231 research outputs found
Exclusion Statistics of Quasiparticles in Condensed States of Composite Fermion Excitations
The exclusion statistics of quasiparticles is found at any level of the
hierarchy of condensed states of composite fermion excitations (for which
experimental indications have recently been found). The hierarchy of condensed
states of excitations in boson Jain states is introduced and the statistics of
quasiparticles is found. The quantum Hall states of charged -anyons
( -- the exclusion statistics parameter) can be described as
incompressible states of -anyons ( -- an even number).Comment: 4 page
The Composite Fermion Hierarchy: Condensed States of Composite Fermion Excitations?
A composite Fermion hierarchy theory is constructed in a way related to the
original Haldane picture by applying the composite Fermion (CF) transformation
to quasiparticles of Jain states. It is shown that the Jain theory coincides
with the Haldane hierarchy theory for principal CF fillings. Within the Fermi
liquid approach for few electron systems on the sphere a simple interpretation
of many-quasiparticle spectra is given and provides an explanation of failure
of CF hierarchy picture when applied to the hierarchical state.Comment: 6 pages, Revtex, 4 figures in PostScript, submitted to Phys. Rev.
Let
Neptune at Summer Solstice: Zonal Mean Temperatures from Ground-Based Observations 2003-2007
Imaging and spectroscopy of Neptune's thermal infrared emission is used to
assess seasonal changes in Neptune's zonal mean temperatures between Voyager-2
observations (1989, heliocentric longitude Ls=236) and southern summer solstice
(2005, Ls=270). Our aim was to analyse imaging and spectroscopy from multiple
different sources using a single self-consistent radiative-transfer model to
assess the magnitude of seasonal variability. Globally-averaged stratospheric
temperatures measured from methane emission tend towards a quasi-isothermal
structure (158-164 K) above the 0.1-mbar level, and are found to be consistent
with spacecraft observations of AKARI. This remarkable consistency, despite
very different observing conditions, suggests that stratospheric temporal
variability, if present, is 5 K at 1 mbar and 3 K at 0.1 mbar during
this solstice period. Conversely, ethane emission is highly variable, with
abundance determinations varying by more than a factor of two. The retrieved
C2H6 abundances are extremely sensitive to the details of the T(p) derivation.
Stratospheric temperatures and ethane are found to be latitudinally uniform
away from the south pole (assuming a latitudinally-uniform distribution of
stratospheric methane). At low and midlatitudes, comparisons of synthetic
Voyager-era images with solstice-era observations suggest that tropospheric
zonal temperatures are unchanged since the Voyager 2 encounter, with cool
mid-latitudes and a warm equator and pole. A re-analysis of Voyager/IRIS 25-50
{\mu}m mapping of tropospheric temperatures and para-hydrogen disequilibrium
suggests a symmetric meridional circulation with cold air rising at
mid-latitudes (sub-equilibrium para-H2 conditions) and warm air sinking at the
equator and poles (super-equilibrium para-H2 conditions). The most significant
atmospheric changes are associated with the polar vortex (absent in 1989).Comment: 35 pages, 19 figures. Accepted for publication in Icaru
Confronting Standard Models of Proto--Planetary Disks With New Mid--Infrared Sizes from the Keck Interferometer
We present near and mid-infrared interferometric observations made with the
Keck Interferometer Nuller and near-contemporaneous spectro-photometry from the
IRTF of 11 well known young stellar objects, several observed for the first
time in these spectral and spatial resolution regimes. With AU-level spatial
resolution, we first establish characteristic sizes of the infrared emission
using a simple geometrical model consisting of a hot inner rim and mid-infrared
disk emission. We find a high degree of correlation between the stellar
luminosity and the mid-infrared disk sizes after using near-infrared data to
remove the contribution from the inner rim. We then use a semi-analytical
physical model to also find that the very widely used "star + inner dust rim +
flared disk" class of models strongly fails to reproduce the SED and
spatially-resolved mid-infrared data simultaneously; specifically a more
compact source of mid-infrared emission is required than results from the
standard flared disk model. We explore the viability of a modification to the
model whereby a second dust rim containing smaller dust grains is added, and
find that the two-rim model leads to significantly improved fits in most cases.
