209 research outputs found
Applications of structural optimization methods to fixed-wing aircraft and spacecraft in the 1980s
This report is the summary of a technical survey on the applications of structural optimization in the U.S. aerospace industry through the 1980s. Since applications to rotary wing aircraft will be covered by other literature, applications to fixed-wing aircraft and spacecraft were considered. It became clear that very significant progress has been made during this decade, indicating this technology is about to become one of the practical tools in computer aided structural design
A photometric search for transients in galaxy clusters
We have begun a program to search for supernovae and other transients in the
fields of galaxy clusters with the 2.3m Bok Telescope on Kitt Peak. We present
our automated photometric methods for data reduction, efficiency
characterization, and initial spectroscopy. With this program, we aim to
ultimately identify 25-35 cluster SN Ia (10 of which will be
intracluster, hostless events) and constrain the SN Ia rate associated with
old, passive stellar populations. With these measurements we will constrain the
relative contribution of hostless and hosted SN Ia to the metal enrichment of
the intracluster medium. In the current work, we have identified a central
excess of transient events within in our cluster fields after
statistically subtracting out the 'background' transient rate taken from an
off-cluster CCD chip. Based on the published rate of SN Ia for cluster
populations we estimate that 20 percent of the excess cluster transients
are due to cluster SN Ia, a comparable fraction to core collapse (CC)
supernovae and the remaining are likely to be active galactic nuclei.
Interestingly, we have identified three intracluster SN candidates, all of
which lay beyond . These events, if truly associated with the
cluster, indicate a large deficit of intracluster (IC) SN at smaller radii, and
may be associated with the IC stars of infalling groups or indicate that the
intracluster light (ICL) in the cluster outskirts is actively forming stars
which contribute CC SN or prompt SN Ia.Comment: Updated to match accepted version; 26 pages, 14 figures, AJ accepte
The Gemini NICI Planet-Finding Campaign
Our team is carrying out a multi-year observing program to directly image and
characterize young extrasolar planets using the Near-Infrared Coronagraphic
Imager (NICI) on the Gemini-South 8.1-meter telescope. NICI is the first
instrument on a large telescope designed from the outset for high-contrast
imaging, comprising a high-performance curvature adaptive optics system with a
simultaneous dual-channel coronagraphic imager. Combined with state-of-the-art
observing methods and data processing, NICI typically achieves ~2 magnitudes
better contrast compared to previous ground-based or space-based programs, at
separations inside of ~2 arcsec. In preparation for the Campaign, we carried
out efforts to identify previously unrecognized young stars, to rigorously
construct our observing strategy, and to optimize the combination of angular
and spectral differential imaging. The Planet-Finding Campaign is in its second
year, with first-epoch imaging of 174 stars already obtained out of a total
sample of 300 stars. We describe the Campaign's goals, design, implementation,
performance, and preliminary results. The NICI Campaign represents the largest
and most sensitive imaging survey to date for massive (~1 Mjup) planets around
other stars. Upon completion, the Campaign will establish the best measurements
to date on the properties of young gas-giant planets at ~5-10 AU separations.
Finally, Campaign discoveries will be well-suited to long-term orbital
monitoring and detailed spectrophotometric followup with next-generation
planet-finding instruments.Comment: Proceedings of the SPIE, vol 7736 (Advances in Adaptive Optics, San
Diego, CA, June 2010 meeting), in pres
Towards a Cosmological Hubble Diagram for Type II-P Supernovae
We present the first high-redshift Hubble diagram for Type II-P supernovae
(SNe II-P) based upon five events at redshift up to z~0.3. This diagram was
constructed using photometry from the Canada-France-Hawaii Telescope Supernova
Legacy Survey and absorption line spectroscopy from the Keck observatory. The
method used to measure distances to these supernovae is based on recent work by
Hamuy & Pinto (2002) and exploits a correlation between the absolute brightness
of SNe II-P and the expansion velocities derived from the minimum of the Fe II
516.9 nm P-Cygni feature observed during the plateau phases. We present three
refinements to this method which significantly improve the practicality of
measuring the distances of SNe II-P at cosmologically interesting redshifts.
These are an extinction correction measurement based on the V-I colors at day
50, a cross-correlation measurement for the expansion velocity and the ability
to extrapolate such velocities accurately over almost the entire plateau phase.
