369 research outputs found
Fiber Optic Control System integration for advanced aircraft. Electro-optic and sensor fabrication, integration, and environmental testing for flight control systems: Laboratory test results
This report presents the data obtained in laboratory testing of the optical sensors and multiplexing architecture developed for flight testing in the NASA F-18 systems research aircraft
Fiber Optic Control System integration for advanced aircraft. Electro-optic and sensor fabrication, integration, and environmental testing for flight control systems
This report describes the design, development, and testing of passive fiber optic sensors and a multiplexing electro-optic architecture (EOA) for installation and flight test on a NASA-owned F-18 aircraft. This hardware was developed under the Fiber Optic Control Systems for Advanced Aircraft program, part of a multiyear NASA initiative to design, develop, and demonstrate through flight test 'fly-by-light' systems for application to advanced aircraft flight and propulsion control. This development included the design and production of 10 passive optical sensors and associated multiplexed EOA hardware based on wavelength division multiplexed (WDM) technology. A variety of sensor types (rotary position, linear position, temperature, and pressure) incorporating a broad range of sensor technologies (WDM analog, WDM digital, analog microbend, and fluorescent time rate of decay) were obtained from different manufacturers and functionally integrated with an independently designed EOA. The sensors were built for installation in a variety of aircraft locations, placing the sensors in a variety of harsh environments. The sensors and EOA were designed and built to have the resulting devices be as close as practical to a production system. The integrated system was delivered to NASA for flight testing on a NASA-owned F-18 aircraft. Development and integration testing of the system provided valuable information as to which sensor types were simplest to design and build for a military aircraft environment and which types were simplest to operate with a multiplexed EOA. Not all sensor types met the full range of performance and environmental requirements. EOA development problems provided information on directions to pursue in future fly-by-light flight control development programs. Lessons learned in the development of the EOA and sensor hardware are summarized
Removing Orbital Debris with Lasers
Orbital debris in low Earth orbit (LEO) are now sufficiently dense that the
use of LEO space is threatened by runaway collisional cascading. A problem
predicted more than thirty years ago, the threat from debris larger than about
1 cm demands serious attention. A promising proposed solution uses a high power
pulsed laser system on the Earth to make plasma jets on the objects, slowing
them slightly, and causing them to re-enter and burn up in the atmosphere. In
this paper, we reassess this approach in light of recent advances in low-cost,
light-weight modular design for large mirrors, calculations of laser-induced
orbit changes and in design of repetitive, multi-kilojoule lasers, that build
on inertial fusion research. These advances now suggest that laser orbital
debris removal (LODR) is the most cost-effective way to mitigate the debris
problem. No other solutions have been proposed that address the whole problem
of large and small debris. A LODR system will have multiple uses beyond debris
removal. International cooperation will be essential for building and operating
such a system.Comment: 37 pages, 15 figures, in preparation for submission to Advances in
Space Researc
Dust and the spectral energy distribution of the OH/IR star OH 127.8+0.0: Evidence for circumstellar metallic iron
We present a fit to the spectral energy distribution of OH 127.8+0.0, a
typical asymptotic giant branch star with an optically thick circumstellar dust
shell. The fit to the dust spectrum is achieved using non-spherical grains
consisting of metallic iron, amorphous and crystalline silicates and water ice.
Previous similar attempts have not resulted in a satisfactory fit to the
observed spectral energy distributions, mainly because of an apparent lack of
opacity in the 3--8 micron region of the spectrum. Non-spherical metallic iron
grains provide an identification for the missing source of opacity in the
near-infrared. Using the derived dust composition, we have calculated spectra
for a range of mass-loss rates in order to perform a consistency check by
comparison with other evolved stars. The L-[12 micron] colours of these models
correctly predict the mass-loss rate of a sample of AGB stars, strengthening
our conclusion that the metallic iron grains dominate the near-infrared flux.
We discuss a formation mechanism for non-spherical metallic iron grains.Comment: 10 pages, 6 figures, accepted for publication by A&
Crystalline silicate dust around evolved stars II. The crystalline silicate complexes
This is the second paper in a series of three in which we present an
exhaustive inventory of the 49 solid state emission bands observed in a sample
of 17 oxygen-rich dust shells surrounding evolved stars. Most of these emission
bands are concentrated in well defined spectral regions (called complexes). We
define 7 of these complexes; the 10, 18, 23, 28, 33, 40 and 60 micron complex.
We derive average properties of the individual bands. Comparison with
laboratory data suggests that both olivines (Mg(2x)Fe(2-2x)SiO(4)) and
pyroxenes (Mg(x)Fe(1-x)SiO(3)) are present, with x close to 1, i.e. the
minerals are very Mg-rich and Fe-poor. This composition is similar to that seen
in disks surrounding young stars and in the solar system comet Hale-Bopp. A
significant fraction of the emission bands cannot be identified with either
olivines or pyroxenes. Possible other materials that may be the carriers of
these unidentified bands are briefly discussed. There is a natural division
into objects that show a disk-like geometry (strong crystalline silicate
bands), and objects whose dust shell is characteristic of an outflow (weak
crystalline silicate bands). In particular, stars with the 33.5 micron olivine
band stronger than about 20 percent over continuum are invariably disk sources.
