1,068 research outputs found

    LIPIcs, Volume 251, ITCS 2023, Complete Volume

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    LIPIcs, Volume 251, ITCS 2023, Complete Volum

    Behavior quantification as the missing link between fields: Tools for digital psychiatry and their role in the future of neurobiology

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    The great behavioral heterogeneity observed between individuals with the same psychiatric disorder and even within one individual over time complicates both clinical practice and biomedical research. However, modern technologies are an exciting opportunity to improve behavioral characterization. Existing psychiatry methods that are qualitative or unscalable, such as patient surveys or clinical interviews, can now be collected at a greater capacity and analyzed to produce new quantitative measures. Furthermore, recent capabilities for continuous collection of passive sensor streams, such as phone GPS or smartwatch accelerometer, open avenues of novel questioning that were previously entirely unrealistic. Their temporally dense nature enables a cohesive study of real-time neural and behavioral signals. To develop comprehensive neurobiological models of psychiatric disease, it will be critical to first develop strong methods for behavioral quantification. There is huge potential in what can theoretically be captured by current technologies, but this in itself presents a large computational challenge -- one that will necessitate new data processing tools, new machine learning techniques, and ultimately a shift in how interdisciplinary work is conducted. In my thesis, I detail research projects that take different perspectives on digital psychiatry, subsequently tying ideas together with a concluding discussion on the future of the field. I also provide software infrastructure where relevant, with extensive documentation. Major contributions include scientific arguments and proof of concept results for daily free-form audio journals as an underappreciated psychiatry research datatype, as well as novel stability theorems and pilot empirical success for a proposed multi-area recurrent neural network architecture.Comment: PhD thesis cop

    Dynamic Nanophotonic Structures Leveraging Chalcogenide Phase-Change Materials

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    Chip-scale nanophotonic devices have the potential to enable next-generation imaging, computing, communication, and engineered quantum systems with very stringent performance requirements on size, power, integrability, stability, and bandwidth. The emergence of meta-optic devices with deep subwavelength features has enabled the formation of ultra-thin flat optical structures to replace bulky conventional counterparts in free-space applications. Nevertheless, progress in meta-optics has been slowed due to the passive nature of existing devices and the urgent need for a reliable, fast, low-power, and robust reconfiguration mechanism. In this research, I devised a new material and device platform to resolve this challenge. Through detailed theoretical design, nanofabrication, and experimental demonstration, I demonstrated the unique features of my proposed platform as an essential building block of truly scalable adaptive flat optics for the active manipulation of optical wavefronts. One of the key attributes of this research is the integration of CMOS-compatible materials for the fabrication of passive devices with phase-change materials that provide the largest known modulation of the index of refraction upon stimulation with an optical or electrical signal. A unique selection of phase-change materials for operation in the near-infrared and visible wavelengths has been made, followed by developing the optimum deposition and fabrication processes for the realization of nanophotonics devices that integrate these functional materials with semiconductor and plasmonic materials. A major breakthrough in this process was the design and realization of integrated electrical stimulation circuitry with far better performance compared to existing solutions. Using this platform, I experimentally demonstrated the first electrically tunable meta-optic structure for fast optical switching with a high contrast ratio and dynamic wavefront scanning with a large steering angle. This is a major achievement as it essentially allows the engineering of a desired optical wavefront with fast reconfigurability at low power consumption. In an independent work, I demonstrated, for the first time, a nonvolatile meta-optic structure for high-resolution, wide-gamut, and high-contrast microdisplays with added polarization controllability and the possibility of implementation on a flexible substrate. Further features of this metaphotonic display include: 1) full addressability at the microscale pixel via fast electrical pulses; 2) super-resolution pixels with controllable brightness and contrast; and 3) a wide range of colors with high saturation and purity. Lastly, for the first time, I realized a hybrid photonic-plasmonic meta-optic platform with active control over the spatial, spectral, and temporal properties of an optical wavefront. This is a major achievement as it essentially allows the engineering of a desired optical wavefront with fast reconfigurability at low power consumption. These demonstrations are now being pursued in different directions for novel systems for imaging, sensing, computing, and quantum applications, just to name a few.Ph.D

