11,099 research outputs found
Generalized Second-Order Thomas-Fermi Method for Superfluid Fermi Systems
Using the -expansion of the Green's function of the
Hartree-Fock-Bogoliubov equation, we extend the second-order Thomas-Fermi
approximation to generalized superfluid Fermi systems by including the
density-dependent effective mass and the spin-orbit potential. We first
implement and examine the full correction terms over different energy intervals
of the quasiparticle spectra in calculations of finite nuclei. Final
applications of this generalized Thomas-Fermi method are intended for various
inhomogeneous superfluid Fermi systems.Comment: 8 pages, 10 figures, PR
Density distributions of superheavy nuclei
We employed the Skyrme-Hartree-Fock model to investigate the density
distributions and their dependence on nuclear shapes and isospins in the
superheavy mass region. Different Skyrme forces were used for the calculations
with a special comparison to the experimental data in Pb. The
ground-state deformations, nuclear radii, neutron skin thicknesses and
-decay energies were also calculated. Density distributions were
discussed with the calculations of single-particle wavefunctions and shell
fillings. Calculations show that deformations have considerable effects on the
density distributions, with a detailed discussion on the 120 nucleus.
Earlier predictions of remarkably low central density are not supported when
deformation is allowed for.Comment: 7 pages, 10 figure
Outflow and dense gas emission from massive Infrared Dark Clouds
Infrared Dark Clouds are expected to harbor sources in different, very young
evolutionary stages. To better characterize these differences, we observed a
sample of 43 massive Infrared Dark Clouds, originally selected as candidate
high-mass starless cores, with the IRAM 30m telescope covering spectral line
tracers of low-density gas, high-density gas, molecular outflows/jets and
temperature effects. The SiO(2-1) observations reveal detections toward 18
sources. Assuming that SiO is exclusively produced by sputtering from dust
grains, this implies that at least in 40% of this sample star formation is
on-going. A broad range of SiO line-widths is observed (between 2.2 and
65km/s), and we discuss potential origins for this velocity spread. While the
low-density tracers 12CO(2-1) and 13CO(1-0) are detected in several velocity
components, the high-density tracer H13CO+(1--0) generally shows only a single
velocity component and is hence well suited for kinematic distance estimates of
IRDCs. Furthermore, the H13CO+ line-width is on average 1.5 times larger than
that of previously observed NH3(1,1). This is indicative of more motion at the
denser core centers, either due to turbulence or beginning star formation
activity. In addition, we detect CH3CN toward only six sources whereas CH3OH is
observed toward approximately 40% of the sample. Estimates of the CH3CN and
CH3OH abundances are low with average values of 1.2x10^{-10} and 4.3x10^{-10},
respectively. These results are consistent with chemical models at the earliest
evolutionary stages of high-mass star formation. Furthermore, the CH3OH
abundances compare well to recently reported values for low-mass starless
cores.Comment: 22 pages (ApJ referee style), 7 figures, accepted for Ap
Phase Transitions in the Symmetric Kondo Lattice Model in Two and Three Dimensions
We present an application of high-order series expansion in the coupling
constants for the ground state properties of correlated lattice fermion
systems. Expansions have been generated up to order for and
for for certain properties of the symmetric Kondo lattice
model. Analyzing the susceptibility series, we find evidence for a continuous
phase transition from the ``spin liquid'' phase characteristic of a ``Kondo
Insulator'' to an antiferromagnetically ordered phase in dimensions as
the antiferromagnetic Kondo coupling is decreased. The critical point is
estimated to be at for square lattice and
for simple-cubic lattice.Comment: 12 pages, Revtex, replace previous corrupted fil
The KX method for producing K-band flux-limited samples of quasars
The longstanding question of the extent to which the quasar population is
affected by dust extinction, within host galaxies or galaxies along the line of
sight, remains open. More generally, the spectral energy distributions of
quasars vary significantly and flux-limited samples defined at different
wavelengths include different quasars. Surveys employing flux measurements at
widely separated wavelengths are necessary to characterise fully the spectral
properties of the quasar population. The availability of panoramic
near-infrared detectors on large telescopes provides the opportunity to
undertake surveys capable of establishing the importance of extinction by dust
on the observed population of quasars. We introduce an efficient method for
selecting K-band, flux-limited samples of quasars, termed ``KX'' by analogy
with the UVX method. This method exploits the difference between the power-law
nature of quasar spectra and the convex spectra of stars: quasars are
relatively brighter than stars at both short wavelengths (the UVX method) and
long wavelengths (the KX method). We consider the feasibility of undertaking a
large-area KX survey for damped Ly-alpha galaxies and gravitational lenses
using the planned UKIRT wide-field near-infrared camera.Comment: 6 pages, 3 figures, to appear in MNRA
4-manifolds and topological modular forms
We build a connection between topology of smooth 4-manifolds and the theory of topological modular forms by considering topologically twisted compactification of 6d (1,0) theories on 4-manifolds with flavor symmetry backgrounds. The effective 2d theory has (0,1) supersymmetry and, possibly, a residual flavor symmetry. The equivariant topological Witten genus of this 2d theory then produces a new invariant of the 4-manifold equipped with a principle bundle, valued in the ring of equivariant weakly holomorphic (topological) modular forms. We describe basic properties of this map and present a few simple examples. As a byproduct, we obtain some new results on 't Hooft anomalies of 6d (1,0) theories and a better understanding of the relation between 2d (0,1) theories and TMF spectra
Simulation of Guided Wave Propagating in Composite Laminates with a Fast Finite Element-Based Method
Discrete-Layer Piezoelectric Plate and Shell Models for Active Tip-Clearance Control
The objectives of this work were to develop computational tools for the analysis of active-sensory composite structures with added or embedded piezoelectric layers. The targeted application for this class of smart composite laminates and the analytical development is the accomplishment of active tip-clearance control in turbomachinery components. Two distinct theories and analytical models were developed and explored under this contract: (1) a discrete-layer plate theory and corresponding computational models, and (2) a three dimensional general discrete-layer element generated in curvilinear coordinates for modeling laminated composite piezoelectric shells. Both models were developed from the complete electromechanical constitutive relations of piezoelectric materials, and incorporate both displacements and potentials as state variables. This report describes the development and results of these models. The discrete-layer theories imply that the displacement field and electrostatic potential through-the-thickness of the laminate are described over an individual layer rather than as a smeared function over the thickness of the entire plate or shell thickness. This is especially crucial for composites with embedded piezoelectric layers, as the actuating and sensing elements within these layers are poorly represented by effective or smeared properties. Linear Lagrange interpolation polynomials were used to describe the through-thickness laminate behavior. Both analytic and finite element approximations were used in the plane or surface of the structure. In this context, theoretical developments are presented for the discrete-layer plate theory, the discrete-layer shell theory, and the formulation of an exact solution for simply-supported piezoelectric plates. Finally, evaluations and results from a number of separate examples are presented for the static and dynamic analysis of the plate geometry. Comparisons between the different approaches are provided when possible, and initial conclusions regarding the accuracy and limitations of these models are given
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