5,009 research outputs found

    Meta-critical thinking, paradox, and probabilities

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    There is as much lack of clarity concerning what “critical thinking” involves, even among those charged with teaching it, as there is consensus that we need more emphasis on it in both academia and society. There is an apparent need to think critically about critical thinking, an exercise that might be called meta-critical thinking. It involves emphasizing a practice in terms of which “critical thinking” is helpfully carried out and clarifying one or more of the concepts in terms of which “critical thinking” is usually defined. The practice is distinction making and the concept that of evidence. Science advances by constructing models that explain real-world processes. Once multiple potential models have been distinguished, there remains the task of identifying which models match the real-world process better than others. Since statistical inference has in large part to do with showing how data provide support, i.e., furnish evidence, that the model/hypothesis is more or less likely while still uncertain, we turn to it to help make the concept more precise and thereby useful. In fact, two of the leading methodological paradigms—Bayesian and likelihood—can be taken to provide answers to the questions of the extent to which as well as how data provide evidence for conclusions. Examining these answers in some detail is a highly promising way to make progress. We do so by way of the analysis of three well-known statistical paradoxes—the Lottery, the Old Evidence, and Humphreys’—and the identification of distinctions on the basis of which their plausible resolutions depend. These distinctions, among others between belief and evidence and different concepts of probability, in turn have more general applications. They are applied here to two highly contested public policy issues—the efficacy of COVID vaccinations and the fossil fuel cause of climate change. Our aim is to provide some tools, they might be called “healthy habits of mind,” with which to assess statistical arguments, in particular with respect to the nature and extent of the evidence they furnish, and to illustrate their use in well-defined ways

    Magnetic Control of Acoustic Resonators and Metamaterials

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    The magneto-elastic coupling between spin and acoustic excitations offers an excellent opportunity to combine, within the same signal processing devices, the magnetic tuneability and re-programmability inherent to magnonics with the energy efficiency of phononics. Relevant recent studies have focused on characterisation of the interaction strength in magnetoacoustic devices and on the excitation and detection of an acoustically induced magnetic signal. The work presented in this thesis focuses on the magnetic control of propagating acoustic waves, with the aim to reveal and to characterise the signatures of the magneto-elastic coupling in reflection and transmission of acoustic waves in magnetoacoustic metamaterials, and to explore their tuning using magnetic stimuli

    Sensing Collectives: Aesthetic and Political Practices Intertwined

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    Are aesthetics and politics really two different things? The book takes a new look at how they intertwine, by turning from theory to practice. Case studies trace how sensory experiences are created and how collective interests are shaped. They investigate how aesthetics and politics are entangled, both in building and disrupting collective orders, in governance and innovation. This ranges from populist rallies and artistic activism over alternative lifestyles and consumer culture to corporate PR and governmental policies. Authors are academics and artists. The result is a new mapping of the intermingling and co-constitution of aesthetics and politics in engagements with collective orders

    The Active CryoCubeSat Technology: Active Thermal Control for Small Satellites

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    Modern CubeSats and Small Satellites have advanced in capability to tackle science and technology missions that would usually be reserved for more traditional, large satellites. However, this rapid growth in capability is only possible through the fast-to-production, low-cost, and advanced technology approach used by modern small satellite engineers. Advanced technologies in power generation, energy storage, and high-power density electronics have naturally led to a thermal bottleneck, where CubeSats and Small Satellites can generate more power than they can easily reject. The Active CryoCubeSat (ACCS) is an advanced active thermal control technology (ATC) for Small Satellites and CubeSats, which hopes to help solve this thermal problem. The ACCS technology is based on a two-stage design. An integrated miniature cryocooler forms the first stage, and a single-phase mechanically pumped fluid loop heat exchanger the second. The ACCS leverages advanced 3D manufacturing techniques to integrate the ATC directly into the satellite structure, which helps to improve the performance while simultaneously miniaturizing and simplifying the system. The ACCS system can easily be scaled to mission requirements and can control zonal temperature, bulk thermal rejection, and dynamic heat transfer within a satellite structure. The integrated cryocooler supports cryogenic science payloads such as advanced LWIR electro-optical detectors. The ACCS hopes to enable future advanced CubeSat and Small Satellite missions in earth science, heliophysics, and deep space operations. This dissertation will detail the design, development, and testing of the ACCS system technology

    Circulation Statistics in Homogeneous and Isotropic Turbulence

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    This is the committee version of a Thesis presented to the PostGrad Program in Physics of the Physics Institute of the Federal University of Rio de Janeiro (UFRJ), as a necessary requirement for the title of Ph.D. in Science (Physics). The development of the Vortex Gas Model (VGM) introduces a novel statistical framework for describing the characteristics of velocity circulation. In this model, the underlying foundations rely on the statistical attributes of two fundamental constituents. The first is a GMC field that governs intermittent behavior and the second constituent is a Gaussian Free field responsible for the partial polarization of the vortices in the gas. The model is revisited in a more sophisticated language, where volume exclusion among vortices is addressed. These additions were subsequently validated through numerical simulations of turbulent Navier-Stokes equations. This revised approach harmonizes with the multifractal characteristics exhibited by circulation statistics, offering a compelling elucidation for the phenomenon of linearization of the statistical circulation moments, observed in recent numerical simulation. In the end, a field theoretical approach, known as Martin-Siggia-Rose-Janssen-de Dominicis (MSRJD) functional method is carried out in the context of circulation probability density function. This approach delves into the realm of extreme circulation events, often referred to as Instantons, through two distinct methodologies: The First investigates the linear solutions and, by a renormalization group argument a time-rescaling symmetry is discussed. Secondly, a numerical strategy is implemented to tackle the nonlinear instanton equations in the axisymmetric approximation. This approach addresses the typical topology exhibited by the velocity field associated with extreme circulation events.Comment: Ph.D. Thesis - preliminary versio

