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Electrical Conductance of Oxidized Rough Sphere Contacts: A Greenwood-Tripp-Based Model
No full textElectrical conductance of rough contacts is strongly affected by the presence of surface oxides, particularly when oxide films are discontinuous and no clear separation of length scales exists between roughness, oxide morphology, and contact size. In this work, we develop a statistical model for electrical conductance in oxidized rough sphere contacts. Oxide films are represented as spatially heterogeneous insulating regions generated by thresholded Gaussian random fields, allowing controlled variation of oxide coverage and correlation length. Mechanical contact is treated within a Greenwood-Tripp-based formulation, while electrical conductance is evaluated using Greenwood's constriction resistance model applied to the resulting population of conducting microcontacts. A comprehensive parametric study reveals the role of oxide morphology and allows to formulate a simple phenomenological model for the average conductance. This new model is in a good agreement with the extended Barber's model
“Bad” Oil, “Worse” Oil, and Carbon Misallocation
No full textInternational audienceNot all barrels of oil are created equal: their extraction varies in both private cost and carbon intensity. Leveraging a comprehensive micro-dataset on world oil fields, alongside detailed estimates of carbon intensities and private extraction costs, this study quantifies the additional emissions and costs from having extracted the “wrong” deposits. We do so by comparing historical deposit-level supplies to counterfactuals that factor in pollution costs, while keeping annual global consumption unchanged. Between 1992 and 2018, carbon misallocation amounted to at least 11.00 gigatons of CO2-equivalent (GtCO2eq), incurring an environmental cost evaluated at 2018). This translates into a significant supply-side ecological debt for major producers of high-carbon oil. Looking forward, we estimate the gains from making deposit-level extraction socially optimal at about 9.30 GtCO2eq, valued at $1.9 trillion, along a future aggregate demand pathway coherent with the objective of net-zero emissions in 2050, and document unequal reserve stranding across oil nations
Dissipating quartets of excitations in a superconducting circuit
No full textInternational audienceOver the past decade, autonomous stabilization of bosonic qubits has emerged as a promising approach for hardware-efficient protection of quantum information. However, applying these techniques to more complex encodings than the Schr\"odinger cat code requires exquisite control of high-order wave mixing processes. The challenge is to enable specific multiphotonic dissipation channels while avoiding unintended non-linear interactions. In this work, we leverage a genuine six-wave mixing process enabled by a near Kerr-free Josephson element to enforce dissipation of quartets of excitations in a high-impedance superconducting resonator. Owing to residual non-linearities stemming from stray inductances in our circuit, this dissipation channel is only effective when the resonator holds a specific number of photons. Applying it to the fourth excited state of the resonator, we show an order of magnitude enhancement of the state decay rate while only marginally impacting the relaxation and coherence of lower energy states. Given that stray inductances could be strongly reduced through simple modifications in circuit design and that our methods can be adapted to activate even higher-order dissipation channels, these results pave the way toward the dynamical stabilization of four-component Schr\"odinger cat qubits and even more complex bosonic qubits
GWTC-4.0: Updating the Gravitational-Wave Transient Catalog with Observations from the First Part of the Fourth LIGO-Virgo-KAGRA Observing Run
No full textInternational audienceVersion 4.0 of the Gravitational-Wave Transient Catalog (GWTC-4.0) adds new candidates detected by the LIGO, Virgo, and KAGRA observatories through the first part of the fourth observing run (O4a: 2023 May 24 15:00:00 to 2024 January 16 16:00:00 UTC) and a preceding engineering run. In this new data, we find 128 new compact binary coalescence candidates that are identified by at least one of our search algorithms with a probability of astrophysical origin and that are not vetoed during event validation. We also provide detailed source property measurements for 86 of these that have a false alarm rate < 1 \rm{yr}^{-1}. Based on the inferred component masses, these new candidates are consistent with signals from binary black holes and neutron star-black hole binaries (GW230518_125908 and GW230529_181500). Median inferred component masses of binary black holes in the catalog now range from (GW230627_015337) to (GW231123_135430), while GW231123_135430 was probably produced by the most massive binary observed in the catalog. For the first time we have discovered binary black hole signals with network signal-to-noise ratio exceeding 30, GW230814_230901 and GW231226_01520, enabling high-fidelity studies of the waveforms and astrophysical properties of these systems. Combined with the 90 candidates included in GWTC-3.0, the catalog now contains 218 candidates with and not otherwise vetoed, doubling the size of the catalog and further opening our view of the gravitational-wave Universe
