320 research outputs found

    Adaptive dynamical networks

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    It is a fundamental challenge to understand how the function of a network is related to its structural organization. Adaptive dynamical networks represent a broad class of systems that can change their connectivity over time depending on their dynamical state. The most important feature of such systems is that their function depends on their structure and vice versa. While the properties of static networks have been extensively investigated in the past, the study of adaptive networks is much more challenging. Moreover, adaptive dynamical networks are of tremendous importance for various application fields, in particular, for the models for neuronal synaptic plasticity, adaptive networks in chemical, epidemic, biological, transport, and social systems, to name a few. In this review, we provide a detailed description of adaptive dynamical networks, show their applications in various areas of research, highlight their dynamical features and describe the arising dynamical phenomena, and give an overview of the available mathematical methods developed for understanding adaptive dynamical networks

    Modeling hippocampal theta-coupled gamma oscillations in learning and memory

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    Two of the most researched domains in the hippocampus are the oscillatory activity and encoding and retrieval of patterns in the hippocampal CA1 and CA3 regions. They are, how- ever, not studied together; and hence, the objective of our work is to study the cross-frequency coupling of theta-coupled gamma oscillations in CA1 and CA3 regions of the hippocampus while encoding and retrieving information. We have studied the cross-frequency coupling of theta-coupled gamma oscillations both individually and in our newly-proposed integrated model of CA1-CA3 to analyze the effects of Schaffer collaterals and CA1 back-projection cells on CA1 and CA3 regions of the hippocampus. Due to lack of literary evidence, we have also contributed our hypotheses about the effects of CA1 back-projection cells on CA1 and CA3 cell-types. Moreover, we have developed a deterministic rule-based cellular automata library to study cross-frequency coupling in single-neuron level and population neuronal net- works at the same time. The discrete model is theta-oscillations-aware and hence encoding and retrieving of patterns takes place during the half-cycles of theta oscillations. We have extended the septo-hippocampal population firing rate model proposed by Den- ham and Borisyuk (2000) to study (i) the influence of inhibitory interneurons, specifically PV-containing basket cells (BCs) and bistratified cells (BSCs) on theta and theta-coupled gamma oscillations in both CA1 and CA3 hippocampal networks; (ii) to study Schaffer col- laterals from CA3 to CA1 and the influence of back-projection cells in CA1 on CA3; (iii) to analyze and compare the phases of cross-frequency coupling of theta-coupled gamma oscil- lations among the different cell types in CA1 and CA3 regions; (iv) to study the influence of external inputs on CA1 and CA3. In our simulations, with constant external inputs, we identify the parameter regions that generate theta oscillations and that BCs and BSCs in CA1 are in anti-phase, as seen experi- mentally by Klausberger et. al (2008). Slow-gamma oscillations are generated due to the ac- tivity of BSCs and BCs in CA1 and CA3, and they are propagated from CA3 to CA1 through the Schaffer collaterals, as seen in Klausberger et. al (2008) where BSCs were observed to synchronize PC activity during theta-coupled gamma oscillations in CA1. In CA3, increas- ing excitation of CA3 pyramidal cells results in theta oscillations without the slow-gamma coupling. Increasing excitatory input to CA1 pyramidal cells results in steady state and de- creasing the excitatory input, results in reduced oscillatory activity in both CA1 and CA3 due to Schaffer collaterals and the feedback projections from CA1 to CA3. This demonstrates that changes in input excitation can move the networks from oscillatory to non-oscillatory states, comparable to the differences seen in animals between exploratory and resting state. Further, Mizuseki et. al (2009) observed experimentally that CA1, CA3 and EC are out- of-theta-phase with each other and that the phase observed in CA1 pyramidal cells are not a result of a simple integration of phases from CA3, EC or the medial septum. We have thus, simulated theta-frequency sine-wave inputs from CA3 and EC of relative phases in the model and observed the same results in our CA1 individual and CA1-CA3 integrated model. To study encoding and retrieval of patterns in an oscillating model, we took an engineer- ing approach by developing a discrete modeling system using cellular automata (CA) derived from the models of Pytte et. al (1991) and Claverol et. al (2002). The aim of this model is to (i) replicate the oscillatory and phasic results obtained using the continuous modeling ap- proach and (ii) extend the same model to study storage and recall of patterns in CA1 taking a theta-oscillations-aware approach. Encoding and retrieval happen at different half-cycles of theta where information pro- cessing takes places in the sub-cycles of the slow-gamma oscillations in each half-cycle of theta oscillation (Cutsuridis et. al, 2010, Hasselmo et. al, 1996). A set of rules is developed to replicate this for the CA model of CA1. The encoding and retrieval half-cycles are identi- fied using the basket cell activity, and hence synaptic learning is enabled during the encoding half-cycle of theta, and is disabled during the recall half-cycle of theta oscillations. This is also a biologically realistic enhancement for studying learning and recall in theta-coupled gamma oscillations using a discrete cellular automata approach

