2,584 research outputs found
Flux Dendrites of Opposite Polarity in Superconducting MgB rings observed with magneto-optical imaging
Magneto-optical imaging was used to observe flux dendrites with opposite
polarities simultaneously penetrate superconducting, ring-shaped MgB films.
By applying a perpendicular magnetic field, branching dendritic structures
nucleate at the outer edge and abruptly propagate deep into the rings. When
these structures reach close to the inner edge, where flux with opposite
polarity has penetrated the superconductor, they occasionally trigger anti-flux
dendrites. These anti-dendrites do not branch, but instead trace the triggering
dendrite in the backward direction. Two trigger mechanisms, a non-local
magnetic and a local thermal, are considered as possible explanations for this
unexpected behaviour. Increasing the applied field further, the rings are
perforated by dendrites which carry flux to the center hole. Repeated
perforations lead to a reversed field profile and new features of dendrite
activity when the applied field is subsequently reduced.Comment: 6 pages, 6 figures, accepted to Phys. Rev.
Fringe proteins modulate Notch-ligand cis and trans interactions to specify signaling states
The Notch signaling pathway consists of multiple types of receptors and ligands, whose interactions can be tuned by Fringe glycosyltransferases. A major challenge is to determine how these components control the specificity and directionality of Notch signaling in developmental contexts. Here, we analyzed same-cell (cis) Notch-ligand interactions for Notch1, Dll1, and Jag1, and their dependence on Fringe protein expression in mammalian cells. We found that Dll1 and Jag1 can cis-inhibit Notch1, and Fringe proteins modulate these interactions in a way that parallels their effects on trans interactions. Fringe similarly modulated Notch-ligand cis interactions during Drosophila development. Based on these and previously identified interactions, we show how the design of the Notch signaling pathway leads to a restricted repertoire of signaling states that promote heterotypic signaling between distinct cell types, providing insight into the design principles of the Notch signaling system, and the specific developmental process of Drosophila dorsal-ventral boundary formation
Mesoscopic colonization of a spectral band
We consider the unitary matrix model in the limit where the size of the
matrices become infinite and in the critical situation when a new spectral band
is about to emerge. In previous works the number of expected eigenvalues in a
neighborhood of the band was fixed and finite, a situation that was termed
"birth of a cut" or "first colonization". We now consider the transitional
regime where this microscopic population in the new band grows without bounds
but at a slower rate than the size of the matrix. The local population in the
new band organizes in a "mesoscopic" regime, in between the macroscopic
behavior of the full system and the previously studied microscopic one. The
mesoscopic colony may form a finite number of new bands, with a maximum number
dictated by the degree of criticality of the original potential. We describe
the delicate scaling limit that realizes/controls the mesoscopic colony. The
method we use is the steepest descent analysis of the Riemann-Hilbert problem
that is satisfied by the associated orthogonal polynomials.Comment: 17 pages, 2 figures, minor corrections and addition
Prospectus, August 1988
https://spark.parkland.edu/prospectus_1988/1000/thumbnail.jp
Iterative graph cuts for image segmentation with a nonlinear statistical shape prior
Shape-based regularization has proven to be a useful method for delineating
objects within noisy images where one has prior knowledge of the shape of the
targeted object. When a collection of possible shapes is available, the
specification of a shape prior using kernel density estimation is a natural
technique. Unfortunately, energy functionals arising from kernel density
estimation are of a form that makes them impossible to directly minimize using
efficient optimization algorithms such as graph cuts. Our main contribution is
to show how one may recast the energy functional into a form that is
minimizable iteratively and efficiently using graph cuts.Comment: Revision submitted to JMIV (02/24/13
UV and FIR selected star-forming galaxies at z=0: differences and overlaps
We study two samples of local galaxies, one is UV (GALEX) selected and the
other FIR (IRAS) selected, to address the question whether UV and FIR surveys
see the two sides ('bright' and 'dark') of the star formation of the same
population of galaxies or two different populations of star forming galaxies.