All-sky search for long-duration gravitational-wave transients in the first part of the fourth LIGO-Virgo-KAGRA Observing run
No full textInternational audienceWe present an all-sky search for long-duration gravitational waves (GWs) from the first part of the LIGO-Virgo-KAGRA fourth observing run (O4), called O4a and comprising data taken between 24 May 2023 and 16 January 2024. The GW signals targeted by this search are the so-called "long-duration" (> 1 s) transients expected from a variety of astrophysical processes, including non-axisymmetric deformations in magnetars or eccentric binary coalescences. We make minimal assumptions on the emitted GW waveforms in terms of morphologies and durations. Overall, our search targets signals with durations ~1-1000 s and frequency content in the range 16-2048 Hz. In the absence of significant detections, we report the sensitivity limits of our search in terms of root-sum-square signal amplitude (hrss) of reference waveforms. These limits improve upon the results from the third LIGO-Virgo-KAGRA observing run (O3) by about 30% on average. Moreover, this analysis demonstrates substantial progress in our ability to search for long-duration GW signals owing to enhancements in pipeline detection efficiencies. As detector sensitivities continue to advance and observational runs grow longer, unmodeled long-duration searches will increasingly be able to explore a range of compelling astrophysical scenarios involving neutron stars and black holes
Reconstructing the network of horizontal gene exchange in bacteria to differentiate direct and indirect transfers
No full textHorizontal gene transfer (HGT) plays a central role in bacterial evolution. Yet, its large-scale dynamics and underlying network structure remain poorly characterized. We present a theoretical framework that models HGT as a continuous stochastic process over a network of bacterial genera and analyze its genomic footprint via the distribution of exact sequence matches shared across taxa---the match length distribution (MLD). We show that different evolutionary regimes imprint distinct statistical signatures on the MLD: single episodic gene transfer events yield exponential distributions, while continuous sustained HGT processes lead to power-law tails. The power-law exponent is analytically linked to the topology of the transfer network, distinguishing between intra-clade transfers and hub-mediated dissemination. Empirical MLDs derived from bacterial genomes recapitulate these predicted patterns. Moreover, we find that defining a genus-specific "transferability" parameter that governs pairwise HGT rates and incorporating a high-transferability hub accurately reproduces the observed data. Our approach provides a general framework for inferring hidden structure in genomic horizontal transfer processes, enabling quantitative analysis of microbial evolution
Balancing positive and negative environmental impacts of urban greening considering future climate: A case study in the Paris region, France
No full textInternational audienceUrban greening enhances summer thermal comfort in cities; however, vegetation requires watering and reduces solar gains on buildings, potentially increasing energy consumption for heating. A methodology was developed to investigate whether the positive effects of urban trees on human health offset the increased water and energy consumption impacts. This method involves four steps: 1. Modelling the urban microclimate based on regional climatic data, accounting for vegetation effects; 2. Evaluating indoor temperatures and possible overheating using building thermal simulation; 3. Deriving the damage of overheating on human health, and 4. Performing a life cycle assessment.This process was applied to a case study on an urban greening project, including renovating an existing social housing building. According to the results, urban greening thanks to trees allows a decrease in outdoor air temperature around 1.7 • C (median value, 1.3 • C and 2.0 • C for 10th and 90th percentile, resp.) and a decrease in indoor temperature around 0.4 • C (median value; 0.25 • C and 0.55 for 10th and 90th percentile, resp.) during the five weeks heat wave period. Some life-cycle environmental impacts were reduced, particularly those related to damage to human health (-12.5 %), with limited impact transfer. The impact reduction due to energy savings from building renovation is higher.While many cities invest in urban greening projects, the importance of energy renovation is often overlooked. This prioritisation may be questioned, and the analysis presented in this article could serve as a valuable tool in guiding decision-making. By using the same indicator (Disability-Adjusted Life Years, DALY) to express life cycle and overheating-related impacts, this approach enables the integration of mitigation and adaptation in decisionmaking processes
