1,517 research outputs found
Political relevance in the eye of the beholder: Determining the substantiveness of TV shows and political debates with Twitter data
Between article and topic: news events as level of analysis and their computational identification
The Size Distribution of Trans-Neptunian Bodies
[Condensed] We search 0.02 deg^2 for trans-Neptunian objects (TNOs) with
m<=29.2 (diameter ~15 km) using the ACS on HST. Three new objects are
discovered, roughly 25 times fewer than expected from extrapolation of the
differential sky density Sigma(m) of brighter objects. The ACS and other recent
TNO surveys show departures from a power law size distribution. Division of the
TNO sample into ``classical Kuiper belt'' (CKB) and ``Excited'' samples reveals
that Sigma(m) differs for the two populations at 96% confidence. A double power
law adequately fits all data. Implications include: The total mass of the CKB
is ~0.010 M_Earth, only a few times Pluto's mass, and is predominately in the
form of ~100 km bodies. The mass of Excited objects is perhaps a few times
larger. The Excited class has a shallower bright-end size distribution; the
largest objects, including Pluto, comprise tens of percent of the total mass
whereas the largest CKBOs are only ~2% of its mass. The predicted mass of the
largest Excited body is close to the Pluto mass; the largest CKBO is ~60 times
less massive. The deficit of small TNOs occurs for sizes subject to disruption
by present-day collisions, suggesting extensive depletion by collisions. Both
accretion and erosion appearing to have proceeded to more advanced stages in
the Excited class than the CKB. The absence of distant TNOs implies that any
distant (60 AU) population must have less than the CKB mass in the form of
objects 40 km or larger. The CKB population is sparser than theoretical
estimates of the required precursor population for short period comets, but the
Excited population could be a viable precursor population.Comment: Revised version accepted to the Astronomical Journal. Numerical
results are very slightly revised. Implications for the origins of
short-period comets are substantially revised, and tedious material on
statistical tests has been collected into a new Appendi
Talking with and about politicians on Twitter:An analysis of tweets containing @-mentions of candidates in the Brazilian presidential elections
Public opinion on Twitter? How vote choice and arguments on Twitter comply with patterns in survey data, evidence from the 2016 Ukraine referendum in the Netherlands
De-biased Populations of Kuiper Belt Objects from the Deep Ecliptic Survey
The Deep Ecliptic Survey (DES) discovered hundreds of Kuiper Belt objects
from 1998-2005. Follow-up observations yielded 304 objects with good dynamical
classifications (Classical, Scattered, Centaur, or 16 mean-motion resonances
with Neptune). The DES search fields are well documented, enabling us to
calculate the probability of detecting objects with particular orbital
parameters and absolute magnitudes at a randomized point in each orbit.
Grouping objects together by dynamical class leads, we estimate the orbital
element distributions (a, e, i) for the largest three classes (Classical, 3:2,
and Scattered) using maximum likelihood. Using H-magnitude as a proxy for the
object size, we fit a power law to the number of objects for 8 classes with at
least 5 detected members (246 objects). The best Classical slope is
alpha=1.02+/-0.01 (observed from 5<=H<=7.2). Six dynamical classes (Scattered
plus 5 resonances) are consistent in slope with the Classicals, though the
absolute number of objects is scaled. The exception to the power law relation
are the Centaurs (non-resonant with perihelia closer than Neptune, and thus
detectable at smaller sizes), with alpha=0.42+/-0.02 (7.5<H<11). This is
consistent with a knee in the H-distribution around H=7.2 as reported elsewhere
(Bernstein et al. 2004, Fraser et al. 2014). Based on the Classical-derived
magnitude distribution, the total number of objects (H<=7) in each class are:
Classical (2100+/-300 objects), Scattered (2800+/-400), 3:2 (570+/-80), 2:1
(400+/-50), 5:2 (270+/-40), 7:4 (69+/-9), 5:3 (60+/-8). The independent
estimate for the number of Centaurs in the same H range is 13+/-5. If instead
all objects are divided by inclination into "Hot" and "Cold" populations,
following Fraser et al. (2014), we find that alphaHot=0.90+/-0.02, while
alphaCold=1.32+/-0.02, in good agreement with that work.Comment: 26 pages emulateapj, 6 figures, 5 tables, accepted by A
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