35,527 research outputs found
Discovery of Radio Emission from the Tight M8 Binary: LP 349-25
We present radio observations of 8 ultracool dwarfs with a narrow spectral
type range (M8-M9.5) using the Very Large Array at 8.5 GHz. Only the tight M8
binary LP 349-25 was detected. LP 349-25 is the tenth ultracool dwarf system
detected in radio and its trigonometric parallax pi = 67.6 mas, recently
measured by Gatewood et al., makes it the furthest ultracool system detected by
the Very Large Array to date, and the most radio-luminous outside of obvious
flaring activity or variability. With a separation of only 1.8 AU, masses of
the components of LP 349-25 can be measured precisely without any theoretical
assumptions (Forveille et al.), allowing us to clarify their fully-convective
status and hence the kind of magnetic dynamo in these components which may play
an important role to explain our detection of radio emission from these
objects. This also makes LP 349-25 an excellent target for further studies with
better constraints on the correlations between X-ray, radio emission and
stellar parameters such as mass, age, temperature, and luminosity in ultracool
dwarfs.Comment: accepted by ApJ, referee's comments included, typo in equation 1
correcte
Reversibility of Red blood Cell deformation
The ability of cells to undergo reversible shape changes is often crucial to
their survival. For Red Blood Cells (RBCs), irreversible alteration of the cell
shape and flexibility often causes anemia. Here we show theoretically that RBCs
may react irreversibly to mechanical perturbations because of tensile stress in
their cytoskeleton. The transient polymerization of protein fibers inside the
cell seen in sickle cell anemia or a transient external force can trigger the
formation of a cytoskeleton-free membrane protrusion of micrometer dimensions.
The complex relaxation kinetics of the cell shape is shown to be responsible
for selecting the final state once the perturbation is removed, thereby
controlling the reversibility of the deformation. In some case, tubular
protrusion are expected to relax via a peculiar "pearling instability".Comment: 4 pages, 3 figure
Submillimeter Array multiline observations of the massive star-forming region IRAS 18089-1732
Submillimeter Array (SMA) observations of the high-mass star-forming region
IRAS 18089-1732 in the 1 mm and 850 m band with 1 GHz bandwidth reveal a
wealth of information. We present the observations of 34 lines from 16
different molecular species. Most molecular line maps show significant
contributions from the outflow, and only few molecules are confined to the
inner core. We present and discuss the molecular line observations and outline
the unique capabilities of the SMA for future imaging line surveys at high
spatial resolution.Comment: Accepted for ApJ Letters, SMA special volum
SMA outflow/disk studies in the massive star-forming region IRAS18089-1732
SMA observations of the massive star-forming region IRAS 18089-1732 in the
1mm and 850mu band reveal outflow and disk signatures in different molecular
lines. The SiO(5--4) data show a collimated outflow in the northern direction.
In contrast, the HCOOCH3(20--19) line, which traces high-density gas, is
confined to the very center of the region and shows a velocity gradient across
the core. The HCOOCH3 velocity gradient is not exactly perpendicular to the
outflow axis but between an assumed disk plane and the outflow axis. We
interpret these HCOOCH3 features as originating from a rotating disk that is
influenced by the outflow and infall. Based on the (sub-)mm continuum emission,
the mass of the central core is estimated to be around 38M_sun. The dynamical
mass derived from the HCOOCH3 data is 22Msun, of about the same order as the
core mass. Thus, the mass of the protostar/disk/envelope system is dominated by
its disk and envelope. The two frequency continuum data of the core indicate a
low dust opacity index beta ~ 1.2 in the outer part, decreasing to beta ~ 0.5
on shorter spatial scales.Comment: 7 pages of text, 1 table, 3 figures, accepted for ApJ Letter
Measurement of Spin Polarization by Andreev Reflection in Ferromagnetic In1-xMnxSb Epilayers
We carried out Point Contact Andreev Reflection (PCAR) spin spectroscopy
measurements on epitaxially-grown ferromagnetic In1-xMnxSb epilayers with a
Curie temperature of ~9K. The spin sensitivity of PCAR in this material was
demonstrated by parallel control studies on its non-magnetic analog,
In1-yBeySb. We found the conductance curves of the Sn point contacts with
In1-yBeySb to be fairly conventional, with the possible presence of
proximity-induced superconductivity effects at the lowest temperatures. The
