École Polytechnique Fédérale de Lausanne
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Electron Emission Regimes of Planar Nano Vacuum Emitters
No full textRecent advancements in nanofabrication have enabled the creation of vacuum electronic devices with nanoscale free-space gaps. These nanoelectronic devices promise the benefits of cold-field emission and transport through free space, such as high nonlinearity and relative insensitivity to temperature and ionizing radiation, all while drastically reducing the footprint, increasing the operating bandwidth, and reducing the power consumption of each device. Furthermore, planarized vacuum nanoelectronics could easily be integrated at scale similar to typical microscale and nanoscale semiconductor electronics. However, the interplay between different electron emission mechanisms from these devices is not well understood, and inconsistencies with pure Fowler-Nordheim (FN) emission have been noted by others. In this work, we systematically study the current-voltage characteristics of planar vacuum nanodevices having few-nanometer radii of curvature and free-space gaps between the emitter and the collector. By investigating the current-voltage characteristics of nearly identical devices fabricated from two different materials and under various environmental conditions, such as temperature and atmospheric pressure, we are able to clearly isolate three distinct emission regimes within a single device: Schottky, FN, and saturation. Our work will enable robust and accurate modeling of vacuum nanoelectronics, which will be critical for future applications requiring high-speed and low-power electronics capable of operation in extreme conditions.LPQ
Graph Theoretical Analysis of Structural Covariance Reveals the Relevance of Visuospatial and Attentional Areas in Essential Tremor Recovery After Stereotactic Radiosurgical Thalamotomy
No full textEssential tremor (ET) is the most common movement disorder. Its pathophysiology is only partially understood. Here, we leveraged graph theoretical analysis on structural covariance patterns quantified from morphometric estimates for cortical thickness, surface area, and mean curvature in patients with ET before and one year after (to account for delayed clinical effect) ventro-intermediate nucleus (Vim) stereotactic radiosurgical thalamotomy. We further contrasted the observed patterns with those from matched healthy controls (HCs). Significant group differences at the level of individual morphometric properties were specific to mean curvature and the post-/pre-thalamotomy contrast, evidencing brain plasticity at the level of the targeted left thalamus, and of low-level visual, high-level visuospatial and attentional areas implicated in the dorsal visual stream. The introduction of cross-correlational analysis across pairs of morphometric properties strengthened the presence of dorsal visual stream readjustments following thalamotomy, as cortical thickness in the right lingual gyrus, bilateral rostral middle frontal gyrus, and left pre-central gyrus was interrelated with mean curvature in the rest of the brain. Overall, our results position mean curvature as the most relevant morphometric feature to understand brain plasticity in drug-resistant ET patients following Vim thalamotomy. They also highlight the importance of examining not only individual features, but also their interactions, to gain insight into the routes of recovery following intervention.MIPLA
Design and Construction of the "Chaumény" Footbridge in Posttensioned UHPFRC
No full textIn 2020/21, the “Chaumény” footbridge was built in posttensioned UHPFRC over a railway line in the city of Montreux, Switzerland. UHPFRC stands for Ultra High Performance Fiber Reinforced Cementitious composite. UHPFRC shows high resistance both in tension and compression as well as excellent durability properties. The design and construction of the lightweight structure is described. The structure consists of a U-shaped trough girder with a span of 22.5m above the railway clearance, resting on one abutment and one pier, as well as a staircase leading from the pier down to the ground. The footbridge is composed of several precast elements that were assembled by posttensioning to achieve monolithically linked structure.MCSGIS-G
Inkjet printed dielectric elastomer actuators for facial reconstruction
No full textThe LAI-CAM lab is investigating dielectric elastomer actuators (DEAs) as artificial muscles for facial reconstruction. As a matter of fact, DEA and muscles both share a linear relation between applied current and elongation although muscles contract under a certain current while DEA elongate. The artificial muscles structure would be composed of a dielectric elastomer (DE) with on each side: a fiber layer to guide the movement in one preferential direction and an electrode layer. Inkjet printing is an additive manufacturing technique allowing to print inks at the micro scale. In this report we will investigate the use of inkjet printing for the specific case of DEA.LA
Evaluating the effect of sparse convolutions on point cloud compression
Full text linkThe use of point clouds as an imaging modality has been rapidly growing, motivating research on compression methods to enable efficient transmission and storage for many applications. While compression standards relying on conven- tional techniques such as planar projection and octree-based representation have been standardized by MPEG, recent research has demonstrated the potential of neural networks in achieving better rate-distortion performance for point cloud geometry cod- ing. Early attempts in learning-based point cloud coding mostly relied on autoencoder architectures using dense convolutional layers, but the majority of recent research has shifted towards the use of sparse convolutions, which are applied only to occupied positions rather than the entire space. Since points are usually distributed on underlying surfaces rather than volumes, such operations allow to reduce the computational complexity required to compress and decompress point clouds. Moreover, recent solutions also achieve better compression efficiency, allocating fewer bits at similar levels of geometric distortion. However, it is not clear to which extent this gain in performance is due to the use of sparse convolutions, if any at all, since the architecture of the model is often modified. In this paper, we conduct an evaluation of the effect of replacing dense convolutions with sparse convolutions on the rate-distortion performance of the JPEG Pleno Point Cloud Verification Model. Results show that the use of sparse convolutions allows for an average BD-rate reduction of approximately 9% for both D1 and D2 PSNR metrics based on similar training procedures, with an even bigger reduction in point clouds featuring reduced point density.GR-EBThis paper received the best student paper awar
