École Polytechnique Fédérale de Lausanne
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Covering Graphs by Monochromatic Trees and Helly-Type Results for Hypergraphs
No full textHow many monochromatic paths, cycles or general trees does one need to cover all vertices of a given r-edge-coloured graph G? These problems were introduced in the 1960s and were intensively studied by various researchers over the last 50 years. In this paper, we establish a connection between this problem and the following natural Helly-type question in hypergraphs. Roughly speaking, this question asks for the maximum number of vertices needed to cover all the edges of a hypergraph H if it is known that any collection of a few edges of H has a small cover. We obtain quite accurate bounds for the hypergraph problem and use them to give some unexpected answers to several questions about covering graphs by monochromatic trees raised and studied by Bal and DeBiasio, Kohayakawa, Mota and Schacht, Lang and Lo, and Cirao, Letzter and Sahasrabudhe.DC
Gabriel Galvez-Behar, Posséder la science. La propriété scientifique au temps du capitalisme industriel, Paris, Éditions de l’EHESS, 2020, 334 p.
No full textLHS
Sensing the structural behavior: A perspective on the usefulness of monitoring information for bridge examination
No full textManaging existing civil infrastructure is challenging due to evolving functional requirements, material aging, and climate change. With increasingly limited economic, environmental, and material resources, more sustainable solutions for practical asset management are required. Significant efforts have been made to monitor civil infrastructure, such as bridges. In-situ measurements are collected with the aim of improving the accuracy of structural capacity evaluations. Monitoring data collected through bridge load testing, continuous condition monitoring, and non-destructive tests provides structural-behavior information that could significantly influence structural-safety examinations. Nonetheless, monitoring techniques are often costly, and the monitoring costs may not always justify the benefits of the information gained. This paper proposes a short perspective of the potential impact of monitoring activities to assess the structural safety of existing bridges. A full-scale bridge in Switzerland is used as an example. Future research needs are also proposed.MCSGIS-G
Moving beyond grand narratives and stigmatizations: provincializing the Green Revolution from Mexican fields
No full textWith the dissolution of the agricultural projects that the Rockefeller Foundation (RF) was leading in China in 1940, it is in Mexico that a new testing ground for development programs based on the dissemination of new agronomic knowledge opens up. Science is seen as a key vector of progress, meant to replace the more political and social dimensions of the reforms needed to transform rural societies. The Mexican State sees, in turn, the possibility of accelerating the emergence of a modern science that would allow the depoliticization of the agrarian reform for technical solutions. In this perspective, Mexico has been a cradle of experimentation of the principles of the Green Revolution, hosting the Mexican Agricultural Program (MAP). It focused on the dissemination of high-yielding varieties and the coordination of extensive variety collection campaigns and breeding. We will review the results of this program through the scientific debates around the idea that poverty in rural areas was mainly due to the lack of technical knowledge. Today the failure of spreading innovations, like hybrid maize or GMOs, is still stigmatized. For some, it is a sign of an irrational attachment to certain habits, for others a laudable expression of political resistance against a modernization imposed from above. While remaining attentive to the political dimension underlying the idea of knowledge and technology transfer, we want to highlight other aspects. On the one hand, we identify more pragmatic reasons that motivate farmers’ choices; on the other hand, we show that scientific approaches were more contrasted than unanimous in the scientific and technical course undertaken in Mexico during the MAP years.LHS
Metal-organic framework-based oxygen carriers with antioxidant activity resulting from the incorporation of gold nanozymes
No full textBlood transfusions are a life-saving procedure since they can preserve the body's oxygen levels in patients suffering from acute trauma, undergoing surgery, receiving chemotherapy or affected by severe blood disorders. Due to the central role of hemoglobin (Hb) in oxygen transport, so-called Hb-based oxygen carriers (HBOCs) are currently being developed for situations where donor blood is not available. In this context, an important challenge that needs to be addressed is the oxidation of Hb into methemoglobin (metHb), which is unable to bind and release oxygen. While several research groups have considered the incorporation of antioxidant enzymes to create HBOCs with minimal metHb conversion, the use of biological enzymes has important limitations related to their high cost, potential immunogenicity or low stability in vivo. Thus, nanomaterials with enzyme-like properties (i.e., nanozymes (NZs)) have emerged as a promising alternative. Amongst the different NZs, gold (Au)-based metallic nanoparticles are widely used for biomedical applications due to their biocompatibility and multi-enzyme mimicking abilities. Thus, in this work, we incorporate Au-based NZs into a type of HBOC previously reported by our group (i.e., Hb-loaded metal-organic framework (MOF)-based nanocarriers (NCs)) and investigate their antioxidant properties. Specifically, we prepare MOF-NCs loaded with Au-based NZs and demonstrate their ability to catalytically deplete over multiple rounds of two prominent reactive oxygen species (ROS) that exacerbate Hb's autoxidation (i.e., hydrogen peroxide and the superoxide radical). Importantly, following loading with Hb, we show how these ROS-scavenging properties translate into a decrease in metHb content. All in all, these results highlight the potential of NZs to create novel HBOCs with antioxidant protection which may find applications as a blood substitute in the future.LSM
