2,262 research outputs found
Ultraviolet television data from the Orbiting Astronomical Observatory. 1: Instrumentation and analysis techniques for the celescope experiment
The celescope instrumentation and data analysis system is described, the major problems encountered during orbital operation are summerized, and a few major problems that were anticipated but did not materialize are listed
A Fresh Catch of Massive Binaries in the Cygnus OB2 Association
Massive binary stars may constitute a substantial fraction of progenitors to
supernovae and gamma-ray bursts, and the distribution of their orbital
characteristics holds clues to the formation process of massive stars. As a
contribution to securing statistics on OB-type binaries, we report the
discovery and orbital parameters for five new systems as part of the Cygnus OB2
Radial Velocity Survey. Four of the new systems (MT070, MT174, MT267, and MT734
(a.k.a. VI Cygni #11) are single-lined spectroscopic binaries while one (MT103)
is a double-lined system (B1V+B2V). MT070 is noteworthy as the longest period
system yet measured in Cyg OB2, with P=6.2 yr. The other four systems have
periods ranging between 4 and 73 days. MT174 is noteworthy for having a
probable mass ratio q<0.1, making it a candidate progenitor to a low-mass X-ray
binary. These measurements bring the total number of massive binaries in Cyg
OB2 to 25, the most currently known in any single cluster or association.Comment: Accepted for publication in the Astrophysical Journa
Assessing variability of wind speed: comparison and validation of 27 methodologies
Because wind resources vary from year to year, the
intermonthly and interannual variability (IAV) of wind speed is a key
component of the overall uncertainty in the wind resource assessment
process, thereby creating challenges for wind farm operators and owners. We
present a critical assessment of several common approaches for calculating
variability by applying each of the methods to the same 37-year monthly
wind-speed and energy-production time series to highlight the differences
between these methods. We then assess the accuracy of the variability
calculations by correlating the wind-speed variability estimates to the
variabilities of actual wind farm energy production. We recommend the robust
coefficient of variation (RCoV) for systematically estimating variability,
and we underscore its advantages as well as the importance of using a
statistically robust and resistant method. Using normalized spread metrics,
including RCoV, high variability of monthly mean wind speeds at a location
effectively denotes strong fluctuations of monthly total energy generation,
and vice versa. Meanwhile, the wind-speed IAVs computed with annual-mean
data fail to adequately represent energy-production IAVs of wind farms.
Finally, we find that estimates of energy-generation variability require 10±3 years of monthly mean wind-speed records to achieve a 90 %
statistical confidence. This paper also provides guidance on the spatial
distribution of wind-speed RCoV.</p
An interactive atlas for marine biodiversity conservation in the Coral Triangle
An online atlas of the Coral Triangle region of the Indo-Pacific
biogeographic realm was developed. This online atlas consists of the three
interlinked parts: (1) Biodiversity Features; (2) Areas of Importance for
Biodiversity Conservation; (3) recommended priorities for Marine Protected
Area (MPA) Network Expansion (http://www.marine.auckland.ac.nz/CTMAPS).
The first map, Biodiversity Features, provides comprehensive data on the
region's marine protected areas and biodiversity features, threats, and
environmental characteristics. The second provides spatial information on
areas of high biodiversity conservation values, while the third map shows
priority areas for expanding the current Coral Triangle MPA network. This
atlas provides the most comprehensive biodiversity datasets that have been
assembled for the region. The datasets were retrieved and generated
systematically from various open-access sources. To engage a wider audience
and to raise participation in biodiversity conservation, the maps were
designed as an interactive and online atlas. This atlas presents
representative information to promote a better understanding of the key
marine and coastal biodiversity characteristics of the region and enables the
application of marine biodiversity informatics to support marine
ecosystem-based management in the Coral Triangle region.</p
Monte Carlo simulation of the solid to super liquid phase transition of Langmuir monolayers using cross‐section potentials
National Geodetic Satellite Program, Part II: Smithsonian Astrophysical Observatory
A sequence of advances in the determination of geodetic parameters presented by the Smithsonian Astrophysical Observatory are described. A Baker-Nunn photographic system was used in addition to a ruby-laser ranging system to obtain data for refinement of geodetic parameters. A summary of the data employed to: (1) derive coordinates for the locations of various tracking stations; and (2) determine the gravitational potential of the earth, is presented
Wind turbine power production and annual energy production depend on atmospheric stability and turbulence
Using detailed upwind and nacelle-based measurements from a
General Electric (GE) 1.5sle model with a 77 m rotor diameter, we calculate
power curves and annual energy production (AEP) and explore their
sensitivity to different atmospheric parameters to provide guidelines for
the use of stability and turbulence filters in segregating power curves. The
wind measurements upwind of the turbine include anemometers mounted on a
135 m meteorological tower as well as profiles from a lidar. We calculate
power curves for different regimes based on turbulence parameters such as
turbulence intensity (TI) as well as atmospheric stability parameters such
as the bulk Richardson number (RB). We also calculate AEP with and without these atmospheric filters and highlight differences between the
results of these calculations. The power curves for different TI regimes
reveal that increased TI undermines power production at wind speeds near
rated, but TI increases power production at lower wind speeds at this site,
the US Department of Energy (DOE) National Wind Technology Center (NWTC).
Similarly, power curves for different RB regimes reveal that periods of stable conditions produce more power at wind speeds near rated and periods of unstable conditions produce more power at lower wind speeds. AEP results suggest that calculations without filtering for these atmospheric regimes may overestimate the AEP. Because of statistically significant differences between power curves and AEP calculated with these turbulence and stability filters for this turbine at this site, we suggest implementing an additional step in analyzing power performance data to incorporate effects of
atmospheric stability and turbulence across the rotor disk
Determining the Magnetic Field Orientation of Coronal Mass Ejections from Faraday Rotation
We describe a method to measure the magnetic field orientation of coronal
mass ejections (CMEs) using Faraday rotation (FR). Two basic FR profiles,
Gaussian-shaped with a single polarity or "N"-like with polarity reversals, are
produced by a radio source occulted by a moving flux rope depending on its
orientation. These curves are consistent with the Helios observations,
providing evidence for the flux-rope geometry of CMEs. Many background radio
sources can map CMEs in FR onto the sky. We demonstrate with a simple flux rope
that the magnetic field orientation and helicity of the flux rope can be
determined 2-3 days before it reaches Earth, which is of crucial importance for
space weather forecasting. An FR calculation based on global
magnetohydrodynamic (MHD) simulations of CMEs in a background heliosphere shows
that FR mapping can also resolve a CME geometry curved back to the Sun. We
discuss implementation of the method using data from the Mileura Widefield
Array (MWA).Comment: 22 pages with 9 figures, accepted for publication in Astrophys.
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