École Polytechnique Fédérale de Lausanne
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Size, Scale and the Physical: How to Represent the Anthropocene as a Model?
No full textHumanity has fundamentally transformed Earth, making the creation of a new geological era: the Anthropocene. If we wanted to physically document the Anthropocene, we could take the sum of human material interventions and divide them over the surface of Earth. By extracting one averaged square meter of Earth’s surface, we could model the impact of the Anthropocene. Following this method, first proposed by the renown geologist and paleontologist Jan Zalasiewicz, we at THEMA have created a pilot model of this Anthropocene square meter for the first time. The representational power of this model is based on three characteristics: size, scale, and the physical. The universal size of one square meter and the precise scale of 1:1 provides a visual reference that we can imagine and understand. The physical, that is the use of real materials, like one kilogram of concrete that humanity produced for each square meter of Earth, gives a tactile sensation that we can feel and comprehend. This model offers the opportunity to discuss how multidisciplinary approaches to the Anthropocene can be explained and represented. Its concept relies on a comprehensive collection of data through an interdisciplinary collaboration involving different sciences, such as political and economical, but also visual and material studies. For the contribution to this conference, we would like to elaborate on the issue of communication and representation of the Anthropocene through this square meter model and how this can involve various disciplines and sciences to create a multilayered and diverse physical model of the Anthropocene. As architects, we have a unique position between design, technology, and the social, and we have a critical role in influencing policy makers, citizens, and students to initiate a discussion that can evolve the way we view our built environment. Using the tools of architects, such as modeling, we contribute to the representation of Earth that is changing drastically through the way we shape and form our environment. Our goal is to question these images and to reflect our responsibility in the context of the crisis our planet is in.THEM
Selective Photonic Gasification of Strained Oxygen Clusters on Graphene for Tuning Pore Size in the Å Regime
No full textControlling the size of single-digit pores, such as those in graphene, with an & Aring; resolution has been challenging due to the limited understanding of pore evolution at the atomic scale. The controlled oxidation of graphene has led to & Aring;-scale pores; however, obtaining a fine control over pore evolution from the pore precursor (i.e., the oxygen cluster) is very attractive. Herein, we introduce a novel "control knob" for gasifying clusters to form pores. We show that the cluster evolves into a core/shell structure composed of an epoxy group surrounding an ether core in a bid to reduce the lattice strain at the cluster core. We then selectively gasified the strained core by exposing it to 3.2 eV of light at room temperature. This allowed for pore formation with improved control compared to thermal gasification. This is because, for the latter, cluster-cluster coalescence via thermally promoted epoxy diffusion cannot be ruled out. Using the oxidation temperature as a control knob, we were able to systematically increase the pore density while maintaining a narrow size distribution. This allowed us to increase H-2 permeance as well as H-2 selectivity. We further show that these pores could differentiate CH4 from N-2 , which is considered to be a challenging separation. Dedicated molecular dynamics simulations and potential of mean force calculations revealed that the free energy barrier for CH4 translocation through the pores was lower than that for N-2. Overall, this study will inspire research on the controlled manipulation of clusters for improved precision in incorporating & Aring;-scale pores in graphene.LASC3M
Latent Representation of Computational Fluid Dynamics Meshes and Application to Airfoil Aerodynamics
No full textMesh manipulation is central to computational fluid dynamics. However, creating appropriate computational meshes often involves substantial manual intervention that has to be repeated each time the target shape changes. To address this problem, we propose an autodecoder-based latent representation approach. Human prior knowledge is embedded into learned geometric patterns, which eliminates the need for further handcrafting. Furthermore, the resulting computational meshes are differentiable with respect to the model parameters, which makes it suitable for inclusion in end-to-end trainable pipelines. We apply the model on two-dimensional airfoils to demonstrate its ability to handle various tasks.CVLA
Does Sharing Lead to Smarter Products? Managing Information Flows for Collective Servitization
No full textPeer-to-peer sharing induces persistent changes in product design. Besides bifurcating product durability, this adaptation increases the compatibility of collaborative use with rent extraction—from a producer’s viewpoint. For owners it decreases the commitment required for taking the item into possession, while for nonowners it standardizes sharing transactions. The resulting sharing-induced design-ideal aligns the flow of utility from shared consumption with the flow of monetary compensation to the seller, thus mimicking a collective lease agreement between seller and an ex ante unknown group of users. Sustaining such a “collective servitization” requires an embedded capacity of user sensing and transmission of information flows ex post the initial product sale, thus implying a fundamental need for smart products in an access-based society.OE
Optimization of elastic wave propagation in a reconfigurable medium by genetic algorithms with adaptive mutation probability
No full textWe introduce a reconfigurable medium for the manipulation of elastic propagation properties of Lamb waves. It is based on a shape memory polymer (SMP) with temperature-dependent Young's modulus. Waves are excited by a laser pulse and detected by a laser vibrometer. A two-dimensional temperature field is controlled by a scanning heating laser. We use genetic algorithms to determine optimal distributions of mechanical properties for the following criteria: the wave amplitude has to be maximized at a given location and at the same time minimized at one or two other locations. Due to the reconfigurability of the medium, the optimization process is performed directly on the object of optimization, and not on a numerical or analytical representative, based on a direct measurement of the fitness. The optimized configuration makes the waves propagate away from (or around) the point of minimization towards the point of maximization. We improve the genetic algorithm by adapting the mutation probability of individual genes according to specific criteria, which depend on the surrounding genes (distributed in two dimensions). This provides the advantages: concentrating the mutations in the areas of genetic inconsistencies and counterbalancing the error of the fitness measurement. The method is applicable for the intelligent design of wave energy harvesters, ultrasonic transducers, and analogue wave computing devices.LW
