6,891 research outputs found
The Maguindanao Massacre, critical elections and armed conflict in the Philippines
The Maguindanao Massacre has sent shock waves through the Philippines and beyond. A convoy of cars was caught in an armed ambush on Monday 23 November, leaving at least 57 persons dead, with mutilated bodies and crushed vehicles found buried in large pits. The convoy was destined for the Commission of Elections office in Shariff Aguak town, Magindanao Province in the Autonomous Region of Muslim Mindanao (ARMM). The purpose was to file local vice mayor Esmael Mangudadatu’s certificate of candidacy to run for the governorship of Maguindanao province in the May 2010 Philippine elections. Among the victims of the massacre were at least 30 journalists, more than 20 women, including the wife and two sisters of Mangudadatu
The shape and dynamics of a heliotropic dusty ringlet in the Cassini Division
The so-called "Charming Ringlet" (R/2006 S3) is a low-optical-depth, dusty
ringlet located in the Laplace gap in the Cassini Division. This ringlet is
particularly interesting because its radial position varies systematically with
longitude relative to the Sun in such a way that the ringlet's geometric center
appears to be displaced away from Saturn's center in a direction roughly toward
the Sun. In other words, the ringlet is always found at greater distances from
the planet's center at longitudes near the sub-solar longitude than it is at
longitudes near Saturn's shadow. This "heliotropic" behavior indicates that the
dynamics of the particles in this ring are being influenced by solar radiation
pressure. In order to investigate this phenomenon, which has been predicted
theoretically but has never been observed this clearly, we analyze multiple
image sequences of this ringlet obtained by Cassini in order to constrain its
shape and orientation. These data can be fit reasonably well with a model in
which both the eccentricity and the inclination of the ringlet have "forced"
components (that maintain a fixed orientation relative to the Sun) as well as
"free" components (that drift around the planet at steady rates determined by
Saturn's oblateness). While the magnitude of the forced eccentricity is roughly
consistent with theoretical expectations for radiation pressure acting on
10-to-100-micron-wide icy grains, the existence of significant free
eccentricities and inclinations poses a significant challenge for models of
low-optical-depth dusty rings.Comment: 31 pages, 6 figures, accepted for publication in Icarus. Slight edits
made to match various proof correction
The B-ring's surface mass density from hidden density waves: Less than meets the eye?
Saturn's B ring is the most opaque ring in our solar system, but many of its
fundamental parameters, including its total mass, are not well constrained.
Spiral density waves generated by mean-motion resonances with Saturn's moons
provide some of the best constraints on the rings' mass density, but detecting
and quantifying such waves in the B ring has been challenging because of this
ring's high opacity and abundant fine-scale structure. Using a wavelet-based
analyses of 17 occultations of the star gamma Crucis observed by the Visual and
Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft, we are
able to examine five density waves in the B ring. Two of these waves are
generated by the Janus 2:1 and Mimas 5:2 Inner Lindblad Resonances at 96,427 km
and 101,311 km from Saturn's center, respectively. Both of these waves can be
detected in individual occultation profiles, but the multi-profile wavelet
analysis reveals unexpected variations in the pattern speed of the Janus 2:1
wave that might arise from the periodic changes in Janus' orbit. The other
three wave signatures are associated with the Janus 3:2, Enceladus 3:1 and
Pandora 3:2 Inner Lindblad Resonances at 115,959 km, 115,207 km and 108,546 km.
These waves are not visible in individual profiles, but structures with the
correct pattern speeds can be detected in appropriately phase-corrected average
wavelets. Estimates of the ring's surface mass density derived from these five
waves fall between 40 and 140 g/cm^2, even though the ring's optical depth in
these regions ranges from 1.5 to almost 5. This suggests that the total mass of
the B ring is most likely between one-third and two-thirds the mass of Saturn's
moon Mimas.Comment: 40 Pages, 21 Figures, Accepted for publication in Icarus, a few typos
fixe
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