlet pairing is preferred, thus
allowing d-wave hole pairing.


title:
Exact analytic expression for a subset of fourth virial coefficients of
  polydisperse hard sphere mixtures

abstract:
  We derive an exact, analytic expression for the fourth virial coefficient of
a system of polydisperse spheres under the constraint that the smallest sphere
has a radius smaller than a given function of the radii of the three remaining
particles.


title: Glassy transition and metastability in four-spin Ising model

abstract:
  Using Monte Carlo simulations we show that the three-dimensional Ising model
with four-spin (plaquette) interactions has some characteristic glassy
features. The model dynamically generates diverging energy barriers, which give
rise to slow dynamics at low temperature. Moreover, in a certain temperature
range the model possesses a metastable (supercooled liquid) phase, which is
presumably supported by certain entropy barriers. Although extremely strong,
metastability in our model is only a finite-size effect and sufficiently large
droplets of stable phase divert evolution of the system toward the stable
phase. Thus, the glassy transitions in this model is a dynamic transition,
preceded by a pronounced peak in the specific heat.


title:
An extended pair tunneling model: studies on bilayer splitting and some
  superconducting state properties

abstract:
  We consider an extended version of the pair tunneling model including
interlayer single particle hopping (ISPH) as a complementary process to pair
tunneling. The normal state gap, as found in cuprates, is taken to suppress the
effective ISPH in conformity with the experimental observations, and this in
turn enhances the pair tunneling process. The effective ISPH involves a
probability factor P for which we consider two choices and provide
phenomenological arguments in favour of them. We address the issue of bilayer
splitting by calculating the spectral density function and corresponding
photoemission intensity curves and show that our calculations conform with the
absence of bilayer splitting observed in ARPES experiments on Bi2212. We have
also studied the temperature variation of the superconducting gap and ratio of
the superconducting gap to T_c. Our results, obtained for both the choices of
P, are reasonably in good agreement with those from experiments on cuprate
superconductors. A linear T-dependent choice of P, however, yields a precise
match to the experimantal data of the temperature varying superconducting gap.


title: Diffusion-limited Reactions of hard-core Particles in one-dimension

abstract:
  We investigate three different methods to tackle the problem of
diffusion-limited reactions (annihilation) of hard-core classical particles in
one dimension. We first extend an approach devised by Lushnikov and calculate
for a single species the asymptotic long-time and/or large distance behavior of
the two-point correlation function. Based on a work by Grynberg et al., which
was developed to treat stochastic adsorption-desorption models, we provide in a
second step the exact two-point correlation function (both for one and
two-time) of Lushnikov's model. We then propose a new formulation of the
problem in terms of path integrals for pseudo-fermions. This formalism can be
used to advantage in the multi-species case, specially when applying
perturbative renormalization group techniques.


title:
Duality in the Quantum Dissipative Villain Model and application to
  Mesoscopic Josephson Junction Circuits

abstract:
  We study exact self duality in the model of a Brownian particle in a
washboard (WB) potential which describes a Josephson Junction (JJ) coupled to
an environment, for arbitrary temperature and arbitrary form of the spectral
density of the environment. To this end we introduce the Quantum Dissipative
Villain Model (QDVM), which models tunneling of a degree of freedom coupled to
a linear quantum environment through an infinite set of states. We derive
general exact mappings on various dual discrete representations
(one-dimensional Coulomb gases or surface roughening models) which are exactly
self-dual. Then we show how the QDVM maps exactly onto the WB model and use
duality relations to calculate the leading terms of the total impedance of a JJ
circuit, for general frequency dependence of the spectral density of the
environment and arbitrary temperature.


title: Atomic-scale modeling of the deformation of nanocrystalline metals

abstract:
  Nanocrystalline metals, i.e. metals with grain sizes from 5 to 50 nm, display
technologically interesting properties, such as dramatically increased
hardness, increasing with decreasing grain size. Due to the small grain size,
direct atomic-scale simulations of plastic deformation of these materials are
possible, as such a polycrystalline system can be modeled with the
computational resources available today.
  We present molecular dynamics simulations of nanocrystalline copper with
grain sizes up to 13 nm. Two different deformation mechanisms are active, one
is deformation through the motion of dislocations, the other is sliding in the
grain boundaries. At the grain sizes studied here the latter dominates, leading
to a softening as the grain size is reduced. This implies that there is an
``optimal'' grain size, where the hardness is maximal.
  Since the grain boundaries participate actively in the deformation, it is
interesting to study the effects of introducing impurity atoms in the grain
boundaries. We study how silver atoms in the grain boundaries influence the
mechanical properties of nanocrystalline copper.


title: A generalized spin ladder in a magnetic field

abstract:
  We study the phase diagram of coupled spin-1/2 chains with bilinear and
(chiral) three-spin exchange interactions in a magnetic field. The model is
soluble on a one-parametric line in the space of coupling constants connecting
the limiting cases of a single and two decoupled Heisenberg chains with nearest
neighbour exchange only. We give a complete classification of the low-energy
properties of the integrable system and introduce a numerical method which
allows to study the possible phases of spin ladder systems away from the
soluble line in a magnetic field.


title:
Monte Carlo simulations of copolymers at homopolymer interfaces:
  Interfacial structure as a function of the copolymer density

abstract:
  By means of extensive Monte Carlo simulations of the bond fluctuation model,
we study the effect of adding AB diblock copolymers on the properties of an
interface between demixed homopolymer phases. The parameters are chosen such
that the homopolymers are strongly segregated, and the whole range of copolymer
concentrations in the two phase coexistence region is scanned. We compare the
``mushroom'' regime, in which copolymers are diluted and do not interact with
each other, with the ``wet brush'' regime, where copolymers overlap and
stretch, but are still swollen by the homopolymers. A ``dry brush'' regime is
never entered for our choice of chain lengths. ``Intrinsic'' profiles are
calculated using a block analysis method introduced by us in earlier work. We
discuss density profiles, orientational profiles and contact number profiles.
In general, the features of the profiles are similar at all copolymer
concentrations, however, the profiles in the concentrated regime are much
broader than in the dilute regime. The results compare well with
self-consistent field calculations.


title: The Quantum Dissipative Villain Model

abstract:
  We introduce the Quantum Dissipative Villain (QDV) model as a prototype model
to study tunneling in dissipative quantum mechanics. Dissipation is provided by
a coupled linear environment. In the QDV model, the discrete character of a
tunneling degree of freedom coupled to an environment is explicit, leading to a
rich dual structure.
  We derive general exact mappings of the QDV model on several dual discrete
representations, including pairs of self-dual models, for general linear
environments and arbitrary temperatures. Self-duality allows to write exact
equations for each correlation function of each representation.
  Analogies with the theory of classical network transformations are also
presented. Finally we discuss the fundamental character of the QDV model.
  For instance, the standard Caldeira-Leggett model, which describes mesoscopic
Josephson junctions in a circuit and many other physical systems, is a special
QDV model. The self-dual structure of the QDV model allows then the exact
generalization of the Schmid approximate self-duality to general linear
environments and arbitrary temperatures.


title:
The metal-insulator transition in amorphous Si_{1-x}Ni_x: Evidence for
  Mott's minimum metallic conductivity

abstract:
  We study the metal-insulator transition in two sets of amorphous Si_{1-x}Ni_x
films. The sets were prepared by different, electron-beam-evaporation-based
technologies: evaporation of the alloy, and gradient deposition from separate
Ni and Si crucibles. The characterization included electron and scanning
tunneling microscopy, glow discharge optical emission spectroscopy, and
Rutherford back scattering. Investigating the logarithmic temperature
derivative of the conductivity, w = d ln sigma / d ln T, we observe that, for
insulating samples, w(T) shows a minimum increasing at both low and high T.
Both the minimum value of w and the corresponding temperature seem to tend to
zero as the transition is approached. The analysis of this feature of w(T,x)
leads to the conclusion that the transition in Si_{1-x}Ni_x is very likely
discontinuous at zero temperature in agreement with Mott's original views.


title:
Cluster formulation of spin glasses and the frustrated percolation
  model: statics and dynamics

abstract:
  We study the properties of the q-state frustrated bond percolation model by a
Monte Carlo "bond flip" dynamics, using an algorithm originally devised by
Sweeny and suitably modified to treat the presence of frustration. We analyze
the percolation transition of the model, and find that it falls in the
universality class of the q/2-state ferromagnetic Potts model. We then
investigate the bond flip dynamics of the model, and find that for temperatures
lower than the percolation transition Tp the relaxation functions show a two
step decay, reminiscent of the relaxation of glass forming liquids. The long
time decay (alpha-relaxation) is well fitted for T<Tp by a stretched
exponential function, showing that in this model the relevant mechanism for the
appearing of stretched exponentials is the percolation transition. At very low
temperatures the relaxation functions develop a long plateau, as observed in
glass forming liquids.


title: Crossover Scaling in Dendritic Evolution at Low Undercooling

abstract:
  We examine scaling in two-dimensional simulations of dendritic growth at low
undercooling, as well as in three-dimensional pivalic acid dendrites grown on
NASA's USMP-4 Isothermal Dendritic Growth Experiment. We report new results on
self-similar evolution in both the experiments and simulations. We find that
the time dependent scaling of our low undercooling simulations displays a
cross-over scaling from a regime different than that characterizing Laplacian
growth to steady-state growth.


title: Cavitation induced by explosion in a model of ideal fluid

abstract:
  We discuss the problem of an explosion in the cubic-quintic superfluid model,
in relation to some experimental observations. We show numerically that an
explosion in such a model might induce a cavitation bubble for large enough
energy. This gives a consistent view for rebound bubbles in superfluid and we
indentify the loss of energy between the successive rebounds as radiated waves.
We compute self-similar solution of the explosion for the early stage, when no
bubbles have been nucleated. The solution also gives the wave number of the
excitations emitted through the shock wave.


