6,361 research outputs found

    Breaking boundaries:Charge density waves, quantum measurement, and black holes in theoretical physics

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    This thesis, titled “Breaking Boundaries” is a journey through three topics united by the theme of boundaries in physics. First, the journey begins with an investigation into charge density waves (CDWs) and their nearly commensurate phase, focusing on the materials 2H-TaSe2 and 1T-TaS2. An extensive treatment of Ginzburg-Landau theory is covered with an extension into truly two-dimensional systems. This extension is used to study spiral patches of commensurate charge density waves observed in experiment. The research leads to a novel perspective on CDW behaviour with the existence of a spiral CDW phase in a range of materials. Secondly, transitioning to the quantum realm, the thesis addresses the quantum measurement problem, emphasizing the constraints any valid theory must possess. It critiques existing models, demonstrates the non-linearity of objective collapse theories, and proposes a minimal model that bridges quantum mechanics and classical physics. Thirdly, the thesis delves into black holes and specifically the phenomena of thermal radiation due to a horizon. First, we explore analogue models that mimic the thermal spectrum near a black hole horizon, to pave the way to experimental realization. Then we focus on the region far away from a black hole horizon and challenge the notion of remnant radiation at this position. With a theoretical toy model, we study the regime and find a non-evaporating black hole. This questions the validity of standard Hawking radiation calculations.In conclusion, the thesis navigates through the boundaries of material behaviours, the quantum-classical divide, and the enigmatic nature of black holes. It highlights the blurring and breaking of boundaries in physics, offering new perspectives and promising avenues for future discoveries

    On Time-Resolved 3D-Tracking of Elastic Waves in Microscale Mechanical Metamaterials

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    Isotope reconstructions of East Asian Monsoon behaviour across Glacial Terminations I and II from Lake Suigetsu, Japan (IAP2−18−54)

