1,428 research outputs found
Global mapping of iron and titanium oxides in the lunar megaregolith and subsurface
[Abstract]:
This paper reports mapping results obtained by remote sensing analysis of Iron and Titanium oxides in the megaregolith under the lunar Highlands regolith and in the subsurface under the Mare and South Pole Aitken basin regolith. FeO and TiO2 images were mosaicked from data extracted from the 1994 Clementine lunar orbiter mission from 600 N to 600 S, using the Lucey et al. technique (2000). These images then used to study the ejecta blanket for each of 2059 craters analysed using ISIS software (US Geological Survey). Average weight percentage values for each crater ejecta blanket were interpolated to derive underlying global Province Maps for FeO and TiO2. The Moon was divided into five (5) provinces as a balance of the needs of analysis requirements and simplicity. Division of global TiO2 weight percentages in the megaregolith /subsurface five provinces was matching the observed distribution of that at the surface. In contrast, division of lunar FeO into 5 Provinces reveals unexpectedly elevated iron concentrations (3.8 to 6.4%) in some areas of the Highland megaregolith. This Province of elevated iron oxide is termed âHighland IIâ
Catastrophic vs Gradual Collapse of Thin-Walled Nanocrystalline Ni Hollow Cylinders As Building Blocks of Microlattice Structures
Lightweight yet stiff and strong lattice structures are attractive for various engineering applications, such as cores of sandwich shells and components designed for impact mitigation. Recent breakthroughs in manufacturing enable efficient fabrication of hierarchically architected microlattices, with dimensional control spanning seven orders of magnitude in length scale. These materials have the potential to exploit desirable nanoscale-size effects in a macroscopic structure, as long as their mechanical behavior at each appropriate scale â nano, micro, and macro levels â is properly understood. In this letter, we report the nanomechanical response of individual microlattice members. We show that hollow nanocrystalline Ni cylinders differing only in wall thicknesses, 500 and 150 nm, exhibit strikingly different collapse modes: the 500 nm sample collapses in a brittle manner, via a single strain burst, while the 150 nm sample shows a gradual collapse, via a series of small and discrete strain bursts. Further, compressive strength in 150 nm sample is 99.2% lower than predicted by shell buckling theory, likely due to localized buckling and fracture events observed during in situ compression experiments. We attribute this difference to the size-induced transition in deformation behavior, unique to nanoscale, and discuss it in the framework of âsize effectsâ in crystalline strength
Dynamic deformation of volcanic ejecta from the Toba caldera: Possible relevance to Cretaceous/Tertiary boundary phenomena
Plagioclase and biotite phenocrysts in ignimbrites erupted from the Toba caldera, Sumatra, show microstructures and textures indicative of shock stress levels higher than 10 GPa. Strong dynamic deformation has resulted in intense kinking in biotite and, with increasing shock intensity, the development in plagioclase of planar features, shock mosaicism, incipient recrystallization, and possible partial melting. Microstructures in quartz indicative of strong shock deformation are rare, however, and many shock lamellae, if formed, may have healed during post-shock residence in the hot ignimbrite; they might be preserved in ash falls. Peak shock stresses from explosive silicic volcanism and other endogenous processes may be high and if so would obviate the need for extraterrestrial impacts to produce all dynamically deformed structures, possibly including shock features observed near the Cretaceous/Tertiary boundary
Spinning Down a Black Hole With Scalar Fields
We study the evolution of a Kerr black hole emitting scalar radiation via the
Hawking process. We show that the rate at which mass and angular momentum are
lost by the black hole leads to a final evolutionary state with nonzero angular
momentum, namely .Comment: 4 pages (including 3 postscript figures), Revtex, uses epsf.tex,
twocolumn.sty and header.sty (included). Submitted to Physical Review Letter
Kepler-413b: a slightly misaligned, Neptune-size transiting circumbinary planet
We report the discovery of a transiting, Rp = 4.347+/-0.099REarth,
circumbinary planet (CBP) orbiting the Kepler K+M Eclipsing Binary (EB) system
KIC 12351927 (Kepler-413) every ~66 days on an eccentric orbit with ap =
0.355+/-0.002AU, ep = 0.118+/-0.002. The two stars, with MA =
0.820+/-0.015MSun, RA = 0.776+/-0.009RSun and MB = 0.542+/-0.008MSun, RB =
0.484+/-0.024RSun respectively revolve around each other every
10.11615+/-0.00001 days on a nearly circular (eEB = 0.037+/-0.002) orbit. The
orbital plane of the EB is slightly inclined to the line of sight (iEB =
87.33+/-0.06 degrees) while that of the planet is inclined by ~2.5 degrees to
the binary plane at the reference epoch. Orbital precession with a period of
~11 years causes the inclination of the latter to the sky plane to continuously
change. As a result, the planet often fails to transit the primary star at
inferior conjunction, causing stretches of hundreds of days with no transits
(corresponding to multiple planetary orbital periods). We predict that the next
transit will not occur until 2020. The orbital configuration of the system
places the planet slightly closer to its host stars than the inner edge of the
extended habitable zone. Additionally, the orbital configuration of the system
is such that the CBP may experience Cassini-States dynamics under the influence
of the EB, in which the planet's obliquity precesses with a rate comparable to
its orbital precession. Depending on the angular precession frequency of the
CBP, it could potentially undergo obliquity fluctuations of dozens of degrees
(and complex seasonal cycles) on precession timescales.Comment: 48 pages, 13 figure
Transit Timing Observations from Kepler. VIII Catalog of Transit Timing Measurements of the First Twelve Quarters
Following Ford et al. (2011, 2012) and Steffen et al. (2012) we derived the
transit timing of 1960 Kepler KOIs using the pre-search data conditioning (PDC)
light curves of the first twelve quarters of the Kepler data. For 721 KOIs with
large enough SNRs, we obtained also the duration and depth of each transit. The
results are presented as a catalog for the community to use. We derived a few
statistics of our results that could be used to indicate significant
variations. Including systems found by previous works, we have found 130 KOIs
that showed highly significant TTVs, and 13 that had short-period TTV
modulations with small amplitudes. We consider two effects that could cause
apparent periodic TTV - the finite sampling of the observations and the
interference with the stellar activity, stellar spots in particular. We briefly
discuss some statistical aspects of our detected TTVs. We show that the TTV
period is correlated with the orbital period of the planet and with the TTV
amplitude.Comment: Accepted for publication to ApJ. 57 pages, 23 Figures. Machine
readable catalogs are available at ftp://wise-ftp.tau.ac.il/pub/tauttv/TT
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