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    Multi-year characterisation of the broad-band emission from the intermittent extreme BL Lac 1ES 2344+514
    (EDP Sciences, 2024-02-01) Hovatta, T.; , MAGIC Collaboration; , Multi-wavelength Collaborators; Metsähovi Radio Observatory
    Aims. The BL Lac 1ES 2344+514 is known for temporary extreme properties characterised by a shift of the synchrotron spectral energy distribution (SED) peak energy νsynch;p above 1 keV. While those extreme states have only been observed during high flux levels thus far, additional multi-year observing campaigns are required to achieve a coherent picture. Here, we report the longest investigation of the source from radio to very high energy (VHE) performed so far, focussing on a systematic characterisation of the intermittent extreme states. Methods.We organised a monitoring campaign covering a 3-year period from 2019 to 2021.Morethan ten instruments participated in the observations in order to cover the emission from radio to VHE. In particular, sensitive X-ray measurements by XMM-Newton, NuSTAR, and AstroSat took place simultaneously with multi-hour MAGIC observations, providing an unprecedented constraint of the two SED components for this blazar. Results. While our results confirm that 1ES 2344+514 typically exhibits νsynch;p > 1 keV during elevated flux periods, we also find periods where the extreme state coincides with low flux activity. A strong spectral variability thus happens in the quiescent state, and is likely caused by an increase in the electron acceleration efficiency without a change in the electron injection luminosity. On the other hand, we also report a strong X-ray flare (among the brightest for 1ES 2344+514) without a significant shift of νsynch;p. During this particular flare, the X-ray spectrum is among the softest of the campaign. It unveils complexity in the spectral evolution, where the common harder-when-brighter trend observed in BL Lacs is violated. By combining Swift-XRT and Swift-UVOT measurements during a low and hard X-ray state, we find an excess of the UV flux with respect to an extrapolation of the X-ray spectrum to lower energies. This UV excess implies that at least two regions significantly contribute to the infrared/optical/ultraviolet/X-ray emission. Using the simultaneous MAGIC, XMM-Newton, NuSTAR, and AstroSat observations, we argue that a region possibly associated with the 10 GHz radio core may explain such an excess. Finally, we investigate a VHE flare, showing an absence of simultaneous variability in the 0.3-2 keV band. Using time-dependent leptonic modelling, we show that this behaviour, in contradiction to single-zone scenarios, can instead be explained by a two-component model.
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    Small effects of electric field on motor cortical excitability following anodal tDCS
    (Cell Press, 2024-02-16) Laakso, Ilkka; Tani, Keisuke; Gomez-Tames, Jose; Hirata, Akimasa; Tanaka, Satoshi; Department of Electrical Engineering and Automation; Electromagnetics in Health Technology; Otemon Gakuin University; Chiba University; Nagoya Institute of Technology; Hamamatsu University School of Medicine
    The dose-response characteristics of transcranial direct current stimulation (tDCS) remain uncertain but may be related to variability in brain electric fields due to individual anatomical factors. Here, we investigated whether the electric fields influence the responses to motor cortical tDCS. In a randomized cross-over design, 21 participants underwent 10 min of anodal tDCS with 0.5, 1.0, 1.5, or 2.0 mA or sham. Compared to sham, all active conditions increased the size of motor evoked potentials (MEP) normalized to the pre-tDCS baseline, irrespective of anterior or posterior magnetic test stimuli. The electric field calculated in the motor cortex of each participant had a nonlinear effect on the normalized MEP size, but its effects were small compared to those of other participant-specific factors. The findings support the efficacy of anodal tDCS in enhancing the MEP size but do not demonstrate any benefits of personalized electric field modeling in explaining tDCS response variability.
