2,930 research outputs found
Detailed pressure distribution measurements obtained on several configurations of an aspect-ratio-7 variable twist wing
Detailed pressure distribution measurements were made for 11 twist configurations of a unique, multisegmented wing model having an aspect ratio of 7 and a taper ratio of 1. These configurations encompassed span loads ranging from that of an untwisted wing to simple flapped wings both with and without upper-surface spoilers attached. For each of the wing twist configurations, electronic scanning pressure transducers were used to obtain 580 surface pressure measurements over the wing in about 0.1 sec. Integrated pressure distribution measurements compared favorably with force-balance measurements of lift on the model when the model centerbody lift was included. Complete plots and tabulations of the pressure distribution data for each wing twist configuration are provided
Wake vortex technology
A brief overview of the highlights of NASA's wake vortex minimization program is presented. The significant results of this program are summarized as follows: (1) it is technically feasible to reduce significantly the rolling upset created on a trailing aircraft; (2) the basic principles or methods by which reduction in the vortex strength can be achieved have been identified; and (3) an analytical capability for investigating aircraft vortex wakes has been developed
Low-speed wind-tunnel tests of an advanced eight-bladed propeller
As part of a research program on advanced turboprop aircraft aerodynamics, a low-speed wind-tunnel investigation was conducted to document the basic performance and force and moment characteristics of an advanced eight-bladed propeller. The results show that in addition to the normal force and pitching moment produced by the propeller/nacelle combination at angle of attack, a significant side force and yawing moment are also produced. Furthermore, it is shown that for test conditions wherein compressibility effects can be ignored, accurate simulation of propeller performance and flow fields can be achieved by matching the nondimensional power loading of the model propeller to that of the full-scale propeller
Benchmarking of 3D space charge codes using direct phase space measurements from photoemission high voltage DC gun
We present a comparison between space charge calculations and direct
measurements of the transverse phase space for space charge dominated electron
bunches after a high voltage photoemission DC gun followed by an emittance
compensation solenoid magnet. The measurements were performed using a
double-slit setup for a set of parameters such as charge per bunch and the
solenoid current. The data is compared with detailed simulations using 3D space
charge codes GPT and Parmela3D with initial particle distributions created from
the measured transverse and temporal laser profiles. Beam brightness as a
function of beam fraction is calculated for the measured phase space maps and
found to approach the theoretical maximum set by the thermal energy and
accelerating field at the photocathode.Comment: 11 pages, 23 figures. submitted to Phys Rev ST-A
The Class 0 Protostar BHR71: Herschel Observations and Dust Continuum Models
We use Herschel spectrophotometry of BHR71, an embedded Class 0 protostar, to
provide new constraints on its physical properties. We detect 645 (non-unique)
spectral lines amongst all spatial pixels. At least 61 different spectral lines
originate from the central region. A CO rotational diagram analysis shows four
excitation temperature components, 43 K, 197 K, 397 K, and 1057 K. Low-J CO
lines trace the outflow while the high-J CO lines are centered on the infrared
source. The low-excitation emission lines of H2O trace the large-scale outflow,
while the high-excitation emission lines trace a small-scale distribution
around the equatorial plane. We model the envelope structure using the dust
radiative transfer code, Hyperion, incorporating rotational collapse, an outer
static envelope, outflow cavity, and disk. The evolution of a rotating
collapsing envelope can be constrained by the far-infrared/millimeter SED along
with the azimuthally-averaged radial intensity profile, and the structure of
the outflow cavity plays a critical role at shorter wavelengths. Emission at
20-40 um requires a cavity with a constant-density inner region and a power-law
density outer region. The best fit model has an envelope mass of 19 solar mass
inside a radius of 0.315 pc and a central luminosity of 18.8 solar luminosity.
The time since collapse began is 24630-44000 yr, most likely around 36000 yr.
The corresponding mass infall rate in the envelope (1.2x10 solar mass
per year) is comparable to the stellar mass accretion rate, while the mass loss
rate estimated from the CO outflow is 20% of the stellar mass accretion rate.
