118,817 research outputs found
Near-infrared (NIR) spectra of Centaurs and Kuiper belt objects
We present here an extensive survey of near-infrared (NIR) spectra of Kuiper belt objects (KBOs) and Centaurs taken with the Keck I Telescope. We find that most spectra in our sample are well characterized by a combination of water ice and a featureless continuum. A comparative analysis reveals that the NIR spectral properties have little correlation to the visible colors or albedo, with the exception of the fragment KBOs produced from the giant impact on 2003 EL61. The results suggest that the surface composition of KBOs is heterogeneous, though the exposure of water ice may be controlled by geophysical processes. The Centaurs also display diverse spectral properties, but the source of the variability remains unclear. The results for both the KBOs and the Centaurs point to inherent heterogeneity in either the processes acting on these objects or materials from which they formed
Candidate Members and Age Estimate of the Family of Kuiper Belt Object 2003 EL61
The collisional family of Kuiper belt object (KBO) 2003 EL61 opens the
possibility for many interesting new studies of processes important in the
formation and evolution of the outer solar system. As the first family in the
Kuiper belt, it can be studied using techniques developed for studying asteroid
families, although some modifications are necessary. Applying these modified
techniques allows for a dynamical study of the 2003 EL61 family. The velocity
required to change orbits is used to quantitatively identify objects near the
collision. A method for identifying family members that have potentially
diffused in resonances (like 2003 EL61) is also developed. Known family members
are among the very closest KBOs to the collision and two new likely family
members are identified: 2003 UZ117 and 1999 OY3. We also give tables of
candidate family members which require future observations to confirm
membership. We estimate that a minimum of ~1 GYr is needed for resonance
diffusion to produce the current position of 2003 EL61, implying that the
family is likely primordial. Future refinement of the age estimate is possible
once (many) more resonant objects are identified. The ancient nature of the
collision contrasts with the seemingly fresh surfaces of known family members,
suggesting that our understanding of outer solar system surfaces is incomplete.Comment: 22 pages, 5 figures, accepted to AJ, author's cv available at
http://www.gps.caltech.edu/~dari
Coulomb blockade in a Si channel gated by an Al single-electron transistor
We incorporate an Al-AlO_x-Al single-electron transistor as the gate of a
narrow (~100 nm) metal-oxide-semiconductor field-effect transistor (MOSFET).
Near the MOSFET channel conductance threshold, we observe oscillations in the
conductance associated with Coulomb blockade in the channel, revealing the
formation of a Si single-electron transistor. Abrupt steps present in sweeps of
the Al transistor conductance versus gate voltage are correlated with
single-electron charging events in the Si transistor, and vice versa. Analysis
of these correlations using a simple electrostatic model demonstrates that the
two single-electron transistor islands are closely aligned, with an
inter-island capacitance approximately equal to 1/3 of the total capacitance of
the Si transistor island, indicating that the Si transistor is strongly coupled
to the Al transistor.Comment: 3 pages, 4 figures, 1 table; typos corrected, minor clarifications
added; published in AP
ALMA Thermal Observations of Europa
We present four daytime thermal images of Europa taken with the Atacama Large
Millimeter Array. Together, these images comprise the first spatially resolved
thermal dataset with complete coverage of Europa's surface. The resulting
brightness temperatures correspond to a frequency of 233 GHz (1.3 mm) and a
typical linear resolution of roughly 200 km. At this resolution, the images
capture spatially localized thermal variations on the scale of geologic and
compositional units. We use a global thermal model of Europa to simulate the
ALMA observations in order to investigate the thermal structure visible in the
data. Comparisons between the data and model images suggest that the
large-scale daytime thermal structure on Europa largely results from bolometric
albedo variations across the surface. Using bolometric albedos extrapolated
from Voyager measurements, a homogenous model reproduces these patterns well,
but localized discrepancies exist. These discrepancies can be largely explained
by spatial inhomogeneity of the surface thermal properties. Thus, we use the
four ALMA images to create maps of the surface thermal inertia and emissivity
at our ALMA wavelength. From these maps, we identify a region of either
particularly high thermal inertia or low emissivity near 90 degrees West and 23
degrees North, which appears anomalously cold in two of our images.Comment: 9 pages, 3 figures, accepted for publication in the Astronomical
Journa
The Mass, Orbit, and Tidal Evolution of the Quaoar-Weywot System
Here we present new adaptive optics observations of the Quaoar-Weywot system.
With these new observations we determine an improved system orbit. Due to a
0.39 day alias that exists in available observations, four possible orbital
solutions are available with periods of , , , and
days. From the possible orbital solutions, system masses of
kg are found. These observations provide an
updated density for Quaoar of 2.7-5.0{g cm^{-3}}. In all cases, Weywot's
orbit is eccentric, with possible values . We present a
reanalysis of the tidal orbital evolution of the Quoaor-Weywot system. We have
found that Weywot has probably evolved to a state of synchronous rotation, and
have likely preserved their initial inclinations over the age of the Solar
system. We find that for plausible values of the effective tidal dissipation
factor tides produce a very slow evolution of Weywot's eccentricity and
semi-major axis. Accordingly, it appears that Weywot's eccentricity likely did
not tidally evolve to its current value from an initially circular orbit.
Rather, it seems that some other mechanism has raised its eccentricity
post-formation, or Weywot formed with a non-negligible eccentricity.Comment: Accepted to Icarus, Nov. 8 201
Evaluation of effectiveness of various devices for attenuation of trailing vortices based on model tests in a large towing basin
The effectiveness of various candidate aircraft-wing devices for attenuation of trailing vortices generated by large aircraft is evaluated on basis of results of experiments conducted with a 0.03-scale model of a Boeing 747 transport aircraft using a technique developed at the HYDRONAUTICS Ship Model Basin. Emphasis is on the effects produced by these devices in the far-field (up to 8 kilometers downstream of full-scale generating aircraft) where the unaltered vortex-wakes could still be hazardous to small following aircraft. The evaluation is based primarily on quantitative measurements of the respective vortex velocity distributions made by means of hot-film probe traverses in a transverse plane at selected stations downstream. The effects of these altered wakes on rolling moment induced on a small following aircraft are also studied using a modified lifting-surface theory with a synthesized Gates Learjet as a typical example. Lift and drag measurements concurrently obtained in the model tests are used to appraise the effects of each device investigated on the performance characteristics of the generating aircraft
The chameleon groups of Richard J. Thompson: automorphisms and dynamics
The automorphism groups of several of Thompson's countable groups of
piecewise linear homeomorphisms of the line and circle are computed and it is
shown that the outer automorphism groups of these groups are relatively small.
These results can be interpreted as stability results for certain structures of
PL functions on the circle. Machinery is developed to relate the structures on
the circle to corresponding structures on the line
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