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    Robotic mirror therapy for stroke rehabilitation through virtual activities of daily living
    (Research Network of Computational and Structural Biotechnology, 2024-12) Nisar, Harris; Annamraju, Srikar; Deka, Shankar A.; Horowitz, Anne; Stipanović, Dušan M.; Department of Electrical Engineering and Automation; Nonlinear Systems and Control; University of Illinois at Urbana-Champaign; OSF Healthcare Saint Francis Medical Center
    Mirror therapy is a standard technique of rehabilitation for recovering motor and vision abilities of stroke patients, especially in the case of asymmetric limb function. To enhance traditional mirror therapy, robotic mirror therapy (RMT) has been proposed over the past decade, allowing for assisted bimanual coordination of paretic (affected) and contralateral (healthy) limbs. However, state-of-the-art RMT platforms predominantly target mirrored motions of trajectories, largely limited to 2-D motions. In this paper, an RMT platform is proposed, which can facilitate the patient to practice virtual activities of daily living (ADL) and thus enhance their independence. Two similar (but mirrored) 3D virtual environments are created in which the patients operate robots with both their limbs to complete ADL (such as writing and eating) with the assistance of the therapist. The recovery level of the patient is continuously assessed by monitoring their ability to track assigned trajectories. The patient's robots are programmed to assist the patient in following these trajectories based on this recovery level. In this paper, the framework to dynamically monitor recovery level and accordingly provide assistance is developed along with the nonlinear controller design to ensure position tracking, force control, and stability. Proof-of-concept studies are conducted with both 3D trajectory tracking and ADL. The results demonstrate the potential use of the proposed system to enhance the recovery of the patients.
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    Safe reinforcement learning in uncertain contexts
    (IEEE, 2024-01-15) Baumann, Dominik; Schon, Thomas B.; Department of Electrical Engineering and Automation; Cyber-physical Systems; Uppsala University
    When deploying machine learning algorithms in the real world, guaranteeing safety is an essential asset. Existing safe learning approaches typically consider continuous variables, i.e., regression tasks. However, in practice, robotic systems are also subject to discrete, external environmental changes, e.g., having to carry objects of certain weights or operating on frozen, wet, or dry surfaces. Such influences can be modeled as discrete context variables. In the existing literature, such contexts are, if considered, mostly assumed to be known. In this work, we drop this assumption and show how we can perform safe learning when we cannot directly measure the context variables. To achieve this, we derive frequentist guarantees for multi-class classification, allowing us to estimate the current context from measurements. Further, we propose an approach for identifying contexts through experiments. We discuss under which conditions we can retain theoretical guarantees and demonstrate the applicability of our algorithm on a Furuta pendulum with camera measurements of different weights that serve as contexts.
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    A computationally lightweight safe learning algorithm
    (2024-01-19) Baumann, Dominik; Kowalczyk, Krzysztof; Tiels, Koen; Wachel, Paweł; Department of Electrical Engineering and Automation; Cyber-physical Systems; Wroclaw University of Science and Technology; Eindhoven University of Technology
    Safety is an essential asset when learning control policies for physical systems, as violating safety constraints during training can lead to expensive hardware damage. In response to this need, the field of safe learning has emerged with algorithms that can provide probabilistic safety guarantees without knowledge of the underlying system dynamics. Those algorithms often rely on Gaussian process inference. Unfortunately, Gaussian process inference scales cubically with the number of data points, limiting applicability to high-dimensional and embedded systems. In this paper, we propose a safe learning algorithm that provides probabilistic safety guarantees but leverages the Nadaraya-Watson estimator instead of Gaussian processes. For the Nadaraya-Watson estimator, we can reach logarithmic scaling with the number of data points. We provide theoretical guarantees for the estimates, embed them into a safe learning algorithm, and show numerical experiments on a simulated seven-degrees-of-freedom robot manipulator.