No significant difference between the L () luminosity
functions of the UV and FIR samples is found. Also, after the correction for
the `Malmquist bias' (bias for flux limited samples), the FIR-to-UV ratio v.s.
L relations of the two samples are consistent with each other. In the
range of 9 \la \log(L_{tot}/L_\sun) \la 12, both can be approximated by a
simple linear relation of \log (L_{60}/L_{FUV})=\log(L_{tot}/L_\sun)-9.66.
These are consistent with the hypothesis that the two samples represent the
same population of star forming galaxies, and their well documented differences
in L and in FIR-to-UV ratio are due only to the selection effect. A
comparison between the UV luminosity functions shows marginal evidence for a
population of faint UV galaxies missing in the FIR selected sample. The
contribution from these 'FIR-quiet' galaxies to the overall UV population is
insignificant, given that the K-band luminosity functions (i.e. the stellar
mass functions) of the two samples do not show any significant difference.Comment: 21 pages, 7 figures. Accepted by Ap
The Pure Virtual Braid Group Is Quadratic
If an augmented algebra K over Q is filtered by powers of its augmentation
ideal I, the associated graded algebra grK need not in general be quadratic:
although it is generated in degree 1, its relations may not be generated by
homogeneous relations of degree 2. In this paper we give a sufficient criterion
(called the PVH Criterion) for grK to be quadratic. When K is the group algebra
of a group G, quadraticity is known to be equivalent to the existence of a (not
necessarily homomorphic) universal finite type invariant for G. Thus the PVH
Criterion also implies the existence of such a universal finite type invariant
for the group G. We apply the PVH Criterion to the group algebra of the pure
virtual braid group (also known as the quasi-triangular group), and show that
the corresponding associated graded algebra is quadratic, and hence that these
groups have a (not necessarily homomorphic) universal finite type invariant.Comment: 53 pages, 15 figures. Some clarifications added and inaccuracies
corrected, reflecting suggestions made by the referee of the published
version of the pape
Extinction Corrected Star Formation Rates Empirically Derived from Ultraviolet-Optical Colors
Using a sample of galaxies from the Sloan Digital Sky Survey spectroscopic
catalog with measured star-formation rates (SFRs) and ultraviolet (UV)
photometry from the GALEX Medium Imaging Survey, we derived empirical linear
correlations between the SFR to UV luminosity ratio and the UV-optical colors
of blue sequence galaxies. The relations provide a simple prescription to
correct UV data for dust attenuation that best reconciles the SFRs derived from
UV and emission line data. The method breaks down for the red sequence
population as well as for very blue galaxies such as the local ``supercompact''
UV luminous galaxies and the majority of high redshift Lyman Break Galaxies
which form a low attenuation sequence of their own.Comment: 20 pages, 11 figures, accepted for publication in the ApJS GALEX
special issu
Aquilegia, Vol. 18 No. 5, September-December 1994: Newsletter of the Colorado Native Plant Society
https://epublications.regis.edu/aquilegia/1073/thumbnail.jp
A Lattice Study of the Nucleon Excited States with Domain Wall Fermions
We present results of our numerical calculation of the mass spectrum for
isospin one-half and spin one-half non-strange baryons, i.e. the ground and
excited states of the nucleon, in quenched lattice QCD. We use a new lattice
discretization scheme for fermions, domain wall fermions, which possess almost
exact chiral symmetry at non-zero lattice spacing. We make a systematic
investigation of the negative-parity spectrum by using two distinct
interpolating operators at on a
lattice. The mass estimates extracted from the two operators are consistent
with each other. The observed large mass splitting between this state,
, and the positive-parity ground state, the nucleon N(939), is well
reproduced by our calculations. We have also calculated the mass of the first
positive-parity excited state and found that it is heavier than the
negative-parity excited state for the quark masses studied.Comment: 46 pages, REVTeX, 11 figures included, revised version accepted for
publication in Phys. Rev.
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