5 research outputs found

    Robust learning algorithms for spiking and rate-based neural networks

    Get PDF
    Inspired by the remarkable properties of the human brain, the fields of machine learning, computational neuroscience and neuromorphic engineering have achieved significant synergistic progress in the last decade. Powerful neural network models rooted in machine learning have been proposed as models for neuroscience and for applications in neuromorphic engineering. However, the aspect of robustness is often neglected in these models. Both biological and engineered substrates show diverse imperfections that deteriorate the performance of computation models or even prohibit their implementation. This thesis describes three projects aiming at implementing robust learning with local plasticity rules in neural networks. First, we demonstrate the advantages of neuromorphic computations in a pilot study on a prototype chip. Thereby, we quantify the speed and energy consumption of the system compared to a software simulation and show how on-chip learning contributes to the robustness of learning. Second, we present an implementation of spike-based Bayesian inference on accelerated neuromorphic hardware. The model copes, via learning, with the disruptive effects of the imperfect substrate and benefits from the acceleration. Finally, we present a robust model of deep reinforcement learning using local learning rules. It shows how backpropagation combined with neuromodulation could be implemented in a biologically plausible framework. The results contribute to the pursuit of robust and powerful learning networks for biological and neuromorphic substrates

    Charged Domain Walls in Ferroelectric Single Crystals

    Get PDF
    Charged domain walls (CDWs) in proper ferroelectrics are a novel route towards the creation of advancing functional electronics. At CDWs the spontaneous polarization obeying the ferroelectric order alters abruptly within inter-atomic distances. Upon screening, the resulting charge accumulation may result in the manifestation of novel fascinating electrical properties. Here, we will focus on electrical conduction. A major advantage of these ferroelectric DWs is the ability to control its motion upon electrical fields. Hence, electrical conduction can be manipulated, which can enrich the possibilities of current electronic devices e.g. in the field of reconfigurability, fast random access memories or any kind of adaptive electronic circuitry. In this dissertation thesis, I want to shed more light onto this new type of interfacial electronic conduction on inclined DWs mainly in lithium niobate/LiNbO3 (LNO). The expectation was: the stronger the DW inclination towards the polar axis of the ferroelectric order and, hence, the larger the bound polarization charge, the larger the conductivity to be displayed. The DW conductance and the correlation with polarization charge was investigated with a multitude of experimental methods as scanning probe microscopy, linear and nonlinear optical microscopy as well as electron microscopy. We were able to observe a clear correlation of the local DW inclination angle with the DW conductivity by comparing the three-dimensional DW data and the local DW conductance. We investigated the conduction mechanisms on CDWs by temperature-dependent two-terminal current-voltage sweeps and were able to deduce the transport to be given by small electron polaron hopping, which are formed after injection into the CDWs. The thermal activated transport is in very good agreement with time-resolved polaron luminescence spectroscopy. The applicability of this effect for non-volatile memories was investigated in metal-ferroelectric-metal stacks with CMOS compatible single-crystalline films. These films showed unprecedented endurance, retention, precise set voltage, and small leakage currents as expected for single crystalline material. The conductance was tuned and switched according to DW switching time and voltage. The formation of CDWs has proven to be extremely stable over at least two months. The conductivity was further investigated via microwave impedance microscopy, which revealed a DW conductivity of about 100 to 1000 