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    Broadband balanced filter with high common-mode suppression and wide stopband based on SIW and SSPP
    (Institute of Electronics, Information and Communication Engineers (IEICE), 2024) Liu, Hao; Xue, B; Xu, Jun; Department of Electronics and Nanoengineering; Katsuyuki Haneda Group; University of Electronic Science and Technology of China
    This paper introduces a novel balanced bandpass filter (BPF) that utilizes the symmetrical F-shaped groove (SFG) substrate-integrated waveguide and spoof surface plasmon polariton (SIW-SSPP) structure. This design combines lowpass SSPP unit cells within a highpass balanced dual-layer SIW structure to realize bandpass filtering response. The SFG SIW-SSPP unit cell’s superior dispersion properties contribute to broad bandwidth and extensive stopband. Additionally, the balanced dual-layer SIW structure, achieved by removing a rectangular aperture from the common ground, allows for high in-band common-mode (CM) suppression and a broad CM suppression range. The proposed filter offers multiple variables to regulate the passband’s lower and upper cut-off frequencies independently. A fabricated prototype of the balanced filter is tested, demonstrating superior performance compared to previously reported balanced SIW and half-mode SIW BPFs. The filter achieves a broad 3-dB fractional bandwidth of 46.55% (6.33-10.17GHz), a wide 20-dB stopband rejection up to 2 f0 (f0: the passband’s center frequency), and simultaneous broad CM suppression range (24-dB up to 4.85 f0).
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    Silicon photonics-based high-energy passively Q-switched laser
    (Nature Publishing Group, 2024) Singh, Neetesh; Lorenzen, Jan; Sinobad, Milan; Wang, Kai; Liapis, Andreas C.; Frankis, Henry C.; Haugg, Stefanie; Francis, Henry; Carreira, Jose; Geiselmann, Michael; Gaafar, Mahmoud A.; Herr, Tobias; Bradley, Jonathan D.B.; Sun, Zhipei; Garcia-Blanco, Sonia M.; Kärtner, Franz X.; Department of Electronics and Nanoengineering; OtaNano; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; German Electron Synchrotron; University of Twente; McMaster University; University of Hamburg
    Chip-scale, high-energy optical pulse generation is becoming increasingly important as integrated optics expands into space and medical applications where miniaturization is needed. Q-switching of the laser cavity was historically the first technique to generate high-energy pulses, and typically such systems are in the realm of large bench-top solid-state lasers and fibre lasers, especially in the long wavelength range >1.8 µm, thanks to their large energy storage capacity. However, in integrated photonics, the very property of tight mode confinement that enables a small form factor becomes an impediment to high-energy applications owing to small optical mode cross-sections. Here we demonstrate a high-energy silicon photonics-based passively Q-switched laser with a compact footprint using a rare-earth gain-based large-mode-area waveguide. We demonstrate high on-chip output pulse energies of >150 nJ and 250 ns pulse duration in a single transverse fundamental mode in the retina-safe spectral region (1.9 µm), with a slope efficiency of ~40% in a footprint of ~9 mm2. The high-energy pulse generation demonstrated in this work is comparable to or in many cases exceeds that of Q-switched fibre lasers. This bodes well for field applications in medicine and space.
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    Distributed Finite-Sum Constrained Optimization subject to Nonlinearity on the Node Dynamics
    (2022) Doostmohammadian, Mohammadreza; Vrakopoulou, Maria; Aghasi, Alireza; Charalambous, Themistoklis; Department of Electrical Engineering and Automation; Bionic and Rehabilitation Engineering; Distributed and Networked Control Systems; University of Melbourne; Georgia State University
    Motivated by recent development in networking and parallel data-processing, we consider a distributed and localized finite-sum (or fixed-sum) allocation technique to solve resource-constrained convex optimization problems over multi-agent networks (MANs). Such networks include (smart) agents representing an intelligent entity capable of communication, processing, and decision-making. In particular, we consider problems subject to practical nonlinear constraints on the dynamics of the agents in terms of their communications and actuation capabilities (referred to as the node dynamics), e.g., networks of mobile robots subject to actuator saturation and quantized communication. The considered distributed sum-preserving optimization solution further enables adding purposeful nonlinear constraints, for example, sign-based nonlinearities, to reach convergence in predefined-time or robust to impulsive noise and disturbances in faulty environments. Moreover, convergence can be achieved under minimal network connectivity requirements among the agents; thus, the solution is applicable over dynamic networks where the channels come and go due to the agent's mobility and limited range. This paper discusses how various nonlinearity constraints on the optimization problem (e.g., collaborative allocation of resources) can be addressed for different applications via a distributed setup (over a network).
