3,097 research outputs found
LNG plume interaction with surface obstacles: final report, September 1980-September 1982
September 1981.CER81-82KMK-RNM-DEN22.Includes bibliographical references.Prepared for Gas Research Institute, Contract No. 5014-352-0203
Behavior of LNG vapor clouds: tests to define the size, shape and structure of LNG vapor clouds
Annual report for 1979-1980.GRI 79/0073.July 1980.Includes bibliographical references (pages 35-37).A terraced 1:240 scale model of the China Lake Naval Weapons Center was constructed to a resolution of one foot vertical increments and placed in the wind tunnel to determine the distances of lower flammability limit (LFL) for 1980, 40 cubic meter spills of Liquefied Natural Gas (LNG) under 4 wind speeds, 5 wind directions, and neutral flow conditions. A set of 8 aspirated hot-wire katharometer probes were made to determine the transient concentration at various downwind locations. Measurements of mean velocities, turbulence intensities, velocity spectra and correlations were performed over the model in the wind tunnel capable of simulating atmospheric phenomena. Data analysis has produced peak concentrations, contours of LFL, and time progressions of the plume ground level LFL. The wind tunnel test should determine the locations of meteorological or concentration instruments set up for field tests. In addition, the expected distances to LFL are determined by wind tunnel tests, thus the field program has the prior knowledge of the distances up to which the measurements should be performed.For Gas Research Institute, contract no. 5014-352-0203
Radio Emission Associated with Ultraluminous X-ray Sources in the Galaxy Merger NGC 3256
We present new 6, 3.6, and 2 cm VLA radio observations of the nearby merger
system NGC 3256, with resolutions of ~100 pc, which reveal compact radio
sources embedded in more diffuse emission at all three wavelengths. The two
radio nuclei are partially resolved, but the two dominant compact sources that
remain coincide with the two most powerful compact Ultraluminous X-ray sources
(ULXs) recently reported by Lira et al. The radio/X-ray ratios for these two
sources are too high by factors of >100-1000 to be normal X-ray binaries.
However, their radio and X-ray powers and ratios are consistent with
low-luminosity active galactic nuclei (LLAGNs), and optical emission lines
suggest the presence of a nuclear disk around the northern nucleus. If the two
nuclear ULXs are LLAGNs, their associated black holes are separated by only
\~1kpc, about 6 times closer to one another than those found recently in the
merger galaxy NGC 6240. A third ULX on the outskirts of the merger is also a
radio source, and probably is a collection of supernova remnants. The remaining
ULXs are not coincident with any source of compact radio emission, and are
consistent with expectations for beamed X-ray binaries or intermediate-mass
black holes.Comment: Accepted for ApJ (10 pages, 5 figures
Image Deblurring and Near-real-time Atmospheric Seeing Estimation through the Employment of Convergence of Variance
A new image reconstruction algorithm is presented that will remove the effect of atmospheric turbulence on motion compensated frame average images. The primary focus of this research was to develop a blind deconvolution technique that could be employed in a tactical military environment where both time and computational power are limited. Additionally, this technique can be employed to measure atmospheric seeing conditions. In a blind deconvolution fashion, the algorithm simultaneously computes a high resolution image and an average model for the atmospheric blur parameterized by Friedâs seeing parameter. The difference in this approach is that it does not assume a prior distribution for the seeing parameter, rather it assesses the convergence of the imageâs variance as the stopping criteria and identification of the proper seeing parameter from a range of candidate values. Experimental results show that the convergence of variance technique allows for estimation of the seeing parameter accurate to within 0.5 cm and often even better depending on the signal to noise ratio
The Emergence of the Modern Universe: Tracing the Cosmic Web
This is the report of the Ultraviolet-Optical Working Group (UVOWG)
commissioned by NASA to study the scientific rationale for new missions in
ultraviolet/optical space astronomy approximately ten years from now, when the
Hubble Space Telescope (HST) is de-orbited. The UVOWG focused on a scientific
theme, The Emergence of the Modern Universe, the period from redshifts z = 3 to
0, occupying over 80% of cosmic time and beginning after the first galaxies,
quasars, and stars emerged into their present form. We considered
high-throughput UV spectroscopy (10-50x throughput of HST/COS) and wide-field
optical imaging (at least 10 arcmin square). The exciting science to be
addressed in the post-HST era includes studies of dark matter and baryons, the
origin and evolution of the elements, and the major construction phase of
galaxies and quasars. Key unanswered questions include: Where is the rest of
the unseen universe? What is the interplay of the dark and luminous universe?
How did the IGM collapse to form the galaxies and clusters? When were galaxies,
clusters, and stellar populations assembled into their current form? What is
the history of star formation and chemical evolution? Are massive black holes a
natural part of most galaxies? A large-aperture UV/O telescope in space
(ST-2010) will provide a major facility in the 21st century for solving these
scientific problems. The UVOWG recommends that the first mission be a 4m
aperture, SIRTF-class mission that focuses on UV spectroscopy and wide-field
imaging. In the coming decade, NASA should investigate the feasibility of an 8m
telescope, by 2010, with deployable optics similar to NGST. No high-throughput
UV/Optical mission will be possible without significant NASA investments in
technology, including UV detectors, gratings, mirrors, and imagers.Comment: Report of UV/O Working Group to NASA, 72 pages, 13 figures, Full
document with postscript figures available at
http://casa.colorado.edu/~uvconf/UVOWG.htm
UV/Optical Detections of Candidate Tidal Disruption Events by GALEX and CFHTLS
We present two luminous UV/optical flares from the nuclei of apparently
inactive early-type galaxies at z=0.37 and 0.33 that have the radiative
properties of a flare from the tidal disruption of a star. In this paper we
report the second candidate tidal disruption event discovery in the UV by the
GALEX Deep Imaging Survey, and present simultaneous optical light curves from
the CFHTLS Deep Imaging Survey for both UV flares. The first few months of the
UV/optical light curves are well fitted with the canonical t^(-5/3) power-law
decay predicted for emission from the fallback of debris from a tidally
disrupted star. Chandra ACIS X-ray observations during the flares detect soft
X-ray sources with T_bb= (2-5) x 10^5 K or Gamma > 3 and place limits on hard
X-ray emission from an underlying AGN down to L_X (2-10 keV) <~ 10^41 ergs/s.
