10,896 research outputs found
The Ultraviolet Attenuation Law in Backlit Spiral Galaxies
(Abridged) The effective extinction law (attenuation behavior) in galaxies in
the emitted ultraviolet is well known only for actively star-forming objects
and combines effects of the grain properties, fine structure in the dust
distribution, and relative distributions of stars and dust. We use GALEX, XMM
Optical Monitor, and HST data to explore the UV attenuation in the outer parts
of spiral disks which are backlit by other UV-bright galaxies, starting with
candidates provided by Galaxy Zoo participants. Our analysis incorporates
galaxy symmetry, using non-overlapping regions of each galaxy to derive error
estimates on the attenuation measurements. The entire sample has an attenuation
law close to the Calzetti et al. (1994) form; the UV slope for the overall
sample is substantially shallower than found by Wild et al. (2011), a
reasonable match to the more distant galaxies in our sample but not to the
weighted combination including NGC 2207. The nearby, bright spiral NGC 2207
alone gives accuracy almost equal to the rest of our sample, and its outer arms
have a very low level of foreground starlight. This "grey" law can be produced
from the distribution of dust alone, without a necessary contribution from
differential escape of stars from dense clouds. The extrapolation needed to
compare attenution between backlit galaxies at moderate redshifts, and local
systems from SDSS data, is mild enough to allow use of galaxy overlaps to trace
the cosmic history of dust. For NGC 2207, the covering factor of clouds with
small optical attenuation becomes a dominant factor farther into the
ultraviolet, which opens the possibility that widespread diffuse dust dominates
over dust in star-forming regions deep into the ultraviolet. Comparison with
published radiative-transfer models indicates that the role of dust clumping
dominates over differences in grain populations, at this spatial resolution.Comment: In press, Astronomical Journa
Sofic-Dyck shifts
We define the class of sofic-Dyck shifts which extends the class of
Markov-Dyck shifts introduced by Inoue, Krieger and Matsumoto. Sofic-Dyck
shifts are shifts of sequences whose finite factors form unambiguous
context-free languages. We show that they correspond exactly to the class of
shifts of sequences whose sets of factors are visibly pushdown languages. We
give an expression of the zeta function of a sofic-Dyck shift
Measurement of correlations between low-frequency vibrational modes and particle rearrangements in quasi-two-dimensional colloidal glasses
We investigate correlations between low-frequency vibrational modes and
rearrangements in two-dimensional colloidal glasses composed of thermosensitive
microgel particles which readily permit variation of sample packing fraction.
At each packing fraction, the particle displacement covariance matrix is
measured and used to extract the vibrational spectrum of the "shadow" colloidal
glass (i.e., the particle network with the same geometry and interactions as
the sample colloid but absent damping). Rearrangements are induced by
successive, small reductions in packing fraction. The experimental results
suggest that low-frequency quasi-localized phonon modes in colloidal glasses,
i.e., modes that present low energy barriers for system rearrangements, are
spatially correlated with rearrangements in this thermal system
Measurements of winds and temperatures at altitudes up to 65 kilometers in the Southern Hemisphere
Meteorological wind, and temperature data from atmospheric radiosonde soundings in Southern Hemispher
Superintegrability on the two-dimensional hyperboloid
In this work we examine the basis functions for classical and quantum mechanical systems on the two-dimensional hyperboloid that admit separation of variables in at least two coordinate systems. We present all of these cases from a unified point of view. In particular, all of the special functions that arise via variable separation have their essential features expressed in terms of their zeros. The principal new results are the details of the polynomial bases for each of the nonsubgroup bases, not just the subgroup spherical coordinate cases, and the details of the structure of the quadratic symmetry algebras
Photon collection from a trapped ion--cavity system
We present the design and implementation of a trapped ion cavity QED system.
A single ytterbium ion is confined by a micron-scale ion trap inside a 2 mm
optical cavity. The ion is coherently pumped by near resonant laser light while
the cavity output is monitored as a function of pump intensity and cavity
detuning. We observe a Purcell enhancement of scattered light into the solid
angle subtended by the optical cavity, as well as a three-peak structure
arising from strongly driving the atom. This system can be integrated into
existing atom{photon quantum network protocols and is a pathway towards an
efficient atom{photon quantum interface
A variant in LIN28B is associated with 2D:4D finger-length ratio, a putative retrospective biomarker of prenatal testosterone exposure
The ratio of the lengths of an individual's second to fourth digit (2D:4D) is commonly used as a noninvasive retrospective biomarker for prenatal androgen exposure. In order to identify the genetic determinants of 2D:4D, we applied a genome-wide association approach to 1507 11-year-old children from the Avon Longitudinal Study of Parents and Children (ALSPAC) in whom 2D:4D ratio had been measured, as well as a sample of 1382 12- to 16-year-olds from the Brisbane Adolescent Twin Study. A meta-analysis of the two scans identified a single variant in the LIN28B gene that was strongly associated with 2D:4D (rs314277: p = 4.1 108) and was subsequently independently replicated in an additional 3659 children from the ALSPAC cohort (p = 1.53 106). The minor allele of the rs314277 variant has previously been linked to increased height and delayed age at menarche, but in our study it was associated with increased 2D:4D in the direction opposite to that of previous reports on the correlation between 2D:4D and age at menarche. Our findings call into question the validity of 2D:4D as a simplistic retrospective biomarker for prenatal testosterone exposure
Temperature Effects on Threshold Counterion Concentration to Induce Aggregation of fd Virus
We seek to determine the mechanism of like-charge attraction by measuring the
temperature dependence of critical divalent counterion concentration
() for the aggregation of fd viruses. We find that an increase in
temperature causes to decrease, primarily due to a decrease in the
dielectric constant () of the solvent. At a constant ,
is found to increase as the temperature increases. The effects of
and on can be combined to that of one parameter:
Bjerrum length (). decreases exponentially as
increases, suggesting that entropic effect of counterions plays an important
role at the onset of bundle formation.Comment: 12 pages, 3 figure
Mass-to-Radius Ratio for the Millisecond Pulsar J0437-4715
Properties of X-ray radiation emitted from the polar caps of a radio pulsar
depend not only on the cap temperature, size, and position, but also on the
surface chemical composition, magnetic field, and neutron star's mass and
radius. Fitting the spectra and the light curves with neutron star atmosphere
models enables one to infer these parameters. As an example, we present here
results obtained from the analysis of the pulsed X-ray radiation of a nearby
millisecond pulsar J0437-4715. In particular, we show that stringent
constraints on the mass-to-radius ratio can be obtained if orientations of the
magnetic and rotation axes are known, e.g., from the radio polarization data.Comment: 2 figures, aasms4.sty; accepted for publication in ApJLetter
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