title: Lectures on Non Perturbative Field Theory and Quantum Impurity Problems

abstract:
  These are lectures presented at the Les Houches Summer School ``Topology and
Geometry in Physics'', July 1998. They provide a simple introduction to non
perturbative methods of field theory in 1+1 dimensions, and their application
to the study of strongly correlated condensed matter problems - in particular
quantum impurity problems. The level is moderately advanced, and takes the
student all the way to the most recent progress in the field: many exercises
and additional references are provided.
  In the first part, I give a sketchy introduction to conformal field theory. I
then explain how boundary conformal invariance can be used to classify and
study low energy, strong coupling fixed points in quantum impurity problems. In
the second part, I discuss quantum integrability from the point of view of
perturbed conformal field theory, with a special emphasis on the recent ideas
of massless scattering. I then explain how these ideas allow the computation of
(experimentally measurable) transport properties in cross-over regimes. The
case of edge states tunneling in the fractional quantum Hall effect is used
throughout the lectures as an example of application.


title:
Quantum Hall Effect: Current Distribution and Existence of Extended
  States

abstract:
  We present a consistent description of the current distribution in the
quantum Hall effect, based on two main ingredients: the location of the
extended states and the distribution of the electric field. We show that the
interaction between electrons produces a boundary line below the Fermi energy,
which extends from source to drain. The existence of this line and that of a
physical boundary are responsible for the formation of a {\em band} of extended
states that carry the Hall current. The number and density of these extended
states are determined by the difference between the energy of this
equipotential boundary line and the energy of the single extended state that
would exist in an infinite system. This is used to prove that the band of
extended states is distributed through the bulk of the sample. We explore the
distribution of the Hall currents and electric fields in by presenting a model
that captures the main features of the charge relaxation processes. Theoretical
predictions based on this model and on the preceding theory are used to
unambiguously explain recent experimental findings.


title:
Crossover exponent for piecewise directed walk adsorption on Sierpinski
  fractals

abstract:
  We study the problem of critical adsorption of piecewise directed random
walks on a boundary of fractal lattices that belong to the Sierpinski gasket
family. By applying the exact real space renormalization group method, we
calculate the crossover exponent $\phi$, associated with the number of adsorbed
steps, for the complete fractal family. We demonstrate that our results are
very close to the results obtained for ordinary self-avoiding walk, and discuss
the asymptotic behaviour of $\phi$ at the fractal to Euclidean lattice
crossover.


title:
Comparison of coherent and weakly incoherent transport models for the
  interlayer magnetoresistance of layered Fermi liquids

abstract:
  The interlayer magnetoresistance of layered metals in a tilted magnetic field
is calculated for two distinct models for the interlayer transport. The first
model involves coherent interlayer transport and makes use of results of
semi-classical or Bloch-Boltzmann transport theory. The second model involves
weakly incoherent interlayer transport where the electron is scattered many
times within a layer before tunneling into the next layer. The results are
relevant to the interpretation of experiments on angular-dependent
magnetoresistance oscillations (AMRO) in quasi-one- and quasi-two-dimensional
metals. We find that the dependence of the magnetoresistance on the direction
of the magnetic field is identical for both models except when the field is
almost parallel to the layers. An important implication of this result is that
a three-dimensional Fermi surface is not necessary for the observation of the
Yamaji and Danner oscillations seen in quasi-two- and quasi-one-dimensional
metals, respectively. A universal expression is given for the dependence of the
resistance at AMRO maxima and minima on the magnetic field and scattering time
(and thus the temperature). We point out three distinctive features of coherent
interlayer transport: (i) a beat frequency in the magnetic oscillations of
quasi-two-dimensional systems, (ii) a peak in the angular-dependent
magnetoresistance when the field is sufficiently large and parallel to the
layers, and (iii) a crossover from a linear to a quadratic field dependence for
the magnetoresistance when the field is parallel to the layers. Properties (i)
and (ii) are compared with published experimental data for a range of
quasi-two-dimensional organic metals and for Sr2RuO4.


title: Optimisation of on-line principal component analysis

abstract:
  Different techniques, used to optimise on-line principal component analysis,
are investigated by methods of statistical mechanics. These include local and
global optimisation of node-dependent learning-rates which are shown to be very
efficient in speeding up the learning process. They are investigated further
for gaining insight into the learning rates' time-dependence, which is then
employed for devising simple practical methods to improve training performance.
Simulations demonstrate the benefit gained from using the new methods.


title: Filling transition for a wedge

abstract:
  We study the formation and the shape of a liquid meniscus in a wedge with
opening angle $2\phi$ which is exposed to a vapor phase. By applying a suitable
effective interface model, at liquid-vapor coexistence and at a temperature
$T_{\phi}$ we find a filling transition at which the height of the meniscus
becomes macroscopically large while the planar walls of the wedge far away from
its center remain nonwet up to the wetting transition occurring at
$T_w>T_{\phi}$. Depending on the fluid and the substrate potential the filling
transition can be either continuous or discontinuous. In the latter case it is
accompanied by a prefilling line extending into the vapor phase of the bulk
phase diagram and describing a transition from a small to a large, but finite,
meniscus height. The filling and the prefilling transitions correspond to
nonanalyticities in the surface and line contributions to the free energy of
the fluid, respectively.


title:
Elasticity, Stability and Ideal Strength of $\beta $-SiC in
  plane-wave-based ab initio calculations

abstract:
  On the basis of the pseudopotential plane-wave(PP-PW) method and the
local-density-functional theory(LDFT), this paper studies energetics,
stress-strain relation, stability and ideal strength of $\beta $-SiC under
various loading modes, where uniform uniaxial extension and tension, biaxial
proportional extension are considered along directions [001] and [111]. The
lattice constant, elastic constants and moduli of equilibrium state are
calculated, and the results agree well with the experimental data. As the four
Si-C bonds along directions [111], [$\bar{1}$11], [11$\bar{1}$] and
[1$\bar{1}$1] are not the same under the loading along [111], internal
relaxation and the corresponding internal displacements must be considered. We
find that, at the beginning of loading, the effect of internal displacement
through shuffle and glide plane diminishes the difference among the four Si-C
bonds length, but will increase the difference at the subsequent loading, which
will result in a crack nucleated on \{111\} shuffle plane and a subsequently
cleavage fracture. Thus the corresponding theoretical strength is 50.8 GPa,
which agrees well with the recent experiment value, 53.4 GPa. However, with the
loading along [001], internal relaxation is not important for tetragonal
symmetry. Elastic constants during the uniaxial tension along [001] are
calculated. Based on the stability analysis with stiffness coefficients, we
find that the spinodal and Born instabilities are triggered almost at the same
strain, which agrees with the previous molecular dynamics simulation. During
biaxial proportional extension, stress and strength vary proportionally with
the biaxial loading ratio at the same longitudinal strain.


title: Autocorrelations from the transfer matrix DMRG method

abstract:
  Extending the transfer matrix DMRG algorithm, we are able to calculate
imaginary time spin autocorrelations with high accuracy (absolute error
$<10^{-6}$) over a wide temperature range ($0<\beta J<20$). After analytic
continuation using the rules of probability theory along with the entropic
prior (MaxEnt), we obtain real frequency spectra for the XY model, the
isotropic Heisenberg and the gaped Heisenberg-Ising model. Available exact
results in some limits allow for a critical evaluation of the quality of
answers expected from this procedure. We find that high precision data are
still insufficient for resolving specific lineshapes such as low frequency
divergences. However, the method is appropriate for identifying low temperature
gaps and peak positions.


title: Crossover properties from random percolation to frustrated percolation

abstract:
  We investigate the crossover properties of the frustrated percolation model
on a two-dimensional square lattice, with asymmetric distribution of
ferromagnetic and antiferromagnetic interactions. We determine the critical
exponents nu, gamma and beta of the percolation transition of the model, for
various values of the density of antiferromagnetic interactions pi in the range
0<pi<0.5. Our data are consistent with the existence of a crossover from random
percolation behavior for pi=0, to frustrated percolation behavior,
characterized by the critical exponents of the ferromagnetic 1/2-state Potts
model, as soon as pi>0.


title: Multifractality of Brownian motion near absorbing polymers

abstract:
  We characterize the multifractal behavior of Brownian motion in the vicinity
of an absorbing star polymer. We map the problem to an O(M)-symmetric
phi^4-field theory relating higher moments of the Laplacian field of Brownian
motion to corresponding composite operators. The resulting spectra of scaling
dimensions of these operators display the convexity properties which are
necessarily found for multifractal scaling but unusual for power of field
operators in field theory. Using a field-theoretic renormalization group
approach we obtain the multifractal spectrum for absorbtion at the core of a
polymer star as an asymptotic series. We evaluate these series using
resummation techniques.


title: Phase Transitions without Thermodynamic Limit

abstract:
  Microcanonical statistics can be well applied to non-extensive systems like
nuclei, atomic clusters and systems at phase transitions of first order with
inhomogeneous configurations like phase separation. No thermodynamic limit has
to be invoked. It allows to determine the transition temperature, latent heat
and surface entropy. In the present paper this is demonstrated for systems of
200 - 3000 Na-, K-, and Fe-atoms at 1 atmosphere. As the energy is an exactly
conserved quantity it is a usefull control parameter to tune through the
development of the transition from the liquid side of the coexistence region
over the evaporation, multifragmentation towards the final gas side.
Microcanonical thermodynamics thus resolves details of the mechanism leading to
the phase transition.


title:
Local non-equilibrium distribution of charge carriers in a
  phase-coherent conductor

abstract:
  We use the scattering matrix approach to derive generalized Bardeen-like
formulae for the conductances between the contacts of a phase-coherent
multiprobe conductor and a tunneling tip which probes its surface. These
conductances are proportional to local partial densities of states, called
injectivities and emissivities. The current and the current fluctuations
measured at the tip are related to an effective local non-equilibrium
distribution function. This distribution function contains the
quantum-mechanical phase-coherence of the charge carriers in the conductor and
is given as products of injectivities and the Fermi distribution functions in
the electron reservoirs. The results are illustrated for measurements on
ballistic conductors with barriers and for diffusive conductors.


title:
On a biphononic origin of the 1125 cm^(-1) absorption band in cuprous
  oxide

abstract:
  We report on the IR spectroscopic studies in both reflection (50-900 cm^{-1})
and transmission (900-3000 cm^{-1}) mode of the vibration spectrum of the
cuprous oxide. A detailed analysis based on a comparison of the temperature
dependences of the absorption band at 1125 cm^{-1} and of IR and Raman active
fundamental vibrations results in assignment of the former to a biphonon.