Heteroclinic orbits for a system of amplitude equations for orthogonal domain walls
No full textUsing a variational method, we prove the existence of heteroclinic solutions for a 6-dimensional system of ordinary differential equations. We derive this system from the classical Benard-Rayleigh problem near the convective instability threshold. The constructed heteroclinic solutions provide first order approximations for domain walls between two orthogonal convective rolls.(c) 2023 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons .org /licenses /by /4 .0/).PD
Influence of Fiber Orientation on the Elastic Limit Tensile Stress of UHPFRC
No full textThe elastic limit tensile stress of UHPFRC is governed by contributions of the cementitious matrix and the fibrous skeleton. This paper finds that fiber orientation has significant influence on the matrix tensile strength of UHPFRC, while this is not considered in current estimation of elastic limit tensile stress. An original model relating fiber orientation to the elastic limit tensile stress is proposed. Uniaxial tensile tests have been conducted on ten dumbbell-shaped specimens, whose local fiber volume and orientation are determined using a magnetic probe before testing. Based on the results of local fiber distribution, the influence of fiber orientation on the elastic limit tensile stress is discussed, showing that the proposed model estimates well the elastic limit tensile stress of UHPFRC.MCSGIS-G
Combined Passive and Active Ultrasonic Stress Wave Monitoring of UHPFRC Properties on a Structural Level
No full textUltra-High-Performance Fiber-Reinforced Cementitious Composite (UHPFRC) is becoming popular in designing lightweight and durable structures. UHPFRC structural elements remain crack-free and waterproof under service conditions, significantly improving durability compared to designs made of conventional reinforced concrete. Due to its unique composition, UHPFRC has specific mechanical properties. In particular, the early-age development of UHPFRC properties, such as the elastic modulus, is difficult to monitor as it occurs while elements are in the formwork. Monitoring of the very early-age behavior of UHPFRC is thus challenging, which is why the hydration process of UHPFRC on a structural level is still not yet fully understood. This paper proposes a novel combined passive and active ultrasonic stress wave monitoring (USW) approach involving a network of ultrasonic transducers and thermocouples. The scheme was applied to a laboratory beam with a span length of 4.0 meters. The monitoring network consisted of 24 embedded ultrasonic transducers and 15 thermocouples and allowed data recording from the beginning of the UHPFRC hardening process. From the beginning, a set of ultrasonic pulses were emitted every 30 minutes and recorded (active USW monitoring), while acoustic emissions (AE) were recorded continuously (passive USW monitoring). After 28 days, the beam was moved into a load frame and tested under four-point bending. Continuous monitoring using this unique passive and active monitoring approach enabled accurate characterization of the evolution of material properties during the very early age of UHPFRC, as well as the structural behavior and degradation processes of the beam during structural load testing.MC
TV-based spline reconstruction with Fourier measurements: Uniqueness and convergence of grid-based methods
No full textWe study the problem of recovering piecewise-polynomial periodic functions from their low-frequency information. This means that we only have access to possibly corrupted versions of the Fourier samples of the ground truth up to a maximum cutoff frequency Kc. The reconstruction task is specified as an optimization problem with total-variation (TV) regularization (in the sense of measures) involving the Mth order derivative regularization operator L = DM. The order M >= 1 determines the degree of the reconstructed piecewise-polynomial spline, whereas the TV regularization norm, which is known to promote sparsity, guarantees a small number of pieces. We show that the solution of our optimization problem is always unique, which, to the best of our knowledge, is a first for TV-based problems. Moreover, we show that this solution is a periodic spline matched to the regularization operator L whose number of knots is upper-bounded by 2Kc. We then consider the grid-based discretization of our optimization problem in the space of uniform L-splines. On the theoretical side, we show that any sequence of solutions of the discretized problem converges uniformly to the unique solution of the gridless problem as the grid size vanishes. Finally, on the algorithmic side, we propose a B-spline-based algorithm to solve the discretized problem, and we demonstrate its numerical feasibility experimentally. On both of these aspects, we leverage the uniqueness of the solution of the original problem.(c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).LI
MEWron: An open-source melt electrowriting platform
No full textMelt electrowriting (MEW) is a distinct class of additive manufacturing technologies that generates fibrous and porous macrostructures with microscale resolution from an electrically charged molten polymer. The high -resolution scaffolds produced by MEW have been primarily used for tissue engineering, cancer research, bio-fabrication and biomaterials. Unfortunately, the commercial MEW device's prohibitive affordability and lack of standardization of custom devices, represent obstacles to further research. Built on the achievements and affordability of material extrusion 3D printers, we convert an open-source Voron 0.1 printer into a highly capable MEW device, termed as MEWron. To guarantee availability, the use of commercial and affordable components is prioritized, while in the cases where this has not been possible, 3D printed, and easy-to-machine components have been employed. Two main approaches have been followed, the first one focused on the existing material extrusion configuration (i.e., filament-based feeding system and material input) while the second one focuses on a conventional MEW pneumatic feeding system and syringe reservoir. When not including the high voltage supply, both approaches have a final budget below $1000. The manuscript describes all required steps and components to modify a Voron 0.1 printer and provides the computer-aided design (CAD) for required custom components reproduction. Moreover, the MEWron devices' reliability is demonstrated, as well as their potential to extend the MEW field boundaries. We believe that the open-source MEWron device will facilitate unprece-dented MEW technology accessibility using a well-established and modifiable platform.LMIS