957 research outputs found
Evaluation of the ALMA Prototype Antennas
The ALMA North American and European prototype antennas have been evaluated
by a variety of measurement systems to quantify the major performance
specifications. Nearfield holography was used to set the reflector surfaces to
17 microns RMS. Pointing and fast switching performance was determined with an
optical telescope and by millimeter wavelength radiometry, yielding 2 arcsec
absolute and 0.6 arcsec offset pointing accuracies. Path length stability was
measured to be less than or approximately equal to 20 microns over 10 minute
time periods using optical measurement devices. Dynamical performance was
studied with a set of accelerometers, providing data on wind induced tracking
errors and structural deformation. Considering all measurements made during
this evaluation, both prototype antennas meet the major ALMA antenna
performance specifications.Comment: 83 pages, 36 figures, AASTex format, to appear in PASP September 2006
issu
Airborne laser scanning of natural forests in New Zealand reveals the influences of wind on forest carbon
Abstract
Background
Forests are a key component of the global carbon cycle, and research is needed
into the effects of human-driven and natural processes on their carbon pools.
Airborne laser scanning (ALS) produces detailed 3D maps of forest canopy structure
from which aboveground carbon density can be estimated. Working with a ALS dataset
collected over the 8049-km2 Wellington Region of New
Zealand we create maps of indigenous forest carbon and evaluate the influence of
wind by examining how carbon storage varies with aspect. Storms flowing from the
west are a common cause of disturbance in this region, and we hypothesised that
west-facing forests exposed to these winds would be shorter than those in
sheltered east-facing sites.
Methods
The aboveground carbon density of 31 forest inventory plots located within the
ALS survey region were used to develop estimation models relating carbon density
to ALS information. Power-law models using rasters of top-of-the-canopy height
were compared with models using tree-level information extracted from the ALS
dataset. A forest carbon map with spatial resolution of 25 m was generated from
ALS maps of forest height and the estimation models. The map was used to evaluate
the influences of wind on forests.
Results
Power-law models were slightly less accurate than tree-centric models (RMSE
35% vs 32%) but were selected for map generation for computational efficiency. The
carbon map comprised 4.5 million natural forest pixels within which canopy height
had been measured by ALS, providing an unprecedented dataset with which to examine
drivers of carbon density. Forests facing in the direction of westerly storms
stored less carbon, as hypothesised. They had much greater above-ground carbon
density for a given height than any of 14 tropical forests previously analysed by
the same approach, and had exceptionally high basal areas for their height. We
speculate that strong winds have kept forests short without impeding basal area
growth.
Conclusion
Simple estimation models based on top-of-the canopy height are almost as
accurate as state-of-the-art tree-centric approaches, which require more computing
power. High-resolution carbon maps produced by ALS provide powerful datasets for
evaluating the environmental drivers of forest structure, such as wind.
</jats:sec
A brief description of geological and geophysical exploration of the Marysville geothermal area
Extensive geological and geophysical surveys were carried out at the Marysville geothermal area during 1973 and 1974. The area has high heat flow (up to microcalories per square centimeter-second, a negative gravity anomaly, high electrical resistivity, low seismic ground noise, and nearby microseismic activity. Significant magnetic and infrared anomalies are not associated with the geothermal area. The geothermal anomaly occupies the axial portion of a dome in Precambrian sedimentary rocks intruded by Cretaceous and Cenozoic granitic rocks. The results from a 2.4-km-deep test well indicate that the cause of the geothermal anomaly is hydrothermal convection in a Cenozoic intrusive. A maximum temperature of 95 C was measured at a depth of 500 m in the test well
Learning to communicate about shared procedural abstractions
Many real-world tasks require agents to coordinate their behavior to achieve
shared goals. Successful collaboration requires not only adopting the same
communicative conventions, but also grounding these conventions in the same
task-appropriate conceptual abstractions. We investigate how humans use natural
language to collaboratively solve physical assembly problems more effectively
over time. Human participants were paired up in an online environment to
reconstruct scenes containing two block towers. One participant could see the
target towers, and sent assembly instructions for the other participant to
reconstruct. Participants provided increasingly concise instructions across
repeated attempts on each pair of towers, using higher-level referring
expressions that captured each scene's hierarchical structure. To explain these
findings, we extend recent probabilistic models of ad-hoc convention formation
with an explicit perceptual learning mechanism. These results shed light on the
inductive biases that enable intelligent agents to coordinate upon shared
procedural abstractions
Recommended from our members
Hanford MOX fuel lead assemblies data report for the surplus plutonium disposition environmental impact statement
