132 research outputs found
Visibility diagrams and experimental stripe structure in the quantum Hall effect
We analyze various properties of the visibility diagrams that can be used in
the context of modular symmetries and confront them to some recent experimental
developments in the Quantum Hall Effect. We show that a suitable physical
interpretation of the visibility diagrams which permits one to describe
successfully the observed architecture of the Quantum Hall states gives rise
naturally to a stripe structure reproducing some of the experimental features
that have been observed in the study of the quantum fluctuations of the Hall
conductance. Furthermore, we exhibit new properties of the visibility diagrams
stemming from the structure of subgroups of the full modular group.Comment: 8 pages in plain TeX, 7 figures in a single postscript fil
The static potential in QED with non-minimal coupling
Here we study the effect of the non-minimal coupling j^{\mu}\eps
\partial^{\nu} A^{\alpha} on the static potential in multiflavor QED.
Both cases of four and two components fermions are studied separately at
leading order in the expansion. Although a non-local Chern-Simons term
appears, in the four components case the photon is still massless leading to a
confining logarithmic potential similar to the classical one. In the two
components case, as expected, the parity breaking fermion mass term generates a
traditional Chern-Simons term which makes the photon massive and we have a
screening potential which vanishes at large inter-charge distance. The extra
non-minimal couplings have no important influence on the static potential at
large inter-charge distances. However, interesting effects show up at finite
distances. In particular, for strong enough non-minimal coupling we may have a
new massive pole in the photon propagator while in the opposite limit there may
be no poles at all in the irreducible case. We also found that, in general, the
non-minimal couplings lead to a finite range {\bf repulsive} force between
charges of opposite signs.Comment: 19 pages and 7 figure
3D MHD Modeling of the Gaseous Structure of the Galaxy: Synthetic Observations
We generated synthetic observations from the four-arm model presented in
Gomez & Cox (2004) for the Galactic ISM in the presence of a spiral
gravitational perturbation. We found that velocity crowding and diffusion have
a strong effect in the l-v diagram. The v-b diagram presents structures at the
expected spiral arm velocities, that can be explained by the off-the-plane
structure of the arms presented in previous papers of this series. Such
structures are observed in the Leiden/Dwingeloo HI survey. The rotation curve,
as measured from the inside of the modeled galaxy, shows similarities with the
observed one for the Milky Way Galaxy, although it has large deviations from
the smooth circular rotation corresponding to the background potential. The
magnetic field inferred from a synthetic synchrotron map shows a largely
circular structure, but with interesting deviations in the midplane due to
distortion of the field from circularity in the interarm regions.Comment: Accepted for publication in ApJ. Better quality figures in
http://www.astro.umd.edu/~gomez/publica/3d_galaxy-3.pd
Duality and Non-linear Response for Quantum Hall Systems
We derive the implications of particle-vortex duality for the electromagnetic
response of Quantum Hall systems beyond the linear-response regime. This
provides a first theoretical explanation of the remarkable duality which has
been observed in the nonlinear regime for the electromagnetic response of
Quantum Hall systems.Comment: 7 pages, 1 figure, typeset in LaTe
Errors in kinematic distances and our image of the Milky Way Galaxy
Errors in the kinematic distances, under the assumption of circular gas
orbits, were estimated by performing synthetic observations of a model disk
galaxy. It was found that the error is < 0.5 kpc for most of the disk when the
measured rotation curve was used, but larger if the real rotation curve is
applied. In both cases, the error is significantly larger at the positions of
the spiral arms. The error structure is such that, when kinematic distances are
used to develope a picture of the large scale density distribution, the most
significant features of the numerical model are significantly distorted or
absent, while spurious structure appears. By considering the full velocity
field in the calculation of the kinematic distances, most of the original
density structures can be recovered.Comment: Accepted for publication in A
An experimental study on (2) modular symmetry in the quantum Hall system with a small spin-splitting
Magnetic-field-induced phase transitions were studied with a two-dimensional
electron AlGaAs/GaAs system. The temperature-driven flow diagram shows the
features of the (2) modular symmetry, which includes distorted
flowlines and shiftted critical point. The deviation of the critical
conductivities is attributed to a small but resolved spin splitting, which
reduces the symmetry in Landau quantization. [B. P. Dolan, Phys. Rev. B 62,
10278.] Universal scaling is found under the reduction of the modular symmetry.
It is also shown that the Hall conductivity could still be governed by the
scaling law when the semicircle law and the scaling on the longitudinal
conductivity are invalid. *corresponding author:[email protected]: The revised manuscript has been published in J. Phys.: Condens.