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    Intermediate-luminosity Type IIP SN 2021gmj : a low-energy explosion with signatures of circumstellar material
    (Oxford University Press, 2024-03-01) Murai, Yuta; Tanaka, Masaomi; Kawabata, Miho; Taguchi, Kenta; Teja, Rishabh Singh; Nakaoka, Tatsuya; Maeda, Keiichi; Kawabata, Koji S.; Nagao, Takashi; Moriya, Takashi J.; Sahu, D. K.; Anupama, G. C.; Tominaga, Nozomu; Morokuma, Tomoki; Imazawa, Ryo; Inutsuka, Satoko; Isogai, Keisuke; Kasuga, Toshihiro; Kobayashi, Naoto; Kondo, Sohei; Maehara, Hiroyuki; Mori, Yuki; Niino, Yuu; Ogawa, Mao; Ohsawa, Ryou; Okumura, Shin Ichiro; Saito, Sei; Sako, Shigeyuki; Takahashi, Hidenori; Uno, Kohki; Yamanaka, Masayuki; Department of Electronics and Nanoengineering; Metsähovi Radio Observatory; Anne Lähteenmäki Group; Tohoku University; University of Hyogo; Kyoto University; Indian Institute of Astrophysics; Hiroshima University; National Astronomical Observatory of Japan; Chiba Institute of Technology; University of Tokyo; Japan Spaceguard Association; Kagoshima University
    We present photometric, spectroscopic, and polarimetric observations of the intermediate-luminosity Type IIP supernova (SN) 2021gmj from 1 to 386 d after the explosion. The peak absolute V-band magnitude of SN 2021gmj is −15.5 mag, which is fainter than that of normal Type IIP SNe. The spectral evolution of SN 2021gmj resembles that of other sub-luminous SNe: The optical spectra show narrow P-Cygni profiles, indicating a low expansion velocity. We estimate the progenitor mass to be about 12 M⊙ from the nebular spectrum and the 56Ni mass to be about 0.02 M⊙ from the bolometric light curve. We also derive the explosion energy to be about 3 × 1050 erg by comparing numerical light-curve models with the observed light curves. Polarization in the plateau phase is not very large, suggesting nearly spherical outer envelope. The early photometric observations capture the rapid rise of the light curve, which is likely due to the interaction with a circumstellar material (CSM). The broad emission feature formed by highly ionized lines on top of a blue continuum in the earliest spectrum gives further indication of the CSM at the vicinity of the progenitor. Our work suggests that a relatively low-mass progenitor of an intermediate-luminosity Type IIP SN can also experience an enhanced mass-loss just before the explosion, as suggested for normal Type IIP SNe.
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    Thermodynamic description for magneto-plastic coupling in electrical steel sheets
    (Elsevier Science B.V., 2024-03-01) Taurines, J.; Martin, F.; Rasilo, P.; Belahcen, A.; Department of Electrical Engineering and Automation; Computational Electromechanics
    The purpose of the study is to propose a thermodynamic description of the full magneto-mechanical coupling in electrical steel sheets, including both elasticity and plasticity influence. Kinematic and isotropic hardening are considered as state variables and included to a second-order magneto-elastic energy written as a function of cubic invariants. The simulation of magnetic behaviour of plastified samples subjected to several elastic stresses reproduce the general trends of measurements carried out on non-oriented Fe-3%Si sheets.
