The Ecosystem of Machine Learning Methods

Machine learning (ML) is a rapidly evolving field and plays an important role in today’s data-driven business environment. Many digital innovations in domains as diverse as healthcare, banking, energy, and retail are powered and enabled by ML. Examples include search engines, recommendation systems, pattern recognition, computer vision, and natural language processing. A key element in ML innovation is the advancement of the underlying methods, which specify how machines should algorithmically process, derive patterns, and learn from data for a given decisioning task. The speed at which this is happening is exponential, with researchers leveraging and building upon existing building blocks as well as introducing entirely new methods. Given the speed, scale, and complexity, understanding this complex evolving ML method space can be challenging. What methods are core and peripheral to ML? Which methods span task areas? How are ML methods evolving? In this exploratory research paper, I address these questions by (1) framing the ML method space and (2) visualizing the evolving structure of the ML methods ecosystem. The results reveal several foundational ML building blocks, different coupling levels between ML areas, and variable speeds of evolution. The study also provides insights into how digital innovation evolves at an algorithmic level. I discuss the implications of the findings and describe opportunities for future ML ecosystem-focused research

Biophysical properties of single-stranded DNA studied with single-molecule force spectroscopy

[eng] In this thesis, single-molecule experiments using LOT are employed to extract accurate information about the thermodynamics and kinetics of various molecular systems, with special emphasis on the elastic properties of single-stranded DNA (ssDNA). The thesis is divided in three parts. Part I provides a general description of the research field as well as the main theoretical framework for the basic concepts that will be developed in parts II and III. In Chapter 2 the miniTweezers and the experimental setup used throughout the thesis is described, as well as the physical basis of its working mechanisms, introducing the phenomenon of optical trapping. Chapter 3 contains a brief introduction of the biomolecules of study in this thesis, with an explanation of their historical discoveries, as well as their structure and function. The main focus of this chapter is on ssDNA, which is the main object of study of the thesis. Chapter 4 introduces the polymer models that are widely used in describing the elasticity of nucleic acids and proteins. Specifically, the Freely-Jointed Chain and Worm-Like Chain models are presented. Part II deals with the elasticity of single-stranded DNA. This is the main part of the thesis, and it includes chapters 5-7. Chapter 5 is about the study of the elasticity of ideal ssDNA chain, i.e. the one that can be modelled as ideal polymers (presented in Chapter 4). The study of the elasticity of different DNA sequences is presented. The blocking-splint oligo technique is described, a experimental technique developed for studying the elasticity of short (tens of bases) DNA molecules. This study shows the need of using extensible models to succesfully describe ssDNA elasticity over a large range of forces, which explains the previous discrepancies on the elastic parameters obtained in different studies. We also provide an explanation for the required extensibility of the model: a transition experienced at the nucleotide level: a change in DNA sugar pucker conformation. A simple two-states model is introduced and preeliminary results regarding its energetics are presented. The characterization of the ssDNA elasticity is central for the works developed in the following chapters. Chapter 6 studies the stacking-unstacking transition for ssDNA, previously observed for certain sequences (mainly purine-rich ones). Several molecules, with different degrees of stacking, are studied by obtaining their force extension curves (FECs). A cooperative helix-coil model including heterogeneity is developed and used to fit the obtained FECs, allowing to obtain elastic parameters to describe the stacked chain. The salt dependence of the unstacking transition is also measured by studying two of the sequences by varying the salt concentration over two decades. The free energy of formation of dsDNA duplexes depends on the salt concentration. The obtained salt dependence on the stacking free-energy of ssDNA provides a possible explanation for the salt dependence of duplex formation. Chapter 7 deals with the non-specific structures that arise at low forces and high salt concentration when pulling ssDNA molecules longer than $\sim 100$ bases. A helix-coil model with cooperativity is proposed and used to extract some mean-field characteristics of these structures. 