6,120 research outputs found
An assembly to provide a time reference for the JPL Network Operations Control Center, Real-Time
A device is described which provides the value of date coordinated universal time (date UTC) to the JPL Network Operations Control Center, Real Time (NOCC-RT) facility. The NOCC-RT is the real time portion of the NOCC upgrade task. The time scale is generated in the NOCC-RT clock processor; however, there is a continuous reference to UTC, as realized by the National Institute of Standards and Technology and transmitted by Earth orbiting satellites. An important functional design requirement is the 99.9 pct. availability
Nuclear gas dynamics in Arp 220 - sub-kiloparsec scale atomic hydrogen disks
We present new, high angular resolution (~0.22") MERLIN observations of
neutral hydrogen (HI) absorption and 21-cm radio continuum emission across the
central ~900 parsecs of the ultraluminous infrared galaxy, Arp220. Spatially
resolved HI absorption is detected against the morphologically complex and
extended 21-cm radio continuum emission, consistent with two counterrotating
disks of neutral hydrogen, with a small bridge of gas connecting the two.
We propose a merger model in which the two nuclei represent the galaxy cores
which have survived the initial encounter and are now in the final stages of
merging, similar to conclusions drawn from previous CO studies (Sakamoto,
Scoville & Yun 1999). However, we suggest that instead of being coplanar with
the main CO disk (in which the eastern nucleus is embedded), the western
nucleus lies above it and, as suggested by bridge of HI connecting the two
nuclei, will soon complete its final merger with the main disk. We suggest that
the collection of radio supernovae (RSN) detected in VLBA studies in the more
compact western nucleus represent the second burst of star formation associated
with this final merger stage and that free-free absorption due to ionised gas
in the bulge-like component can account for the observed RSN distribution.
(Abridged)Comment: 26 pages including 8 figures and 1 table; accepted for publication in
Ap
The SCUBA Local Universe Galaxy Survey I: First Measurements of the Submillimetre Luminosity and Dust Mass Functions
We have used SCUBA to observe a complete sample of 104 galaxies selected at
60 microns from the IRAS BGS and we present here the 850 micron measurements.
Fitting the 60,100 and 850 micron fluxes with a single temperature dust model
gives the sample mean temperature T=36 K and beta = 1.3. We do not rule out the
possibility of dust which is colder than this, if a 20 K component was present
then our dust masses would increase by factor 1.5-3. We present the first
measurements of the luminosity and dust mass functions, which were well fitted
by Schechter functions (unlike those 60 microns). We have correlated many
global galaxy properties with the submillimetre and find that there is a
tendancy for less optically luminous galaxies to contain warmer dust and have
greater star formation efficiencies (cf. Young 1999). The average gas-to-dust
ratio for the sample is 581 +/- 43 (using both atomic and molecular hydrogen),
significantly higher than the Galactic value of 160. We believe this
discrepancy is due to a cold dust component at T < 20 K. There is a suprisingly
tight correlation between dust mass and the mass of molecular hydrogen as
estimated from CO measurements, with an intrinsic scatter of ~50%.Comment: 24 pages, 15 figures, 8 tables, accepted for publication in MNRA
Development and application of operational techniques for the inventory and monitoring of resources and uses for the Texas coastal zone
The author has identified the following significant results. The most significant ADP result was the modification of the DAM package to produce classified printouts, scaled and registered to U.S.G.S., 71/2 minute topographic maps from LARSYS-type classification files. With this modification, all the powerful scaling and registration capabilities of DAM become available for multiclass classification files. The most significant results with respect to image interpretation were the application of mapping techniques to a new, more complex area, and the refinement of an image interpretation procedure which should yield the best results
Fracture toughness of the cancellous bone of FNF femoral heads in relation to its microarchitecture
This study considers the relationship between microarchitecture and mechanical properties for cancellous bone specimens collected from a cohort of patients who had suffered fractured necks of femur. OP
is an acute skeletal condition with huge socioeconomic impact [1] and it is associated with changes in both bone quantity and quality [2], which affect greatly the strength and toughness of the tissue [3].Support was provided by the EPSRC (EP/K020196: Point-ofCare High Accuracy Fracture Risk Prediction), the UK Department of Transport under the BOSCOS (Bone Scanning for Occupant Safety) project, and approved by Gloucester and Cheltenham NHS Trust hospitals under ethical consent (BOSCOS – Mr. Curwen CI REC ref 01/179G)
Star formation in z>1 3CR host galaxies as seen by Herschel
We present Herschel (PACS and SPIRE) far-infrared (FIR) photometry of a
complete sample of z>1 3CR sources, from the Herschel GT project The Herschel
Legacy of distant radio-loud AGN (PI: Barthel). Combining these with existing
Spitzer photometric data, we perform an infrared (IR) spectral energy
distribution (SED) analysis of these landmark objects in extragalactic research
to study the star formation in the hosts of some of the brightest active
galactic nuclei (AGN) known at any epoch. Accounting for the contribution from
an AGN-powered warm dust component to the IR SED, about 40% of our objects
undergo episodes of prodigious, ULIRG-strength star formation, with rates of
hundreds of solar masses per year, coeval with the growth of the central
supermassive black hole. Median SEDs imply that the quasar and radio galaxy
hosts have similar FIR properties, in agreement with the orientation-based
unification for radio-loud AGN. The star-forming properties of the AGN hosts
are similar to those of the general population of equally massive non-AGN
galaxies at comparable redshifts, thus there is no strong evidence of universal
quenching of star formation (negative feedback) within this sample. Massive
galaxies at high redshift may be forming stars prodigiously, regardless of
whether their supermassive black holes are accreting or not.Comment: 30 pages, 13 figures, 4 tables. Accepted for publication in A&
Submillimeter Observations of the Ultraluminous BAL Quasar APM 08279+5255
With an inferred bolometric luminosity of 5\times10^{15}{\rm \lsun}, the
recently identified z=3.87, broad absorption line quasar APM 08279+5255 is
apparently the most luminous object currently known. As half of its prodigious
emission occurs in the infrared, APM 08279+5255 also represents the most
extreme example of an Ultraluminous Infrared Galaxy. Here, we present new
submillimeter observations of this phenomenal object; while indicating that a
vast quantity of dust is present, these data prove to be incompatible with
current models of emission mechanisms and reprocessing in ultraluminous
systems. The influence of gravitational lensing upon these models is considered
and we find that while the emission from the central continuum emitting region
may be significantly enhanced, lensing induced magnification cannot easily
reconcile the models with observations. We conclude that further modeling,
including the effects of any differential magnification is required to explain
the observed emission from APM 08279+5255.Comment: 12 Pages with Two figures. Accepted for publication in the
Astrophysical Journal Letter
Excitations in confined helium
We design models for helium in matrices like aerogel, Vycor or Geltech from a
manifestly microscopic point of view. For that purpose, we calculate the
dynamic structure function of 4He on Si substrates and between two Si walls as
a function of energy, momentum transfer, and the scattering angle. The
angle--averaged results are in good agreement with the neutron scattering data;
the remaining differences can be attributed to the simplified model used here
for the complex pore structure of the materials. A focus of the present work is
the detailed identification of coexisting layer modes and bulk--like
excitations, and, in the case of thick films, ripplon excitations. Involving
essentially two--dimensional motion of atoms, the layer modes are sensitive to
the scattering angle.Comment: Phys. Rev. B (2003, in press
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