    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

    Elements of Ion Linear Accelerators, Calm in The Resonances, Other_Tales

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    The main part of this book, Elements of Linear Accelerators, outlines in Part 1 a framework for non-relativistic linear accelerator focusing and accelerating channel design, simulation, optimization and analysis where space charge is an important factor. Part 1 is the most important part of the book; grasping the framework is essential to fully understand and appreciate the elements within it, and the myriad application details of the following Parts. The treatment concentrates on all linacs, large or small, intended for high-intensity, very low beam loss, factory-type application. The Radio-Frequency-Quadrupole (RFQ) is especially developed as a representative and the most complicated linac form (from dc to bunched and accelerated beam), extending to practical design of long, high energy linacs, including space charge resonances and beam halo formation, and some challenges for future work. Also a practical method is presented for designing Alternating-Phase- Focused (APF) linacs with long sequences and high energy gain. Full open-source software is available. The following part, Calm in the Resonances and Other Tales, contains eyewitness accounts of nearly 60 years of participation in accelerator technology. (September 2023) The LINACS codes are released at no cost and, as always,with fully open-source coding. (p.2 & Ch 19.10)Comment: 652 pages. Some hundreds of figures - all images, there is no data in the figures. (September 2023) The LINACS codes are released at no cost and, as always,with fully open-source coding. (p.2 & Ch 19.10

    Photophysical and Photocatalytic Properties of Covalent Organic Frameworks

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    This dissertation is most interested in how a class of materials known as covalent organic frameworks (COFs) can be designed to capture photon energy to initiate chemical reactions. Different COF designs change how long the energy is held, how it migrates, and how it is dispersed – and these differences can be used to change their performance as artificial photosynthesis platforms. Thus, it is helpful to have an informative discussion about the processes behind natural photosynthesis, that is, nature’s light harvesting strategies and photocatalytic schemes (Section 1.2) and will lead into an introduction of COFs and why they possess unique potential as artificial photosynthesis platforms (Section 1.3). Their beneficial physical qualities are complemented by understanding their electronic structures from theoretically predicted properties with specific focus on topological symmetry (Section 1.4). Synthesizing and characterizing COF systems then becomes an important consideration (Section 1.5) along with how their excited state behaviors are probed and interpreted at reaction timescales by ultrafast spectroscopic techniques (Section 1.6). Finally, a look is taken at how COF structure versatility adds unique potential in catalyst engineering (Section 1.7). The main body of this dissertation will present five main research projects that seek to test theoretical predictions, assess the impact of COF planarity, or fine tune electronic structures. To test theoretical predictions, “Tuning Photoexcited Charge Transfer in Imine-Linked Two-Dimensional Covalent Organic Frameworks, which involves exploring nodal symmetry in topologically similar COFs by varying monomers, is reported. This work has implications on charge separation characteristics of COFs which is important to retain activated catalytic sites for chemical reactions. The second project, “Impact of πConjugation Length on the Excited-State Dynamics of Star-Shaped Carbazole-π-Triazine Organic Chromophores,” doesn’t directly probe COF systems, but looks at the role of dihedral angles on intersystem crossing (ISC) rates in organic chromophores with similar star-shaped motifs like those often found in COFs. Another study on planarity is “Conjugation- and Aggregation-Directed Design of Covalent Organic Frameworks as White-Light-Emitting Diodes” that explores planar and non-planar COFs and the how this affects the deactivation of their photoexcited states. “Wavelength Dependent Excitonic Properties of Imine-Linked Covalent Organic Frameworks,” explores how subtle changes in donor-acceptor arrangements can lead to differences in excited state populations. Finally, the seminal work in this dissertation, “Imine Reversal Mediates Charge Separation and CO2 Photoreduction in Covalent Organic Frameworks,” explores the effect of the imine bond on photophysical and photocatalytic properties

    Organic photosensitizers for light-driven hydrogen evolution: synthesis, characterization and application

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    This work utilizes organic chromophores, namely perylene dyes and BODIPYs, as light-active component in light-driven hydrogen evolution

    Simulating the nonlinear QED vacuum

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    Exploring Animal Behavior Through Sound: Volume 1

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    This open-access book empowers its readers to explore the acoustic world of animals. By listening to the sounds of nature, we can study animal behavior, distribution, and demographics; their habitat characteristics and needs; and the effects of noise. Sound recording is an efficient and affordable tool, independent of daylight and weather; and recorders may be left in place for many months at a time, continuously collecting data on animals and their environment. This book builds the skills and knowledge necessary to collect and interpret acoustic data from terrestrial and marine environments. Beginning with a history of sound recording, the chapters provide an overview of off-the-shelf recording equipment and analysis tools (including automated signal detectors and statistical methods); audiometric methods; acoustic terminology, quantities, and units; sound propagation in air and under water; soundscapes of terrestrial and marine habitats; animal acoustic and vibrational communication; echolocation; and the effects of noise. This book will be useful to students and researchers of animal ecology who wish to add acoustics to their toolbox, as well as to environmental managers in industry and government
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