experimental Z-values of interfacial scattering agreed well with the estimates
based on the Fermi velocity mismatch between the semiconductor and the
superconductor. These measurements provided control data for subsequent PCAR
measurements on ferromagnetic In1-xMnxSb, which indicated spin polarization in
In1-xMnxSb to be 52 +- 3%
Cell division: a source of active stress in cellular monolayers
We introduce the notion of cell division-induced activity and show that the
cell division generates extensile forces and drives dynamical patterns in cell
assemblies. Extending the hydrodynamic models of lyotropic active nematics we
describe turbulent-like velocity fields that are generated by the cell division
in a confluent monolayer of cells. We show that the experimentally measured
flow field of dividing Madin-Darby Canine Kidney (MDCK) cells is reproduced by
our modeling approach. Division-induced activity acts together with intrinsic
activity of the cells in extensile and contractile cell assemblies to change
the flow and director patterns and the density of topological defects. Finally
we model the evolution of the boundary of a cellular colony and compare the
fingering instabilities induced by cell division to experimental observations
on the expansion of MDCK cell cultures.Comment: Accepted Manuscript for Celebrating Soft Matter's 10th Anniversar
Angular Momentum Exchange by Gravitational Torques and Infall in the Circumbinary Disk of the Protostellar System L1551 NE
We report the ALMA observation of the Class I binary protostellar system
L1551 NE in the 0.9-mm continuum, C18O (3-2), and 13CO (3-2) lines at a ~1.6
times higher resolution and a ~6 times higher sensitivity than those of our
previous SMA observations, which revealed a r ~300 AU-scale circumbinary disk
in Keplerian rotation. The 0.9-mm continuum shows two opposing U-shaped
brightenings in the circumbinary disk, and exhibits a depression between the
circumbinary disk and the circumstellar disk of the primary protostar. The
molecular lines trace non-axisymmetric deviations from Keplerian rotation in
the circumbinary disk at higher velocities relative to the systemic velocity,
where our previous SMA observations could not detect the lines. In addition, we
detect inward motion along the minor axis of the circumbinary disk. To explain
the newly-observed features, we performed a numerical simulation of gas orbits
in a Roche potential tailored to the inferred properties of L1551 NE. The
observed U-shaped dust features coincide with locations where gravitational
torques from the central binary system are predicted to impart angular momentum
to the circumbinary disk, producing shocks and hence density enhancements seen
as a pair of spiral arms. The observed inward gas motion coincides with
locations where angular momentum is predicted to be lowered by the
gravitational torques. The good agreement between our observation and model
indicates that gravitational torques from the binary stars constitute the
primary driver for exchanging angular momentum so as to permit infall through
the circumbinary disk of L1551 NE.Comment: 38 pages, 11 figures, accepted for publication in Ap
The Taiwan ECDFS Near-Infrared Survey: Ultra-deep J and Ks Imaging in the Extended Chandra Deep Field-South
We present ultra-deep J and Ks imaging observations covering a 30' * 30' area
of the Extended Chandra Deep Field-South (ECDFS) carried out by our Taiwan
ECDFS Near-Infrared Survey (TENIS). The median 5-sigma limiting magnitudes for
all detected objects in the ECDFS reach 24.5 and 23.9 mag (AB) for J and Ks,
respectively. In the inner 400 arcmin^2 region where the sensitivity is more
uniform, objects as faint as 25.6 and 25.0 mag are detected at 5-sigma. So this
is by far the deepest J and Ks datasets available for the ECDFS. To combine the
TENIS with the Spitzer IRAC data for obtaining better spectral energy
distributions of high-redshift objects, we developed a novel deconvolution
technique (IRACLEAN) to accurately estimate the IRAC fluxes. IRACLEAN can
minimize the effect of blending in the IRAC images caused by the large
point-spread functions and reduce the confusion noise. We applied IRACLEAN to
the images from the Spitzer IRAC/MUSYC Public Legacy in the ECDFS survey
(SIMPLE) and generated a J+Ks selected multi-wavelength catalog including the
photometry of both the TENIS near-infrared and the SIMPLE IRAC data. We
publicly release the data products derived from this work, including the J and
Ks images and the J+Ks selected multiwavelength catalog.Comment: 25 pages, 25 figures, ApJS in pres
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