S/m at microwave frequencies of about 1 GHz.:1 INTRODUCTION 1 I THEORETICAL BASICS 5 2 FUNDAMENTALS 7 2.1 Ferroelectricity 7 2.1.1 Spontaneous polarization 8 2.1.2 Domains and domain walls 9 2.1.3 Charged domain walls 13 2.1.4 Conductive domain walls 16 2.2 Visualization of ferroelectric domains and domain walls 21 2.2.1 Light microscopy 22 2.2.2 Second-harmonic generation microscopy 22 2.2.3 Cherenkov second-harmonic generation microscopy 25 2.2.4 Optical coherence tomography 28 2.2.5 Piezo-response force microscopy 30 2.2.6 Ferroelectric lithography 31 2.2.7 Further methods 34 2.3 Lithium niobate and tantalate 37 2.3.1 General Properties 37 2.3.2 Stoichiometry 38 2.3.3 Optical properties 40 2.3.4 Intrinsic and extrinsic defects 43 2.3.5 Polarons 47 2.3.6 Ionic conductivity 51 3 METHODS 53 3.1 Sample Preparation 53 3.1.1 Poling stage 53 3.1.2 Thermal treatment 56 3.1.3 Ion slicing of LNO crystals 57 3.2 Atomic force microscopy 59 3.2.1 Non-contact and contact mode AFM microscopy 59 3.2.2 Piezo-response force microscopy (PFM) 60 3.2.3 Conductive atomic force microscopy (cAFM) 62 3.2.4 Scanning microwave impedance microscopy (sMIM) 63 3.2.5 AFM probes 66 3.3 Laser scanning microscope 67 3.4 Time-resolved luminescence spectroscopy 71 3.5 Energy-resolved photoelectron emission spectromicroscopy 72 II EXPERIMENTS 75 4 RESULTS 77 4.1 Three-dimensional profiling of domain walls 78 4.1.1 Randomly poled LNO and LTO domains 78 4.1.2 Periodically Poled Lithium Niobate 81 4.1.3 AFM-written Domains 83 4.1.4 Thermally treated LNO 84 4.1.5 Laser-written domains 86 4.2 Polarization charge textures 90 4.2.1 Random domains in Mg:LNO and Mg:LTO 90 4.2.2 Thermally-treated LNO 92 4.3 Quasi-phase matching SHG 92 4.4 Photoelectron microspectroscopy 97 4.5 Activated polaron transport 101 4.6 High voltage treated LNO 113 4.7 Conductive domain walls in exfoliated thin-film LNO 115 4.7.1 Conductance maps 116 4.7.2 Resistive switching by conductive domain walls 120 4.8 Microwave impedance microscopy 134 4.8.1 Finite-element method simulation 134 4.8.2 Scanning microwave impedance microscopy 136 5 conclusion & outlook 143 III EPILOGUE 147 a APPENDIX 149 a.1 Laser ablation dynamics on LNO surfaces 149 a.2 XPS across a conductive DW in LNO 150 a.3 XRD of thin-film exfoliated LNO 151 a.4 Domain writing in exfoliated thin-film LNO 152 a.5 Retention in conductance at DWs in thin-film exfoliated LNO 155 a.6 sMIM on DWs in thin-film exfoliated LNO 157 a.7 Domain inversion evolution under a tip by phase-field modeling 159 a.8 Current transients in exfoliated LNO 161 a.9 Surface acoustic wave excitation damping at DWs 162 a.10 Influence of UV illumination on domains in Mg:LNO 162 Acronyms 165 Symbols 169 List of figures 172 List of tables 176 Bibliography 177 Publications 225 Erklärung 233Geladene Domänenwände (DW) in reinen Ferroelektrika stellen eine neue Möglichkeit zur Erzeugung zukünftiger, funktionalisierter Elektroniken dar. An geladenen DW ändert sich die Polarisation sehr abrupt - innerhalb nur weniger Atomabstände. Sofern die dadurch hervorgerufene Ladungsträgeranreicherung elektrisch abgeschirmt werden kann, könnte dies zu faszinierenden elektrischen Eigenschaften führen. Wir möchten uns hierbei jedoch auf die elektrische Leitfähigkeit beschränken. Ein großer Vorteil für die Anwendung leitfähiger DW ist deren kontrollierte Bewegung unter Einwirkung elektrischer Felder. Dies ermöglicht die Manipulation das Ladungstransports, welches zum Beispiel im Bereich der Rekonfigurierbarkeit, schneller Speicherbauelemente und jeder Art von adaptiven elektronischen Schaltungen Anwendung finden kann. In dieser Dissertationsschrift möchte ich diesen neuen Typus grenzflächiger elektronischen Ladungstransports an geladenen DW hauptsächlich am Beispiel von Lithiumniobat/-LiNbO3 (LNO) untersuchen. Die Annahme lautete hierbei: umso stärker die DW zur ferroelektrischen Achse geneigt ist, also desto stärker die gebundene Polarisationsladung und folglich die elektrische DW-Leitfähigkeit. Die elektrische DW-Leitfähigkeit und die Korrelation mit der Polarisationsladung wurde mit verschiedenen experimentellen Methoden wie Rasterkraftmikroskopie, linearer und nichtlinearer optischer Mikroskopie als auch