Matte
The Southern Galactic Plane Survey: The Test Region
The Southern Galactic Plane Survey (SGPS) is a project to image the HI line
emission and 1.4 GHz continuum in the fourth quadrant of the Milky Way at high
resolution using the Australia Telescope Compact Array (ATCA) and the Parkes
Radio Telescope. In this paper we describe the survey details and goals,
present lambda 21-cm continuum data, and discuss HI absorption and emission
characteristics of the SGPS Test Region (325.5 deg < l < 333.5 deg; -0.5 deg <
b < +3.5 deg). We explore the effects of massive stars on the interstellar
medium (ISM) through a study of HI shells and the HI environments of HII
regions and supernova remnants. We find an HI shell surrounding the HII region
RCW 94 which indicates that the region is embedded in a molecular cloud. We
give lower limits for the kinematic distances to SNRs G327.4+0.4 and G330.2+1.0
of 4.3 kpc and 4.9 kpc, respectively. We find evidence of interaction with the
surrounding HI for both of these remnants. We also present images of a possible
new SNR G328.6-0.0. Additionally, we have discovered two small HI shells with
no counterparts in continuum emission.Comment: 17 pages, 7 embedded EPS figures, 10 low-res jpeg figures, uses
emulateapj5.sty. Accepted for publication in the Astrophysical Journal.
Version with all full resolution figures embedded is available at
http://www.astro.umn.edu/~naomi/sgps/papers/SGPS.ps.g
The Stellar Content of Obscured Galactic Giant H II Regions III.: W31
We present near infrared (J, H, and K) photometry and moderate resolution
(lambda/Deltalambda = 3000) K-band spectroscopy of the embedded stellar cluster
in the giant H II region W31. Four of the brightest five cluster members are
early O--type stars based on their spectra. We derive a spectro--photometric
distance for W31 of 3.4 +/- 0.3 kpc using these new spectral types and infrared
photometry. The brightest cluster source at K is a red object which lies in the
region of the J - H vs. H - K color--color plot inhabited by stars with excess
emission in the K-band. This point source has an H plus K-band spectrum which
shows no photospheric features, which we interpret as being the result of
veiling by local dust emission. Strong Brackett series emission and permitted
FeII emission are detected in this source; the latter feature is suggestive of
a dense inflow or outflow. The near infrared position of this red source is
consistent with the position of a 5 GHz thermal radio source seen in previous
high angular resolution VLA images. We also identify several other K-band
sources containing excess emission with compact radio sources. These objects
may represent stars in the W31 cluster still embedded in their birth cocoons.Comment: LaTeX2e/aastex, 29 pages including 9 figures, 3 table
A Study of Cyg OB2: Pointing the Way Towards Finding Our Galaxy's Super Star Clusters
New optical MK classification spectra have been obtained for 14 OB star
candidates identified by Comeron et al. (2002) and presumed to be possible
members of the Cyg OB2 cluster. All 14 candidate OB stars observed are indeed
early-type stars, strongly suggesting the remaining 31 candidates identified by
Comeron et al. are also early-type stars. However, as many as half of the new
stars appear to be significantly older than the previously studied optical
cluster, making their membership in Cyg OB2 suspect. Despite this, the
recognition of Cyg OB2 being a more massive and extensive star cluster than
previously realized, along with the recently recognized candidate super star
cluster Westerlund 1 only a few kpc away (Clark & Negueruela 2002), reminds us
that we are woefully under-informed about the massive cluster population in our
Galaxy. Extrapolations of the locally derived cluster luminosity function
indicate 10s to perhaps 100 of these very massive open clusters (Mcl ~ 10^4
M_sun, Mv ~ -11) should exist within our galaxy. Radio surveys will not detect
these massive clusters if they are more than a few million years old. Our best
hope for remedying this shortfall is through deep infrared searches and follow
up near-infrared spectroscopic observations, as was used by Comeron et al. to
locate candidate members of the Cyg OB2 association.Comment: 30 pages, 12 figures, ApJ in pres
modular symmetry, renormalization, group flow and the quantum Hall effect
We construct a family of holomorphic -functions whose RG flow
preserves the modular symmetry and reproduces the observed
stability of the Hall plateaus. The semi-circle law relating the longitudinal
and Hall conductivities that has been observed experimentally is obtained from
the integration of the RG equations for any permitted transition which can be
identified from the selection rules encoded in the flow diagram. The generic
scale dependance of the conductivities is found to agree qualitatively with the
present experimental data. The existence of a crossing point occuring in the
crossover of the permitted transitions is discussed.Comment: 14 pages plain TeX, 7 figures in a postscript fil
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