177 research outputs found
Bovine oocytes in secondary follicles grow and acquire meiotic competence in severe combined immunodeficient mice
A rigorous methodology is developed
that addresses numerical and
statistical issues when developing group contribution (GC) based property
models such as regression methods, optimization algorithms, performance
statistics, outlier treatment, parameter identifiability, and uncertainty
of the prediction. The methodology is evaluated through development
of a GC method for the prediction of the heat of combustion (Î<i>H</i><sub>c</sub><sup>o</sup>) for pure components. The results showed that robust regression
lead to best performance statistics for parameter estimation. The
bootstrap method is found to be a valid alternative to calculate parameter
estimation errors when underlying distribution of residuals is unknown.
Many parameters (first, second, third order group contributions) are
found unidentifiable from the typically available data, with large
estimation error bounds and significant correlation. Due to this poor
parameter identifiability issues, reporting of the 95% confidence
intervals of the predicted property values should be mandatory as
opposed to reporting only single value prediction, currently the norm
in literature. Moreover, inclusion of higher order groups (additional
parameters) does not always lead to improved prediction accuracy for
the GC-models; in some cases, it may even increase the prediction
error (hence worse prediction accuracy). However, additional parameters
do not affect calculated 95% confidence interval. Last but not least,
the newly developed GC model of the heat of combustion (Î<i>H</i><sub>c</sub><sup>o</sup>) shows predictions of great accuracy and quality (the most data
falling within the 95% confidence intervals) and provides additional
information on the uncertainty of each prediction compared to other
Î<i>H</i><sub>c</sub><sup>o</sup> models reported in literature
Morphology of powerful suction organs from blepharicerid larvae living in raging torrents
BackgroundSuction organs provide powerful yet dynamic attachments for many aquatic animals, including octopus, squid, remora, and clingfish. While the functional morphology of suction organs from some cephalopods and fishes has been investigated in detail, there are only few studies on such attachment devices in insects. Here we characterise the morphology and ultrastructure of the suction attachment organs of net-winged midge larvae (genus Liponeura; Diptera: Blephariceridae) â aquatic insects that live on rocks in rapid alpine waterways where flow speeds can reach 3âmâsââ1 â using scanning electron microscopy, confocal laser scanning microscopy, and X-ray computed micro-tomography (micro-CT). Furthermore, we study the function of these organs in vivo using interference reflection microscopy.ResultsWe identified structural adaptations important for the function of the suction attachment organs in L. cinerascens and L. cordata. First, a dense array of spine-like microtrichia covering each suction disc comes into contact with the substrate upon attachment, analogous to hairy structures on suction organs from octopus, clingfish, and remora fish. These spine-like microtrichia may contribute to the seal and provide increased shear force resistance in high-drag environments. Second, specialised rim microtrichia at the suction disc periphery were found to form a continuous ring in close contact and may serve as a seal on a variety of surfaces. Third, a V-shaped cut on the suction disc (âV-notchâ) is actively opened via two cuticular apodemes inserting on its flanks. The apodemes are attached to dedicated V-notch opening muscles, thereby providing a unique detachment mechanism. The complex cuticular design of the suction organs, along with specialised muscles that attach to them, allows blepharicerid larvae to generate powerful attachments which can withstand strong hydrodynamic forces and quickly detach for locomotion.ConclusionThe suction organs from Liponeura are underwater attachment devices specialised for resisting extremely fast flows. Structural adaptations from these suction organs could translate into future bioinspired attachment systems that perform well on a wide range of surfaces
Modified p-modes in penumbral filaments?
Aims: The primary objective of this study is to search for and identify wave
modes within a sunspot penumbra.
Methods: Infrared spectropolarimetric time series data are inverted using a
model comprising two atmospheric components in each spatial pixel. Fourier
phase difference analysis is performed on the line-of-sight velocities
retrieved from both components to determine time delays between the velocity
signals. In addition, the vertical separation between the signals in the two
components is calculated from the Stokes velocity response functions.