Characterization of affine surfaces with a torus action by their automorphism groups
No full textIn this paper we prove that if two normal affine surfaces S and S' have isomorphic automophism groups, then every connected algebraic group acting regularly and faithfully on S acts also regularly and faithfully on S'. Moreover, if S is non-toric, we show that the dynamical type of a 1-torus action is preserved in presence of an additive group action. We also show that complex affine toric surfaces are determined by the abstract group structure of their regular automorphism groups in the category of complex normal affine surfaces using properties of the Cremona group. As a generalization to arbitrary dimensions, we show that complex affine toric varieties, with the exception of the algebraic torus, are uniquely determined in the category of complex affine normal varieties by their automorphism groups seen as ind-groups.SB-SM
Effect of Mo addition on the mechanical and tribological properties of magnetron sputtered TiN films
No full textTernary-based titanium nitride (TiN) thin films have drawn attention toward rational applications due to their wear resistance, high hardness, and corrosion resistance. The influence of Mo content on the structural, tribo-logical, and mechanical properties of TiN films is reported in this study. The microstructure and elemental composition of the as-deposited TiMoN films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), nanoindentation, and ball-on-disc wear tests. XRD results showed that the as-sputtered TiMoN films consisted of a formation of solid solution of TiN and MoN mixture phases. With 18 at. % of Mo, the me-chanical property of TiMoN films was enhanced, and the film exhibited a high hardness of 28 GPa. Moreover, this addition led to a wear rate of 0.40 and 6.34 x 10-6 mm3/Nm and to lower the friction coefficient to values lower than the corresponding binary TiN film. This was attributed to the multi-phase strengthening and higher (H/E, H3/E2) values, which indicate that the mechanical properties and the wear resistance of TiN can be enhanced by alloying with Mo.GPA
Taking Back Our Commons: Social Media APIs as Subversive Tools
No full textOur actual internet landscape is dominated by a handful of private actors we use on a daily basis: Twitter, Facebook, Instagram, amongst others. These actors, in constant search of an optimization of their data transmission processes and user experiences, all share the same political agenda: obfuscate the way their services operate (Wu, 2003) and gain control of our data. By doing so, their will is to turn their platforms into blackboxes (Hertz & Parikka, 2012) we, as users, passively observe from afar. This short paper argues for the pertinence of using Application Programming Interfaces (APIs) outside of their primary market-based usage in order to regain control of our data and, ultimately, turn our social media platforms’ data into commons we, as makers, can reappropriate to enhance our critical technical practices (Dourish, 2004). In the context of critical art and design inquiries, this short paper investigates moreover the importance of interacting with these social media APIs in order to turn our data as inputs for the creation of alternative infrastructures (Dragona & Charitos, 2018); infrastructures from where we can deconstruct our mainstream understandings of the internet. As entry points from where we can detour the way these platforms showcase our transmit our data, this paper argues that critically interacting with these APIs offers then, inside a commoning perspective, an innovative way to reappropriate our data as commons to foster citizen engagement and awareness towards how the internet is perceived (Wyatt, 2021) and used. The pertinence of using APIs as a commoning practice to extract and reappropriate how our data manifests online will be supported along this short paper by the case study and analysis of the 2XTWEETSXMODEMSXTEXTXTWEET (Khalatbari, 2020). In this critical making (Ratto, 2011) prototype and analog/digital installation that is site-specific to the Twitter platform, our data streams are being accessed and inputted to a dial-up modem. This turns these silent processes into explicitly audible signals; signals we can then decrypt back to their digital format. In opposition to the way the internet is depicted by Twitter and other private stakeholders of our internet, this case study subverts the opacity of the technological blackbox. It echoes moreover with a more community driven approach to extract and reappropriate our data as commons in order to enhance our critical reflection practices.LHS
Method for Design Materialization (MDM) for artists, educators and archivists: an introduction
No full textThis contribution argues for the potential of Barr, Khaled and Lessard’s Method for Design Materialization (MDM) as a research through design tool that is specifically suited for new media preservation. Building moreover from the ISEA first and second Summits on New Media Art Archiving, this article introduces the reader to this methodological and epistemological design framework through four existing articles: both addressing important issues in the context of new media practice, education, display and archiving. Placing these articles in dialogue with four structuring ideas of the MDM initiative, it posits the importance of further introducing new media artists to processes of self-archiving through the use of cohesive platforms such as MDM.LHS
From the Cloud to Agbogbloshie: The Case of the Agbogbloshie Makerspace Platform and Akwasi Bediako Afrane’s TRONS
No full textThis contribution sheds light on discarded electronics repair in Accra, Ghana. After placing these practices in dialogue with the Western and Eurocentric narratives around the materiality of digital interactions and infrastructure, it delves into two arts and design contexts that gravitate around the electronic waste landfill and processing site of Agbogbloshie (Ghana). The first case study is the Agbogbloshie Makerspace (AMP), a critical making (and unmaking) platform empowering local repairers and dismantlers through open-source collaborative design methods. The contribution then focuses on the work of Akwasi Bediako Afrane, a Ghanaian media artist who re-appropriates discarded computers to critique and speculate on our sociotechnical condition. Situating these initiatives in the light of our broader dominant internet and computing narratives, the article situates the importance of these practices in order to tackle and raise awareness about the planetary electronic waste condition we live in.LHS