This complexity is largely missed when carrying out SED modelling alone,
although detailed silicate feature fitting by McClure et al. 2013 recently came
to a similar conclusion. As has been suggested recently by Menu et al. 2015,
the difficulty in predicting mid-infrared sizes from the SED alone might hint
at "transition disk"-like gaps in the inner AU; however, the relatively high
correlation found in our mid-infrared disk size vs. stellar luminosity relation
favors layered disk morphologies and points to missing disk model ingredients
instead
Effects of a 75-km mountain ultra-marathon on heart rate variability in amateur runners
BACKGROUND: This study examined the effects of a mountain ultra-marathon (MUM) on the activity of the autonomous nervous system through heart rate variability (HRV) monitoring and determined whether this variable related to final performance.
METHODS: Heart rate and HRV were measured in eight male amateur runners (aged 37-60 years). Measurements were recorded before and after the event, in resting conditions, as well as continuously throughout the whole MUM. In addition, percentage (%) of heart rate reserve (HRres) and partial and total times during the race were analyzed.
RESULTS: Average heart rate (HRavg) measured at rest was increased after the event (+37%). Standard deviation of successive differences (SDSD) and the square root of the mean squared differences of successive NN intervals (RMSSD) were reduced after the MUM (-56% and -59%, respectively). There was a positive relationship between the frequency-domain index normalized low frequency power (PLFn) measured at rest before the event and race time (0.79) while there was a negative relationship between race time and the difference in HRavg before and after the event. In the last half of the event, there was a high correlation (Spearman coefficient of correlation >0.9) between race time and the standard deviation of the NN intervals (SDNN) registered during the race.
CONCLUSIONS: Autonomous cardiac regulation can be related to the performance in a mountain ultra-marathon. HRV monitoring could represent a practical tool for the evaluation of the relationship between the autonomous nervous system activity and performance in a mountain ultra-marathon
Effective mass staircase and the Fermi liquid parameters for the fractional quantum Hall composite fermions
Effective mass of the composite fermion in the fractional quantum Hall
system, which is of purely interaction originated, is shown, from a numerical
study, to exhibit a curious nonmonotonic behavior with a staircase correlated
with the number (=2,4,...) of attached flux quanta. This is surprising since
the usual composite-fermion picture predicts a smooth behavior. On top of that,
significant interactions are shown to exist between composite fermions, where
the excitation spectrum is accurately reproduced in terms of Landau's Fermi
liquid picture with negative (i.e., Hund's type) orbital and spin exchange
interactions.Comment: 4 pages, 3 figures, REVTe
Sparse aperture masking interferometry survey of transitional discs: Search for substellar-mass companions and asymmetries in their parent discs
This is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this record.Context. Transitional discs are a class of circumstellar discs around young stars with extensive clearing of dusty material within their
inner regions on 10s of au scales. One of the primary candidates for this kind of clearing is the formation of planet(s) within the disc
that then accrete or clear their immediate area as they migrate through the disc.
Aims. The goal of this survey was to search for asymmetries in the brightness distribution around a selection of transitional disc
targets. We then aimed to determine whether these asymmetries trace dynamically-induced structures in the disc or the gap-opening
planets themselves.
Methods. Our sample included eight transitional discs. Using the Keck/NIRC2 instrument we utilised the Sparse Aperture Masking
(SAM) interferometry technique to search for asymmetries indicative of ongoing planet formation. We searched for close-in companions
using both model fitting and interferometric image reconstruction techniques. Using simulated data, we derived diagnostics that
helped us to distinguish between point sources and extended asymmetric disc emission. In addition, we investigated the degeneracy
between the contrast and separation that appear for marginally resolved companions.
Results. We found FP Tau to contain a previously unseen disc wall, and DM Tau, LkHα330, and TW Hya to contain an asymmetric
signal indicative of point source-like emission. We placed upper limits on the contrast of a companion in RXJ1842.9-3532 and
V2246 Oph. We ruled the asymmetry signal in RXJ1615.3-3255 and V2062 Oph to be false positives. In the cases where our data
indicated a potential companion we computed estimates for the value of McMË™
c and found values in the range of 10−5 − 10−3M2
J
yr−1
.
