2,333 research outputs found
Panchromatic Imaging of a Transitional Disk: The Disk of GM Aur in Optical and FUV Scattered Light
We have imaged GM Aur with HST, detected its disk in scattered light at 1400A
and 1650A, and compared these with observations at 3300A, 5550A, 1.1 microns,
and 1.6 microns. The scattered light increases at shorter wavelengths. The
radial surface brightness profile at 3300A shows no evidence of the 24AU radius
cavity that has been previously observed in sub-mm observations. Comparison
with dust grain opacity models indicates the surface of the entire disk is
populated with sub-micron grains. We have compiled an SED from 0.1 microns to 1
mm, and used it to constrain a model of the star+disk system that includes the
sub-mm cavity using the Monte Carlo Radiative Transfer code by Barbara Whitney.
The best-fit model image indicates that the cavity should be detectable in the
F330W bandpass if the cavity has been cleared of both large and small dust
grains, but we do not detect it. The lack of an observed cavity can be
explained by the presence of sub-microns grains interior to the sub-mm cavity
wall. We suggest one explanation for this which could be due to a planet of
mass <9 Jupiter masses interior to 24 AU. A unique cylindrical structure is
detected in the FUV data from the Advanced Camera for Surveys/Solar Blind
Channel. It is aligned along the system semi-minor axis, but does not resemble
an accretion-driven jet. The structure is limb-brightened and extends 190 +/-
35 AU above the disk midplane. The inner radius of the limb-brightening is 40
+/- 10 AU, just beyond the sub-millimeter cavity wall.Comment: 40 pages, 11 figures, 4 tables, accepted to Ap
Investigations of γ′, γ″ and δ precipitates in heat-treated Inconel 718 alloy fabricated by selective laser melting
Inconel 718 alloy samples were fabricated by selective laser melting (SLM). Microstructure and precipitation in solution-heat-treated- and double-aging-SLM-made Inconel 718 were studied by scanning and transmission electron microscopy. Electron microscope observations showed that disc-shaped and cuboidal γ″, and circular γ′ precipitates with an average size of 10–50 nm developed within cellular γ austenite matrix. The simulated, experimentally observed electron diffraction patterns, and dark-field imaging further revealed that the precipitation of three variants of γ″ in the γ matrix occurred. The coarser acicular γ″, and globular as well as plate-like δ phases precipitated at grain boundaries and also within the interior of austenite matrix. The morphology, distribution and crystallography of these precipitates and their formation mechanisms were analyzed and discussed
Introgression reshapes recombination distribution in grapevine interspecific hybrids
In grapevine interspecific hybrids, meiotic recombination is suppressed in homeologous regions and enhanced in homologous regions of recombined chromosomes, whereas crossover rate remains unchanged when chromosome pairs are entirely homeologous
Subpellicular and flagellar microtubules of Trypanosoma brucei brucei contain the same alpha-tubulin isoforms.
Agency, qualia and life: connecting mind and body biologically
Many believe that a suitably programmed computer could act for its own goals and experience feelings. I challenge this view and argue that agency, mental causation and qualia are all founded in the unique, homeostatic nature of living matter. The theory was formulated for coherence with the concept of an agent, neuroscientific data and laws of physics. By this method, I infer that a successful action is homeostatic for its agent and can be caused by a feeling - which does not motivate as a force, but as a control signal. From brain research and the locality principle of physics, I surmise that qualia are a fundamental, biological form of energy generated in specialized neurons. Subjectivity is explained as thermodynamically necessary on the supposition that, by converting action potentials to feelings, the neural cells avert damage from the electrochemical pulses. In exchange for this entropic benefit, phenomenal energy is spent as and where it is produced - which precludes the objective observation of qualia
AGN feedback and iron enrichment in the powerful radio galaxy, 4C+55.16
We present a detailed X-ray analysis of 4C+55.16, an unusual and interesting
radio galaxy, located at the centre of a cool core cluster of galaxies.
