3,032 research outputs found
High altitude Robin data-reduction program
Computer program for Robin data reductio
Interrelated structure of high altitude atmospheric profiles
A preliminary development of a mathematical model to compute probabilities of thermodynamic profiles is presented. The model assumes an exponential expression for pressure and utilizes the hydrostatic law and equation of state in the determination of density and temperature. It is shown that each thermodynamic variable can be factored into the produce of steady state and perturbation functions. The steady state functions have profiles similar to those of the 1962 standard atmosphere while the perturbation functions oscillate about 1. Limitations of the model and recommendations for future work are presented
Applications Technology Satellite and Communications Technology Satellite user experiments for 1967-1980 reference book. Volume 4: Abstracts
The important user experiments conducted during the fourteen year period from 1966 to 1980 are summarized. A description of each of the satellites and a brief summary of each user experiment is presented. A cross index of user experiments sorted by various parameters and a listing of keywords versus experiment number is included. The experiments are grouped by type of service offered; for example, education, health services, and data transmission. A bibliography of reports by accession number and by author is also presented. User viewpoints of the systems are presented
Applications Technology Satellite and Communications Technology Satellite user experiments for 1967 - 1980 reference book, volume 1
A description of each of the satellites is given and a brief summary of each user experiment is presented. A Cross Index of User Experiments sorted by various parameters and a listing of keywords versus Experiment Number are presented
Compendium of Applications Technology Satellite user experiments
The achievements of the user experiments performed with ATS satellites from 1967 to 1973 are summarized. Included are fixed and mobile point to point communications experiments involving voice, teletype and facsimile transmissions. Particular emphasis is given to the Alaska and Hawaii satellite communications experiments. The use of the ATS satellites for ranging and position fixing of ships and aircraft is also covered. The structure and operating characteristics of the various ATS satellite are briefly described
A Pseudolikelihood Approach for Simultaneous Analysis of Array Comparative Genomic Hybridizations (aCGH)
DNA sequence copy number has been shown to be associated with cancer development and progression. Array-based Comparative Genomic Hybridization (aCGH) is a recent development that seeks to identify the copy number ratio at large numbers of markers across the genome. Due to experimental and biological variations across chromosomes and across hybridizations, current methods are limited to analyses of single chromosomes. We propose a more powerful approach that borrows strength across chromosomes and across hybridizations. We assume a Gaussian mixture model, with a hidden Markov dependence structure, and with random effects to allow for intertumoral variation, as well as intratumoral clonal variation. For ease of computation, we base estimation on a pseudolikelihood function. The method produces quantitative assessments of the likelihood of genetic alterations at each clone, along with a graphical display for simple visual interpretation. We assess the characteristics of the method through simulation studies and through analysis of a brain tumor aCGH data set. We show that the pseudolikelihood approach is superior to existing methods both in detecting small regions of copy number alteration and in accurately classifying regions of change when intratumoral clonal variation is present
The challenge of measuring the phase function of debris disks. Application to HR\,4796
Abridged: Debris disks are valuable systems to study dust properties. Because
they are optically thin at all wavelengths, we have direct access to the
properties of dust grains. One very promising technique to study them is to
measure their phase function. Disks that are highly inclined are promising
targets as a wider range of scattering angles can be probed. The phase function
is usually either inferred by comparing the observations to synthetic disk
models assuming a parametrized phase function, or estimating it from the
surface brightness of the disk. We argue here that the latter approach can be
biased due to projection effects leading to an increase in column density along
the major axis of a non flat disk. We present a novel approach to account for
those column density effects. The method remains model dependent, as one still
requires a disk model to estimate the density variations as a function of the
scattering angle. This method allows us however to estimate the shape of the
phase function without having to invoke any parametrized form. We apply our
method to SPHERE/ZIMPOL observations of HR\,4796 and highlight the differences
with previous measurements. Our modelling results suggest that the disk is not
vertically flat at optical wavelengths. We discuss some of the caveats of the
approach, mostly that our method remains blind to real local increase of the
dust density, and that it cannot yet be readily applied to angular differential
imaging observations. Similarly to previous studies on HR\,4796, we still
cannot reconcile the full picture using a given scattering theory to explain
the shape of the phase function, a long lasting problem for debris disks.
Nonetheless, we argue that similar effects as the ones highlighted in this
study can also bias the determination of the phase function in total intensity.Comment: Accepted for publication in A&A, 13 pages, 11 Figure
Continuation of the compendium of applications technology satellite and communications technology satellite user experiments 1967-1977, volume 2
Approximately 453 reports, papers, and articles catalogued into an information retrieval system, covering communications experiments and demonstrations conducted, utilizing the Communications Technology Satellite and the Applications Technology Satellites 1, 3, 5, and 6 are listed
Detection of scattered light from the hot dust in HD 172555
Debris disks or belts are important signposts for the presence of colliding
planetesimals and, therefore, for ongoing planet formation and evolution
processes in young planetary systems. Imaging of debris material at small
separations from the star is very challenging but provides valuable insights
into the spatial distribution of so-called hot dust produced by solid bodies
located in or near the habitable zone. We report the first detection of
scattered light from the hot dust around the nearby (d = 28.33 pc) A star HD
172555. We want to constrain the geometric structure of the detected debris
disk using polarimetric differential Imaging (PDI) with a spatial resolution of
25 mas and an inner working angle of about 0.1. We measured the polarized
light of HD 172555, with SPHERE-ZIMPOL, in the very broad band (VBB;
nm) filter for the projected separations between 0.08 (2.3
au) and 0.77 (22 au). We constrained the disk parameters by fitting models
for scattering of an optically thin dust disk taking the limited spatial
resolution and coronagraphic attenuation of our data into account. The
geometric structure of the disk in polarized light shows roughly the same
orientation and outer extent as obtained from thermal emission at 18 m.
Our image indicates the presence of a strongly inclined (),
roughly axisymmetric dust belt with an outer radius in the range between
0.3 (8.5 au) and 0.4 (11.3 au). We derive a lower limit for the
polarized flux contrast ratio for the disk of in the VBB filter. This ratio is small, only
9 %, when compared to the fractional infrared flux excess (). The model simulations show that more polarized light could be
produced by the dust located inside 2 au, which cannot be detected with the
instrument configuration used.Comment: 16 pages, 10 figure
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