Blackbody fits to the UV/optical spectral energy distributions of the flares
indicate peak flare luminosities of > 10^44-10^45 ergs/s. The temperature,
luminosity, and light curves of both flares are in excellent agreement with
emission from a tidally disrupted main sequence star onto a central black hole
of several times 10^7 msun. The observed detection rate of our search over ~
2.9 deg^2 of GALEX Deep Imaging Survey data spanning from 2003 to 2007 is
consistent with tidal disruption rates calculated from dynamical models, and we
use these models to make predictions for the detection rates of the next
generation of optical synoptic surveys.Comment: 28 pages, 27 figures, 11 tables, accepted to ApJ, final corrections
from proofs adde
Lyman alpha emitting galaxies at 0.2 < z < 0.35 from GALEX spectroscopy
The GALEX (Galaxy Evolution Explorer) spectroscopic survey mode, with a
resolution of about 8 A in the FUV (1350 - 1750 A) and about 20 A in the NUV
(1950 - 2750 A) is used for a systematic search of Ly-a emitting galaxies at
low redshift. This aims at filling a gap between high-redshift surveys and a
small set of objects studied in detail in the nearby universe. A blind search
of 7018 spectra extracted in 5 deep exposures (5.65 sq.deg) has resulted in 96
Ly-a emitting galaxy candidates in the FUV domain, after accounting for
broad-line AGNs. The Ly-a EWs (equivalent width) are consistent with stellar
population model predictions and show no trends as a function of UV color or UV
luminosity, except a possible decrease in the most luminous that may be due to
small-number statistics. Their distribution in EW is similar to that at z about
3 but their fraction among star-forming galaxies is smaller. Avoiding uncertain
candidates, a sub-sample of 66 objects in the range 0.2 < z < 0.35 has been
used to build a Ly-a LF (luminosity function). The incompleteness due to
objects with significant Ly-a emission but a UV continuum too low for spectral
extraction has been evaluated. A comparison with H-a LF in the same redshift
domain is consistent with an average Ly-a/H-a of about 1 in about 15 % of the
star-forming galaxies. A comparison with high-redshift Ly-a LFs implies an
increase of the Ly-a luminosity density by a factor of about 16 from z about
0.3 to z about 3. By comparison with the factor 5 increase of the UV luminosity
density in the same redshift range, this suggests an increase of the average
Ly-a escape fraction with redshift.Comment: 18 pages, 9 figures, accepted for publication in Ap
Fluid-rock interaction, skarn genesis, and hydrothermal alteration within an upper crustal fault zone (Island of Elba, Italy)
The Terranera magnetite-hematite-pyrite deposit of the Island of Elba (Italy) is an historical skarn deposit hosted by a fault zone of regional importance (Zuccale Fault) and by its hanging wall rocks.
We combine field observations with petrographic data, electron probe microanalyses (EPMA), XRPD data, fluid inclusion microthermometry, and element imaging by Laser Ablation-Inductively Coupled Plasma-Time of Flight Mass Spectrometry (LA-ICP-TOFMS) to define the ore-forming process at Terranera. We show that in this location the fault is made of four levels of mineralized fault rocks having distinct mineral compositions. In these levels, a mineral association made of diopside, clinozoisite, and other Mg-rich minerals is replaced by magnetite, hematite, pyrite, Mg-hornblende, clinochlore, and other Mg-rich phyllosilicates. This paragenesis is overprinted by goethite and clay minerals. Chlorite-quartz geothermometry and fluid inclusion microthermometry show that ore precipitation occurred at 350â180 °C from fluids of distinct bulk salinities, but goethite and clay mineral overprinting progressed at lower T.
We propose that Terranera is a magnesian Fe skarn formed due to the interaction between distinct hydrothermal fluids and a dolomitic protolith, which was preserved within the fault zone. These fluids mixed and cooled during protolith metasomatism, causing ore precipitation due to oxidation and desulfidation. A very similar process was described in a large deposit of Elba (Rio Marina). Argillic alteration was widespread within the fault but met permanently intermediate sulfidation conditions. Trace element composition of hematite shows that Terranera has features that overlap those of skarn and epithermal deposits. In particular, elements that are typical of epithermal deposits (Sb, Ga, Ge, As) occur at mass fractions (50â200 ÎŒg/g) that are either unreported or not typical of hematite from skarn deposits. These features identify Terranera as formed in an ore environment that was transitional between that of a skarn and of an epithermal deposit. These features are shared by other historical deposits located at Elba and in the massive pyritic ore district of south Tuscany (e.g., Gavorrano, Fenice Capanne). This indicates that a similar environment might have occurred during the Neogene beyond Elba, in a much larger ore district of south Tuscany
- âŠ