    Control of crystallization by polymer additives

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    Understanding how crystallization processes are controlled by polymer additives is relevant for a vastly diverse number of fields, for example in biomineralization, where the morphology of minerals is controlled by proteins or in scale inhibition strategies in industrial plants, in which macromolecules are added to prevent the precipitation of minerals. While numerous investigations have focused on elucidating additive-controlled crystallization, a detailed understanding of the underlying mechanisms is still desired. Herein, based on calcium carbonate as a mineral system, a comprehensive study on the manifold effects of selected polycarboxylate additives on the distinct species along the crystallization pathway is presented. Poly(glutamic acid) and poly(aspartic acid) are chosen as additives, as these polyaminoacids resemble biomineralization-associated peptides, as well as poly(acrylic acid), a commercially used scale inhibitor. Using potentiometric titrations, it is shown that even the basic interaction of polycarboxylates with calcium ions is more complex than commonly assumed. Quantitative determination of the Langmuir parameters of the binding process reveals that higher order effects and contributions arising from the whole polymer chain play a significant role, while the chemistry of the monomer unit constituting the polymer plays a subordinate role. The results put a question mark on whether the binding processes can be accurately described using solely the Langmuir binding model that assumes non-interacting binding sites. The investigation of the following stages of the crystallization pathway reveals that the polymer additives show the largest effect in the stabilization of liquid-like mineral precursors. A key step of this inhibition is the additive-driven binding of bicarbonates. Quantitative evaluation of ion association in the prenucleation regime reveals that more than 20% of bicarbonate species are bound in mineral precursors at pH 9.8, which can also be detected in isolated solid amorphous intermediates. Surprisingly, the protons introduced by bicarbonates are highly mobile, causing the formation of amorphous mineral ion conductors, which opens up possibilities for novel applications of mineral materials. The importance of liquid-like precursors for the mineral formation pathway is still highly debated in the community, and they are often ignored in the explanation of crystal formation. Using a refined gas diffusion method, it is demonstrated that liquid-like precursors show sufficient kinetic stability to be detected, both in presence of polymers and in additive-free systems. Observing the time dependent formation and transformation of the precursors shows that they play an important role in the early stages of crystallization and must be generally considered for the interpretation of gas diffusion experiments. Regarding the technological application of liquid-like minerals, a new and easily scalable synthesis method is presented, which solves existing limitations of the available synthesis methods. The “scalable controlled synthesis and utilization of liquid-like precursors for technological applications” (SCULPT) method effectively allows the isolation of the precursor on a gram scale and to access to the full potential of these mineral precursors for material synthesis. Implementing the gained insights into the current picture of nonclassical mineral formation, which was subject of many advancements in recent years, an updated view on additive-controlled mineralization is presented. The discoveries presented in this work are beneficial for the scientific and industrially-related communities far beyond the field of nucleation and crystallization mechanisms, such as materials chemistry, and improve the understanding of the mechanisms underlying biomineralization and mineral formation in general

    Brain Computations and Connectivity [2nd edition]

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    This is an open access title available under the terms of a CC BY-NC-ND 4.0 International licence. It is free to read on the Oxford Academic platform and offered as a free PDF download from OUP and selected open access locations. Brain Computations and Connectivity is about how the brain works. In order to understand this, it is essential to know what is computed by different brain systems; and how the computations are performed. The aim of this book is to elucidate what is computed in different brain systems; and to describe current biologically plausible computational approaches and models of how each of these brain systems computes. Understanding the brain in this way has enormous potential for understanding ourselves better in health and in disease. Potential applications of this understanding are to the treatment of the brain in disease; and to artificial intelligence which will benefit from knowledge of how the brain performs many of its extraordinarily impressive functions. This book is pioneering in taking this approach to brain function: to consider what is computed by many of our brain systems; and how it is computed, and updates by much new evidence including the connectivity of the human brain the earlier book: Rolls (2021) Brain Computations: What and How, Oxford University Press. Brain Computations and Connectivity will be of interest to all scientists interested in brain function and how the brain works, whether they are from neuroscience, or from medical sciences including neurology and psychiatry, or from the area of computational science including machine learning and artificial intelligence, or from areas such as theoretical physics