title: Orbital dynamics in ferromagnetic transition metal oxides

abstract:
  We consider a model of strongly correlated $e_g$ electrons interacting by
superexchange orbital interactions in the ferromagnetic phase of LaMnO$_3$. It
is found that the classical orbital order with alternating occupied $e_g$
orbitals has a full rotational symmetry at orbital degeneracy, and the
excitation spectrum derived using the linear spin-wave theory is gapless. The
quantum (fluctuation) corrections to the order parameter and to the ground
state energy restore the cubic symmetry of the model. By applying a uniaxial
pressure orbital degeneracy is lifted in a tetragonal field and one finds an
orbital-flop phase with a gap in the excitation spectrum. In two dimensions the
classical order is more robust near the orbital degeneracy point and quantum
effects are suppressed. The orbital excitation spectra obtained using finite
temperature diagonalization of two-dimensional clusters consist of a
quasiparticle accompanied by satellite structures. The orbital waves found
within the linear spin-wave theory provide an excellent description of the
dominant pole of these spectra.


title: Short-time Dynamic Behaviour of Critical XY Systems

abstract:
  Using Monte Carlo methods, the short-time dynamic scaling behaviour of
two-dimensional critical XY systems is investigated. Our results for the XY
model show that there exists universal scaling behaviour already in the
short-time regime, but the values of the dynamic exponent $z$ differ for
different initial conditions. For the fully frustrated XY model, power law
scaling behaviour is also observed in the short-time regime.
  However, a violation of the standard scaling relation between the exponents
is detected.


title: Auger Recombination in Semiconductor Quantum Wells

abstract:
  The principal mechanisms of Auger recombination of nonequilibrium carriers in
semiconductor heterostructures with quantum wells are investigated. It is shown
for the first time that there exist three fundamentally different Auger
recombination mechanisms of (i) thresholdless, (ii) quasi-threshold, and (iii)
threshold types. The rate of the thresholdless Auger process depends on
temperature only slightly. The rate of the quasi-threshold Auger process
depends on temperature exponentially. However, its threshold energy essentially
varies with quantum well width and is close to zero for narrow quantum wells.
It is shown that the thresholdless and the quasi-threshold Auger processes
dominate in narrow quantum wells, while the threshold and the quasi-threshold
processes prevail in wide quantum wells. The limiting case of a
three-dimensional (3D)Auger process is reached for infinitely wide quantum
wells. The critical quantum well width is found at which the quasi-threshold
and threshold Auger processes merge into a single 3D Auger process. Also
studied is phonon-assisted Auger recombination in quantum wells. It is shown
that for narrow quantum wells the act of phonon emission becomes resonant,
which in turn increases substantially the coefficient of phonon-assisted Auger
recombination. Conditions are found under which the direct Auger process
dominates over the phonon-assisted Auger recombination at various temperatures
and quantum well widths.


title: Quasiparticle spectra in the vicinity of a d-wave vortex

abstract:
  We discuss the evolution of the local quasiparticle spectral density and the
related tunneling conductance measurable by the scanning tunneling microscope,
as a function of distance r and angle \theta from the vortex core in a
d_{x^2-y^2} superconductor. We consider the effects of electronic disorder and
of a strongly anisotropic tunneling matrix element, and show that in real
materials they will likely obscure the ~1/r asymptotic tail in the zero-bias
tunneling conductance expected from the straightforward semiclassical analysis.
We also give a prediction for the tunneling conductance anisotropy around the
vortex core and establish a connection to the structure of the tunneling matrix
element.


title: Highly Optimized Tolerance: Robustness and Power Laws in Complex Systems

abstract:
  We introduce highly optimized tolerance (HOT), a mechanism that connects
evolving structure and power laws in interconnected systems. HOT systems arise,
e.g., in biology and engineering, where design and evolution create complex
systems sharing common features, including (1) high efficiency, performance,
and robustness to designed-for uncertainties, (2) hypersensitivity to design
flaws and unanticipated perturbations, (3) nongeneric, specialized, structured
configurations, and (4) power laws. We introduce HOT states in the context of
percolation, and contrast properties of the high density HOT states with random
configurations near the critical point. While both cases exhibit power laws,
only HOT states display properties (1-3) associated with design and evolution.


title: Chiral Mesophases of DNA

abstract:
  In the hexagonal columnar phase of chiral polymers a bias towards cholesteric
twist competes with braiding along an average direction. When the chirality is
strong, topological defects proliferate, leading to either a tilt grain
boundary phase or a new ``moire state'' with twisted bond order. This moire
phase can melt leading to a new phase: the chiral hexatic. I will discuss some
recent experimental results from the NIH on DNA liquid crystals in the context
of these theories.


title: Quasiparticle Spectrum of Vortices in Cuprates

abstract:
  The quasiparticle excitation spectrum of an isolated vortex in a clean
layered d-wave superconductor is calculated, using both the Bogoliubov--de
Gennes and the quasiclassical Eilenberger equations. Analytical solutions are
obtained within the model of step-variation of the gap function, adjusting the
Caroli, de Gennes and Matricon approach for low-lying excitations in cuprates.
A large peak in the density of states in the "pancake" vortex core is found,
caused by the two-dimensional and strong coupling nature of high-temperature
superconductivity.


title: Properties of spin-triplet, even-parity superconductors

abstract:
  The physical consequences of the spin-triplet, even-parity pairing that has
been predicted to exist in disordered two-dimensional electron systems are
considered in detail. We show that the presence of an attractive interaction in
the particle-particle spin-triplet channel leads to an instability of the
normal metal that competes with the localizing effects of the disorder. The
instability is characterized by a diverging length scale, and has all of the
characteristics of a continuous phase transition. The transition and the
properties of the ordered phase are studied in mean-field theory, and by taking
into account Gaussian fluctuations. We find that the ordered phase is indeed a
superconductor with an ordinary Meissner effect and a free energy that is lower
than that of the normal metal. Various technical points that have given rise to
confusion in connection with this and other manifestations of odd-gap
superconductivity are also discussed.


title: Bound States in the Vortex Core

abstract:
  The quasiparticle excitation spectrum of isolated vortices in clean layered
d-wave superconductors is calculated. A large peak in the density of states in
the "pancake" vortex core is found, in an agreement with the recent
experimental data for high-temperature superconductors.


title:
Quasiparticle Excitation Spectrum of an Isolated Vortex in a
  High--Temperature Superconductor

abstract:
  The quasiparticle energy spectrum of an isolated vortex in a clean layered
d-wave superconductor is calculated. The Bogoliubov--de Gennes equations are
solved perturbatively, within the model of step-variation of the gap function,
adjusting the Caroli, de Gennes and Matricon approach for low-lying excitations
in cuprates. A large peak in the density of states in a "pancake" vortex is
found, as a consequence of two-dimensionality and strong coupling.


title: Anomalous Low Temperature States in CeNi2Ge2

abstract:
  Ambient pressure studies on high purity single crystals of the stoichiometric
4f-electron metal CeNi2Ge2 reveal anomalous low temperature forms of the
resistivity which challenge our understanding of the metallic state.
Comparisons are made with the isostructural and isoelectronic compound CePd2Si2
near the border of magnetism at high pressure, and possible reasons for this
novel non-Fermi liquid form of the resistivity are discussed. Phase diagrams of
further anomalies are presented, which involve a loss of resistance at low
temperature in some samples of CeNi2Ge2 and unexpected high pressure phases.


title:
Temperature Evolution of the Pseudogap State in the Infra-Red Response
  of Underdoped La_(2-x)Sr_xCuO_4

abstract:
  The ab-plane optical spectra of two single crystals of underdoped
La_(2-x)Sr_xCuO_4 were investigated. The reflectivity of
La_(1.87)Sr_(0.13)CuO_4 has been measured in the frequency range 30- 9,000 cm-1
(0.004 -- 1 eV) both parallel and perpendicular to the CuO_2 planes, whereas
La_(1.86)Sr_(0.14)CuO_4 was studied only in the ab-plane. The extended Drude
model shows that the frequency-dependent effective scattering rate
1/tau(omega)is strongly suppressed below the high-frequency straight-line
extrapolation, a signature of the pseudogap state. This suppression can be seen
from temperatures below the superconducting transition up to 400 K. In the case
of underdoped LSCO the straight-line extrapolation is temperature independent
below 200 K, whereas above 200 K there is a strong temperature dependence of
the high-frequency 1/tau(omega,T). The out-of-plane direction is also examined
for evidence of the pseudogap state.


title: Half-filled Landau level as a Fermi liquid of dipolar quasiparticles

abstract:
  In this paper we study the relation between the conventional
Fermion-Chern-Simons (FCS) theory of the half-filled Landau level (nu=1/2), and
alternate descriptions that are based on the notion of neutral quasi-particles
that carry electric dipole moments. We have previously argued that these two
approaches are equivalent, and that e.g., the finite compressibility obtained
in the FCS approach is also obtained from the alternate approach, provided that
one properly takes into account a peculiar symmetry of the dipolar
quasiparticles --- the invariance of their energy to a shift of their center of
mass momentum. Here, we demonstrate the equivalence of these two approaches in
detail. We first study a model where the charge and flux of each fermion is
smeared over a radius Q^{-1} where results can be calculated to leading order
in the small parameter Q/k_f. We study two dipolar-quasiparticle descriptions
of the nu=1/2 state in the small-Q model and confirm that they yield the same
density response function as in the FCS approach. We also study the
single-particle Green's function and the effective mass, for one form of
dipolar quasiparticles, and find the effective mass to be infra-red divergent,
exactly as in the FCS approach. Finally, we propose a form for a Fermi-liquid
theory for the dipolar quasiparticles, which should be valid in the physical
case where Q is infinite.


title: Excess conductance in normal-metal/superconductor junctions

abstract:
  The current-voltage characteristics of Au/InOx/Pb tunnel junctions exhibit
peculiar zero-bias anomalies. At low temperature the zero-bias resistance
attains values that are smaller than the normal state resistance by a factor
that often esceeds 2. The width of this anomaly increases with the thickness of
the InOx layer. The possibility that these features arise from the nature of
the barrier being an Anderson insulator is discussed.


title: Power-Laws in Nonlinear Granular Chain under Gravity

abstract:
  The signal generated by a weak impulse propagates in an oscillatory way and
dispersively in a gravitationally compacted granular chain. For the power-law
type contact force, we show analytically that the type of dispersion follows
power-laws in depth. The power-law for grain displacement signal is given by
$h^{-1/4(1-1/p)}$ where $h$ and $p$ denote depth and the exponent of contact
force, and the power-law for the grain velocity is $h^{-1/4({1/3}+1/p)}$. Other
depth-dependent power-laws for oscillation frequency, wavelength, and period
are given by combining above two and the phase velocity power-law
$h^{1/2(1-1/p)}$. We verify above power-laws by comparing with the data
obtained by numerical simulations.