Advanced Virgo Plus for O5 -- Design Report Overview
No full textInternational audienceThis document presents an overview of the design, implementation, and expected performance of the Advanced Virgo Plus (AdV+) upgrades in view of the O5 observing run. Following the experience gained during the O4 commissioning and operations, the Virgo Collaboration has revised the upgrade strategy to address limitations associated with marginally stable recycling cavities. The O5 upgrade program combines elements from the original AdV+ Phase II project with new design solutions, including the implementation of stable recycling cavities, a major modification to the central interferometer layout, and a comprehensive renewal of critical subsystems. The planned upgrades are organized in two steps, targeting progressive improvements in operational stability, noise reduction, and detector sensitivity. Key developments include new vacuum infrastructures, suspensions, mirrors, optical configurations, quantum noise reduction systems, and high-power laser technologies. The resulting configuration is expected to significantly enhance the interferometer performance, enabling a substantial increase in astrophysical reach and scientific return during O5
DRUID LCA: a methodological approach to consider the effects of disaster risks in life cycle assessment
No full textInternational audiencePurpose Critical infrastructure systems face increasing challenges from natural hazards. However, traditional Life Cycle Assessment (LCA) applications rarely account for the environmental impacts of hazard-induced damage and subsequent repair or replacement activities. Methods This paper introduces an exploratory methodological framework called the Disaster Risk-gUided scenarIo Definition (DRUID) method for integrating disaster risk considerations into LCA of infrastructure systems. The framework combines three components: (i) scenario development based on climate projections and socio-technical pathways, (ii) resilience simulation under disruption scenarios, and (iii) modeling of the consequences of disruptions on the environmental impact results. A pedagogical case study of a 1 MWp photovoltaic (PV) installation in southeastern France demonstrates the methodological approach by examining environmental consequences of strong wind events over a 30-year horizon using simplified assumptions and hypothetical parameters. Results and discussionThe exploratory case study compares baseline LCA results with DRUID LCA scenarios incorporating different decision-making responses to wind-induced damage, including repair and repowering activities. Results suggest that traditional LCA may underestimate potential environmental impacts across multiple categories under certain circumstances, depending on hazard frequency, system vulnerability, and response strategies. Most scenario results showed minimal deviation from baseline impacts due to low incidence of severe wind events. However, cases involving repowering demonstrated potential for doubled impacts on most categories (EF 3.0 midpoint no LT), while land use impacts decreased due to the use of higher-efficiency PV panels. Conclusion This methodological exploration shows the conceptual feasibility of integrating disaster risk considerations into LCA. The findings suggest potential value in considering hazards, disaster risks, and adaptation measures in LCA, particularly for regions facing more intense climate hazards. However, significant empirical validation and methodological refinement are required before DRUID LCA can support practical infrastructure planning decisions. The study provides preliminary foundations for continued development toward more comprehensive disaster risk-informed environmental assessment capabilities.</div
Can we trust purpose? Corporate legal forms and built‐in purpose
No full textInternational audienceThe literature on corporate purpose rarely considers how legal structures shape fidelity to purpose over time. Yet, recent developments, such as OpenAI's transformation into a Public Benefit Corporation, highlight the critical role of legal forms in determining whether companies can sustain their purpose credibly and over time. We introduce the concept of built‐in purpose as the set of purposes that a legal form can credibly and durably support through its embedded governance mechanisms. Further, we propose a framework to characterize the built‐in purpose of legal forms along two key functions that governance mechanisms must provide to ensure purpose fidelity: a protective function, which safeguards purpose from changing shareholder expectations or external pressures, and an enforcement function, which ensures that the purpose is effectively integrated into managerial decision‐making. We argue that the concept of built‐in purpose enriches the analysis of alternative legal forms and provides a tool for navigating their growing diversity. The alignment between a company's declared purpose and the built‐in purpose of its legal form also constitutes a driver of integrity, opening new perspectives for choosing governance structures suited to each specific purpose