19,542 research outputs found
Bubble Growth in Superfluid 3-He: The Dynamics of the Curved A-B Interface
We study the hydrodynamics of the A-B interface with finite curvature. The
interface tension is shown to enhance both the transition velocity and the
amplitudes of second sound. In addition, the magnetic signals emitted by the
growing bubble are calculated, and the interaction between many growing bubbles
is considered.Comment: 20 pages, 3 figures, LaTeX, ITP-UH 11/9
Phase Variation in the Pulse Profile of SMC X-1
We present the results of timing and spectral analysis of X-ray high state
observations of the high-mass X-ray pulsar SMC X-1 with Chandra, XMM-Newton,
and ROSAT, taken between 1991 and 2001. The source has L_X ~ 3-5 x 10^38
ergs/s, and the spectra can be modeled as a power law plus blackbody with kT_BB
\~ 0.18 keV and reprocessed emission radius R_BB ~ 2 x 10^8 cm, assuming a
distance of 60 kpc to the source. Energy-resolved pulse profiles show several
distinct forms, more than half of which include a second pulse in the soft
profile, previously documented only in hard energies. We also detect
significant variation in the phase shift between hard and soft pulses, as has
recently been reported in Her X-1. We suggest an explanation for the observed
characteristics of the soft pulses in terms of precession of the accretion
disk.Comment: 4 pages, 4 figures, accepted for publication in ApJL; v2 minor
corrections, as will appear in ApJ
Narrow Line Photoassociation in an Optical Lattice
With ultracold Sr in a 1D magic wavelength optical lattice, we
performed narrow line photoassociation spectroscopy near the SP intercombination transition. Nine least-bound vibrational molecular
levels associated with the long-range and potential energy surfaces
were measured and identified. A simple theoretical model accurately describes
the level positions and treats the effects of the lattice confinement on the
line shapes. The measured resonance strengths show that optical tuning of the
ground state scattering length should be possible without significant atom
loss.Comment: 4 pages, 4 figure
Resolving velocity space dynamics in continuum gyrokinetics
Many plasmas of interest to the astrophysical and fusion communities are
weakly collisional. In such plasmas, small scales can develop in the
distribution of particle velocities, potentially affecting observable
quantities such as turbulent fluxes. Consequently, it is necessary to monitor
velocity space resolution in gyrokinetic simulations. In this paper, we present
a set of computationally efficient diagnostics for measuring velocity space
resolution in gyrokinetic simulations and apply them to a range of plasma
physics phenomena using the continuum gyrokinetic code GS2. For the cases
considered here, it is found that the use of a collisionality at or below
experimental values allows for the resolution of plasma dynamics with
relatively few velocity space grid points. Additionally, we describe
implementation of an adaptive collision frequency which can be used to improve
velocity space resolution in the collisionless regime, where results are
expected to be independent of collision frequency.Comment: 20 pages, 11 figures, submitted to Phys. Plasma
Dissipation of the 3^He A-B Transition
A rigorous hydrodynamic theory of the A-B transition is presented. All
dissipative processes are considered. At low interface velocities, those
occurring on hydrodynamic length scales, not considered hitherto, are most
probably the dominant ones.Comment: 13 pages, REVTeX, 2 figures, ITP-UH 13/9
ShapeFit and ShapeKick for Robust, Scalable Structure from Motion
We introduce a new method for location recovery from pair-wise directions
that leverages an efficient convex program that comes with exact recovery
guarantees, even in the presence of adversarial outliers. When pairwise
directions represent scaled relative positions between pairs of views
(estimated for instance with epipolar geometry) our method can be used for
location recovery, that is the determination of relative pose up to a single
unknown scale. For this task, our method yields performance comparable to the
state-of-the-art with an order of magnitude speed-up. Our proposed numerical
framework is flexible in that it accommodates other approaches to location
recovery and can be used to speed up other methods. These properties are
demonstrated by extensively testing against state-of-the-art methods for
location recovery on 13 large, irregular collections of images of real scenes
in addition to simulated data with ground truth
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