42,946 research outputs found
Density dependence of the pairing interaction and pairing correlation in unstable nuclei
This work aims at a global assessment of the effect of the density dependence
of the zero-range pairing interaction. Systematic
Skyrme-Hartree-Fock-Bogoliubov calculations with the volume, surface and mixed
pairing forces are carried out to study the pairing gaps in even-even nuclei
over the whole nuclear chart. Calculations are also done in coordinate
representation for unstable semi-magic even-even nuclei. The calculated pairing
gaps are compared with empirical values from four different odd-even staggering
formulae. Calculations with the three pairing interactions are comparable for
most nuclei close to -stability line. However, the surface interaction
calculations predict neutron pairing gaps in neutron-rich nuclei that are
significantly stronger than those given by the mixed and volume pairing. On the
other hand, calculations with volume and mixed pairing forces show noticeable
reduction of neutron pairing gaps in nuclei far from the stability.Comment: 9 pages, 10 figures, 3 tables, printer-friendl
Survival ensembles by the sum of pairwise differences with application to lung cancer microarray studies
Lung cancer is among the most common cancers in the United States, in terms
of incidence and mortality. In 2009, it is estimated that more than 150,000
deaths will result from lung cancer alone. Genetic information is an extremely
valuable data source in characterizing the personal nature of cancer. Over the
past several years, investigators have conducted numerous association studies
where intensive genetic data is collected on relatively few patients compared
to the numbers of gene predictors, with one scientific goal being to identify
genetic features associated with cancer recurrence or survival. In this note,
we propose high-dimensional survival analysis through a new application of
boosting, a powerful tool in machine learning. Our approach is based on an
accelerated lifetime model and minimizing the sum of pairwise differences in
residuals. We apply our method to a recent microarray study of lung
adenocarcinoma and find that our ensemble is composed of 19 genes, while a
proportional hazards (PH) ensemble is composed of nine genes, a proper subset
of the 19-gene panel. In one of our simulation scenarios, we demonstrate that
PH boosting in a misspecified model tends to underfit and ignore
moderately-sized covariate effects, on average. Diagnostic analyses suggest
that the PH assumption is not satisfied in the microarray data and may explain,
in part, the discrepancy in the sets of active coefficients. Our simulation
studies and comparative data analyses demonstrate how statistical learning by
PH models alone is insufficient.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS426 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Competition of different coupling schemes in atomic nuclei
Shell model calculations reveal that the ground and low-lying yrast states of
the nuclei Pd and Cd are mainly built upon isoscalar
spin-aligned neutron-proton pairs each carrying the maximum angular momentum
J=9 allowed by the shell which is dominant in this nuclear region.
This mode of excitation is unique in nuclei and indicates that the spin-aligned
pair has to be considered as an essential building block in nuclear structure
calculations. In this contribution we will discuss this neutron-proton pair
coupling scheme in detail. In particular, we will explore the competition
between the normal monopole pair coupling and the spin-aligned coupling
schemes. Such a coupling may be useful in elucidating the structure properties
of and neighboring nuclei.Comment: 10 pages, 7 figures, 1 table. Proceedings of the Conference on
Advanced Many-Body and Statistical Methods in Mesoscopic Systems, Constanta,
Romania, June 27th - July 2nd 2011. To appear in Journal of Physics:
Conference Serie
Renormalization of the EWCL and its Application to LEP2
We perform a systematic one-loop renormalization on the electroweak chiral
Lagrangian (EWCL) up to operators and construct the renormalization
group equations (RGE) for the anomalous couplings. We examine the impact of the
triple gauge coupling (TGC) measurement from LEP2 to the uncertainty of the
parameter at the , and find that the uncertainty in the
TGC measurements can shift at least .Comment: 4 pages, 1 eps figure, uses ws-ijmpa.cls. Paralell talk given at
"International Conference on QCD and hadronic Physics", Beijing, China, 16-20
June, 200
Entanglement entropy and entanglement spectrum of the Kitaev model
In this paper, we obtain an exact formula for the entanglement entropy of the
ground state and all excited states of the Kitaev model. Remarkably, the
entanglement entropy can be expressed in a simple separable form S=S_G+S_F,
with S_F the entanglement entropy of a free Majorana fermion system and S_G
that of a Z_2 gauge field. The Z_2 gauge field part contributes to the
universal "topological entanglement entropy" of the ground state while the
fermion part is responsible for the non-local entanglement carried by the Z_2
vortices (visons) in the non-Abelian phase. Our result also enables the
calculation of the entire entanglement spectrum and the more general Renyi
entropy of the Kitaev model. Based on our results we propose a new quantity to
characterize topologically ordered states--the capacity of entanglement, which
can distinguish the states with and without topologically protected gapless
entanglement spectrum.Comment: 4.0 pages + supplementary material, published version in Phys. Rev.
Let
Floquet band structure of a semi-Dirac system
In this work we use Floquet-Bloch theory to study the influence of circularly
and linearly polarized light on two-dimensional band structures with semi-Dirac
band touching points, taking the anisotropic nearest neighbor hopping model on
the honeycomb lattice as an example. We find circularly polarized light opens a
gap and induces a band inversion to create a finite Chern number in the
two-band model. By contrast, linearly polarized light can either open up a gap
(polarized in the quadratically dispersing direction) or split the semi-Dirac
band touching point into two Dirac points (polarized in the linearly dispersing
direction) by an amount that depends on the amplitude of the light. Motivated
by recent pump-probe experiments, we investigated the non-equilibrium spectral
properties and momentum-dependent spin-texture of our model in the Floquet
state following a quench in absence of phonons, and in the presence of phonon
dissipation that leads to a steady-state independent of the pump protocol.
Finally, we make connections to optical measurements by computing the frequency
dependence of the longitudinal and transverse optical conductivity for this
two-band model. We analyze the various contributions from inter-band
transitions and different Floquet modes. Our results suggest strategies for
optically controlling band structures and experimentally measuring topological
Floquet systems.Comment: 17 pages, 8 figure
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