1,442 research outputs found
Destiny: A Candidate Architecture for the Joint Dark Energy Mission
Destiny is a simple, direct, low cost mission to determine the properties of
dark energy by obtaining a cosmologically deep supernova (SN) type Ia Hubble
diagram. Operated at L2, its science instrument is a 1.65m space telescope,
featuring a grism-fed near-infrared (NIR) (0.85-1.7micron) survey
camera/spectrometer with a 0.12 square degree field of view. During its
two-year primary mission, Destiny will detect, observe, and characterize ~3000
SN Ia events over the redshift interval 0.4<z<1.7 within a 3 square degree
survey area. In conjunction with ongoing ground-based SN Ia surveys for z<0.8,
Destiny mission data will be used to construct a high-precision Hubble diagram
and thereby constrain the dark energy equation of state from a time when it was
strongly matter-dominated to the present when dark energy dominates. The
grism-images simultaneously provide broad-band photometry, redshifts, and SN
classification, as well as time-resolved diagnostic data for investigating
additional SN luminosity diagnostics. Destiny will be used in its third year as
a high resolution, wide-field imager to conduct a multicolor NIR weak lensing
(WL) survey covering 1000 square degrees. The large-scale mass power spectrum
derived from weak lensing distortions of field galaxies as a function of
redshift will provide independent and complementary constraints on the dark
energy equation of state. The combination of SN and WL is much more powerful
than either technique on its own. Used together, these surveys will have more
than an order of magnitude greater sensitivity than will be provided by ongoing
ground-based projects. The dark energy parameters, w_0 and w_a, will be
measured to a precision of 0.05 and 0.2 respectively.Comment: Contains full color figure
Dual Fabry-Perot filter for measurement of CO rotational spectra: design and application to the CO spectrum of Venus
We present the design of a harmonic resonant filter that can be used with a Fourier transform spectrometer (FTS) for simultaneous measurement of a series of lines in the CO rotational ladder. To enable studies of both broad CO absorptions in Venus and modestly red-shifted CO emission from external galaxies, relatively broad (approximately 10-30-GHz FWHM) transmission passbands are desirable. Because a single low-finesse Fabry Perot (FP) etalon has insufficient interline rejection, a dual-FP etalon was considered. Such a design provides significantly better interband rejection and somewhat more flattopped transmission spikes. A prototype filter of this type, made of two thin silicon disks spaced by an air gap, has been constructed and used with our FTS at the Caltech Submillimeter Observatory for simultaneous measurement of the four submillimeter CO transitions in the atmosphere of Venus that are accessible from the ground
Exploring the Universe with WISE and Cloud Computing
WISE is a recently-completed astronomical survey mission that has imaged the entire sky in four infrared wavelength bands. The large quantity of science images returned consists of 2,776,922 individual snapshots in various locations in each band which, along with ancillary data, totals around 110TB of raw, uncompressed data. Making the most use of this data requires advanced computing resources. I will discuss some initial attempts in the use of cloud computing to make this large problem tractable
WISE and the Dusty Universe
The Wide-field Infrared Survey is a medium class Explorer mission that was launched onl4Dec 2009. WISE should detect hundreds of millions of stars and galaxies, including millions of ULIRGS and QSOs; hundreds of thousands of asteroids; and hundreds of cold brown dwarfs. The telescope cover was ejected on 29 Dec 2009 and the all-sky survey started on 14 Jan 2010. WISE takes more the 7000 framesets per day, with each frameset covering 0.6 square degrees in four bands centered at 3.4, 4.6, 12 and 22 microns. WISE is well-suited to the discovery of brown dwarfs, ultraluminous infrared galaxies, and near-Earth objects. With an angular resolution of 6 arcsecouds at 12 microns, a 5(sigma) point-source sensitivity of around 1 mJy at 12 microns and 6 mJy at 22 microns, and coverage of over 99% of the sky, WISE also provides a powerful database for the study of the dusty ISM in our own galaxy. A preliminary release of WISE data will be made available to the community 6 months after the end of the cryogenic survey, or about May 2011. The final data release will be 11 months later, about April 2012
Exploratory study of construction safety culture through systems thinKing
Since its conception, in 1986 after the Chernobyl accident, the term safety culture has gained major popularity throughout many systems, especially the construction industry. Although this concept has gained much popularity over the course of two decades, it remains a heavily debated topic between advocates and skeptics for various reasons. Much of the skepticism is due to the failure of proponents of the concept to clearly define and provide an understanding of those factors that comprise what safety culture is, and how it can be achieved. A system (particularly a construction system) that possesses a safety culture is one in which safety is the first priority of all individuals involved from top-level management to those at the operational level including, but not limited to owners, architects, engineers, general contractors, subcontractors, vendors, workers, etc. Hence, construction safety culture is a top-down approach to achieving safety within systems; System Dynamics, as defined by founder Jay Forrester, is the combination of theory, methods, and philosophy intended to analyze the behavior of systems in not only management, but also in environmental change, politics, economic behavior, medicine, engineering, and other fields. The objective of this thesis is to provide clarity to existing research and literature which defines construction safety culture, and explain how System Thinking/Dynamics is an effective tool for understanding and achieving a construction safety culture in a complex system. The program Vensim is used to construct a visual systems thinking model of causal loops that will ultimately provide a better understanding of construction safety culture. This model will illustrate the causal relationships between various safety-related variables as they pertain to the construction industry; Keywords: Construction safety culture, systems thinking, safety
