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Recent Submissions
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Multi-window approaches for direct and stable STFT phase retrieval
(2024)SAM Research ReportPhase retrieval from phaseless short-time Fourier transform (STFT) measurements is known to be inherently unstable when measurements are taken with respect to a single window. While an explicit inversion formula exists, it is useless in practice due to its instability. In this paper, we overcome this lack of stability by presenting two multi-window approaches that rely on a "good coverage" of the time-frequency plane by the ambiguity ...Report -
Solving Electromagnetic Scattering Problems by Isogeometric Analysis with Deep Operator Learning
(2024)SAM Research ReportWe present a hybrid approach combining isogeometric analysis with deep operator networks to solve electromagnetic scattering problems. The neural network takes a computer-aided design representation as input and predicts the electromagnetic field in a de Rham conforming B-spline basis such that for example the tangential continuity of the electric field is respected. The physical problem is included in the loss function during training. ...Report -
Applications of Chebyshev polynomials and Toeplitz theory to topological metamaterials
(2024)SAM Research ReportWe survey the use of Chebyshev polynomials and Toeplitz theory for studying topological metamaterials. We consider both Hermitian and non-Hermitian systems of subwavelength resonators and provide a mathematical framework to explain some spectacular properties of metamaterials.Report -
Homogenization and Numerical Upscaling for Spectral Fractional Diffusion
(2024)SAM Research ReportWe consider two-scale, linear spectral fractional diffusion of order \(2s\in (0,2)\) with homogeneous Dirichlet boundary condition and locally periodic, two-scale coefficients in a bounded domain \(D \subset \mathbb{R}^d\), with fundamental period \(Y=(0,1)^d \subset \mathbb{R}^d\). We derive a local limiting two-scale homogenized equation for the so-called Caffarelli-Sylvestre (CS) extension in the tensorized domain \(D\times Y \times ...Report -
Space-Time Wave Localisation in Systems of Subwavelength Resonators
(2024)SAM Research ReportIn this paper we study the dynamics of metamaterials composed of high-contrast subwavelength resonators and show the existence of localised modes in such a setting. A crucial assumption in this paper is time-modulated material parameters. We prove a so-called capacitance matrix approximation of the wave equation in the form of an ordinary differential equation. These formulas set the ground for the derivation of a first-principles ...Report -
A methodology for automating the determination of optimal intervention programmes for multi-component railway networks: A case study of Zollikofen-Brügg railway network
(2023)To ensure the stability of the train schedules, it is crucial to determine the optimal component-level intervention programs, their associated required possession windows, and their execution costs. This is a key step in the later phases of the intervention planning process. Network, production, and capacity managers at SBB would, therefore, benefit from an efficient and automated method for determining optimal intervention programs for ...Report -
D2.4 Stakeholder-informed research questions
(2024)The DIAMOND project undertakes a transdisciplinary (TD) approach to update, expand, open, and develop scenarios for six Integrated Assessment Models, with the aim of addressing net zero emissions and sustainable development. WP2: Codesign leads this TD approach, which is broken down into three multi-stage phases: i) mutual understanding; ii) knowledge co-production; and iii) model co-ownership. Deliverable D2.4 presents the results of the ...Report -
Civil Protection Roadmap for Drought Resilience in Switzerland
(2024)CSS Risk and Resilience ReportsReport -
AV-MAVT 2024 Happiness Survey
(2024)The general happiness of non-faculty scientific staff at D-MAVT has slightly decreased in the last two years, in line with a slight decline in overall satisfaction with supervision, even if both indicators stay at a relatively stable high level. The percentage of doctoral students and staff members who have experienced discrimination has increased. For the first time in this happiness survey, the impact of teaching duties in terms of ...Report -
Hacking the Cosmos: Cyber operations against the space sector
(2024)CSS Cyberdefense ReportsA few hours prior to the Russian invasion of Ukraine on February 24, 2022, Russia’s military intelligence (GRU) launched a destructive cyberattack against ViaSat’s KA-SAT satellite network, which was used by the Ukrainian Armed Forces. It prevented them from using satellite communications to respond to the invasion. After the ViaSat hack, numerous cyber operations were conducted against the space sector from both sides of the conflict. ...Report -
Community-wide Waste Management System for Cape Maclear
(2024)Five students from ETH Zürich completed their Master’s theses at the chair of Global Health Engineering. They spent two months in the town of Cape Maclear, Malawi and four months in Zürich, Switzerland trying to establish a community-wide waste management system. This policy brief presents the results: a comprehensive proposal for developing and implementing a solid waste collection system for Cape Maclear. The study provides detailed ...Report -
Wave packets propagation in the subwavelength regime near the Dirac point
(2024)SAM Research ReportIn [Ammari et al., SIAM J Math Anal., 52 (2020), pp. 5441–5466], the first author with collaborators proved the existence of Dirac dispersion cones at subwavelength scales in bubbly honeycomb phononic crystals. In this paper, we study the time-evolution of wave packets, which are spectrally concentrated near such conical points. We prove that the wave packets dynamics is governed by a time-dependent effective Dirac system, which still ...Report -
Expression Rates of Neural Operators for Linear Elliptic PDEs in Polytopes
(2024)SAM Research ReportWe study the approximation rates of a class of deep neural network approximations of operators, which arise as data-to-solution maps G † of linear elliptic partial differential equations (PDEs), and act between pairs X, Y of suitable infinite-dimensional spaces. We prove expression rate bounds for approximate neural operators G with the structure G = R ◦ A ◦ E, with linear encoders E and decoders R. The constructive proofs are via a ...Report -
H(curl)-based approximation of the Stokes problem with slip boundary conditions
(2024)SAM Research ReportThe equations governing incompressible Stokes flow are reformulated such that the velocity is sought in the space H(curl). This relaxed regularity assump tion leads to conforming finite element methods using spaces common to dis cretizations of Maxwell’s equations. A drawback of this approach, however, is that it is not immediately clear how to enforce Navier-slip boundary conditions. By recognizing the slip condition as a Robin boundary ...Report