195,471 research outputs found
Multi-Atlas based Segmentation of Head and Neck CT Images using Active Contour
This paper presents the segmentation of bilateral parotid glands in the Head and Neck (H&N) CT images using an active contour based atlas registration. We compare segmentation results from three atlas selection strategies: (i) selection of "single-most-similar" atlas for each image to be segmented, (ii) fusion of segmentation results from multiple atlases using STAPLE, and (iii) fusion of segmentation results using majority voting. Among these three approaches, fusion using majority voting provided the best results. Finally, we present a detailed evaluation on a dataset of eight images (provided as a part of H&N auto segmentation challenge conducted in conjunction with MICCAI-2010 conference) using majority voting strategy
Automatic classification of spectra from the Infrared Astronomical Satellite (IRAS)
A new classification of Infrared spectra collected by the Infrared Astronomical Satellite (IRAS) is presented. The spectral classes were discovered automatically by a program called Auto Class 2. This program is a method for discovering (inducing) classes from a data base, utilizing a Bayesian probability approach. These classes can be used to give insight into the patterns that occur in the particular domain, in this case, infrared astronomical spectroscopy. The classified spectra are the entire Low Resolution Spectra (LRS) Atlas of 5,425 sources. There are seventy-seven classes in this classification and these in turn were meta-classified to produce nine meta-classes. The classification is presented as spectral plots, IRAS color-color plots, galactic distribution plots and class commentaries. Cross-reference tables, listing the sources by IRAS name and by Auto Class class, are also given. These classes show some of the well known classes, such as the black-body class, and silicate emission classes, but many other classes were unsuspected, while others show important subtle differences within the well known classes
Dark matter allowed scenarios for Yukawa-unified SO(10) SUSY GUTs
Simple supersymmetric grand unified models based on the gauge group SO(10)
require --in addition to gauge and matter unification-- the unification of
t-b-\tau Yukawa couplings. Yukawa unification, however, only occurs for very
special values of the soft SUSY breaking parameters. We perform a search using
a Markov Chain Monte Carlo (MCMC) technique to investigate model parameters and
sparticle mass spectra which occur in Yukawa-unified SUSY models, where we also
require the relic density of neutralino dark matter to saturate the
WMAP-measured abundance. We find the spectrum is characterizd by three mass
scales: first/second generation scalars in the multi-TeV range, third
generation scalars in the TeV range, and gauginos in the \sim 100 GeV range.
Most solutions give far too high a relic abundance of neutralino dark matter.
The dark matter discrepancy can be rectified by 1. allowing for neutralino
decay to axino plus photon, 2. imposing gaugino mass non-universality or 3.
imposing generational non-universality. In addition, the MCMC approach finds 4.
a compromise solution where scalar masses are not too heavy, and where
neutralino annihilation occurs via the light Higgs h resonance. By imposing
weak scale Higgs soft term boundary conditions, we are also able to generate 5.
low \mu, m_A solutions with neutralino annihilation via a light A resonance,
though these solutions seem to be excluded by CDF/D0 measurements of the B_s\to
\mu^+\mu^- branching fraction. Based on the dual requirements of Yukawa
coupling unification and dark matter relic density, we predict new physics
signals at the LHC from pair production of 350--450 GeV gluinos. The events are
characterized by very high b-jet multiplicity and a dilepton mass edge around
mz2-mz1 \sim 50-75 GeV.Comment: 35 pages with 21 eps figure
Auto-Concealment of Supersymmetry in Extra Dimensions
In supersymmetric (SUSY) theories with extra dimensions the visible energy in
sparticle decays can be significantly reduced and its energy distribution
broadened, thus significantly weakening the present collider limits on SUSY.
The mechanism applies when the lightest supersymmetric particle (LSP) is a bulk
state-- e.g. a bulk modulino, axino, or gravitino-- the size of the extra
dimensions larger than ~ cm, and for a broad variety of visible
sparticle spectra. In such cases the lightest ordinary supersymmetric particle
(LOSP), necessarily a brane-localised state, decays to the Kaluza-Klein (KK)
discretuum of the LSP. This dynamically realises the compression mechanism for
hiding SUSY as decays into the more numerous heavier KK LSP states are favored.
We find LHC limits on right-handed slepton LOSPs evaporate, while LHC limits on
stop LOSPs weaken to ~350-410 GeV compared to ~700 GeV for a stop decaying to a
massless LSP. Similarly, for the searches we consider, present limits on direct
production of degenerate first and second generation squarks drop to ~450 GeV
compared to ~800 GeV for a squark decaying to a massless LSP. Auto-concealment
typically works for a fundamental gravitational scale of ~10-100 TeV, a
scale sufficiently high that traditional searches for signatures of extra
dimensions are mostly avoided. If superpartners are discovered, their prompt,
displaced, or stopped decays can also provide new search opportunities for
extra dimensions with the potential to reach ~ GeV. This mechanism
applies more generally than just SUSY theories, pertaining to any theory where
there is a discrete quantum number shared by both brane and bulk sectors.Comment: 22 pages, 13 figures. Minor changes to match published versio
Deep Learning vs. Atlas-Based Models for Fast Auto-Segmentation of the Masticatory Muscles on Head and Neck CT Images
BACKGROUND: Impaired function of masticatory muscles will lead to trismus. Routine delineation of these muscles during planning may improve dose tracking and facilitate dose reduction resulting in decreased radiation-related trismus. This study aimed to compare a deep learning model with a commercial atlas-based model for fast auto-segmentation of the masticatory muscles on head and neck computed tomography (CT) images.
