5,087 research outputs found
Challenges in experimental data integration within genome-scale metabolic models
A report of the meeting "Challenges in experimental data integration within
genome-scale metabolic models", Institut Henri Poincar\'e, Paris, October 10-11
2009, organized by the CNRS-MPG joint program in Systems Biology.Comment: 5 page
Domain convexification: a simple model for invasion processes
We propose an invasion model where domains grow up to their convex hulls and
merge when they overlap. This model can be seen as a continuum and isotropic
counterpart of bootstrap percolation models. From numerical investigations of
the model starting with randomly scattered discs in two dimensions, we find an
invasion transition that occurs via macroscopic avalanches. The disc
concentration threshold and the sharpness of the transition are found to
decrease as the system size is increased. Our results are consistent with a
vanishing threshold in the limit of infinitely large system sizes. However this
limit could not be investigated by simulations. For finite initial
concentrations of discs, the cluster size distribution presents a power-law
tail characterized by an exponent that varies approximately linearly with the
initial concentration of discs. These results at finite initial concentration
open novel directions for the understanding of the transition in systems of
finite size. Furthermore, we find that the domain area distribution has
oscillations with discontinuities. In addition, the deviation from circularity
of large domains is constant. Finally, we compare our results to experimental
observations on de-adhesion of graphene induced by the intercalation of
nanoparticles.Comment: 19 pages, 17 figure
Research-grade CMOS image sensors for remote sensing applications
Imaging detectors are key elements for optical instruments and sensors on board space missions dedicated to Earth
observation (high resolution imaging, atmosphere spectroscopy...), Solar System exploration (micro cameras, guidance for autonomous vehicle...) and Universe observation (space telescope focal planes, guiding sensors...). This market has been dominated by CCD technology for long. Since the mid-90s, CMOS Image Sensors (CIS) have been competing with CCDs for consumer domains (webcams, cell phones, digital cameras...). Featuring significant advantages over CCD sensors for space applications (lower power consumption, smaller system size, better radiations behaviour...), CMOS technology is also expanding in this field, justifying specific R&D and development programs funded by national and European space agencies (mainly CNES, DGA and ESA). All along the 90s and thanks to their increasingly improving performances, CIS have started to be successfully used for more and more demanding space applications, from vision and control functions requiring low-level performances to guidance applications requiring medium-level performances. Recent technology improvements have made possible the manufacturing of research-grade CIS that are able to compete with CCDs in the high-performances arena. After an introduction outlining the growing interest of optical instruments designers for CMOS image sensors, this paper will present the existing and foreseen ways to reach
high-level electro-optics performances for CIS. The developments and performances of CIS prototypes built using an imaging CMOS process will be presented in the corresponding section
A batch scheduler with high level components
In this article we present the design choices and the evaluation of a batch
scheduler for large clusters, named OAR. This batch scheduler is based upon an
original design that emphasizes on low software complexity by using high level
tools. The global architecture is built upon the scripting language Perl and
the relational database engine Mysql. The goal of the project OAR is to prove
that it is possible today to build a complex system for ressource management
using such tools without sacrificing efficiency and scalability. Currently, our
system offers most of the important features implemented by other batch
schedulers such as priority scheduling (by queues), reservations, backfilling
and some global computing support. Despite the use of high level tools, our
experiments show that our system has performances close to other systems.