8 different sequences are studied, characterizing their elasticity and deviation from the ideal elastic behaviour. The results for a $14$kb molecule for 3 decades of varying \ce{NaCl} and \ce{MgCl2} are also shown. All experimental FECs are fitted to the helix-coil model. The model can be used to predict the formation of secondary structures at zero force. A comparison between the predicted structures from the model and those obtained from Mfold is also investigated. Part III contains two studies which also need of the correct determination of ssDNA elasticity. In Chapter 8, we study the interaction between the RecQ helicase from E. coli and DNA, i.e. how the RecQ unwinds double-stranded DNA molecules, releasing single-stranded DNA. We obtain some of its kinematic properties as well as study the entropy production of the system using the Fluctuation Theorem. In Chapter 9, the effect of DNA mismatches, i.e. non complementary base pairing, on the stability of DNA is studied. To do so, two types of experiments on several DNA sequences are performed: stretching and releasing the molecule by moving the optical trap (pulling experiments) and monitoring the folding/unfolding of the molecule passively (hopping experiments).[cat] En aquesta tesi hem realitzat experiments fent servir pinces òptiques per tal d’extreure informació precisa sobre les propietats termodinàmiques i cinètiques de diferents sistemes moleculars, posant especial èmfasi en les propietats elàstiques de la cadena simple d’ADN (ssDNA, pel seu acrònim en anglès). La tesi es troba dividida en tres parts. A la primera part s’introdueix de forma general el camp de recerca dels experiments de molècula única, així com s’expliquen els conceptes més bàsics que es desenvoluparan en les parts II i III. La configuració experimental emprada al llarg de tota la tesi, les pinces òptiques, s’introdueix al capítol 2. Per a fer-ho, s’expliquen els principis físics de funcionament de les pinces, que es basen en l’atrapament òptic. Breument, la focalització d’un feix de llum d’alta intensitat permet atrapar i exercir forces en micropartícules dielèctriques (pilotes fetes de plàstic de la mida d’un bacteri), que són recobertes químicament de manera que la molècula d’estudi pot estirar-se, de forma individual, repetides vegades. El capítol 3 conté una breu introducció a les biomolècules que apareixen en aquesta tesi, amb una breu explicació de la seva descoberta, així com la seva estructura i funció (íntimament relacionades). Ens centrem en la descripció de la ssDNA que és el principal objecte d’estudi de la tesi. Al capítol 4 s’introdueixen els models de polímers que s’empren habitualment per a descriure l’elasticitat d’àcids nucleics i proteïnes. En concret, es descriuen els models de la Freely-Jointed Chain i la Worm-Like Chain. La Part II tracta de l’elasticitat de la ssDNA, i inclou els capítols 5, 6 i 7. El capítol 5 es basa en la caracterització de l’elasticitat de la cadena ideal de ssDNA, és a dir, aquella que pot ser modelitzada pels polímers ideals introduïts en el capítol 4. S’estudia l’elasticitat de diferents seqüències de ssDNA, introduint un nou mètode experimental, blocking-splint oligo, per tal d’ampliar el rang de forces estudiat habitualment en molècules curtes (d’una longitud de desenes de bases) de ssDNA. L’estudi mostra la necessitat d’emprar models elàstics extensibles per a la correcte caracterització de l’elasticitat de ssDNA, que explica les discrepàncies existents entre els paràmetres elàstics trobats a la literatura. També hipotetitzem que l’extensibilitat del model pot ser explicada gràcies a la transició experimentada a nivell de nucleòtids: el canvi que experimenta la distància interfosfat de l’ADN es veu modificada segons quina sigui la configuració de l’anell de desoxiribosa. Tot i que és un fenomen molt més conegut en la cadena doble d’ADN, l’apilament-desapilament de bases també s’ha observat en certes seqüències de ssDNA (especialment les que són riques en contingut de purines). Al capítol 6 s’estudien quatre molècules amb un grau d’apilament diferent a partir de les seves corbes força-extensió (FECs). Es desenvolupa un model helix-coil (hèlix-cabdell) per tal d’ajustar les FECs, fet que permet d’obtenir, indirectament, les propietats elàstiques de la cadena apilada. També s’estudia la dependència d’aquesta transició variant la concentració de sal dels experiments en més de dos ordres de magnitud. A través d’aquests experiments, trobem una dependència amb la concentració de sal de l’energia lliure de formació de l’apilament de la ssDNA, fet que ens permet explicar, parcialment, la dependència que es troba en la literatura per la hibridació de la cadena doble d’ADN. El capítol 7 tracta de la formació d’estructures no específiques que apareixen a forces baixes i a concentració de sal alta per a molècules de ssDNA de més de ~100bases. Es proposa un model helix-coil amb cooperativitat per tal de caracteritzar