11,522 research outputs found
EUROMOD: the European Union tax-benefit microsimulation model
This paper aims to provide an introduction to the current state of the art of EUROMOD, the European Union tax-benefit microsimulation model. It explains the original motivations for building a multi-country EU-wide model and summarises its current organisation. It provides an overview of EUROMOD components, covering its policy scope, the input data, the validation process and some technical aspects such as the tax-benefit programming language and the user interface. The paper also reviews some recent applications of EUROMOD and, finally, considers future developments
Solution of Some Integrable One-Dimensional Quantum Systems
In this paper, we investigate a family of one-dimensional multi-component
quantum many-body systems. The interaction is an exchange interaction based on
the familiar family of integrable systems which includes the inverse square
potential. We show these systems to be integrable, and exploit this
integrability to completely determine the spectrum including degeneracy, and
thus the thermodynamics. The periodic inverse square case is worked out
explicitly. Next, we show that in the limit of strong interaction the "spin"
degrees of freedom decouple. Taking this limit for our example, we obtain a
complete solution to a lattice system introduced recently by Shastry, and
Haldane; our solution reproduces the numerical results. Finally, we emphasize
the simple explanation for the high multiplicities found in this model
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
Crossover from Fermi Liquid to Non-Fermi Liquid Behavior in a Solvable One-Dimensional Model
We consider a quantum moany-body problem in one-dimension described by a
Jastrow type, characterized by an exponent and a parameter .
We show that with increasing , the Fermi Liquid state (
crosses over to non-Fermi liquid states, characterized by effective
"temperature".Comment: 8pp. late
Spectral flow in the supersymmetric - model with a interaction
The spectral flow in the supersymmetric {\it t-J} model with
interaction is studied by analyzing the exact spectrum with twisted boundary
conditions. The spectral flows for the charge and spin sectors are shown to
nicely fit in with the motif picture in the asymptotic Bethe ansatz. Although
fractional exclusion statistics for the spin sector clearly shows up in the
period of the spectral flow at half filling, such a property is generally
hidden once any number of holes are doped, because the commensurability
condition in the motif is not met in the metallic phase.Comment: 8 pages, revtex, Phys. Rev. B54 (1996) August 15, in pres
Partially Solvable Anisotropic t-J Model with Long-Range Interactions
A new anisotropic t-J model in one dimension is proposed which has long-range
hopping and exchange. This t-J model is only partially solvable in contrast to
known integrable models with long-range interaction. In the high-density limit
the model reduces to the XXZ chain with the long-range exchange. Some exact
eigenfunctions are shown to be of Jastrow-type if certain conditions for an
anisotropy parameter are satisfied. The ground state as well as the excitation
spectrum for various cases of the anisotropy parameter and filling are derived
numerically. It is found that the Jastrow-type wave function is an excellent
trial function for any value of the anisotropy parameter.Comment: 10 pages, 3 Postscript figure
Dyson's Brownian Motion and Universal Dynamics of Quantum Systems
We establish a correspondence between the evolution of the distribution of
eigenvalues of a matrix subject to a random Gaussian perturbing
matrix, and a Fokker-Planck equation postulated by Dyson. Within this model, we
prove the equivalence conjectured by Altshuler et al between the space-time
correlations of the Sutherland-Calogero-Moser system in the thermodynamic limit
and a set of two-variable correlations for disordered quantum systems
calculated by them. Multiple variable correlation functions are, however, shown
to be inequivalent for the two cases.Comment: 10 pages, revte
Future freeze forecasting
Real time GOES thermal data acquisition, an energy balance minimum temperature prediction model and a statistical model are incorporated into a minicomputer system. These components make up the operational "Satellite Freeze Forecast System" being used to aid NOAA, NWS forecasters in developing their freeze forecasts. The general concept of the system is presented in this paper. Specific detailed aspects of the system can be found in the reference cited
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