1,582 research outputs found
Rapidly Rotating Fermions in an Anisotropic Trap
We consider a cold gas of non-interacting fermions in a two dimensional
harmonic trap with two different trapping frequencies ,
and discuss the effect of rotation on the density profile. Depending on the
rotation frequency and the trap anisotropy , the
density profile assumes two qualitatively different shapes. For small
anisotropy (), the
density consists of elliptical plateaus of constant density, corresponding to
Landau levels and is well described by a two dimensional local density
approximation. For large anisotropy (), the density profile is Gaussian in the strong confining
direction and semicircular with prominent Friedel oscillations in the weak
direction. In this regime, a one dimensional local density approximation is
well suited to describe the system. The crossover between the two regimes is
smooth where the step structure between the Landau level edges turn into
Friedel oscillations. Increasing the temperature causes the step structure or
the Friedel oscillations to wash out leaving a Boltzmann gas density profile.Comment: 14 pages, 7 figure
W Boson Inclusive Decays to Quarkonium at the LHC
In this paper, the production rates of quarkonia eta_c, J/psi, eta_b,
Upsilon, B_c and B_c^* through W boson decay at the LHC are calculated, at the
leading order in both the QCD coupling constant and in v, the typical velocity
of the heavy quark inside of mesons. It shows that a sizable number of
quarkonia from W boson decay will be produced at the LHC. Comparison with the
predictions by using quark fragmentation mechanism is also discussed. Results
show that, for the charmonium production through W decay, the difference
between predictions by the fragmentation mechanism and complete leading order
calculation is around 3%, and it is insensitive to the uncertainties of
theoretical parameters; however, for the bottomonium and B_c^(*) productions,
the difference cannot be ignored as the fragmentation mechanism is less
applicable here due to the relatively large ratio mb/mw.Comment: Updated to match the published version in EPJ
Quasi-Normal Modes of Schwarzschild Anti-De Sitter Black Holes: Electromagnetic and Gravitational Perturbations
We study the quasi-normal modes (QNM) of electromagnetic and gravitational
perturbations of a Schwarzschild black hole in an asymptotically Anti-de Sitter
(AdS) spacetime. Some of the electromagnetic modes do not oscillate, they only
decay, since they have pure imaginary frequencies. The gravitational modes show
peculiar features: the odd and even gravitational perturbations no longer have
the same characteristic quasinormal frequencies. There is a special mode for
odd perturbations whose behavior differs completely from the usual one in
scalar and electromagnetic perturbation in an AdS spacetime, but has a similar
behavior to the Schwarzschild black hole in an asymptotically flat spacetime:
the imaginary part of the frequency goes as 1/r+, where r+ is the horizon
radius. We also investigate the small black hole limit showing that the
imaginary part of the frequency goes as r+^2. These results are important to
the AdS/CFT conjecture since according to it the QNMs describe the approach to
equilibrium in the conformal field theory.Comment: 2 figure
The Correlated Colors of Transneptunian Binaries
We report resolved photometry of the primary and secondary components of 23
transneptunian binaries obtained with the Hubble Space Telescope. V-I colors of
the components range from 0.7 to 1.5 with a median uncertainty of 0.06
magnitudes. The colors of the primaries and secondaries are correlated with a
Spearman rank correlation probability of 99.99991%, 5 sigma for a normal
distribution. Fits to the primary vs. secondary colors are identical to within
measurement uncertainties. The color range of binaries as a group is
indistinguishable from that of the larger population of apparently single
transneptunian objects. Whatever mechanism produced the colors of apparently
single TNOs acted equally on binary systems. The most likely explanation is
that the colors of transneptunian objects and binaries alike are primordial and
indicative of their origin in a locally homogeneous, globally heterogeneous
protoplanetary disk.Comment: 28 pages, 4 figure, 4 tables. accepted to Icaru
Airborne observations of arctic-boreal water surface elevations from AirSWOT Ka-Band InSAR and LVIS LiDAR
AirSWOT is an experimental airborne Ka-band radar interferometer developed by NASA-JPL as a validation instrument for the forthcoming NASA Surface Water and Ocean Topography (SWOT) satellite mission. In 2017, AirSWOT was deployed as part of the NASA Arctic Boreal Vulnerability Experiment (ABoVE) to map surface water elevations across Alaska and western Canada. The result is the most extensive known collection of near-nadir airborne Ka-band interferometric synthetic aperture radar (InSAR) data and derivative high-resolution (3.6 m pixel) digital elevation models to produce water surface elevation (WSE) maps. This research provides a synoptic assessment of the 2017 AirSWOT ABoVE dataset to quantify regional WSE errors relative to coincident in situ field surveys and LiDAR data acquired from the NASA Land, Vegetation, and Ice Sensor (LVIS) airborne platform. Results show that AirSWOT WSE data can penetrate cloud cover and have nearly twice the swath-width of LVIS as flown for ABoVE (3.2 km vs. 1.8 km nominal swath-width). Despite noise and biases, spatially averaged AirSWOT WSEs can be used to estimate sub-seasonal hydrologic variability, as confirmed with field GPS surveys and in situ pressure transducers. This analysis informs AirSWOT ABoVE data users of known sources of measurement error in the WSEs as influenced by radar parameters including incidence angle, magnitude, coherence, and elevation uncertainty. The analysis also provides recommended best practices for extracting information from the dataset by using filters for these four parameters. Improvements to data handing would significantly increase the accuracy and spatial coverage of future AirSWOT WSE data collections, aiding scientific surface water studies, and improving the platform’s capability as an airborne validation instrument for SWOT
