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Multi-output subspace identification of complex Bloch wavenumbers in 1D periodic structures
No full textInternational audienceThe experimental characterization of complex dispersion curves is challenging in phononic crystals, composites, periodic, architected or metamaterials. Recent studies have highlighted the importance of subspace identification methods in determining wave propagation properties through complex wavenumbers and, consequently, in characterizing a complex structure experimentally. Still, such methods have not yet been adapted for 1D periodic structures with periodic sampling limitations. This work introduces a Subspace-based complex Bloch WAveNumber identification method (SWAN) which can take advantage of full-field vibration measurements (i.e., multiple data points per unit cell) to statistically reduce the negative impact of having a limited number of unit cells. The SWAN method is based on a state-space representation of the wave finite element method. A symplectic state-space model is formulated and mathematically proved to represent the original system. Eventually, the proposed method enhances complex wavenumber estimates when a small number of unit cells is available. In addition, a general-purpose, adaptive spectral mask is introduced to reject physically irrelevant identification results, enabling straightforward denoising of the identified dispersion curves. The proposed approach is validated through numerical and experimental applications
A Cauchy-Piola framework for micro-based micromorphic continua
No full textInternational audienceMany results on micromorphic media can be found in the literature, where the equations of motion and the energetic foundations of the Eringen micromorphic continuum have been well established. The present paper has been devoted to the continuum modeling of a finite number of interacting, separated continua (microdomains) at the microscale, in which the strain energy has been formulated through a generalization of the Cauchy-Green deformation tensor, resulting in a degenerate metric at the considered scale, and a (6 × 6) Green-Lagrange strain tensor. The equilibrium equations have been obtained by systematically applying the method of virtual power. For one of the first time, boundary-layer conditions appear in micromorphic mechanics. The paper concludes with a discussion on the number of constitutive parameters, shown to coincide, in number, with those of classical (Cauchy) elasticity, together with the recovery of micropolar continua as a special case and wide spectrum of applications of the proposed framework. Further details concerning the algebraic expressions of the tensors involved are provided in the Appendices
Rosa Parks railway station area in Paris as an Equitable Transit-oriented development
No full textPart of special issueSustainable Transit-Oriented Development: New Perspectives and AdvancesEdited by Professor Richard Knowles (University of Salford, Salford, , United Kingdom), Dr. Chia-Lin Chen (University of Liverpool, Liverpool, , United Kingdom)International audienceThe surrounding area of the Rosa Parks railway station, located in the administrative district of Pont de Flandres in the 19th borough of Paris, has witnessed significant growth, transitioning from brownfields to vibrant, mixed-use neighbourhoods. This development includes transforming the Calberson warehouses along Boulevard McDonald, considered as Paris's largest building (615 meters long), into new housing, retail offices, and community facilities. These urban developments have created multiple dynamics in a district with a high proportion of social housing and where the average salary is the lowest in Paris. These evolutions include improving the district's connectivity with a range of public transport services (suburban train, buses and lightrail and the development of active modes. Furthermore, the land-use mix tends to bring daily services closer to residents. The paper explores three critical aspects of the Rosa Parks area’s development. Firstly we captured the inhabitants’ proximity experience through Transit- oriented development and a 15-min City approaches: in this case study, the focus is brought to the low income in order to specify their local mobility experience as an indicator of an Equitable TOD experience. Secondly, we investigate the district’s embracement of Equitable TOD principles: this is studied through the percentage of social housing in the area, the reviewing of policy tools to tackle potential gentrification and the inhabitants’ commitment in the urban development of Rosa Parks area. Thirdly, we expose the lessons learned from applying these principles as a framework for social justice and environmental resilience in urban planning: as part of the study, we present a critical review of the Rosa Parks neighborhood as an equitable TOD and provide further recommendations. Highlights: Rosa Parks railway station area illustrates the case of an equitable-TOD experience; Assessing equitable housing policies requires a thorough examination of social housing programs; A substantial percentage (44% vs 25% in the rest of Paris) of permanent affordable housing; Current commercial supply is perceived as inadequate by many residents (focus group insight); Revenue and cultural preferences influence the perceived liveability of the neighborhood
Key challenges in tackling undeclared work in the Courier, Express, and Parcel Delivery sector
No full textThe Courier, Express, and Parcel (CEP) sector faces significant challenges related to undeclared work, complex subcontracting structures, and enforcement difficulties. Undeclared work in the CEP sector is driven by both supply- and demand-side factors. On the demand side, the cost factor of labour is key in encouraging non-compliant employment practices. Large logistics companies often outsource their parcel delivery operations to businesses commonly referred to as ‘service partners to reduce costs, shifting responsibility for working conditions onto these subcontractors. Findings from inspections and reporting by social partner organisations indicate that service partners often engage in non-compliant business practices, such as misclassifying workers (bogus self-employment) or underreporting employment to evade taxes and social security contributions. Additionally, cross-border operations complicate compliance when couriers drive vehicles registered in