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Monitoring of Riverine Aquatic Vegetation Using Satellite PlanetScope Imagery: Feasibility, Limitations and Prospects
No full textInternational audienceSpectral interference induced by the water and the spatial resolution of many satellite images (≥ 10 m) limit the efficiency of remote sensing for monitoring riverine aquatic plant stands. In this study, the potential of using PlanetScope satellite images (3 m in spatial resolution, ~daily acquisition) for monitoring seasonal and interannual aquatic vegetation surface area was evaluated. Airborne images (≤ 0.2 m) acquired on four dates on three aquatic plant stands were used to create, through visual interpretation, reference maps indicating whether the pixels of each PlanetScope image acquired at ±8 days correspond to aquatic vegetation or nonvegetated aquatic areas. For each PlanetScope image, the green normalized difference vegetation index (GNDVI) was calculated and centred on the mean (GNDVI centred ) to distinguish aquatic vegetation from nonvegetated aquatic areas while minimizing variations in their spectral signature over time. Reference maps from the date when aquatic vegetation was the least developed were used to calculate the GNDVI centred classification threshold. To reduce classification errors from radiometric inconsistencies, the frequency at which pixels of PlanetScope images acquired at ±8 days from airborne images were classified as aquatic vegetation was also calculated. Aquatic vegetation was then empirically defined as pixels with a frequency ≥ 85%. Although the classification of PlanetScope images indicates that low abundances of aquatic vegetation cannot be detected, our results show that large changes in stand surface area can be monitored using a multidate classification threshold, thus providing new opportunities for the monitoring of riverine aquatic vegetation on large scales
Making democracy work: fixing and simplifying egalitarian paxos (extended version)
No full textClassical state-machine replication protocols, such as Paxos, rely on a distinguished leader process to order commands. Unfortunately, this approach makes the leader a single point of failure and increases the latency for clients that are not co-located with it. As a response to these drawbacks, Egalitarian Paxos introduced an alternative, leaderless approach, that allows replicas to order commands collaboratively. Not relying on a single leader allows the protocol to maintain non-zero throughput with up to crashes of any processes out of a total of . The protocol furthermore allows any process to execute a command fast, in message delays, provided no more than other processes fail, and all concurrently submitted commands commute with ; the latter condition is often satisfied in practical systems. Egalitarian Paxos has served as a foundation for many other replication protocols. But unfortunately, the protocol is very complex, ambiguously specified and suffers from nontrivial bugs. In this paper, we present EPaxos* -- a simpler and correct variant of Egalitarian Paxos. Our key technical contribution is a simpler failure-recovery algorithm, which we have rigorously proved correct. Our protocol also generalizes Egalitarian Paxos to cover the whole spectrum of failure thresholds and such that -- the number of processes that we show to be optimal
Adjusted objects: an efficient and principled approach to scalable programming (extended version)
No full textParallel programs require software support to coordinate access to shared data. For this purpose, modern programming languages provide strongly-consistent shared objects. To account for their many usages, these objects offer a large API. However, in practice, each program calls only a tiny fraction of the interface. Leveraging such an observation, we propose to tailor a shared object for a specific usage. We call this principle adjusted objects. Adjusted objects already exist in the wild. This paper provides their first systematic study. We explain how everyday programmers already adjust common shared objects (such as queues, maps, and counters) for better performance. We present the formal foundations of adjusted objects using a new tool to characterize scalability, the indistinguishability graph. Leveraging this study, we introduce a library named DEGO to inject adjusted objects in a Java program. In micro-benchmarks, objects from the DEGO library improve the performance of standard JDK shared objects by up to two orders of magnitude. We also evaluate DEGO with a Retwis-like benchmark modeled after a social network application. On a modern server-class machine, DEGO boosts by up to 1.7x the performance of the benchmark
What can we do in a symmetry-constrained perspective? The importance of the total charge's status in quantum reference frame frameworks
No full text25+6 pages. Comments are welcome!The study of quantum reference frames has received renewed interest over the lastyears, leading to the parallel development of non-equivalent frameworks by different com-munities. We clarify the differences between these frameworks. At the mathematical level,they mainly differ in the kind of symmetry (either weak or strong) employed to constrainthe system. We show that this mathematical difference corresponds to a fundamentalphysical question: whether the global charge associated to the symmetry group is acces-sible to symmetry-constrained observers. In this context, we formulate a definition of aperspective in terms of operational capacities, or lack thereof. Turning to consequences ofadopting either approach, we discuss how adopting the weak approach induces an ambi-guity in the momenta included in each perspective and bars from defining reversible QRFtransformations. We then review and analyze the existing arguments motivating eachapproach, and show how they bear upon the problem of charge accessibility. Finally, weintroduce a simple operational scenario in which upholding two reasonable physical pos-tulates leads to the conclusion that internal observers could measure the global charge by1/ performing a relativized interference measurement and 2/ classically communicating
Many-body Quantum Score: a scalable benchmark for digital and analog quantum processors and first test on a commercial neutral atom device
