2,468 research outputs found
Evidence For Ecological Character Displacement In Western American Catostomid Fishes
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137612/1/evo04742.pd
Toward a Better Benchmark: Assessing the Utility of Not-at-Fault Traffic Crash Data in Racial Profiling Research
As studies on racial profiling and biased policing have begun to proliferate, researchers are debating which benchmark is most appropriate for comparison with police traffic stop data. Existing benchmark populations, which include populations estimated from census figures, licensed drivers, arrestees, reported crime suspects, and observed drivers and traffic violators, all have significant limitations. This article offers a new, alternative benchmark for police traffic stops, a benchmark that has not been previously applied or tested in a racial profiling research setting. The analysis presented compares traffic observation data, gathered at selected, high volume intersections during an ongoing racial profiling study in Miami-Dade County, Florida, to not-at-fault driver demographic data from two-vehicle crashes at those same intersections. Findings indicate that non-responsible drivers in two-vehicle crashes appear to represent a reasonably accurate estimate of the racial composition of drivers on the roadways at selected intersections and within areas of varying racial composition. The implications of this finding for racial profiling research are discussed, and suggested areas for future inquiry are identified
Heavy rain effects on airplane performance
The objective is to determine if the aerodynamic characteristics of an airplane are altered while flying in the rain. Wind-tunnel tests conducted at the NASA Langley Research Center (LaRC) have shown losses in maximum lift, reduction in stall angle, and increases in drag when a wing is placed in a simulated rain spray. For these tests the water spray concentration used represented a very heavy rainfall. A lack of definition of the scaling laws for aerodynamic testing in a two-phase, two-component flow makes interpolation of the wind-tunnel test uncertain. Tests of a large-scale wing are to be conducted at the LaRC. The large-scale wing is mounted on top of the Aircraft Landing Dynamics Facility (ALDF) carriage. This carriage (which is 70-foot long, 30-foot wide, and 30-foot high) is propelled with the wing model attached down a 3000-foot long test track by a water jet at speeds of up to 170 knots. A simulated rain spray system has been installed along 500 feet of the test track and can simulate rain falls from 2 to 40 inches/hour. Operational checks are underway and the initial tests should be completed by the Fall of 1989
Filter parameter tuning analysis for operational orbit determination support
The use of an extended Kalman filter (EKF) for operational orbit determination support is being considered by the Goddard Space Flight Center (GSFC) Flight Dynamics Division (FDD). To support that investigation, analysis was performed to determine how an EKF can be tuned for operational support of a set of earth-orbiting spacecraft. The objectives of this analysis were to design and test a general purpose scheme for filter tuning, evaluate the solution accuracies, and develop practical methods to test the consistency of the EKF solutions in an operational environment. The filter was found to be easily tuned to produce estimates that were consistent, agreed with results from batch estimation, and compared well among the common parameters estimated for several spacecraft. The analysis indicates that there is not a sharply defined 'best' tunable parameter set, especially when considering only the position estimates over the data arc. The comparison of the EKF estimates for the user spacecraft showed that the filter is capable of high-accuracy results and can easily meet the current accuracy requirements for the spacecraft included in the investigation. The conclusion is that the EKF is a viable option for FDD operational support
ALMA Cycle 1 Observations of the HH46/47 Molecular Outflow: Structure, Entrainment and Core Impact
We present ALMA Cycle 1 observations of the HH46/47 molecular outflow using
combined 12m array and ACA observations. The improved angular resolution and
sensitivity of our multi-line maps reveal structures that help us study the
entrainment process in much more detail and allow us to obtain more precise
estimates of outflow properties than previous observations. We use 13CO(1-0)
and C18O(1-0) emission to correct for the 12CO(1-0) optical depth to accurately
estimate the outflow mass, momentum and kinetic energy. This correction
increases the estimates of the mass, momentum and kinetic energy by factors of
about 9, 5 and 2, respectively, with respect to estimates assuming optically
thin emission. The new 13CO and C18O data also allow us to trace denser and
slower outflow material than that traced by the 12CO maps, and they reveal an
outflow cavity wall at very low velocities (as low as 0.2km/s with respect to
the cores central velocity). Adding with the slower material traced only by
13CO and C18O, there is another factor of 3 increase in the mass estimate and
50% increase in the momentum estimate. The estimated outflow properties
indicate that the outflow is capable of dispersing the parent core within the
typical lifetime of the embedded phase of a low-mass protostar, and that it is
responsible for a core-to-star efficiency of 1/4 to 1/3. We find that the
outflow cavity wall is composed of multiple shells associated with a series of
jet bow-shock events. Within about 3000AU of the protostar the 13CO and C18O
emission trace a circumstellar envelope with both rotation and infall motions,
which we compare with a simple analytic model. The CS(2-1) emission reveals
tentative evidence of a slowly-moving rotating outflow, which we suggest is
entrained not only poloidally but also toroidally by a disk wind that is
launched from relatively large radii from the source.Comment: Accepted for publication in ApJ. 26 pages, 20 figure
The RMS Survey: Ammonia and water maser analysis of massive star forming regions
The Red MSX Source (RMS) survey has identified a sample of ~1200 massive
young stellar objects (MYSOs), compact and ultra compact HII regions from a
sample of ~2000 MSX and 2MASS colour selected sources. We have used the 100 m
Green Bank telescope to search for 22-24 GHz water maser and ammonia (1,1),
(2,2) and (3,3) emission towards ~600 RMS sources located within the northern
Galactic plane. We have identified 308 H2O masers which corresponds to an
overall detection rate of ~50%. Abridged: We detect ammonia emission towards
479 of these massive young stars, which corresponds to ~80%. Ammonia is an
