2,659 research outputs found
Dynamics and thermodynamics in spinor quantum gases
We discuss magnetism in spinor quantum gases theoretically and experimentally
with emphasis on temporal dynamics of the spinor order parameter in the
presence of an external magnetic field. In a simple coupled Gross-Pitaevskii
picture we observe a dramatic suppression of spin dynamics due to quadratic
Zeeman ''dephasing''. In view of an inhomogeneous density profile of the
trapped condensate we present evidence of spatial variations of spin dynamics.
In addition we study spinor quantum gases as a model system for thermodynamics
of Bose-Einstein condensation. As a particular example we present measurements
on condensate magnetisation due to the interaction with a thermal bath.Comment: 8 pages, 7 figure
Epithelial Migration and Non-adhesive Periderm Are Required for Digit Separation during Mammalian Development.
The fusion of digits or toes, syndactyly, can be part of complex syndromes, including van der Woude syndrome. A subset of van der Woude cases is caused by dominant-negative mutations in the epithelial transcription factor Grainyhead like-3 (GRHL3), and Grhl3-/-mice have soft-tissue syndactyly. Although impaired interdigital cell death of mesenchymal cells causes syndactyly in multiple genetic mutants, Grhl3-/- embryos had normal interdigital cell death, suggesting alternative mechanisms for syndactyly. We found that in digit separation, the overlying epidermis forms a migrating interdigital epithelial tongue (IET) when the epithelium invaginates to separate the digits. Normally, the non-adhesive surface periderm allows the IET to bifurcate as the digits separate. In contrast, in Grhl3-/- embryos, the IET moves normally between the digits but fails to bifurcate because of abnormal adhesion of the periderm. Our study identifies epidermal developmental processes required for digit separation
An empirical comparison of convertible bond valuation models
This paper empirically compares three convertible bond valuation models. We use an innovative approach where all model parameters are estimated by the Marquardt algorithm using a subsample of convertible bond prices. The model parameters are then used for out-of-sample forecasts of convertible bond prices. The mean absolute deviation is 1.86% for the Ayache-Forsyth-Vetzal model, 1.94% for the Tsiveriotis-Fernandes model, and 3.73% for the Brennan-Schwartz model. For this and other measures of fit, the Ayache-Forsyth-Vetzal and Tsiveriotis-Fernandes models outperform the Brennan-Schwartz model
White Light Interferometry for Quantitative Surface Characterization in Ion Sputtering Experiments
White light interferometry (WLI) can be used to obtain surface morphology
information on dimensional scale of millimeters with lateral resolution as good
as ~1 {\mu}m and depth resolution down to 1 nm. By performing true
three-dimensional imaging of sample surfaces, the WLI technique enables
accurate quantitative characterization of the geometry of surface features and
compares favorably to scanning electron and atomic force microscopies by
avoiding some of their drawbacks. In this paper, results of using the WLI
imaging technique to characterize the products of ion sputtering experiments
are reported. With a few figures, several example applications of the WLI
method are illustrated when used for (i) sputtering yield measurements and
time-to-depth conversion, (ii) optimizing ion beam current density profiles,
the shapes of sputtered craters, and multiple ion beam superposition and (iii)
quantitative characterization of surfaces processed with ions. In particular,
for sputter depth profiling experiments of 25Mg, 44Ca and 53Cr ion implants in
Si (implantation energy of 1 keV per nucleon), the depth calibration of the
measured depth profile curves determined by the WLI method appeared to be
self-consistent with TRIM simulations for such projectile-matrix systems. In
addition, high depth resolution of the WLI method is demonstrated for a case of
a Genesis solar wind Si collector surface processed by gas cluster ion beam: a
12.5 nm layer was removed from the processed surface, while the transition
length between the processed and untreated areas was 150 {\mu}m.Comment: Applied Surface Science, accepted: 7 pages and 8 figure
Applicability of the Broken-Bond Rule to the Surface Energy of the fcc Metals
We apply the Green's function based full-potential screened
Korringa-Kohn-Rostoker method in conjunction with the local density
approximation to study the surface energies of the noble and the fcc transition
and metals. The orientation dependence of the transition metal surface
energies can be well described taking into account only the broken bonds
between first neighbors, quite analogous to the behavior we recently found for
the noble metals [see cond-mat/0105207]. The (111) and (100) surfaces of the
metals show a jellium like behavior but for the more open surfaces we find
again the noble metals behavior but with larger deviation from the broken-bond
rule compared to the transition metals. Finally we show that the use of the
full potential is crucial to obtain accurate surface energy anisotropy ratios
for the vicinal surfaces.Comment: 13 pages, 5 figures, to appear in July in Surface Science Vol. 511,1
(2002
Evidence-Based Decompression in Malignant Biliary Obstruction