Development and validation of a computational model of the knee joint for the evaluation of surgical treatments for osteoarthritis
A three-dimensional (3D) knee joint computational model was developed and validated to predict knee joint contact forces
and pressures for different degrees of malalignment. A 3D computational knee model was created from high-resolution
radiological images to emulate passive sagittal rotation (full-extension to 658-flexion) and weight acceptance. A cadaveric
knee mounted on a six-degree-of-freedom robot was subjected to matching boundary and loading conditions. A ligamenttuning
process minimised kinematic differences between the robotically loaded cadaver specimen and the finite element
(FE) model. The model was validated by measured intra-articular force and pressure measurements. Percent full scale error
between FE-predicted and in vitro-measured values in the medial and lateral compartments were 6.67% and 5.94%,
respectively, for normalised peak pressure values, and 7.56% and 4.48%, respectively, for normalised force values. The knee
model can accurately predict normalised intra-articular pressure and forces for different loading conditions and could be
further developed for subject-specific surgical planning
Academic freedom: in justification of a universal ideal
This paper examines the justification for, and benefits of, academic freedom to academics, students, universities and the world at large. The paper surveys the development of the concept of academic freedom within Europe, more especially the impact of the reforms at the University of Berlin instigated by Wilhelm von Humboldt. Following from this, the paper examines the reasons why the various facets of academic freedom are important and why the principle should continue to be supported
How does the electromagnetic field couple to gravity, in particular to metric, nonmetricity, torsion, and curvature?
The coupling of the electromagnetic field to gravity is an age-old problem.
Presently, there is a resurgence of interest in it, mainly for two reasons: (i)
Experimental investigations are under way with ever increasing precision, be it
in the laboratory or by observing outer space. (ii) One desires to test out
alternatives to Einstein's gravitational theory, in particular those of a
gauge-theoretical nature, like Einstein-Cartan theory or metric-affine gravity.
A clean discussion requires a reflection on the foundations of electrodynamics.
If one bases electrodynamics on the conservation laws of electric charge and
magnetic flux, one finds Maxwell's equations expressed in terms of the
excitation H=(D,H) and the field strength F=(E,B) without any intervention of
the metric or the linear connection of spacetime. In other words, there is
still no coupling to gravity. Only the constitutive law H= functional(F)
mediates such a coupling. We discuss the different ways of how metric,
nonmetricity, torsion, and curvature can come into play here. Along the way, we
touch on non-local laws (Mashhoon), non-linear ones (Born-Infeld,
Heisenberg-Euler, Plebanski), linear ones, including the Abelian axion (Ni),
and find a method for deriving the metric from linear electrodynamics (Toupin,
Schoenberg). Finally, we discuss possible non-minimal coupling schemes.Comment: Latex2e, 26 pages. Contribution to "Testing Relativistic Gravity in
Space: Gyroscopes, Clocks, Interferometers ...", Proceedings of the 220th
Heraeus-Seminar, 22 - 27 August 1999 in Bad Honnef, C. Laemmerzahl et al.
(eds.). Springer, Berlin (2000) to be published (Revised version uses
Springer Latex macros; Sec. 6 substantially rewritten; appendices removed;
the list of references updated
TALPID3/KIAA0586 Regulates Multiple Aspects of Neuromuscular Patterning During Gastrointestinal Development in Animal Models and Human
TALPID3/KIAA0586 is an evolutionary conserved protein, which plays an essential role in protein trafficking. Its role during gastrointestinal (GI) and enteric nervous system (ENS) development has not been studied previously. Here, we analyzed chicken, mouse and human embryonic GI tissues with TALPID3 mutations. The GI tract of TALPID3 chicken embryos was shortened and malformed. Histologically, the gut smooth muscle was mispatterned and enteric neural crest cells were scattered throughout the gut wall. Analysis of the Hedgehog pathway and gut extracellular matrix provided causative reasons for these defects. Interestingly, chicken intra-species grafting experiments and a conditional knockout mouse model showed that ENS formation did not require TALPID3, but was dependent on correct environmental cues. Surprisingly, the lack of TALPID3 in enteric neural crest cells (ENCC) affected smooth muscle and epithelial development in a non-cell-autonomous manner. Analysis of human gut fetal tissues with a KIAA0586 mutation showed strikingly similar findings compared to the animal models demonstrating conservation of TALPID3 and its necessary role in human GI tract development and patterning
Search for Higgs bosons decaying to tautau pairs in ppbar collisions at sqrt(s) = 1.96 TeV
We present a search for the production of neutral Higgs bosons decaying into
tautau pairs in ppbar collisions at a center-of-mass energy of 1.96 TeV. The
data, corresponding to an integrated luminosity of 5.4 fb-1, were collected by
the D0 experiment at the Fermilab Tevatron Collider. We set upper limits at the
95% C.L. on the product of production cross section and branching ratio for a
scalar resonance decaying into tautau pairs, and we then interpret these limits
as limits on the production of Higgs bosons in the minimal supersymmetric
standard model (MSSM) and as constraints in the MSSM parameter space.Comment: 7 pages, 5 figures, submitted to PL
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