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    Understanding the response of the East Asian Monsoon to rising temperatures is crucial in light of recent anthropogenic climate change and the vulnerability of East Asia to future climatic hazards. However, East Asian Monsoon dynamics during warming periods in the late Quaternary are poorly understood, particularly on decadal to millennial timescales. Significant sources of this uncertainty are the spatially and temporally heterogeneous responses of the East Asian Monsoon to submillennial temperature fluctuations. The conflicting patterns observed in available reconstructions of East Asian Monsoon strength suggest that the teleconnections acting during these intervals were complex. Understanding the behaviours of the East Asian Monsoon by accounting for links to remote climatic perturbations allows for a more holistic understanding of deglacial climate changes. A means of tackling this ambiguity is by contributing well−dated, high−resolution records of East Asian Monsoon evolution spanning Glacial Terminations I and II (which typify accessible, contrasting examples of rapid global warming) to the growing network of reconstructions from across the region. The aim of this thesis is to deconvolve East Asian Monsoon evolution during the last two glacial terminations by utilising the unique hydrological distribution of East Asian Monsoon precipitation over Japan to reconstruct both seasonal modes of the system (i.e., the East Asian Winter Monsoon and East Asian Summer Monsoon). This aim is met by the construction of isotope−based, season−specific East Asian Monsoon records across Glacial Terminations I and II using materials from the Lake Suigetsu sediment cores. This thesis is comprised of four interconnected research papers, preceded by an introduction and succeeded by a summary of findings, discussion of relevance, suggestions for future work and conclusions. In the first research paper, we utilise extended contemporary monitoring of the stable isotope composition of precipitation, river water and lake water in the Lake Suigetsu catchment to understand the factors affecting these variables and aid robust interpretation of isotope−based proxy reconstructions from the Lake Suigetsu sediment cores. Our results show that the composition of precipitation was influenced by the dual East Asian Monsoon system, and that these signals were then transferred to the lake system where they were combined with secondary local influences on lake water composition. Based on our knowledge of late Quaternary catchment dynamics, these observations suggest that the palaeo−isotope composition of Lake Suigetsu was closely related to the East Asian Monsoon. In the second research paper, we examine the influence of remote climatic processes on the East Asian Winter Monsoon and East Asian Summer Monsoon in Japan during Glacial Termination I by reconstructing trends in the strength of each seasonal mode. This is achieved using oxygen isotope analysis of diatom silica and compound−specific hydrogen isotope analysis of n−alkanoic acids from the Lake Suigetsu sediment cores. Our results support distinctive seasonal behaviours of the East Asian Monsoon during Glacial Termination I, with evidence for East Asian Winter Monsoon weakening and East Asian Summer Monsoon strengthening. The East Asian Summer Monsoon also exhibited variations in strength which were synchronous with Antarctic temperature fluctuations after 16,000 years ago, which supports a temporally restricted climatic link between Japan and the Southern Hemisphere at this time. In the third research paper, we reconstruct the East Asian Summer Monsoon in Japan during Glacial Termination II, and contrast the findings to those from Glacial Termination I. The reconstruction presented in this chapter, which is based on compound−specific hydrogen isotope analysis of n−alkanoic acids, provides evidence for early East Asian Summer Monsoon strengthening followed by a gradual weakening phase with submillennial−scale variability. Comparison of this record to others derived from mainland China supports the assertion that East Asian Summer Monsoon behaviours during Glacial Termination II were spatially heterogenous. Additionally, the different evolutions of the East Asian Summer Monsoon during Glacial Terminations I and II indicate that the system operated distinctively under contrasting boundary conditions, although the new reconstructions from Japan were consistently more closely linked with Southern Hemisphere (Antarctic) temperatures than Northern Hemisphere (Greenlandic) temperatures during both intervals. The fourth research paper was motivated by a lack of an absolute chronology for the oldest (pre−50,000 years ago) parts of the Lake Suigetsu sediment cores (which includes Glacial Termination II). In this paper, we appraise the luminescence characteristics of the cores using rapid profiling techniques. These are employed across four key time periods in order to assess the application of these methods for the detection of local and environmental shifts, and to assess the suitability of the core materials for luminescence dating. We show that the luminescence characteristics of the cores were susceptible to a range of environmental perturbations, best illustrating local changes by using high−resolution contiguous sampling. The feasibility of future luminescence dating is supported by quantifiable luminescence signals, and first order approximate ages suggest that blue light optically stimulated luminescence dating of feldspar provides the most accurate and most practical assessment of burial age. This technique should be the subject of dating efforts in pursuit of refinements to the Suigetsu core chronology before 50,000 years ago. The findings of this thesis contribute to our collective knowledge of East Asian Monsoon behaviours during glacial terminations. Critically, they represent a geographical expansion of the regional high−resolution record network to include Japan. The value of this process is demonstrated by the decoupled evolutions of each seasonal mode during Glacial Termination I, and a remote link between Antarctic temperatures and East Asian Summer Monsoon evolution in Japan during Glacial Terminations I and II, which were hitherto unconstrained by high resolution analysis. These findings acknowledge and begin to rationalise spatial and temporal heterogeneities in East Asian Monsoon behaviours by comparison to other records. This work highlights the complexity of the East Asian Monsoon, and the value of long records from contrasting deglacial periods for a better comprehension of this system in the context of anthropogenic climate change

