20,092 research outputs found
GNSS troposphere tomography based on two-step reconstructions using GPS observations and COSMIC profiles
Traditionally, balloon-based radiosonde soundings are
used to study the spatial distribution of atmospheric water vapour. However,
this approach cannot be frequently employed due to its high cost. In
contrast, GPS tomography technique can obtain water vapour in a high temporal
resolution. In the tomography technique, an iterative or non-iterative
reconstruction algorithm is usually utilised to overcome rank deficiency of
observation equations for water vapour inversion. However, the single
iterative or non-iterative reconstruction algorithm has their limitations.
For instance, the iterative reconstruction algorithm requires accurate
initial values of water vapour while the non-iterative reconstruction
algorithm needs proper constraint conditions. To overcome these drawbacks,
we present a combined iterative and non-iterative reconstruction approach
for the three-dimensional (3-D) water vapour inversion using GPS observations
and COSMIC profiles. In this approach, the non-iterative reconstruction
algorithm is first used to estimate water vapour density based on a priori
water vapour information derived from COSMIC radio occultation data. The
estimates are then employed as initial values in the iterative
reconstruction algorithm. The largest advantage of this approach is that
precise initial values of water vapour density that are essential in the
iterative reconstruction algorithm can be obtained. This combined
reconstruction algorithm (CRA) is evaluated using 10-day GPS observations in
Hong Kong and COSMIC profiles. The test results indicate that the water
vapor accuracy from CRA is 16 and 14% higher than that of iterative
and non-iterative reconstruction approaches, respectively. In addition, the
tomography results obtained from the CRA are further validated using
radiosonde data. Results indicate that water vapour densities derived from
the CRA agree with radiosonde results very well at altitudes above 2.5 km.
The average RMS value of their differences above 2.5 km is 0.44 g m<sup>−3</sup>
Vortex State in Na_xCoO_2.yH_2O: p_x\pm ip_y-wave versus d_{x^2-y^2}\pm id_{xy}-wave Pairing
Based on an effective Hamiltonian specified in the triangular lattice with
possible - or -wave pairing, which has
close relevance to the newly discovered NaCoOHO, the
electronic structure of the vortex state is studied by solving the
Bogoliubov-de Gennes equations. It is found that -wave is favored
for the electron doping as the hopping integral . The lowest-lying vortex
bound states are found to have respectively zero and positive energies for
- and -wave superconductors, whose vortex
structures exhibit the intriguing six-fold symmetry. In the presence of strong
on-site repulsion, the antiferromagnetic and ferromagnetic orders are induced
around the vortex cores for the former and the latter, respectively, both of
which cause the splitting of the LDOS peaks due to the lifting of spin
degeneracy. STM and NMR measurements are able to probe the new features of
vortex states uncovered in this work.Comment: 4 pages, 4 figures, The slightly shorter version was submitted to PR
Spectroscopy of reflection-asymmetric nuclei with relativistic energy density functionals
Quadrupole and octupole deformation energy surfaces, low-energy excitation
spectra and transition rates in fourteen isotopic chains: Xe, Ba, Ce, Nd, Sm,
Gd, Rn, Ra, Th, U, Pu, Cm, Cf, and Fm, are systematically analyzed using a
theoretical framework based on a quadrupole-octupole collective Hamiltonian
(QOCH), with parameters determined by constrained reflection-asymmetric and
axially-symmetric relativistic mean-field calculations. The microscopic QOCH
model based on the PC-PK1 energy density functional and -interaction
pairing is shown to accurately describe the empirical trend of low-energy
quadrupole and octupole collective states, and predicted spectroscopic
properties are consistent with recent microscopic calculations based on both
relativistic and non-relativistic energy density functionals. Low-energy
negative-parity bands, average octupole deformations, and transition rates show
evidence for octupole collectivity in both mass regions, for which a
microscopic mechanism is discussed in terms of evolution of single-nucleon
orbitals with deformation.Comment: 36 pages, 21 figures, Accepted for Publication in Physical Review
Spectroscopic Properties of QSOs Selected from Ultraluminous Infrared Galaxy Samples
We performed spectroscopic observations for a large infrared QSO sample with
a total of 25 objects. The sample was compiled from the QDOT redshift survey,
the 1 Jy ULIRGs survey and a sample obtained by a cross-correlation study of
the IRAS Point Source Catalogue with the ROSAT All Sky Survey Catalogue.
Statistical analyses of the optical spectra show that the vast majority of
infrared QSOs have narrow permitted emission lines (with FWHM of Hbeta less
than 4000 km/s) and more than 60% of them are luminous narrow line Seyfert 1
galaxies. Two of the infrared QSOs are also classified as low ionization BAL
QSOs. More than 70% of infrared QSOs are moderately or extremely strong Fe II
emitters. This is the highest percentage of strong Fe II emitters in all
subclasses of QSO/Seyfert 1 samples. We found that the Fe II to Hbeta, line
ratio is significantly correlated with the [OIII]5007 peak and Hbeta blueshift.
Soft X-ray weak infrared QSOs tend to have large blueshifts in permitted
emission lines and significant Fe II48,49 (5100--5400 A) residuals relative to
the Boroson & Green Fe II template. If the blueshifts in permitted lines are
caused by outflows, then they appear to be common in infrared QSOs. As the
infrared-selected QSO sample includes both luminous narrow line Seyfert 1
galaxies and low ionization BAL QSOs, it could be a useful laboratory to
investigate the evolutionary connection among these objects.Comment: 35 pages,14 figures, 4 tables, accepted for publication in A
Anisotropic magnetoresistance in topological insulator Bi1.5Sb0.5Te1.8Se1.2/CoFe heterostructures
Topological insulator is composed of an insulating bulk state and time
reversal symmetry protected two-dimensional surface states. One of the
characteristics of the surface states is the locking between electron momentum
and spin orientation. Here, we report a novel in-plane anisotropic
magnetoresistance in topological insulator Bi1.5Sb0.5Te1.8Se1.2/CoFe
heterostructures. To explain the novel effect, we propose that the
Bi1.5Sb0.5Te1.8Se1.2/CoFe heterostructure forms a spin-valve or Giant
magnetoresistance device due to spin-momentum locking. The novel in-plane
anisotropic magnetoresistance can be explained as a Giant magnetoresistance
effect of the Bi1.5Sb0.5Te1.8Se1.2/CoFe heterostructures.Comment: 19 pages including 7 figure
- …