641 research outputs found
Arc termination cracks in Inconel 718 and Incoloy 903
The welding of the nickel base, heat resistant alloys that are used extensively for welded Shuttle engine components revealed solidification cracking characteristics at weld termination points. If not detected and removed, these crater cracks may cause costly component failure. To better understand this characteristic, welding termination techniques were studied and methods developed to eliminate crater cracks. It was determined that weld termination solidification cracking can be eliminated by controlled decrease of welding current, welding voltage, wire feed, and travel speed
High-temperature LM cathode ion thrusters Quarterly progress report, 5 Aug. - 4 Nov. 1968
Thermodynamic and operating characteristics of high temperature liquid mercury cathode ion thruster
Weld peaking on heavy aluminum structures
Weld peaking is usually undesirable in any welded structure. In heavy structures, the forces involved in the welding process become very large and difficult to handle. With the shuttle's solid rocket booster, the weld peaking resulted in two major problems: (1) reduced mechanical properties across the weld joint, and (2) fit-up difficulties in subsequent assembly operation. Peaking from the weld shrinkage forces can be fairly well predicted in simple structures; however, in welding complicated assemblies, the amount of peaking is unpredictable because of unknown stresses from machining and forming, stresses induced by the fixturing, and stresses from welds in other parts of the assembly. When excessive peaking is encountered, it can be corrected using the shrinkage forces resulting from the welding process. Application of these forces is discussed in this report
Synchronous seasonal change in fin whale song in the North Pacific.
Fin whale (Balaenoptera physalus) song consists of down-swept pulses arranged into stereotypic sequences that can be characterized according to the interval between successive pulses. As in blue (B. musculus) and humpback whales (Megaptera novaeangliae), these song sequences may be geographically distinct and may correlate with population boundaries in some regions. We measured inter-pulse intervals of fin whale songs within year-round acoustic datasets collected between 2000 and 2006 in three regions of the eastern North Pacific: Southern California, the Bering Sea, and Hawaii. A distinctive song type that was recorded in all three regions is characterized by singlet and doublet inter-pulse intervals that increase seasonally, then annually reset to the same shorter intervals at the beginning of each season. This song type was recorded in the Bering Sea and off Southern California from September through May and off Hawaii from December through April, with the song interval generally synchronized across all monitoring locations. The broad geographic and seasonal occurrence of this particular fin whale song type may represent a single population broadly distributed throughout the eastern Pacific with no clear seasonal migratory pattern. Previous studies attempting to infer population structure of fin whales in the North Pacific using synchronous individual song samples have been unsuccessful, likely because they did not account for the seasonal lengthening in song intervals observed here
LM cathode thruster system Quarterly progress report, 4 Jan. 1969 - 4 Apr. 1970
Development of 20 cm liquid metal cathode thruster syste
Optical and Infrared Light Curves of the Eclipsing X-ray Binary V395 Car = 2S 0921-630
We present results of optical and infrared photometric monitoring of the
eclipsing low-mass X-ray binary V395 Car (2S 0921-630). Our observations reveal
a clear, repeating orbital modulation with an amplitude of about one magnitude
in B, and V and a little less in J. Combining our data with archival
observations spanning about 20 years, we derive an updated ephemeris with
orbital period 9.0026+/-0.0001d. We attribute the modulation to a combination
of the changing aspect of the irradiated face of the companion star and
eclipses of the accretion disk around the neutron star. Both appear to be
necessary as a secondary eclipse of the companion star is clearly seen. We
model the B, V, and J lightcurves using a simple model of an accretion disk and
companion star and find a good fit is possible for binary inclinations of
82.2+/-1.0 degrees. We estimate the irradiating luminosity to be about 8x10^35
erg/s, in good agreement with X-ray constraints.Comment: 6 pages, accepted for publication in MNRA
LM cathode thruster system Quarterly progress report, 4 Oct. 1969 - 4 Jan. 1970
Optimization testing of thermally integrated liquid mercury cathode thruster syste
The Structure Of The Accretion Disk In The ADC Source 4U 1822-371
The low-mass X-ray binary (LMXB) 4U 1822-371 has an accretion disk corona (ADC) that scatters X-ray photons from the inner disk and neutron star out of the line of sight. It has a high orbital inclination and the secondary star eclipses the disk and ADC. We have obtained new time-resolved UV spectrograms and V- and I-band photometry of 4U 1822-371. The large quadratic term in our new optical eclipse ephemeris confirms that the system has an extremely high rate of mass transfer and mass accretion. The C IV lambda lambda = 1548 - 1550 angstrom emission line has a half width of similar to 4400 km/s, indicating a strong, high velocity wind is being driven off the accretion disk. Near the disk the wind is optically thick in UV, V, and J and the eclipse analysis shows that in V and J the optically thick wind extends nearly to the outer edge of the disk. The ADC must also extend vertically to a height equal to approximately half the disk radius.Astronom
2MASS J05162881+2607387: A New Low-Mass Double-Lined Eclipsing Binary
We show that the star known as 2MASS J05162881+2607387 (hereafter J0516) is a
double-lined eclipsing binary with nearly identical low-mass components. The
spectroscopic elements derived from 18 spectra obtained with the High
Resolution Spectrograph on the Hobby-Eberly Telescope during the Fall of 2005
are K_1=88.45 +/- 0.48 km/s and K_2=90.43 +/- 0.60 km/s, resulting in a mass
ratio of$q=K_1/K_2 = 0.978 +/- 0.018 and minimum masses of M_1 sin^{3}i=0.775
+/- 0.016 solar masses and M_2 sin^{3}i=0.759 +/- 0.012 solar masses,
respectively. We have extensive differential photometry of J0516 obtained over
several nights between 2004 January-March (epoch 1) and 2004 October-2005
January plus 2006 January (epoch 2) using the 1m telescope at the Mount Laguna
Observatory. The source was roughly 0.1 mag brighter in all three bandpasses
during epoch 1 when compared to epoch 2. Also, phased light curves from epoch 1
show considerable out-of-eclipse variability, presumably due to bright spots on
one or both stars. In contrast, the phased light curves from epoch 2 show
little out-of-eclipse variability. The light curves from epoch 2 and the radial
velocity curves were analyzed using our ELC code with updated model atmospheres
for low-mass stars. We find the following: M_1=0.787 +/- 0.012 solar masses,
R_1=0.788 +/- 0.015 solar radii, M_2=0.770 +/- 0.009 solar masses, and
R_2=0.817 +/- 0.010 solar radii. The stars in J0516 have radii that are
significantly larger than model predictions for their masses, similar to what
is seen in a handful of other well-studied low-mass double-lined eclipsing
binaries. We compiled all recent mass and radius determinations from low-mass
binaries and determine an empirical mass-radius relation of the form R = 0.0324
+ 0.9343M + 0.0374M^2, where the quantities are in solar units.Comment: 16 pages, 10 figures (Figure 1 has degraded quality), to appear in
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