Conditions of habitability in a Persistent Company Town. Rethinking the industrial cities and their productive habitats
No full textA company town can be defined as a settlement completely owned by an entrepreneur or a company, which builds and manages the community following business and production needs, coordinating all the facilities, including the houses, stores, the school, and even the chapel. To understand the company town palimpsest and truly consider these cities and their different historical strata, it is necessary to observe the temporalities these cities encompassed. In Dalmine, the reading of the company town allow us to have a glance in a past utopia, materialised in architecture and immortalised in their business archives.LAB-
When the ‘periphery is the center’ and the ‘last shall be first’: plant genetic diversity and rural development in the Americas
No full textLHS
On the symmetries in the dynamics of wide two-layer neural networks
No full textWe consider the idealized setting of gradient flow on the population risk for infinitely wide two-layer ReLU neural networks (without bias), and study the effect of symmetries on the learned parameters and predictors. We first describe a general class of symmetries which, when satisfied by the target function f* and the input distribution, are preserved by the dynamics. We then study more specific cases. When f* is odd, we show that the dynamics of the predictor reduces to that of a (non -linearly parameterized) linear predictor, and its exponential convergence can be guaranteed. When f* has a low-dimensional structure, we prove that the gradient flow PDE reduces to a lower-dimensional PDE. Furthermore, we present informal and numerical arguments that suggest that the input neurons align with the lower-dimensional structure of the problem.DOL
1805-1898 Census Records of Lausanne : a Long Digital Dataset for Demographic History
No full textThis historical dataset stems from the project of automatic extraction of 72 census records of Lausanne, Switzerland. The complete dataset covers a century of historical demography in Lausanne (1805-1898), which corresponds to 18,831 pages, and nearly 6 million cells. Content. The data published in this repository correspond to a first release, i.e. a diachronic slice of one register every 8 to 9 years. Unfortunately, the remaining data are currently under embargo. Their publication will take place as soon as possible, and at the latest by the end of 2023. In the meantime, the data presented here correspond to a large subset of 2,844 pages, which already allows to investigate most research hypotheses. The population censuses, digitized by the Archives of the city of Lausanne, continuously cover the evolution of the population in Lausanne throughout the 19th century, starting in 1805, with only one long interruption from 1814 to 1831. Highly detailed, they are an invaluable source for studying migration, economic and social history, and traces of cultural exchanges not only with Bern, but also with France and Italy. Indeed, the system of tracing family origin, specific to Switzerland, allows to follow the migratory movements of families long before the censuses appeared. The bourgeoisie is also an essential economic tracer. In addition, censuses extensively describe the organization of the social fabric into family nuclei, around which gravitate various boarders, workers, servants or apprentices, often living in the same apartment with the family. Production. The structure and richness of censuses have also provided an opportunity to develop automatic methods for processing structured documents. The processing of censuses includes several steps, from the identification of text segments to the restructuring of information as digital tabular data, through Handwritten Text Recognition and the automatic segmentation of the structure using neural networks. Please note that the detailed extraction methodology, as well as the complete evaluation of performance and reliability is published in: Petitpierre R., Rappo L., Kramer M. (2023). An end-to-end pipeline for historical censuses processing. International Journal on Document Analysis and Recognition (IJDAR). doi: 10.1007/s10032-023-00428-9 Data structure. The data are structured in rows and columns, with each row corresponding to a household. Multiple entries in the same column for a single household are separated by vertical bars 〈|〉. The center point 〈·〉 indicates an empty entry. For some columns (e.g., street name, house number, owner name), an empty entry indicates that the last non-empty value should be carried over. The page number is in the last column. Liability. The data presented here are not curated nor verified. They are the raw results of the extraction, the reliability of which was thoroughly assessed in the above-mentioned publication. We insist on the fact that for any reuse of this data for research purposes, the implementation of an appropriate methodology is necessary. This may typically include string distance heuristics, or statistical methodologies to deal with noise and uncertainty. References: ["Petitpierre R., Rappo L., Kramer M. (2023). An end-to-end pipeline for historical censuses processing. International Journal on Document Analysis and Recognition (IJDAR). doi: 10.1007/s10032-023-00428-9"]DHI-GE1.