632 research outputs found
ChronoMID-Cross-modal neural networks for 3-D temporal medical imaging data.
ChronoMID-neural networks for temporally-varying, hence Chrono, Medical Imaging Data-makes the novel application of cross-modal convolutional neural networks (X-CNNs) to the medical domain. In this paper, we present multiple approaches for incorporating temporal information into X-CNNs and compare their performance in a case study on the classification of abnormal bone remodelling in mice. Previous work developing medical models has predominantly focused on either spatial or temporal aspects, but rarely both. Our models seek to unify these complementary sources of information and derive insights in a bottom-up, data-driven approach. As with many medical datasets, the case study herein exhibits deep rather than wide data; we apply various techniques, including extensive regularisation, to account for this. After training on a balanced set of approximately 70000 images, two of the models-those using difference maps from known reference points-outperformed a state-of-the-art convolutional neural network baseline by over 30pp (> 99% vs. 68.26%) on an unseen, balanced validation set comprising around 20000 images. These models are expected to perform well with sparse data sets based on both previous findings with X-CNNs and the representations of time used, which permit arbitrarily large and irregular gaps between data points. Our results highlight the importance of identifying a suitable description of time for a problem domain, as unsuitable descriptors may not only fail to improve a model, they may in fact confound it
Low-voltage Ge avalanche photodetector for highly sensitive 10Gb/s Si photonic receivers
We demonstrate low-voltage germanium waveguide avalanche photodetectors (APD) with gain-bandwidth product of 88GHz. A 7.1dB sensitivity improvement is demonstrated for an APD wire-bonded to a 10Gb/s CMOS transimpedance amplifier, at -6.2V APD bias
Ion Charge States in Halo CMEs: What can we Learn about the Explosion?
We describe a new modeling approach to develop a more quantitative
understanding of the charge state distributions of the ions of various elements
detected in situ during halo Coronal Mass Ejection (CME) events by the Advanced
Composition Explorer (ACE) satellite. Using a model CME hydrodynamic evolution
based on observations of CMEs propagating in the plane of the sky and on
theoretical models, we integrate time dependent equations for the ionization
balance of various elements to compare with ACE data. We find that plasma in
the CME ``core'' typically requires further heating following filament
eruption, with thermal energy input similar to the kinetic energy input. This
extra heating is presumably the result of post eruptive reconnection. Plasma
corresponding to the CME ``cavity'' is usually not further ionized, since
whether heated or not, the low density gives freeze-in close the the Sun. The
current analysis is limited by ambiguities in the underlying model CME
evolution. Such methods are likely to reach their full potential when applied
to data to be acquired by STEREO when at optimum separation. CME evolution
observed with one spacecraft may be used to interpret CME charge states
detected by the other.Comment: 20 pages, accepted by Ap
Electron Heating and Cosmic Rays at a Supernova Shock from Chandra X-ray Observations of E0102.2-7219
In this Letter we use the unprecedented spatial resolution of the Chandra
X-ray Observatory to carry out, for the first time, a measurement of the
post-shock electron temperature and proper motion of a young SNR, specifically
to address questions about the post-shock partition of energy among electrons,
ions, and cosmic rays. The expansion rate, 0.100 +/- 0.025 percent per yr, and
inferred age, ~1000 yr, of E0102.2-7219, from a comparison of X-ray
observations spanning 20 years, are fully consistent with previous estimates
based on studies of high velocity oxygen-rich optical filaments in the remnant.
With a radius of 6.4 pc for the blast wave estimated from the Chandra image,
our expansion rate implies a blast wave velocity of ~6000 km/s and a range of
electron temperatures 2.5 - 45 keV, dependent on the degree of collisionless
electron heating. Analysis of the Chandra ACIS spectrum of the immediate
post-shock region reveals a thermal plasma with abundances and column density
typical of the Small Magellanic Cloud and an electron temperature of 0.4-1 keV.
The measured electron temperature is significantly lower than the plausible
range above, which can only be reconciled if we assume that a significant
fraction of the shock energy, rather than contributing to the heating of the
post-shock electrons and ions, has gone into generating cosmic rays.Comment: 13 pages, including 2 postscript figs, LaTeX. Accepted by Ap
On Dijkgraaf-Witten Type Invariants
We explicitly construct a series of lattice models based upon the gauge group
which have the property of subdivision invariance, when the coupling
parameter is quantized and the field configurations are restricted to satisfy a
type of mod- flatness condition. The simplest model of this type yields the
Dijkgraaf-Witten invariant of a -manifold and is based upon a single link,
or -simplex, field. Depending upon the manifold's dimension, other models
may have more than one species of field variable, and these may be based on
higher dimensional simplices.Comment: 18 page
Mitral regurgitation in hypertrophic obstructive cardiomyopathy: relationship to obstruction and relief with myectomy
AbstractOBJECTIVESThis study examined: 1) the impact of myectomy on postoperative mitral regurgitation (MR) and 2) the association between the severity of MR and the left ventricular outflow tract (LVOT) gradient.BACKGROUNDFor patients with hypertrophic obstructive cardiomyopathy (HOCM) and MR, controversy exists as to whether myectomy alone is sufficient in eliminating MR. Furthermore, the relationship between the degree of MR and the LVOT peak gradient has not been well defined.METHODSWe performed pre- and postoperative transthoracic as well as intraoperative transesophageal studies in 104 consecutive patients with HOCM undergoing septal myectomy. Left ventricular outflow tract gradient and the nature of MR were assessed.RESULTSIn the 93 patients without independent mitral valve disease, a relationship was observed between MR severity and the LVOT gradient. Left ventricular outflow tract gradient (mean ± standard deviation) for trivial, mild, moderate and severe MR were: 23.2 ± 19.1, 43.8 ± 25.4, 70.1 ± 21.0 and 104 ± 21.0 mm Hg (p < 0.001). Early postoperative, MR was absent or trivial in 80%, mild in 19% and moderate in 1%. None of these patients required additional mitral valve surgery. For patients with independent mitral valve disease (n = 11), five required mitral valve surgery as well as myectomy. The remainder had significant reductions in the degree of MR with myectomy alone.CONCLUSIONSFor patients with HOCM and MR not due to independent mitral valve disease, myectomy significantly reduced the degree of MR, without requirement for additional mitral valve surgery. In these patients the severity of MR was directly related to the magnitude of the LVOT gradient