Elektronenmikroskopie untersucht. Es konnte eine klare Korrelation durch Vergleich der dreidimensionalen DW-Aufzeichnungsdaten mit der lokalen Leitfähigkeit gezeigt werden. Wir haben weiterhin den Leitfähigkeitsmechanismus an geladenen DW mittels temperaturabhängiger Strom-Spannungskennlinien untersucht und konnten hierbei einen Hopping-Transport kleiner Elektronenpolaronen nachweisen, welche nach Elektroneninjektion in die geladene DW generiert werden. Der thermisch aktivierte Ladungsträgertransport ist in guter Übereinstimmung mit zeitaufgelöster Polaron-Lumineszenzspektroskopie. Die Anwendbarkeit dieses Effektes für nicht-volatile Speicherbauelemente wurde an Metall-Ferroelektrika-Metall Schichtstrukturen mit CMOS-kompatiblen einkristalliner Filmen untersucht. Die Filme zeigen bisher nichtgesehene Durchhalte- und Speichervermögen, genau definierte Schaltspannung sowie sehr geringe Leckageströme wie dies für einkristalline Materialsysteme erwartet wird. Die Leitfähigkeit konnte mittels entsprechender Wahl der elektrischen Schaltzeiten und -spannungen zielgerichtet manipuliert und geschalten werden. Es konnte darüber hinaus gezeigt werden, dass die hergestellten geladenen DW über eine Zeitspanne von mindestens zwei Monaten stabil sind und hierbei leitfähig bleiben. Die Leitfähigkeit der DW wurde weiterhin mittels Mikrowellenimpedanzmikroskopie untersucht. Dabei konnten DW-Leitfähigkeiten von 100 bis 1000 S/m für Mikrowellenfrequenzen von etwa 1GHz ermittelt werden.:1 INTRODUCTION 1 I THEORETICAL BASICS 5 2 FUNDAMENTALS 7 2.1 Ferroelectricity 7 2.1.1 Spontaneous polarization 8 2.1.2 Domains and domain walls 9 2.1.3 Charged domain walls 13 2.1.4 Conductive domain walls 16 2.2 Visualization of ferroelectric domains and domain walls 21 2.2.1 Light microscopy 22 2.2.2 Second-harmonic generation microscopy 22 2.2.3 Cherenkov second-harmonic generation microscopy 25 2.2.4 Optical coherence tomography 28 2.2.5 Piezo-response force microscopy 30 2.2.6 Ferroelectric lithography 31 2.2.7 Further methods 34 2.3 Lithium niobate and tantalate 37 2.3.1 General Properties 37 2.3.2 Stoichiometry 38 2.3.3 Optical properties 40 2.3.4 Intrinsic and extrinsic defects 43 2.3.5 Polarons 47 2.3.6 Ionic conductivity 51 3 METHODS 53 3.1 Sample Preparation 53 3.1.1 Poling stage 53 3.1.2 Thermal treatment 56 3.1.3 Ion slicing of LNO crystals 57 3.2 Atomic force microscopy 59 3.2.1 Non-contact and contact mode AFM microscopy 59 3.2.2 Piezo-response force microscopy (PFM) 60 3.2.3 Conductive atomic force microscopy (cAFM) 62 3.2.4 Scanning microwave impedance microscopy (sMIM) 63 3.2.5 AFM probes 66 3.3 Laser scanning microscope 67 3.4 Time-resolved luminescence spectroscopy 71 3.5 Energy-resolved photoelectron emission spectromicroscopy 72 II EXPERIMENTS 75 4 RESULTS 77 4.1 Three-dimensional profiling of domain walls 78 4.1.1 Randomly poled LNO and LTO domains 78 4.1.2 Periodically Poled Lithium Niobate 81 4.1.3 AFM-written Domains 83 4.1.4 Thermally treated LNO 84 4.1.5 Laser-written domains 86 4.2 Polarization charge textures 90 4.2.1 Random domains in Mg:LNO and Mg:LTO 90 4.2.2 Thermally-treated LNO 92 4.3 Quasi-phase matching SHG 92 4.4 Photoelectron microspectroscopy 97 4.5 Activated polaron transport 101 4.6 High voltage treated LNO 113 4.7 Conductive domain walls in exfoliated thin-film LNO 115 4.7.1 Conductance maps 116 4.7.2 Resistive switching by conductive domain walls 120 4.8 Microwave impedance microscopy 134 4.8.1 Finite-element method simulation 134 4.8.2 Scanning microwave impedance microscopy 136 5 conclusion & outlook 143 III EPILOGUE 147 a APPENDIX 149 a.1 Laser ablation dynamics on LNO surfaces 149 a.2 XPS across a conductive DW in LNO 150 a.3 XRD of thin-film exfoliated LNO 151 a.4 Domain writing in exfoliated thin-film LNO 152 a.5 Retention in conductance at DWs in thin-film exfoliated LNO 155 a.6 sMIM on DWs in thin-film exfoliated LNO 157 a.7 Domain inversion evolution under a tip by phase-field modeling 159 a.8 Current transients in exfoliated LNO 161 a.9 Surface acoustic wave excitation damping at DWs 162 a.10 Influence of UV illumination on domains in Mg:LNO 162 Acronyms 165 Symbols 169 List of figures 172 List of tables 176 Bibliography 177 Publications 225 Erklärung 23