title:
Parallel updating cellular automaton models of driven diffusive
  Frenkel-Kontorova-type systems

abstract:
  Three cellular automaton (CA) models of increasing complexity are introduced
to model driven diffusive systems related to the generalized Frenkel-Kontorova
(FK) models recently proposed by Braun [Phys.Rev.E58, 1311 (1998)]. The models
are defined in terms of parallel updating rules. Simulation results are
presented for these models. The features are qualitatively similar to those
models defined previously in terms of sequentially updating rules. Essential
features of the FK model such as phase transitions, jamming due to atoms in the
immobile state, and hysteresis in the relationship between the fraction of
atoms in the running state and the bias field are captured. Formulating in
terms of parallel updating rules has the advantage that the models can be
treated analytically by following the time evolution of the occupation on every
site of the lattice. Results of this analytical approach are given for the two
simpler models. The steady state properties are found by studying the stable
fixed points of a closed set of dynamical equations obtained within the
approximation of retaining spatial correlations only upto two nearest
neighboring sites. Results are found to be in good agreement with numerical
data.


title: Phonon-phason coupling in icosahedral quasicrystals

abstract:
  From relaxation simulations of decoration-based quasicrystal structure models
using microscopically based interatomic pair potentials, we have calculated the
(usually neglected) phonon-phason coupling constant. Its sign is opposite for
the two alloys studied, i-AlMn and i-(Al,Cu)Li; a dimensionless measure of its
magnitude relative to the phonon and phason elastic constants is of order 1/10,
suggesting its effects are small but detectable. We also give a criterion for
when phonon-phason effects are noticeable in diffuse tails of Bragg peaks.


title: Exact ground and excited states of a t-J ladder doped with two holes

abstract:
  A two chain ladder model is considered described by the strong coupling
$t-t^\prime-J-J^\prime$ Hamiltonian. For the case of two holes moving in a
background of antiferromagnetically interacting spins, exact, analytical
results are derived for the ground state energy and low-lying excitation
spectrum. The ground state is a bound state of two holes with total spin S=0.
The charge excitation is gapless and the spin excitation has a gap. The
corresponding wavefunctions are also exactly determined. The bound hole pair is
found to have symmetry of the d-wave type. In the limit of strong rung
coupling, the model maps onto an effective hard core boson model which exhibits
dominant superconducting pairing correlations.


title: Fast algorithm for calculating two-photon absorption spectra

abstract:
  We report a numerical calculation of the two-photon absorption coefficient of
electrons in a binding potential using the real-time real-space higher-order
difference method. By introducing random vector averaging for the intermediate
state, the task of evaluating the two-dimensional time integral is reduced to
calculating two one-dimensional integrals. This allows the reduction of the
computation load down to the same order as that for the linear response
function. The relative advantage of the method compared to the straightforward
multi-dimensional time integration is greater for the calculation of non-linear
response functions of higher order at higher energy resolution.


title: Inelastic tunneling through mesoscopic structures

abstract:
  Our objective is to study resonant tunneling of an electron in the presence
of inelastic scattering by optical phonons. Using a recently developed
technique, based on exact mapping of a many-body problem onto a one-body
problem, we compute transmission through a single site at finite temperatures.
We also compute current through a single site at finite temperatures and an
arbitrary strength of the potential drop over the tunneling region.
Transmission vs. incident electron energy at finite temperatures displays
additional peaks due to phonon absorption processes. Current at a voltage bias
smaller than the phonon frequency is dominated by elastic processes. We apply
the method to an electron tunneling through the Aharonov-Bohm ring coupled to
optical phonons. Elastic part of electron-phonon scattering does not affect the
phase of the electron. Dephasing occurs only through inelastic processes.


title:
Nonlinear dynamic susceptibilities of interacting and noninteracting
  nanoparticle systems

abstract:
  The linear and cubic dynamic susceptibilities of solid dispersions of
nano-sized maghemite particles have been measured for three samples with a
volume concentration of magnetic particles ranging from 0.3 % to 17 %, in order
to study the effect of dipole-dipole interactions. Significant differences
between the dynamic response of the three samples are observed. The dynamic
susceptibilities of the most dilute sample compare reasonably well with an
existing theory for the linear and cubic dynamic susceptibilities of an
assembly of noninteracting, uniaxial magnetic particles. The nonlinear dynamic
response of the most concentrated sample exhibits at low temperatures some of
the features observed in a Ag(11 at.% Mn) spin glass.


title:
Thermodynamics of the t-J Ladder: A Stable Finite Temperature Density
  Matrix Renormalization Group Calculation

abstract:
  Accurate numerical simulations of a doped t-J model on a two-leg ladder are
presented for the particle number, chemical potential, magnetic susceptibility
and entropy in the limit of large exchange coupling on the rung using a finite
temperature density matrix renormalization group (TDMRG) method. This required
an improved algorithm to achieve numerical stability down to low temperatures.
The thermal dissociation of hole pairs and of the rung singlets are separately
observed and the evolution of the hole pair binding energy and magnon spin gap
with hole doping is determined.


title:
Local Optical Spectroscopy in Quantum Confined Systems: A Theoretical
  Description

abstract:
  A theoretical description of local absorption is proposed in order to
investigate spectral variations on a length scale comparable with the extension
of the relevant quantum states. A general formulation is derived within the
density-matrix formalism including Coulomb correlation, and applied to the
prototypical case of coupled quantum wires. The results show that excitonic
effects may have a crucial impact on the local absorption with implications for
the spatial resolution and the interpretation of near-field optical spectra.


title:
Monte Carlo Simulations of a Generalized n--spin facilitated kinetic
  Ising Model

abstract:
  A kinetic Ising model is analyzed where spin variables correspond to lattice
cells with mobile or immobile particles. Introducing additional restrictions
for the flip processes according to the n-spin facilitated kinetic Ising model
and using Monte Carlo methods we study the freezing process under the influence
of an additional nearest-neighbor interaction. The stretched exponential decay
of the auto-correlation function is observed and the exponent $\gamma$ as well
as the relaxation time are determined depending on the activation energy $h$
and the short range coupling $J$. The magnetization corresponding to the
density of immobile particles is found to be the controlling parameter for the
dynamic evolution.


title: Critical Relaxation and Critical Exponents

abstract:
  Dynamic relaxation of the XY model and fully frustrated XY model quenched
from an initial ordered state to the critical temperature or below is
investigated with Monte Carlo methods. Universal power law scaling behaviour is
observed. The dynamic critical exponent $z$ and the static exponent $\eta$ are
extracted from the time-dependent Binder cumulant and magnetization. The
results are competitive to those measured with traditional methods.


title:
Spatio-temporal organization of vehicles in a cellular automata model of
  traffic with 'slow-to-start' rule

abstract:
  The spatio-temporal organizations of vehicular traffic in cellular-automata
models with "slow-to-start" rules are qualitatively different from those in the
Nagel-Schreckenberg (NaSch) model of highway traffic. Here we study the effects
of such a slow-to-start rule, introduced by Benjamin, Johnson and Hui (BJH), on
the the distributions of the distance-headways, time-headways, jam sizes and
sizes of the gaps between successive jams by a combination of approximate
analytical calculations and extensive computer simulations. We compare these
results for the BJH model with the corresponding results for the NaSch model
and interpret the qualitative differences in the nature of the spatio-temporal
organizations of traffic in these two models in terms of a phase separation of
the traffic caused by the slow-to-start rule in the BJH model.


title: Dynamic Simulations of the Kosterlitz-Thouless Phase Transition

abstract:
  Based on the short-time dynamic scaling form, a novel dynamic approach is
proposed to tackle numerically the Kosterlitz-Thouless phase transition. Taking
the two-dimensional XY model as an example, the exponential divergence of the
spatial correlation length, the transition temperature $T_{KT}$ and all
critical exponents are computed. Compared with Monte Carlo simulations in
equilibrium, we obtain data at temperatures nearer to $T_{KT}$.


title: Nano-ploughed Josephson Junctions as on-chip Radiation Sources

abstract:
  A new technique is presented which enables the fabrication of highly
transparent Josephson junctions in combination with mesoscopic devices. We
utilize a modified AFM tip to plough grooves into superconducting material,
thus defining a weak link. This weak link is made within the superconducting
split-gates, which are used to electrostatically form a conventional quantum
dot and serves as a source of millimeter wave radiation around 100 GHz. We show
the characteristics of typical junctions built and discuss their high-frequency
properties. We find that the millimeter wave emission of the weak link leads to
a bolometric effect in the case of quantum point contact spectroscopy.


title:
Ferromagnetism and the temperature-dependent electronic structure in
  thin Hubbard films

abstract:
  The magnetic behavior of thin ferromagnetic itinerant-electron films is
investigated within the strongly correlated single-band Hubbard model. For its
approximate solution we apply a generalization of the modified alloy analogy
(MAA) to deal with the modifications due to the reduced translational symmetry.
The theory is based on exact results in the limit of strong Coulomb interaction
which are important for a reliable description of ferromagnetism. Within the
MAA the actual type of the alloy analogy is determined selfconsistently. The
MAA allows, in particular, the investigation of quasiparticle lifetime effects
in the paramagnetic as well as the ferromagnetic phase. For thin fcc(100) and
fcc(111) films the layer magnetizations are discussed as a function of
temperature as well as film thickness. The magnetization at the surface-layer
is found to be reduced compared to the inner layers. This reduction is stronger
in fcc(100) than in fcc(111) films. The magnetic behavior can be
microscopically understood by means of the layer-dependent spectral density and
the quasiparticle density of states. The quasiparticle lifetime that
corresponds to the width of the quasiparticle peaks in the spectral density is
found to be strongly spin- and temperature-dependent.


title: Polyelectrolytes in Solution - Recent Computer Simulations

abstract:
  We present a short overview over recent MD simulations of systems of fully
flexible polyelectrolyte chains with explicitly treated counter ions using the
full Coulomb potential. The main emphasis is given on the conformational
properties of the polymers, with a short discussion on counter ion
condensation.