Results: The inversion yields two atmospheric components, one permeated by a
nearly horizontal magnetic field, the other with a less-inclined magnetic
field. Time delays between the oscillations in the two components in the
frequency range 2.5-4.5 mHz are combined with speeds of atmospheric wave modes
to determine wave travel distances. These are compared to expected path lengths
obtained from response functions of the observed spectral lines in the
different atmospheric components. Fast-mode (i.e., modified p-mode) waves
exhibit the best agreement with the observations when propagating toward the
sunspot at an angle ~50 degrees to the vertical.Comment: 8 pages, 12 figures, accepted for publication in Astronomy &
Astrophysic
Model selection for spectro-polarimetric inversions
Inferring magnetic and thermodynamic information from spectropolarimetric
observations relies on the assumption of a parameterized model atmosphere whose
parameters are tuned by comparison with observations. Often, the choice of the
underlying atmospheric model is based on subjective reasons. In other cases,
complex models are chosen based on objective reasons (for instance, the
necessity to explain asymmetries in the Stokes profiles) but it is not clear
what degree of complexity is needed. The lack of an objective way of comparing
models has, sometimes, led to opposing views of the solar magnetism because the
inferred physical scenarios are essentially different. We present the first
quantitative model comparison based on the computation of the Bayesian evidence
ratios for spectropolarimetric observations. Our results show that there is not
a single model appropriate for all profiles simultaneously. Data with moderate
signal-to-noise ratios favor models without gradients along the line-of-sight.
If the observations shows clear circular and linear polarization signals above
the noise level, models with gradients along the line are preferred. As a
general rule, observations with large signal-to-noise ratios favor more complex
models. We demonstrate that the evidence ratios correlate well with simple
proxies. Therefore, we propose to calculate these proxies when carrying out
standard least-squares inversions to allow for model comparison in the future.Comment: 16 pages, 2 figures, 8 tables, accepted for publication in Ap
Comparing magnetic field extrapolations with measurements of magnetic loops
We compare magnetic field extrapolations from a photospheric magnetogram with
the observationally inferred structure of magnetic loops in a newly developed
active region. This is the first time that the reconstructed 3D-topology of the
magnetic field is available to test the extrapolations. We compare the
observations with potential fields, linear force-free fields and non-linear
force-free fields. This comparison reveals that a potential field extrapolation
is not suitable for a reconstruction of the magnetic field in this young,
developing active region. The inclusion of field-line-parallel electric
currents, the so called force-free approach, gives much better results.
Furthermore, a non-linear force-free computation reproduces the observations
better than the linear force-free approximation, although no free parameters
are available in the former case.Comment: 5 pages, 3 figure
On the fine structure of the sunspot penumbrae. III The vertical extension of penumbral filaments
In this paper we study the fine structure of the penumbra as inferred from
the uncombed model (flux tube embedded in a magnetic surrounding) when applied
to penumbral spectropolarimetric data from the neutral iron lines at 6300 \AA.
The inversion infers very similar radial dependences in the physical quantities
(LOS velocity, magnetic field strength etc) as those obtained from the
inversion of the Fe I 1.56 m lines. In addition, the large Stokes area
asymmetry exhibited by the visible lines helps to constrain the size of the
penumbral flux tubes. As we demonstrate here, the uncombed model is able to
reproduce the area asymmetry with striking accuracy, returning flux tubes as
thick as 100-300 kilometers in the vertical direction, in good agreement with
previous investigations.Comment: submitted to Astronomy and Astrophysic
Time series of high resolution photospheric spectra in a quiet region of the Sun. II. Analysis of the variation of physical quantities of granular structures
From the inversion of a time series of high resolution slit spectrograms
obtained from the quiet sun, the spatial and temporal distribution of the
thermodynamical quantities and the vertical flow velocity is derived as a
function of logarithmic optical depth and geometrical height. Spatial coherence
and phase shift analyzes between temperature and vertical velocity depict the
height variation of these physical quantities for structures of different size.
