325 research outputs found
Pixel-lensing as a way to detect extrasolar planets in M31
We study the possibility to detect extrasolar planets in M31 through
pixel-lensing observations. Using a Monte Carlo approach, we select the
physical parameters of the binary lens system, a star hosting a planet, and we
calculate the pixel-lensing light curve taking into account the finite source
effects. Indeed, their inclusion is crucial since the sources in M31
microlensing events are mainly giant stars. Light curves with detectable
planetary features are selected by looking for significant deviations from the
corresponding Paczy\'{n}ski shapes. We find that the time scale of planetary
deviations in light curves increase (up to 3-4 days) as the source size
increases. This means that only few exposures per day, depending also on the
required accuracy, may be sufficient to reveal in the light curve a planetary
companion. Although the mean planet mass for the selected events is about , even small mass planets () can
cause significant deviations, at least in the observations with large
telescopes. However, even in the former case, the probability to find
detectable planetary features in pixel-lensing light curves is at most a few
percent of the detectable events, and therefore many events have to be
collected in order to detect an extrasolar planet in M31. Our analysis also
supports the claim that the anomaly found in the candidate event PA-99-N2
towards M31 can be explained by a companion object orbiting the lens star.Comment: Accepted for publication on Monthly Notices of the Royal Astronomical
Society (MNRAS), 200
Inflationary Universe in Higher Derivative Induced Gravity
In an induced-gravity model, the stability condition of an inflationary
slow-rollover solution is shown to be . The presence of higher derivative terms
will, however, act against the stability of this expanding solution unless
further constraints on the field parameters are imposed. We find that these
models will acquire a non-vanishing cosmological constant at the end of
inflation. Some models are analyzed for their implication to the early
universe.Comment: 6 pages, two typos correcte
Timing of glioblastoma surgery and patient outcomes: a multicenter cohort study.
BACKGROUND:
The impact of time-to-surgery on clinical outcome for patients with glioblastoma has not been determined. Any delay in treatment is perceived as detrimental, but guidelines do not specify acceptable timings. In this study, we relate the time to glioblastoma surgery with the extent of resection and residual tumor volume, performance change, and survival, and we explore the identification of patients for urgent surgery.
METHODS:
Adults with first-time surgery in 2012–2013 treated by 12 neuro-oncological teams were included in this study. We defined time-to-surgery as the number of days between the diagnostic MR scan and surgery. The relation between time-to-surgery and patient and tumor characteristics was explored in time-to-event analysis and proportional hazard models. Outcome according to time-to-surgery was analyzed by volumetric measurements, changes in performance status, and survival analysis with patient and tumor characteristics as modifiers.
RESULTS:
Included were 1033 patients of whom 729 had a resection and 304 a biopsy. The overall median time-to-surgery was 13 days. Surgery was within 3 days for 235 (23%) patients, and within a month for 889 (86%). The median volumetric doubling time was 22 days. Lower performance status (hazard ratio [HR] 0.942, 95% confidence interval [CI] 0.893–0.994) and larger tumor volume (HR 1.012, 95% CI 1.010–1.014) were independently associated with a shorter time-to-surgery. Extent of resection, residual tumor volume, postoperative performance change, and overall survival were not associated with time-to-surgery.
CONCLUSIONS:
With current decision-making for urgent surgery in selected patients with glioblastoma and surgery typically within 1 month, we found equal extent of resection, residual tumor volume, performance status, and survival after longer times-to-surgery
Multi-class glioma segmentation on real-world data with missing MRI sequences: comparison of three deep learning algorithms
This study tests the generalisability of three Brain Tumor Segmentation (BraTS) challenge models using a multi-center dataset of varying image quality and incomplete MRI datasets. In this retrospective study, DeepMedic, no-new-Unet (nn-Unet), and NVIDIA-net (nv-Net) were trained and tested using manual segmentations from preoperative MRI of glioblastoma (GBM) and low-grade gliomas (LGG) from the BraTS 2021 dataset (1251 in total), in addition to 275 GBM and 205 LGG acquired clinically across 12 hospitals worldwide. Data was split into 80% training, 5% validation, and 15% internal test data. An additional external test-set of 158 GBM and 69 LGG was used to assess generalisability to other hospitals’ data. All models’ median Dice similarity coefficient (DSC) for both test sets were within, or higher than, previously reported human inter-rater agreement (range of 0.74–0.85). For both test sets, nn-Unet achieved the highest DSC (internal = 0.86, external = 0.93) and the lowest Hausdorff distances (10.07, 13.87 mm, respectively) for all tumor classes (p < 0.001). By applying Sparsified training, missing MRI sequences did not statistically affect the performance. nn-Unet achieves accurate segmentations in clinical settings even in the presence of incomplete MRI datasets. This facilitates future clinical adoption of automated glioma segmentation, which could help inform treatment planning and glioma monitoring
Microlensing search towards M31
We present the first results of the analysis of data collected during the
1998-99 observational campaign at the 1.3 meter McGraw-Hill Telescope, towards
the Andromeda galaxy (M31), aimed to the detection of gravitational
microlensing effects as a probe of the presence of dark matter in our and in
M31 halo. The analysis is performed using the pixel lensing technique, which
consists in the study of flux variations of unresolved sources and has been
proposed and implemented by the AGAPE collaboration. We carry out a shape
analysis by demanding that the detected flux variations be achromatic and
compatible with a Paczynski light curve. We apply the Durbin-Watson hypothesis
test to the residuals. Furthermore, we consider the background of variables
sources. Finally five candidate microlensing events emerge from our selection.