    A systematic risk management model for construction project management: a case study of the new infrastructure project in the University of Mpumalanga

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    The construction industry has become the significant player in the economy of many developed and developing countries in the world. The industry contributes to the Gross Domestic Product (GDP) and employment rate of many nations. As such, the industry is the engine for the economic development and growth across the world. Recently, African countries have received global attention due to its calls for massive infrastructure development and maintenance thereof. Accordingly, the South African government has adopted a National Infrastructure Development Plan (NIDP), which seeks not only to transform the economic landscape of the country, but also to support the integration of the African economies through infrastructure development. To ensure that the execution of these infrastructure projects is successfully delivered in terms of time, cost, and scope; project risk management in the construction industry has become an important area of interest in the execution and delivery of the infrastructure projects. However, the constantly increasing complexity and dynamics in the delivery of construction projects have serious effects on the risk management processes during the execution of the project. In practice, risk methods and techniques have proven to be unrealistic when using the traditional risk management approach in the context of the complexity and dynamic environments wherein construction projects are delivered. Worryingly, project management practitioners in engineering and construction projects still lack the holistic and systematic insight and understanding of construction projects when applying the risk management procedures in the complex and dynamic projects environments. As a result, there are growing reports of unsatisfactory delivery of construction projects in terms of time, cost, quality, and environmental objectives. In this regard, the call for embracing the systems thinking paradigm as the alternative approach that will provide more clarity in dealing with the complex management challenges and which will gradually substitute the traditional theoretical approach of dealing with construction project management, is becoming prominent. Against this background, this study uses a multiple case study approach to explore how a systematic risk management approach could be developed and applied towards successful delivery of construction projects, and subsequently to propose a systematic risk management model that is designed to depict and grasp the underlying complexities and dynamics embedded ix | P a g e in construction projects. The choice of the case study design is founded on its utility and appropriateness for in-depth investigations into phenomena in its context as well as its usefulness for exploratory studies. Therefore, to explore the risk management phenomenon in real-life settings, the unit of analysis in this study was based on three construction projects built in one of the new Institutions of Higher Learning in South Africa during the period between 2017 and 2019. Notwithstanding the unique characteristics of these projects, the complexity and dynamic environments of these projects also emanated from the facts that i) the successful delivery of the projects was a predecessor activity to the academic schedule and activities; ii) this was one of the first universities to be built by the democratic Republic of South Africa; and, iii) the construction contract used for the delivery of the construction projects is relatively new to the professionals in the country’s construction industry. This qualitative case study design has its backbone in the constructivism philosophical paradigm which is underpinned by the ontology that there are multiple realities as conceptualized, experienced, and perceived by the people in their real-life situations or natural settings. Accordingly, the construction professionals, projects’ documents as well as field work observations were purposively chosen as the essential and reliable methods of data collection for this case study. For analysis, a conventional content data analysis methodology was applied on the empirical data that was obtained from the multiple data sources to provide a clearer understanding of the contexts in which the risk management for construction projects is performed. Accordingly, a qualitative data analysis software system called MAXQDA was used to enable the performance of data coding, managing coding, and eventually the retrieving of the coded segments in a form of visual models and summary tables. Ultimately, the qualitative content analysis approach in this thesis was performed in terms of a ‘critical filter of thick description’ which involved a balanced approach between the deductive analysis and the inductive analysis processes. With the assistance of the MAXQDA, performing the multiple levels coding and analysis processes in this thesis has not only been efficient, but also more reliable. To shed insight into the empirical findings of the study, a hybrid theoretical framework has been applied in the discussion and interpretation of the findings. The theoretical framework of this study is underpinned by the complexity theory and the theory of systems engineering. The applicability of these theories in this study is essential in providing a x | P a g e systematic and logical explanation of the practices of risk management in construction projects and further helps to explain why particular events occurred in the processes of risk management. Eventually, the theoretical framework has enabled the designing and developing of a systematic risk management model that will assist in depicting and grasping the underlying complexities while supporting proactive decision making in the delivery of construction projects. To this end, this study has made several major contributions in three multiple folds in the body of knowledge. Firstly, this study makes theoretical contributions by developing an empirically underpinned systematic risk management model which provide more clarity on comprehending the multifaceted and complex risk factors embedded in construction projects. Secondly, the qualitative case study approach and the associated analysis methods thereof in this thesis provides novelty and lays the groundwork for future research and methodological replicability in another similar phenomenon elsewhere in the world. Thirdly, this study has gone some way towards expanding the understanding and the basis for managerial decision making in relation to front-end planning and proactive approach for risk management, and eventually to improve projects’ performances on cost, time, scope, and environmental sustainability. In this regard, the key practical implication for project management practitioners is that the adoption and embracing of the systematic and holistic thinking approach in the risk management processes could enhance the successful delivery of construction projects. In the literature, there is paucity and need for more research into the exploration and analysis of the integration and interplay between the systems engineering and complexity perspectives and the other knowledge areas in the PMBOK. In conclusion, this thesis therefore argues that to address the deficiencies in risk management practices during construction projects’ delivery, the solution requires a paradigm shift from the traditional linear approach which, by design, overlooks the complexities, non-linearity and interdependences of the elements that are underpinning and characterizing the nature of the contemporary construction projects. Therefore, this thesis supports the increasingly emerging debate on the discourse that the superior traditional and linear approaches do not solve the current problems, and as such they should be replaced with the systems and holistic thinking approach that will provide more clarity in dealing with the complex management challenges in contemporary construction projects.Thesis (PhD) -- Faculty of Engineering, Built environment and Information Technology, School of the built Environment 202

