4,243 research outputs found
Effects of wing leading-edge deflection on low-speed aerodynamic characteristics of a low-aspect-ratio highly swept arrow-wing configuration
Static force tests were conducted in the Langley V/STOL tunnel at a Reynolds number (based on the mean aerodynamic chord) of about 2.0 x 10 to the 6th power for an angle-of-attack range from about - 10 deg to 17 deg and angles of sideslip of 0 and + or - 5 deg. Limited flow visualization studies were also conducted in order to provide a qualitative assessment of leading-edge upwash characteristics
A major outburst from the X-ray binary RX J0520.5-6932
We report on the analysis of 8 years of MAssive Compact Halo Objects (MACHO)
data for the source RX J0520.5-6932. A regular period of 24.4 days has been
confirmed, however this is manifest almost entirely in the red part of the
spectrum. A major outburst, lasting approximately 200 days, was observed which
increased the apparent brightness of the object by approximately 0.15
magnitudes without significantly altering its V-R colour index. This outburst
was also seen in X-ray data. The evidence from this analysis points to the
identification of this object as a Be/X-ray binary with a periodically variable
circumstellar disk and a very early optical counterpart.Comment: Paper has been accepted by MNRA
Summary of information on low-speed lateral-directional derivatives due to rate of change of sideslip beta prime
The results presented show that the magnitudes of the aerodynamic stability derivatives due to rate of change of sideslip become quite large at high angles of attack for swept- and delta-wing configurations, and that such derivatives have large effects on the calculated dynamic stability of these configurations at high angles of attack. The wind-tunnel test techniques used to measure the beta prime derivatives and various approaches used to predict them are discussed. Both the conventional oscillating-airfoil theory and the lag-of-the-sidewash theory are shown to be inadequate for predicting the vertical-tail contribution to the acceleration-in-sideslip derivative; a flow-field-lag theory, which is discussed, appears to give qualitative agreement with experimental data for a current twin-jet fighter configuration
Wind-tunnel free-flight investigation of a model of a spin-resistant fighter configuration
An investigation was conducted to provide some insight into the features affecting the high-angle-of-attack characteristics of a high-performance twin-engine fighter airplane which in operation has exhibited excellent stall characteristics with a general resistance to spinning. Various techniques employed in the study included wind-tunnel free-flight tests, flow-visualization tests, static force tests, and dynamic (forced-oscillation) tests. In addition to tests conducted on the basic configuration tests were made with the wing planform and the fuselage nose modified. The results of the study showed that the model exhibited good dynamic stability characteristics at angles of attack well beyond that for wing stall. The directional stability of the model was provided by the vertical tail at low and moderate angles of attack and by the fuselage forebody at high angles of attack. The wing planform was found to have little effect on the stability characteristics at high angles of attack. The tests also showed that although the fuselage forebody produced beneficial contributions to static directional stability at high angles of attack, it also produced unstable values of damping in yaw. Nose strakes located in a position which eliminated the beneficial nose contributions produced a severe directional divergence
New Species of Carboniferous Spores from the Des Moines Coals of Iowa
A stratigraphic study of the plant microfossils m the Iowa Pennsylvanian coals by the maceration method has been in progress during the past three years. A statistical correlation was made between two coal sections near what Cheer, Iowa, by the selection and use of six distinctive microfossils. Further examination of 42 samples of coal from eight Iowa counties yielded many spore types of which eight are now described as new genera and species. No serious attempt has been made to use the described spores as horizon markers
Discovery of Radio Emission from Transient Anomalous X-ray Pulsar XTE J1810-197
We report the first detection of radio emission from any anomalous X-ray
pulsar (AXP). Data from the Very Large Array (VLA) MAGPIS survey with angular
resolution 6" reveals a point-source of flux density 4.5 +/- 0.5 mJy at 1.4 GHz
at the precise location of the 5.54 s pulsar XTE J1810-197. This is greater
than upper limits from all other AXPs and from quiescent states of soft
gamma-ray repeaters (SGRs). The detection was made in 2004 January, 1 year
after the discovery of XTE J1810-197 during its only known outburst. Additional
VLA observations both before and after the outburst yield only upper limits
that are comparable to or larger than the single detection, neither supporting
nor ruling out a decaying radio afterglow related to the X-ray turn-on. Another
hypothesis is that, unlike the other AXPs and SGRs, XTE J1810-197 may power a
radio synchrotron nebula by the interaction of its particle wind with a
moderately dense environment that was not evacuated by previous activity from
this least luminous, in X-rays, of the known magnetars.Comment: 13 pages, 1 figure, to appear in ApJ Letter
Spin period change and the magnetic fields of neutron stars in Be X-ray binaries in the Small Magellanic Cloud
We report on the long-term average spin period, rate of change of spin period
and X-ray luminosity during outbursts for 42 Be X-ray binary systems in the
Small Magellanic Cloud. We also collect and calculate parameters of each system
and use these data to determine that all systems contain a neutron star which
is accreting via a disc, rather than a wind, and that if these neutron stars
are near spin equilibrium, then over half of them, including all with spin
periods over about 100 s, have magnetic fields over the quantum critical level
of 4.4x10^13 G. If these neutron stars are not close to spin equilibrium, then
their magnetic fields are inferred to be much lower, of the order of 10^6-10^10
G, comparable to the fields of neutron stars in low-mass X-ray binaries. Both
results are unexpected and have implications for the rate of magnetic field
decay and the isolated neutron star population.Comment: 22 pages, 50 figures; to appear in MNRA
The XMM-Newton survey of the Small Magellanic Cloud: XMMUJ005011.2-730026 = SXP214, a Be/X-ray binary pulsar
In the course of the XMM-Newton survey of the Small Magellanic Cloud (SMC), a
region to the east of the emission nebula N19 was observed in November 2009. To
search for new candidates for high mass X-ray binaries the EPIC PN and MOS data
of the detected point sources were investigated and their spectral and temporal
characteristics identified. A new transient (XMMUJ005011.2-730026= SXP214) with
a pulse period of 214.05 s was discovered; the source had a hard X-ray spectrum
with power-law index of ~0.65. The accurate X-ray source location permits the
identification of the X-ray source with a ~15th magnitude Be star, thereby
confirming this system as a new Be/X-ray binary.Comment: 8 pages 11 figures. Accepted for publication in MNRA
The binary period and outburst behaviour of the SMC X-ray binary pulsar system SXP504
A probable binary period has been detected in the optical counterpart to the
X-ray source CXOU J005455.6-724510 = RX J0054.9-7245 = AXJ0054.8-7244 = SXP504
in the Small Magellanic Cloud. This source was detected by Chandra on 04 Jul
2002 and subsequently observed by XMM-Newton on 18 Dec 2003. The source is
coincident with an Optical Gravitational Lensing (OGLE) object in the
lightcurves of which several optical outburst peaks are visible at ~ 268 day
intervals. Timing analysis shows a period of 268.6 +/- 0.1 days at > 99%
significance. Archival Rossi X-ray Timing Explorer (RXTE) data for the 504s
pulse-period has revealed detections which correspond closely with predicted or
actual peaks in the optical data. The relationship between this orbital period
and the pulse period of 504s is within the normal variance found in the Corbet
diagram.Comment: Accepted by MNRAS. 1 LATEX page. 4 figure
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