302 research outputs found
Modelling Gaia CCD pixels with Silvaco 3D engineering software
Gaia will only achieve its unprecedented measurement accuracy requirements
with detailed calibration and correction for radiation damage. We present our
Silvaco 3D engineering software model of the Gaia CCD pixel and two of its
applications for Gaia: (1) physically interpreting supplementary buried channel
(SBC) capacity measurements (pocket-pumping and first pixel response) in terms
of e2v manufacturing doping alignment tolerances; and (2) deriving electron
densities within a charge packet as a function of the number of constituent
electrons and 3D position within the charge packet as input to microscopic
models being developed to simulate radiation damage.Comment: 4 pages, 3 figures, contributed poster, appearing in proceedings of
the ELSA conference: Gaia, at the frontiers of astrometry, 7-11 June 2010,
S\`evres, Pari
Detecting stars, galaxies, and asteroids with Gaia
(Abridged) Gaia aims to make a 3-dimensional map of 1,000 million stars in
our Milky Way to unravel its kinematical, dynamical, and chemical structure and
evolution. Gaia's on-board detection software discriminates stars from spurious
objects like cosmic rays and Solar protons. For this, parametrised
point-spread-function-shape criteria are used. This study aims to provide an
optimum set of parameters for these filters. We developed an emulation of the
on-board detection software, which has 20 free, so-called rejection parameters
which govern the boundaries between stars on the one hand and sharp or extended
events on the other hand. We evaluate the detection and rejection performance
of the algorithm using catalogues of simulated single stars, double stars,
cosmic rays, Solar protons, unresolved galaxies, and asteroids. We optimised
the rejection parameters, improving - with respect to the functional baseline -
the detection performance of single and double stars, while, at the same time,
improving the rejection performance of cosmic rays and of Solar protons. We
find that the minimum separation to resolve a close, equal-brightness double
star is 0.23 arcsec in the along-scan and 0.70 arcsec in the across-scan
direction, independent of the brightness of the primary. We find that, whereas
the optimised rejection parameters have no significant impact on the
detectability of de Vaucouleurs profiles, they do significantly improve the
detection of exponential-disk profiles. We also find that the optimised
rejection parameters provide detection gains for asteroids fainter than 20 mag
and for fast-moving near-Earth objects fainter than 18 mag, albeit this gain
comes at the expense of a modest detection-probability loss for bright,
fast-moving near-Earth objects. The major side effect of the optimised
parameters is that spurious ghosts in the wings of bright stars essentially
pass unfiltered.Comment: Accepted for publication in A&
From electrons to stars : modelling and mitigation of radiation damage effects on astronomical CCDs
The work presented in this thesis is part of an on-going effort to understand and mitigate the effects of radiation damage in astronomical CCDs. My research was motivated by and took place in the challenging context of the European Space Agency__s (ESA) astrometric mission, Gaia, for which radiation damage has been considered since its conception as one of the most important threats to its scientific performance. In this context my research focused primarily on the modelling of the effects of radiation-induced Charge Transfer Inefficiency (CTI) supported by the analysis of the experimental test data. I developed the most detailed model to date of CTI in CCDs that enables simulating the operation of irradiated devices (Chapter 2). Using this model I have been able to verify and enhance our current understanding of CTI as well as support the characterization of CCDs and the understanding of experimental results (Chapters 3 and 6). As part of this research I conducted the comprehensive re-assessment of the performance of Gaia taking into account radiation damage (Chapters 3 and 4). Finally I took part in the effort of countering CTI by elaborating, testing, and improving a forward modelling approach at the image processing level to mitigate the CTI effects on the Gaia easurements (Chapters 3 and 5), as well as test and explore the potential of a specific hardware mitigation tool (Chapter 6).European Marie-Curie research training network ELSA (MRTN-CT-2006-033481)UBL - phd migration 201
Digging supplementary buried channels: investigating the notch architecture within the CCD pixels on ESA's Gaia satellite
The European Space Agency (ESA) Gaia satellite has 106 CCD image sensors
