39,543 research outputs found
Observational bias and the clustering of distant eccentric Kuiper belt objects
The hypothesis that a massive Planet Nine exists in the outer solar system on
a distant eccentric orbit was inspired by observations showing that the objects
with the most distant eccentric orbits in the Kuiper belt have orbits which are
physically aligned, that is, they are clustered in longitude of perihelion and
have similar orbital planes. Questions have remained, however, about the
effects of observational bias on these observations, particularly on the
longitudes of perihelion. Specifically, distant eccentric Kuiper belt objects
tend to be faint and only observable near their perihelia, suggesting that the
longitudes of perihelion of the known distant objects could be strongly biased
by the limited number of locations in the sky where deep surveys have been
carried out. We have developed a method to rigorously estimate the longitude of
perihelion bias for Kuiper belt observations. We find that the probability that
the 10 known Kuiper belt objects with semimajor axis beyond 230 AU are drawn
from a population with uniform longitude of perihelion is 1.2%. Combined with
the observation that the orbital poles of these object are also clustered, the
overall probability of detecting these two independent clusterings in a
randomly distributed sample is 0.025%. While observational bias is clearly
present in these observations, it is unlikely to explain the observed alignment
of the distant eccentric Kuiper belt objects.Comment: AJ, in pres
Observation of mass loading in the Io plasma torus
Ground‐based high‐resolution spectra of emission from the Io plasma torus obtained during 53 nights of observation over a seven month period are used to measure the torus rotation speed and discern regions of the torus that are slowed by mass loading of newly ionized materials. The amount of torus slowing implies that between 2000 and 3000 kg sec^(−1) are being ionized by the torus. The slowing is spread azimuthally throughout the orbit of Io, suggesting that neutral materials emanating from Io are distributed around Jupiter much more uniformly than currently believed
The 3-4 m Spectra of Jupiter Trojan Asteroids
To date, reflectance spectra of Jupiter Trojan asteroids have revealed no
distinctive absorption features. For this reason, the surface composition of
these objects remains a subject of speculation. Spectra have revealed, however,
that the Jupiter Trojan asteroids consist of two distinct sub-populations which
differ in the optical to near-infrared colors. The origins and compositional
differences between the two sub-populations remain unclear. Here we report the
results from a 2.2-3.8 m spectral survey of a collection of 16 Jupiter
Trojan asteroids, divided equally between the two sub-populations. We find
clear spectral absorption features centered around 3.1 m in the less red
population. Additional absorption consistent with expected from organic
materials might also be present. No such features are see in the red
population. A strong correlation exists between the strength of the 3.1 m
absorption feature and the optical to near-infrared color of the objects. While
traditionally absorptions such as these in dark asteroids are modeled as being
due to fine-grain water frost, we find it physically implausible that the
special circumstances required to create such fine-grained frost would exist on
a substantial fraction of the Jupiter Trojan asteroids. We suggest, instead,
that the 3.1 m absorption on Trojans and other dark asteroids could be due
to N-H stretch features. Additionally, we point out that reflectivities derived
from WISE observations show a strong absorption beyond 4m for both
populations. The continuum of 3.1 m features and the common absorption
beyond 4 m might suggest that both sub-populations of Jupiter Trojan
asteroids formed in the same general region of the early solar system.Comment: AJ, in pres
Periodicities in the Io plasma torus
We present a 6-month baseline of spatially resolved measurements of the Io plasma torus intensity and perpendicular ion temperature which we use to determine the periodicities of the torus during this time. We find large anticorrelated variations in the intensity and ion temperature which are periodic with the Jovian rotation rate (System III). The intensity variations are found to be a simple manifestation of the temperature variations, though no explanation for the temperature variations is apparent. Periodogram analysis shows an additional intensity periodicity which rotates 2.91±0.06% more slowly than System III. This period is found only in the intensity and not in the ion temperature. We conclude from these observations that the torus has a sinusoidal ion temperature variation locked into the rotation of Jupiter and that superimposed on this is a long-lived density pattern which rotates 2.91% more slowly than Jupiter. Based on the spatial structure and physical properties, we rule out all currently proposed mechanisms for the creation of these periodicities within the torus
