628 research outputs found
A multidisciplinary Amazon Shelf SEDiment Study (AmasSeds) : physical oceanography moored array component
A Multidisciplinary Amazon Shelf SEDiment Study (AmasSeds) is a cooperative research program by geological, chemical,
physical, and biological oceanographers from Brazil and the United States to study sedimentary processes occurring over the
continental shelf near the mouth of the Amazon River. The physical oceanography component of AmasSeds included a moored
array deployed on the continental shelf approximately 300km northwest of the Amazon River mouth near 3.5°N. The moored array
consisted of a cross-shelf transect of three mooring sites located on the 18-m, 65-m, and 103-m isobaths. The moored array was
deployed for approximately 4 months, from early February, 1990 to mid-June, 1990, obtaining time series measurements of current, temperature, conductivity, and wind. This report describes the physical oceanography moored array component and provides a statistical and graphical summary of the moored observations.Funding was provided by the National Science Foundation through Grant Nos.
OCE 88-12917 and OCE 91-15712
A Spectroscopic Study of Field and Runaway OB Stars
Identifying binaries among runaway O- and B-type stars offers valuable
insight into the evolution of open clusters and close binary stars. Here we
present a spectroscopic investigation of 12 known or suspected binaries among
field and runaway OB stars. We find new orbital solutions for five single-lined
spectroscopic binaries (HD 1976, HD 14633, HD 15137, HD 37737, and HD 52533),
and we classify two stars thought to be binaries (HD 30614 and HD 188001) as
single stars. In addition, we reinvestigate their runaway status using our new
radial velocity data with the UCAC2 proper motion catalogs. Seven stars in our
study appear to have been ejected from their birthplaces, and at least three of
these runaways are spectroscopic binaries and are of great interest for future
study.Comment: 21 pages, 1 figure, 7 tables; Accepted to Ap
The EoR Sensitivity of the Murchison Widefield Array
Using the final 128 antenna locations of the Murchison Widefield Array (MWA),
we calculate its sensitivity to the Epoch of Reionization (EoR) power spectrum
of red- shifted 21 cm emission for a fiducial model and provide the tools to
calculate the sensitivity for any model. Our calculation takes into account
synthesis rotation, chro- matic and asymmetrical baseline effects, and excludes
modes that will be contaminated by foreground subtraction. For the fiducial
model, the MWA will be capable of a 14{\sigma} detection of the EoR signal with
one full season of observation on two fields (900 and 700 hours).Comment: 5 pages, 4 figures, 1 table, Accepted for publication in MNRAS
Letters. Supplementary material will be available in the published version,
or by contacting the author
CODE-1 : moored array and large-scale data report
The Coastal Ocean Dynamics Experiment
(CODE) was undertaken to identify and study
the important dynamical processes which
govern the wind-driven motion of coastal
water over the continental shelf. The
initial effort in this multi-year, multi-institutional
research program was to obtain
high-quality data sets of all the
relevant physical variables needed to construct
accurate kinematic and dynamic descriptions
of the response of shelf water
to strong wind forcing in the 2 to 10 day
band. A series of two small-scale, densely-instrumented
field experiments of approximately
four months duration (called CODE-1
and CODE-2) were designed to explore and
to determine the kinematics and momentum
and heat balances of the local wind-driven
flow over a region of the northern California shelf which is characterized by both
relatively simple bottom topography and
large wind stress events in both winter
and summer. A more lightly instrumented,
long-term, large-scale component was designed
to help separate the local wind-driven
response in the region of the small-scale
experiments from motions generated either offshore by the California Current
system or in some distant region along the
coast, and also to help determine the seasonal
cycles of the atmospheric forcing,
water structure, and coastal currents over
the northern California shelf.