propietats de camp mitjà de les estructures estudiades. S’estudien vuit seqüències diferents, entre 120 i ~14000 bases, i es caracteritza el seu desviament respecte de la corba elàstica ideal amb el model. També s’estudia la dependència de l’estructura secundària de la ssDNA en funció de la concentració de la sal. Analitzant experiments variant la concentració de MgCl2 i NaCl, aconseguim reproduir les FECs a partir de fer dependre els paràmetres del model amb la sal. Finalment, el model desenvolupat ens permet predir la formació d’estructura secundària a força zero (fet que no podem detectar directament a partir d’experiments d’espectroscopia de forces). Es comparen les previsions del model amb les trobades per Mfold, trobant una compatibilitat per als resultats per a molècules de de menys de 1000 bases. La darrera part se centra en col·laboracions que he fet durant a tesi i que necessiten una determinació precisa de les propietats elàstiques de la ssDNA. Al capítol 8 s’estudia la interacció entre l’helicasa del bacteri E. coli i l’ADN, que s’encarrega d’obrir la cadena doble d’ADN, alliberant ssDNA. S’extreuen les seves propietats cinètiques, com la velocitat de translocació – obtenim, independentment de la força aplicada, d’uns 50bp/s, d’acord amb la literatura –. També n’estudiem les seves propietats termodinàmiques, a partir del Teorema de Fluctuació. Finalment, al capítol 9 s’estudien els efectes de certs defectes en molècules d’ADN. A partir d’experiments fora de l’equilibri s’extrau la penalització que suposa per a la hibridització d’ADN la presència d’aquestes bases no complementàries (és a dir, que no són enllaços de A-T o G-C)

Application of Wavelets-based SVM Classification for Automated Fault Diagnosis and Prognosis of Mechanical Systems

Anwendung der Wavelet-basierte SVM Klassifizierung für die automatisierte Fehlerdiagnose und -prognose mechanischer Systeme In dieser Arbeit werden Techniken der Mustererkennung auf verschiedene Problemstellungen der Fehlerdiagnose und -prognose angewendet. Die untersuchten Anwendungen stellen reale industrielle Anwendungen dar, bei denen verschiedene Messeigenschaften (wie zyklische, impulsive, und periodische Signale), verschiedene Charakteristik der Erkennungsobjektiven (wie kumulativ und einmalige Ereignisse), verschiedene Betriebsbedingungen und -parameter der Maschine, und verschiedene Fehler und Erkennungssystemanforderungen (wie Verschleiß, Riss, und Objekterkennung; Systemzustand und Restlebensdauer) die modulare Mustererkennungsverfahren und -techniken erfordern. Verschiedene Ansätze werden untersucht und angewendet, wie Support Vector Machine (SVM), Continuous Wavelet-Transform (CWT),Wavelet Packet Transform (WPT) und Diskrete Wavelet-Transform (DWT), und viele Konzepte und Lösungen werden vorgeschlagen und überprüft, um ein zuverlässiges Zustandsüberwachungssystem zu erreichen, dass die Instandhaltungsplanung der Maschine unterstützt und die Produktionsqualität und Produktionskosten verbessert. In der ersten untersuchten Anwendung in dieser Arbeit wird ein Ansatz für die Entwicklung eines Fehlerdiagnose- und -prognosesystems vorgestellt. Das System wird als Vorwarnmodul verwendet, um die Notwendigkeit für das Ersetzen von Verschleißteilen von Produktionsmaschinen zu erkennen und die Restlebensdauer des überwachten Teils zu bewerten. In der zweiten untersuchten Anwendung wird ein Produktionsverfahren überwacht. Ziel ist die Erkennung eines Objektes mit einer möglichst geringen Fehlalarmrate. Die Signale beinhalten nichtstationäre, impulsartige bzw. einmalige Ereignisse. Ein weiteres Merkmal der Sensorcluster-Signale ist die nicht gleichzeitige Erzeugung von Ereignissen, die die Verwendung von geeigneten Entscheidungsfusionstechniken erfordert. In der letzten untersuchten Anwendung, werden modell- und signalbasierte Verfahren für die Risserkennung und Prognose in rotierenden Maschinen untersucht, um eine Vorwarnung für Rotor-Risse zu erreichen für Online- Überwachung in Turbomaschinen. Die angetroffenen Signale sind periodische Schwingungssignale mit kumulativen Auswirkungen der Fehlerereignisse. Offene Fragen stellen sich bei den Themen Zustandsbewertung, Fehlerschweregrad und Restlebensdauer, basierend auf spezifischen Sensordaten mit besonderen anwendungsorientierten Eigenschaften. Diese Arbeit befasst sich mit diesen offenen Fragen, um ein zuverlässiges Zustandsüberwachungssystem zu erreichen. Es kann festgestellt werden, dass Wavelets und SVM sehr nützliche Werkzeuge für die Merkmalsextraktion und Klassifikation im Bereich der Zustandsüberwachung sind. Der Merkmalsraum von SVM ist nützlich für die Bewertung der verbleibenden Lebensdauer. Allerdings zeigt sich ebenfalls, dass angesichts der Herausforderungen anwendungsorientierte Lösungen gefunden werden müssen.In this thesis, the application of pattern recognition techniques is considered for different kinds of fault diagnosis and prognosis problems and