No full textWe propose the Many-body Quantum Score (MBQS), a practical and scalable application level benchmark protocol designed to evaluate the capabilities of quantum processing units (QPUs)—both gate-based and analog—for simulating many-body quantum dynamics. MBQS quantifies performance by identifying the maximum number of qubits with which a QPU can reliably reproduce correlation functions of the transverse-field Ising model following a specific quantum quench. This paper presents the MBQS protocol and highlights its design principles, supported by analytical insights, classical simulations, and experimental data. It also displays results obtained with Ruby, an analogQPU based on Rydberg atoms developed by the Pasqal company. These findings demonstrateMBQS’s potential as a robust and informative tool for benchmarking near-term quantum devices for many-body physics
Order Matters: 3D Shape Generation from Sequential VR Sketches
No full textVR sketching lets users explore and iterate on ideas directly in 3D, offering a faster and more intuitive alternative to conventional CAD tools. However, existing sketch-to-shape models ignore the temporal ordering of strokes, discarding crucial cues about structure and design intent. We introduce VRSketch2Shape, the first framework and multi-category dataset for generating 3D shapes from sequential VR sketches. Our contributions are threefold: (i) an automated pipeline that generates sequential VR sketches from arbitrary shapes, (ii) a dataset of over 20k synthetic and 900 hand-drawn sketch-shape pairs across four categories, and (iii) an order-aware sketch encoder coupled with a diffusion-based 3D generator. Our approach yields higher geometric fidelity than prior work, generalizes effectively from synthetic to real sketches with minimal supervision, and performs well even on partial sketches. All data and models will be released open-source at https://chenyizi086.github.io/VRSketch2Shape_website
The North Balearic Front as an ecological boundary: zooplankton fine-scale distribution patterns in late spring
No full textInternational audienceObservations, models and theory have suggested that ocean fronts are ecological hotspots, generally associated with higher diversity and biomass across many trophic levels. Nutrient injections are often associated with higher chlorophyll concentrations at fronts, but the response of the zooplankton community is still insufficiently understood. The present study investigates mesozooplankton stocks and composition during late spring, northeast of Menorca, along two north-south transects that crossed the North Balearic Front separating central waters of the Northwestern Mediterranean Sea gyre from peripheral waters originating from the Algerian basin. During the BioSWOT-Med campaign, vertical triple-net tows with 200 and 500 µm meshes were carried out at three depths (100, 200, and 400 m), and the samples were processed with ZooScan to classify organisms into eight taxonomic groups. Zooplankton distributions were analyzed for the surface layer (0–100 m), a mid-depth layer (100–200 m), and a deeper layer (200–400 m). The results did not show a significant increase in biomass in the front in any layers. The NBF appears to act as a boundary between communities rather than a pronounced area of active or passive zooplankton accumulation. Analyses of stratified vertical distributions of zooplankton highlighted distinct taxonomic compositions in the three layers, and a progressive homogenization of community structure with depth, reflecting a weaker impact of hydrological processes on deeper communities. The clearest impact of the front was within the upper 100 m, where the mesozooplanktonic taxonomic composition differed between the front and adjacent water masses, with a decrease in all taxonomic groups except Cnidaria, which increased dramatically. In the two deeper layers, the front also influenced community composition, although to a lesser extent, with marked increases in Foraminifera and Cnidaria. Moreover, the northern water mass and the front were dominated by large copepods, while the southern water mass exhibited higher zooplankton diversity and smaller-sized copepods. The results of this study highlight the complexity of processes shaping planktonic communities over time and space in the NBF zone and its adjacent waters. These processes include zooplankton stock reduction in the transitional post-bloom period, marked effect of diel variation linked to vertical migrations, and potentially the impact of storm-related mixing in the surface layer that can disrupt established ecological patterns
Modélisation et analyse économique du comportement des acteurs sur les marchés énergétiques: Des producteurs aux consommateurs
No full textSecond-moment turbulent models for incompressible flows : some recent -and less recent- results
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Computation of the elastodynamic response of finite doubly periodic cylinders by the wave finite element method
No full textInternational audiencePeriodic media are widely studied for their industrial applications and unique ability to block wave propagation within certain frequency bands. For one-dimensional periodic systems, the Wave Finite Element (WFE) method efficiently computes dispersion relations and dynamic responses. Research on two-dimensional periodic structures extended this approach to periodicity along two directions, using finite element and reduction techniques such as Craig-Bampton and Bloch mode projection, including cases with damping and anisotropy. Beyond planar geometries, curved and helical periodic structures have been modeled with WFE and semi-analytical finite element methods to capture complex cyclic or screw symmetries for computing dispersion relations. Cylindrical configurations have also been explored, from simple vibration studies to wave propagation in layered or ribbed cylinders and metamaterial shells mainly for dispersion analysis or studies of infinite structures. As real structures are bounded, the present work focuses on finite elastic cylinders with double periodicity, using WFE to compute their dynamic response. Based on finite element matrices of a substructure, circumferential wavenumbers are imposed to obtain axial modes and responses as linear combination of modes. Numerical examples illustrate the method's effectiveness for modeling finite, doubly periodic cylindrical systems such as homogeneous structures, structures with holes and finally structures with resonators. The low computing time of the present approach allows the consideration of structures with a large number of substructures