3,565 research outputs found
CO gas inside the protoplanetary disk cavity in HD 142527: disk structure from ALMA
Inner cavities and annular gaps in circumstellar disks are possible signposts
of giant planet formation. The young star HD 142527 hosts a massive
protoplanetary disk with a large cavity that extends up to 140 au from the
central star, as seen in continuum images at infrared and millimeter
wavelengths. Estimates of the survival of gas inside disk cavities are needed
to discriminate between clearing scenarios. We present a spatially and
spectrally resolved carbon monoxide isotopologue observations of the gas-rich
disk HD 142527, in the J=2-1 line of 12CO, 13CO and C18O, obtained with the
Atacama Large Millimeter Array (ALMA). We detect emission coming from inside
the dust-depleted cavity in all three isotopologues. Based on our analysis of
the gas in the dust cavity, the 12CO emission is optically thick, while 13CO
and C18O emission are both optically thin. The total mass of residual gas
inside the cavity is about 1.5-2 Jupiter masses. We model the gas with an
axisymmetric disk model. Our best fit model shows that the cavity radius is
much smaller in CO than it is in millimeter continuum and scattered light
observations, with a gas cavity that does not extend beyond 105 au (at
3-sigma). The gap wall at its outer edge is diffuse and smooth in the gas
distribution, while in dust continuum it is manifestly sharper. The inclination
angle, as estimated from the high velocity channel maps, is 28+/-0.5 degrees,
higher than in previous estimates, assuming a fix central star mass of 2.2
Solar masses.Comment: 13 pages, 10 figures. Accepted for publication in ApJ Main Journa
Observations of gas flows inside a protoplanetary gap
Gaseous giant planet formation is thought to occur in the first few million
years following stellar birth. Models predict that giant planet formation
carves a deep gap in the dust component (shallower in the gas). Infrared
observations of the disk around the young star HD142527, at ~140pc, found an
inner disk ~10AU in radius, surrounded by a particularly large gap, with a
disrupted outer disk beyond 140AU, indicative of a perturbing planetary-mass
body at ~90 AU. From radio observations, the bulk mass is molecular and lies in
the outer disk, whose continuum emission has a horseshoe morphology. The
vigorous stellar accretion rate would deplete the inner disk in less than a
year, so in order to sustain the observed accretion, matter must flow from the
outer-disk into the cavity and cross the gap. In dynamical models, the putative
protoplanets channel outer-disk material into gap-crossing bridges that feed
stellar accretion through the inner disk. Here we report observations with the
Atacama Large Millimetre Array (ALMA) that reveal diffuse CO gas inside the
gap, with denser HCO+ gas along gap-crossing filaments, and that confirm the
horseshoe morphology of the outer disk. The estimated flow rate of the gas is
in the range 7E-9 to 2E-7 Msun/yr, which is sufficient to maintain accretion
onto the star at the present rate
Millimagnitude Photometry for Transiting Extrasolar Planetary Candidates IV: The Puzzle of the Extremely Red OGLE-TR-82 Primary Solved
We present precise new V, I, and K-band photometry for the planetary transit
candidate star OGLE-TR-82. Good seeing V-band images acquired with VIMOS
instrument at ESO VLT allowed us to measure V=20.6+-0.03 mag star in spite of
the presence of a brighter neighbour about 1" away. This faint magnitude
answers the question why it has not been possible to measure radial velocities
for this object. One transit of this star has been observed with GMOS-S
instrument of GEMINI-South telescope in i and g-bands. The measurement of the
transit allows us to verify that this is not a false positive, to confirm the
transit amplitude measured by OGLE, and to improve the ephemeris. The transit
is well defined in i-band light curve, with a depth of A_i=0.034 mag. It is
however, less well defined, but deeper (A_g=0.1 mag) in the g-band, in which
the star is significantly fainter. The near-infrared photometry obtained with
SofI array at the ESO-NTT yields K=12.2+-0.1 and V-K=8.4+-0.1, so red that it
is unlike any other transit candidate studied before. Due to the extreme nature
of this object, we have not yet been able to measure velocities for this star,
but based on the new data we consider two different possible configurations:(1)
a nearby M7V star, or (2) a blend with a very reddened distant red giant. The
nearby M7V dwarf hypothesis would give a radius for the companion of
R_p=0.3+-0.1 R_J, i.e. the size of Neptune. Quantitative analysis of near-IR
spectroscopy finally shows that OGLE-TR-82 is a distant, reddened metal poor
early K giant. This result is confirmed by direct comparison with stellar
templates that gives the best match for a K3III star. Therefore, we discard the
planetary nature of the companion. Based on all the new data, we conclude that
this system is a main-sequence binary blended with a background red giant.Comment: 26 pages, 9 figures, ApJ accepte
Strong interfacial exchange field in a heavy metal/ferromagnetic insulator system determined by spin Hall magnetoresistance
Spin-dependent transport at heavy metal/magnetic insulator interfaces is at
the origin of many phenomena at the forefront of spintronics research. A proper
quantification of the different interfacial spin conductances is crucial for
many applications. Here, we report the first measurement of the spin Hall
magnetoresistance (SMR) of Pt on a purely ferromagnetic insulator (EuS). We
perform SMR measurements in a wide range of temperatures and fit the results by
using a microscopic model. From this fitting procedure we obtain the
temperature dependence of the spin conductances (, and ),
disentangling the contribution of field-like torque (), damping-like
torque (), and spin-flip scattering (). An interfacial exchange field
of the order of 1 meV acting upon the conduction electrons of Pt can be
estimated from , which is at least three times larger than below the
Curie temperature. Our work provides an easy method to quantify this