We find no evidence for episodic accretion.Comment: Accepted for publication in ApJ. 33 pages; 34 figures; 4 table
Revealing The Millimeter Environment of the New FU Orionis Candidate HBC722 with the Submillimeter Array
We present 230 GHz Submillimeter Array continuum and molecular line
observations of the newly discovered FUor candidate HBC722. We report the
detection of seven 1.3 mm continuum sources in the vicinity of HBC722, none of
which correspond to HBC722 itself. We compile infrared and submillimeter
continuum photometry of each source from previous studies and conclude that
three are Class 0 embedded protostars, one is a Class I embedded protostar, one
is a Class I/II transition object, and two are either starless cores or very
young, very low luminosity protostars or first hydrostatic cores. We detect a
northwest-southeast outflow, consistent with the previous detection of such an
outflow in low-resolution, single-dish observations, and note that its axis may
be precessing. We show that this outflow is centered on and driven by one of
the nearby Class 0 sources rather than HBC722, and find no conclusive evidence
that HBC722 itself is driving an outflow. The non-detection of HBC722 in the
1.3 mm continuum observations suggests an upper limit of 0.02 solar masses for
the mass of the circumstellar disk. This limit is consistent with typical T
Tauri disks and with a disk that provides sufficient mass to power the burst.Comment: 12 pages, 7 figures, accepted by Ap
Mass transport from the envelope to the disk of V346 Nor: a case study for the luminosity problem in an FUor-type young eruptive star
A long-standing open issue of the paradigm of low-mass star formation is the
luminosity problem: most protostars are less luminous than theoretically
predicted. One possible solution is that the accretion process is episodic. FU
Ori-type stars (FUors) are thought to be the visible examples for objects in
the high accretion state. FUors are often surrounded by massive envelopes,
which replenish the disk material and enable the disk to produce accretion
outbursts. However, we have insufficient information on the envelope dynamics
in FUors, about where and how mass transfer from the envelope to the disk
happens. Here we present ALMA observations of the FUor-type star V346 Nor at
1.3 mm continuum and in different CO rotational lines. We mapped the density
and velocity structure of its envelope and analyze the results using channel
maps, position-velocity diagrams, and spectro-astrometric methods. We found
that V346 Nor is surrounded by gaseous material on 10000 au scale in which a
prominent outflow cavity is carved. Within the central 700 au, the
circumstellar matter forms a flattened pseudo-disk where material is infalling
with conserved angular momentum. Within 350 au, the velocity profile is
more consistent with a disk in Keplerian rotation around a central star of 0.1
. We determined an infall rate from the envelope onto the disk of
610yr, a factor of few higher than the
quiescent accretion rate from the disk onto the star, hinting for a mismatch
between the infall and accretion rates as the cause of the eruption.Comment: 16 pages, 8 figures, published in Ap
The second US Naval Observatory CCD Astrograph Catalog (UCAC2)
The second USNO CCD Astrograph Catalog, UCAC2 was released in July 2003.
Positions and proper motions for 48,330,571 sources (mostly stars) are
available on 3 CDs, supplemented with 2MASS photometry for 99.5% of the
sources. The catalog covers the sky area from -90 to +40 degrees declination,
going up to +52 in some areas; this completely supersedes the UCAC1 released in
2001. Current epoch positions are obtained from observations with the USNO
8-inch Twin Astrograph equipped with a 4k CCD camera. The precision of the
positions are 15 to 70 mas, depending on magnitude, with estimated systematic
errors of 10 mas or below. Proper motions are derived by utilizing over 140
ground-and space-based catalogs, including Hipparcos/Tycho, the AC2000.2, as
well as yet unpublished re-measures of the AGK2 plates and scans from the NPM
and SPM plates. Proper motion errors are about 1 to 3 mas/yr for stars to 12th
magnitude, and about 4 to 7 mas/yr for fainter stars to 16th magnitude. The
observational data, astrometric reductions, results, and important information
for the users of this catalog are presented.Comment: accepted by AJ, AAS LaTeX, 14 figures, 10 table
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
The WKB Approximation without Divergences
In this paper, the WKB approximation to the scattering problem is developed
without the divergences which usually appear at the classical turning points. A
detailed procedure of complexification is shown to generate results identical
to the usual WKB prescription but without the cumbersome connection formulas.Comment: 13 pages, TeX file, to appear in Int. J. Theor. Phy
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