different countries, potentially violating cabotage and posted worker regulations.On the supply side, although there is little evidence based on studies, labour inspectorates and trade unions assume that a high proportion of CEP workers are EU mobile workers or third countries nationals, with limited access to the local labour market. This structural vulnerability makes them more susceptible to labour abuse, particularly in subcontracting chains where compliance monitoring is difficult. The mobile nature of courier work further complicates enforcement, as workers are constantly on the move. Paradoxically, while logistics companies use digital handheld devices to track parcel deliveries, these same devices are rarely used to monitor working hours, creating a regulatory blind spot. The most common forms of undeclared work in the CEP sector include underreporting workers to social security institutions , remuneration below the minimum wage due to underreporting of working hours, and unregistered businesses. While bogus self-employment remains an issue in some countries, such as France, it appears to be decreasing in others, including Germany and Spain. Violations of posting regulations, however, exist to a small extent, as cross-border parcel delivery does not account for the majority of shipments.The study highlights that undeclared work in the CEP sector remains a pressing issue but increasing awareness and targeted measures, including inspections and legislative reforms, are gradually addressing the problem. The complexity of subcontracting chains hinders accountability, underscoring the need for stronger enforcement mechanisms and clearer regulatory frameworks
How to Achieve the Best Trade-off Between Robustness and Performance
No full textThe work presents an innovative approach to addressing the trade-off between robustness and performance, known as the optimality criterion. Moreover, the procedure relies on well-established methods that effectively support the search for the best trade-off, namely multi-criteria optimization problem. Thus, by separating the robustness and performance problems, it becomes possible to achieve the best trade-off between these two criteria. In this search for a trade-off, two complementary approaches are combined: robust control for the closed-loop system by minimizing Hinf-norm, and performance optimization in open-loop by minimizing l2-norm. This combination is made possible by the Youla-Kučera parameterization. However, to implement this parameterization in the presence of model errors, a new approach is used: estimating the Youla-Kučera parameterization.</div
Les collectivités territoriales et l’énergie : une décentralisation en courant alternatif
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Data Science: a Natural Ecosystem
No full textInternational audienceThis manuscript provides a systemic and data-centric view of what we term essential data science, as a natural ecosystem with challenges and missions stemming from the fusion of data universe with its multiple combinations of the 5D complexities (data structure, domain, cardinality, causality, and ethics) with the phases of the data life cycle. Data agents perform tasks driven by specific goals. The data scientist is an abstract entity that comes from the logical organization of data agents with their actions. Data scientists face challenges that are defined according to the missions. We define specific discipline-induced data science, which in turn allows for the definition of pan-data science, a natural ecosystem that integrates specific disciplines with the essential data science.We semantically split the essential data science into computational, and foundational.By formalizing this ecosystemic view, we contribute a general-purpose, fusion-oriented architecture for integrating heterogeneous knowledge, agents, and workflows—relevant to a wide range of disciplines and high-impact applications
Approximating stable translation lengths on fine curve graphs
No full text17 pages, 2 figuresWe study the stable translation length of homeomorphisms of a surface acting on the fine nonseparating curve graph and compare it to the stable translation lengths of its finite approximations - mapping classes relative to a finite invariant set - acting on the nonseparating curve graph. We prove that the stable translation length of a homeomorphism with a dense set of periodic points is the supremum of the stable translation lengths of its approximations, and that the stable translation length is preserved under cell-like extensions. We deduce that homotopically triv ial homeomorphisms of the torus have stable translation length which is the supremum of the stable translation lengths of their finite approximations. We show that the supremum is not always a maximum, by proving that the stable translation length of a mapping class acting on the nonseparating curve graph is rational
19F magnetic resonance imaging-informed fate models of PFAS in porous media
No full textInternational audiencePer-and polyfluoroalkyl substances (PFAS) are persistent contaminants. Predicting their fate in natural or engineered porous media, using accurate models, is essential for effective remediation and contamination management strategies. The mechanisms of transport and retention included in such models, and the associated parameters, are mostly inferred from PFAS concentration vs. time breakthrough curves (BTCs) measured during transport experiments. Still, the interpretation of BTCs may not be unique as they result from a succession of mechanisms taking place inside the porous media. We addressed this issue using 19 F magnetic resonance imaging (MRI) to monitor the transport of perfluorobutanoic acid (PFBA) inside a sand-packed column. The experimental BTC was slightly asymmetric, suggesting that some PFBA may have been adsorbed onto the sand. Hence, a transport model based on the hypothesis that PFBA behaved as a non-sorbing tracer slightly overestimated the concentrations in two regions of the BTC. Surprisingly, the same model matched well the MRI profiles, pointing out that the BTC asymmetry stemmed from an imperfect column exit. Although 19 F MRI requires PFAS concentration above those found in environmental samples, this study showed that the combination of this technique and modeling constitutes a powerful tool to determine the mechanisms involved in PFAS transport in natural or engineered porous media andselect appropriate fate model