The purpose of this document is to support the US Department of Energy (DOE) Fissile Materials Disposition Program`s preparation of the draft surplus plutonium disposition environmental impact statement. This is one of several responses to data call requests for background information on activities associated with the operation of the lead assembly (LA) mixed-oxide (MOX) fuel fabrication facility. DOE-MD requested that the DOE Site Operations Offices nominate DOE sites that meet established minimum requirements that could produce MOX LAs. Six initial site combinations were proposed: (1) Argonne National Laboratory-West (ANL-W) with support from Idaho National Engineering and Environmental Laboratory (INEEL), (2) Hanford, (3) Los Alamos National Laboratory (LANL) with support from Pantex, (4) Lawrence Livermore National Laboratory (LLNL), (5) Oak Ridge Reservation (ORR), and (6) Savannah River Site (SRS). After further analysis by the sites and DOE-MD, five site combinations were established as possible candidates for producing MOX LAs: (1) ANL-W with support from INEEL, (2) Hanford, (3) LANL, (4) LLNL, and (5) SRS. Hanford has proposed an LA MOX fuel fabrication approach that would be done entirely inside an S and S Category 1 area. An alternate approach would allow fabrication of fuel pellets and assembly of fuel rods in an S and S Category 1 facility. In all, a total of three LA MOX fuel fabrication options were identified by Hanford that could accommodate the program. In every case, only minor modification would be required to ready any of the facilities to accept the equipment necessary to accomplish the LA program
Recommended from our members
SRS MOX fuel lead assemblies data report for the surplus plutonium disposition environmental impact statement
The purpose of this document is to support the US Department of Energy (DOE) Fissile Materials Disposition Program`s preparation of the draft surplus plutonium disposition environmental impact statement. This is one of several responses to data call requests for background information on activities associated with the operation of the lead assembly (LA) mixed-oxide (MOX) fuel fabrication facility. DOE-MD requested that the DOE Site Operations Offices nominate DOE sites that meet established minimum requirements that could produce MOX LAs. Six initial site combinations were proposed: (1) Argonne National Laboratory-West (ANL-W) with support from Idaho National Engineering and Environmental Laboratory (INEEL), (2) Hanford, (3) Los Alamos National Laboratory (LANL) with support from Pantex, (4) Lawrence Livermore National Laboratory (LLNL), (5) Oak Ridge Reservation (ORR), and (6) Savannah River Site(SRS). After further analysis by the sites and DOE-MD, five site combinations were established as possible candidates for producing MOX LAs: (1) ANL-W with support from INEEL, (2) Hanford, (3) LANL, (4) LLNL, and (5) SRS. SRS has proposed an LA MOX fuel fabrication approach that would be done entirely inside an S and S Category 1 area. An alternate approach would allow fabrication of fuel pellets and assembly of fuel rods in an S and S Category 2 or 3 facility with storage of bulk PuO{sub 2} and assembly, storage, and shipping of fuel bundles in an S and S Category 1 facility. The total Category 1 approach, which is the recommended option, would be done in the 221-H Canyon Building. A facility that was never in service will be removed from one area, and a hardened wall will be constructed in another area to accommodate execution of the LA fuel fabrication. The non-Category 1 approach would require removal of process equipment in the FB-Line metal production and packaging glove boxes, which requires work in a contamination area. The Immobilization Hot Demonstration Program equipment in the Savannah River Technology Center would need to be removed to accommodate pellet fabrication. This work would also be in a contaminated area
Historical Criminology and the Explanatory Power of the Past
To what extent can the past ‘explain’ the present? This deceptively simple question lies at the heart of historical criminology (research which incorporates historical primary sources while addressing present-day debates and practices in the criminal justice field). This article seeks first to categorise the ways in which criminologists have used historical data thus far, arguing that it is most commonly deployed to ‘problematize’ the contemporary rather than to ‘explain’ it. The article then interrogates the reticence of criminologists to attribute explicative power in relation to the present to historical data. Finally, it proposes the adoption of long time-frame historical research methods, outlining three advantages which would accrue from this: the identification and analysis of historical continuities; a more nuanced, shared understanding of micro/macro change over time in relation to criminal justice; and a method for identifying and analysing instances of historical recurrence, particularly in perceptions and discourses around crime and justice
Quasars in the MAMBO blank field survey
Our MAMBO 1.2 mm blank field imaging survey of ~0.75 sqd has uncovered four
unusually bright sources, with flux densities between 10 and 90 mJy, all
located in the Abell 2125 field. The three brightest are flat spectrum radio
sources with bright optical and X-ray counterparts. Their mm and radio flux
densities are variable on timescales of months. Their X-ray luminosities
classify them as quasars. The faintest of the four mm bright sources appears to
be a bright, radio-quiet starburst at z~3, similar to the sources seen at lower
flux densities in the MAMBO and SCUBA surveys. It may also host a mildly
obscured AGN of quasar-like X-ray luminosity. The three non-thermal mm sources
imply an areal density of flat spectrum radio sources higher by at least 7
compared with that expected from an extrapolation of the lower frequency radio
number counts.Comment: 8 pages, 7 figures. Accepted for publication by A&
- …