title: Anomalous Kondo-effect in Quantum Dot at non-zero bias

abstract:
  We present measurements on the Kondo-effect in a small quantum dot connected
strongly to one lead and weakly to the other. The conductance of the dot
reveals an offset of the Kondo resonance at zero magnetic field. While the
resonance persists in the negative bias regime, it is suppressed in the
opposite direction. This demonstrates the pinning of the Kondo resonance to the
Fermi levels of the left and right lead. As an outlook we exploit the spin
blockade effect to gain information about the spin state of the quantum dot in
the Kondo regime.


title: Navier-Stokes Equations for Generalized Thermostatistics

abstract:
  Tsallis has proposed a generalization of Boltzmann-Gibbs thermostatistics by
introducing a family of generalized nonextensive entropy functionals with a
single parameter $q$. These reduce to the extensive Boltzmann-Gibbs form for
$q=1$, but a remarkable number of statistical and thermodynamic properties have
been shown to be $q$-invariant -- that is, valid for any $q$. In this paper, we
address the question of whether or not the value of $q$ for a given viscous,
incompressible fluid can be ascertained solely by measurement of the fluid's
hydrodynamic properties. We find that the hydrodynamic equations expressing
conservation of mass and momentum are $q$-invariant, but that for conservation
of energy is not. Moreover, we find that ratios of transport coefficients may
also be $q$-dependent. These dependences may therefore be exploited to measure
$q$ experimentally.


title: Quantum Hall plateau transitions in disordered superconductors

abstract:
  We study a delocalization transition for non-interacting quasiparticles
moving in two dimensions, which belongs to a new symmetry class. This symmetry
class can be realised in a dirty, gapless superconductor in which time reversal
symmetry for orbital motion is broken, but spin rotation symmetry is intact. We
find a direct transition between two insulating phases with quantized Hall
conductances of zero and two for the conserved quasiparticles. The energy of
quasiparticles acts as a relevant, symmetry-breaking field at the critical
point, which splits the direct transition into two conventional plateau
transitions.


title:
Demonstration of the quantum mechanics applicability limits and solution
  of the irreversibility problem

abstract:
  An experimental study of the applicability of mechanics equations to
describing the process of equilibrium establishing in an isolated spin system
was performed. The time-reversion effects were used at the experiments. It was
demonstrated, that the equations of mechanics do not describe the experimental
results. The demonstration of the incomleteness of quantum mechanics
description of the macrosystems annuls the contradiction which lays in the
basis of the irreversibility problem.


title:
Positional Disorder (Random Gaussian Phase Shifts) in the Fully
  Frustrated Josephson Junction Array (2D XY Model)

abstract:
  We consider the effect of positional disorder on a Josephson junction array
with an applied magnetic field of f=1/2 flux quantum per unit cell. This is
equivalent to the problem of random Gaussian phase shifts in the fully
frustrated 2D XY model. Using simple analytical arguments and numerical
simulations, we present evidence that the ground state vortex lattice of the
pure model becomes disordered, in the thermodynamic limit, by any amount of
positional disorder.


title: The structure of large 3He-4He mixed drops around a dopant molecule

abstract:
  We have investigated how helium atoms are distributed within a mixed
$^3$He$_{N_3}$-$^4$He$_{N_4}$ large drop with $N_3 \gg N_4$. For drops doped
with a SF$_6$ molecule or a Xe atom, we have found that the number of $^3$He
atoms within the volume containing the first two solvation shells increases
when $N_4$ decreases in a way such that these dopants may be in a superfluid
environment for $N_4 \geq$ 60, which gradually disappears as $N_4$ decreases.
The result is in qualitative agreement with recent experimental data.


title:
Mesoscopic phenomena in Bose-Einstein systems: Persistent currents,
  population oscillations and quantal phases

abstract:
  Mesoscopic phenomena - including population oscillations and persistent
currents driven by quantal phases - are explored theoretically in the context
of multiply-connected Bose-Einstein systems composed of trapped alkali-metal
gas atoms. These atomic phenomena are bosonic analogues of electronic
persistent currents in normal metals and Little-Parks oscillations in
superconductors.


title: Spin current in ferromagnet/insulator/superconductor junctions

abstract:
  A theory of spin polarized tunneling spectroscopy based on a scattering
theory is given for tunneling junctions between ferromagnets and d-wave
superconductors. The spin filtering effect of an exchange field in the
insulator is also treated. We clarify that the properties of the Andreev
reflection are largely modified due to a presence of an exchange field in the
ferromagnets, and consequently the Andreev reflected quasiparticle shows an
evanescent-wave behavior depending on the injection angle of the quasiparticle.
Conductance formulas for the spin current as well as the charge current are
given as a function of the applied voltage and the spin-polarization in the
ferromagnet for arbitrary barrier heights. It is shown that the surface bound
states do not contribute to the spin current and that the zero-bias conductance
peak expected for a d-wave superconductor splits into two peaks under the
influence of the exchange interaction in the insulator.


title: Self-Organized States in Cellular Automata: Exact Solution

abstract:
  The spatial structure, fluctuations as well as all state probabilities of
self-organized (steady) states of cellular automata can be found (almost)
exactly and {\em explicitly} from their Markovian dynamics. The method is shown
on an example of a natural sand pile model with a gradient threshold.

categories: cond-mat.stat-mech adap-org astro-ph comp-gas nlin.AO nlin.CG physics.class-ph physics.flu-dyn physics.plasm-ph


title:
Quasi-one-dimensional charge density wave in electromagnetic field
  arbitrarily oriented to conducting chains: generalized Frohlich relations

abstract:
  We derive equations for the collective CDW-current transverse conducting
chains in a quasi-one-dimensional CDW-conductor. Generalized Frohlich relations
between the transverse currents and phase gradients are due to the polarization
corrections to the 1+1 chiral anomaly Lagrangean. The CDW Hall constant is
calculated.


title:
Magnetoresistance, Micromagnetism and Domain Wall Effects in Epitaxial
  Fe and Co Structures with Stripe Domains

abstract:
  We review our recent magnetotransport and micromagnetic studies of
lithographically defined epitaxial thin film structures of bcc Fe and hcp Co
with stripe domains. Micromagnetic structure and resistivity anisotropy are
shown to be the predominant sources of low field magnetoresistance (MR) in
these microstructures, with domain wall (DW) effects smaller but observable
(DW-MR $\lesssim 1 %$). In Fe, at low temperature, in a regime in which fields
have a significant effect on electron trajectories, a novel negative DW
contribution to the resistivity is observed. In hcp Co microstructures,
temperature dependent transport measurements for current perpendicular and
parallel to walls show that any additional resistivity due to DW scattering is
very small.


title: Steady-State Cracks in Viscoelastic Lattice Models

abstract:
  We study the steady-state motion of mode III cracks propagating on a lattice
exhibiting viscoelastic dynamics. The introduction of a Kelvin viscosity $\eta$
allows for a direct comparison between lattice results and continuum
treatments. Utilizing both numerical and analytical (Wiener-Hopf) techniques,
we explore this comparison as a function of the driving displacement $\Delta$
and the number of transverse sites $N$. At any $N$, the continuum theory misses
the lattice-trapping phenomenon; this is well-known, but the introduction of
$\eta$ introduces some new twists. More importantly, for large $N$ even at
large $\Delta$, the standard two-dimensional elastodynamics approach completely
misses the $\eta$-dependent velocity selection, as this selection disappears
completely in the leading order naive continuum limit of the lattice problem.

categories: cond-mat.soft cond-mat.mtrl-sci nlin.PS patt-sol


title:
Chaos in Quantum Dots: Dynamical Modulation of Coulomb Blockade Peak
  Heights

abstract:
  The electrostatic energy of an additional electron on a conducting grain
blocks the flow of current through the grain, an effect known as the Coulomb
blockade. Current can flow only if two charge states of the grain have the same
energy; in this case the conductance has a peak. In a small grain with
quantized electron states, referred to as a quantum dot, the magnitude of the
conductance peak is directly related to the magnitude of the wavefunction near
the contacts to the dot. Since dots are generally irregular in shape, the
dynamics of the electrons is chaotic, and the characteristics of Coulomb
blockade peaks reflects those of wavefunctions in chaotic systems. Previously,
a statistical theory for the peaks was derived by assuming these wavefunctions
to be completely random. Here we show that the specific internal dynamics of
the dot, even though it is chaotic, modulates the peaks: because all systems
have short-time features, chaos is not equivalent to randomness. Semiclassical
results are derived for both chaotic and integrable dots, which are
surprisingly similar, and compared to numerical calculations. We argue that
this modulation, though unappreciated, has already been seen in experiments.


title: Interaction of quantum Hall systems with waveguide elastic modes

abstract:
  An interaction of non-uniform plane elastic modes of the waveguide type with
monolayer and double-layer quantum Hall systems is considered. It is shown,
that unlike the case of the surface acoustic wave propagation, the restriction
on maximal values of the wave vectors for which the velocity shift can be
observed experimentally does not take place for the waveguide modes. In case of
study of incompressible fractional quantum Hall states the effect can be used
for measuring a dependence of the effective magnetic length on the filling
factor and for observing phase transitions in double-layer system under the
interlayer distance variation


title:
Electric field and potential around localized scatterers in thin metal
  films studied by scanning tunneling potentiometry

abstract:
  Direct observation of electric potential and field variation near local
scatterers like grain boundaries, triple points and voids in thin platinum
films studied by scanning tunneling potentiometry is presented. The field is
highest at a void, followed by a triple point and a grain boundary. The local
field near a void can even be four orders of magnitude higher than the
macroscopic field. This indicates that the void is the most likely place for an
electromigration induced failure. The field build up near a scatterer strongly
depends on the grain connectivity which is quantified by the average grain
boundary reflection coefficient, estimated from the resistivity.


title:
Phase Coherence Appearance in Thin Superconducting Film with Strong
  Disorders. The Return to the Mendelssohn Model

abstract:
  It is shown that transition from the mixed state without the phase coherence
to the mixed state with the long-range phase coherence (i.e. to the Abrikosov
state) of superconductors without disorder must be first order phase
transition. The phase coherence appearance in thin superconducting film with
strong disorder is considered. The observed smooth transition is explained by
increasing of the effective fluctuation dimensionality (from zero to one) in
superconductors with strong disorder. Mendelssohn model is used for the
explanation of the resistive properties of film with strong disorder.