applications. The investigated applications represent real industrial applications, in which different measurement characteristics (such as cyclic, impulsive, and periodic signals), different recognition objective characteristics (such as accumulative and one-time events), different operational conditions and parameters of the machine, and different faults and detection system requirements (such as wear, crack, and object detection; System state and remaining life time) are challenging the existence of modular pattern recognition procedures and techniques. Different approaches are investigated and applied such as Support Vector Machine (SVM), Discrete Wavelet Transform (DWT), Wavelet Packet Transform (WPT), and Continuous Wavelet Transform (CWT), and many concepts and solutions are proposed and verified, in order to achieve a reliable condition monitoring system, which supports the maintenance planning of the machine and adds value to the production quality and cost. In the first investigated application in this thesis, an approach for developing a fault diagnosis and prognosis system is presented. The system is used as a prewarning module to detect the necessity for replacing wear parts of production machines and to evaluate the remaining life time of the supervised part. The sensor signals encountered for processing are nondeterministic with cyclic nature related to the operation cycle of the machine. In the second investigated application, the goal is to monitor a production process for online detection of a target object with the lowest possible false alarm rate. The signals encountered in the system of this work are characterized with nonstationary impulsive one-time events representing the goal object. Another characteristic of the sensor cluster signals is the partly simultaneous stimulation of events which requires the use of suitable decision fusion techniques. In the last investigated application, two main approaches used for crack detection and prediction in rotating machinery; model based and signal based, are investigated, in order to achieve a prewarning technique for rotor cracks to be applied for online monitoring in turbo-machinery. The signals encountered are periodic vibration signals with accumulative impact of the fault incident. Open questions arise in the issues of state evaluation, severity estimation, and remaining life time prediction, based on specific sensor data with particular applicationoriented characteristics. This work deals with these open questions, in order to achieve a reliable condition monitoring system. As a general conclusion of the work, it can be stated that Wavelets and SVM are reliable tools for feature extraction and classification in the field of condition monitoring, and the feature space of SVM is useful for remaining life prediction. However; specific application oriented Solutions and tricks are necessary, considering the diversity of fault diagnosis and prognosis problems and difficulties

Free energy and information-content measurements in thermodynamic and molecular ensembles

[eng] Single-molecule experiments have emerged as a powerful tool that allow researchers to investigate the physical behavior of individual molecules with unprecedented resolution. The feasibility exerting forces at the piconewton scale (10^-12 N) and measuring nanometric displacements in the sub-millisecond scale, offer a widespread range of exciting possibilities. The major part of this thesis is devoted to address fundamental topics of statistical physics using single-molecule experiments. In particular, in the first part of the thesis, we aimed to study one of the eldest questions in statistical mechanics: the issue of ensemble inequivalence. By performing single- molecule experiments on a well-known molecule (the CD4 DNA hairpin), we have been able of exploring two conjugate ensembles: the fixed-extension and the force-fixed ensemble. Both ensembles are conjugate with respect to energy since the product force times extension equals has energy dimensions. We carried out experiments in the fixed-force ensemble using both optical tweezers and magnetic tweezers, and in the fixed-extension using optical tweezers. We have found that these two conjugate ensembles are not equivalent at the level of thermodynamics nor in kinetics. Moreover, we showed that the often-neglected boundary terms in the definition of the thermodynamic work are essential to the validity of the fluctuation theorem. The second part of this thesis is also merely theoretical. Recent single-molecule assays confirmed the connection between information theory and statistical physics. Single- molecule experiments have turned out to be the perfect playground to explore the thermodynamic implications of having —or lacking— information. It is worthwhile to mention the experimental realization of the Szilard engine and the experimental verification of Landauer’s limit. With