2,324 research outputs found
Coupling of Nonlocal Potentials to Electromagnetic Fields
Nonlocal Hamiltonians are used widely in first-principles quantum
calculations; the nonlocality stems from eliminating undesired degrees of
freedom, e.g. core electrons. To date, attempts to couple nonlocal systems to
external electromagnetic (EM) fields have been heuristic or limited to weak or
long wavelength fields. Using Feynman path integrals, we derive an exact,
closed-form coupling of arbitrary EM fields to nonlocal systems. Our results
justify and clarify the couplings used to date and are essential for systematic
computation of linear and especially nonlinear response.Comment: 1 figure, 1 tabl
Competing topological superconducting phases in FeSeTe
We demonstrate that recent angle-resolved photo-emission spectroscopy
experiments provide strong evidence for the existence of two competing
topological superconducting phases in FeSeTe. The coupling of
their underlying microscopic mechanisms -- one based on a three-dimensional
topological insulator, one based on two-dimensional superconductivity --
stabilizes topological superconductivity over a wide range of parameters, and
gives rise to two disjoint topological regions in the phase diagram of
FeSeTe. We show that the topological origin of these regions
can be identified by considering the form of Majorana edge modes at domain
walls
The Halo Boundary of Galaxy Clusters in the SDSS
Mass around dark matter halos can be divided into "infalling" material and
"collapsed" material that has passed through at least one pericenter.
Analytical models and simulations predict a rapid drop in the halo density
profile associated with the transition between these two regimes. Using data
from SDSS, we explore the evidence for such a feature in the density profiles
of galaxy clusters and investigate the connection between this feature and a
possible phase space boundary. We first estimate the steepening of the outer
galaxy density profile around clusters: the profiles show an abrupt steepening,
providing evidence for truncation of the halo profile. Next, we measure the
galaxy density profile around clusters using two sets of galaxies selected
based on color. We find evidence of an abrupt change in the galaxy colors that
coincides with the location of the steepening of the density profile. Since
galaxies are likely to be quenched of star formation and turn red inside of
clusters, this change in the galaxy color distribution can be interpreted as
the transition from an infalling regime to a collapsed regime. We also measure
this transition using a model comparison approach which has been used recently
in studies of the "splashback" phenomenon, but find that this approach is not a
robust way to quantify the significance of detecting a splashback-like feature.
Finally, we perform measurements using an independent cluster catalog to test
for potential systematic errors associated with cluster selection. We identify
several avenues for future work: improved understanding of the small-scale
galaxy profile, lensing measurements, identification of proxies for the halo
accretion rate, and other tests. With upcoming data from the DES, KiDS and HSC
surveys, we can expect significant improvements in the study of halo
boundaries.Comment: 17 pages, 8 figure
QCD Radiative Corrections to the Leptonic Decay Rate of the B_c Meson
The QCD radiative corrections to the leptonic decay rate of the meson
are calculated using the formalism of nonrelativistic QCD (NRQCD) to separate
short-distance and long-distance effects. The decay constant is factored
into a sum of NRQCD matrix elements each multiplied by a short-distance
coefficient. The short-distance coefficient for the leading matrix element is
calculated to order by matching a perturbative calculation in full
QCD with the corresponding perturbative calculation in NRQCD. This
short-distance correction decreases the leptonic decay rate by approximately
.Comment: Changed Eq. 2 to read 1/(8 \pi), put in a missing i M_{B_c} in Eq.
18, and put in a normalisation factor of 2 M_{B_c} in Eq. 19
Anomalous Exponent of the Spin Correlation Function of a Quantum Hall Edge
The charge and spin correlation functions of partially spin-polarized edge
electrons of a quantum Hall bar are studied using effective Hamiltonian and
bosonization techniques. In the presence of the Coulomb interaction between the
edges with opposite chirality we find a different crossover behavior in spin
and charge correlation functions. The crossover of the spin correlation
function in the Coulomb dominated regime is characterized by an anomalous
exponent, which originates from the finite value of the effective interaction
for the spin degree of freedom in the long wavelength limit. The anomalous
exponent may be determined by measuring nuclear spin relaxation rates in a
narrow quantum Hall bar or in a quantum wire in strong magnetic fields.Comment: 4 pages, Revtex file, no figures. To appear in Physical Revews B,
Rapid communication
Understanding open ports in Android applications: Discovery, diagnosis, and security assessment
Perturbative QCD Fragmentation Functions for and Production
The dominant production mechanism for bound states in high
energy processes is the production of a high energy or quark,
followed by its fragmentation into the state. We calculate the
fragmentation functions for the production of the S-wave states and
to leading order in the QCD coupling constant. The fragmentation
probabilities for and
are approximately and , while those
for and are smaller by almost two
orders of magnitude.Comment: Latex, 12 pages, 3 figures available upon request, NUHEP-TH-93-
External Tank (ET) Foam Thermal/Structural Analysis Project
An independent study was performed to assess the pre-launch thermally induced stresses in the Space Shuttle External Tank Bipod closeout and Ice/Frost ramps (IFRs). Finite element models with various levels of detail were built that included the three types of foam (BX-265, NCFI 24-124, and PDL 1034) and the underlying structure and bracketry. Temperature profiles generated by the thermal analyses were input to the structural models to calculate the stress levels. An area of high stress in the Bipod closeout was found along the aluminum tank wall near the phenolic insulator and along the phenolic insulator itself. This area of high stress might be prone to cracking and possible delamination. There is a small region of slightly increased stress in the NCFI 24-124 foam near its joint with the Bipod closeout BX-265 foam. The calculated stresses in the NCFI 24-124 acreage foam are highest at the NCFI 24-124/PDL 1034/tank wall interface under the LO2 and LH2 IFRs. The highest calculated stresses in the LH2 NCFI 24-124 foam are higher than in similar locations in the LO2 IFR. This finding is consistent with the dissection results of IFRs on ET-120
The Embryonic Transcriptome Of The Red-Eared Slider Turtle (Trachemys Scripta)
The bony shell of the turtle is an evolutionary novelty not found in any other group of animals, however, research into its formation has suggested that it has evolved through modification of conserved developmental mechanisms. Although these mechanisms have been extensively characterized in model organisms, the tools for characterizing them in non-model organisms such as turtles have been limited by a lack of genomic resources. We have used a next generation sequencing approach to generate and assemble a transcriptome from stage 14 and 17 Trachemys scripta embryos, stages during which important events in shell development are known to take place. The transcriptome consists of 231,876 sequences with an N-50 of 1,166 bp. GO terms and EC codes were assigned to the 61,643 unique predicted proteins identified in the transcriptome sequences. All major GO categories and metabolic pathways are represented in the transcriptome. Transcriptome sequences were used to amplify several cDNA fragments designed for use as RNA in situ probes. One of these, BMP5, was hybridized to a T. scripta embryo and exhibits both conserved and novel expression patterns. The transcriptome sequences should be of broad use for understanding the evolution and development of the turtle shell and for annotating any future T. scripta genome sequences
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