27 research outputs found
The LYRA Instrument Onboard PROBA2: Description and In-Flight Performance
The Large Yield Radiometer (LYRA) is an XUV-EUV-MUV (soft X-ray to
mid-ultraviolet) solar radiometer onboard the European Space Agency PROBA2
mission that was launched in November 2009. LYRA acquires solar irradiance
measurements at a high cadence (nominally 20 Hz) in four broad spectral
channels, from soft X-ray to MUV, that have been chosen for their relevance to
solar physics, space weather and aeronomy. In this article, we briefly review
the design of the instrument, give an overview of the data products distributed
through the instrument website, and describe the way that data are calibrated.
We also briefly present a summary of the main fields of research currently
under investigation by the LYRA consortium
Detection of Solar Rotational Variability in the LYRA 190 - 222 nm Spectral Band
We analyze the variability of the spectral solar irradiance during the period
from 7 January, 2010 until 20 January, 2010 as measured by the Herzberg channel
(190-222 nm) of the Large Yield RAdiometer (LYRA) onboard PROBA2. In this
period of time observations by the LYRA nominal unit experienced degradation
and the signal produced by the Herzberg channel frequently jumped from one
level to another. Both these factors significantly complicates the analysis. We
present the algorithm which allowed us to extract the solar variability from
the LYRA data and compare the results with SORCE/SOLSTICE measurements and with
modeling based on the Code for the Solar Irradiance (COSI)
Physics of Solar Prominences: I - Spectral Diagnostics and Non-LTE Modelling
This review paper outlines background information and covers recent advances
made via the analysis of spectra and images of prominence plasma and the
increased sophistication of non-LTE (ie when there is a departure from Local
Thermodynamic Equilibrium) radiative transfer models. We first describe the
spectral inversion techniques that have been used to infer the plasma
parameters important for the general properties of the prominence plasma in
both its cool core and the hotter prominence-corona transition region. We also
review studies devoted to the observation of bulk motions of the prominence
plasma and to the determination of prominence mass. However, a simple inversion
of spectroscopic data usually fails when the lines become optically thick at
certain wavelengths. Therefore, complex non-LTE models become necessary. We
thus present the basics of non-LTE radiative transfer theory and the associated
multi-level radiative transfer problems. The main results of one- and
two-dimensional models of the prominences and their fine-structures are
presented. We then discuss the energy balance in various prominence models.
Finally, we outline the outstanding observational and theoretical questions,
and the directions for future progress in our understanding of solar
prominences.Comment: 96 pages, 37 figures, Space Science Reviews. Some figures may have a
better resolution in the published version. New version reflects minor
changes brought after proof editin
Self-Organized Criticality in Developing Neuronal Networks
Recently evidence has accumulated that many neural networks exhibit self-organized criticality. In this state, activity is similar across temporal scales and this is beneficial with respect to information flow. If subcritical, activity can die out, if supercritical epileptiform patterns may occur. Little is known about how developing networks will reach and stabilize criticality. Here we monitor the development between 13 and 95 days in vitro (DIV) of cortical cell cultures (n = 20) and find four different phases, related to their morphological maturation: An initial low-activity state (≈19 DIV) is followed by a supercritical (≈20 DIV) and then a subcritical one (≈36 DIV) until the network finally reaches stable criticality (≈58 DIV). Using network modeling and mathematical analysis we describe the dynamics of the emergent connectivity in such developing systems. Based on physiological observations, the synaptic development in the model is determined by the drive of the neurons to adjust their connectivity for reaching on average firing rate homeostasis. We predict a specific time course for the maturation of inhibition, with strong onset and delayed pruning, and that total synaptic connectivity should be strongly linked to the relative levels of excitation and inhibition. These results demonstrate that the interplay between activity and connectivity guides developing networks into criticality suggesting that this may be a generic and stable state of many networks in vivo and in vitro
Pre-flight calibration of LYRA, the solar VUV radiometer on board PROBA2
Aims. LYRA, the Large Yield Radiometer, is a vacuum ultraviolet (VUV) solar radiometer, planned to be launched in November 2009 on the European Space Agency PROBA2, the Project for On-Board Autonomy spacecraft. Methods: The instrument was radiometrically calibrated in the radiometry laboratory of the Physikalisch-Technische Bundesanstalt (PTB) at the Berlin Electron Storage ring for SYnchroton radiation (BESSY II). The calibration was done using monochromatized synchrotron radiation at PTB's VUV and soft X-ray radiometry beamlines using reference detectors calibrated with the help of an electrical substitution radiometer as the primary detector standard. Results: A total relative uncertainty of the radiometric calibration of the LYRA instrument between 1 and 11 was achieved. LYRA will provide irradiance data of the Sun in four UV passbands and with high temporal resolution down to 10 ms. The present state of the LYRA pre-flight calibration is presented as well as the expected instrument performance