interfacial spin-splitting field, which play a key role in emerging fields such
as superconducting spintronics and caloritronics, and topological quantum
computation.Comment: 15 pages, 3 figures, Supporting information included at the en
Rhesus TRIM5α disrupts the HIV-1 capsid at the inter-hexamer interfaces
TRIM proteins play important roles in the innate immune defense against retroviral infection, including human immunodeficiency virus type-1 (HIV-1). Rhesus macaque TRIM5α (TRIM5αrh) targets the HIV-1 capsid and blocks infection at an early post-entry stage, prior to reverse transcription. Studies have shown that binding of TRIM5α to the assembled capsid is essential for restriction and requires the coiled-coil and B30.2/SPRY domains, but the molecular mechanism of restriction is not fully understood. In this study, we investigated, by cryoEM combined with mutagenesis and chemical cross-linking, the direct interactions between HIV-1 capsid protein (CA) assemblies and purified TRIM5αrh containing coiled-coil and SPRY domains (CC-SPRYrh). Concentration-dependent binding of CC-SPRYrh to CA assemblies was observed, while under equivalent conditions the human protein did not bind. Importantly, CC-SPRYrh, but not its human counterpart, disrupted CA tubes in a non-random fashion, releasing fragments of protofilaments consisting of CA hexamers without dissociation into monomers. Furthermore, such structural destruction was prevented by inter-hexamer crosslinking using P207C/T216C mutant CA with disulfide bonds at the CTD-CTD trimer interface of capsid assemblies, but not by intra-hexamer crosslinking via A14C/E45C at the NTD-NTD interface. The same disruption effect by TRIM5αrh on the inter-hexamer interfaces also occurred with purified intact HIV-1 cores. These results provide insights concerning how TRIM5α disrupts the virion core and demonstrate that structural damage of the viral capsid by TRIM5α is likely one of the important components of the mechanism of TRIM5α-mediated HIV-1 restriction. © 2011 Zhao et al
A Comparison of Eight Optimization Methods Applied to a Wind Farm Layout Optimization Problem
Selecting a wind farm layout optimization method is difficult. Comparisons between optimization methods in different papers can be uncertain due to the difficulty of exactly reproducing the objective function. Comparisons by just a few authors in one paper can be uncertain if the authors do not have experience using each algorithm. In this work we provide an algorithm comparison for a wind farm layout optimization case study between eight optimization methods applied, or directed, by researchers who developed those algorithms or who had other experience using them. We provided the objective function to each researcher to avoid ambiguity about relative performance due to a difference in objective function. While these comparisons are not perfect, we try to treat each algorithm more fairly by having researchers with experience using each algorithm apply each algorithm and by having a common objective function provided for analysis. The case study is from the IEA Wind Task 37, based on the Borssele III and IV wind farms with 81 turbines. Of particular interest in this case study is the presence of disconnected boundary regions and concave boundary features. The optimization methods studied represent a wide range of approaches, including gradient-free, gradient-based, and hybrid methods; discrete and continuous problem formulations; single-run and multi-start approaches; and mathematical and heuristic algorithms. We provide descriptions and references (where applicable) for each optimization method as well as lists of pros and cons to help readers determine an appropriate method for their use case. All the optimization methods perform similarly, with optimized wake loss values between 15.48 % and 15.70 % as compared to 17.28 % for the unoptimized provided layout. Each of the layouts found were different, but all layouts exhibited similar characteristics. Strong similarities across all the layouts include tightly packing wind turbines along the outer borders, loosely spacing turbines in the internal regions, and allocating similar numbers of turbines to each discrete boundary region. The best layout by AEP was found using a new sequential allocation method, discreet exploration-based optimization (DEBO). Based on the results in this study, it appears that using an optimization algorithm can significantly improve wind farm performance, but there are many optimization methods that can perform well on the wind farm layout optimization problem given that they are applied correctly.</p
Mosaic DNA imports with interspersions of recipient sequence after natural transformation of Helicobacter pylori
Helicobacter pylori colonizes the gastric mucosa of half of the human population, causing gastritis, ulcers, and cancer. H. pylori
is naturally competent for transformation by exogenous DNA, and recombination during mixed infections of one stomach
with multiple H. pylori strains generates extensive allelic diversity. We developed an in vitro transformation protocol to study
genomic imports after natural transformation of H. pylori. The mean length of imported fragments was dependent on the
combination of donor and recipient strain and varied between 1294 bp and 3853 bp. In about 10% of recombinant clones, the
imported fragments of donor DNA were interrupted by short interspersed sequences of the recipient (ISR) with a mean length
of 82 bp. 18 candidate genes were inactivated in order to identify genes involved in the control of import length and
generation of ISR. Inactivation of the antimutator glycosylase MutY increased the length of imports, but did not have a
significant effect on ISR frequency. Overexpression of mutY strongly increased the frequency of ISR, indicating that MutY, while
not indispensable for ISR formation, is part of at least one ISR-generating pathway. The formation of ISR in H. pylori increases
allelic diversity, and contributes to the uniquely low linkage disequilibrium characteristic of this pathogen
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