685 research outputs found
The Contributions of United Nations Security Council Resolutions to the Law of Non-International Armed Conflict: New Evidence of Customary International Law
Does Schopenhauer accept any positive pleasures?
Schopenhauer repeatedly claims that all pleasure is negative, and this view seems to play key roles throughout his work. Nonetheless, many scholars have argued that Schopenhauer actually acknowledges certain positive pleasures. Two major arguments have been offered for this reading, one focused on the link between Schopenhauer's view of pleasure and Plato's, and one focused on Schopenhauer's distinction between two components of aesthetic pleasure. I argue that neither way of motivating the positive pleasure reading succeeds. Both overlook a key aspect of Schopenhauer's account: namely, his suggestion that there are two distinct kinds of negative pleasure, pleasures of satisfaction and pleasures of distraction. When Schopenhauer claims that all pleasure is negative, he means it
CubeSat Proximity Operations Demonstration (CPOD) Mission Results
CubeSat rendezvous and proximity operation (RPO) technology development is critical for improving the performance and economics of space debris remediation and the inspection, servicing, and assembly of larger space systems. The CubeSat Proximity Operations Demonstration (CPOD) is a program led by Terran Orbital and funded by NASA to achieve autonomous on-orbit RPO with two identical 3U CubeSats, thereby maturing CubeSat RPO technology. This article presents the CPOD RPO guidance architecture and its on-orbit outcomes. The architecture advances the autonomy, fuel-efficiency, and safety of CubeSat RPO through the synthesis of optimization-based control theory and orbital dynamics analysis, with different optimization techniques tailored to different stages of the mission. Fully autonomous stages frequently, regularly recompute optimization solutions onboard the vehicles, each time using new measured data to provide robustness to unmodeled force disturbances. RPO is supported by a unique docking magnet control scheme for angular momentum management, a thruster configuration yielding 3DOF translational control, and a data-driven intersatellite distance prediction method for advance (12-200 hours) RPO planning. Ultimately this framework yielded rendezvous of the vehicles from intersatellite distances up to 997 km, a minimum intersatellite distance of 361 m, and passively safe formation flying across 5 major on-orbit experiments
Constraints on the Progenitor of SN 2010jl and Pre-Existing Hot Dust in its Surrounding Medium
A search for the progenitor of SN~2010jl, an unusually luminous core-collapse
supernova of Type~IIn, using pre-explosion {\it Hubble}/WFPC2 and {\it
Spitzer}/IRAC images of the region, yielded upper limits on the UV and
near-infrared (IR) fluxes from any candidate star. These upper limits constrain
the luminosity and effective temperature of the progenitor, the mass of any
preexisting dust in its surrounding circumstellar medium (CSM), and dust
proximity to the star. A {\it lower} limit on the CSM dust mass is required to
hide a luminous progenitor from detection by {\it Hubble}. {\it Upper} limits
on the CSM dust mass and constraints on its proximity to the star are set by
requiring that the absorbed and reradiated IR emission not exceed the IRAC
upper limits. Using the combined extinction-IR emission constraints we present
viable combinations, where and are the CSM dust mass and
its inner radius. These depend on the CSM outer radius, dust composition and
grain size, and the properties of the progenitor. The results constrain the
pre-supernova evolution of the progenitor, and the nature and origin of the
observed post-explosion IR emission from SN~2010jl. In particular, an
~Car-type progenitor will require at least 4~mag of visual extinction to
avoid detection by the {\it Hubble}. This can be achieved with dust masses
~\msun\ (less than the estimated 0.2-0.5~\msun\ around
~Car) which must be located at distances of ~cm from the
star to avoid detection by {\it Spitzer}.Comment: Accepted for publication in the ApJ. 14 pages 10 figures. The
complete figure set for Figure 10 (24 images) is available in the online
journa
Asphericity, Interaction, and Dust in the Type II-P/II-L Supernova 2013ej in Messier 74
SN 2013ej is a well-studied core-collapse supernova (SN) that stemmed from a
directly identified red supergiant (RSG) progenitor in galaxy M74. The source
exhibits signs of substantial geometric asphericity, X-rays from persistent
interaction with circumstellar material (CSM), thermal emission from warm dust,
and a light curve that appears intermediate between supernovae of Types II-P
and II-L. The proximity of this source motivates a close inspection of these
physical characteristics and their potential interconnection. We present
multi-epoch spectropolarimetry of SN 2013ej during the first 107 days, and deep
optical spectroscopy and ultraviolet through infrared photometry past ~800
days. SN 2013ej exhibits the strongest and most persistent continuum and line
polarization ever observed for a SN of its class during the recombination
phase. Modeling indicates that the data are consistent with an oblate
ellipsoidal photosphere, viewed nearly edge-on, and probably augmented by
optical scattering from circumstellar dust. We suggest that interaction with an
equatorial distribution of CSM, perhaps the result of binary evolution, is
responsible for generating the photospheric asphericity. Relatedly, our
late-time optical imaging and spectroscopy shows that asymmetric CSM
interaction is ongoing, and the morphology of broad H-alpha emission from
shock-excited ejecta provides additional evidence that the geometry of the
interaction region is ellipsoidal. Alternatively, a prolate ellipsoidal
geometry from an intrinsically bipolar explosion is also a plausible
interpretation of the data, but would probably require a ballistic jet of
radioactive material capable of penetrating the hydrogen envelope early in the
recombination phase (abridged).Comment: Post-proof edit. Accepted to ApJ on Nov. 23 2016; 21 pages, 16
figure
Neural Networks and Dynamic Complex Systems
We describe the use of neural networks for optimization and inference associated with a variety of complex systems. We show how a string formalism can be used for parallel computer decomposition, message routing and sequential optimizing compilers. We extend these ideas to a general treatment of spatial assessment and distributed artificial intelligence
The Progenitor of Supernova 2011dh Has Vanished
We conducted Hubble Space Telescope (HST) Snapshot observations of the Type
IIb Supernova (SN) 2011dh in M51 at an age of ~641 days with the Wide Field
Camera 3. We find that the yellow supergiant star, clearly detected in pre-SN
HST images, has disappeared, implying that this star was almost certainly the
progenitor of the SN. Interpretation of the early-time SN data which led to the
inference of a compact nature for the progenitor, and to the expected survival
of this yellow supergiant, is now clearly incorrect. We also present
ground-based UBVRI light curves obtained with the Katzman Automatic Imaging
Telescope (KAIT) at Lick Observatory up to SN age ~70 days. From the
light-curve shape including the very late-time HST data, and from recent
interacting binary models for SN 2011dh, we estimate that a putative surviving
companion star to the now deceased yellow supergiant could be detectable by
late 2013, especially in the ultraviolet. No obvious light echoes are
detectable yet in the SN environment.Comment: 6 pages, new versions of the 3 figures, improved U-band SN
photometry, to appear in ApJ Letter
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