    Preliminaries for distributed natural computing inspired by the slime mold Physarum Polycephalum

    Get PDF
    This doctoral thesis aims towards distributed natural computing inspired by the slime mold Physarum polycephalum. The vein networks formed by this organism presumably support efficient transport of protoplasmic fluid. Devising models which capture the natural efficiency of the organism and form a suitable basis for the development of natural computing algorithms is an interesting and challenging goal. We start working towards this goal by designing and executing wet-lab experi- ments geared towards producing a large number of images of the vein networks of P. polycephalum. Next, we turn the depicted vein networks into graphs using our own custom software called Nefi. This enables a detailed numerical study, yielding a catalogue of characterizing observables spanning a wide array of different graph properties. To share our results and data, i.e. raw experimental data, graphs and analysis results, we introduce a dedicated repository revolving around slime mold data, the Smgr. The purpose of this repository is to promote data reuse and to foster a practice of increased data sharing. Finally we present a model based on interacting electronic circuits including current controlled voltage sources, which mimics the emergent flow patterns observed in live P. polycephalum. The model is simple, distributed and robust to changes in the underlying network topology. Thus it constitutes a promising basis for the development of distributed natural computing algorithms.Diese Dissertation dient als Vorarbeit für den Entwurf von verteilten Algorithmen, inspiriert durch den Schleimpilz Physarum polycephalum. Es wird vermutet, dass die Venen-Netze dieses Organismus den effizienten Transport von protoplasmischer Flüssigkeit ermöglichen. Die Herleitung von Modellen, welche sowohl die natürliche Effizienz des Organismus widerspiegeln, als auch eine geeignete Basis für den Entwurf von Algorithmen bieten, gilt weiterhin als schwierig. Wir nähern uns diesem Ziel mittels Laborversuchen zur Produktion von zahlreichen Abbildungen von Venen-Netzwerken. Weiters führen wir die abgebildeten Netze in Graphen über. Hierfür verwenden wir unsere eigene Software, genannt Nefi. Diese ermöglicht eine numerische Studie der Graphen, welche einen Katalog von charakteristischen Grapheigenschaften liefert. Um die gewonnenen Erkenntnisse und Daten zu teilen, führen wir ein spezialisiertes Daten-Repository ein, genannt Smgr. Hiermit begünstigen wir die Wiederverwendung von Daten und fördern das Teilen derselben. Abschließend präsentieren wir ein Modell, basierend auf elektrischen Elementen, insbesondere stromabhängigen Spannungsquellen, welches die Flüsse von P. poly- cephalum nachahmt. Das Modell ist simpel, verteilt und robust gegenüber topolo- gischen änderungen. Aus diesen Gründen stellt es eine vielversprechende Basis für den Entwurf von verteilten Algorithmen dar

    Systematic Approaches for Telemedicine and Data Coordination for COVID-19 in Baja California, Mexico

    Get PDF
    Conference proceedings info: ICICT 2023: 2023 The 6th International Conference on Information and Computer Technologies Raleigh, HI, United States, March 24-26, 2023 Pages 529-542We provide a model for systematic implementation of telemedicine within a large evaluation center for COVID-19 in the area of Baja California, Mexico. Our model is based on human-centric design factors and cross disciplinary collaborations for scalable data-driven enablement of smartphone, cellular, and video Teleconsul-tation technologies to link hospitals, clinics, and emergency medical services for point-of-care assessments of COVID testing, and for subsequent treatment and quar-antine decisions. A multidisciplinary team was rapidly created, in cooperation with different institutions, including: the Autonomous University of Baja California, the Ministry of Health, the Command, Communication and Computer Control Center of the Ministry of the State of Baja California (C4), Colleges of Medicine, and the College of Psychologists. Our objective is to provide information to the public and to evaluate COVID-19 in real time and to track, regional, municipal, and state-wide data in real time that informs supply chains and resource allocation with the anticipation of a surge in COVID-19 cases. RESUMEN Proporcionamos un modelo para la implementación sistemática de la telemedicina dentro de un gran centro de evaluación de COVID-19 en el área de Baja California, México. Nuestro modelo se basa en factores de diseño centrados en el ser humano y colaboraciones interdisciplinarias para la habilitación escalable basada en datos de tecnologías de teleconsulta de teléfonos inteligentes, celulares y video para vincular hospitales, clínicas y servicios médicos de emergencia para evaluaciones de COVID en el punto de atención. pruebas, y para el tratamiento posterior y decisiones de cuarentena. Rápidamente se creó un equipo multidisciplinario, en cooperación con diferentes instituciones, entre ellas: la Universidad Autónoma de Baja California, la Secretaría de Salud, el Centro de Comando, Comunicaciones y Control Informático. de la Secretaría del Estado de Baja California (C4), Facultades de Medicina y Colegio de Psicólogos. Nuestro objetivo es proporcionar información al público y evaluar COVID-19 en tiempo real y rastrear datos regionales, municipales y estatales en tiempo real que informan las cadenas de suministro y la asignación de recursos con la anticipación de un aumento de COVID-19. 19 casos.ICICT 2023: 2023 The 6th International Conference on Information and Computer Technologieshttps://doi.org/10.1007/978-981-99-3236-

