5,916 research outputs found
Water Ice in 2060 Chiron and its Implications for Centaurs and Kuiper Belt Objects
We report the detection of water ice in the Centaur 2060 Chiron, based on
near-infrared spectra (1.0 - 2.5 micron) taken with the 3.8-meter United
Kingdom Infrared Telescope (UKIRT) and the 10-meter Keck Telescope. The
appearance of this ice is correlated with the recent decline in Chiron's
cometary activity: the decrease in the coma cross-section allows previously
hidden solid-state surface features to be seen. We predict that water ice is
ubiquitous among Centaurs and Kuiper Belt objects, but its surface coverage
varies from object to object, and thus determines its detectability and the
occurrence of cometary activity.Comment: 18 pages, 3 figures, accepted by ApJ Letter
Population of the Scattered Kuiper Belt
We present the discovery of three new Scattered Kuiper Belt Objects (SKBOs)
from a wide-field survey of the ecliptic. This continuing survey has to date
covered 20.2 square degrees to a limiting red magnitude of 23.6. We combine the
data from this new survey with an existing survey conducted at the University
of Hawaii 2.2m telescope to constrain the number and mass of the SKBOs. The
SKBOs are characterized by large eccentricities, perihelia near 35 AU, and
semi-major axes > 50 AU. Using a maximum-likelihood model, we estimate the
total number of SKBOs larger than 100 km in diameter to be N = 3.1 (+1.9/-1.3)
x 10^4 (1 sigma) and the total mass of SKBOs to be about 0.05 Earth masses,
demonstrating that the SKBOs are similar in number and mass to the Kuiper Belt
inside 50 AU.Comment: 15 pages, 3 figure
Exploring the evolutionary paths of the most massive galaxies since z~2
We use Spitzer MIPS data from the FIDEL Legacy Project in the Extended Groth
Strip to analyze the stellar mass assembly of massive (M>10^11 M_sun) galaxies
at z<2 as a function of structural parameters. We find 24 micron emission for
more than 85% of the massive galaxies morphologically classified as disks, and
for more than 57% of the massive systems morphologically classified as
spheroids at any redshift, with about 8% of sources harboring a bright X-ray
and/or infrared emitting AGN. More noticeably, 60% of all compact massive
galaxies at z=1-2 are detected at 24 micron, even when rest-frame optical
colors reveal that they are dead and evolving passively. For spheroid-like
galaxies at a given stellar mass, the sizes of MIPS non-detections are smaller
by a factor of 1.2 in comparison with IR-bright sources. We find that disk-like
massive galaxies present specific SFRs ranging from 0.04 to 0.2 Gyr^-1 at z<1
(SFRs ranging from 1 to 10 M_sun/yr), typically a factor of 3-6 higher than
massive spheroid-like objects in the same redshift range. At z>1, and more
pronouncedly at z>1.3, the median specific SFRs of the disks and spheroids
detected by MIPS are very similar, ranging from 0.1 to 1 Gyr^-1 (SFR=10-200
M_sun/yr). We estimate that massive spheroid-like galaxies may have doubled (at
the most) their stellar mass from star-forming events at z<2: less than 20%
mass increase at 1.7<z<2.0, up to 40% more at 1.1<z<1.7, and less than 20%
additional increase at z<1. Disk-like galaxies may have tripled (at the most)
their stellar mass at z<2 from star formation alone: up to 40% mass increase at
1.7<z<2.0, and less than 180% additional increase below z=1.7 occurred at a
steady rate.Comment: Accepted for publication in ApJ; 10 pages, 5 figures, 1 tabl
Paper to Electronic Questionnaires: Effects on Structured Questionnaire Forms
With the use of computers, paper questionnaires are being replaced by electronic questionnaires. The formats of traditional paper questionnaires have been found to effect a subject's rating. Consequently, the transition from paper to electronic format can subtly change results. The research presented begins to determine how electronic questionnaire formats change subjective ratings. For formats where subjects used a flow chart to arrive at their rating, starting at the worst and middle ratings of the flow charts were the most accurate but subjects took slightly more time to arrive at their answers. Except for the electronic paper format, starting at the worst rating was the most preferred. The paper and electronic paper versions had the worst accuracy. Therefore, for flowchart type of questionnaires, flowcharts should start at the worst rating and work their way up to better ratings
Discovery of a planetary-sized object in the scattered Kuiper belt
We present the discovery and initial physical and dynamical characterization
of the object 2003 UB313. The object is sufficiently bright that for all
reasonable values of the albedo it is certain to be larger than Pluto.