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    Broadening spectral responses and achieving environmental stability in SnS2/Ag-NPs/HfO2 flexible phototransistors
    (Royal Society of Chemistry, 2024-01-09) Khan, Mohammad; Sadaqat, S; Khan, Muhammad Ashgar; Rehman, Shania; Subhani, Waqas; Ouladsmane, Mohamed; Rehman, Malik; Ali, F; Lipsanen, H; Sun, ZP; Eom, J; Ahmed, Faisal; Department of Electronics and Nanoengineering; Zhipei Sun Group; Harri Lipsanen Group; Centre of Excellence in Quantum Technology, QTF; Sejong University; Riphah International University; The University of Lahore; King Saud University; New Uzbekistan University
    Layered two-dimensional (2D) materials have gained popularity thanks to their atomically thin physique and strong coupling with light. Here, we investigated a wide band gap (≥ 2 eV) 2D material, i.e., tin disulfide (SnS2), and decorated it with silver nanoparticles, Ag-NPs, for broadband photodetection. Our results show that the SnS2/Ag-NPs devices exhibit broadband photodetection ranging from the ultraviolet to near-infrared (250-1050 nm) spectrum with decreased rise/decay times from 8/20 s to 7/16 s under 250 nm wavelength light compared to the bare SnS2 device. This is attributed to the localized surface plasmon resonance effect and the wide band gap of SnS2 crystal. Furthermore, the HfO2-passivated SnS2/Ag-NPs devices exhibited high photodetection performance in terms of photoresponsivity (∼12 500 A W−1), and external quantum efficiency (∼6 × 106%), which are significantly higher compared to those of bare SnS2. Importantly, after HfO2 passivation, the SnS2/Ag-NPs photodetector maintained the stable performance for several weeks with merely ∼5.7% reduction in photoresponsivity. Lastly, we fabricated a flexible SnS2/Ag-NPs photodetector, which shows excellent and stable performance under various bending curvatures (0, 20, and 10 mm), as it retains ∼80% of its photoresponsivity up to 500 bending cycles. Thus, our study provides a simple route to realize broadband and stable photoactivity in flexible 2D material-based devices.
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    Back-Pressure Traffic Signal Control in the Presence of Noisy Queue Information
    (2023-07-01) Charalambous, Themistoklis; Liaquat, Muwahida; Kulcsár, Balázs; Wymeersch, Henk; Department of Electrical Engineering and Automation; Ishii, Hideaki; Ebihara, Yoshio; Imura, Jun-ichi; Yamakita, Masaki; Distributed and Networked Control Systems; Chalmers University of Technology
    In this paper, we consider centralized traffic signal control policies using the max-weight algorithm when the queue size measurement is noisy. We first show analytically that the standard max-weight algorithm is throughput optimal even under noisy queue measurements. However, the average steady-state queue lengths and subsequently the average delays are increased. In order to alleviate the effect of these noisy measurements we add filtering to the max-weight algorithm; more specifically, we propose the Filtered-max-weight algorithm, which is based on particle filtering. We demonstrate via simulations that the Filtered-max-weight algorithm performs better than the standard max-weight algorithm in the presence of noisy measurements.
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    Is activation of the vestibular system by electromagnetic induction a possibility in an MRI context?
    (John Wiley & Sons, 2024-02-13) Bouisset, Nicolas; Nissi, Janita; Laakso, Ilkka; Reynolds, Raymond F.; Legros, Alexandre; Department of Electrical Engineering and Automation; Electromagnetics in Health Technology; Western University; Department of Electrical Engineering and Automation; University of Birmingham
    In recent years, an increasing number of studies have discussed the mechanisms of vestibular activation in strong magnetic field settings such as occur in a magnetic resonance imaging scanner environment. Amid the different hypotheses, the Lorentz force explanation currently stands out as the most plausible mechanism, as evidenced by activation of the vestibulo-ocular reflex. Other hypotheses have largely been discarded. Nonetheless, both human data and computational modeling suggest that electromagnetic induction could be a valid mechanism which may coexist alongside the Lorentz force. To further investigate the induction hypothesis, we provide, herein, a first of its kind dosimetric analysis to estimate the induced electric fields at the vestibular system and compare them with what galvanic vestibular stimulation would generate. We found that electric fields strengths from induction match galvanic vestibular stimulation strengths generating vestibular responses. This review examines the evidence in support of electromagnetic induction of vestibular responses, and whether movement-induced time-varying magnetic fields should be further considered and investigated.
