61 research outputs found

    Beam scanning by liquid-crystal biasing in a modified SIW structure

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    A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

    Electron Thermal Runaway in Atmospheric Electrified Gases: a microscopic approach

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    Thesis elaborated from 2018 to 2023 at the Instituto de AstrofĂ­sica de AndalucĂ­a under the supervision of Alejandro Luque (Granada, Spain) and Nikolai Lehtinen (Bergen, Norway). This thesis presents a new database of atmospheric electron-molecule collision cross sections which was published separately under the DOI : With this new database and a new super-electron management algorithm which significantly enhances high-energy electron statistics at previously unresolved ratios, the thesis explores general facets of the electron thermal runaway process relevant to atmospheric discharges under various conditions of the temperature and gas composition as can be encountered in the wake and formation of discharge channels

    1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

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    A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

    The Fifteenth Marcel Grossmann Meeting

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    The three volumes of the proceedings of MG15 give a broad view of all aspects of gravitational physics and astrophysics, from mathematical issues to recent observations and experiments. The scientific program of the meeting included 40 morning plenary talks over 6 days, 5 evening popular talks and nearly 100 parallel sessions on 71 topics spread over 4 afternoons. These proceedings are a representative sample of the very many oral and poster presentations made at the meeting.Part A contains plenary and review articles and the contributions from some parallel sessions, while Parts B and C consist of those from the remaining parallel sessions. The contents range from the mathematical foundations of classical and quantum gravitational theories including recent developments in string theory, to precision tests of general relativity including progress towards the detection of gravitational waves, and from supernova cosmology to relativistic astrophysics, including topics such as gamma ray bursts, black hole physics both in our galaxy and in active galactic nuclei in other galaxies, and neutron star, pulsar and white dwarf astrophysics. Parallel sessions touch on dark matter, neutrinos, X-ray sources, astrophysical black holes, neutron stars, white dwarfs, binary systems, radiative transfer, accretion disks, quasars, gamma ray bursts, supernovas, alternative gravitational theories, perturbations of collapsed objects, analog models, black hole thermodynamics, numerical relativity, gravitational lensing, large scale structure, observational cosmology, early universe models and cosmic microwave background anisotropies, inhomogeneous cosmology, inflation, global structure, singularities, chaos, Einstein-Maxwell systems, wormholes, exact solutions of Einstein's equations, gravitational waves, gravitational wave detectors and data analysis, precision gravitational measurements, quantum gravity and loop quantum gravity, quantum cosmology, strings and branes, self-gravitating systems, gamma ray astronomy, cosmic rays and the history of general relativity

    Ultrafast Laser Control of Molecular Quantum Dynamics from a Core-Electron Perspective

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    This work introduces two experimental approaches to control quantum dynamics in molecules, employing core electrons as messengers. A laser source providing ultrashort pulses has been developed to access the timescale of electronic and structural dynamics inside molecules. Pulses of few-cycle durations in the 1 ”m to 2 ”m short-wavelength infrared (SWIR) spectral region provide intensities up to 1015 W/cm2 . In combination with a vacuum beamline, this experimental setup allows for ultrafast laser control of molecular dynamics probed by core-electron transitions via x-ray absorption spectroscopy (XAS). The first experiment investigates the manipulation of molecular electronic structure. Here, a soft x-ray (SXR) pulse probes simultaneously to an SWIR pulse of variable intensity. The measured intensityvii dependent absorbance changes in SF6 reveal an increased effective electronic-exchange energy. This demonstrates the alteration of this purely quantum-mechanical component of the electron-electron interaction for the first time. In a second experiment, an SWIR pulse induces coherent molecular vibrations with amplitudes of ten times the diameter of the nucleus. Subsequently, a time-delayed SXR pulse probes the bond-length changes via core-level transitions. This enables an unprecedented 14 femtometer precision which paves the way for site-specific vibrational metrology in gas-phase molecules. Overall, these results enable ultrafast chemical control on a quantum level

    Understanding Quantum Technologies 2022

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    Understanding Quantum Technologies 2022 is a creative-commons ebook that provides a unique 360 degrees overview of quantum technologies from science and technology to geopolitical and societal issues. It covers quantum physics history, quantum physics 101, gate-based quantum computing, quantum computing engineering (including quantum error corrections and quantum computing energetics), quantum computing hardware (all qubit types, including quantum annealing and quantum simulation paradigms, history, science, research, implementation and vendors), quantum enabling technologies (cryogenics, control electronics, photonics, components fabs, raw materials), quantum computing algorithms, software development tools and use cases, unconventional computing (potential alternatives to quantum and classical computing), quantum telecommunications and cryptography, quantum sensing, quantum technologies around the world, quantum technologies societal impact and even quantum fake sciences. The main audience are computer science engineers, developers and IT specialists as well as quantum scientists and students who want to acquire a global view of how quantum technologies work, and particularly quantum computing. This version is an extensive update to the 2021 edition published in October 2021.Comment: 1132 pages, 920 figures, Letter forma

    Wave-based numerical methods for damage identification in components and structures

