27,853 research outputs found
Pion and Kaon Decay Constants: Lattice vs. Resonance Chiral Theory
The Lattice results for the pion and kaon decay constants are analysed within
the Resonance Chiral Theory framework in the large NC limit. The approximately
linear behaviour of the observable at large light-quark mass is explained
through the interaction with the lightest multiplet of scalar resonances. The
analysis of the Lattice results allows to obtain the resonance mass MS=1049 +-
25 MeV and the Chiral Perturbation Theory parameters at leading order in 1/NC.Comment: 10 pages, 2 figure
Generic suppression of conductance quantization of interacting electrons in graphene nanoribbons in a perpendicular magnetic field
The effects of electron interaction on the magnetoconductance of graphene
nanoribbons (GNRs) are studied within the Hartree approximation. We find that a
perpendicular magnetic field leads to a suppression instead of an expected
improvement of the quantization. This suppression is traced back to
interaction-induced modifications of the band structure leading to the
formation of compressible strips in the middle of GNRs. It is also shown that
the hard wall confinement combined with electron interaction generates overlaps
between forward and backward propagating states, which may significantly
enhance backscattering in realistic GNRs. The relation to available experiments
is discussed.Comment: 4 pages, 3 figure
A Survey for Low-Surface-Brightness Galaxies Around M31. I. The Newly Discovered Dwarf Andromeda V
We present images and a color-magnitude diagram for And V, a new dwarf
spheroidal companion to M31 that was found using a digital filtering technique
applied to 1550 square degrees of the second Palomar Sky Survey. And V resolves
into stars easily in follow-up 4-m V- and I-band images, from which we deduce a
distance of 810 +/- 45 kpc using the tip of the red giant branch method. Within
the uncertainties, this distance is identical to the Population II distances
for M31 and, combined with a projected separation of 112 kpc, provides strong
support for a physical association between the two galaxies. There is no
emission from And V detected in H alpha, 1.4 GHz radio continuum, or IRAS
bandpasses, and there is no young population seen in the color-magnitude
diagram that might suggest that And V is an irregular. Thus, the classification
as a new dwarf spheroidal member of the Local Group seems secure. With an
extinction-corrected central surface brightness of 25.2 V mag per square
arcsec, a mean metal abundance of [Fe/H] approximately -1.5, and no evidence
for upper AGB stars, And V resembles And I & III.Comment: Accepted for publication in The Astronomical Journal, November 1998
issue; 4 embedded PostScript figures, 4 JPEG figures; see
http://aloe.tuc.noao.edu/jacoby/dwarfs.html for a complete full-resolution
PostScript versio
On the reduced density matrix for a chain of free electrons
The properties of the reduced density matrix describing an interval of N
sites in an infinite chain of free electrons are investigated. A commuting
operator is found for arbitrary filling and also for open chains. For a half
filled periodic chain it is used to determine the eigenfunctions for the
dominant eigenvalues analytically in the continuum limit. Relations to the
critical six-vertex model are discussed.Comment: 8 pages, small changes, Equ.(24) corrected, final versio
Reconstruction of tomographic images of dry aqueous foams
WOS:000328011500007International audienceX-ray tomography offers the possibility to examine the local changes in the structure of a three-dimensional aqueous foam as it flows, allowing a better fundamental understanding of foam rheology and the validation of models. We present an automated algorithm that reconstructs a dry aqueous foam from such images. Our algorithm uses ImageJ to extract from an image the topology of the network of Plateau borders in the foam, and then analyses this network to re-create the films and then the bubbles, and equilibrates the structure in Surface Evolver. We validate our algorithm and demonstrate its precision by applying it to simulated foam structures and analysing the topology and geometry obtained. We then apply our algorithm to a sequence of images from an experiment in which a spherical bead falls under its own weight through a polydisperse dry foam. This allows us to describe the evolution of the foam's bubble volumes with time as well as the distribution of bubble pressure and the forces exerted on a falling sphere. (C) 2013 Elsevier B.V. All rights reserved
The Low Surface Brightness Extent of the Fornax Cluster
We have used a large format CCD camera to survey the nearby Fornax cluster
and its immediate environment for low luminosity low surface brightness
galaxies. Recent observations indicate that these are the most dark matter
dominated galaxies known and so they are likely to be a good tracer of the dark
matter in clusters. We have identified large numbers of these galaxies
consistent with a steep faint end slope of the luminosity function (alpha~ -2)
down to MB ~ -12. These galaxies contribute almost the same amount to the total
cluster light as the brighter galaxies and they have a spatial extent that is
some four times larger. They satisfy two of the important predictions of N-body
hierarchical simulations of structure formation using dark halos. The
luminosity (mass ?) function is steep and the mass distribution is more
extended than that defined by the brighter galaxies. We also find a large
concentration of low surface brightness galaxies around the nearby galaxy
NGC1291.Comment: 16 pages, 6 figure
Magnetosubband and edge state structure in cleaved-edge overgrown quantum wires
We provide a systematic quantitative description of the structure of edge
states and magnetosubband evolution in hard wall quantum wires in the integer
quantum Hall regime. Our calculations are based on the self-consistent Green's
function technique where the electron- and spin interactions are included
within the density functional theory in the local spin density approximation.