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    Modeling User’s Body Effects on 5G Millimeter-Wave Cellphone Antenna Array
    (IEEE, 2024) Xue, Bing; Haneda, Katsuyuki; Koivumaki, Pasi; Icheln, Clemens; Department of Electronics and Nanoengineering; Katsuyuki Haneda Group
    5G millimeter-wave (mmW) wireless communication is an important study hotspot in recent years. Human blockage has been a part of multipath radio channels, and its extra losses to received powers of wireless links are modeled in different works. This manuscript aims at establishing an analytically tractable and hence fast way to estimate user body effects on radiations of cellphone antennas at mmW frequencies. Mathematical operators are first defined to represent the user-body effects on cellphone antenna radiation where shadowing and backscattering are modeled through knife-edge diffraction and geometrical optics. Next, the proposed operators are tested for a cellphone antenna array which is held in landscape and portrait modes. Agreement of radiation pattern cuts and spherical coverage statistics is observed between full-wave simulations with complex human body models and our proposed mathematical operators. Finally, compared with full-wave simulations, the proposed model has a clear computational advantage in predicting user body effects on cellphone radiations without the need for a complex human body model, while maintaining a decent level of accuracy. The proposed operators, therefore, contribute to expediting the calculation of antenna-body interaction in mmW cellphone-communication channel simulations.
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    Optical Tellegen metamaterial with spontaneous magnetization
    (Nature Publishing Group, 2024-12) Safaei Jazi, Shadi; Faniayeu, Ihar; Cichelero, Rafael; Tzarouchis, Dimitrios C.; Asgari, Mohammad Mahdi; Dmitriev, Alexandre; Fan, Shanhui; Asadchy, Viktar; Department of Electronics and Nanoengineering; Viktar Asadchy Group; University of Gothenburg; Stanford University; University of Pennsylvania
    The nonreciprocal magnetoelectric effect, also known as the Tellegen effect, promises a number of groundbreaking phenomena connected to fundamental (e.g., electrodynamics of axion and relativistic matter) and applied physics (e.g., magnetless isolators). We propose a three-dimensional metamaterial with an isotropic and resonant Tellegen response in the visible frequency range. The metamaterial is formed by randomly oriented bi-material nanocylinders in a host medium. Each nanocylinder consists of a ferromagnet in a single-domain magnetic state and a high-permittivity dielectric operating near the magnetic Mie-type resonance. The proposed metamaterial requires no external magnetic bias and operates on the spontaneous magnetization of the nanocylinders. By leveraging the emerging magnetic Weyl semimetals, we further show how a giant bulk effective magnetoelectric effect can be achieved in a proposed metamaterial, exceeding that of natural materials by almost four orders of magnitude.
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    CNN-based local features for navigation near an asteroid
    (IEEE, 2024) Knuuttila, Olli; Kestila, Antti; Kallio, Esa; Department of Electronics and Nanoengineering; Esa Kallio Group
    This article addresses the challenge of vision-based proximity navigation in asteroid exploration missions and on-orbit servicing. Traditional feature extraction methods struggle with the significant appearance variations of asteroids due to limited scattered light. To overcome this, we propose a lightweight feature extractor specifically tailored for asteroid proximity navigation, designed to be robust to illumination changes and affine transformations. We compare and evaluate state-of-the-art feature extraction networks and three lightweight network architectures in the asteroid context. Our proposed feature extractors and their evaluation leverage synthetic images and real-world data from missions such as NEAR Shoemaker, Hayabusa, Rosetta, and OSIRIS-REx. Our contributions include a trained feature extractor, incremental improvements over existing methods, and a pipeline for training domain-specific feature extractors. Experimental results demonstrate the effectiveness of our approach in achieving accurate navigation and localization. This work aims to advance the field of asteroid navigation and provides insights for future research in this domain.
