981 research outputs found
Generation and reduction of the data for the Ulysses gravitational wave experiment
A procedure for the generation and reduction of the radiometric data known as REGRES is described. The software is implemented on a HP-1000F computer and was tested on REGRES data relative to the Voyager I spacecraft. The REGRES data are a current output of NASA's Orbit Determination Program. The software package was developed in view of the data analysis of the gravitational wave experiment planned for the European spacecraft Ulysses
SpaceOAR to improve dosimetric outcomes for monotherapy high-dose-rate prostate implantation in a patient with ulcerative colitis.
High-dose-rate (HDR) brachytherapy is an attractive option for patients receiving definitive radiation therapy for prostate cancer with decreased overall dose to the pelvis. However, ulcerative colitis increases rectal toxicity risk and may be a contraindication. A synthetic hydrogel, SpaceOAR (Augmentix Inc., Waltham, MA, USA), can facilitate the use of HDR brachytherapy for patients where rectal toxicity is a limiting factor. SpaceOAR gel (13.19 cc) was utilized in a monotherapy HDR prostate treatment with Ir-192 under transrectal ultrasound guidance, with the intention of decreasing rectal dose. SpaceOAR gel was inserted transperineally into the patient 18 days prior to the procedure. The HDR brachytherapy procedure was tolerated without incident. All planning constraints were met, and the following dosimetry was achieved: Prostate – V100% = 97.3%, V150% = 35%, V200% = 14.5%; Urethra – V118% = 0%; Rectum – D2 cc = 51.6%, V75% = 0 cc. The rectum-catheter spacing was on average between 6-8 mm. Average spacing for our 10 most recent patients without SpaceOAR was 3 mm. SpaceOAR did not hinder or distort ultrasound imaging or increase treatment time. SpaceOAR successfully increases catheter-rectal wall spacing and decreases rectal dose due to improved planning capabilities, while decreasing the likelihood of rectal perforation. One application of this tool is presented to mitigate potential toxicities associated with ulcerative colitis. At five months, one week, and one day follow-up, the patient reported no bowel issues following HDR brachytherapy. © 2018 Termedia Publishing House Ltd. All Rights Reserved
On the Age and Metallicity Estimation of Spiral Galaxies Using Optical and Near-Infrared Photometry
In integrated-light, some color-color diagrams that use optical and
near-infrared photometry show surprisingly orthogonal grids as age and
metallicity are varied, and they are coming into common usage for estimating
the average age and metallicity of spiral galaxies. In this paper we
reconstruct these composite grids using simple stellar population models from
several different groups convolved with some plausible functional forms of star
formation histories at fixed metallicity. We find that the youngest populations
present (t<2 Gyr) dominate the light, and because of their presence the
age-metallicity degeneracy can be partially broken with broad-band colors,
unlike older populations. The scatter among simple stellar population models by
different authors is, however, large at ages t<2 Gyr. The dominant
uncertainties in stellar population models arise from convective core overshoot
assumptions and the treatment of the thermally pulsing asymptotic giant branch
phase and helium abundance may play a significant role at higher metallicities.