title: Symmetric Vertex Models on Planar Random Graphs

abstract:
  We solve a 4-(bond)-vertex model on an ensemble of 3-regular Phi3 planar
random graphs, which has the effect of coupling the vertex model to 2D quantum
gravity. The method of solution, by mapping onto an Ising model in field, is
inspired by the solution by Wu et.al. of the regular lattice equivalent -- a
symmetric 8-vertex model on the honeycomb lattice, and also applies to higher
valency bond vertex models on random graphs when the vertex weights depend only
on bond numbers and not cyclic ordering (the so-called symmetric vertex
models).
  The relations between the vertex weights and Ising model parameters in the
4-vertex model on Phi3 graphs turn out to be identical to those of the
honeycomb lattice model, as is the form of the equation of the Ising critical
locus for the vertex weights. A symmetry of the partition function under
transformations of the vertex weights, which is fundamental to the solution in
both cases, can be understood in the random graph case as a change of
integration variable in the matrix integral used to define the model.
  Finally, we note that vertex models, such as that discussed in this paper,
may have a role to play in the discretisation of Lorentzian metric quantum
gravity in two dimensions.


title:
Effect of Ferromagnetic Spin Correlations on Superconductivity in
  Ferromagnetic Metals

abstract:
  We study the renormalization of the quasiparticle properties in weak
ferromagnetic metals, due to spin fluctuations, away from the quantum critical
point for small magnetic moment. We explain the origin of the s-wave
superconducting instability in the ferromagnetic phase and find that the vertex
corrections are small and Migdal's theorem is satisfied away from the quantum
critical point.


title: Negative Specific Heat in Astronomy, Physics and Chemistry

abstract:
  Starting from Antonov's discovery that there is no maximum to the entropy of
a gravitating system of point particles at fixed energy in a spherical box if
the density contrast between centre and edge exceeds 709, we review progress in
the understanding of gravitational thermodynamics. We pinpoint the error in the
proof that all systems have positive specific heat and say when it can occur.
We discuss the development of the thermal runaway in both the gravothermal
catastrophe and its inverse. The energy range over which microcanonical
ensembles have negative heat capacity is replaced by a first order phase
transition in the corresponding canonical ensembles. We conjecture that all
first order phase transitions may be viewed as caused by negative heat
capacities of units within them. We find such units in the theory of
ionisation, chemical dissociation and in the Van der Waals gas so these
concepts are applicable outside the realm of stars, star clusters and black
holes.


title: Domain wall dynamics in soft magnetic materials

abstract:
  The dynamics of a domain wall in magnetostrictive materials is investigated.
The domain wall is modeled by a d-dimensional interface moving in a
d+1-dimensional environment. Long-range demagnetization effects and quenched
disorder are considered, while the external magnetic field is increased at
constant rate. Exact expressions for the average interface velocity and
susceptibility are obtained, resulting that the system is critical when the
demagnetization constant and the average interface velocity vanishes. The
critical exponents are computed to O(4-d). Our predictions are compared with
numerical simulations and Barkhausen noise measurements reported in the
literature.


title:
Investigation of soliton bound states in the Raman spectrum of pure and
  doped spin-Peierls chains

abstract:
  We investigate the occurrence of singlet bound states in the Raman spectrum
of dimerized spin 1/2 chains by Exact Diagonalization and Density Matrix
Renormalization Group techniques. We predict that several bulk $\delta$-peaks
could be observed in pure systems. Furthermore, we show that new low energy
lines arise from non-magnetic impurity doping. These features are interpreted
in terms of soliton-antisoliton and soliton-impurity bound states respectively.
Energies and spectral weights associated with these bound states are sensitive
to lattice relaxation effects. Our results are discussed in the context of the
inorganic spin-Peierls compound CuGeO$_3$ and quantitatively compared to recent
Raman experiments.


title:
Shot noise and coherent multiple charge transfer in superconducting
  quantum point-contacts

abstract:
  We analyze the shot noise in a voltage biased superconducting quantum
point-contact. Results are presented for the single channel case with arbitrary
transmission. In the limit of very low transmission it is found that the
effective charge, defined from the noise-current ratio, exhibits a step-like
behavior as a function of voltage with well defined plateaus at integer values
of the electronic charge. This multiple charge corresponds to the transmitted
charge in a Multiple Andreev Reflection (MAR) process. This effect gradually
disappears for increasing transmission due to interference between different
MAR processes.


title:
Tsallis statistics with normalized q-expectation values is
  thermodynamically stable: illustrations

abstract:
  We present a study of both the ``Iterative Procedure'' and the ``$\beta \to
\beta'$ transformation'', proposed by Tsallis et al (Physica A261, 534) to find
the probabilities $p_i$ of a system to be in a state with energy $\epsilon_i$,
within the framework of a generalized statistical mechanics. Using stability
and convexity arguments, we argue that the iterative procedure does not always
provide the right temperature dependence of thermodynamic observables. In
addition, we show how to get the correct answers from the ``$\beta \to \beta'$
transformation''. Our results provide an evidence that the Tsallis statistics
with normalized q-expectation values is stable for all ranges of temperatures.
We also show that the cut-off in the computation of probabilities is required
to achieve the stable solutions.


title: Dispersive stabilization of the inverse cascade for the Kolmogorov flow

abstract:
  It is shown by perturbation techniques and numerical simulations that the
inverse cascade of kink-antikink annihilations, characteristic of the
Kolmogorov flow in the slightly supercritical Reynolds number regime, is halted
by the dispersive action of Rossby waves in the beta-plane approximation. For
beta tending to zero, the largest excited scale is proportional to the
logarithm of one over beta and differs strongly from what is predicted by
standard dimensional phenomenology which ignores depletion of nonlinearity.


title: Dynamical Model and Path Integral Formalism for Hubbard Operators

abstract:
  In this paper, the possibility to construct a path integral formalism by
using the Hubbard operators as field dynamical variables is investigated. By
means of arguments coming from the Faddeev-Jackiw symplectic Lagrangian
formalism as well as from the Hamiltonian Dirac method, it can be shown that it
is not possible to define a classical dynamics consistent with the full algebra
of the Hubbard $X$-operators. Moreover, from the Faddeev-Jackiw symplectic
algorithm, and in order to satisfy the Hubbard $X$-operators commutation rules,
it is possible to determine the number of constraint that must be included in a
classical dynamical model. Following this approach it remains clear how the
constraint conditions that must be introduced in the classical Lagrangian
formulation, are weaker than the constraint conditions imposed by the full
Hubbard operators algebra. The consequence of this fact is analyzed in the
context of the path integral formalism. Finally, in the framework of the
perturbative theory, the diagrammatic and the Feynman rules of the model are
discussed.


title: Broadband Dielectric Spectroscopy on Glass-Forming Propylene Carbonate

abstract:
  Dielectric spectroscopy covering more than 18 decades of frequency has been
performed on propylene carbonate in its liquid and supercooled-liquid state.
Using quasi-optic submillimeter and far-infrared spectroscopy the dielectric
response was investigated up to frequencies well into the microscopic regime.
We discuss the alpha-process whose characteristic timescale is observed over 14
decades of frequency and the excess wing showing up at frequencies some three
decades above the peak frequency. Special attention is given to the
high-frequency response of the dielectric loss in the crossover regime between
alpha-peak and boson-peak. Similar to our previous results in other glass
forming materials we find evidence for additional processes in the crossover
regime. However, significant differences concerning the spectral form at high
frequencies are found. We compare our results to the susceptibilities obtained
from light scattering and to the predictions of various models of the glass
transition.


title: A first principle computation of the thermodynamics of glasses

abstract:
  We propose a first principle computation of the equilibrium thermodynamics of
simple fragile glasses starting from the two body interatomic potential. A
replica formulation translates this problem into that of a gas of interacting
molecules, each molecule being built of m atoms, and having a gyration radius
(related to the cage size) which vanishes at zero temperature. We use a small
cage expansion, valid at low temperatures, which allows to compute the cage
size, the specific heat (which follows the Dulong and Petit law), and the
configurational entropy.


title:
Comment on ``Activation Gaps and Mass Enhancement of Composite
  Fermions''

abstract:
  In a recent Letter (Phys. Rev. Lett. 81, 4200 (1998)) Park and Jain presented
results of gap calculations for polarized states at \nu=1/3, 2/5, 3/7 and 4/9.
They computed the effects on the gaps due the finite width of the interfacial
wave function (wf). In this Comment, it is shown that the reduction of the gaps
due to the finite width of the wf is overestimated by about a factor of two.
The agreement between theoretical and experimental gap values cannot be taken
seriously, but results from an incorrect determination of the width parameter.


title:
Simple Bosonization Solution of the 2-channel Kondo Model: I. Analytical
  Calculation of Finite-Size Crossover Spectrum

abstract:
  We present in detail a simple, exact solution of the anisotropic 2-channel
Kondo (2CK) model at its Toulouse point. We reduce the model to a quadratic
resonant-level model by generalizing the bosonization-refermionization approach
of Emery and Kivelson to finite system size, but improve their method in two
ways: firstly, we construct all boson fields and Klein factors explicitly in
terms of the model's original fermion operators $c_{k \sigma j}$, and secondly
we clarify explicitly how the Klein factors needed when refermionizing act on
the original Fock space. This enables us to explicitly follow the adiabatic
evolution of the 2CK model's free-fermion states to its exact eigenstates,
found by simply diagonalizing the resonant-level model for arbitrary magnetic
fields and spin-flip coupling strengths. In this way we obtain an {\em
analytic} description of the cross-over from the free to the non-Fermi-liquid
fixed point. At the latter, it is remarkably simple to recover the conformal
field theory results for the finite-size spectrum (implying a direct proof of
Affleck and Ludwig's fusion hypothesis). By analyzing the finite-size spectrum,
we directly obtain the operator content of the 2CK fixed point and the
dimension of various relevant and irrelevant perturbations. Our method can
easily be generalized to include various symmetry-breaking perturbations.
Furthermore it establishes instructive connections between different
renormalization group schemes such as poor man's scaling, Anderson-Yuval type
scaling, the numerical renormalization group and finite-size scaling.