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    Distributed Optimization with Gradient Descent and Quantized Communication
    (2023-07-01) Rikos, Apostolos I.; Jiang, Wei; Charalambous, Themistoklis; Johansson, Karl H.; Department of Electrical Engineering and Automation; Ishii, Hideaki; Ebihara, Yoshio; Imura, Jun-ichi; Yamakita, Masaki; Bionic and Rehabilitation Engineering; Distributed and Networked Control Systems; KTH Royal Institute of Technology
    In this paper, we consider the unconstrained distributed optimization problem, in which the exchange of information in the network is captured by a directed graph topology, thus, nodes can only communicate with their neighbors. Additionally, in our problem, the communication channels among the nodes have limited bandwidth. In order to alleviate this limitation, quantized messages should be exchanged among the nodes. For solving this distributed optimization problem, we combine a gradient descent method with a distributed quantized consensus algorithm (which requires the nodes to exchange quantized messages and converges in a finite number of steps). Specifically, at every optimization step, each node (i) performs a gradient descent step (i.e., subtracts the scaled gradient from its current estimate), and (ii) performs a finite-time calculation of the quantized average of every node's estimate in the network. As a consequence, this algorithm approximately mimics the centralized gradient descent algorithm. We show that our algorithm asymptotically converges to a neighborhood of the optimal solution with linear convergence rate. The performance of the proposed algorithm is demonstrated via simple illustrative examples.
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    M5 — Mars Magnetospheric Multipoint Measurement Mission: A multi-spacecraft plasma physics mission to Mars
    (Elsevier Science Ltd., 2024-03-15) Larkin, Cormac J.K.; Lundén, Ville; Schulz, Leonard; Baumgartner-Steinleitner, Markus; Brekkum, Marianne; Dazzi, Pietro; Cegla, Adam; Iuliis, Alessia De; Gesch, Jonas; Lennerstrand, Sofia; Nesbit-Östman, Sara; Pires, Vasco D.C.; Palanca, Inés Terraza; Teubenbacher, Daniel; Enengl, Florine; Hallmann, Marcus; Department of Electronics and Nanoengineering; Jaan Praks Group; Heidelberg University ; Technical University of Braunschweig; Graz University of Technology; University of South-Eastern Norway; Université d'Orléans; Wroclaw University of Environmental and Life Sciences; Polytechnic University of Turin; Deutsches Zentrum für Luft- und Raumfahrt e.V.; Luleå University of Technology; Umeå University; University of Porto; University of Barcelona; Austrian Academy of Sciences; University of Oslo; German Aerospace Center
    Mars, lacking an intrinsic dynamo, is an ideal laboratory to comparatively study induced magnetospheres, which can be found in other terrestrial bodies as well as comets. Additionally, Mars is of particular interest to further exploration due to its loss of habitability by atmospheric escape and possible future human exploration. In this context, we propose the Mars Magnetospheric Multipoint Measurement Mission (M5), a multi-spacecraft mission to study the dynamics and energy transport of the Martian induced magnetosphere comprehensively. Particular focus is dedicated to the largely unexplored magnetotail region, where signatures of magnetic reconnection have been found. Furthermore, a reliable knowledge of the upstream solar wind conditions is needed to study the dynamics of the Martian magnetosphere, especially the different dayside boundary regions but also for energy transport phenomena like the current system and plasma waves. This will aid the study of atmospheric escape processes of planets with induced magnetospheres. In order to resolve the three-dimensional structures varying both in time and space, multi-point measurements are required. Thus, M5 is a five spacecraft mission, with one solar wind monitor orbiting Mars in a circular orbit at 5 Martian radii, and four smaller spacecraft in a tetrahedral configuration orbiting Mars in an elliptical orbit, spanning the far magnetotail up to 6 Mars radii with a periapsis just outside the Martian magnetosphere of 1.8 Mars radii. We not only present a detailed assessment of the scientific need for such a mission but also show the resulting mission and spacecraft design taking into account all aspects of the mission requirements and constraints such as mass, power, and link budgets. Additionally, different aspects of the mission programmatics like a possible mission timeline, cost estimates, or public outreach are shown. The common requirements for acceptance for an ESA mission are considered. The mission outlined in this paper was developed during the Alpbach Summer School 2022 on the topic of “Comparative Plasma Physics in the Universe”.