4C+55.16 is X-ray bright (L(cluster)~10^45 erg/s), radio powerful, and shows
clear signs of interaction with the surrounding intracluster medium. By
combining deep Chandra (100 ks) with 1.4 GHz VLA observations, we find evidence
of multiple outbursts from the central AGN, providing enough energy to offset
cooling of the ICM (P_bubbles=6.7x10^44 erg/s). Furthermore, 4C+55.16 has an
unusual intracluster iron distribution showing a plume-like feature rich in Fe
L emission that runs along one of the X-ray cavities. The excess of iron
associated with the plume is around 10^7M_sol. The metal abundances are
consistent with being Solar-like, indicating that both SNIa and SNII contribute
to the enrichment. The plume and southern cavity form a region of cool
metal-rich gas, and at the edge of this region, there is a clear discontinuity
in temperature (from kT~2.5 keV to kT~5.0 keV), metallicity (from ~0.4 solar to
0.8 solar), and surface brightness distribution, consistent with it being
caused by a cold front. However, we also suggest that this discontinuity could
be caused by cool metal-rich gas being uplifted from the central AGN along one
of its X-ray cavities.Comment: 12 pages, 11 figures, 1 table, Accepted to MNRAS (minor revision
The dust obscuration bias in Damped Lyman alpha systems
We present a new study of the effects of quasar obscuration on the statistics
of Damped Ly alpha (DLA) systems. We show that the extinction of any Galactic
or extragalactic HI region increases with the column density of zinc with a
turning point above which background sources are suddenly obscured. We derive a
relation between the extinction of a DLA system and its HI column density, N,
metallicity, Z, fraction of iron in dust, f_Fe(Z), and redshift, z. From this
relation we estimate the fraction of DLA systems missed as a consequence of
their own extinction in magnitude-limited surveys. We derive a method for
recovering the true frequency distributions of N and Z in DLAs, f_N and f_Z,
using the biased distributions measured in the redshift range where the
observations have sufficient statistics (1.8 </= z </= 3). By applying our
method we find that the well-known empirical thresholds of DLA column
densities, N(ZnII) </~ 10^13.1 cm^-2 and N(HI) </~ 10^22 cm^-2 can be
successfully explained in terms of the obscuration effect without tuning of the
local dust parameters. The obscuration has a modest effect on the distribution
of quasar apparent magnitudes, but plays an important role in shaping the
statistical distributions of DLAs. The exact estimate of the bias is still
limited by the paucity of the data (~40 zinc measurements at 1.8 </~ z </~ 3).
We find that the fraction of DLAs missed as a consequence of obscuration is
\~30% to 50%, consistent with the results of surveys of radio-selected quasars.
By modelling the metallicity distribution with a Schechter function we find
that the mean metallicity can be ~5 to 6 times higher than the value commonly
reported for DLAs at z~2.3.Comment: Astronomy and Astrophysics, in press, 20 pages, 10 figures; abridged
abstract; improved figs. 3 and 5; most of mathematical formulation moved to
the Appendix; minor change
The photochemistry of carbon monoxide in the stratosphere and mesosphere evaluated from observations by the Microwave Limb Sounder on the Aura satellite
Pinning quantum phase transition for a Luttinger liquid of strongly interacting bosons
One of the most remarkable results of quantum mechanics is the fact that
many-body quantum systems may exhibit phase transitions even at zero
temperature. Quantum fluctuations, deeply rooted in Heisenberg's uncertainty
principle, and not thermal fluctuations, drive the system from one phase to
another. Typically, the relative strength of two competing terms in the
system's Hamiltonian is changed across a finite critical value. A well-known
example is the Mott-Hubbard quantum phase transition from a superfluid to an
insulating phase, which has been observed for weakly interacting bosonic atomic
gases. However, for strongly interacting quantum systems confined to
lower-dimensional geometry a novel type of quantum phase transition may be
induced for which an arbitrarily weak perturbation to the Hamiltonian is
sufficient to drive the transition. Here, for a one-dimensional (1D) quantum
gas of bosonic caesium atoms with tunable interactions, we observe the
commensurate-incommensurate quantum phase transition from a superfluid
Luttinger liquid to a Mott-insulator. For sufficiently strong interactions, the
transition is induced by adding an arbitrarily weak optical lattice
commensurate with the atomic granularity, which leads to immediate pinning of
the atoms. We map out the phase diagram and find that our measurements in the
strongly interacting regime agree well with a quantum field description based
on the exactly solvable sine-Gordon model. We trace the phase boundary all the
way to the weakly interacting regime where we find good agreement with the
predictions of the 1D Bose-Hubbard model. Our results open up the experimental
study of quantum phase transitions, criticality, and transport phenomena beyond
Hubbard-type models in the context of ultracold gases
Weak Lensing with SDSS Commissioning Data: The Galaxy-Mass Correlation Function To 1/h Mpc
(abridged) We present measurements of galaxy-galaxy lensing from early
commissioning imaging data from the Sloan Digital Sky Survey (SDSS). We measure
a mean tangential shear around a stacked sample of foreground galaxies in three
bandpasses out to angular radii of 600'', detecting the shear signal at very
high statistical significance. The shear profile is well described by a
power-law. A variety of rigorous tests demonstrate the reality of the
gravitational lensing signal and confirm the uncertainty estimates. We
interpret our results by modeling the mass distributions of the foreground
galaxies as approximately isothermal spheres characterized by a velocity
dispersion and a truncation radius. The velocity dispersion is constrained to
be 150-190 km/s at 95% confidence (145-195 km/s including systematic
uncertainties), consistent with previous determinations but with smaller error
bars. Our detection of shear at large angular radii sets a 95% confidence lower
limit , corresponding to a physical radius of
kpc, implying that galaxy halos extend to very large radii. However, it is
likely that this is being biased high by diffuse matter in the halos of groups
and clusters. We also present a preliminary determination of the galaxy-mass
correlation function finding a correlation length similar to the galaxy
autocorrelation function and consistency with a low matter density universe
with modest bias. The full SDSS will cover an area 44 times larger and provide
spectroscopic redshifts for the foreground galaxies, making it possible to
greatly improve the precision of these constraints, measure additional
parameters such as halo shape, and measure the properties of dark matter halos
separately for many different classes of galaxies.Comment: 28 pages, 11 figures, submitted to A
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