47 research outputs found
The Sariçiçek Howardite Fall in Turkey: Source Crater of HED Meteorites on Vesta and İmpact Risk of Vestoids
The Sariçiçek howardite meteorite shower consisting of 343 documented stones
occurred on 2 September 2015 in Turkey and is the first documented howardite fall. Cosmogenic
isotopes show that Sariçiçek experienced a complex cosmic ray exposure history, exposed during
~12–14 Ma in a regolith near the surface of a parent asteroid, and that an ~1 m sized meteoroid
was launched by an impact 22 ± 2 Ma ago to Earth (as did one third of all HED meteorites). SIMS
dating of zircon and baddeleyite yielded 4550.4 ± 2.5 Ma and 4553 ± 8.8 Ma crystallization ages
for the basaltic magma clasts. The apatite U-Pb age of 4525 ± 17 Ma, K-Ar age of ~3.9 Ga, and
the U,Th-He ages of 1.8 ± 0.7 and 2.6 ± 0.3 Ga are interpreted to represent thermal metamorphic
and impact-related resetting ages, respectively. Petrographic, geochemical and O-, Cr- and Tiisotopic
studies confirm that Sariçiçek belongs to the normal clan of HED meteorites. Petrographic
observations and analysis of organic material indicate a small portion of carbonaceous chondrite
material in the Sariçiçek regolith and organic contamination of the meteorite after a few days on
soil. Video observations of the fall show an atmospheric entry at 17.3 ± 0.8 kms-1 from NW,
fragmentations at 37, 33, 31 and 27 km altitude, and provide a pre-atmospheric orbit that is the
first dynamical link between the normal HED meteorite clan and the inner Main Belt. Spectral data
indicate the similarity of Sariçiçek with the Vesta asteroid family (V-class) spectra, a group of
asteroids stretching to delivery resonances, which includes (4) Vesta. Dynamical modeling of
meteoroid delivery to Earth shows that the complete disruption of a ~1 km sized Vesta family
asteroid or a ~10 km sized impact crater on Vesta is required to provide sufficient meteoroids ≤4
m in size to account for the influx of meteorites from this HED clan. The 16.7 km diameter Antonia
impact crater on Vesta was formed on terrain of the same age as given by the 4He retention age of
Sariçiçek. Lunar scaling for crater production to crater counts of its ejecta blanket show it was
formed ~22 Ma ago
HLA-DQA1*05 carriage associated with development of anti-drug antibodies to infliximab and adalimumab in patients with Crohn's Disease
Anti-tumor necrosis factor (anti-TNF) therapies are the most widely used biologic drugs for treating immune-mediated diseases, but repeated administration can induce the formation of anti-drug antibodies. The ability to identify patients at increased risk for development of anti-drug antibodies would facilitate selection of therapy and use of preventative strategies.This article is freely available via Open Access. Click on Publisher URL to access the full-text
Cooperative path planning for timing-critical missions
This paper presents a cooperative path planning approach for teams of vehicles operating under timing constraints. A cooperative control approach based on coordination variables and coordination functions is introduced and applied to cooperative timing problems. Three types of timing constraints are considered: simultaneous arrival, tight sequencing, and loose sequencing. Simulation results demonstrating the approach are presented.
Vector field path following for small unmanned air vehicles
Abstract — This paper presents a new method for unmanned aerial vehicle path following using vector fields to represent desired ground track headings to direct the vehicle onto the desired path. The key feature of this approach is that ground track heading error and lateral following error approach zero asymptotically even in the presence of constant wind disturbances. Methods for following straight-line and circularorbit paths, as well as combinations of straight lines and arcs, are presented. Experimental results validate the effectiveness of this path following approach for small air vehicles flying in high-wind conditions. I
Visionbased target localization from a fixed-wing miniature air vehicle
Abstract — This paper presents a method for localizing a ground-based object when imaged from a small fixed-wing unmanned aerial vehicle (UAV). Using the pixel location of the target in an image, with measurements of UAV position and attitude, and camera pose angles, the target is localized in world coordinates. This paper presents a study of possible error sources and localization sensitivities to each source. The localization method has been implemented and experimental results are presented demonstrating the localization of a target to within 11 m of its known location. I