We apply this revised method to our dataset of high-redshift SNe II-P and find
that the resulting Hubble diagram has a scatter of only 0.26 magnitudes, thus
demonstrating the feasibility of measuring the expansion history, with present
facilities, using a method independent of that based upon supernovae of Type
Ia.Comment: 36 pages, 16 figures, accepted for publication in Ap
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
Serum neurofilament dynamics predicts neurodegeneration and clinical progression in presymptomatic Alzheimer's disease
Neurofilament light chain (NfL) is a promising fluid biomarker of disease progression for various cerebral proteopathies. Here we leverage the unique characteristics of the Dominantly Inherited Alzheimer Network and ultrasensitive immunoassay technology to demonstrate that NfL levels in the cerebrospinal fluid (nâ=â187) and serum (nâ=â405) are correlated with one another and are elevated at the presymptomatic stages of familial Alzheimer's disease. Longitudinal, within-person analysis of serum NfL dynamics (nâ=â196) confirmed this elevation and further revealed that the rate of change of serum NfL could discriminate mutation carriers from non-mutation carriers almost a decade earlier than cross-sectional absolute NfL levels (that is, 16.2 versus 6.8 years before the estimated symptom onset). Serum NfL rate of change peaked in participants converting from the presymptomatic to the symptomatic stage and was associated with cortical thinning assessed by magnetic resonance imaging, but less so with amyloid-ÎČ deposition or glucose metabolism (assessed by positron emission tomography). Serum NfL was predictive for both the rate of cortical thinning and cognitive changes assessed by the Mini-Mental State Examination and Logical Memory test. Thus, NfL dynamics in serum predict disease progression and brain neurodegeneration at the early presymptomatic stages of familial Alzheimer's disease, which supports its potential utility as a clinically useful biomarker
Decreased body mass index in the preclinical stage of autosomal dominant Alzheimer\u27s disease
The relationship between body-mass index (BMI) and AlzheimeĆs disease (AD) has been extensively investigated. However, BMI alterations in preclinical individuals with autosomal dominant AD (ADAD) have not yet been investigated. We analyzed cross-sectional data from 230 asymptomatic members of families with ADAD participating in the Dominantly Inherited Alzheimer Network (DIAN) study including 120 preclinical mutation carriers (MCs) and 110 asymptomatic non-carriers (NCs). Differences in BMI and their relation with cerebral amyloid load and episodic memory as a function of estimated years to symptom onset (EYO) were analyzed. Preclinical MCs showed significantly lower BMIs compared to NCs, starting 11.2 years before expected symptom onset. However, the BMI curves begun to diverge already at 17.8 years before expected symptom onset. Lower BMI in preclinical MCs was significantly associated with less years before estimated symptom onset, higher global AÎČ brain burden, and with lower delayed total recall scores in the logical memory test. The study provides cross-sectional evidence that weight loss starts one to two decades before expected symptom onset of ADAD. Our findings point toward a link between the pathophysiology of ADAD and disturbance of weight control mechanisms. Longitudinal follow-up studies are warranted to investigate BMI changes over time
LSST: from Science Drivers to Reference Design and Anticipated Data Products
(Abridged) We describe here the most ambitious survey currently planned in
the optical, the Large Synoptic Survey Telescope (LSST). A vast array of
science will be enabled by a single wide-deep-fast sky survey, and LSST will
have unique survey capability in the faint time domain. The LSST design is
driven by four main science themes: probing dark energy and dark matter, taking
an inventory of the Solar System, exploring the transient optical sky, and
mapping the Milky Way. LSST will be a wide-field ground-based system sited at
Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m
effective) primary mirror, a 9.6 deg field of view, and a 3.2 Gigapixel
camera. The standard observing sequence will consist of pairs of 15-second
exposures in a given field, with two such visits in each pointing in a given
night. With these repeats, the LSST system is capable of imaging about 10,000
square degrees of sky in a single filter in three nights. The typical 5
point-source depth in a single visit in will be (AB). The
project is in the construction phase and will begin regular survey operations
by 2022. The survey area will be contained within 30,000 deg with
, and will be imaged multiple times in six bands, ,
covering the wavelength range 320--1050 nm. About 90\% of the observing time
will be devoted to a deep-wide-fast survey mode which will uniformly observe a
18,000 deg region about 800 times (summed over all six bands) during the
anticipated 10 years of operations, and yield a coadded map to . The
remaining 10\% of the observing time will be allocated to projects such as a
Very Deep and Fast time domain survey. The goal is to make LSST data products,
including a relational database of about 32 trillion observations of 40 billion
objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures
available from https://www.lsst.org/overvie
The compound machinery of government: The case of seconded officials in the European commission
This article explores the compound machinery of government. Attention is directed toward decision making within the core executive of the European Union - the European Commission. The article studies seconded national civil servants (SNEs) hired on short-term contracts. The analysis benefits from an original and rich body of surveys and interview data derived from current and former SNEs. The decision-making dynamics of SNEs are shown to contain a compound mix of departmental, epistemic, and supranational dynamics. This study clearly demonstrates that the socializing power of the Commission is conditional and only partly sustained when SNEs exit the Commission. Any long-lasting effect of socialization within European Union's executive machinery of government is largely absent. The compound decision-making dynamics of SNEs are explained by (1) the organizational affiliations of SNEs, (2) the formal organization of the Commission apparatus, and (3) only partly by processes of resocialization of SNEs within the Commission
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