Scientific Objectives for UV/Visible Astrophysics Investigations: A Summary of Responses by the Community (2012)
Following several recommendations presented by the Astrophysics Decadal
Survey 2010 centered around the need to define "a future ultraviolet-optical
space capability," on 2012 May 25, NASA issued a Request for Information (RFI)
seeking persuasive ultraviolet (UV) and visible wavelength astrophysics science
investigations. The goal was to develop a cohesive and compelling set of
science objectives that motivate and support the development of the next
generation of ultraviolet/visible space astrophysics missions. Responses were
due on 10 August 2012 when 34 submissions were received addressing a number of
potential science drivers. A UV/visible Mission RFI Workshop was held on 2012
September 20 where each of these submissions was summarized and discussed in
the context of each other. We present a scientific analysis of these
submissions and presentations and the pursuant measurement capability needs,
which could influence ultraviolet/visible technology development plans for the
rest of this decade. We also describe the process and requirements leading to
the inception of this community RFI, subsequent workshop and the expected
evolution of these ideas and concepts for the remainder of this decade.Comment: 22 pages, 1 figure, 3 table
Near-Infrared Photometry of the High-Redshift Quasar RDJ030117+002025: Evidence for a Massive Starburst at z=5.5
With a redshift of z=5.5 and an optical blue magnitude M_B ~ -24.2 mag (~4.5
10^12 L_sun), RDJ030117+002025 is the most distant optically faint (M_B > -26
mag) quasar known. MAMBO continuum observations at lambda=1.2 mm (185
micrometer rest-frame) showed that this quasar has a far-IR luminosity
comparable to its optical luminosity. We present near-infrared J- and K-band
photometry obtained with NIRC on the Keck I telescope, tracing the slope of the
rest frame UV spectrum of this quasar. The observed spectral index is close to
the value of alpha_nu ~ -0.44 measured in composite spectra of optically-bright
SDSS quasars. It thus appears that the quasar does not suffer from strong dust
extinction, which further implies that its low rest-frame UV luminosity is due
to an intrinsically-faint AGN. The FIR to optical luminosity ratio is then much
larger than that observed for the more luminous quasars, supporting the
suggestion that the FIR emission is not powered by the AGN but by a massive
starburst.Comment: 6 pages, APJ in pres
Pulse shortening in high power microwave sources
Observations show that the ubiquitous pulse shortening in high-power microwave (HPM) devices arises from the formation of plasma, electron streaming, high-E-field breakdown, and beam disruption. We review recent experiments in terms of these causes. Linear beam devices exhibit all of these mechanisms; in particular, beam disruption by E × B drifts in the strong microwave fields and diffusion in turbulent electric fields appear common. In relativistic magnetrons, the dominant effect is resonance destruction by cathode plasma motion, possibly from water contamination of the surface. Wall plasma effects shorten pulses in most sources. We call for the introduction of improved surface conditioning, cathodes which do not produce plasmas, and increased effort on the measurements of the high-field and plasma properties of HPM sources. Because of the broad nature of the phenomena in pulse shortening, we appeal for increased participation of the plasma, intense particle beam, and traditional microwave tube communities in pulse-shortening research. © 1997 IEEE
Dust formation, evolution, and obscuration effects in the very high-redshift universe
The evolution of dust at redshifts z>9, and consequently the dust properties,
differs greatly from that in the local universe. In contrast to the local
universe, core collapse supernovae (CCSNe) are the only source of
thermally-condensed dust. Because of the low initial dust-to-gas mass ratio,
grain destruction rates are low, so that CCSNe are net producers of
interstellar dust. Galaxies with large initial gas mass or high mass infall
rate will therefore have a more rapid net rate of dust production comported to
galaxies with lower gas mass, even at the same star formation rate. The dust
composition is dominated by silicates, which exhibit a strong rise in the UV
opacity near the Lyman break. This "silicate-UV break" may be confused with the
Lyman break, resulting in a misidentification of a galaxies' photometric
redshift. In this paper we demonstrate these effects by analyzing the spectral
energy distribution (SED) of MACS1149-JD, a lensed galaxy at z=9.6. A potential
2mm counterpart of MACS1149-JD has been identified with GISMO. While additional
observations are required to corroborate this identification, we use this
possible association to illustrate the physical processes and the observational
effects of dust in the very high redshift universe.Comment: Accepted for publication in ApJ Letter
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