396 research outputs found
The Primary Volatile Composition of Comet C/2012 K1 (PanSTARRS)
On 2014 May 22 and 24 we characterized the volatile composition of the dynamically new Oort cloud comet C/2012 K1 (PanSTARRS) using the long-slit, high resolution (λ/Îλ â 25,000) infrared echelle spectrograph (NIRSPEC) at the 10 m Keck 2 telescope on Maunakea, HI. We detected fluorescent emission from six primary volatiles (H2O, HCN, CH4, C2H6, CH3OH, and CO). Upper limits were derived for C2H2, NH3, and H2CO. We report rotational temperatures, production rates, and mixing ratios (relative to water). Compared with median abundance ratios for primary volatiles in other sampled Oort cloud comets, trace gas abundance ratios in C/2012 K1 (PanSTARRS) for CO, CH4, and HCN are consistent, but CH3OH and C2H6 are enriched while H2CO and possibly C2H2 are depleted. When placed in context with comets observed in the near infrared to date, the data suggest a continuous distribution of abundances of some organic volatiles among the comet population
PSpectRe: A Pseudo-Spectral Code for (P)reheating
PSpectRe is a C++ program that uses Fourier-space pseudo-spectral methods to
evolve interacting scalar fields in an expanding universe. PSpectRe is
optimized for the analysis of parametric resonance in the post-inflationary
universe, and provides an alternative to finite differencing codes, such as
Defrost and LatticeEasy. PSpectRe has both second- (Velocity-Verlet) and
fourth-order (Runge-Kutta) time integrators. Given the same number of spatial
points and/or momentum modes, PSpectRe is not significantly slower than finite
differencing codes, despite the need for multiple Fourier transforms at each
timestep, and exhibits excellent energy conservation. Further, by computing the
post-resonance equation of state, we show that in some circumstances PSpectRe
obtains reliable results while using substantially fewer points than a finite
differencing code. PSpectRe is designed to be easily extended to other problems
in early-universe cosmology, including the generation of gravitational waves
during phase transitions and pre-inflationary bubble collisions. Specific
applications of this code will be pursued in future work.Comment: 22 pages; source code for PSpectRe available:
http://easther.physics.yale.edu v2 Typos fixed, minor improvements to
wording; v3 updated as per referee comment
A unified model for tidal disruption events
In the past few years wide-field optical and UV transient surveys as well as
X-ray telescopes have allowed us to identify a few dozen candidate tidal
disruption events (TDEs). While in theory the physical processes in TDEs are
expected to be ubiquitous, a few distinct classes of TDEs have been observed.
Some TDEs radiate mainly in NUV/optical while others produce prominent X-rays.
Moreover, relativistic jets have been observed in only a handful of TDEs. This
diversity might be related to the details of the super-Eddington accretion and
emission physics relevant to TDE disks. In this Letter, we utilize novel
three-dimensional general relativistic radiation magnetohydrodynamics
simulations to study the super-Eddington compact disk phase expected in TDEs.
Consistent with previous studies, geometrically thick disks, wide-angle
optically-thick fast outflows and relativistic jets are produced. The outflow
density and velocity depend sensitively on the inclination angle, and hence so
does the reprocessing of emission produced from the inner disk. We then use
Monte-Carlo radiative transfer to calculate the reprocessed spectra and find
that that the observed ratio of optical to X-ray fluxes increases with
increasing inclination angle. This naturally leads to a unified model for
different classes of TDEs in which the spectral properties of the TDE depend
mainly on the viewing-angle of the observer with respect to the orientation of
the disk.Comment: Accepted to ApJ Letter
Radiative Emission Mechanisms of Tidal Disruption Events
We describe how the various outcomes of stellar tidal disruption give rise to
observable radiation. We separately consider the cases where gas circularizes
rapidly into an accretion disc, as well as the case when shocked debris streams
provide the observable emission without having fully circularized. For the
rapid circularization case, we describe how outflows, absorption by
reprocessing layers, and Comptonization can cause the observed radiation to
depart from that of a bare disc, possibly giving rise to the observed
optical/UV emission along with soft X-rays from the disc. If, instead, most of
the debris follows highly eccentric orbits for a significant time, many
properties of the observed optical/UV emission can be explained by the scale of
those eccentric orbits and the shocks embedded in the debris flow near orbital
apocenter. In this picture, soft X-ray emission at early times results from the
smaller amount of debris mass deflected into a compact accretion disc by weak
shocks near the stellar pericenter. A general proposal for the near-constancy
of the ultraviolet/optical color temperatures is provided, by linking it to
incomplete thermalization of radiation in the atmosphere of the emitting
region. We also briefly discuss the radio signals from the interaction of
unbound debris and jets with the black hole environment.Comment: Accepted for publication in Springer Space Science Reviews. Chapter
in ISSI review "The Tidal Disruption of Stars by Massive Black Holes" vol. 7
Biocompatibility and Physiological Thiolytic Degradability of Radically Made Thioester-Functional Copolymers: Opportunities for Drug Release
Being nondegradable, vinyl polymers have limited biomedical applicability. Unfortunately, backbone esters incorporated through conventional radical ring-opening methods do not undergo appreciable abiotic hydrolysis under physiologically relevant conditions. Here, PEG acrylate and di(ethylene glycol) acrylamide-based copolymers containing backbone thioesters were prepared through the radical ring-opening copolymerization of the thionolactone dibenzo[c,e]oxepin-5(7H)-thione. The thioesters degraded fully in the presence of 10 mM cysteine at pH 7.4, with the mechanism presumed to involve an irreversible SâN switch. Degradations with N-acetylcysteine and glutathione were reversible through the thiolâthioester exchange polycondensation of RâSC(âO)âpolymerâSH fragments with full degradation relying on an increased thiolate/thioester ratio. Treatment with 10 mM glutathione at pH 7.2 (mimicking intracellular conditions) triggered an insolubleâsoluble switch of a temperature-responsive copolymer at 37 °C and the release of encapsulated Nile Red (as a drug model) from core-degradable diblock copolymer micelles. Copolymers and their cysteinolytic degradation products were found to be noncytotoxic, making thioester backbone-functional polymers promising for drug delivery applications
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