excellent probe of high density gas allowing us to measure key parameters such
as gas temperatures, opacities, and column densities, as well as providing an
insight into the gas kinematics. The average kinetic temperature, FWHM line
width and total NH3 column density for the sample are approximately 22 K, 2
km/s and 2x10^{15} cm^{-2}, respectively. We find that the NH3 (1,1) line width
and kinetic temperature are correlated with luminosity and finding no
underlying dependence of these parameters on the evolutionary phase of the
embedded sources, we conclude that the observed trends in the derived
parameters are more likely to be due to the energy output of the central source
and/or the line width-clump mass relationship. The velocities of the peak H2O
masers and the NH3 emission are in excellent agreement with each other, which
would strongly suggest an association between the dense gas and the maser
emission. Moreover, we find the bolometric luminosity of the embedded source
and the isotropic luminosity of the H2O maser are also correlated. We conclude
from the correlations of the cloud and water maser velocities and the
bolometric and maser luminosity that there is a strong dynamical relationship
between the embedded young massive star and the H2O maser.Comment: 17 pages and 17 figures and 8 tables. Tables\,2 and 5 and full
versions of Figs. 3 and 7 are only available in electronic form at the CDS
via anonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A
Separated flow
A brief overview of flow separation phenomena is provided. Langley has many active research programs in flow separation related areas. Three cases are presented which describe specific examples of flow separation research. In each example, a description of the fundamental fluid physics and the complexity of the flow field is presented along with a method of either reducing or controlling the extent of separation. The following examples are discussed: flow over a smooth surface with an adverse pressure gradient; flow over a surface with a geometric discontinuity; and flow with shock-boundary layer interactions. These results will show that improvements are being made in the understanding of flow separation and its control
The Bolocam Galactic Plane Survey. XIV. Physical Properties of Massive Starless and Star Forming Clumps
We sort molecular clouds between from the
Bolocam Galactic Plane Survey based on observational diagnostics of star
formation activity: compact sources, mid-IR color-selected
YSOs, and masers, and UCHII regions. We also
present a combined -derived gas kinetic temperature and maser catalog for clumps from our own GBT 100m observations and
from the literature. We identify a subsample of () starless
clump candidates, the largest and most robust sample identified from a blind
survey to date. Distributions of flux density, flux concentration, solid angle,
kinetic temperature, column density, radius, and mass show strong ( dex)
progressions when sorted by star formation indicator. The median starless clump
candidate is marginally sub-virial () with of clumps
with known distance being gravitationally bound (). These samples
show a statistically significant increase in the median clump mass of M from the starless candidates to clumps associated with
protostars. This trend could be due to (i) mass growth of the clumps at
Msun Myr for an average free-fall Myr
time-scale, (ii) a systematic factor of two increase in dust opacity from
starless to protostellar phases, (iii) and/or a variation in the ratio of
starless to protostellar clump lifetime that scales as . By
comparing to the observed number of maser containing clumps we
estimate the phase-lifetime of massive ( M) starless clumps to
be ; the majority
( M) have phase-lifetimes longer than their average free-fall
time.Comment: Accepted for publication in ApJ; 33 pages; 22 figures; 7 table
Results of two multi-chord stellar occultations by dwarf planet (1) Ceres
We report the results of two multi-chord stellar occultations by the dwarf
planet (1) Ceres that were observed from Brazil on 2010 August 17, and from the
USA on 2013 October 25. Four positive detections were obtained for the 2010
occultation, and nine for the 2013 occultation. Elliptical models were adjusted
to the observed chords to obtain Ceres' size and shape. Two limb fitting
solutions were studied for each event. The first one is a nominal solution with
an indeterminate polar aspect angle. The second one was constrained by the pole
coordinates as given by Drummond et al. Assuming a Maclaurin spheroid, we
determine an equatorial diameter of 972 6 km and an apparent oblateness
of 0.08 0.03 as our best solution. These results are compared to all
available size and shape determinations for Ceres made so far, and shall be
confirmed by the NASA's Dawn space mission.Comment: 9 pages, 6 figures. Accepted for publication in MNRA
GreenSCIES – Green Smart Community Integrated Energy Systems – Integration with Data Centres
The GreenSCIES project aims to deliver low carbon, affordable energy through a novel smart energy system that connects flexible electricity demands such as heat pumps and electric vehicles to intermittent renewable energy sources such as solar power. This paper presents the results of the feasibility study of a 5th generation district mobility, power and heat network in the London Borough of Islington.
The smart network facilitates the transition to electric vehicles and vehicle-to-grid supply to make the most
of intermittent renewable energy and ensure end-users always get the best tariff. Heating and cooling are provided by heat pumps in buildings connected to a local network, which integrates thermal energy storage and waste heat recovered from local datacentres. Artificial intelligence underpins the system optimisation and demand side response. Low carbon heating and cooling is achieved by sharing heat between buildings and by shifting the timing of their demand to off-peak cheaper electricity; this requires a sophisticated control system and thermal energy storage.
The feasibility study also worked with key stakeholders to understand the views of end-users and others in
the supply chain. The role of key thermal energy providers such as Transport for London and Data Centres
is fundamental. The preliminary results indicate that the smart network can deliver up to 25% reduction on energy bills and 80% CO2 savings compared to a baseline scenario with gas boilers, chillers and grid electricity. As the electricity grid decarbonises further it is forecasted that the network will tend to net zero carbon before 2050. The GreenSCIES concept is suitable to be replicated throughout the country and has the potential to become a world-leading example
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