We analyze the evolution of the magnetosubband structure as magnetic field
varies and show that it exhibits different features as compared to the case of
a smooth confinement. In particularly, in the hard-wall wire a deep and narrow
triangular potential well (of the width of magnetic length ) is formed in
the vicinity of the wire boundary. The wave functions are strongly localized in
this well which leads to the increase of the electron density near the edges.
Because of the presence of this well, the subbands start to depopulate from the
central region of the wire and remain pinned in the well region until they are
eventually pushed up by increasing magnetic field. We also demonstrate that the
spin polarization of electron density as a function of magnetic field shows a
pronounced double-loop pattern that can be related to the successive
depopulation of the magnetosubbands. In contrast to the case of a smooth
confinement, in hard-wall wires the compressible strips do not form in the
vicinity of wire boundaries and spatial spin separation between spin-up and
spin-down states near edges is absent.Comment: 9 pages, submitted to Phys. Rev.
Local Swift-BAT active galactic nuclei prefer circumnuclear star formation
We use Herschel data to analyze the size of the far-infrared 70micron
emission for z<0.06 local samples of 277 hosts of Swift-BAT selected active
galactic nuclei (AGN), and 515 comparison galaxies that are not detected by
BAT. For modest far-infrared luminosities 8.5<log(LFIR)<10.5, we find large
scatter of half light radii Re70 for both populations, but a typical Re70 <~ 1
kpc for the BAT hosts that is only half that of comparison galaxies of same
far-infrared luminosity. The result mostly reflects a more compact distribution
of star formation (and hence gas) in the AGN hosts, but compact AGN heated dust
may contribute in some extremely AGN-dominated systems. Our findings are in
support of an AGN-host coevolution where accretion onto the central black hole
and star formation are fed from the same gas reservoir, with more efficient
black hole feeding if that reservoir is more concentrated. The significant
scatter in the far-infrared sizes emphasizes that we are mostly probing spatial
scales much larger than those of actual accretion, and that rapid accretion
variations can smear the distinction between the AGN and comparison categories.
Large samples are hence needed to detect structural differences that favour
feeding of the black hole. No size difference AGN host vs. comparison galaxies
is observed at higher far-infrared luminosities log(LFIR)>10.5 (star formation
rates >~ 6 Msun/yr), possibly because these are typically reached in more
compact regions in the first place.Comment: 7 pages, 3 figures, accepted for publication in Astronomy &
Astrophysic
Method of complex paths and general covariance of Hawking radiation
We apply the technique of complex paths to obtain Hawking radiation in
different coordinate representations of the Schwarzschild space-time. The
coordinate representations we consider do not possess a singularity at the
horizon unlike the standard Schwarzschild coordinate. However, the event
horizon manifests itself as a singularity in the expression for the
semi-classical action. This singularity is regularized by using the method of
complex paths and we find that Hawking radiation is recovered in these
coordinates indicating the covariance of Hawking radiation. This also shows
that there is no correspondence between the particles detected by the model
detector and the particle spectrum obtained by the quantum field theoretic
analysis -- a result known in other contexts as well.Comment: 9 pages, uses MPLA Style file, Accepted for publication in Mod. Phys.
Letts.
Impurity Operators in RSOS Models
We give a construction of impurity operators in the `algebraic analysis'
picture of RSOS models. Physically, these operators are half-infinite
insertions of certain fusion-RSOS Boltzmann weights. They are the face analogue
of insertions of higher spin lines in vertex models. Mathematically, they are
given in terms of intertwiners of modules. We present a
detailed perturbation theory check of the conjectural correspondence between
the physical and mathematical constructions in a particular simple example.Comment: Latex, 24 pages, uses amsmath, amsthm, amssymb, epic, eepic and
texdraw style files (Minor typos corrected) (minor changes
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