10,051 research outputs found
SU(m|n) supersymmetric Calogero-Sutherland model confined in harmonic potential
In this work, we study a continuous quantum system of a mixture of bosons and
fermions with the supersymmetry SU(m|n). The particles are confined in a
harmonic well and interact with each other through the 1/r2 interaction. The
ground state wavefunction is constructed explicitly for the most general
SU(m|n) case, with the ground state energy given explicitly. The full energy
spectrum of excitations in the SU(m|n) model is also equal spaced. In the
limiting case where there are no bosons in the system, our results reduce to
those obtained previously.Comment: 9 pages, preprint of ETH-Lausanne (August 1996
Ground States and Flux Configurations of the Two-dimensional Falicov-Kimball Model
The Falicov-Kimball model is a lattice model of itinerant spinless fermions
("electrons") interacting by an on-site potential with classical particles
("ions"). We continue the investigations of the crystalline ground states that
appear for various filling of electrons and ions, for large coupling. We
investigate the model for square as well as triangular lattices. New ground
states are found and the effects of a magnetic flux on the structure of the
phase diagram is studied. The flux phase problem where one has to find the
optimal flux configurations and the nuclei configurations is also solved in
some cases. Finaly we consider a model where the fermions are replaced by
hard-core bosons. This model also has crystalline ground states. Therefore
their existence does not require the Pauli principle, but only the on-site
hard-core constraint for the itinerant particles.Comment: 42 pages, uuencoded postscript file. Missing pages adde
Trailing Edge Noise Reduction by Passive and Active Flow Controls
This paper presents the results on the use of porous metal foams (passive control) and dielectric barrier surface plasma actuations (active control) for the reduction of vortex shedding tonal noises from the nonflat plate type trailing edge serration in a NACA0012 airfoil previously discussed in Chong et al. (AIAA J. Vol. 51, 2013, pp. 2665-2677). The use of porous metal foams to fill the interstices between adjacent members of the sawtooth can almost completely suppress the vortex shedding tonal noise, whilst the serration effect on the broadband noise reduction is retained. This concept will promote the nonflat plate type serrated trailing edge to become a genuine alternative to the conventional flat plate type serrated trailing edge, which is known to have drawbacks in the structural stability, aerodynamic performances and implementation issues. For the plasma actuators, configuration which produces electric wind in a tangential direction is found to be not very effective in suppressing the vortices emanated from the serration blunt root. On the other hand, for the plasma configuration which produces electric wind in a vertical direction, good level of vortex shedding tonal noise reduction has been demonstrated. However, the self noise produced by the plasma actuators negates the noise benefits on the tonal noise reduction. This characteristic illustrates the need to further develop the plasma actuators in a two pronged approach. First is to increase the electric wind speed, thereby allowing the plasma actuators to be used in a higher free jet velocity which naturally produces a larger level of jet noise. Second, the self noise radiated by the plasma actuators should be reduced
Influence of anisotropic next-nearest-neighbor hopping on diagonal charge-striped phases
We consider the model of strongly-correlated system of electrons described by
an extended Falicov-Kimball Hamiltonian where the stability of some axial and
diagonal striped phases was proved. Introducing a next-nearest-neighbor
hopping, small enough not to destroy the striped structure, we examine
rigorously how the presence of the next-nearest-neighbor hopping anisotropy
reduces the -rotation degeneracy of the diagonal-striped phase. The
effect appears to be similar to that in the case of anisotropy of the
nearest-neighbor hopping: the stripes are oriented in the direction of the
weaker next-nearest-neighbor hopping.Comment: 9 pages, 3 figures, 1 tabl
The average X-ray/gamma-ray spectrum of radio-quiet Seyfert 1s
We have obtained the average 1--500 keV spectrum of radio-quiet Seyfert 1s
using data from EXOSAT, Ginga, HEAO, and GRO/OSSE. The spectral fit to the
combined average EXOSAT and OSSE data is fully consistent with that for Ginga
and OSSE, confirming results from an earlier Ginga/OSSE sample. The average
spectrum is well-fitted by a power-law X-ray continuum with an energy spectral
index of moderately absorbed by an ionized medium and with
a Compton reflection component. A high-energy cutoff (or a break) in the the
power-law component at a few hundred keV or more is required by the data. We
also show that the corresponding average spectrum from HEAO A1 and A4 is fully
compatible with that obtained from EXOSAT, Ginga and OSSE. These results
confirm that the apparent discrepancy between the results of Ginga (with
) and the previous results of EXOSAT and HEAO (with ) is indeed due to ionized absorption and Compton reflection first
taken into account for Ginga but not for the previous missions. Also, our
results confirm that the Seyfert-1 spectra are on average cut off in gamma-rays
at energies of at least a few hundred keV, not at keV (as suggested
earlier by OSSE data alone). The average spectrum is compatible with emission
from either an optically-thin relativistic thermal plasma in a disk corona, or
with a nonthermal plasma with a power-law injection of relativistic electrons.Comment: 7 pages, 3 Postscript figures, MNRAS accepte
Scalable Text and Link Analysis with Mixed-Topic Link Models
Many data sets contain rich information about objects, as well as pairwise
relations between them. For instance, in networks of websites, scientific
papers, and other documents, each node has content consisting of a collection
of words, as well as hyperlinks or citations to other nodes. In order to
perform inference on such data sets, and make predictions and recommendations,
it is useful to have models that are able to capture the processes which
generate the text at each node and the links between them. In this paper, we
combine classic ideas in topic modeling with a variant of the mixed-membership
block model recently developed in the statistical physics community. The
resulting model has the advantage that its parameters, including the mixture of
topics of each document and the resulting overlapping communities, can be
inferred with a simple and scalable expectation-maximization algorithm. We test
our model on three data sets, performing unsupervised topic classification and
link prediction. For both tasks, our model outperforms several existing
state-of-the-art methods, achieving higher accuracy with significantly less
computation, analyzing a data set with 1.3 million words and 44 thousand links
in a few minutes.Comment: 11 pages, 4 figure
Expert chess memory: Revisiting the chunking hypothesis
After reviewing the relevant theory on chess expertise, this paper re-examines experimentally the finding of Chase and Simon (1973a) that the differences in ability of chess players at different skill levels to copy and to recall positions are attributable to the experts' storage of thousands of chunks (patterned clusters of pieces) in long-term memory. Despite important differences in the experimental apparatus, the data of the present experiments regarding latencies and chess relations between successively placed pieces are highly correlated with those of Chase and Simon. We conclude that the 2-second inter-chunk interval used to define chunk boundaries is robust, and that chunks have psychological reality. We discuss the possible reasons why Masters in our new study used substantially larger chunks than the Master of the 1973 study, and extend the chunking theory to take account of the evidence for large retrieval structures (templates) in long-term memory
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