155 research outputs found
A Privacy Preserving Distributed Reputation Mechanism
International audienceReputation systems allow to estimate the trustworthiness of entities based on their past behavior. Electronic commerce, peer-to-peer routing and collaborative environments, just to cite a few, highly benefit from using reputation systems. To guarantee an accurate estimation, reputation systems typically rely on a central authority, on the identification and authentication of all the participants, or both. In this paper, we go a step further by presenting a distributed reputation mechanism which is robust against malicious behaviors and that preserves the privacy of its clients. Guaranteed error bounds on the estimation are provided
A Privacy Preserving Distributed Reputation Mechanism
International audienceReputation systems allow to estimate the trustworthiness of entities based on their past behavior. Electronic commerce, peer-to-peer routing and collaborative environments, just to cite a few, highly benefit from using reputation systems. To guarantee an accurate estimation, reputation systems typically rely on a central authority, on the identification and authentication of all the participants, or both. In this paper, we go a step further by presenting a distributed reputation mechanism which is robust against malicious behaviors and that preserves the privacy of its clients. Guaranteed error bounds on the estimation are provided
Nonlinear dynamics of waves and modulated waves in 1D thermocapillary flows. I: General presentation and periodic solutions
We present experimental results on hydrothermal traveling-waves dynamics in
long and narrow 1D channels. The onset of primary traveling-wave patterns is
briefly presented for different fluid heights and for annular or bounded
channels, i.e., within periodic or non-periodic boundary conditions. For
periodic boundary conditions, by increasing the control parameter or changing
the discrete mean-wavenumber of the waves, we produce modulated waves patterns.
These patterns range from stable periodic phase-solutions, due to supercritical
Eckhaus instability, to spatio-temporal defect-chaos involving traveling holes
and/or counter-propagating-waves competition, i.e., traveling sources and
sinks. The transition from non-linearly saturated Eckhaus modulations to
transient pattern-breaks by traveling holes and spatio-temporal defects is
documented. Our observations are presented in the framework of coupled complex
Ginzburg-Landau equations with additional fourth and fifth order terms which
account for the reflection symmetry breaking at high wave-amplitude far from
onset. The second part of this paper (nlin.PS/0208030) extends this study to
spatially non-periodic patterns observed in both annular and bounded channel.Comment: 45 pages, 21 figures (elsart.cls + AMS extensions). Accepted in
Physica D. See also companion paper "Nonlinear dynamics of waves and
modulated waves in 1D thermocapillary flows. II: Convective/absolute
transitions" (nlin.PS/0208030). A version with high resolution figures is
available on N.G. web pag
Global wetland contribution to 2000-2012 atmospheric methane growth rate dynamics
Increasing atmospheric methane (CH4) concentrations have contributed to approximately 20% of anthropogenic climate change. Despite the importance of CH4 as a greenhouse gas, its atmospheric growth rate and dynamics over the past two decades, which include a stabilization period (1999â2006), followed by renewed growth starting in 2007, remain poorly understood. We provide an updated estimate of CH4 emissions from wetlands, the largest natural global CH4 source, for 2000â2012 using an ensemble of biogeochemical models constrained with remote sensing surface inundation and inventory-based wetland area data. Between 2000â2012, boreal wetland CH4 emissions increased by 1.2 Tgâyrâ1 (â0.2â3.5 Tgâyrâ1), tropical emissions decreased by 0.9 Tgâyrâ1 (â3.2â1.1 Tgâyrâ1), yet globally, emissions remained unchanged at 184 ± 22 Tgâyrâ1. Changing air temperature was responsible for increasing high-latitude emissions whereas declines in low-latitude wetland area decreased tropical emissions; both dynamics are consistent with features of predicted centennial-scale climate change impacts on wetland CH4 emissions. Despite uncertainties in wetland area mapping, our study shows that global wetland CH4 emissions have not contributed significantly to the period of renewed atmospheric CH4 growth, and is consistent with findings from studies that indicate some combination of increasing fossil fuel and agriculture-related CH4 emissions, and a decrease in the atmospheric oxidative sink
The global methane budget 2000â2017
Understanding and quantifying the global methane (CH4) budget is important for assessing realistic pathways to mitigate climate change. Atmospheric emissions and concentrations of CH4 continue to increase, making CH4 the second most important human-influenced greenhouse gas in terms of climate forcing, after carbon dioxide (CO2). The relative importance of CH4 compared to CO2 depends on its shorter atmospheric lifetime, stronger warming potential, and variations in atmospheric growth rate over the past decade, the causes of which are still debated. Two major challenges in reducing uncertainties in the atmospheric growth rate arise from the variety of geographically overlapping CH4 sources and from the destruction of CH4 by short-lived hydroxyl radicals (OH). To address these challenges, we have established a consortium of multidisciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate new research aimed at improving and regularly updating the global methane budget. Following Saunois et al. (2016), we present here the second version of the living review paper dedicated to the decadal methane budget, integrating results of top-down studies (atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up estimates (including process-based models for estimating land surface emissions and atmospheric chemistry, inventories of anthropogenic emissions, and data-driven extrapolations).