Furthermore, OAR is currently exploited for the management of 700 nodes (a
metropolitan GRID) and has shown good efficiency and robustness
Space optical instruments optimisation thanks to CMOS image sensor technology
Today, both CCD and CMOS sensors can be envisaged for nearly all visible sensors and instruments designed for space needs. Indeed, detectors built with both technologies allow excellent electro-optics performances to be reached, the selection of the most adequate device being driven by their functional and technological features and limits. The first part of the paper presents electro-optics characterisation results of CMOS Image Sensors (CIS) built with an optimised CMOS process, demonstrating the large improvements of CIS electro-optics performances. The second part reviews the advantages of CMOS technology for space applications, illustrated by examples of CIS developments performed by EADS Astrium and Supaéro/CIMI for current and short term coming space programs
CMOS detectors for space applications: from R&D to operational program with large volume foundry
Nowadays, CMOS image sensors are widely considered for space applications. The use of CIS (CMOS Image sensor)
processes has significantly enhanced their performances such as dark current, quantum efficiency and conversion gain. However, in order to fulfil specific space mission requirements, dedicated research and development work has to be performed to address specific detector performance issues. This is especially the case for dynamic range improvement through output voltage swing optimisation, control of conversion gain and noise reduction. These issues have been addressed in a 0.35μm CIS process, based on a large volume CMOS foundry, by several joint ISAE- EADS Astrium R&D programs. These results have been applied to the development of the visible and near-infrared multi-linear imager for the SENTINEL 2 mission (LEO Earth observation mission for the Global Measurement Environment and Security program). For this high performance multi-linear device, output voltage swing improvement is achieved by process optimisation done in collaboration with foundry. Conversion gain control is also achieved for each spectral band by managing photodiode capacitance. A low noise level at sensor output is reached by the use of an architecture allowing Correlated Double Sampling readout in order to eliminate reset noise (KTC noise). KTC noise elimination reveals noisy pixels due to RTS noise. Optimisation of transistors’s dimensions, taking into account conversion gain constraints, is done to minimise these noisy pixels. Additional features have been also designed: 1) Due to different integration times between spectral bands required by mission, a specific readout mode was developed in order to avoid electrical perturbations during the integration time and readout. This readout mode leads to specific power supply architecture. 2)Post processing steps can be achieved by alignment marks design allowing a very good accuracy. These alignment marks can be used for a black coating deposition between spectral bands (pixel line) in order to minimise straight lighteffects. In conclusion a review of design improvements and performances of the final component is performed
High performances monolithic CMOS detectors for space applications
During the last 10 years, research about CMOS image sensors (also called APS -Active Pixel Sensors) has been intensively carried out, in order to offer an alternative to CCDs as image sensors. This is particularly the case for space applications as CMOS image sensors feature characteristics which are obviously of interest for flight hardware: parallel or semi-parallel architecture, on chip control and processing electronics, low power dissipation, high level ofradiation tolerance... Many image sensor companies, institutes and laboratories have demonstrated the compatibility of CMOS image sensors with consumer applications: micro-cameras, video-conferencing, digital-still cameras. And recent designs have shown that APS is getting closer to the CCD in terms ofperformance level. However, the large majority ofthe existing products do not offer the specific features which are required for many space applications. ASTRI1JM and SUPAERO/CIMI have decided to work together in view of developing CMOS image sensors dedicated to space business. After a brief presentation of the team organisation for space image sensor design and production, the latest results of a high performances 512x512 pixels CMOS device characterisation are presented with emphasis on the achieved electro-optical performance. Finally, the on going and short-term coming activities of the team are discussed
Development of high-performances monolithic CMOS detectors for space applications
This paper describes the development of a 750x750 pixels CMOS image sensor for star tracker applications. A first
demonstrator of such a star tracker called SSM star tracker built around a 512x512 detector has been recently developed and proves the feasibility of such instrument. In order to take fully advantage of the CMOS image sensor step, the 750x750 device called SSM CMOS detector which will take part of the final star tracker, can be considered as a major technical breakthrough that gives a decisive advantage in terms of on satellite implementation cost and flexibility (sensor mass and power consumption minimisation, electronics and architecture flexibility). Indeed, built using the 0.5μm Alcatel Microelectronics standard CMOS technology, the SSM CMOS detector will feature on-chip temperature sensor and on-chip sequencer. In order to evaluate the radiation tolerance of such manufacturing technology, a radiation campaign that contains studies of total dose and latch-up effects has been led on a specific test vehicle
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