17,374 research outputs found
Multiple Radial Cool Molecular Filaments in NGC 1275
We have extended our previous observation (Lim et al. 2008) of NGC1275
covering a central radius of ~10kpc to the entire main body of cool molecular
gas spanning ~14kpc east and west of center. We find no new features beyond the
region previously mapped, and show that all six spatially-resolved features on
both the eastern and western sides (three on each side) comprise radially
aligned filaments. Such radial filaments can be most naturally explained by a
model in which gas deposited "upstream" in localized regions experiencing an
X-ray cooling flow subsequently free falls along the gravitational potential of
PerA, as we previously showed can explain the observed kinematics of the two
longest filaments. All the detected filaments coincide with locally bright
Halpha features, and have a ratio in CO(2-1) to Halpha luminosity of ~1e-3; we
show that these filaments have lower star formation efficiencies than the
nearly constant value found for molecular gas in nearby normal spiral galaxies.
On the other hand, some at least equally luminous Halpha features, including a
previously identified giant HII region, show no detectable cool molecular gas
with a corresponding ratio at least a factor of ~5 lower; in the giant HII
region, essentially all the pre-existing molecular gas may have been converted
to stars. We demonstrate that all the cool molecular filaments are
gravitationally bound, and without any means of support beyond thermal pressure
should collapse on timescales ~< 1e6yrs. By comparison, as we showed previously
the two longest filaments have much longer dynamical ages of ~1e7yrs. Tidal
shear may help delay their collapse, but more likely turbulent velocities of at
least a few tens km/s or magnetic fields with strengths of at least several
~10uG are required to support these filaments.Comment: 52 pages, 11 figures. Accepted to Ap
Supervised machine learning based multi-task artificial intelligence classification of retinopathies
Artificial intelligence (AI) classification holds promise as a novel and
affordable screening tool for clinical management of ocular diseases. Rural and
underserved areas, which suffer from lack of access to experienced
ophthalmologists may particularly benefit from this technology. Quantitative
optical coherence tomography angiography (OCTA) imaging provides excellent
capability to identify subtle vascular distortions, which are useful for
classifying retinovascular diseases. However, application of AI for
differentiation and classification of multiple eye diseases is not yet
established. In this study, we demonstrate supervised machine learning based
multi-task OCTA classification. We sought 1) to differentiate normal from
diseased ocular conditions, 2) to differentiate different ocular disease
conditions from each other, and 3) to stage the severity of each ocular
condition. Quantitative OCTA features, including blood vessel tortuosity (BVT),
blood vascular caliber (BVC), vessel perimeter index (VPI), blood vessel
density (BVD), foveal avascular zone (FAZ) area (FAZ-A), and FAZ contour
irregularity (FAZ-CI) were fully automatically extracted from the OCTA images.
A stepwise backward elimination approach was employed to identify sensitive
OCTA features and optimal-feature-combinations for the multi-task
classification. For proof-of-concept demonstration, diabetic retinopathy (DR)
and sickle cell retinopathy (SCR) were used to validate the supervised machine
leaning classifier. The presented AI classification methodology is applicable
and can be readily extended to other ocular diseases, holding promise to enable
a mass-screening platform for clinical deployment and telemedicine.Comment: Supplemental material attached at the en
Gauge-Fixing and Residual Symmetries in Gauge/Gravity Theories with Extra Dimensions
We study compactified pure gauge/gravitational theories with gauge-fixing
terms and show that these theories possess quantum mechanical SUSY-like
symmetries between unphysical degrees of freedom. These residual symmetries are
global symmetries and generated by quantum mechanical N=2 supercharges. Also,
we establish new one-parameter family of gauge choices for higher-dimensional
gravity, and calculate as a check of its validity one graviton exchange
amplitude in the lowest tree-level approximation. We confirm that the result is
indeed -independent and the cancellation of the -dependence is
ensured by the residual symmetries. We also give a simple interpretation of the
vDVZ-discontinuity, which arises in the lowest tree-level approximation, from
the supersymmetric point of view.Comment: REVTeX4, 17 pages, 1 figur
Neutrino scattering on polarized electron target and neutrino magnetic moment
The completed and proposed experiments for the measurement of the neutrino
magnetic moment are discussed. To improve the sensitivity of the search for the
neutrino magnetic moment we suggest to use a polarized electron target in the
processes of neutrino (antineutrino) -- electron scattering. It is shown that
in this case the weak interaction term in the total cross section is few times
smaller comparing with unpolarized case, but the electromagnetic term does not