The first small-scale experiment
(CODE-1) was conducted between April and
August, 1981 as a pilot study in which
primary emphasis was placed on characterizing
the wind-driven "signal" and the
"noise" from which this signal must be
extracted. In particular, CODE-1 was
designed to identify the key features of
the circulation and its variability over
the northern California shelf and to
determine the important time and length
scales of the wind-driven response. This
report presents a basic description of the
moored array data and some other Eulerian
data collected during CODE-1. A brief
description of the CODE-1 field program is
presented first, followed by a description
of the common data analysis procedures used
to produce the various data sets presented
here. Then basic descriptions of the following
data sets are presented: (a) the
coastal and moored meteorological measurements,
(b) the moored current measurements,
(c) the moored temperature and conductivity
observations, (d) the bottom pressure measurements,
and (e) the wind and adjusted
coastal sea level observations obtained as
part of the CODE-1 large-scale component.Prepared for the National Science
Foundation under Grant OCE 80-14941
Computationally Efficient Field-Theoretic Simulations for Block Copolymer Melts
Field-theoretic simulations (FTS) provide fluctuation corrections to self-consistent field theory (SCFT) by simulating its field-theoretic Hamiltonian rather than applying the saddle-point approximation. Although FTS work well for ultrahigh molecular weights, they have struggled with experimentally relevant values. Here, we consider FTS for two-component (i.e., AB-type) melts, where the composition field fluctuates but the saddle-point approximation is still applied to the pressure field that enforces incompressibility. This results in real-valued fields, thereby allowing for conventional simulation methods. We discover that Langevin simulations are one to two orders of magnitude faster than previous Monte Carlo simulations, which permits us to accurately calculate the order-disorder transition of symmetric diblock copolymer melts at realistic molecular weights. This remarkable speedup will, likewise, facilitate FTS for more complicated block copolymer systems, which might otherwise be unfeasible with traditional particle-based simulations.National Science and Engineering Research Council (NSERC) of Canada || Compute Canad
A new layout optimization technique for interferometric arrays, applied to the MWA
Antenna layout is an important design consideration for radio interferometers
because it determines the quality of the snapshot point spread function (PSF,
or array beam). This is particularly true for experiments targeting the 21 cm
Epoch of Reionization signal as the quality of the foreground subtraction
depends directly on the spatial dynamic range and thus the smoothness of the
baseline distribution. Nearly all sites have constraints on where antennas can
be placed---even at the remote Australian location of the MWA (Murchison
Widefield Array) there are rock outcrops, flood zones, heritages areas,
emergency runways and trees. These exclusion areas can introduce spatial
structure into the baseline distribution that enhance the PSF sidelobes and
reduce the angular dynamic range. In this paper we present a new method of
constrained antenna placement that reduces the spatial structure in the
baseline distribution. This method not only outperforms random placement
algorithms that avoid exclusion zones, but surprisingly outperforms random
placement algorithms without constraints to provide what we believe are the
smoothest constrained baseline distributions developed to date. We use our new
algorithm to determine antenna placements for the originally planned MWA, and
present the antenna locations, baseline distribution, and snapshot PSF for this
array choice.Comment: 12 pages, 6 figures, 1 table. Accepted for publication in MNRA
Gridded and direct Epoch of Reionisation bispectrum estimates using the Murchison Widefield Array
We apply two methods to estimate the 21~cm bispectrum from data taken within
the Epoch of Reionisation (EoR) project of the Murchison Widefield Array (MWA).
Using data acquired with the Phase II compact array allows a direct bispectrum
estimate to be undertaken on the multiple redundantly-spaced triangles of
antenna tiles, as well as an estimate based on data gridded to the -plane.
The direct and gridded bispectrum estimators are applied to 21 hours of
high-band (167--197~MHz; =6.2--7.5) data from the 2016 and 2017 observing
seasons. Analytic predictions for the bispectrum bias and variance for point
source foregrounds are derived. We compare the output of these approaches, the
foreground contribution to the signal, and future prospects for measuring the
bispectra with redundant and non-redundant arrays. We find that some triangle
configurations yield bispectrum estimates that are consistent with the expected
noise level after 10 hours, while equilateral configurations are strongly
foreground-dominated. Careful choice of triangle configurations may be made to
reduce foreground bias that hinders power spectrum estimators, and the 21~cm
bispectrum may be accessible in less time than the 21~cm power spectrum for
some wave modes, with detections in hundreds of hours.Comment: 19 pages, 10 figures, accepted for publication in PAS
Neuroaesthetics: The Cognitive Neuroscience of Aesthetic Experience
This research was supported by Grant AAEE124/09 from the Govern de les Illes Balears, Spain
Between the Natural and the Artificial: The Sublime Sexual Sensation of Car Crashes in J.G. Ballard’s Crash
At a time when technology progressively pushes back nature, the sexual act runs the risk of being denaturalised. The notion of the sublime, which I argue is how humans react to the machine as a surrogate for nature and as a sexual stimulus in Crash (1973), is therefore of central interest in this article. Ballard himself has described Crash as ‘the first pornographic novel based on technology’ (1973, 6). This engagement with a technologised sexuality is explored as a subjective narrative stance, which grants authenticity to the fictive alter ego, who can probe alternatives to an extra-textual reality. This narrative mode is notably potent in relation to the narrator’s estimation of the merge between sexuality and technology in the form of car crashes uniting Eros and Thanatos. I therefore suggest that Crash can be read as an attempt to localise the natural and human in a world dictated by artificiality and technology
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