4,545 research outputs found
Estimating Column Density in Molecular Clouds with FIR and Sub-mm Emission Maps
We have used a numerical simulation of a turbulent cloud to synthesize maps
of the thermal emission from dust at a variety of far-IR and sub-mm
wavelengths. The average column density and external radiation field in the
simulation is well matched to clouds such as Perseus and Ophiuchus. We use
pairs of single-wavelength emission maps to derive the dust color temperature
and column density, and we compare the derived column densities with the true
column density. We demonstrate that longer wavelength emission maps yield less
biased estimates of column density than maps made towards the peak of the dust
emission spectrum. We compare the scatter in the derived column density with
the observed scatter in Perseus and Ophiuchus. We find that while in Perseus
all of the observed scatter in the emission-derived versus the
extinction-derived column density can be attributed to the flawed assumption of
isothermal dust along each line of sight, in Ophiuchus there is additional
scatter above what can be explained by the isothermal assumption. Our results
imply that variations in dust emission properties within a molecular cloud are
not necessarily a major source of uncertainty in column density measurements.Comment: Accepted to ApJ Letter
High-frequency gate manipulation of a bilayer graphene quantum dot
We report transport data obtained for a double-gated bilayer graphene quantum
dot. In Coulomb blockade measurements, the gate dielectric Cytop(TM) is found
to provide remarkable electronic stability even at cryogenic temperatures.
Moreover, we demonstrate gate manipulation with square shaped voltage pulses at
frequencies up to 100 MHz and show that the signal amplitude is not affected by
the presence of the capacitively coupled back gate
Understanding angular momentum transport in red giants: the case of KIC 7341231
Context. Thanks to recent asteroseismic observations, it has been possible to
infer the radial differential rotation profile of subgiants and red giants.
Aims. We want to reproduce through modeling the observed rotation profile of
the early red giant KIC 7341231 and constrain the physical mechanisms
responsible for angular momentum transport in stellar interiors.
Methods. We compute models of KIC 7341231 including a treatment of shellular
rotation and we compare the rotation profiles obtained with the one derived by
Deheuvels et al. (2012). We then modify some modeling parameters in order to
quantify their effect on the obtained rotation profile. Moreover, we mimic a
powerful angular momentum transport during the Main Sequence and study its
effect on the evolution of the rotation profile during the subgiant and red
giant phases.
Results. We show that meridional circulation and shear mixing alone produce a
rotation profile for KIC 7341231 too steep compared to the observed one. An
additional mechanism is then needed to increase the internal transport of
angular momentum. We find that this undetermined mechanism has to be efficient
not only during the Main Sequence but also during the much quicker subgiant
phase. Moreover, we point out the importance of studying the whole rotational
history of a star in order to explain its rotation profile during the red giant
evolution.Comment: 8 pages, 8 figures, 5 table
Senior Reflections
Wow, I made it! It’s hard to believe that only four years ago I was moving into a place where I didn’t know anybody and had no idea what to expect. I thought seniors were old and graduation was a very distant goal, but now I’m a graduated senior wondering where those four years went
VEISHEA 2002
VEISHEA 2002 brought with it a lot of success for the forestry club. This year’s co-chairs were T.J. Mathis and Brooke Arp, but we couldn’t have pulled it off without the help of many people within the university
Simulating circuits with impasse points
In this paper circuits with impasse points, i.e. with jumps in their
configuration space will be analyzed. These non-regularized circuits exhibit
a fold in their configuration space, which can lead to difficulties during
the simulation with standard circuit simulators like SPICE. The former
developed geometric approach to simulate these circuits without
regularization will be extended by a detailed discussion of which coordinate
system has to be chosen. Furthermore, two new approaches for a numerically
efficient calculation of the hit points will be shown
When the going gets rough – studying the effect of surface roughness on the adhesive abilities of tree frogs
Tree frogs need to adhere to surfaces of various roughnesses in their natural habitats; these include bark, leaves and rocks. Rough
surfaces can alter the effectiveness of their toe pads, due to factors such as a change of real contact area and abrasion of the pad
epithelium. Here, we tested the effect of surface roughness on the attachment abilities of the tree frog Litoria caerulea. This was
done by testing shear and adhesive forces on artificial surfaces with controlled roughness, both on single toe pads and whole animal
scales. It was shown that frogs can stick 2–3 times better on small scale roughnesses (3–6 µm asperities), producing higher adhesive
and frictional forces, but relatively poorly on the larger scale roughnesses tested (58.5–562.5 µm asperities). Our experiments
suggested that, on such surfaces, the pads secrete insufficient fluid to fill the space under the pad, leaving air pockets that would
significantly reduce the Laplace pressure component of capillarity. Therefore, we measured how well the adhesive toe pad would
conform to spherical asperities of known sizes using interference reflection microscopy. Based on experiments where the conformation
of the pad to individual asperities was examined microscopically, our calculations indicate that the pad epithelium has a low
elastic modulus, making it highly deformable
CP and related phenomena in the context of Stellar Evolution
We review the interaction in intermediate and high mass stars between their
evolution and magnetic and chemical properties. We describe the theory of
Ap-star `fossil' fields, before touching on the expected secular diffusive
processes which give rise to evolution of the field. We then present recent
results from a spectropolarimetric survey of Herbig Ae/Be stars, showing that
magnetic fields of the kind seen on the main-sequence already exist during the
pre-main sequence phase, in agreement with fossil field theory, and that the
origin of the slow rotation of Ap/Bp stars also lies early in the pre-main
sequence evolution; we also present results confirming a lack of stars with
fields below a few hundred gauss. We then seek which macroscopic motions
compete with atomic diffusion in determining the surface abundances of AmFm
stars. While turbulent transport and mass loss, in competition with atomic
diffusion, are both able to explain observed surface abundances, the interior
abundance distribution is different enough to potentially lead to a test using
asterosismology. Finally we review progress on the turbulence-driving and
mixing processes in stellar radiative zones.Comment: Proceedings of IAU GA in Rio, JD4 on Ap stars; 10 pages, 7 figure
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