    Nonperturbative Aspects of Quantum Field Theory in Curved Spacetime

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    Quantum field theory in curved spacetime is perhaps the most reliable framework in which one can investigate quantum effects in the presence of strong gravitational fields. Nevertheless, it is often studied by means of perturbative treatments. In this thesis, we aim at using the functional renormalization group -- a nonperturbative realization of the renormalization group -- as a technique to describe nonperturbative quantum phenomena in curved spacetimes. The chosen system is an Unruh--DeWitt particle detector coupled to a scalar quantum field. We discuss how to formulate such a system in terms of an action and how one can compute its renormalization group flow in the case of an inertial detector in flat spacetime, for simplicity. We learn, however, that the results are divergent in the limit in which the detector's energy gap vanishes. Possible workarounds are discussed at the end. This thesis also presents a review of quantum field theory in curved spacetimes by means of the algebraic approach, although it assumes no previous experience with functional analysis. Hence, it fills a pedagogical gap in the literature. Furthermore, we also review the functional renormalization group and derive the Wetterich equation assuming a general field content that might include both bosonic and fermionic fields. Such a derivation is also hardly found in pedagogical introductions available in the high energy physics literature.Comment: MSc thesis defended at the Federal University of ABC (Brazil) on 28 April 2023. xxiv + 152 pages, 22 figure

    Navigating the Skies: An Exploration of Stakeholder Perspectives on Rules for Orbital Traffic Coordination using Grounded Theory and Case Study Research Methodologies

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    This dissertation explored standards, rules, or regulations ( rules ) of orbital traffic coordination to reduce the risk of collisions in space between active space objects. The research questions explored topics associated with areas for potential implementation of rules include maneuvering capabilities, liability and insurance, zoning, right-of-way, and tracking of objects in space. The researcher utilized an exploratory qualitative research method because of the developing field of study and a growing domain for potential regulation. The research design is a mixture of a case study for bounding and structuring the data collection and grounded theory for a rigorous and well-defined analysis approach. The primary data source is semi-structured interviews used to explore the perspectives of three stakeholder groups with a vested interest in space traffic management. The three groups are space industry, space insurance industry, and space law and policy experts. Amongst the three groups, 19 interviews were conducted. The data were analyzed to summarize and compare the different perspectives of each group and across the groups. From the summarized perspectives, the intent was to recommend a set of rules, but participants offered few specific rules. Instead, the dissertation’s results present shared considerations across the six research questions to provide the current state of thinking across the community. Results from this dissertation will provide valuable insight to policymakers beyond feedback generally received during comment periods associated with federal rulemaking. National space traffic management legal frameworks need to harmonize globally to optimize space transportation operations and practices. This dissertation contributes to a larger global effort to standardize and solidify rules defining interactions between space operators by capturing the perspectives of experts primarily in and concerning the United States

    Carrier-envelope phase (CEP)-dependent strong-field ionization at infrared (IR) wavelengths

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    Intense laser-matter interactions are generally determined by the instantaneous electric field of the laser pulse. For light-matter interactions with few-cycle pulses, the carrier-envelope phase (CEP) plays a critical role as the temporal variation of the electric field depends on the phase. This has a profound impact on many scientific applications. More importantly, controlling the CEP provides an additional degree of freedom to control field-driven processes in atomic, molecular and solid-state systems. In this thesis, we will demonstrate the development and implementation of a single-shot CEP measurement technique, i.e., the so-called carrier-envelope phasemeter based on stereo-above-threshold ionization in Xe and operating at short-wave infrared (SWIR) wavelengths, which allows for simultaneous pulse duration measurement. The experimental results are compared to simulations with two different theoretical models. Next, we will demonstrate the significance of the phase-volume effect, i.e. the reduction of the CEP-dependence due to the spatial distribution of the CEP in focused few-cycle pulsed beams. We formulate a general description of the impact of the focal phase for laser-matter interactions of different nonlinear orders to answer the general question: if, when, and how much should one be concerned about the phase-volume effect? At last, CEP-dependent strong-field ionization of Xe using 3.2um few-cycle pulses as a benchmark will be studied. In order to find an alternative target for a single-shot CEPM at mid-infrared (MIR) wavelengths, Cs will be investigated. We observed an anomalous CEP-dependence in Cs, particularly at high intensities, which can be interpreted as the interference of two backscattered quantum orbits from adjacent optical cycles. Viewed from a higher perspective, this thesis demonstrates a precise characterization of the CEP and an accurate analysis of CEP-dependent light-matter interaction from the NIR, via the SWIR to the MIR range

    Absence of Localization in Two-Dimensional Clifford Circuits

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    We analyze a Floquet circuit with random Clifford gates in one and two spatial dimensions. By using random graphs and methods from percolation theory, we prove in the two-dimensional (2D) setting that some local operators grow at a ballistic rate, which implies the absence of localization. In contrast, the one-dimensional model displays a strong form of localization, characterized by the emergence of left- and right-blocking walls in random locations. We provide additional insights by complementing our analytical results with numerical simulations of operator spreading and entanglement growth, which show the absence (presence) of localization in two dimensions (one dimension). Furthermore, we unveil how the spectral form factor of the Floquet unitary in 2D circuits behaves like that of quasifree fermions with chaotic single-particle dynamics, with an exponential ramp that persists up to times scaling linearly with the size of the system. Our work sheds light on the nature of disordered Floquet Clifford dynamics and their relationship to fully chaotic quantum dynamics
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