    An examination of the verbal behaviour of intergroup discrimination

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    This thesis examined relationships between psychological flexibility, psychological inflexibility, prejudicial attitudes, and dehumanization across three cross-sectional studies with an additional proposed experimental study. Psychological flexibility refers to mindful attention to the present moment, willing acceptance of private experiences, and engaging in behaviours congruent with one’s freely chosen values. Inflexibility, on the other hand, indicates a tendency to suppress unwanted thoughts and emotions, entanglement with one’s thoughts, and rigid behavioural patterns. Study 1 found limited correlations between inflexibility and sexism, racism, homonegativity, and dehumanization. Study 2 demonstrated more consistent positive associations between inflexibility and prejudice. And Study 3 controlled for right-wing authoritarianism and social dominance orientation, finding inflexibility predicted hostile sexism and racism beyond these factors. While showing some relationships, particularly with sexism and racism, psychological inflexibility did not consistently correlate with varied prejudices across studies. The proposed randomized controlled trial aims to evaluate an Acceptance and Commitment Therapy intervention to reduce sexism through enhanced psychological flexibility. Overall, findings provide mixed support for the utility of flexibility-based skills in addressing complex societal prejudices. Research should continue examining flexibility integrated with socio-cultural approaches to promote equity

    From abuse to trust and back again

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    Sizing the Actuators for a Dragon Fly Prototype

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    In order to improve the design of the actuators of a Dragon Fly prototype, we study the loads applied to the actuators in operation. Both external and inertial forces are taken into account, as well as internal loads, for the purposes of evaluating the influence of the compliance of the arms on that of the "end-effector". We have shown many inadequacies of the arms regarding the stiffness needed to meet the initial design requirements. In order to reduce these inadequacies, a careful structural analysis of the stiffness of the actuators is carried out with a FEM technique, aimed at identifying the design methodology necessary to identify the mechanical elements of the arms to be stiffened. As an example, the design of the actuators is presented, with the aim of proposing an indirect calibration strategy. We have shown that the performances of the Dragon Fly prototype can be improved by developing and including in the control system a suitable module to compensate the incoming errors. By implementing our model in some practical simulations, with a maximum load on the actuators, and internal stresses, we have shown the efficiency of our model by collected experimental data. A FEM analysis is carried out on each actuator to identify the critical elements to be stiffened, and a calibration strategy is used to evaluate and compensate the expected kinematic errors due to gravity and external loads. The obtained results are used to assess the size of the actuators. The sensitivity analysis on the effects of global compliance within the structure enables us to identify and stiffen the critical elements (typically the extremities of the actuators). The worst loading conditions have been evaluated, by considering the internal loads in the critical points of the machine structure results in enabling us the sizing of the actuators. So that the Dragon fly prototype project has been set up, and the first optimal design of the arms has been performed by means of FEM analysis

    LIPIcs, Volume 251, ITCS 2023, Complete Volume

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    LIPIcs, Volume 251, ITCS 2023, Complete Volum