For the 2008â2017 decade, global methane emissions are estimated by atmospheric inversions (a top-down approach) to be 576âTgâCH4âyrâ1 (range 550â594, corresponding to the minimum and maximum estimates of the model ensemble). Of this total, 359âTgâCH4âyrâ1 or âŒâ60â% is attributed to anthropogenic sources, that is emissions caused by direct human activity (i.e. anthropogenic emissions; range 336â376âTgâCH4âyrâ1 or 50â%â65â%). The mean annual total emission for the new decade (2008â2017) is 29âTgâCH4âyrâ1 larger than our estimate for the previous decade (2000â2009), and 24âTgâCH4âyrâ1 larger than the one reported in the previous budget for 2003â2012 (Saunois et al., 2016). Since 2012, global CH4 emissions have been tracking the warmest scenarios assessed by the Intergovernmental Panel on Climate Change. Bottom-up methods suggest almost 30â% larger global emissions (737âTgâCH4âyrâ1, range 594â881) than top-down inversion methods. Indeed, bottom-up estimates for natural sources such as natural wetlands, other inland water systems, and geological sources are higher than top-down estimates. The atmospheric constraints on the top-down budget suggest that at least some of these bottom-up emissions are overestimated. The latitudinal distribution of atmospheric observation-based emissions indicates a predominance of tropical emissions (âŒâ65â% of the global budget, <â30ââN) compared to mid-latitudes (âŒâ30â%, 30â60ââN) and high northern latitudes (âŒâ4â%, 60â90ââN). The most important source of uncertainty in the methane budget is attributable to natural emissions, especially those from wetlands and other inland waters.
Some of our global source estimates are smaller than those in previously published budgets (Saunois et al., 2016; Kirschke et al., 2013). In particular wetland emissions are about 35âTgâCH4âyrâ1 lower due to improved partition wetlands and other inland waters. Emissions from geological sources and wild animals are also found to be smaller by 7âTgâCH4âyrâ1 by 8âTgâCH4âyrâ1, respectively. However, the overall discrepancy between bottom-up and top-down estimates has been reduced by only 5â% compared to Saunois et al. (2016), due to a higher estimate of emissions from inland waters, highlighting the need for more detailed research on emissions factors. Priorities for improving the methane budget include (i) a global, high-resolution map of water-saturated soils and inundated areas emitting methane based on a robust classification of different types of emitting habitats; (ii) further development of process-based models for inland-water emissions; (iii) intensification of methane observations at local scales (e.g., FLUXNET-CH4 measurements) and urban-scale monitoring to constrain bottom-up land surface models, and at regional scales (surface networks and satellites) to constrain atmospheric inversions; (iv) improvements of transport models and the representation of photochemical sinks in top-down inversions; and (v) development of a 3D variational inversion system using isotopic and/or co-emitted species such as ethane to improve source partitioning
Altimetry for the future: Building on 25 years of progress
In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the ââGreenâ Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instrumentsâ development and satellite missionsâ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion
Altimetry for the future: building on 25 years of progress
In 2018 we celebrated 25âŻyears of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology.
The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the âGreenâ Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instrumentsâ development and satellite missionsâ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion
Protocole Ad hoc Proactif Anonyme Ă Base de Cryptographie Homomorphique
National audienceAvec l'avĂšnement des systĂšmes ubiquitaires, la question du respect de la vie privĂ©e devient primordiale. DĂ» aux spĂ©cificitĂ©s de ces systĂšmes, il est particuliĂšrement difficile d'empĂȘcher la fuite d'informations telles que l'identitĂ© des personnes, leur emplacement gĂ©ographique, leurs relations, etc. Dans le monde des rĂ©seaux ad hoc, il est nĂ©cessaire que les protocoles de routage assurent la protection des identitĂ©s des noeuds ainsi que leur position tant gĂ©ographique que relative. Dans cet article, nous proposons un nouveau protocole de routage ad hoc proactif se basant sur la cryptographie homomorphique complĂšte pour assurer la protection des informations privĂ©es des noeuds. Cette technologie offre de nouvelles possibilitĂ©s : il n'est plus nĂ©cessaire de dĂ©chiffrer une information pour l'utiliser. Avec un minimum d'hypothĂšses, nous montrons qu'un protocole de routage ad hoc proactif garantissant un fort respect de la vie privĂ©e est possible
Contributions à la sécurité des réseaux dynamiques auto-configurables (application aux réseaux domestiques)
Un rĂ©seau domestique est constituĂ© d'appareils (ordinateurs, PDAs, tĂ©lĂ©phones mobiles, etc.) interconnectĂ©s et appartenant aux habitants d'un mĂȘme foyer. Ces appareils s'auto-configurent et interagissent pour offrir de maniĂšre transparente des services aux utilisateurs. Bien qu'il faille protĂ©ger les rĂ©seaux domestiques, les mĂ©canismes de sĂ©curitĂ© traditionnels requiĂšrent souvent une configuration trop complexes pour l'utilisateur. Nous dĂ©fendons ici la thĂšse suivante : pour ĂȘtre utiles, les mĂ©canismes de sĂ©curitĂ© dans les rĂ©seaux domestiques doivent eux aussi privilĂ©gier l'auto-configuration pour ne pas nuire Ă la facilitĂ© d'usage. Pour Ă©tayer cette thĂšse, nous proposons tout d'abord un systĂšme dĂ©centralisĂ© et simple d'utilisation de gestion sĂ©curisĂ©e du groupe des appareils du rĂ©seau domestique. Puis nous proposons le concept de pare-feu omniprĂ©sent, dans lequel un service prĂ©sent sur chaque appareil configure automatiquement les outils de sĂ©curitĂ© locaux en fonction de la politique de sĂ©curitĂ© et de son environnement.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF
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