title: Maximum Metallic Conductivity in Si-MOS Structures

abstract:
  We found that the conductivity of the two-dimensional electron system in
Si-MOS structures is limited to a maximum value, G_{max}, as either density
increases or temperature decreases. This value G_{max} is weakly disorder
dependent and ranging from 100 to 140 e^2/h for samples whose mobilities differ
by a factor of 4.


title: Genetic Correlations in Mutation Processes

abstract:
  We study the role of phylogenetic trees on correlations in mutation
processes. Generally, correlations decay exponentially with the generation
number. We find that two distinct regimes of behavior exist. For mutation rates
smaller than a critical rate, the underlying tree morphology is almost
irrelevant, while mutation rates higher than this critical rate lead to strong
tree-dependent correlations. We show analytically that identical critical
behavior underlies all multiple point correlations. This behavior generally
characterizes branching processes undergoing mutation.

categories: cond-mat.stat-mech adap-org nlin.AO physics.bio-ph q-bio.GN


title: The RKKY interactions and the Mott Transition

abstract:
  A two-site cluster generalization of the Hubbard model in large dimensions is
examined in order to study the role of short-range spin correlations near the
metal-insulator transition (MIT). The model is mapped to a two-impurity
Kondo-Anderson model in a self-consistently determined bath, making it possible
to directly address the competition between the Kondo effect and RKKY
interactions in a lattice context. Our results indicate that the RKKY
interactions lead to qualitative modifications of the MIT scenario even in the
absence of long range antiferromagnetic ordering.


title:
The Chern-Simons Fermi Liquid Description of Fractional Quantum Hall
  States

abstract:
  The composite fermion picture has had a remarkable number of recent successes
both in the description of the fractional quantized Hall states and in the
description on the even denominator Fermi liquid like states. In this review we
give an introductory account of the Chern-Simons fermion theory, focusing on
the description of the even denominator states as unusual Fermi liquids.
Contents include:
  1. Introduction
  2. Introduction to Chern-Simons Fermions
  3. RPA
  4. Landau Fermi Liquid Theory and MRPA
  5. Magnetization and M2RPA
  6. Perturbative Approaches and Trouble in the Infrared
  7. Wavefunction Picture of Composite Fermions and Dipole Approach
  8. Selected Experiments
  9. Last Words


title: Competition Between Stripes and Pairing in a t-t'-J Model

abstract:
  As the number of legs n of an n-leg, t-J ladder increases, density matrix
renormalization group calculations have shown that the doped state tends to be
characterized by a static array of domain walls and that pairing correlations
are suppressed. Here we present results for a t-t'-J model in which a diagonal,
single particle, next-near-neighbor hopping t' is introduced. We find that this
can suppress the formation of stripes and, for t' positive, enhance the
d_{x^2-y^2}-like pairing correlations. The effect of t' > 0 is to cause the
stripes to evaporate into pairs and for t' < 0 to evaporate into
quasi-particles. Results for n=4 and 6-leg ladders are discussed.


title:
Spin-Pseudospin Coherence and CP$^{3}$ Skyrmions in Bilayer Quantum Hall
  Ferromagnets

abstract:
  We analyze bilayer quantum Hall ferromagnets, whose underlying symmetry group
is SU(4). Spin-pseudospin coherence develops spontaneously when the total
electron density is low enough. Quasiparticles are CP^3 skyrmions. One skyrmion
induces charge modulations on both of the two layers. At the filling factor$\nu
=2/m$ one elementary excitation consists of a pair of skyrmions and its charge
is $2e/m$. Recent experimental data due to Sawada et al. [Phys. Rev. Lett. {\bf
80}, 4534 (1998)] support this conclusion.


title: Weak force detection using a double Bose-Einstein condensate

abstract:
  A Bose-Einstein condensate may be used to make precise measurements of weak
forces, utilizing the macroscopic occupation of a single quantum state. We
present a scheme which uses a condensate in a double well potential to do this.
The required initial state of the condensate is discussed, and the limitations
on the sensitivity due to atom collisions and external coupling are analyzed.


title: Bulk Tunneling at Integer Quantum Hall Transitions

abstract:
  The tunneling into the {\em bulk} of a 2D electron system (2DES) in strong
magnetic field is studied near the integer quantum Hall transitions. We present
a nonperturbative calculation of the tunneling density of states (TDOS) for
both Coulomb and short-ranged electron-electron interactions. In the case of
Coulomb interaction, the TDOS exhibits a 2D quantum Coulomb gap behavior,
$\nu(\ve)=C_Q\ave/e^4$, with $C_Q$ a nonuniversal coefficient of quantum
mechanical origin. For short-ranged interactions, we find that the TDOS at low
bias follows $\nu(\ve)/\nu (0)=1+(\ave/\ve_0)^\gamma$, where $\gamma$ is a
universal exponent determined by the scaling dimension of short-ranged
interactions.


title:
Thermodynamics of doped Kondo insulator in one dimension: Finite
  Temperature DMRG Study

abstract:
  The finite-temperature density-matrix renormalization-group method is applied
to the one-dimensional Kondo lattice model near half filling to study its
thermodynamics. The spin and charge susceptibilities and entropy are calculated
down to T=0.03t. We find two crossover temperatures near half filling. The
higher crossover temperature continuously connects to the spin gap at half
filling, and the susceptibilities are suppressed around this temperature. At
low temperatures, the susceptibilities increase again with decreasing
temperature when doping is finite. We confirm that they finally approach to the
values obtained in the Tomonaga-Luttinger (TL) liquid ground state for several
parameters. The crossover temperature to the TL liquid is a new energy scale
determined by gapless excitations of the TL liquid. The transition from the
metallic phase to the insulating phase is accompanied by the vanishing of the
lower crossover temperature.


title: Anomalous impurity effects in nonadiabatic superconductors

abstract:
  We show that, in contrast with the usual electron-phonon Migdal-Eliashberg
theory, the critical temperature Tc of an isotropic s-wave nonadiabatic
superconductor is strongly reduced by the presence of diluted non-magnetic
impurities. Our results suggest that the recently observed Tc-suppression
driven by disorder in K3C60 [Phys. Rev. B vol.55, 3866 (1997)] and in
Nd(2-x)CexCuO(4-delta) [Phys. Rev. B vol.58, 8800 (1998)] could be explained in
terms of a nonadiabatic electron-phonon coupling. Moreover, we predict that the
isotope effect on Tc has an impurity dependence qualitatively different from
the one expected for anisotropic superconductors.


title: Mesoscopic superconducting disks

abstract:
  Using the non-linear Ginzburg-Landau (GL) eqs. type I superconducting disks
of finite radius ($R$) and thickness ($d$) are studied in a perpendicular
magnetic field. Depending on $R$ and $d$, first or second order phase
transitions are found for the normal to superconducting state. For sufficiently
large $R$ several transitions in the superconducting phase are found
corresponding to different angular momentum giant vortex states. In increasing
magnetic field the superconductor is in its ground state, while in field down
sweep it is possible to drive the system into metastable states. We also
present a quantitative analysis of the relation between the detector output and
the sample magnetization. The latter, and the incorporation of the finite
thickness of the disks, are essential in order to obtain quantitative agreement
with experiment.


title: Crystal stability and optical properties of organic chain compounds

abstract:
  The solution to the long standing problem of the cohesion of organic chain
compounds is proposed. We consider the tight-binding dielectric matrix with two
electronic bands per chain, determine the corresponding hybridized collective
modes, and show that three among them are considerably softened due to strong
dipole-dipole and monopole-dipole interactions. By this we explain the unusual
low frequency optical activity of TTF-TCNQ, including the observed 10meV
anomaly. The softening of the modes also explains the cohesion of the
mixed-stack lattice, the fractional charge transfer almost independent of the
material, and the formation of the charged sheets in some compounds.


title: The Small Polaron Crossover: Role of Dimensionality

abstract:
  The crossover from quasi free electron to small polaron in the Holstein model
for a single electron is studied by means of both exact and self-consistent
calculations in one dimension and on an infinite coordination lattice, in order
to understand the role of dimensionality in such a crossover. We show that a
small polaron ground-state occurs when both strong coupling ($\lambda>1$) and
multiphonon ($\alpha^2 >1$) conditions are fulfilled leading to different
relevant coupling constants ($\lambda$) in adiabatic and ($\alpha^2$) anti
adiabatic region of the parameters space. We also show that the self-consistent
calculations obtained by including the first electron-phonon vertex correction
give accurate results in a sizeable region of the phase diagram well separated
from the polaronic crossover.


title:
Universality of the Wigner time delay distribution for one-dimensional
  random potentials

abstract:
  We show that the distribution of the time delay for one-dimensional random
potentials is universal in the high energy or weak disorder limit. Our
analytical results are in excellent agreement with extensive numerical
simulations carried out on samples whose sizes are large compared to the
localisation length (localised regime). The case of small samples is also
discussed (ballistic regime). We provide a physical argument which explains in
a quantitative way the origin of the exponential divergence of the moments. The
occurence of a log-normal tail for finite size systems is analysed. Finally, we
present exact results in the low energy limit which clearly show a departure
from the universal behaviour.


title: Statistical physics and practical training of soft-committee machines

abstract:
  Equilibrium states of large layered neural networks with differentiable
activation function and a single, linear output unit are investigated using the
replica formalism. The quenched free energy of a student network with a very
large number of hidden units learning a rule of perfectly matching complexity
is calculated analytically. The system undergoes a first order phase transition
from unspecialized to specialized student configurations at a critical size of
the training set. Computer simulations of learning by stochastic gradient
descent from a fixed training set demonstrate that the equilibrium results
describe quantitatively the plateau states which occur in practical training
procedures at sufficiently small but finite learning rates.


title: An Oscillator Neural Network Retrieving Sparsely Coded Phase Patterns

abstract:
  Little is known theoretically about the associative memory capabilities of
neural networks in which information is encoded not only in the mean firing
rate but also in the timing of firings. Particularly, in the case that the
fraction of active neurons involved in memorizing patterns becomes small, it is
biologically important to consider the timings of firings and to study how such
consideration influences storage capacities and quality of recalled patterns.
For this purpose, we propose a simple extended model of oscillator neural
networks to allow for expression of non-firing state. %which is able to
memorize sparsely coded phase patterns including non-firing states. Analyzing
both equilibrium states and dynamical properties in recalling processes, we
find that the system possesses good associative memory.


