Flux Dendrites of Opposite Polarity in Superconducting MgB2_2 rings observed with magneto-optical imaging

Magneto-optical imaging was used to observe flux dendrites with opposite polarities simultaneously penetrate superconducting, ring-shaped MgB$_2$ 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$_{tot}$ ($=L_{60}+L_{FUV}$) 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$_{tot}$ 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$_{tot}$ 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 $N^*$ spectrum by using two distinct interpolating operators at $\beta=6/g^2=6.0$ on a $16^3 \times 32 \times 16$ lattice. The mass estimates extracted from the two operators are consistent with each other. The observed large mass splitting between this state, $N^*(1535)$, 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.