    MECHANICAL ENERGY HARVESTER FOR POWERING RFID SYSTEMS COMPONENTS: MODELING, ANALYSIS, OPTIMIZATION AND DESIGN

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    Finding alternative power sources has been an important topic of study worldwide. It is vital to find substitutes for finite fossil fuels. Such substitutes may be termed renewable energy sources and infinite supplies. Such limitless sources are derived from ambient energy like wind energy, solar energy, sea waves energy; on the other hand, smart cities megaprojects have been receiving enormous amounts of funding to transition our lives into smart lives. Smart cities heavily rely on smart devices and electronics, which utilize small amounts of energy to run. Using batteries as the power source for such smart devices imposes environmental and labor cost issues. Moreover, in many cases, smart devices are in hard-to-access places, making accessibility for disposal and replacement difficult. Finally, battery waste harms the environment. To overcome these issues, vibration-based energy harvesters have been proposed and implemented. Vibration-based energy harvesters convert the dynamic or kinetic energy which is generated due to the motion of an object into electric energy. Energy transduction mechanisms can be delivered based on piezoelectric, electromagnetic, or electrostatic methods; the piezoelectric method is generally preferred to the other methods, particularly if the frequency fluctuations are considerable. In response, piezoelectric vibration-based energy harvesters (PVEHs), have been modeled and analyzed widely. However, there are two challenges with PVEH: the maximum amount of extractable voltage and the effective (operational) frequency bandwidth are often insufficient. In this dissertation, a new type of integrated multiple system comprised of a cantilever and spring-oscillator is proposed to improve and develop the performance of the energy harvester in terms of extractable voltage and effective frequency bandwidth. The new energy harvester model is proposed to supply sufficient energy to power low-power electronic devices like RFID components. Due to the temperature fluctuations, the thermal effect over the performance of the harvester is initially studied. To alter the resonance frequency of the harvester structure, a rotating element system is considered and analyzed. In the analytical-numerical analysis, Hamilton’s principle along with Galerkin’s decomposition approach are adopted to derive the governing equations of the harvester motion and corresponding electric circuit. It is observed that integration of the spring-oscillator subsystem alters the boundary condition of the cantilever and subsequently reforms the resulting characteristic equation into a more complicated nonlinear transcendental equation. To find the resonance frequencies, this equation is solved numerically in MATLAB. It is observed that the inertial effects of the oscillator rendered to the cantilever via the restoring force effects of the spring significantly alter vibrational features of the harvester. Finally, the voltage frequency response function is analytically and numerically derived in a closed-from expression. Variations in parameter values enable the designer to mutate resonance frequencies and mode shape functions as desired. This is particularly important, since the generated energy from a PVEH is significant only if the excitation frequency coming from an external source matches the resonance (natural) frequency of the harvester structure. In subsequent sections of this work, the oscillator mass and spring stiffness are considered as the design parameters to maximize the harvestable voltage and effective frequency bandwidth, respectively. For the optimization, a genetic algorithm is adopted to find the optimal values. Since the voltage frequency response function cannot be implemented in a computer algorithm script, a suitable function approximator (regressor) is designed using fuzzy logic and neural networks. The voltage function requires manual assistance to find the resonance frequency and cannot be done automatically using computer algorithms. Specifically, to apply the numerical root-solver, one needs to manually provide the solver with an initial guess. Such an estimation is accomplished using a plot of the characteristic equation along with human visual inference. Thus, the entire process cannot be automated. Moreover, the voltage function encompasses several coefficients making the process computationally expensive. Thus, training a supervised machine learning regressor is essential. The trained regressor using adaptive-neuro-fuzzy-inference-system (ANFIS) is utilized in the genetic optimization procedure. The optimization problem is implemented, first to find the maximum voltage and second to find the maximum widened effective frequency bandwidth, which yields the optimal oscillator mass value along with the optimal spring stiffness value. As there is often no control over the external excitation frequency, it is helpful to design an adaptive energy harvester. This means that, considering a specific given value of the excitation frequency, energy harvester system parameters (oscillator mass and spring stiffness) need to be adjusted so that the resulting natural (resonance) frequency of the system aligns with the given excitation frequency. To do so, the given excitation frequency value is considered as the input and the system parameters are assumed as outputs which are estimated via the neural network fuzzy logic regressor. Finally, an experimental setup is implemented for a simple pure cantilever energy harvester triggered by impact excitations. Unlike the theoretical section, the experimental excitation is considered to be an impact excitation, which is a random process. The rationale for this is that, in the real world, the external source is a random trigger. Harmonic base excitations used in the theoretical chapters are to assess the performance of the energy harvester per standard criteria. To evaluate the performance of a proposed energy harvester model, the input excitation type consists of harmonic base triggers. In summary, this dissertation discusses several case studies and addresses key issues in the design of optimized piezoelectric vibration-based energy harvesters (PVEHs). First, an advanced model of the integrated systems is presented with equation derivations. Second, the proposed model is decomposed and analyzed in terms of mechanical and electrical frequency response functions. To do so, analytic-numeric methods are adopted. Later, influential parameters of the integrated system are detected. Then the proposed model is optimized with respect to the two vital criteria of maximum amount of extractable voltage and widened effective (operational) frequency bandwidth. Corresponding design (influential) parameters are found using neural network fuzzy logic along with genetic optimization algorithms, i.e., a soft computing method. The accuracy of the trained integrated algorithms is verified using the analytical-numerical closed-form expression of the voltage function. Then, an adaptive piezoelectric vibration-based energy harvester (PVEH) is designed. This final design pertains to the cases where the excitation (driving) frequency is given and constant, so the desired goal is to match the natural frequency of the system with the given driving frequency. In this response, a regressor using neural network fuzzy logic is designed to find the proper design parameters. Finally, the experimental setup is implemented and tested to report the maximum voltage harvested in each test execution