    Collected Papers (on Neutrosophic Theory and Applications), Volume VI

    Get PDF
    This sixth volume of Collected Papers includes 74 papers comprising 974 pages on (theoretic and applied) neutrosophics, written between 2015-2021 by the author alone or in collaboration with the following 121 co-authors from 19 countries: Mohamed Abdel-Basset, Abdel Nasser H. Zaied, Abduallah Gamal, Amir Abdullah, Firoz Ahmad, Nadeem Ahmad, Ahmad Yusuf Adhami, Ahmed Aboelfetouh, Ahmed Mostafa Khalil, Shariful Alam, W. Alharbi, Ali Hassan, Mumtaz Ali, Amira S. Ashour, Asmaa Atef, Assia Bakali, Ayoub Bahnasse, A. A. Azzam, Willem K.M. Brauers, Bui Cong Cuong, Fausto Cavallaro, Ahmet Çevik, Robby I. Chandra, Kalaivani Chandran, Victor Chang, Chang Su Kim, Jyotir Moy Chatterjee, Victor Christianto, Chunxin Bo, Mihaela Colhon, Shyamal Dalapati, Arindam Dey, Dunqian Cao, Fahad Alsharari, Faruk Karaaslan, Aleksandra Fedajev, Daniela Gîfu, Hina Gulzar, Haitham A. El-Ghareeb, Masooma Raza Hashmi, Hewayda El-Ghawalby, Hoang Viet Long, Le Hoang Son, F. Nirmala Irudayam, Branislav Ivanov, S. Jafari, Jeong Gon Lee, Milena Jevtić, Sudan Jha, Junhui Kim, Ilanthenral Kandasamy, W.B. Vasantha Kandasamy, Darjan Karabašević, Songül Karabatak, Abdullah Kargın, M. Karthika, Ieva Meidute-Kavaliauskiene, Madad Khan, Majid Khan, Manju Khari, Kifayat Ullah, K. Kishore, Kul Hur, Santanu Kumar Patro, Prem Kumar Singh, Raghvendra Kumar, Tapan Kumar Roy, Malayalan Lathamaheswari, Luu Quoc Dat, T. Madhumathi, Tahir Mahmood, Mladjan Maksimovic, Gunasekaran Manogaran, Nivetha Martin, M. Kasi Mayan, Mai Mohamed, Mohamed Talea, Muhammad Akram, Muhammad Gulistan, Raja Muhammad Hashim, Muhammad Riaz, Muhammad Saeed, Rana Muhammad Zulqarnain, Nada A. Nabeeh, Deivanayagampillai Nagarajan, Xenia Negrea, Nguyen Xuan Thao, Jagan M. Obbineni, Angelo de Oliveira, M. Parimala, Gabrijela Popovic, Ishaani Priyadarshini, Yaser Saber, Mehmet Șahin, Said Broumi, A. A. Salama, M. Saleh, Ganeshsree Selvachandran, Dönüș Șengür, Shio Gai Quek, Songtao Shao, Dragiša Stanujkić, Surapati Pramanik, Swathi Sundari Sundaramoorthy, Mirela Teodorescu, Selçuk Topal, Muhammed Turhan, Alptekin Ulutaș, Luige Vlădăreanu, Victor Vlădăreanu, Ştefan Vlăduţescu, Dan Valeriu Voinea, Volkan Duran, Navneet Yadav, Yanhui Guo, Naveed Yaqoob, Yongquan Zhou, Young Bae Jun, Xiaohong Zhang, Xiao Long Xin, Edmundas Kazimieras Zavadskas
    corecore