Efficient Hamiltonian, structure and trace distance learning of Gaussian states

In this work, we initiate the study of Hamiltonian learning for positive temperature bosonic Gaussian states, the quantum generalization of the widely studied problem of learning Gaussian graphical models. We obtain efficient protocols, both in sample and computational complexity, for the task of inferring the parameters of their underlying quadratic Hamiltonian under the assumption of bounded temperature, squeezing, displacement and maximal degree of the interaction graph. Our protocol only requires heterodyne measurements, which are often experimentally feasible, and has a sample complexity that scales logarithmically with the number of modes. Furthermore, we show that it is possible to learn the underlying interaction graph in a similar setting and sample complexity. Taken together, our results put the status of the quantum Hamiltonian learning problem for continuous variable systems in a much more advanced state when compared to spins, where state-of-the-art results are either unavailable or quantitatively inferior to ours. In addition, we use our techniques to obtain the first results on learning Gaussian states in trace distance with a quadratic scaling in precision and polynomial in the number of modes, albeit imposing certain restrictions on the Gaussian states. Our main technical innovations are several continuity bounds for the covariance and Hamiltonian matrix of a Gaussian state, which are of independent interest, combined with what we call the local inversion technique. In essence, the local inversion technique allows us to reliably infer the Hamiltonian of a Gaussian state by only estimating in parallel submatrices of the covariance matrix whose size scales with the desired precision, but not the number of modes. This way we bypass the need to obtain precise global estimates of the covariance matrix, controlling the sample complexity

The uncommon intracluster medium features of the first massive clusters selected independently of their baryon content

International audienceOur current knowledge of the thermodynamic properties of galaxy clusters comes primarily from detailed studies of clusters selected by their minority components: hot baryons. Most of these studies select the clusters using the component that is being investigated, the intracluster medium (ICM), making the sample choice prone to selection effects. Weak-gravitational lensing allows us to select clusters by the total mass component and, being independent of the type of matter, makes the sample choice unbiased with respect to the baryon content. In this paper, we study four galaxy clusters at intermediate redshift ($0.252\sigma$) features, while we observed on average two rare features in each one of the seven explored properties: richness, core-excised luminosity, Compton parameter, pressure and electron pressure profiles, and central values of them. The abundance of rare and unique features in such a small sample indicates a fundamental bias in our knowledge of the thermodynamic properties of clusters when derived from ICM-selected samples

AnCoGen: Analysis, Control and Generation of Speech with a Masked Autoencoder

International audienceThis article introduces AnCoGen, a novel method that leverages a masked autoencoder to unify the analysis, control, and generation of speech signals within a single model. AnCoGen can analyze speech by estimating key attributes, such as speaker identity, pitch, content, loudness, signal-to-noise ratio, and clarity index. In addition, it can generate speech from these attributes and allow precise control of the synthesized speech by modifying them. Extensive experiments demonstrated the effectiveness of AnCoGen across speech analysisresynthesis, pitch estimation, pitch modification, and speech enhancement. Code and audio examples are available online 1 .Index Terms-Speech analysis/transformation/synthesis, masked autoencoder, pitch estimation and modification, speech enhancement.</div

All, most, some? On diffeomorphisms of the interval that are distorted and/or conjugate to powers of themselves

32 pages, 3 figuresWe study the problem of conjugating a diffeomorphism of the interval to (positive) powers of itself. Although this is always possible for homeomorphisms, the smooth setting is rather interesting. Besides the obvious obstruction given by hyperbolic fixed points, several other aspects need to be considered. As concrete results we show that, in class $C^1$, if we restrict to the (closed) subset of diffeomorphisms having only parabolic fixed points, then the set of diffeomorphisms that are conjugate to their powers is dense, but its complement is generic. In higher regularity, however, the complementary set contains an open and dense set. The text is complemented with several remarks and results concerning distortion elements of the group of diffeomorphisms of the interval in several regularities

Suspensions of attractive microcapsules: A noncolloidal fragile gel?

International audienceWe investigated the rheological properties of suspensions of attractive microcapsules, which formed a weak gel at volume fractions ϕ as low as 0.1. These microcapsules, measuring 100 μm in diameter, were constructed with a droplet of positively charged chitosan solution protected by a membrane formed through the complexation of chitosan with a negatively charged surfactant. Iso-density matched suspensions were achieved by dispersing these microcapsules in silicone oils. Plate-plate rheometry revealed that these suspensions displayed a yield stress ranging from about 0.1 to 3 Pa for ϕ increasing from 0.1 to 0.5. At much higher stresses, the suspension viscosity was almost shear independent. Furthermore, these suspensions exhibited a frequency sweep signature akin to attractive colloidal suspensions, with a shear elastic modulus plateauing at low frequencies, indicative of an elastic microstructure within the suspensions. Remarkably, a degree of microstructural anisotropy, reminiscent of fragile matter, was evidenced by the transient fluidization of the suspension when the direction of applied stress, which remained below the yield stress, was reversed. Beyond the yield stress, both symmetric and asymmetric stress reversal experiments demonstrated that the suspension structure was influenced by the applied stress. It changed from an anisotropic and fragile network at low stress levels to a dispersion of isolated particles at high stress levels. We concluded that suspensions of attractive microcapsules could be classified as a fragile particulate gel, whose microstructure depends on the stress and its direction