    Kinetic energy fluctuation-driven locomotor transitions on potential energy landscapes of beam obstacle traversal and self-righting

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    Despite contending with constraints imposed by the environment, morphology, and physiology, animals move well by physically interactingwith the environment to use and transition between modes such as running, climbing, and self-righting. By contrast, robots struggle to do so in real world. Understanding the principles of how locomotor transitions emerge from constrained physical interaction is necessary for robots to move robustly using similar strategies. Recent studies discovered that discoid cockroaches use and transition between diverse locomotor modes to traverse beams and self-right on ground. For both systems, animals probabilistically transitioned between modes via multiple pathways, while its self-propulsion created kinetic energy fluctuation. Here, we seek mechanistic explanations for these observations by adopting a physics-based approach that integrates biological and robotic studies. We discovered that animal and robot locomotor transitions during beam obstacle traversal and ground self-righting are barrier-crossing transitions on potential energy landscapes. Whereas animals and robot traversed stiff beams by rolling their body betweenbeam, they pushed across flimsy beams, suggesting a concept of terradynamic favorability where modes with easier physical interaction are more likely to occur. Robotic beam traversal revealed that, system state either remains in a favorable mode or transitions to one when energy fluctuation is comparable to the transition barrier. Robotic self-righting transitions occurred similarly and revealed that changing system parameters lowers barriers over which comparable fluctuation can induce transitions. Thetransitionsof animalsin both systems mostly occurred similarly, but sensory feedback may facilitate its beam traversal. Finally, we developed a method to measure animal movement across large spatiotemporal scales in a terrain treadmill.Comment: arXiv admin note: substantial text overlap with arXiv:2006.1271

    Towards Reliable and Accurate Global Structure-from-Motion

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    Reconstruction of objects or scenes from sparse point detections across multiple views is one of the most tackled problems in computer vision. Given the coordinates of 2D points tracked in multiple images, the problem consists of estimating the corresponding 3D points and cameras\u27 calibrations (intrinsic and pose), and can be solved by minimizing reprojection errors using bundle adjustment. However, given bundle adjustment\u27s nonlinear objective function and iterative nature, a good starting guess is required to converge to global minima. Global and Incremental Structure-from-Motion methods appear as ways to provide good initializations to bundle adjustment, each with different properties. While Global Structure-from-Motion has been shown to result in more accurate reconstructions compared to Incremental Structure-from-Motion, the latter has better scalability by starting with a small subset of images and sequentially adding new views, allowing reconstruction of sequences with millions of images. Additionally, both Global and Incremental Structure-from-Motion methods rely on accurate models of the scene or object, and under noisy conditions or high model uncertainty might result in poor initializations for bundle adjustment. Recently pOSE, a class of matrix factorization methods, has been proposed as an alternative to conventional Global SfM methods. These methods use VarPro - a second-order optimization method - to minimize a linear combination of an approximation of reprojection errors and a regularization term based on an affine camera model, and have been shown to converge to global minima with a high rate even when starting from random camera calibration estimations.This thesis aims at improving the reliability and accuracy of global SfM through different approaches. First, by studying conditions for global optimality of point set registration, a point cloud averaging method that can be used when (incomplete) 3D point clouds of the same scene in different coordinate systems are available. Second, by extending pOSE methods to different Structure-from-Motion problem instances, such as Non-Rigid SfM or radial distortion invariant SfM. Third and finally, by replacing the regularization term of pOSE methods with an exponential regularization on the projective depth of the 3D point estimations, resulting in a loss that achieves reconstructions with accuracy close to bundle adjustment
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