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    Investigative characterization of delamination at TiW-Cu interface in low-temperature bonded interconnects
    (Elsevier Inc., 2024-03) Golim, Obert; Vuorinen, Vesa; Ross, Glenn; Suihkonen, Sami; Paulasto-Kröckel, Mervi; Department of Electrical Engineering and Automation; Department of Electronics and Nanoengineering; Electronics Integration and Reliability; Department of Electrical Engineering and Automation
    The trend for heterogeneous integration has driven the need for a low-temperature bonding process. Cu-Sn-In based solid-liquid interdiffusion (SLID) bonding technology has been presented as a viable option. However, previous studies have also reported that issues might exist in the interconnect interface towards the substrate, leading to the formation of intermetallic layers at undesired locations. This study carried out a series of characterization methods to determine the root cause of this issue. Cross-sectional observations showed that the problem occurs particularly at the TiW-Cu interface. Examination of the adhesion layer showed possible impurities existing in the layers, compromising its adhesion to copper. Residual stress analyses displayed opposing loading conditions at the interface. The interplay of the two factors resulted in the delamination of the TiW-Cu interface, leading to a pathway for Sn–In atoms. Furthermore, several methods are proposed to mitigate this issue.
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    A Comprehensive Review on Recent Developments of Hosting Capacity Estimation and Optimization for Active Distribution Networks
    (IEEE, 2024-01-29) Mousa, Hossam H. H.; Mahmoud, Karar; Lehtonen, Matti; Department of Electrical Engineering and Automation; Power Systems and High Voltage Engineering
    Recently, several types of distributed energy resources (DERs) have been developed to reduce the environmental impact and support the global demand for electrical energy. However, the continuous penetration of the DERs into modern power systems (MPSs) may cause several adverse impacts in terms of operation performance indices (PIs) and power quality issues, especially in low-voltage distribution systems (LVDSs). To cope with these serious impacts and achieve optimal control, the hosting capacity (HC) of DERs must be accurately estimated and optimally optimized. However, it requires an extensive communication infrastructure, which is hardly offered without clear financial benefits. In this regard, this article investigates the historical developments of HC definitions as well as the recent developments in terms of operational performance indices, and estimation methods for active distribution networks (ADNs) with the high-penetration level existence of the DERs, energy storage systems (ESSs), electric vehicle (EV) charging systems, sector coupling, hydrogen technologies, and multi-carrier energy systems (MESs) to deal with electrical, thermal, and cooling demands. In this regard, this review article is intended to exhibit an appropriate reference for comprehensive research trends in HC estimation and optimization based on ADNs. Additionally, it involves and covers most current research HC topics in detail compared to other published review articles. Moreover, the authors deliberate the recent approaches for evaluating and improving the HC, especially concerning data-driven methods, with the aid of various software for simulating real systems. Moreover, modern research trends and main factors of MPS operations are deliberated with current energy market developments. Also, prominent challenges, current status, and future aspects are discussed.