5,627 research outputs found
Exact Solution of the Asymmetric Exclusion Model with Particles of Arbitrary Size
A generalization of the simple exclusion asymmetric model is introduced. In
this model an arbitrary mixture of molecules with distinct sizes , in units of lattice space, diffuses asymmetrically on the lattice.
A related surface growth model is also presented. Variations of the
distribution of molecules's sizes may change the excluded volume almost
continuously. We solve the model exactly through the Bethe ansatz and the
dynamical critical exponent is calculated from the finite-size corrections
of the mass gap of the related quantum chain. Our results show that for an
arbitrary distribution of molecules the dynamical critical behavior is on the
Kardar-Parizi-Zhang (KPZ) universality.Comment: 28 pages, 2 figures. To appear in Phys. Rev. E (1999
A Generalized Duality Transformation of the Anisotropic Xy Chain in a Magnetic Field
We consider the anisotropic chain in a magnetic field with special
boundary conditions described by a two-parameter Hamiltonian. It is shown that
the exchange of the parameters corresponds to a similarity transformation,
which reduces in a special limit to the Ising duality transformation.Comment: 6 pages, LaTeX, BONN-HE-93-4
Critical Behaviour of Mixed Heisenberg Chains
The critical behaviour of anisotropic Heisenberg models with two kinds of
antiferromagnetically exchange-coupled centers are studied numerically by using
finite-size calculations and conformal invariance. These models exhibit the
interesting property of ferrimagnetism instead of antiferromagnetism. Most of
our results are centered in the mixed Heisenberg chain where we have at even
(odd) sites a spin-S (S') SU(2) operator interacting with a XXZ like
interaction (anisotropy ). Our results indicate universal properties
for all these chains. The whole phase, , where the models change
from ferromagnetic to ferrimagnetic behaviour is
critical. Along this phase the critical fluctuations are ruled by a c=1
conformal field theory of Gaussian type. The conformal dimensions and critical
exponents, along this phase, are calculated by studying these models with
several boundary conditions.Comment: 21 pages, standard LaTex, to appear in J.Phys.A:Math.Ge
The Wave Functions for the Free-Fermion Part of the Spectrum of the Quantum Spin Models
We conjecture that the free-fermion part of the eigenspectrum observed
recently for the Perk-Schultz spin chain Hamiltonian in a finite
lattice with is a consequence of the existence of a
special simple eigenvalue for the transfer matrix of the auxiliary
inhomogeneous vertex model which appears in the nested Bethe ansatz
approach. We prove that this conjecture is valid for the case of the SU(3) spin
chain with periodic boundary condition. In this case we obtain a formula for
the components of the eigenvector of the auxiliary inhomogeneous 6-vertex model
(), which permit us to find one by one all components of
this eigenvector and consequently to find the eigenvectors of the free-fermion
part of the eigenspectrum of the SU(3) spin chain. Similarly as in the known
case of the case at our numerical and analytical
studies induce some conjectures for special rates of correlation functions.Comment: 25 pages and no figure
GAPS IN THE HEISENBERG-ISING MODEL
We report on the closing of gaps in the ground state of the critical
Heisenberg-Ising chain at momentum . For half-filling, the gap closes at
special values of the anisotropy , integer. We explain
this behavior with the help of the Bethe Ansatz and show that the gap scales as
a power of the system size with variable exponent depending on . We use
a finite-size analysis to calculate this exponent in the critical region,
supplemented by perturbation theory at . For rational
fillings, the gap is shown to be closed for {\em all} values of and
the corresponding perturbation expansion in shows a remarkable
cancellation of various diagrams.Comment: 12 RevTeX pages + 4 figures upon reques
One dimensional strongly interacting Luttinger liquid of lattice spinless fermions
The spinless fermion model with hard core repulsive potential extended on a
few lattice sites is considered.The Luttinger liquid behaviour is studied for
the different values of a hard core radius. A critical exponent of the one
particle correlation function for arbitrary electron density and coupling
constant are obtained.Comment: 4 pages, 4 figures, Late
On the density matrix for the kink ground state of higher spin XXZ chain
The exact expression for the density matrix of the kink ground state of
higher spin XXZ chain is obtained
The XX-model with boundaries. Part III:Magnetization profiles and boundary bound states
We calculate the magnetization profiles of the and
operators for the XX-model with hermitian boundary terms. We study the profiles
on the finite chain and in the continuum limit. The results are discussed in
the context of conformal invariance. We also discuss boundary excitations and
their effect on the magnetization profiles.Comment: 30 pages, 3 figure
Stealthy Deception Attacks Against SCADA Systems
SCADA protocols for Industrial Control Systems (ICS) are vulnerable to
network attacks such as session hijacking. Hence, research focuses on network
anomaly detection based on meta--data (message sizes, timing, command
sequence), or on the state values of the physical process. In this work we
present a class of semantic network-based attacks against SCADA systems that
are undetectable by the above mentioned anomaly detection. After hijacking the
communication channels between the Human Machine Interface (HMI) and
Programmable Logic Controllers (PLCs), our attacks cause the HMI to present a
fake view of the industrial process, deceiving the human operator into taking
manual actions. Our most advanced attack also manipulates the messages
generated by the operator's actions, reversing their semantic meaning while
causing the HMI to present a view that is consistent with the attempted human
actions. The attacks are totaly stealthy because the message sizes and timing,
the command sequences, and the data values of the ICS's state all remain
legitimate.
We implemented and tested several attack scenarios in the test lab of our
local electric company, against a real HMI and real PLCs, separated by a
commercial-grade firewall. We developed a real-time security assessment tool,
that can simultaneously manipulate the communication to multiple PLCs and cause
the HMI to display a coherent system--wide fake view. Our tool is configured
with message-manipulating rules written in an ICS Attack Markup Language (IAML)
we designed, which may be of independent interest. Our semantic attacks all
successfully fooled the operator and brought the system to states of blackout
and possible equipment damage
Excited states in the twisted XXZ spin chain
We compute the finite size spectrum for the spin 1/2 XXZ chain with twisted
boundary conditions, for anisotropy in the regime , and
arbitrary twist . The string hypothesis is employed for treating
complex excitations. The Bethe Ansatz equtions are solved within a coupled
non-linear integral equation approach, with one equation for each type of
string. The root-of-unity quantum group invariant periodic chain reduces to the
XXZ_1/2 chain with a set of twist boundary conditions (,
an integer multiple of ). For this model, the restricted
Hilbert space corresponds to an unitary conformal field theory, and we recover
all primary states in the Kac table in terms of states with specific twist and
strings.Comment: 16 pages, Latex; added discussion on quantum group invariance and
arbitrary magnon numbe
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