Conclusions. We found significant asymmetries in four targets. Of these, three were consistent with companions. We resolved a
previously unseen gap in the disc of FP Tau extending inwards from approximately 10 au.We acknowledge support from a STFC Rutherford Fellowship
and Grant (ST/J004030/1, ST/K003445/1), Marie Sklodowska-Curie CIG
grant (Ref. 618910), and Philip Leverhulme Prize (PLP-2013-110). We additionally
acknowledge support from NASA KPDA grants (JPL-1452321, 1474717,
1485953, 1496788). The authors wish to recognise and acknowledge the very
significant cultural role and reverence that the summit of Mauna Kea has always
had within the indigenous Hawaiian community. We are most fortunate to have
the opportunity to conduct observations from this mountain. Some of the data
presented herein were obtained at the W.M. Keck Observatory, which is operated
as a scientific partnership among the California Institute of Technology, the
University of California and the National Aeronautics and Space Administration.
The Observatory was made possible by the generous financial support of
the W.M. Keck Foundatio
``Fermi Liquid'' Shell Model Approach to Composite Fermion Excitation Spectra in Fractional Quantum Hall States
Numerical results for the energy spectra of electrons on a spherical
surface are used as input data to determine the quasiparticle energies and the
pairwise ``Fermi liquid'' interactions of composite Fermion (CF) excitations in
fractional quantum Hall systems. The quasiparticle energies and their
interactions are then used to determine the energy spectra, vs total
angular momentum , of states containing more than two quasiparticles. The
qualitative agreement with the numerical results gives a remarkable new
confirmation of the CF picture.Comment: LaTex, 4 pages, including 4 .eps-figures, to be appear in pr
Sparse aperture masking interferometry survey of transitional discs. Search for substellar-mass companions and asymmetries in their parent discs
This is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this record.Context. Transitional discs are a class of circumstellar discs around young stars with extensive clearing of dusty material within their inner regions on 10s of au scales. One of the primary candidates for this kind of clearing is the formation of planet(s) within the disc that then accrete or clear their immediate area as they migrate through the disc.
Aims. The goal of this survey was to search for asymmetries in the brightness distribution around a selection of transitional disc targets. We then aimed to determine whether these asymmetries trace dynamically-induced structures in the disc or the gap-opening planets themselves.
Methods. Our sample included eight transitional discs. Using the Keck/NIRC2 instrument we utilised the Sparse Aperture Masking (SAM) interferometry technique to search for asymmetries indicative of ongoing planet formation. We searched for close-in companions using both model fitting and interferometric image reconstruction techniques. Using simulated data, we derived diagnostics that helped us to distinguish between point sources and extended asymmetric disc emission. In addition, we investigated the degeneracy between the contrast and separation that appear for marginally resolved companions.
Results. We found FP Tau to contain a previously unseen disc wall, and DM Tau, LkHα330, and TW Hya to contain an asymmetric signal indicative of point source-like emission. We placed upper limits on the contrast of a companion in RXJ 1842.9-3532 and V2246 Oph. We ruled the asymmetry signal in RXJ 1615.3-3255 and V2062 Oph to be false positives. In the cases where our data indicated a potential companion we computed estimates for the value of McṀc and found values in the range of 10−5−10−3 M2J yr−1.
Conclusions. We found significant asymmetries in four targets. Of these, three were consistent with companions. We resolved a previously unseen gap in the disc of FP Tau extending inwards from approximately 10 au.We acknowledge support from a STFC Rutherford Fellowship and Grant (ST/J004030/1, ST/K003445/1), Marie Sklodowska-Curie CIG grant (Ref. 618910), and Philip Leverhulme Prize (PLP-2013-110). We additionally acknowledge support from NASA KPDA grants (JPL-1452321, 1474717, 1485953, 1496788). The authors wish to recognise and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation
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