Aftershocks as a Time Independent Phenomenon

International audienceSequences of aftershocks following Omori&#039;s empirical law are observed after most major earthquakes, as well as in laboratory‐scale fault‐mimicking experiments. Nevertheless, the origin of this memory effect is still unclear. In this letter, we present an analytical framework for treating labquake and earthquake catalogs on an equal footing. Using this analysis method, we show that when memory is considered to be in deformation and not in time, all data collapse onto a single master curve, showing that the timescale is entirely fixed by the inverse of the strain rate

Espaces de transformation et de réinvention plurilingues : un voyage artistique et créatif avec des élèves de l’école primaire

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Sources and fates of NO₃⁻ and PO₄³⁻ in an alluvial plain wetland - Insights from the Auzon oxbow and the alluvial aquifer of the Allier (Auvergne, France)

International audienceThe continental hydrosystems of wetlands play fundamental socio-economic and environmental roles in all aquatic environments. These ecosystems, when located at the interface between surface and groundwater, such as oxbows, are of crucial importance in regulating water and nutrient flows. They help control water quality and provide ideal habitats for often fragile species. The transfer of contaminants into the different compartments of the groundwater-wetland-river continuum is difficult to characterize because they are most often of different types and origins within the same hydrosystem. The objective of this study is to characterize water quality and water exchange using a multi-tracer approach combining monthly hydrochemical monitoring, isotopic characterization of NO3− molecules (δ18ONO3 and δ15NNO3) and concentration of chemical micropollutant particles. This methodology is applied to a fluvial annex of the Allier River, the Auzon oxbow hydrosystem, subject to moderate environmental and anthropogenic pressure (low level of industrialization and urbanization, mixed conventional farming). Nitrate (NO3−) and phosphate (PO43−) concentrations do not behave in the same way over time: NO3− has a seasonal dynamic, whereas phosphates are disconnected from the hydrological regime. Some subsystems of the Auzon oxbow are undergoing denitrification, demonstrating the importance of preserving these environments for their nutrient regulation potential. As for chemical micropollutants and PO43−, the low overall concentration of these two contaminants, coupled with the high dilution potential of the Auzon oxbow hydrosystem, means that average concentrations remain within acceptable standards for surface waters. Based on these results, the Auzon hydrosystem is maintaining good ecological quality despite nutrient flows from multiple sources. The multitracer approach used in this study demonstrates its effectiveness in determining the origin of nutrients, and it could be applied to other studies in contexts where environmental and societal pressures are significantly higher

Methane and volatile organic compounds and their influence on air quality in Boulder, Colorado

International audienceThe Northern Colorado Front Range (NCFR) has a long history of air pollution problems, which include summertime ozone levels regularly exceeding the ozone National Ambient Air Quality Standard (NAAQS). The NCFR has been designated as a nonattainment area for the ozone NAAQS since 2007. Contributing factors to the elevated pollution buildup include meteorological conditions such as the mountain-valley thermal forcing that recirculates air enriched in volatile organic compound (VOC) emissions from oil and natural gas (O&amp;NG) production and other sources such as vehicle traffic. This study examines data collected from continuous monitoring of methane and VOCs between 2017 and 2021 at the Boulder Reservoir (BRZ) to pinpoint the sources contributing to this pollution; 19,335 VOC samples of alkanes, alkenes, and aromatic hydrocarbons were collected during this period, with measurements taken every 1-2 h. BRZ is located on the outskirts of the Denver metropolitan area and lies between the oil and gas fields that are predominantly located in Weld County (starting about 15 km to the east) and the Rocky Mountain foothills (5 km to the west). The VOC composition is dominated by light alkanes with a "wet" (i.e., &gt;15% weight of total VOCs in relation to methane) natural gas signature. VOCs are highly variable, with concentrations spanning %2 orders of magnitude. Plumes that carry elevated (&gt;10 times the background) O&amp;NG VOCs were observed on the order of &gt;100 times per year. These events were mostly associated with winds from the north to southeast sector, which is the direction that aligns with the densest O&amp;NG development. Averaged over a full year, O&amp;NG and total VOC mole fractions were higher than in most U.S. cities, including those with much higher total population than that of Boulder County. A correlation and scaling analysis yielded total (excluding ethane) NCFR O&amp;NG VOC emissions of 183.6 ± 12.6 Gg yr À1 for 2015, and 81.3 ± 16.1 Gg yr À1 for 2021, respectively, which is %2-2.5 times higher than the State's reported inventory flux. A preliminary data evaluation indicates no changes in methane emissions in the Denver-Julesburg Basin (DJB) that are outside of the measurement uncertainty. O&amp;NG tracer VOCs (e.g., ethane, propane) show signs of possibly declining emissions. The identified discrepancies between the inferred emissions from air monitoring data and the emissions stated in the inventory reemphasize the importance of considering field observations in directing the State's air quality policy, rather than solely relying on inventory data

Finding the Common Ground: Visibility, Cooperation and Tensions between Russian and Georgian Civil Society Initiatives in Tbilisi, 2023

International audienceThis article explores the coexistence of the Russian émigré community and Georgian civil society in Tbilisi and the tensions between them since the Russian invasion of Ukraine in 2022. It analyzes how these interactions reflect broader post-colonial dynamics, particularly focusing on the differing political grammars and histories that shape both communities. Drawing from extensive fieldwork, the study highlights the complexities of this encounter, emphasizing the influence of historical narratives, collective action, and the post-Soviet socio-political context. The paper uncovers the nuances of visibility, integration, and mutual perceptions, ultimately contributing to the broader debates on post-socialist societies, migration, and civil society development