As recent advances in chemotherapy and surgical treatment have improved outcomes in patients with biliary cancers, the search for an optimal strategy for relief of their obstructive jaundice has become even more important. Without satisfactory relief of biliary obstruction, many patients would be ineligible for treatment. We review all prospective randomized trials and recent retrospective non-randomized studies for evidence that would support such a strategy. For distal malignant biliary obstruction, an optimal strategy would be insertion of metallic stents either endoscopically or percutaneously. Evidence shows that a metallic stent inserted percutaneously has better outcomes than plastic stents inserted endoscopically. For malignant hilar obstruction, percutaneous biliary drainage with or without metallic stents is preferred
Dimensional and Temperature Crossover in Trapped Bose Gases
We investigate the long-range phase coherence of homogeneous and trapped Bose
gases as a function of the geometry of the trap, the temperature, and the
mean-field interactions in the weakly interacting limit. We explicitly take
into account the (quasi)condensate depletion due to quantum and thermal
fluctuations, i.e., we include the effects of both phase and density
fluctuations. In particular, we determine the phase diagram of the gas by
calculating the off-diagonal one-particle density matrix and discuss the
various crossovers that occur in this phase diagram and the feasibility of
their experimental observation in trapped Bose gases.Comment: One figure added, typos corrected, refernces adde
Tweaking the spin-wave dispersion and suppressing the incommensurate phase in LiNiPO4 by iron substitution
Elastic and inelastic neutron scattering studies of
Li(NiFe)PO single crystals reveal anomalous spin-wave
dispersions along the crystallographic direction parallel to the characteristic
wave vector of the magnetic incommensurate phase. The anomalous spin-wave
dispersion ({\it magnetic soft mode}) indicates the instability of the
Ising-like ground state that eventually evolves into the incommensurate phase
as the temperature is raised. The pure LiNiPO system (), undergoes a
first-order magnetic phase transition from a long-range incommensurate phase to
an antiferromagnetic ground state at {\it T} = 20.8 K. At 20% Fe
concentrations, although the AFM ground state is to a large extent preserved as
that of the pure system, the phase transition is second-order, and the
incommensurate phase is completely suppressed. Analysis of the dispersion
curves using a Heisenberg spin Hamiltonian that includes inter- and in-plane
nearest and next-nearest neighbor couplings reveals frustration due to strong
competing interactions between nearest- and a next-nearest neighbor site,
consistent with the observed incommensurate structure. The Fe substitution only
slightly lowers the extent of the frustration, sufficient to suppress the IC
phase. An energy gap in the dispersion curves gradually decreases with the
increase of Fe content from 2 meV for the pure system () to
0.9 meV for
Resonantly-paired fermionic superfluids
We present a theory of a degenerate atomic Fermi gas, interacting through a
narrow Feshbach resonance, whose position and therefore strength can be tuned
experimentally, as demonstrated recently in ultracold trapped atomic gases. The
distinguishing feature of the theory is that its accuracy is controlled by a
dimensionless parameter proportional to the ratio of the width of the resonance
to Fermi energy. The theory is therefore quantitatively accurate for a narrow
Feshbach resonance. In the case of a narrow s-wave resonance, our analysis
leads to a quantitative description of the crossover between a weakly-paired
BCS superconductor of overlapping Cooper pairs and a strongly-paired molecular
Bose-Einstein condensate of diatomic molecules. In the case of pairing via a
p-wave resonance, that we show is always narrow for a sufficiently low density,
we predict a detuning-temperature phase diagram, that in the course of a
BCS-BEC crossover can exhibit a host of thermodynamically-distinct phases
separated by quantum and classical phase transitions. For an intermediate
strength of the dipolar anisotropy, the system exhibits a p_x + i p_y paired
superfluidity that undergoes a topological phase transition between a
weakly-coupled gapless ground state at large positive detuning and a
strongly-paired fully-gapped molecular superfluid for a negative detuning. In
two dimensions the former state is characterized by a Pfaffian ground state
exhibiting topological order and non-Abelian vortex excitations familiar from
fractional quantum Hall systems.Comment: 71 pgs, 28 eps figure
Bar fraction in lenticular galaxies: dependence on luminosity and environment
We present a study of bars in lenticular galaxies based on a sample of 371
galaxies from the SDSS-DR 7 and 2MASS in optical and near-infrared bands,
respectively. We found a bar in 15% of the lenticular galaxies in our sample,
which is consistent with recent studies. The barred galaxy fraction shows a
luminosity dependence, with faint lenticular galaxies (MK > -24.5, total
absolute magnitude in K band) having a larger fraction of bars than bright
lenticular galaxies (MK < -24.5). A similar trend is seen when Mr = -21.5, the
total absolute magnitude in SDSS r band is used to divide the sample into faint
and bright lenticular galaxies. We find that faint galaxies in clusters show a
higher bar fraction than their counterparts in the field. This suggests that
the formation of bars in lenticular galaxies not only depends on the total
luminosity of galaxy but also on the environment of the host galaxy.Comment: Accepted for publication in MNRAS: Letters, 5 pages, 4 figure
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