673 research outputs found
Entanglement and particle correlations of Fermi gases in harmonic traps
We investigate quantum correlations in the ground state of noninteracting
Fermi gases of N particles trapped by an external space-dependent harmonic
potential, in any dimension. For this purpose, we compute one-particle
correlations, particle fluctuations and bipartite entanglement entropies of
extended space regions, and study their large-N scaling behaviors. The
half-space von Neumann entanglement entropy is computed for any dimension,
obtaining S_HS = c_l N^(d-1)/d ln N, analogously to homogenous systems, with
c_l=1/6, 1/(6\sqrt{2}), 1/(6\sqrt{6}) in one, two and three dimensions
respectively. We show that the asymptotic large-N relation S_A\approx \pi^2
V_A/3, between the von Neumann entanglement entropy S_A and particle variance
V_A of an extended space region A, holds for any subsystem A and in any
dimension, analogously to homogeneous noninteracting Fermi gases.Comment: 15 pages, 22 fig
Static and dynamic structure factors in three-dimensional randomly diluted Ising models
We consider the three-dimensional randomly diluted Ising model and study the
critical behavior of the static and dynamic spin-spin correlation functions
(static and dynamic structure factors) at the paramagnetic-ferromagnetic
transition in the high-temperature phase. We consider a purely relaxational
dynamics without conservation laws, the so-called model A. We present Monte
Carlo simulations and perturbative field-theoretical calculations. While the
critical behavior of the static structure factor is quite similar to that
occurring in pure Ising systems, the dynamic structure factor shows a
substantially different critical behavior. In particular, the dynamic
correlation function shows a large-time decay rate which is momentum
independent. This effect is not related to the presence of the Griffiths tail,
which is expected to be irrelevant in the critical limit, but rather to the
breaking of translational invariance, which occurs for any sample and which, at
the critical point, is not recovered even after the disorder average.Comment: 43 page
Expression of SPANX proteins in normal prostatic tissue and in prostate cancer
The sperm protein associated with the nucleus in the X chromosome (SPANX) gene family encodes for proteins that are not only expressed in germ cells, but also in a number of tumors. In addition, SPANX genes map in an interval of the X chromosome (namely, Xq27), which has been found to be associated with familial prostate cancer by linkage analysis. The aim of this study was therefore to evaluate SPANX protein expression in normal prostate tissues and in prostate carcinoma. For this purpose, formalin-fixed and paraffin-embedded sections obtained from 15 normal (at autopsy) donors and 12 men with prostate cancer were analyzed by immunohistochemistry. About 40% of both normal and tumor prostate samples resulted SPANX positive. Signals were exclusively within the nucleus in normal prostate cells, whereas both nuclear and cytoplasmic positivity was observed in tumor cells. In conclusion, these findings showed that SPANX genes are expressed in both normal and tumor prostate gland, but the latter showed a peculiar cytoplasmic staining positivity. This suggests a possible association between SPANX over expression and prostate cancer development. Additional studies are needed to corroborate this hypothesis
Strong coupling expansion of chiral models
A general precedure is outlined for an algorithmic implementation of the
strong coupling expansion of lattice chiral models on arbitrary lattices. A
symbolic character expansion in terms of connected values of group integrals on
skeleton diagrams may be obtained by a fully computerized approach.Comment: 2 pages, PostScript file, contribution to conference LATTICE '9
Large-N phase transition in lattice 2-d principal chiral models
We investigate the large-N critical behavior of 2-d lattice chiral models by
Monte Carlo simulations of U(N) and SU(N) groups at large N. Numerical results
confirm strong coupling analyses, i.e. the existence of a large-N second order
phase transition at a finite .Comment: 12 pages, Revtex, 8 uuencoded postscript figure
Critical behavior of the random-anisotropy model in the strong-anisotropy limit
We investigate the nature of the critical behavior of the random-anisotropy
Heisenberg model (RAM), which describes a magnetic system with random uniaxial
single-site anisotropy, such as some amorphous alloys of rare earths and
transition metals. In particular, we consider the strong-anisotropy limit
(SRAM), in which the Hamiltonian can be rewritten as the one of an Ising
spin-glass model with correlated bond disorder. We perform Monte Carlo
simulations of the SRAM on simple cubic L^3 lattices, up to L=30, measuring
correlation functions of the replica-replica overlap, which is the order
parameter at a glass transition. The corresponding results show critical
behavior and finite-size scaling. They provide evidence of a finite-temperature
continuous transition with critical exponents and
. These results are close to the corresponding estimates that
have been obtained in the usual Ising spin-glass model with uncorrelated bond
disorder, suggesting that the two models belong to the same universality class.
We also determine the leading correction-to-scaling exponent finding .Comment: 24 pages, 13 figs, J. Stat. Mech. in pres
Universality class of 3D site-diluted and bond-diluted Ising systems
We present a finite-size scaling analysis of high-statistics Monte Carlo
simulations of the three-dimensional randomly site-diluted and bond-diluted
Ising model. The critical behavior of these systems is affected by
slowly-decaying scaling corrections which make the accurate determination of
their universal asymptotic behavior quite hard, requiring an effective control
of the scaling corrections. For this purpose we exploit improved Hamiltonians,
for which the leading scaling corrections are suppressed for any thermodynamic
quantity, and improved observables, for which the leading scaling corrections
are suppressed for any model belonging to the same universality class.
The results of the finite-size scaling analysis provide strong numerical
evidence that phase transitions in three-dimensional randomly site-diluted and
bond-diluted Ising models belong to the same randomly dilute Ising universality
class. We obtain accurate estimates of the critical exponents, ,
, , , ,
, and of the leading and next-to-leading correction-to-scaling
exponents, and .Comment: 45 pages, 22 figs, revised estimate of n
Merging of globular clusters within inner galactic regions. I. Do they survive the tidal interaction?
The main topic of this paper is the investigation of the modes of interaction
of globular clusters (GCs) moving in the inner part of a galaxy. This is
tackled by means of high-resolution N-body simulations, whose first results are
presented in this article. Our simulations dealt with primordial very massive
(order of 10^7 solar masses) GCs that were able to decay, because of dynamical
friction, into the inner regions of triaxial galaxies on a time much shorter
than their internal relaxation time. To check the disruptive role of both tidal
forces and GC-GC collisions, we maximised the tidal interaction considering GCs
on quasi-radial orbits.
The available CPU resources allowed us to follow 8 oscillations of the GCs
along their orbits and the main findings are: i) clusters with an initial high
enough King concentration parameter (c>=1.2), preserve up to 50% of their
initial mass; ii) the inner density distribution of the survived clusters keep
a King model profile; iii) GC-GC collisions have a negligible effect with
respect to that caused by the passage through the galactic center; iv) the
orbital energy dissipation due to the tidal interaction is of the same order of
that caused by dynamical friction; v) complex sub-structures like "ripples" and
"clumps" formed, as observed around real clusters.
These findings support the validity of the hypothesis of merging of GCs in
the galactic central region, with modes that deserve further careful
investigations.Comment: LaTeX 2e, AASTeX v5.x, 23 pages with 14 figures. Accepted for
publication on the Astrophysical Journal. Final version with major change
Resummation of Cactus Diagrams in Lattice QCD
We show how to perform a resummation, to all orders in perturbation theory,
of a certain class of gauge invariant diagrams in Lattice QCD. These diagrams
are often largely responsible for lattice artifacts. Our resummation leads to
an improved perturbative expansion. Applied to a number of cases of interest,
this expansion yields results remarkably close to corresponding nonperturbative
estimates.Comment: 18 page
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