The Longitudinal Properties of a Solar Energetic Particle Event Investigated Using Modern Solar Imaging
We use combined high-cadence, high-resolution, and multi-point imaging by the Solar-Terrestrial Relations Observatory (STEREO) and the Solar and Heliospheric Observatory to investigate the hour-long eruption of a fast and wide coronal mass ejection (CME) on 2011 March 21 when the twin STEREO spacecraft were located beyond the solar limbs. We analyze the relation between the eruption of the CME, the evolution of an Extreme Ultraviolet (EUV) wave, and the onset of a solar energetic particle (SEP) event measured in situ by the STEREO and near-Earth orbiting spacecraft. Combined ultraviolet and white-light images of the lower corona reveal that in an initial CME lateral "expansion phase," the EUV disturbance tracks the laterally expanding flanks of the CME, both moving parallel to the solar surface with speeds of ~450 km s^(–1). When the lateral expansion of the ejecta ceases, the EUV disturbance carries on propagating parallel to the solar surface but devolves rapidly into a less coherent structure. Multi-point tracking of the CME leading edge and the effects of the launched compression waves (e.g., pushed streamers) give anti-sunward speeds that initially exceed 900 km s^(–1) at all measured position angles. We combine our analysis of ultraviolet and white-light images with a comprehensive study of the velocity dispersion of energetic particles measured in situ by particle detectors located at STEREO-A (STA) and first Lagrange point (L1), to demonstrate that the delayed solar particle release times at STA and L1 are consistent with the time required (30-40 minutes) for the CME to perturb the corona over a wide range of longitudes. This study finds an association between the longitudinal extent of the perturbed corona (in EUV and white light) and the longitudinal extent of the SEP event in the heliosphere
High Resolution X-Ray Spectroscopy of SN 1987A: Monitoring with XMM-Newton
We report the results of our XMM-Newton monitoring of SN 1987A. The ongoing
propagation of the supernova blast wave through the inner circumstellar ring
caused a drastic increase in X-ray luminosity during the last years, enabling
detailed high resolution X-ray spectroscopy with the Reflection Grating
Spectrometer. The observations can be used to follow the detailed evolution of
the arising supernova remnant. The fluxes and broadening of the numerous
emission lines seen in the dispersed spectra provide information on the
evolution of the X-ray emitting plasma and its dynamics. These were analyzed in
combination with the EPIC-pn spectra, which allow a precise determination of
the higher temperature plasma. We modeled individual emission lines and fitted
plasma emission models. Especially from the observations between 2003 and 2007
we can see a significant evolution of the plasma parameters and a deceleration
of the radial velocity of the lower temperature plasma regions. We found an
indication (3-sigma-level) of an iron K feature in the co-added EPIC-pn
spectra. The comparison with Chandra grating observations in 2004 yields a
clear temporal coherence of the spectral evolution and the sudden deceleration
of the expansion velocity seen in X-ray images ~6100 days after the explosion.Comment: 10 pages, 8 Figures; accepted by A&
State Sum Models and Simplicial Cohomology
We study a class of subdivision invariant lattice models based on the gauge
group , with particular emphasis on the four dimensional example. This
model is based upon the assignment of field variables to both the - and
-dimensional simplices of the simplicial complex. The property of
subdivision invariance is achieved when the coupling parameter is quantized and
the field configurations are restricted to satisfy a type of mod- flatness
condition. By explicit computation of the partition function for the manifold
, we establish that the theory has a quantum Hilbert space
which differs from the classical one.Comment: 28 pages, Latex, ITFA-94-13, (Expanded version with two new sections
Observability and diagnostics in the X-ray band of shock-cloud interactions in supernova remnants
X-ray emitting features originating from the interaction of supernova shock
waves with small interstellar gas clouds are revealed in many X-ray
observations of evolved supernova remnants (e.g. Cygnus Loop and Vela), but
their interpretation is not straightforward.
We develop a self-consistent method for the analysis and interpretation of
shock-cloud interactions in middle-aged supernova remnants, which can provide
the key parameters of the system and the role of relevant physical effects like
the thermal conduction, without the need to run ad-hoc numerical simulations
and to bother of morphology details.
We explore all the possible values of the shock speed and cloud density
contrast relevant to middle-aged SNRs with a set of hydrodynamic simulations of
shock-cloud interaction, including the effects of thermal conduction and
radiative cooling. From the simulations, we synthesize spatially and spectrally
resolved focal-plane data as they would be collected with XMM-Newton/EPIC, an
X-ray instrument commonly used in these studies.
We devise and tune up two diagnostic tools, the first based on the
mean-photon energy vs. count rate scatter plot and the second on the spectral
analysis of the interaction region, that can be used to highlight the effects
of thermal conduction and to derive the shock speed in case of efficient
conduction at work. These tools can be used to ascertain information from X-ray
observations, without the need to develop detailed and ad-hoc numerical models
for the interpretation of the data.Comment: 9 pages, 7 Figures; accepted for publication on A&A. Version with
full resolution images can be found at
http://www.astropa.unipa.it/~orlando/PREPRINTS/sorlando_13801.pd
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