Pre-discovery observations back to 1989 are used to obtain an orbit with
extremely small errors. The object is currently at aphelion in what appears to
be a typical orbit for a scattered Kuiper belt object except that it is
inclined by about 44 degrees from the ecliptic. The presence of such a large
object at this extreme inclination suggests that high inclination Kuiper belt
objects formed preferentially closer to the sun. Observations from Gemini
Observatory show that the infrared spectrum is, like that of Pluto, dominated
by the presence of frozen methane, though visible photometry shows that the
object is almost neutral in color compared to Pluto's extremely red color. 2003
UB313 is likely to undergo substantial seasonal change over the large range of
heliocentric distances that it travels; Pluto at its current distance is likely
to prove a useful analog for better understanding the range of seasonal changes
on this body.Comment: 9 pages, 1 figur
Wind erosion in semiarid landscapes: Predictive models and remote sensing methods for the influence of vegetation
Wind erosion in semi-arid regions is a significant problem for which the sheltering effect of rangeland vegetation is poorly understood. Individual plants may be considered as porous roughness elements which absorb or redistribute the wind's momentum. The saltation threshold is the minimum wind velocity at which soil movement begins. The dependence of the saltation threshold on geometrical parameters of a uniform roughness array was studied in a wind tunnel. Both solid and porous elements were used to determine relationships between canopy structure and the threshold velocity for soil transport. The development of a predictive relation for the influence of vegetation canopy structure on wind erosion of soil is discussed
Agrobacterium-mediated transformation of Mycosphaerella fijiensis, the devastating Black Sigatoka pathogen of bananas
Mycosphaerella fijiensis, M. musicola en M. eumusae veroorzaken de Sigatoka-ziekte in banaan. Op dit moment is de toepassing van fungiciden de enige optie om deze ziekte te bestrijden. Het PRPB (Pesticide Reduction Program for Banana) investeert in de ontwikkeling van technieken voor de genotype- en fenotypebepaling van M. fijiensis. Hierbij wordt gebruikt gemaakt van ATMT (Agrobacterium tumefaciens-mediated transformation)
Observations of solar scattering polarization at high spatial resolution
The weak, turbulent magnetic fields that supposedly permeate most of the
solar photosphere are difficult to observe, because the Zeeman effect is
virtually blind to them. The Hanle effect, acting on the scattering
polarization in suitable lines, can in principle be used as a diagnostic for
these fields. However, the prediction that the majority of the weak, turbulent
field resides in intergranular lanes also poses significant challenges to
scattering polarization observations because high spatial resolution is usually
difficult to attain. We aim to measure the difference in scattering
polarization between granules and intergranules. We present the respective
center-to-limb variations, which may serve as input for future models. We
perform full Stokes filter polarimetry at different solar limb positions with
the CN band filter of the Hinode-SOT Broadband Filter Imager, which represents
the first scattering polarization observations with sufficient spatial
resolution to discern the granulation. Hinode-SOT offers unprecedented spatial
resolution in combination with high polarimetric sensitivity. The CN band is
known to have a significant scattering polarization signal, and is sensitive to
the Hanle effect. We extend the instrumental polarization calibration routine
to the observing wavelength, and correct for various systematic effects. The
scattering polarization for granules (i.e., regions brighter than the median
intensity of non-magnetic pixels) is significantly larger than for
intergranules. We derive that the intergranules (i.e., the remaining
non-magnetic pixels) exhibit (9.8 \pm 3.0)% less scattering polarization for
0.2<u<0.3, although systematic effects cannot be completely excluded. These
observations constrain MHD models in combination with (polarized) radiative
transfer in terms of CN band line formation, radiation anisotropy, and magnetic
fields.Comment: Accepted for publication in A&
Ocean Dynamics South Shore of Oahu, Hawaiâi: From Mean Circulation to Near-Inertial Waves and Submesocale.
Ph.D. Thesis. University of HawaiÊ»i at MÄnoa 2018
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