the current existing results, the information-to- energy connection is well established. We have been able to experimentally demonstrate, for the first time, the reversed implication. We have been able to quantify the information-content of neutral molecular ensembles by means of thermodynamic measurements. That is, we experimentally demonstrated the energy- to-information conversion. Our works are built on what we call ensemble force spectroscopy, a systematic procedure capable of obtaining a robust characterization of molecular ensembles in the best tradition of statistical physics, by measuring few tens of molecules. In the final part of the thesis we aimed to measure the specific binding energy of a metallic ion to the tertiary structure of a three-way RNA junction belonging to the central domain of the 16S ribosomal RNA (rRNA). From the physics perspective, to the best of our knowledge, first time we have been able to discern the free energy contribution due to the specific binding of magnesium ions to an RNA substrate by means of single-molecule assays. On the other hand, such molecule is able to form, besides its native conformation, a force-induced misfolded state. Despite this fact was already pointed out in previous single-molecule studies, there was a lack of knowledge regarding the molecular kinetics and the folding pathway. Aiming to fill this gap, we performed a thorough study of the three-helix RNA junction using dynamic force spectroscopy. As a result, we have characterized the full folding pathway of the molecule, including both the native and the misfolded structure. Furthermore, we have experimentally confirmed the fact that the presence of magnesium promotes the stabilization of the native structure and we have measured this contribution. We have found that magnesium is able to rescue the native structure from the misfolded structure via electrostatic interactions due to magnesium binding. This fact is biologically relevant, since we have been able to characterize the conditions in which a misfolded molecule is able to recover its native conformation.[spa] En esta tesis hemos abordado cuestiones fundamentales de la física estadística. En particular, hemos estudiado el problema de la equivalencia entre colectivos estadísticos, la conversión de energía a información y el estudio de las energías específicas de unión de iones metálicos a sustratos de RNA. Esta tesis doctoral se ha llevado a cabo empleando dos de los instrumentos de molécula individual más conocidos, las pinzas ópticas y las pinzas magnéticas. Ambas son técnicas que permiten la aplicación controlada de fuerzas mecánicas a los extremos de una molécula individual. El poder aplicar fuerzas a sistemas moleculares permite llevar a cabo una profunda caracterización de las propiedades físicas de los llamados sistemas pequeños. Las dimensiones de estos sistemas abarcan desde unos pocos nanómetros —una millonésima parte del metro— hasta varios cientos de nanómetros. Además, los sistemas pequeños están lejos del llamado límite termodinámico y están dominados por las fluctuaciones térmicas del entorno. Por lo tanto, debido a estas peculiaridades, el estudio de sistemas pequeños mediante los instrumentos de molécula individual permite impulsar y extender los horizontes de la física de no equilibrio

Desagregação de consumos de smart homes por tipologia

Relatório de estágio de mestrado em Estatística e Investigação Operacional, apresentada à Universidade de Lisboa, através da Faculdade de Ciências, em 2018O presente trabalho tem como tema a desagregação de consumos no setor doméstico e a sua aplicação ao projeto re:dy da EDP, cuja frequência de amostragem dos valores de consumo dos clientes é relativamente baixa. Os conceitos da desagregação de consumos e do projecto EDP re:dy são explicados no capítulo de contextualização. O capítulo de metodologia contém uma explicação para cada um dos métodos matemáticos que foram utilizados proeminentemente durante o estágio. As abordagens exploradas para resolução do problema podem ser essencialmente divididas em dois processos preditivos: o processo utilizado para prever o consumo de frigoríficos e máquinas e o processo desenvolvido especificamente para a estimação do consumo de aquecimento ambiente. O primeiro processo segue uma estrutura de Ensemble Learning contando com 7 algoritmos e 5 meta-algoritmos cujos desempenhos são comparados após a análise dos valores preditos para o consumo de frigoríficos e máquinas dos clientes. Antes da construção do processo, as amostras dos consumos das categorias de equipamento em questão foram sujeitas a uma análise exploratória para facilitar a escolha de algoritmos mais adequados. O conjunto de variáveis independentes (input do algoritmo) foi derivado da informação disponível para todos os clientes e processado através de uma análise em componentes principais. O processo preditivo para consumo de aquecimento