1,186 research outputs found
Ornamental colors reveal age in the king penguin
We investigated whether delayed plumage maturation occurred in king penguins (Aptenodytes patagonicus). Therefore we examined the relationships between age and sex on spectral properties and size of two colored plumage patches and a UV-reflective beak spot, using known-age cohorts. Unlike the colored patch on the breast, we found age differences in ear and beak coloration. These results suggest that head ornaments in king penguins could signal sexual maturity or social status. No sex differences were found in the intensity of colored ornaments, which can result from mutual mate choice or genetic correlation between sexes. Size of colored patches did not relate to age or sex
SGARFACE: A Novel Detector For Microsecond Gamma Ray Bursts
The Short GAmma Ray Front Air Cherenkov Experiment (SGARFACE) is operated at
the Whipple Observatory utilizing the Whipple 10m gamma-ray telescope. SGARFACE
is sensitive to gamma-ray bursts of more than 100MeV with durations from 100ns
to 35us and provides a fluence sensitivity as low as 0.8 gamma-rays per m^2
above 200MeV (0.05 gamma-rays per m^2 above 2GeV) and allows to record the
burst time structure.Comment: 29 pages, 14 figures, accepted for publication in Astroparticle
Physic
Polyoxazoline-Based Bottlebrush and Brush-Arm Star Polymers via ROMP: Syntheses and Applications as Organic Radical Contrast Agents
Copyright © 2019 American Chemical Society. The synthesis of functional poly(2-alkyl-2-oxazoline) (PAOx) copolymers with complex nanoarchitectures using a graft-through ring-opening metathesis polymerization (ROMP) approach is described. First, well-defined norbornene-terminated poly(2-ethyl-2-oxazoline) (PEtOx) macromonomers (MM) were prepared by cationic ring-opening polymerization. ROMP of these MMs produced bottlebrush copolymers with PEtOx side chains. In addition, PEtOx-based branched MMs bearing a terminal alkyne group were prepared and conjugated to an azide-containing bis-spirocyclohexyl nitroxide via Cu-catalyzed azide-alkyne cycloaddition (CuAAC). ROMP of this branched MM, followed by in situ cross-linking, provided PEtOx-based brush-arm star polymers (BASPs) with nitroxide radicals localized at the core-shell interface. These PEtOx-based nitroxide-containing BASPs displayed relaxivity values on par with state-of-the-art polyethylene glycol (PEG)-based nitroxide materials, making them promising as organic radical contrast agents for metal-free magnetic resonance imaging (MRI)
Large time behavior and asymptotic stability of the two-dimensional Euler and linearized Euler equations
We study the asymptotic behavior and the asymptotic stability of the
two-dimensional Euler equations and of the two-dimensional linearized Euler
equations close to parallel flows. We focus on spectrally stable jet profiles
with stationary streamlines such that , a case that
has not been studied previously. We describe a new dynamical phenomenon: the
depletion of the vorticity at the stationary streamlines. An unexpected
consequence, is that the velocity decays for large times with power laws,
similarly to what happens in the case of the Orr mechanism for base flows
without stationary streamlines. The asymptotic behaviors of velocity and the
asymptotic profiles of vorticity are theoretically predicted and compared with
direct numerical simulations. We argue on the asymptotic stability of these
flow velocities even in the absence of any dissipative mechanisms.Comment: To be published in Physica D, nonlinear phenomena (accepted January
2010
Models of turbulent dissipation regions in the diffuse interstellar medium
Supersonic turbulence is a large reservoir of suprathermal energy in the
interstellar medium. Its dissipation, because it is intermittent in space and
time, can deeply modify the chemistry of the gas. We further explore a hybrid
method to compute the chemical and thermal evolution of a magnetized
dissipative structure, under the energetic constraints provided by the observed
properties of turbulence in the cold neutral medium. For the first time, we
model a random line of sight by taking into account the relative duration of
the bursts with respect to the thermal and chemical relaxation timescales of
the gas. The key parameter is the turbulent rate of strain "a" due to the
ambient turbulence. With the gas density, it controls the size of the
dissipative structures, therefore the strength of the burst. For a large range
of rates of strain and densities, the models of turbulent dissipation regions
(TDR) reproduce the CH+ column densities observed in the diffuse medium and
their correlation with highly excited H2. They do so without producing an
excess of CH. As a natural consequence, they reproduce the abundance ratios of
HCO+/OH and HCO+/H2O, and their dynamic range of about one order of magnitude
observed in diffuse gas. Large C2H and CO abundances, also related to those of
HCO+, are another outcome of the TDR models that compare well with observed
values. The abundances and column densities computed for CN, HCN and HNC are
one order of magnitude above PDR model predictions, although still
significantly smaller than observed values
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