Real spiral galaxies are unlikely to have smooth, exponential star formation
histories, and burstiness will cause a partial reversion to the single-burst
case, which has even larger model-to-model scatter. Finally, it is emphasized
that the current composite stellar population models need some implementation
of chemical enrichment histories for the proper analysis of the observational
data.Comment: 33 pages, 15 figures. Accepted to ApJ (Apr 2007). The major surgery
was Fig. 1
Reduction-Based Creative Telescoping for Algebraic Functions
Continuing a series of articles in the past few years on creative telescoping
using reductions, we develop a new algorithm to construct minimal telescopers
for algebraic functions. This algorithm is based on Trager's Hermite reduction
and on polynomial reduction, which was originally designed for hyperexponential
functions and extended to the algebraic case in this paper
Coincident electron channeling and cathodoluminescence studies of threading dislocations in GaN
We combine two scanning electron microscopy techniques to investigate the influence of dislocations on the light emission from nitride semiconductors. Combining electron channeling contrast imaging and cathodoluminescence imaging enables both the structural and luminescence properties of a sample to be investigated without structural damage to the sample. The electron channeling contrast image is very sensitive to distortions of the crystal lattice, resulting in individual threading dislocations appearing as spots with black–white contrast. Dislocations giving rise to nonradiative recombination are observed as black spots in the cathodoluminescence image. Comparison of the images from exactly the same micron-scale region of a sample demonstrates a one-to-one correlation between the presence of single threading dislocations and resolved dark spots in the cathodoluminescence image. In addition, we have also obtained an atomic force microscopy image from the same region of the sample, which confirms that both pure edge dislocations and those with a screw component (i.e., screw and mixed dislocations) act as nonradiative recombination centers for the Si-doped c-plane GaN thin film investigated
Radially extended kinematics and stellar populations of the massive ellipticals NGC1600, NGC4125 and NGC7619. Constraints on the outer dark halo density profile
We present high quality long slit spectra along the major and minor axes out
to 1.5-2 Re (14-22 kpc) of three bright elliptical galaxies (NGC1600, NGC4125,
NGC7619) obtained at the Hobby-Eberly Telescope (HET). We derive stellar
kinematic profiles and Lick/IDS indices (Hbeta, Mgb, Fe5015, Fe5270, Fe5335,
Fe5406). Moreover, for NGC4125 we derive gas kinematics and emission line
strengths. We model the absorption line strengths using Simple Stellar
Populations models that take into account the variation of [\alpha/Fe] and
derive ages, total metallicity and element abundances. Overall, we find that
the three galaxies have old and [\alpha/Fe] overabundant stellar populations
with no significant gradients. The metallicity is supersolar at the center with
a strong negative radial gradient. For NGC4125, several pieces of evidence
point to a recent dissipational merger event. We calculate the broad band color
profiles with the help of SSP models. All of the colors show sharp peaks at the
center of the galaxies, mainly caused by the metallicity gradients, and agree
well with the measured colors. Using the Schwarzschild's axisymmetric orbit
superposition technique, we model the stellar kinematics to constrain the dark
halos of the galaxies. We use the tight correlation between the Mgb strength
and local escape velocity to set limits on the extent of the halos by testing
different halo sizes. Logarithmic halos - cut at 60 kpc -minimize the overall
scatter of the Mgb-Vesc relation. Larger cutoff radii are found if the dark
matter density profile is decreasing more steeply at large radii.Comment: Accepted for publication in Astronomy and Astrophysic
The stellar population histories of early-type galaxies. III. The Coma Cluster
We present stellar population parameters of twelve early-type galaxies (ETGs)
in the Coma Cluster based on spectra obtained using the Low Resolution Imaging
Spectrograph on the Keck II Telescope. Our data allow us to examine in detail
the zero-point and scatter in their stellar population properties. Our ETGs
have SSP-equivalent ages of on average 5-8 Gyr with the models used here, with
the oldest galaxies having ages of ~10 Gyr old. This average age is identical
to the mean age of field ETGs. Our ETGs span a large range in velocity
dispersion but are consistent with being drawn from a population with a single
age. Specifically, ten of the twelve ETGs are consistent within their formal
errors of having the same age, 5.2+/-0.2 Gyr, over a factor of more than 750 in
mass. We therefore find no evidence for downsizing of the stellar populations
of ETGs in the core of the Coma Cluster. We suggest that Coma Cluster ETGs may
have formed the majority of their mass at high redshifts but suffered small but
detectable star formation events at z~0.1-0.3. Previous detections of
'downsizing' from stellar populations of local ETGs may not reflect the same
downsizing seen in lookback studies of RSGs, as the young ages of the local
ETGs represent only a small fraction of their total masses. (abridged)Comment: 49 pages, 20 figures (19 EPS, 1 JPEG). MNRAS, in press. For version
with full resolution of Fig. 1 see
http://www.astro.rug.nl/~sctrager/coma.pdf; for Table 2, see
http://www.astro.rug.nl/~sctrager/coma_table2.pdf; for Table B3, see
http://www.astro.rug.nl/~sctrager/coma_tableB3.pd
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