ambiente foi desenvolvido estudando o impacto desta classe de equipamentos no consumo global dos clientes ao longo do ano. Ao contrário do primeiro processo, que é maioritariamente constituído por modelos estatísticos, este é um algoritmo empírico. Por fim, no capítulo de discussão, analisam-se as várias abordagens e possíveis direções futuras da sua aplicação ao projeto.The present work is focused on household energy disaggregation and its application to EDP's re:dy project, that has a relatively low sampling frequency for clients' consumption values. The concepts of energy disaggregation and of the re:dy project are explained in a contextualization chapter. The methodology chapter contains explanations for each mathematical method that was prominently used throughout the internship. The approaches to the problem can be split into two predictive processes: the process used to predict the consumption of fridges and washers and the process specifically designed to estimate the consumption of heaters. The first process follows an Ensemble Learning framework, including 7 algorithms and 5 meta algorithms whose performances are compared after analyzing the predicted values for fridges' and washers' consumption. Before the construction of the predictive process, the consumptions of the said equipment categories were analyzed to help choose better suited algorithms. The set of input variables was derived from the information available for every client and processed through a principal component analysis. The predictive process for heater consumption was developed by studying the impact of this equipment class on the global consumption of the clients throughout the year. Unlike the first approach, that was mainly composed of statistical models, this one is an empirical algorithm. Finally, in the discussion chapter, both approaches are analyzed as well as the future of their application to the project

Effects of target properties on the formation of lunar impact craters in the simple-to-complex transition

Thesis (Ph.D.) University of Alaska Fairbanks, 2019The transition from simple to complex crater morphology in impact craters with increase in crater size has been modelled and observed in planetary bodies across the Solar System. The transition diameter depends upon the strength and gravity of the planetary body. On the Moon, this transition takes place over a diameter range of several kilometers. This range spans a diversity of crater morphologies including simple, transitional and complex craters. The diameter range of 15 20 km falls within the lunar simple-to-complex transition. All other impactor properties held constant, the 15-20 km range corresponds to a factor of three in the magnitude of impact kinetic energy. I conducted detailed geologic investigation of 244 well-preserved craters in this diameter range to elucidate the root causes of morphological variations. I used panchromatic data for observing crater and surface morphology, Digital Elevation Models (DEMs) for evaluating crater morphometry and topographic variation of pre-impact terrain, near-infrared (NIR) bands for determining the composition of crater cavity and surrounding terrain, thermal infrared bands for examining rock abundance, and Synthetic Aperture Radar (SAR) data for detecting impact melt deposits. The results of my investigation indicate that the morphological differences are primarily governed by target properties. Simple craters are confined to the highlands, and the mare are more abundant in complex craters. The mare are composed of solidified basaltic lava flows interlayered with regolith. The layering creates vertical strength heterogeneities that drive the destabilization of the transient cavity and its collapse, causing the transition to complex craters at smaller diameters in the mare. The non-layered highlands are more vertically homogeneous in strength and therefore favor simple crater formation. Eight atypically deep simple craters were identified in the highlands near the mare highlands boundaries, the most porous terrains on the lunar surface. After detailed examination of these craters in comparison to their normal-depth counterparts, I conclude that part of the energy from impact on porous target was spent in target compaction. The higher the porosity of the target, the deeper the crater and greater its volume, due to increased compaction. That only some of the craters in the high porosity terrains are deep suggests that those craters are on locally extreme-high porosity patches. However, an unusual impactor property, such as a high velocity impact, a high density impactor, or a near-vertical impact may also be a contributor. The simple craters in the highlands were observed to be located on flat or gradually sloping surfaces or degraded rims and terraces of pre-existing craters. Most craters with localized slumps superpose sharp topographic breaks such as well-developed