472 research outputs found
Difficulties with the genetic improvement of feed efficiency in broiler lines using group cage information
International audienc
Free Thyroxine Level in the High Normal Reference Range Prescribed for Nonpregnant Women May Reduce the Preterm Delivery Rate in Multiparous
Preterm birth is the most common reason for perinatal morbidity and mortality in the western world. It has been shown that in euthyreotic pregnant women with thyroid autoimmune antibodies, L-Thyroxine replacement reduces preterm delivery rate in singleton pregnancies. We investigated in a nonrandomized retrospective observational study whether L-Thyroxine replacement, maintaining maternal free thyroxine serum level in the high normal reference range prescribed for nonpregnant women also influences the rate of preterm delivery in women without thyroid autoimmune antibodies. As control group for preterm delivery rate, data from perinatal statistics of the State of Baden-Württemberg from 2006 were used. The preterm delivery rate in the study group was significantly reduced. The subgroup analysis shows no difference in primiparous but a decline in multiparous by approximately 61% with L-Thyroxine replacement. Maintaining free thyroxine serum level in the high normal reference range prescribed for nonpregnant women may reduce the preterm delivery rate
Consequences of selection for egg weight on hatchability
International audienc
The properties of the inner disk around HL Tau: Multi-wavelength modeling of the dust emission
We conducted a detailed radiative transfer modeling of the dust emission from
the circumstellar disk around HL Tau. The goal of our study is to derive the
surface density profile of the inner disk and its structure. In addition to the
Atacama Large Millimeter/submillimeter Array images at Band 3 (2.9mm), Band 6
(1.3mm), and Band 7 (0.87mm), the most recent Karl G. Jansky Very Large Array
(VLA) observations at 7mm were included in the analysis. A simulated annealing
algorithm was invoked to search for the optimum model. The radiative transfer
analysis demonstrates that most radial components (i.e., >6AU) of the disk
become optically thin at a wavelength of 7mm, which allows us to constrain, for
the first time, the dust density distribution in the inner region of the disk.
We found that a homogeneous grain size distribution is not sufficient to
explain the observed images at different wavelengths simultaneously, while
models with a shallower grain size distribution in the inner disk work well. We
found clear evidence that larger grains are trapped in the first bright ring.
Our results imply that dust evolution has already taken place in the disk at a
relatively young (i.e., ~1Myr) age. We compared the midplane temperature
distribution, optical depth, and properties of various dust rings with those
reported previously. Using the Toomre parameter, we briefly discussed the
gravitational instability as a potential mechanism for the origin of the dust
clump detected in the first bright ring via the VLA observations.Comment: Accepted for publication in A&A (10 pages
The Radial Distribution of Dust Particles in the HL Tau Disk from ALMA and VLA Observations
Understanding planet formation requires one to discern how dust grows in protoplanetary disks. An important parameter to measure in disks is the maximum dust grain size present. This is usually estimated through measurements of the dust opacity at different millimeter wavelengths assuming optically thin emission and dust opacity dominated by absorption. However, Atacama Large Millimeter/submillimeter Array (ALMA) observations have shown that these assumptions might not be correct in the case of protoplanetary disks, leading to overestimation of particle sizes and to underestimation of the disk\u27s mass. Here, we present an analysis of high-quality ALMA and Very Large Array images of the HL Tau protoplanetary disk, covering a wide range of wavelengths, from 0.8 mm to 1 cm, and with a physical resolution of ~7.35 au. We describe a procedure to analyze a set of millimeter images without any assumption about the optical depth of the emission, and including the effects of absorption and scattering in the dust opacity. This procedure allows us to obtain the dust temperature, the dust surface density, and the maximum particle size at each radius. In the HL Tau disk, we found that particles have already grown to a few millimeters in size. We detect differences in the dust properties between dark and bright rings, with dark rings containing low dust density and small dust particles. Different features in the HL Tau disk seem to have different origins. Planet–disk interactions can explain substructure in the external half of the disk, but the internal rings seem to be associated with the presence of snow lines of several molecules
