1,798 research outputs found
Protoplanetary Disks in the Orion Nebula Cluster: Gas Disk Morphologies and Kinematics as seen with ALMA
We present Atacama Large Millimeter Array CO(32) and HCO(43)
observations covering the central region of
the Orion Nebula Cluster (ONC). The unprecedented level of sensitivity
(0.1 mJy beam) and angular resolution ( AU) of these line observations enable us to search for gas-disk
detections towards the known positions of submillimeter-detected dust disks in
this region. We detect 23 disks in gas: 17 in CO(32), 17 in HCO(43),
and 11 in both lines. Depending on where the sources are located in the ONC, we
see the line detections in emission, in absorption against the warm background,
or in both emission and absorption. We spectrally resolve the gas with km
s channels, and find that the kinematics of most sources are consistent
with Keplerian rotation. We measure the distribution of gas-disk sizes and find
typical radii of 50-200 AU. As such, gas disks in the ONC are compact in
comparison with the gas disks seen in low-density star-forming regions. Gas
sizes are universally larger than the dust sizes. However, the gas and dust
sizes are not strongly correlated. We find a positive correlation between gas
size and distance from the massive star Ori C, indicating that disks
in the ONC are influenced by photoionization. Finally, we use the observed
kinematics of the detected gas lines to model Keplerian rotation and infer the
masses of the central pre-main-sequence stars. Our dynamically-derived stellar
masses are not consistent with the spectroscopically-derived masses, and we
discuss possible reasons for this discrepancy.Comment: 42 pages, 31 figure
Dynamic stability characteristics of the combination space shuttle orbiter and ferry vehicle
Subsonic forced-oscillation tests of a 0.015 scale model of the space shuttle orbiter/747 ferry vehicle were conducted in the Langley high speed 7- by 10-foot tunnel at Mach numbers of 0.2, 0.4, and 0.5 for angles of attack up to 12 deg. Tests were made of the basic 747 airplane, of the modified 747 (tip fins and struts added), of the ferry configuration, (747 plus orbiter at an incidence angle of 3 deg), and of the approach and landing test configuration (747 plus orbiter at an incidence angle of 6 deg)
Supersonic dynamic stability characteristics of a space shuttle orbiter
Supersonic forced-oscillation tests of a 0.0165-scale model of a modified 089B Rockwell International shuttle orbiter were conducted in a wind tunnel for several configurations over a Mach range from 1.6 to 4.63. The tests covered angles of attack up to 30 deg. The period and damping of the basic unaugmented vehicle were calculated along the entry trajectory using the measured damping results. Some parameter analysis was made with the measured dynamic derivatives. Photographs of the test configurations and test equipment are shown
Further buffeting tests in a cryogenic wind tunnel
Further measurements of buffeting, using wing-root strain gauges, were made in the NASA Langley 0.3 m Cryogenic Wind Tunnel to refine techniques which will be used in larger cryogenic facilities such as the United States National Transonic Facility (NTF) and European Transonic Wind Tunnel (ETW). The questions addressed included the relative importance of variations in frequency parameter and Reynolds number, the choice of model material (considering both stiffness and damping) and the effects of static aeroelastic distortion. The main series of tests was made on half models of slender 65 deg delta wings with a sharp leading edge. The three delta wings had the same planform but widely different bending stiffness and frequencies (obtained by varying both the material and the thickness of the wings). It was known that the flow on this configuration would be insensitive to variations in Reynold number. Additional tests were made on one unswept half-wing of aspect ratio 1.5 with an NPL 9510 aerofoil section, known to be sensitive to variations in Reynolds number at transonic speeds. For brevity the test Mach numbers were restricted to M = 0.21 and 0.35 for the delta wings and to M = 0.30 for the unswept wing
TurbuStat: Turbulence Statistics in Python
We present TurbuStat (v1.0): a Python package for computing turbulence
statistics in spectral-line data cubes. TurbuStat includes implementations of
fourteen methods for recovering turbulent properties from observational data.
