17 research outputs found
Thermodynamics of an integrable model for electrons with correlated hopping
A new supersymmetric model for electrons with generalized hopping terms and
Hubbard interaction on a one-dimensional lattice is solved by means of the
Bethe Ansatz. We investigate the phase diagram of this model by studying the
ground state and excitations of the model as a function of the interaction
parameter, electronic density and magnetization. Using arguments from conformal
field theory we can study the critical exponents describing the asymptotic
behaviour of correlation functions at long distances.Comment: 24 pp., latex+epsf, figures include
Bethe ansatz solution of the closed anisotropic supersymmetric U model with quantum supersymmetry
The nested algebraic Bethe ansatz is presented for the anisotropic
supersymmetric model maintaining quantum supersymmetry. The Bethe ansatz
equations of the model are obtained on a one-dimensional closed lattice and an
expression for the energy is given.Comment: 7 pages (revtex), minor modifications. To appear in Mod. Phys. Lett.
Friedel Oscillations and Charge Density Waves in Chains and Ladders
The density matrix renormalization group method for ladders works much more
efficiently with open boundary conditions. One consequence of these boundary
conditions is groundstate charge density oscillations that often appear to be
nearly constant in magnitude or to decay only slightly away from the
boundaries. We analyse these using bosonization techniques, relating their
detailed form to the correlation exponent and distinguishing boundary induced
generalized Friedel oscillations from true charge density waves. We also
discuss a different approach to extracting the correlation exponent from the
finite size spectrum which uses exclusively open boundary conditions and can
therefore take advantage of data for much larger system sizes. A general
discussion of the Friedel oscillation wave-vectors is given, and a convenient
Fourier transform technique is used to determine it. DMRG results are analysed
on Hubbard and t-J chains and 2 leg t-J ladders. We present evidence for the
existence of a long-ranged charge density wave state in the t-J ladder at a
filling of n=0.75 and near J/t \approx 0.25.Comment: Revtex, 15 pages, 15 postscript figure
Luttinger liquid behavior in spin chains with a magnetic field
Antiferromagnetic Heisenberg spin chains in a sufficiently strong magnetic
field are Luttinger liquids, whose parameters depend on the actual
magnetization of the chain. Here we present precise numerical estimates of the
Luttinger liquid dressed charge , which determines the critical exponents,
by calculating the magnetization and quadrupole operator profiles for
and S=1 chains using the density matrix renormalization group method. Critical
amplitudes and the scattering length at the chain ends are also determined.
Although both systems are Luttinger liquids the characteristic parameters
differ considerably.Comment: Final version, 6 pages, 6 EPS figure
Generalized q-Onsager Algebras and Dynamical K-matrices
A procedure to construct -matrices from the generalized -Onsager
algebra \cO_{q}(\hat{g}) is proposed. This procedure extends the intertwiner
techniques used to obtain scalar (c-number) solutions of the reflection
equation to dynamical (non-c-number) solutions. It shows the relation between
soliton non-preserving reflection equations or twisted reflection equations and
the generalized -Onsager algebras. These dynamical -matrices are
important to quantum integrable models with extra degrees of freedom located at
the boundaries: for instance, in the quantum affine Toda field theories on the
half-line they yield the boundary amplitudes. As examples, the cases of
\cO_{q}(a^{(2)}_{2}) and \cO_{q}(a^{(1)}_{2}) are treated in details
Hecke algebraic approach to the reflection equation for spin chains
We use the structural similarity of certain Coxeter Artin Systems to the
Yang--Baxter and Reflection Equations to convert representations of these
systems into new solutions of the Reflection Equation. We construct certain
Bethe ansatz states for these solutions, using a parameterisation suggested by
abstract representation theory.Comment: 27 pages, multiple figures, late
Identificación de parámetros de líneas de transmisión usando estimación de estado
Este artículo presenta dos algoritmos, basados en estimación de estado, para la identificación de parámetros de líneas de transmisión. Las técnicas utilizadas se fundamentan en la inclusión de los parámetros de las líneas en el vector de estado y la solución del estimador de estado por mínimos cuadrados ponderados. En ambos casos se construyerón sistemas de potencia ficticios que se componen de copias de la misma línea de transmisión para diferentes instantes de tiempo. Uno de los algoritmos usó mediciones de magnitud de voltaje y potencia activa y reactiva, mientras que el otro implementó mediciones fasoriales sincronizadas de voltaje y corriente. Los algoritmos fueron evaluados utilizando mediciones simuladas en el sistema de 30 nodos de IEEE. Ambas soluciones identificaron la totalidad de los parámetros de las líneas con errores menores del 1%.This article presents two state-estimation-based algorithms for identifying transmission line parameters. The identification technique used simultaneous state-parameter estimation on an artificial power system composed of several copies of the same transmission line, using measurements at different points in time. The first algorithm used active and reactive power measurements at both ends of the line. The second method used synchronised phasor voltage and current measurements at both ends. The algorithms were tested in simulated conditions on the 30-node IEEE test system. All line parameters for this system were estimated with errors below 1%