The VLA view of the HL Tau Disk - Disk Mass, Grain Evolution, and Early Planet Formation
The first long-baseline ALMA campaign resolved the disk around the young star
HL Tau into a number of axisymmetric bright and dark rings. Despite the very
young age of HL Tau these structures have been interpreted as signatures for
the presence of (proto)planets. The ALMA images triggered numerous theoretical
studies based on disk-planet interactions, magnetically driven disk structures,
and grain evolution. Of special interest are the inner parts of disks, where
terrestrial planets are expected to form. However, the emission from these
regions in HL Tau turned out to be optically thick at all ALMA wavelengths,
preventing the derivation of surface density profiles and grain size
distributions. Here, we present the most sensitive images of HL Tau obtained to
date with the Karl G. Jansky Very Large Array at 7.0 mm wavelength with a
spatial resolution comparable to the ALMA images. At this long wavelength the
dust emission from HL Tau is optically thin, allowing a comprehensive study of
the inner disk. We obtain a total disk dust mass of 0.001 - 0.003 Msun,
depending on the assumed opacity and disk temperature. Our optically thin data
also indicate fast grain growth, fragmentation, and formation of dense clumps
in the inner densest parts of the disk. Our results suggest that the HL Tau
disk may be actually in a very early stage of planetary formation, with planets
not already formed in the gaps but in the process of future formation in the
bright rings.Comment: Accepted by The Astrophysical Journal Letter
Millimeter Gap Contrast as a Probe for Turbulence Level in Protoplanetary Disks
Turbulent motions are believed to regulate angular momentum transport and
influence dust evolution in protoplanetary disks. Measuring the strength of
turbulence is challenging through gas line observations because of the
requirement for high spatial and spectral resolution data, and an exquisite
determination of the temperature. In this work, taking the well-known HD 163296
disk as an example, we investigated the contrast of gaps identified in high
angular resolution continuum images as a probe for the level of turbulence.
With self-consistent radiative transfer models, we simultaneously analyzed the
radial brightness profiles along the disk major and minor axes, and the
azimuthal brightness profiles of the B67 and B100 rings. By fitting all the gap
contrasts measured from these profiles, we constrained the gas-to-dust scale
height ratio to be , and
for the D48, B67 and B100 regions, respectively. The varying
gas-to-dust scale height ratios indicate that the degree of dust settling
changes with radius. The inferred values for translate into a
turbulence level of in the D48 and
B100 regions, which is consistent with previous upper limits set by gas line
observations. However, turbulent motions in the B67 ring are strong with
. Due to the degeneracy
between and the depth of dust surface density drops, the turbulence
strength in the D86 gap region is not constrained.Comment: 13 pages, 7 figures, accepted for publication in Science China
Physics, Mechanics & Astronom
Crystal structure of rhodopsin in complex with a mini-G_o sheds light on the principles of G protein selectivity
Selective coupling of G protein (heterotrimeric guanine nucleotide–binding protein)–coupled receptors (GPCRs) to specific Gα-protein subtypes is critical to transform extracellular signals, carried by natural ligands and clinical drugs, into cellular responses. At the center of this transduction event lies the formation of a signaling complex between the receptor and G protein. We report the crystal structure of light-sensitive GPCR rhodopsin bound to an engineered mini-Go protein. The conformation of the receptor is identical to all previous structures of active rhodopsin, including the complex with arrestin. Thus, rhodopsin seems to adopt predominantly one thermodynamically stable active conformation, effectively acting like a “structural switch,” allowing for maximum efficiency in the visual system. Furthermore, our analysis of the well-defined GPCR–G protein interface suggests that the precise position of the carboxyl-terminal “hook-like” element of the G protein (its four last residues) relative to the TM7/helix 8 (H8) joint of the receptor is a significant determinant in selective G protein activation
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