rims and terraces of pre-existing craters. However, the topographic settings of 35% of the craters with localized slumps appeared to be similar to that of the simple craters. More detailed topographic study of the pre-impact terrains of these two morphologies revealed that the pre-impact terrains of 35% of the craters with localized slumps are gradually sloping or have subtle topographic breaks. Both sharp and subtle breaks are characterized with similar sloping directions as the adjacent craters' walls, which led to over steepening of the transient cavity walls around this part of the rim and their collapse, thereby causing the accumulation of localized slumped material. Several simple craters were also identified to have formed on pre-impact topographic breaks. However, the simple craters' walls that superpose these breaks were observed to be sloping in directions opposite to that of the breaks. So the ejecta around these walls was deposited along the break slopes, and thus syn-impact mass wasting occurred external (and not internal) to the crater cavity.Chapter 1 Introduction -- 1.1 Chapter 2: Geologic analyses of the causes of morphological variations in lunar craters within the simple-to-complex transition -- 1.2 Chapter 3: Geologic investigation of deep simple craters in the lunar simple-to complex transition -- 1.3 Chapter 4: Influence of target properties on wall slumping in lunar craters within the simple-to-complex transition -- 1.4 References. Chapter 2: Geologic analyses of the causes of morphological variations in lunar craters within the simple-to-complex transition -- Abstract -- 2.1 Introduction -- 2.1.1 Lunar simple-to-complex impact crater transition -- 2.1.2 Objectives -- 2.2 Methods and data -- 2.2.1 Morphological characterization -- 2.2.2 Close-proximity analyses -- 2.2.3 Data sets used -- 2.3 Results -- 2.3.1 Morphological characterization -- 2.3.1.1 Simple crater -- 2.3.1.2 Crater with localized slumps -- 2.3.1.3 Crater with localized slumps and terraces -- 2.3.1.4 Crater with localized slumps and central uplift -- 2.3.1.5 Crater with localized slumps, terraces, and central uplift -- 2.3.1.6 Floor-fractured crater -- 2.3.1.7 Concentric crater -- 2.3.2 Highlands versus mare craters -- 2.3.3 Close-proximity craters -- 2.4 Discussion -- 2.4.1 Mare-highlands differences -- 2.4.2 Unusually deep craters -- 2.4.2.1 Impact into a high-porosity target -- 2.4.2.2 The highlands are more coherent in these locations and less susceptible to minor slumping of the transient cavity -- 2.4.3 Potential impactor-caused variations -- 2.4.4 Comparison with other planets -- 2.5 Conclusions -- 2.6 Acknowledgments -- 2.7 References -- Appendix A. Chapter 3: Geologic investigation of deep simple craters in the lunar simple-to-complex transition -- Abstract -- 3.1 Introduction -- 3.1.1 Deep simple craters -- 3.1.2 Objectives -- 3.1.2.1 Greater compaction of target with increase in porosity results in larger crater depths -- 3.1.2.2 The highlands are more coherent in these locations and more resistant to minor slumping of the transient cavity -- 3.2 Methods and data sets -- 3.2.1 Crater depths from SLDEM and LOLA tracks -- 3.2.2 Depths of proximity craters -- 3.2.3 Trends in crater morphometry -- 3.2.4 impact melt deposits -- 3.2.5 Visual examinations of crater cavities -- 3.3 Results -- 3.3.1 Crater depths from SLDEM and LOLA tracks -- 3.3.2 Depths of proximity craters -- 3.3.3 Trends in crater morphometry -- 3.3.3.1 Association of crater depth with porosity -- 3.3.3.2 Rim height -- 3.3.3.3 Wall slope -- 3.3.3.4 Floor size -- 3.3.3.5 Cavity profiles -- 3.3.3.6 Ejecta-cavity volume ratio -- 3.3.4 Impact melt deposits -- 3.3.5 Visual examinations of crater cavities -- 3.4 Discussion -- 3.4.1 Greater compaction of target with increase in porosity results in larger crater depths -- 3.4.2 The highlands are more coherent in these locations and more resistant to minor slumping of the transient cavity -- 3.5 Conclusions -- 3.6 Acknowledgements -- 3.7 References -- Appendix B. Chapter 4: Influence of target properties on wall slumping in lunar craters within the simple-to-complex transition -- Abstract -- 4.1 Introduction -- 4.1.1 Wall slumping -- 4.1.2 Objectives -- 4.1.2.1 Localized slumping occurred post-crater formation -- 4.1.2.2 Localized slumping occurred on weaker target -- 4.1.2.3 Impact cratering on a slope causes the localized slumping -- 4.2 Methods and data sets -- 4.2.1 Testing hypothesis 1: Comparison of crater densities on slumps and ejecta units of craters with localized slumps -- 4.2.2 Testing hypothesis 2: Frequencies of proximal simple craters and craters with localized slumps -- 4.2.3 Testing hypothesis 3: Topographic variation in pre-impact terrains of the simple craters and craters with localized slumps along with rim circularity -- 4.3 Results -- 4.3.1 Comparison of crater densities on slumps and ejecta units of craters with localized slumps -- 4.3.2 Frequencies of proximal simple craters and craters with localized slumps -- 4.3.3 Topographic variation in pre-impact terrains of the simple craters and craters with localized slumps along with rim circularity -- 4.4 Discussion -- 4.5 Conclusions -- 4.6 Acknowledgements -- 4.7 References -- Appendix C. Chapter 5: Conclusion -- 5.1 Target properties -- 5.2 Impactor properties