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    Components and structures accumulate damage during operation, which degrades their load bearing capacity and is prone to causing catastrophic failure. The demand for fuel efficiency and reduction of pollutant emissions has shifted the design of many structures, predominantly aerospace, to incorporate more composite materials. Composite materials are especially susceptible to critical failure due to operation-induced and accidental damage modes, that have adverse impact on the material strength. Timely detection and identification of damage is important in ensuring structural integrity and safety. Continuous and reliable condition monitoring of components is even more important in lightweight structures that have lower loadbearing redundancy. Recent advances in sensors and signal processing, along with the availability of computational power, have rendered model-based monitoring and damage identification solutions attractive. Computational models for wave simulation remain, however, too heavy for conventional use. Robust and efficient modelling of certain damage modes, such as cracks, introduces additional complexities in numerical models for solids. Computational cost for inverse schemes, where multiple solutions for the unknown and sought damage parameters are required, even becomes prohibitive. This work introduces mesh-independent modelling of damage through XFEM, in wave analysis. The behaviour of damage is investigated with the developed method, and validated by established explicit Finite Element models. A signal processing methodology with wavelet transform is also implemented to further investigate the feasibility of wave scattering as means of damage identification, with a view over available wave actuation and measurement methods. The proposed methodology can achieve significant model reduction calculating wave scattering. Furthermore, identification of cracks is feasible, provided multiple wavemodes can be identified and measured

    Statistical photoionization theory of atoms in soft XUV free-electron laser fields

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    The goal is to develop a rigorous theory to study the effects of stochastic fluctuations of self amplified spontaneous emission free-electron laser (SASE FEL) on the near-resonant ionization of atomic/ionic systems. To this end, density matrix equations of motion are utilised in their raw form for the sake of Monte Carlo simulations and in their particular averaged forms. First, a couple of simpler averaging methods were used to quickly understand the general behavior of the interaction of fluctuating fields with atoms. To this end, the particular case of neon (Ne) and helium (He) were used, where the effects of the interplay of the pulse duration and the coherence time on the oscillations of the yield profile, which manifest due to Rabi oscillations, were studied in comparison to a coherent pulse. Second, a rigorous method of perturbative approach is developed, which is based on the expansion in terms of multitime cumulants which are a particular combination of the field’s coherence functions. The range of validity of the model is tested in terms of the field’s coherence temporal length and peak intensity. Particularly, the photoionization of helium (He) and lithium ion (Li+ ) via their doubly-excited state 2s2p 1 P has been studied with the interacting FEL’s 1st-order coherence function modelled as square-exponentially dependent. The traditional asymmetric resonant Fano-profile is broadened and is shown to acquire a Voigt profile. The effects of pulse duration, coherence time and peak intensity on the lineshape are clearly shown. The two approaches of averaging were compared and the supremacy of the latter is shown. When compared to Monte Carlo, it is seen that the rigorous averaging approach results in competing values up to higher peak intensities. This suggests that in the scenarios of low coherence time and peak intensities, the averaging method developed in this thesis is highly preferable over the traditional Monte Carlo given its high computational demands

    Wavelet Theory

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    The wavelet is a powerful mathematical tool that plays an important role in science and technology. This book looks at some of the most creative and popular applications of wavelets including biomedical signal processing, image processing, communication signal processing, Internet of Things (IoT), acoustical signal processing, financial market data analysis, energy and power management, and COVID-19 pandemic measurements and calculations. The editor’s personal interest is the application of wavelet transform to identify time domain changes on signals and corresponding frequency components and in improving power amplifier behavior

    Coupled nuclear and electron dynamics in molecules

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    The interaction of light with a molecular system is the fundamental step of various chemical, physical and biological phenomena. Investigating the nuclear and electron dynamics initiated by light-matter interaction is important to understand, optimize and control the underlying processes. In this thesis two theoretical methods describing the coupled nuclear and electron dynamics in molecular systems are addressed. In the presented studies the coupled dynamics induced by photoexcitation, the subsequent relaxation processes and the possibility to control the dynamics in the vicinity of conical intersections (CoIns) are investigated for different molecular systems. In the first part of this work the photorelaxation pathways of a group of molecules commonly used in organic-based optoelectronic devices are characterized with the help of semiclassical ab intio molecular dynamics simulations. The relaxation pathways starting from the first excited singlet state of thiophene and of small oligothiophenes containing up to three rings is characterized by the interplay of internal conversion (IC) and intersystem crossing (ISC). Especially the ISC is mediated by ring-opening via a carbon-sulfur bond cleavage. The resulting entropically favored open-ring structures trap the molecules in a complex equilibrium between singlet and triplet states and a fast ring closure in the ground state is hindered. The extension of the π-system going from the monomer to the trimer weakens and slows down the ring opening process. Consequently the ISC is reduced for longer thiophene chains. The following two chapters are centered around the topics of controlling the molecular dynamics near a CoIn and monitoring the coherent electron dynamics induced by CoIns and laser interactions in the nucleobase uracil and the symmetric molecule NO2. In order to investigate the coherent electron dynamics, the ansatz used in this work allows a full-quantum description of the electron and nuclear motion and is called nuclear and electron dynamics in molecular systems (NEMol). As part of this work NEMol was extended to capture the coupled dynamics in complex high dimensional molecular systems. The observed electron dynamics both in NO2 and uracil reflects coherence, decoherence and reappearance which are all determined by the associated nuclear dynamics. The control of the molecular dynamics at a CoIn is realized with the help of a few-cycle infrared (IR) pulse. The applied control schema utilizes the carrierenvelope phase (CEP) of the pulse and allows to control the population distribution after the CoIn, the nuclear dynamics as well as the coherent electron dynamics. Depending on the chosen laser parameters and the molecular properties around the CoIn given by nature, two different mechanisms enable the control of the system. Both depend on the CEP but one is based on interference, which is generated by the interaction with the CoIn, and the other one is solely due to the few-cycle waveform of the pulse. As demonstrated for NO2 and uracil, the CEP control scheme even works for quite challenging boundary conditions. Therefore, it seems to be a general concept which can be used also in different molecules
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