    Toxic Timescapes: Examining Toxicity across Time and Space

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    An interdisciplinary environmental humanities volume that explores human-environment relationships on our permanently polluted planet. While toxicity and pollution are ever present in modern daily life, politicians, juridical systems, media outlets, scholars, and the public alike show great difficulty in detecting, defining, monitoring, or generally coming to terms with them. This volume’s contributors argue that the source of this difficulty lies in the struggle to make sense of the intersecting temporal and spatial scales working on the human and more-than-human body, while continuing to acknowledge race, class, and gender in terms of global environmental justice and social inequality. The term toxic timescapes refers to this intricate intersectionality of time, space, and bodies in relation to toxic exposure. As a tool of analysis, it unpacks linear understandings of time and explores how harmful substances permeate temporal and physical space as both event and process. It equips scholars with new ways of creating data and conceptualizing the past, present, and future presence and possible effects of harmful substances and provides a theoretical framework for new environmental narratives. To think in terms of toxic timescapes is to radically shift our understanding of toxicants in the complex web of life. Toxicity, pollution, and modes of exposure are never static; therefore, dose, timing, velocity, mixture, frequency, and chronology matter as much as the geographic location and societal position of those exposed. Together, these factors create a specific toxic timescape that lies at the heart of each contributor’s narrative. Contributors from the disciplines of history, human geography, science and technology studies, philosophy, and political ecology come together to demonstrate the complex reality of a toxic existence. Their case studies span the globe as they observe the intersection of multiple times and spaces at such diverse locations as former battlefields in Vietnam, aging nuclear-weapon storage facilities in Greenland, waste deposits in southern Italy, chemical facilities along the Gulf of Mexico, and coral-breeding laboratories across the world.https://ohioopen.library.ohio.edu/oupress/1014/thumbnail.jp
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