Active Perception for Autonomous Systems : In a Deep Space Navigation Scenario

Autonomous systems typically pursue certain goals for an extended amount of time in a self-sustainable fashion. To this end, they are equipped with a set of sensors and actuators to perceive certain aspects of the world and thereupon manipulate it in accordance with some given goals. This kind of interaction can be thought of as a closed loop in which a perceive-reason-act process takes place. The bi-directional interface between an autonomous system and the outer world is then given by a sequence of imperfect observations of the world and corresponding controls which are as well imperfectly actuated. To be able to reason in such a setting, it is customary for an autonomous system to maintain a probabilistic state estimate. The quality of the estimate -- or its uncertainty -- is, in turn, dependent on the information acquired within the perceive-reason-act loop described above. Hence, this thesis strives to investigate the question of how to actively steer such a process in order to maximize the quality of the state estimate. The question will be approached by introducing different probabilistic state estimation schemes jointly working on a manifold-based encapsuled state representation. On top of the resultant state estimate different active perception approaches are introduced, which determine optimal actions with respect to uncertainty minimization. The informational value of the particular actions is given by the expected impact of measurements on the uncertainty. The latter can be obtained by different direct and indirect measures, which will be introduced and discussed. The active perception schemes for autonomous systems will be investigated with a focus on two specific deep space navigation scenarios deduced from a potential mining mission to the main asteroid belt. In the first scenario, active perception strategies are proposed, which foster the correctional value of the sensor information acquired within a heliocentric navigation approach. Here, the expected impact of measurements is directly estimated, thus omitting counterfactual updates of the state based on hypothetical actions. Numerical evaluations of this scenario show that active perception is beneficial, i.e., the quality of the state estimate is increased. In addition, it is shown that the more uncertain a state estimate is, the more the value of active perception increases. In the second scenario, active autonomous deep space navigation in the vicinity of asteroids is investigated. A trajectory and a map are jointly estimated by a Graph SLAM algorithm based on measurements of a 3D Flash-LiDAR. The active perception strategy seeks to trade-off the exploration of the asteroid against the localization performance. To this end, trajectories are generated as well as evaluated in a novel twofold approach specifically tailored to the scenario. Finally, the position uncertainty can be extracted from the graph structure and subsequently be used to dynamically control the trade-off between localization and exploration. In a numerical evaluation, it is shown that the localization performance of the Graph SLAM approach to navigation in the vicinity of asteroids is generally high. Furthermore, the active perception strategy is able to trade-off between localization performance and the degree of exploration of the asteroid. Finally, when the latter process is dynamically controlled, based on the current localization uncertainty, a joint improvement of localization as well as exploration performance can be achieved. In addition, this thesis comprises an excursion into active sensorimotor object recognition. A sensorimotor feature is derived from biological principles of the human perceptual system. This feature is then employed in different probabilistic classification schemes. Furthermore, it enables the implementation of an active perception strategy, which can be thought of as a feature selection process in a classification scheme. It is shown that those strategies might be driven by top-down factors, i.e., based on previously learned information, or by bottom-up factors, i.e., based on saliency detected in the currently considered data. Evaluations are conducted based on real data acquired by a camera mounted on a robotic arm as well as on datasets. It is shown that the integrated representation of perception and action fosters classification performance and that the application of an active perception strategy accelerates the classification process