depend on electron polarization.Comment: 12 pages, 7 figures. Talk given at the XXVIII ITEP Winter School of
Physics, Snegiri, Russia, February 22 - March 1, 200
Local thermometry technique based on proximity-coupled superconductor/normal-metal/superconductor devices
In mesoscopic superconductor/normal-metal/superconductor (SNS)
heterostructures, it is known that the resistance of the normal metal between
the superconductors has a strong temperature dependence. Based on this
phenomenon, we have developed a new type of thermometer, which dramatically
enhances our ability to measure the local electron temperature Te at low
temperatures. Using this technique, we have been able to measure small
temperature gradients across a micron-size sample, opening up the possibility
of quantitatively measuring the thermal properties of mesoscopic devices.Comment: 4 pages, 4 figure
Theory of the propagation of coupled waves in arbitrarily-inhomogeneous stratified media
We generalize the invariant imbedding theory of the wave propagation and
derive new invariant imbedding equations for the propagation of arbitrary
number of coupled waves of any kind in arbitrarily-inhomogeneous stratified
media, where the wave equations are effectively one-dimensional. By doing this,
we transform the original boundary value problem of coupled second-order
differential equations to an initial value problem of coupled first-order
differential equations, which makes the numerical solution of the coupled wave
equations much easier. Using the invariant imbedding equations, we are able to
calculate the matrix reflection and transmission coefficients and the wave
amplitudes inside the inhomogeneous media exactly and efficiently. We establish
the validity and the usefulness of our results by applying them to the
propagation of circularly-polarized electromagnetic waves in one-dimensional
photonic crystals made of isotropic chiral media. We find that there are three
kinds of bandgaps in these structures and clarify the nature of these bandgaps
by exact calculations.Comment: 7 pages, 1 figure, to appear in Europhys. Let
Large mixing angle oscillations as a probe of the deep solar interior
We re-examine the sensitivity of solar neutrino oscillations to noise in the
solar interior using the best current estimates of neutrino properties. Our
results show that the measurement of neutrino properties at KamLAND provides
new information about fluctuations in the solar environment on scales to which
standard helioseismic constraints are largely insensitive. We also show how the
determination of neutrino oscillation parameters from a combined fit of KamLAND
and solar data depends strongly on the magnitude of solar density fluctuations.
We argue that a resonance between helioseismic and Alfven waves might provide a
physical mechanism for generating these fluctuations and, if so,
neutrino-oscillation measurements could be used to constrain the size of
magnetic fields deep within the solar radiative zone.Comment: 13 pages, LaTeX file using AASLaTeX, 6 figures included. Improved
version including the new KamLAND data. To appear in APJ letter
1/m_b^2 correction to the left-right lepton polarization asymmetry in the decay B -> X_s mu^+ mu^-
Using a known result by Falk et al. for the 1/m_b^2 correction to the
dilepton invariant mass spectrum in the decay B \rightarrow X_s \mu^+ \mu^-, we
calculate the 1/m_b^2 correction to the left-right muon polarization asymmetry
in this decay. Employing an up-to-date range of values for the non-perturbative
parameter \lambda_1, we find that the correction is much smaller than it should
have been expected from the previous work by Falk et al.Comment: 8 pages, 2 figures included. Uses epsf.sty and rotate.sty. To appear
in Physical Review D. The complete postscript file is also available from URL
ftp://feynman.t30.physik.tu-muenchen.de/pub/preprints/ tum_t31_98_96.ps.g
Dirac and Majorana neutrinos in matter
We consider the matter effects on neutrinos moving in background on the basis
of the corresponding quantum wave equations. Both Dirac and Majorana neutrino
cases are discussed. The effects for Dirac neutrino reflection and trapping as
well as neutrino-antineutrino annihilation and pair
creation in matter at the interface between two media with different densities
are considered. The spin light of neutrino in matter is also discussed.Comment: 11 pages, 2 figures, in: Proceedings of the 5th International
Conference on Non-Accelerator New Physics (Dubna, Russia, June 20-25, 2005).
V2: typos correcte
Accelerating and Retarding Anomalous Diffusion
In this paper Gaussian models of retarded and accelerated anomalous diffusion
are considered. Stochastic differential equations of fractional order driven by
single or multiple fractional Gaussian noise terms are introduced to describe
retarding and accelerating subdiffusion and superdiffusion. Short and long time
asymptotic limits of the mean squared displacement of the stochastic processes
associated with the solutions of these equations are studied. Specific cases of
these equations are shown to provide possible descriptions of retarding or
accelerating anomalous diffusion.Comment: 18 page, 1 figur
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