Prospects for weak lensing studies with new radio telescopes
I outline the prospects for performing weak lensing studies with the new
generation of radio telescopes that are coming online now and in the future. I
include a description of a proposed technique to use polarization observations
in radio weak lensing analyses which could prove extremely useful for removing
a contaminating signal from intrinsic alignments. Ultimately, the Square
Kilometre Array promises to be an exceptional instrument for performing weak
lensing studies due to the high resolution, large area surveys which it will
perform. In the nearer term, the e-MERLIN instrument in the UK offers the high
sensitivity and sub-arcsec resolution required to prove weak lensing techniques
in the radio band. I describe the SuperCLASS survey -- a recently accepted
e-MERLIN legacy programme which will perform a pioneering radio weak lensing
analysis of a supercluster of galaxies.Comment: to appear in the proceedings of the 2012 Moriond cosmology meetin
The Inclination Distribution of the Kuiper Belt
We develop a general method for determining the unbiased inclination distribution of the Kuiper belt using only the inclination and latitude of discovery of known Kuiper belt objects (KBOs). These two parameters are well determined for each discovered object, so we can use all 379 known KBOs (as of 2001 January 1)—without knowing the object's precise orbit, area, detection efficiency, or the latitudinal coverage of the survey that found the object—to determine the inclination distribution. We find that a natural analytic form for the inclination distribution is a sine of the inclination multiplied by a Gaussian. The inclination distribution of all KBOs is well fitted by sin i multiplied by a sum of two Gaussians with widths 2°.6^(+.8)_(-.2) and 15° ± 1°. For this inclination distribution, the Kuiper belt has an effective area of 8100^(+1500)-(-1100) deg^2 and a FWHM of 12.5° ± 3.5° in latitude. The inclination distribution of the different dynamical classes appear different. The Plutinos are well fit by sin i mulitplied by a single Gaussian of width 10°.2^(+2.5)_(-1.8), the classical KBOs cannot be fit to a single Gaussian but are well fit by sin i multiplied by the sum of two Gaussians of widths 2°.2^(+.2)_(-.6) and 17° ± 3°, and the scattered KBOs are poorly fit by sin i multiplied by a single Gaussian of width 20° ± 4°. The poor fit of the scattered objects is possibly a result of limitations of the method in dealing with large eccentricities. The effective areas of the Plutinos, classical KBOs, and scattered KBOs are 9300 ± 1800, 6100 ± 2100, and 17000 ± 3000 deg^2, respectively. The FWHMs are 23° ± 5°, 6°.8^(+2.0)_(-3.6), and 44° ± 10°, respectively. In all cases, the inclinations of the Kuiper belt objects appear larger than expected from dynamical simulations of possible perturbations
A case study of student projects for industry clients
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Conformity, deformity and reformity
In any given field of artistic practice, practitioners position themselves—or find themselves positioned—according to interests and allegiances with specific movements, genres, and traditions. Selecting particular frameworks through which to approach the development of new ideas, patterns and expressions, balance is invariably maintained between the desire to contribute towards and connect with a particular set of domain conventions, whilst at the same time developing distinction and recognition as a creative individual. Creativity through the constraints of artistic domain, discipline and style provides a basis for consideration of notions of originality in the context of activity primarily associated with reconfiguration, manipulation and reorganisation of existing elements and ideas. Drawing from postmodern and post-structuralist perspectives in the analysis of modern hybrid art forms and the emergence of virtual creative environments, the transition from traditional artistic practice and notions of craft and creation, to creative spaces in which elements are manipulated, mutated, combined and distorted with often frivolous or subversive intent are considered. This paper presents an educational and musically focused perspective of the relationship between the individual and domain-based creative practice. Drawing primarily from musical and audio-visual examples with particular interest in creative disruption of pre-existing elements, creative strategies of appropriation and recycling are explored in the context of music composition and production. Conclusions focus on the interpretation of creativity as essentially a process of recombination and manipulation and highlight how the relationship between artist and field of practice creates unique creative spaces through which new ideas emerge
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