1,251 research outputs found
Lamination Speeds the Functional Development of Visual Circuits
SummaryA common feature of the brain is the arrangement of synapses in layers. To examine the significance of this organizational feature, we studied the functional development of direction-selective (DS) circuits in the tectum of astray mutant zebrafish in which lamination of retinal ganglion cell (RGC) axons is lost. We show that although never laminar, the tuning of DS-RGC axons targeting the mutant tectum is normal. Analysis of mutant tectal neurons at late developmental stages reveals that directional tuning is indistinguishable from wild-type larvae. Furthermore, we show that structural plasticity of tectal dendrites and RGC axons compensates for the loss of lamination, establishing connectivity between DS-RGCs and their normal tectal targets. However, tectal direction selectivity is severely perturbed at earlier developmental stages. Thus, the formation of synaptic laminae is ultimately dispensable for the correct wiring of direction-selective tectal circuits, but it is crucial for the rapid assembly of these networks.Video Abstrac
Detrending Exoplanetary Transit Light Curves with Long Short-Term Memory Networks
The precise derivation of transit depths from transit light curves is a key
component for measuring exoplanet transit spectra, and henceforth for the study
of exoplanet atmospheres. However, it is still deeply affected by various kinds
of systematic errors and noise. In this paper we propose a new detrending
method by reconstructing the stellar flux baseline during transit time. We
train a probabilistic Long Short-Term Memory (LSTM) network to predict the next
data point of the light curve during the out-of-transit, and use this model to
reconstruct a transit-free light curve - i.e. including only the systematics -
during the in-transit. By making no assumption about the instrument, and using
only the transit ephemeris, this provides a general way to correct the
systematics and perform a subsequent transit fit. The name of the proposed
model is TLCD-LSTM, standing for Transit Light Curve Detrending LSTM. Here we
present the first results on data from six transit observations of HD 189733b
with the IRAC camera on board the Spitzer Space Telescope, and discuss some of
its possible further applications.Comment: 12 pages, 10 figures, 4 tables, accepted for publication in The
Astronomical Journa
PyLightcurve-torch: a transit modelling package for deep learning applications in PyTorch
We present a new open source python package, based on PyLightcurve and
PyTorch, tailored for efficient computation and automatic differentiation of
exoplanetary transits. The classes and functions implemented are fully
vectorised, natively GPU-compatible and differentiable with respect to the
stellar and planetary parameters. This makes PyLightcurve-torch suitable for
traditional forward computation of transits, but also extends the range of
possible applications with inference and optimisation algorithms requiring
access to the gradients of the physical model. This endeavour is aimed at
fostering the use of deep learning in exoplanets research, motivated by an ever
increasing amount of stellar light curves data and various incentives for the
improvement of detection and characterisation techniques.Comment: 7 pages, 3 figures; submission status updated, fig 2 caption adde
Dynamic coupling of photoacclimation and photoinhibition in a model of microalgae growth.
International audienceThe development of mathematical models that can predict photosynthetic productivity of microalgae under transient conditions is crucial for enhancing large-scale industrial culturing systems. Particularly important in outdoor culture systems, where the light irradiance varies greatly, are the processes of photoinhibition and photoacclimation, which can affect photoproduction significantly. The former is caused by an excess of light and occurs on a fast time scale of minutes, whereas the latter results from the adjustment of the light harvesting capacity to the incoming irradiance and takes place on a slow time scale of days. In this paper, we develop a dynamic model of microalgae growth that simultaneously accounts for the processes of photoinhibition and photoacclimation, thereby spanning multiple time scales. The properties of the model are analyzed in connection to PI-response curves, under a quasi steady-state assumption for the slow processes and by neglecting the fast dynamics. For validation purposes, the model is calibrated and compared against multiple experimental data sets from the literature for several species. The results show that the model can describe the difference in photosynthetic unit acclimation strategies between Dunaliella tertiolecta (n-strategy) and Skeletonema costatum (s-strategy)
Use of 137 Cs isotopic technique in soil erosion studies in Central Greece
The 137Cs technique was used to study soil erosion and deposition rates in soils in the Viotia prefecture, central Greece. Three sites with different soil types were selected and studied. Soils were sampled along transects and analyzed for 137Cs. The main goal of this field investigation was to study the 137Cs 3-D distribution pattern within key sites and to apply this information for the assessment of soil redistribution. The erosion and deposition rates were estimated using the proportional and the simplified mass balance models (Walling and He, 1997). Erosion and deposition rates predicted through the spatial distribution of 137Cs depended on the location of the profile studied in the landscape and were determined by the soil plough depth, the soil structure (bulk density), and the calibration model used to conve rt soil 137Cs measurements to estimates of soil redistribution rates. Estimated erosion rates for the Mouriki area site, varied from 16.62 to 102.56 t ha-1 y-1 for the top of the slope soil profile and from 5.37 to 25.68 t ha-1 y-1 for the middle of the slope soil profile. The deposition rates varied from 7.26 to 42.95 t ha-1 y-1 for the bottom of the slope soil profile
Inhaler technique mastery and maintenance in healthcare professionals trained on different devices
Peer reviewedPostprin
Use of 137 Cs isotopic technique in soil erosion studies in Central Greece
The 137Cs technique was used to study soil erosion and deposition rates in soils in the Viotia prefecture, central Greece. Three sites with different soil types were selected and studied. Soils were sampled along transects and analyzed for 137Cs. The main goal of this field investigation was to study the 137Cs 3-D distribution pattern within key sites and to apply this information for the assessment of soil redistribution. The erosion and deposition rates were estimated using the proportional and the simplified mass balance models (Walling and He, 1997). Erosion and deposition rates predicted through the spatial distribution of 137Cs depended on the location of the profile studied in the landscape and were determined by the soil plough depth, the soil structure (bulk density), and the calibration model used to conve rt soil 137Cs measurements to estimates of soil redistribution rates. Estimated erosion rates for the Mouriki area site, varied from 16.62 to 102.56 t ha-1 y-1 for the top of the slope soil profile and from 5.37 to 25.68 t ha-1 y-1 for the middle of the slope soil profile. The deposition rates varied from 7.26 to 42.95 t ha-1 y-1 for the bottom of the slope soil profile
Predicting Landslide Risk Combining Space Measurements and Geotechnical Modeling: Application at Kerasia Slide
The work developed and applied a methodology combining (a) space measurement of past displacement and (b) geotechnical modelling of displacement to predict and mitigate the risk of ground displacement cased by progressive slope instability. The area of study is in Kerasea village in Plastiras Lake Municipality. The problem under treatment is a creeping landslide in an inhabited area. Mitigation measures were analyzed
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