Likewise, the 60 micron region is dominated by crystalline silicates in the
disk sources, while it is dominated by crystalline H(2)O ice in the outflow
sources. We show that the disk and outflow sources have significant differences
in the shape of the emission bands. This difference must be related to the
composition or grain shapes of the dust particles. The incredible richness of
the crystalline silicate spectra observed by ISO allows detailed studies of the
mineralogy of these dust shells, and is the origin and history of the dust.Comment: 20 pages, 21 figures, accepted by A&A, this paper and others (in this
serie) can also be found at http://zon.wins.uva.nl/~frankm/papers.htm
SPITZER survey of dust grain processing in stable discs around binary post-AGB stars
Aims: We investigate the mineralogy and dust processing in the circumbinary
discs of binary post-AGB stars using high-resolution TIMMI2 and SPITZER
infrared spectra. Methods: We perform a full spectral fitting to the infrared
spectra using the most recent opacities of amorphous and crystalline dust
species. This allows for the identification of the carriers of the different
emission bands. Our fits also constrain the physical properties of different
dust species and grain sizes responsible for the observed emission features.
Results: In all stars the dust is oxygen-rich: amorphous and crystalline
silicate dust species prevail and no features of a carbon-rich component can be
found, the exception being EPLyr, where a mixed chemistry of both oxygen- and
carbon-rich species is found. Our full spectral fitting indicates a high degree
of dust grain processing. The mineralogy of our sample stars shows that the
dust is constituted of irregularly shaped and relatively large grains, with
typical grain sizes larger than 2 micron. The spectra of nearly all stars show
a high degree of crystallinity, where magnesium-rich end members of olivine and
pyroxene silicates dominate. Other dust features of e.g. silica or alumina are
not present at detectable levels. Temperature estimates from our fitting
routine show that a significant fraction of grains must be cool, significantly
cooler than the glass temperature. This shows that radial mixing is very
efficient is these discs and/or indicates different thermal conditions at grain
formation. Our results show that strong grain processing is not limited to
young stellar objects and that the physical processes occurring in the discs
are very similar to those in protoplanetary discs.Comment: 22pages, 50 figures (in appendix), accepted for A&
Largest GWAS of PTSD (N=20 070) yields genetic overlap with schizophrenia and sex differences in heritability
The Psychiatric Genomics Consortium-Posttraumatic Stress Disorder group (PGC-
PTSD) combined genome-wide case–control molecular genetic data across 11
multiethnic studies to quantify PTSD heritability, to examine potential shared
genetic risk with schizophrenia, bipolar disorder, and major depressive
disorder and to identify risk loci for PTSD. Examining 20 730 individuals, we
report a molecular genetics-based heritability estimate (h2SNP) for European-
American females of 29% that is similar to h2SNP for schizophrenia and is
substantially higher than h2SNP in European-American males (estimate not
distinguishable from zero). We found strong evidence of overlapping genetic
risk between PTSD and schizophrenia along with more modest evidence of overlap
with bipolar and major depressive disorder. No single-nucleotide polymorphisms
(SNPs) exceeded genome-wide significance in the transethnic (overall) meta-
analysis and we do not replicate previously reported associations. Still, SNP-
level summary statistics made available here afford the best-available
molecular genetic index of PTSD—for both European- and African-American
individuals—and can be used in polygenic risk prediction and genetic
correlation studies of diverse phenotypes. Publication of summary statistics
for ∼10 000 African Americans contributes to the broader goal of increased
ancestral diversity in genomic data resources. In sum, the results demonstrate
genetic influences on the development of PTSD, identify shared genetic risk
between PTSD and other psychiatric disorders and highlight the importance of
multiethnic/racial samples. As has been the case with schizophrenia and other
complex genetic disorders, larger sample sizes are needed to identify specific
risk loci
Severity of Depressive Symptoms and Accuracy of Dietary Reporting among Obese Women with Major Depressive Disorder Seeking Weight Loss Treatment
An elevation in symptoms of depression has previously been associated with greater accuracy of reported dietary intake, however this association has not been investigated among individuals with a diagnosis of major depressive disorder. The purpose of this study was to investigate reporting accuracy of dietary intake among a group of women with major depressive disorder in order to determine if reporting accuracy is similarly associated with depressive symptoms among depressed women. Reporting accuracy of dietary intake was calculated based on three 24-hour phone-delivered dietary recalls from the baseline phase of a randomized trial of weight loss treatment for 161 obese women with major depressive disorder. Regression models indicated that higher severity of depressive symptoms was associated with greater reporting accuracy, even when controlling for other factors traditionally associated with reporting accuracy (coefficient  = 0.01 95% CI = 0.01 – 0.02). Seventeen percent of the sample was classified as low energy reporters. Reporting accuracy of dietary intake increases along with depressive symptoms, even among individuals with major depressive disorder. These results suggest that any study investigating associations between diet quality and depression should also include an index of reporting accuracy of dietary intake as accuracy varies with the severity of depressive symptoms
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