MATERIAL AND METHODS: Paired masseter (M), temporalis (T), medial and lateral pterygoid (MP, LP) muscles were manually segmented on 56 CT images. CT images were randomly divided into training (nâ=â27) and validation (nâ=â29) cohorts. Two methods were used for automatic delineation of masticatory muscles (MMs): Deep learning auto-segmentation (DLAS) and atlas-based auto-segmentation (ABAS). The automatic algorithms were evaluated using Dice similarity coefficient (DSC), recall, precision, Hausdorff distance (HD), HD95, and mean surface distance (MSD). A consolidated score was calculated by normalizing the metrics against interobserver variability and averaging over all patients. Differences in dose (âDose) to MMs for DLAS and ABAS segmentations were assessed. A paired t-test was used to compare the geometric and dosimetric difference between DLAS and ABAS methods.
RESULTS: DLAS outperformed ABAS in delineating all MMs (pâ\u3câ0.05). The DLAS mean DSC for M, T, MP, and LP ranged from 0.83â±â0.03 to 0.89â±â0.02, the ABAS mean DSC ranged from 0.79â±â0.05 to 0.85â±â0.04. The mean value for recall, HD, HD95, MSD also improved with DLAS for auto-segmentation. Interobserver variation revealed the highest variability in DSC and MSD for both T and MP, and the highest scores were achieved for T by both automatic algorithms. With few exceptions, the mean âD98%, âD95%, âD50%, and âD2% for all structures were below 10% for DLAS and ABAS and had no detectable statistical difference (Pâ\u3eâ0.05). DLAS based contours had dose endpoints more closely matched with that of the manually segmented when compared with ABAS.
CONCLUSIONS: DLAS auto-segmentation of masticatory muscles for the head and neck radiotherapy had improved segmentation accuracy compared with ABAS with no qualitative difference in dosimetric endpoints compared to manually segmented contours
A boost for the EW SUSY hunt: monojet-like search for compressed sleptons at LHC14 with 100 fb^-1
Current Large Hadron Collider (LHC) analyses are blind to compressed
supersymmetry (SUSY) models with sleptons near the lightest super partner (LSP)
in mass:
GeV. We present a search sensitive to the very compressed range using the channel with soft same-flavor leptons and one hard jet from initial state
radiation ( GeV). The sleptons recoil against the jet
boosting them and their decay products, making the leptons detectable and
providing substantial missing transverse momentum. We use the kinematic
variable along with a different-flavor control region to reduce
the large standard model backgrounds and control systematic uncertainty. We
find the analysis should allow LHC14 with to search for
degenerate left-handed selectrons and smuons in the compressed region up to
GeV. In addition, it should be sensitive to
GeV for the very challenging case of
auto-concealed SUSY, in which left-handed sleptons decay to the Kaluza-Klein
tower of a modulino LSP which lives in extra dimensions. In both the
compressed spectrum and auto-concealed SUSY scenarios this analysis will need
more data to improve on LEP2 limits for right-handed sleptons due to their
smaller cross sections.Comment: 15 pages, 3 figures, updated citations in v
The photospheric solar oxygen project: II. Non-concordance of the oxygen abundance derived from two forbidden lines
In the Sun, the two forbidden [OI] lines at 630 and 636 nm were previously
found to provide discrepant oxygen abundances. aims: We investigate whether
this discrepancy is peculiar to the Sun or whether it is also observed in other
stars. method: We make use of high-resolution, high signal-to-noise ratio
spectra of four dwarf to turn-off stars, five giant stars, and one sub-giant
star observed with THEMIS, HARPS, and UVES to investigate the coherence of the
two lines. results: The two lines provide oxygen abundances that are
consistent, within observational errors, in all the giant stars examined by us.
On the other hand, for the two dwarf stars for which a measurement was
possible, for Procyon, and for the sub-giant star Capella, the 636 nm line
provides systematically higher oxygen abundances, as already seen for the Sun.
conclusions: The only two possible reasons for the discrepancy are a serious
error in the oscillator strength of the NiI line blending the 630 nm line or
the presence of an unknown blend in the 636 nm line, which makes the feature
stronger. The CN lines blending the 636 nm line cannot be responsible for the
discrepancy. The CaI autoionisation line, on the red wing of which the 636 nm
line is formed, is not well modelled by our synthetic spectra. However, a
better reproduction of this line would result in even higher abundances from
the 636 nm, thus increasing the discrepancy.Comment: A&A accepte
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