Comparing with the predictions of a Monte Carlo simulation, assuming a standard
spherical model for the M31 and Galactic haloes, and typical values for the
MACHO mass, we find that our events are only marginally consistent with the
distribution of observable parameters predicted by the simulation.Comment: 13 pages, To appear in A&
MOA-2010-BLG-477Lb: constraining the mass of a microlensing planet from microlensing parallax, orbital motion and detection of blended light
Microlensing detections of cool planets are important for the construction of
an unbiased sample to estimate the frequency of planets beyond the snow line,
which is where giant planets are thought to form according to the core
accretion theory of planet formation. In this paper, we report the discovery of
a giant planet detected from the analysis of the light curve of a
high-magnification microlensing event MOA-2010-BLG-477. The measured
planet-star mass ratio is and the projected
separation is in units of the Einstein radius. The angular
Einstein radius is unusually large mas. Combining
this measurement with constraints on the "microlens parallax" and the lens
flux, we can only limit the host mass to the range . In
this particular case, the strong degeneracy between microlensing parallax and
planet orbital motion prevents us from measuring more accurate host and planet
masses. However, we find that adding Bayesian priors from two effects (Galactic
model and Keplerian orbit) each independently favors the upper end of this mass
range, yielding star and planet masses of
and at a distance of kpc,
and with a semi-major axis of AU. Finally, we show that the
lens mass can be determined from future high-resolution near-IR adaptive optics
observations independently from two effects, photometric and astrometric.Comment: 3 Tables, 12 Figures, accepted in Ap
The Interstellar Environment of our Galaxy
We review the current knowledge and understanding of the interstellar medium
of our galaxy. We first present each of the three basic constituents - ordinary
matter, cosmic rays, and magnetic fields - of the interstellar medium, laying
emphasis on their physical and chemical properties inferred from a broad range
of observations. We then position the different interstellar constituents, both
with respect to each other and with respect to stars, within the general
galactic ecosystem.Comment: 39 pages, 12 figures (including 3 figures in 2 parts
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
Longitudinal double-spin asymmetry and cross section for inclusive neutral pion production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV
We report a measurement of the longitudinal double-spin asymmetry A_LL and
the differential cross section for inclusive Pi0 production at midrapidity in
polarized proton collisions at sqrt(s) = 200 GeV. The cross section was
measured over a transverse momentum range of 1 < p_T < 17 GeV/c and found to be
in good agreement with a next-to-leading order perturbative QCD calculation.
The longitudinal double-spin asymmetry was measured in the range of 3.7 < p_T <
11 GeV/c and excludes a maximal positive gluon polarization in the proton. The
mean transverse momentum fraction of Pi0's in their parent jets was found to be
around 0.7 for electromagnetically triggered events.Comment: 6 pages, 3 figures, submitted to Phys. Rev. D (RC
Inclusive charged hadron elliptic flow in Au + Au collisions at = 7.7 - 39 GeV
A systematic study is presented for centrality, transverse momentum ()
and pseudorapidity () dependence of the inclusive charged hadron elliptic
flow () at midrapidity() in Au+Au collisions at
= 7.7, 11.5, 19.6, 27 and 39 GeV. The results obtained with
different methods, including correlations with the event plane reconstructed in
a region separated by a large pseudorapidity gap and 4-particle cumulants
(), are presented in order to investigate non-flow correlations and
fluctuations. We observe that the difference between and
is smaller at the lower collision energies. Values of , scaled by
the initial coordinate space eccentricity, , as a function
of are larger in more central collisions, suggesting stronger collective
flow develops in more central collisions, similar to the results at higher
collision energies. These results are compared to measurements at higher
energies at the Relativistic Heavy Ion Collider ( = 62.4 and 200
GeV) and at the Large Hadron Collider (Pb + Pb collisions at =
2.76 TeV). The values for fixed rise with increasing collision
energy within the range studied (). A comparison to
viscous hydrodynamic simulations is made to potentially help understand the
energy dependence of . We also compare the results to UrQMD
and AMPT transport model calculations, and physics implications on the
dominance of partonic versus hadronic phases in the system created at Beam
Energy Scan (BES) energies are discussed.Comment: 20 pages, 12 figures. Version accepted by PR
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