Additional features of the software include: distance metrics for comparing two
data sets; a segmented linear model for fitting lines with a break-point; a
two-dimensional elliptical power-law model; multi-core fast-fourier-transform
support; a suite for producing simulated observations of fractional Brownian
Motion fields, including two-dimensional images and optically-thin HI data
cubes; and functions for creating realistic world coordinate system information
for synthetic observations. This paper summarizes the TurbuStat package and
provides representative examples using several different methods. TurbuStat is
an open-source package and we welcome community feedback and contributions.Comment: Accepted in AJ. 21 pages, 8 figure
Subsonic and transonic dynamic stability characteristics of a space shuttle orbiter
Subsonic and transonic forced oscillation tests of a 0.0165-scale model of a modified 089B space shuttle orbiter were made in the Langley 8-foot transonic pressure tunnel. The period and damping of the basic unaugmented vehicle were calculated along the entry trajectory utilizing these measured dynamic data. Some parameter analyses were made with the measured dynamic derivatives
Supersonic dynamic stability derivatives of a modified 089B shuttle orbiter
An experimental test program was conducted to measure the dynamic stability derivatives of a modified 089B shuttle orbiter. Supersonic forced oscillation tests were conducted in the Langley Unitary Plan Wind Tunnel over a range of Mach numbers from 1.6 to 4.63 for angles of attack up to 30 deg. The data were measured at the model resonant frequency with pitch and yaw amplitudes of 1 deg and a roll amplitude of 2.5 deg
Subsonic and transonic dynamic stability characteristics of the space shuttle launch vehicle
An investigation has been conducted to determine the subsonic and transonic dynamic stability characteristics of a 0.015 scale model of the space shuttle launch vehicle. These tests were conducted in the Langley 8-foot transonic pressure tunnel over a Mach number range from 0.3 to 1.2. Forced oscillation equipment was used to determine the damping characteristics of several configurations about all three axes. The test results show that the model exhibited positive damping in pitch except at the highest Mach number (1.2) where there was a region of negative damping at 2 deg angle of attack. The yawing oscillation tests show that the model exhibited nonlinearities and negative damping at Mach numbers of 0.3 and 0.6. The model exhibited positive roll damping throughout the test angle of attack and Mach range
Supersonic dynamic-stability derivatives of the space shuttle launch vehicle
An investigation was made to determine the dynamic stability characteristics of a 0.015-scale model of the space shuttle launch vehicle at supersonic speeds. These tests were made at angles of attack from -10 deg to 10 deg at Mach numbers of 2.00, 2.86, 3.96, and 4.63. The complete launch vehicle, consisting of the orbiter, external tank, and solid rocket boosters, has positive damping in pitch, roll, and yaw over the angle-of-attack and Mach number range. The orbiter external tank configuration has a region of negative angles pitch damping for small negative of attack at a Mach number of 2.00. At all other test conditions, the orbiter external tank configuration has positive damping about all three axes
Assessing the Impact of Astrochemistry on Molecular Cloud Turbulence Statistics
We analyze hydrodynamic simulations of turbulent, star-forming molecular
clouds that are post-processed with the photo-dissociation region
astrochemistry code 3D-PDR. We investigate the sensitivity of 15 commonly
applied turbulence statistics to post-processing assumptions, namely variations
in gas temperature, abundance and external radiation field. We produce
synthetic CO(1-0) and CI(P-P) observations and
examine how the variations influence the resulting emission distributions. To
characterize differences between the datasets, we perform statistical
measurements, identify diagnostics sensitive to our chemistry parameters, and
quantify the statistic responses by using a variety of distance metrics. We
find that multiple turbulent statistics are sensitive not only to the chemical
complexity but also to the strength of the background radiation field. The
statistics with meaningful responses include principal component analysis,
spatial power spectrum and bicoherence. A few of the statistics, such as the
velocity coordinate spectrum, are primarily sensitive to the type of tracer
being utilized, while others, like the delta-variance, strongly respond to the
background radiation field. Collectively, these findings indicate that more
realistic chemistry impacts the responses of turbulent statistics and is
necessary for accurate statistical comparisons between models and observed
molecular clouds.Comment: 27 pages, 21 figures, accepted to Ap
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