An average granular cell model is presented, showing the granule-intergranular
lane stratification of temperature, vertical velocity, gas pressure and density
as a function of logarithmic optical depth and geometrical height. Studies of a
specific small and a specific large granular cell complement these results. A
strong decay of the temperature fluctuations with increasing height together
with a less efficient penetration of smaller cells is revealed. The T -T
coherence at all granular scales is broken already at log tau =-1 or z~170 km.
At the layers beyond, an inversion of the temperature contrast is revealed.
Vertical velocities are in phase throughout the photosphere and penetrate into
the highest layers under study.Comment: 13 pages, 12 figures, 1 table; Astronomy & Astrophysics, Volume 441,
Issue 3, pp.1157-1169, 200
Chemical Abundances from Inversions of Stellar Spectra: Analysis of Solar-Type Stars with Homogeneous and Static Model Atmospheres
Spectra of late-type stars are usually analyzed with static model atmospheres
in local thermodynamic equilibrium (LTE) and a homogeneous plane-parallel or
spherically symmetric geometry. The energy balance requires particular
attention, as two elements which are particularly difficult to model play an
important role: line blanketing and convection. Inversion techniques are able
to bypass the difficulties of a detailed description of the energy balance.
Assuming that the atmosphere is in hydrostatic equilibrium and LTE, it is
possible to constrain its structure from spectroscopic observations. Among the
most serious approximations still implicit in the method is a static and
homogeneous geometry. In this paper, we take advantage of a realistic
three-dimensional radiative hydrodynamical simulation of the solar surface to
check the systematic errors incurred by an inversion assuming a plane-parallel
horizontally-homogeneous atmosphere. The thermal structure recovered resembles
the spatial and time average of the three-dimensional atmosphere. Furthermore,
the abundances retrieved are typically within 10% (0.04 dex) of the abundances
used to construct the simulation. The application to a fairly complete dataset
from the solar spectrum provides further confidence in previous analyses of the
solar composition. There is only a narrow range of one-dimensional thermal
structures able to fit the absorption lines in the spectrum of the Sun. With
our carefully selected dataset, random errors are about a factor of two smaller
than systematic errors. A small number of strong metal lines can provide very
reliable results. We foresee no major difficulty in applying the technique to
other similar stars, and obtaining similar accuracies, using spectra with a
resolving power about 50,000 and a signal-to-noise ratio as low as 30.Comment: 65 pages, figures included; uses aastex; to appear in The
Astrophysical Journa
Exploiting solar visible-range observations by inversion techniques: from flows in the solar subsurface to a flaring atmosphere
Observations of the Sun in the visible spectral range belong to standard
measurements obtained by instruments both on the ground and in the space.
Nowadays, both nearly continuous full-disc observations with medium resolution
and dedicated campaigns of high spatial, spectral and/or temporal resolution
constitute a holy grail for studies that can capture (both) the long- and
short-term changes in the dynamics and energetics of the solar atmosphere.
Observations of photospheric spectral lines allow us to estimate not only the
intensity at small regions, but also various derived data products, such as the
Doppler velocity and/or the components of the magnetic field vector. We show
that these measurements contain not only direct information about the dynamics
of solar plasmas at the surface of the Sun but also imprints of regions below
and above it. Here, we discuss two examples: First, the local time-distance
helioseismology as a tool for plasma dynamic diagnostics in the near subsurface
and second, the determination of the solar atmosphere structure during flares.
The methodology in both cases involves the technique of inverse modelling.Comment: 29 pages, 15 figures. Accepted for publication in the book "Reviews
in Frontiers of Modern Astrophysics: From Space Debris to Cosmology" (eds
Kabath, Jones and Skarka; publisher Springer Nature) funded by the European
Union Erasmus+ Strategic Partnership grant "Per Aspera Ad Astra Simul"
2017-1-CZ01-KA203-03556
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