title:
First Order Metal-Insulator Transition in Two-dimensional Disordered
  Systems

abstract:
  In the absence of magnetic field or spin-orbit coupling the one-parameter
scaling theory predicts localization of all states in two-dimensional (2D)
disordered systems, for any amount of disorder. However, a 2D metallic phase
has been recently reported in high mobility Si-MOS and GaAs-based materials
without magnetic field. We study numerically a recently proposed 2D model which
consists of a compactly coupled pure-random plane structure. This allows to
obtain exactly a continuum of one-dimensional ballistic extended states which
can lead to a marginal metallic phase of finite conductivity
$\sigma_{0}=2e^2/h$, in a wide energy range whose boundaries define the
mobility edges of a first-order metal-insulator transition. We present
numerical diagonalization results and the conductivity of the system in
perpendicular magnetic field, which verify the above analytical predictions.
The model is also discussed in connection to recent experiments.


title: Recent results on multiplicative noise

abstract:
  Recent developments in the analysis of Langevin equations with multiplicative
noise (MN) are reported. In particular, we:
  (i) present numerical simulations in three dimensions showing that the MN
equation exhibits, like the Kardar-Parisi-Zhang (KPZ) equation both a weak
coupling fixed point and a strong coupling phase, supporting the proposed
relation between MN and KPZ;
  (ii) present dimensional, and mean field analysis of the MN equation to
compute critical exponents;
  (iii) show that the phenomenon of the noise induced ordering transition
associated with the MN equation appears only in the Stratonovich representation
and not in the Ito one, and
  (iv) report the presence of a new first-order like phase transition at zero
spatial coupling, supporting the fact that this is the minimum model for noise
induced ordering transitions.


title:
On the ubiquity of matrix-product states in one-dimensional stochastic
  processes with boundary interactions

abstract:
  Recently it has been shown that the zero-energy eigenstate -- corresponding
to the stationary state -- of a stochastic Hamiltonian with nearest-neighbour
interaction in the bulk and single-site boundary terms, can always be written
in the form of a so-called matrix-product state. We generalize this result to
stochastic Hamiltonians with arbitrary, but finite, interaction range. As an
application two different particle-hopping models with three-site bulk
interaction are studied. For these models which can be interpreted as cellular
automata for traffic flow, we present exact solutions for periodic boundary
conditions and some suitably chosen boundary interactions.


title: On the rooted Tutte polynomial

abstract:
  The Tutte polynomial is a generalization of the chromatic polynomial of graph
colorings. Here we present an extension called the rooted Tutte polynomial,
which is defined on a graph where one or more vertices are colored with
prescribed colors. We establish a number of results pertaining to the rooted
Tutte polynomial, including a duality relation in the case that all roots
reside around a single face of a planar graph. The connection with the Potts
model is also reviewed.


title: Restricted random walks on a graph

abstract:
  The problem of a restricted random walk on graphs which keeps track of the
number of immediate reversal steps is considered by using a transfer matrix
formulation. A closed-form expression is obtained for the generating function
of the number of n-step walks with r reversal steps for walks on any graph. In
the case of graphs of a uniform valence, we show that our result has a
probabilistic meaning, and deduce explicit expressions for the generating
function in terms of the eigenvalues of the adjacency matrix. Applications to
periodic lattices and the complete graph are given.


title:
On Phase Transition and Self-Organized Critical State in Granular
  Packings

abstract:
  We model two-dimensional systems of granular aggregates confined between two
planes and demonstrate that at a critical grain volume fraction an abrupt
rigidity transition occurs. This transition is observed both in static and
shear tests. The grain volume fraction at which the transition occurs, $\nu_c$,
decreases with increasing friction between the grains. Densely packed grains,
with a volume fraction $\nu> \nu_c$, display an elastic-plastic rheology.
Dilute packings, with $\nu<\nu_c$, display gas-like characteristics. Packings
with $\nu=\nu_c$ display phase coexistance. It is shown that when volume
fraction is allowed to change freely (using constant normal stress boundary
condition), it evolves spontaneously to $\nu_c$ under a wide range of boundary
conditions, exhibiting 'self-organized criticality'.


title: Statistics of knots and entangled random walks

abstract:
  The lectures review the state of affairs in modern branch of mathematical
physics called probabilistic topology. In particular we consider the following
problems: (i) We estimate the probability of a trivial knot formation on the
lattice using the Kauffman algebraic invariants and show the connection of this
problem with the thermodynamic properties of 2D disordered Potts model; (ii) We
investigate the limit behavior of random walks in multi-connected spaces and on
non-commutative groups related to the knot theory. We discuss the application
of the above mentioned problems in statistical physics of polymer chains. On
the basis of non-commutative probability theory we derive some new results in
statistical physics of entangled polymer chains which unite rigorous
mathematical facts with more intuitive physical arguments.


title: Band-Structure Effects in the Spin Relaxation of Conduction Electrons

abstract:
  Spin relaxation of conduction electrons in metals is significantly influenced
by the Fermi surface topology. Electrons near Brillouin zone boundaries,
special symmetry points, or accidental degeneracy lines have spin flip rates
much higher than an average electron. A realistic calculation and analytical
estimates show that these regions dominate the spin relaxation, explaining why
polyvalent metals have much higher spin relaxation rates (up to three orders of
magnitude) than similar monovalent metals. This suggests that spin relaxation
in metals can be tailored by band-structure modifications like doping,
alloying, reducing the dimensionality, etc.


title: Diffusional Growth of Colloids

abstract:
  We consider incorporation of particle detachment in Smoluchowski model of
colloidal growth. Two approaches are considered, utilizing phenomenological
rate equation and exact large-time results. Our main conclusion is that the
value of the large-time diffusing particle concentration at the aggregate
surface is the only parameter needed to describe the added effect of
detachment. Explicit expression is given for the particle intake rate.


title: Screening of electrostatic potential in a composite fermion system

abstract:
  Screening of the electric field of a test charge by monolayer and
double-layer composite fermion systems is considered. It is shown that the
electric field of the test charge is partly screened at distances much large
then the magnetic length. The value of screening as a function of the distance
depends considerably on the filling factor. The effect of variation of the
value of screening in the double-layer system upon a transition to a state
described by the Halperin wave function is determined.


title:
Localization and Mobility Edge in One-Dimensional Potentials with
  Correlated Disorder

abstract:
  We show that a mobility edge exists in 1D random potentials provided specific
long-range correlations. Our approach is based on the relation between binary
correlator of a site potential and the localization length. We give the
algorithm to construct numerically potentials with mobility edge at any given
energy inside allowed zone. Another natural way to generate such potentials is
to use chaotic trajectories of non-linear maps. Our numerical calculations for
few particular potentials demonstrate the presence of mobility edges in 1D
geometry.


title: Shot noise suppression in multimode ballistic Fermi conductors

abstract:
  We have derived a general formula describing current noise in multimode
ballistic channels connecting source and drain electrodes with Fermi electron
gas. In particular (at $eV\gg k_{B}T$), the expression describes the
nonequilibrium ''shot'' noise, which may be suppressed by both Fermi
correlations and space charge screening. The general formula has been applied
to an approximate model of a 2D nanoscale, ballistic MOSFET. At large negative
gate voltages, when the density of electrons in the channel is small, shot
noise spectral density $S_{I}(0)$ approaches the Schottky value $2eI$, where
$I$ is the average current. However, at positive gate voltages, when the
maximum potential energy in the channel is below the Fermi level of the
electron source, the noise can be at least an order of magnitude smaller than
the Schottky value, mostly due to Fermi effects.


title:
On possible superconductivity in the doped ladder compound
  La_(1-x)Sr_xCuO_2.5

abstract:
  LaCuO_2.5 is a system of coupled, two-chain, cuprate ladders which may be
doped systematically by Sr substitution. Motivated by the recent synthesis of
single crystals, we investigate theoretically the possibility of
superconductivity in this compound. We use a model of spin fluctuation-mediated
superconductivity, where the pairing potential is strongly peaked at \pi in the
ladder direction. We solve the coupled gap equations on the bonding and
antibonding ladder bands to find superconducting solutions across the range of
doping, and discuss their relevance to the real material.


title: Critical behavior of a traffic flow model

abstract:
  The Nagel-Schreckenberg traffic flow model shows a transition from a free
flow regime to a jammed regime for increasing car density. The measurement of
the dynamical structure factor offers the chance to observe the evolution of
jams without the necessity to define a car to be jammed or not. Above the
jamming transition the dynamical structure factor exhibits for a given k-value
two maxima corresponding to the separation of the system into the free flow
phase and jammed phase. We obtain from a finite-size scaling analysis of the
smallest jam mode that approaching the transition long range correlations of
the jams occur.


title:
Transverse depinning and melting of a moving vortex lattice in driven
  periodic Josephson junction arrays

abstract:
  We study the effect of thermal fluctuations in a vortex lattice driven in the
periodic pinning of a Josephson junction array. The phase diagram current ($I$)
vs. temperature ($T$) is studied. Above the critical current $I_c(T)$ we find a
moving vortex lattice (MVL) with anisotropic Bragg peaks. For large currents
$I\gg I_c(T)$, there is a melting transition of the MVL at $T_M(I)$. When
applying a small transverse current to the MVL, there is no dissipation at low
$T$. We find an onset of transverse vortex motion at a transverse depinning
temperature $T_{tr}(I)<T_M(I)$.


title:
Statistical Mechanical Calculation of Anisotropic Step Stiffness of a
  Two-Dimensional Hexagonal Lattice Gas Model with Next-Nearest-Neighbor
  Interactions: Application to Si(111) Surface

abstract:
  We study a two-dimensional honeycomb lattice gas model with both nearest- and
next-nearest-neighbor interactions in a staggered field, which describes the
surface of stoichiometrically binary crystal.
  We calculate anisotropic step tension, step stiffness, and equilibrium island
shape, by an extended random walk method. We apply the results to Si(111)
7$\times$7 reconstructed surface and high-temperature Si(111) 1$\times$1
surface. We also calculate inter-step interaction coefficient.


title: Irrelevance of memory in the minority game

abstract:
  By means of extensive numerical simulations we show that all the distinctive
features of the minority game introduced by Challet and Zhang (1997), are
completely independent from the memory of the agents. The only crucial
requirement is that all the individuals must posses the same information,
irrespective of the fact that this information is true or false.