which will suffer from increased charge transfer inefficiency (CTI) as a result
of radiation damage. To aid the mitigation at low signal levels, the CCD design
includes Supplementary Buried Channels (SBCs, otherwise known as `notches')
within each CCD column. We present the largest published sample of Gaia CCD SBC
Full Well Capacity (FWC) laboratory measurements and simulations based on 13
devices. We find that Gaia CCDs manufactured post-2004 have SBCs with FWCs in
the upper half of each CCD that are systematically smaller by two orders of
magnitude (<50 electrons) compared to those manufactured pre-2004 (thousands of
electrons). Gaia's faint star (13 < G < 20 mag) astrometric performance
predictions by Prod'homme et al. and Holl et al. use pre-2004 SBC FWCs as
inputs to their simulations. However, all the CCDs already integrated onto the
satellite for the 2013 launch are post-2004. SBC FWC measurements are not
available for one of our five post-2004 CCDs but the fact it meets Gaia's image
location requirements suggests it has SBC FWCs similar to pre-2004. It is too
late to measure the SBC FWCs onboard the satellite and it is not possible to
theoretically predict them. Gaia's faint star astrometric performance
predictions depend on knowledge of the onboard SBC FWCs but as these are
currently unavailable, it is not known how representative of the whole focal
plane the current predictions are. Therefore, we suggest Gaia's initial
in-orbit calibrations should include measurement of the onboard SBC FWCs. We
present a potential method to do this. Faint star astrometric performance
predictions based on onboard SBC FWCs at the start of the mission would allow
satellite operating conditions or CTI software mitigation to be further
optimised to improve the scientific return of Gaia.Comment: Accepted for publication in MNRAS, 16 pages, 19 figure
Transport infrastructures safety: a case study about public policy-making
People see and evaluate risks in a very different way, this is probably the most changeable variable that we must take into account developing some public policy on risk. People's judgements depend on both their personal experiences and from the context in which they are, thus, these conditions make impossible to evaluate them a priori. In this paper we present a French real case on transport infrastructure and risk management, namely the safety of their users. The aim of this paper is to provide, on the one side, an example of public policy management in which people safety and economic constraints are involved. And on the other side, open a discussion about risk reduction and the policies achieving it
Héritabilités et interactions génotype × régime pour le poids a huit semaines de poulets en présence de deux aliments
International audienc
Systematic Physics-Compliant Analysis of Over-the-Air Channel Equalization in RIS-Parametrized Wireless Networks-on-Chip
Wireless networks-on-chip (WNoCs) are an enticing complementary interconnect
technology for multi-core chips but face severe resource constraints. Being
limited to simple on-off-keying modulation, the reverberant nature of the chip
enclosure imposes limits on allowed modulation speeds in sight of inter-symbol
interference, casting doubts on the competitiveness of WNoCs as interconnect
technology. Fortunately, this vexing problem was recently overcome by
parametrizing the on-chip radio environment with a reconfigurable intelligent
surface (RIS). By suitably configuring the RIS, selected channel impulse
responses (CIRs) can be tuned to be (almost) pulse-like despite rich scattering
thanks to judiciously tailored multi-bounce path interferences. However, the
exploration of this "over-the-air" (OTA) equalization is thwarted by (i) the
overwhelming complexity of the propagation environment, and (ii) the non-linear
dependence of the CIR on the RIS configuration, requiring a costly and lengthy
full-wave simulation for every optimization step. Here, we show that a
reduced-basis physics-compliant model for RIS-parametrized WNoCs can be
calibrated with a single full-wave simulation. Thereby, we unlock the
possibility of predicting the CIR for any RIS configuration almost
instantaneously without any additional full-wave simulation. We leverage this
new tool to systematically explore OTA equalization in RIS-parametrized WNoCs
regarding the optimal choice of delay time for the RIS-shaped CIR's peak. We
also study the simultaneous optimization of multiple on-chip wireless links for
broadcasting. Looking forward, the introduced tools will enable the efficient
exploration of various types of OTA analog computing in RIS-parametrized WNoCs.Comment: 10 pages, 7 figures, submitted to an IEEE Journa
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