20,848 research outputs found
Robust variable selection in partially varying coefficient single-index model
By combining basis function approximations and smoothly clipped absolute deviation (SCAD) penalty, this paper proposes a robust variable selection procedure for a partially varying coefficient single-index model based on modal regression. The proposed procedure simultaneously selects significant variables in the parametric components and the nonparametric components. With appropriate selection of the tuning parameters, we establish the theoretical properties of our procedure, including consistency in variable selection and the oracle property in estimation. Furthermore, we also discuss the bandwidth selection and propose a modified expectation-maximization (EM)-type algorithm for the proposed estimation procedure. The finite sample properties of the proposed estimators are illustrated by some simulation examples.The research of Zhu is partially supported by National Natural Science Foundation of China (NNSFC) under Grants 71171075, 71221001 and 71031004. The research of Yu is supported by NNSFC under Grant 11261048
Temperature - pressure phase diagram of the superconducting iron pnictide LiFeP
Electrical-resistivity and magnetic-susceptibility measurements under
hydrostatic pressure up to p = 2.75 GPa have been performed on superconducting
LiFeP. A broad superconducting (SC) region exists in the temperature - pressure
(T-p) phase diagram. No indications for a spin-density-wave transition have
been found, but an enhanced resistivity coefficient at low pressures hints at
the presence of magnetic fluctuations. Our results show that the
superconducting state in LiFeP is more robust than in the isostructural and
isoelectronic LiFeAs. We suggest that this finding is related to the nearly
regular [FeP_4] tetrahedron in LiFeP.Comment: 4 pages, 4 figure
Generation of entangled photons by trapped ions in microcavities under a magnetic field gradient
We propose a potential scheme to generate entangled photons by manipulating
trapped ions embedded in two-mode microcavities, respectively, assisted by a
magnetic field gradient. By means of the spin-spin coupling due to the magnetic
field gradient and the Coulomb repulsion between the ions, we show how to
efficiently generate entangled photons by detecting the internal states of the
trapped ions. We emphasize that our scheme is advantageous to create complete
sets of entangled multi-photon states. The requirement and the experimental
feasibility of our proposal are discussed in detail.Comment: 2 Tables, 2 Figures, To appear in Phys. Rev.
Generation of N-qubit W state with rf-SQUID qubits by adiabatic passage
A simple scheme is presented to generate n-qubit W state with
rf-superconducting quantum interference devices (rf-SQUIDs) in cavity QED
through adiabatic passage. Because of the achievable strong coupling for
rf-SQUID qubits embedded in cavity QED, we can get the desired state with high
success probability. Furthermore, the scheme is insensitive to position
inaccuracy of the rf-SQUIDs. The numerical simulation shows that, by using
present experimental techniques, we can achieve our scheme with very high
success probability, and the fidelity could be eventually unity with the help
of dissipation.Comment: to appear in Phys. Rev.
Dynamical study of the possible molecular state X(3872) with the s-channel one gluon exchange interaction
The recently observed X(3872) resonance, which is difficult to be assigned a
conventional charmonium state in the quark model, may be interpreted
as a molecular state. Such a molecular state is a hidden flavor four quark
state because of its charmonium-like quantum numbers. The s-channel one gluon
exchange is an interaction which only acts in the hidden flavor multi-quark
system. In this paper, we will study the X(3872) and other similiar hidden
flavor molecular states in a quark model by taking into account of the
s-channel one gluon exchange interaction
Luminous Infrared Galaxies in the Local Universe
We study the morphology and star formation properties of 159 local luminous
infrared galaxy (LIRG) using multi-color images from Data Release 2 (DR2) of
the Sloan Digital Sky Survey (SDSS). The LIRGs are selected from a
cross-correlation analysis between the IRAS survey and SDSS. They are all
brighter than 15.9 mag in the r-band and below redshift ~ 0.1, and so can be
reliably classified morphologically. We find that the fractions of
interacting/merging and spiral galaxies are ~ 48% and ~ 40% respectively. Our
results complement and confirm the decline (increase) in the fraction of spiral
(interacting/merging) galaxies from z ~1 to z ~ 0.1, as found by Melbourne, Koo
& Le Floc'h (2005). About 75% of spiral galaxies in the local LIRGs are barred,
indicating that bars may play an important role in triggering star formation
rates > 20 M_{sun}/yr in the local universe. Compared with high redshift LIRGs,
local LIRGs have lower specific star formation rates, smaller cold gas
fractions and a narrower range of stellar masses. Local LIRGs appear to be
either merging galaxies forming intermediate mass ellipticals or spiral
galaxies undergoing high star formation activities regulated by bars.Comment: 22 pages, 5 figures, accepted for publication in ApJ, title changed,
typos corrected,major revisions following referee's comments,updated
reference
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