22 research outputs found

    Seismic Waves

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    The importance of seismic wave research lies not only in our ability to understand and predict earthquakes and tsunamis, it also reveals information on the Earth's composition and features in much the same way as it led to the discovery of Mohorovicic's discontinuity. As our theoretical understanding of the physics behind seismic waves has grown, physical and numerical modeling have greatly advanced and now augment applied seismology for better prediction and engineering practices. This has led to some novel applications such as using artificially-induced shocks for exploration of the Earth's subsurface and seismic stimulation for increasing the productivity of oil wells. This book demonstrates the latest techniques and advances in seismic wave analysis from theoretical approach, data acquisition and interpretation, to analyses and numerical simulations, as well as research applications. A review process was conducted in cooperation with sincere support by Drs. Hiroshi Takenaka, Yoshio Murai, Jun Matsushima, and Genti Toyokuni

    Radar Technology

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    In this book “Radar Technology”, the chapters are divided into four main topic areas: Topic area 1: “Radar Systems” consists of chapters which treat whole radar systems, environment and target functional chain. Topic area 2: “Radar Applications” shows various applications of radar systems, including meteorological radars, ground penetrating radars and glaciology. Topic area 3: “Radar Functional Chain and Signal Processing” describes several aspects of the radar signal processing. From parameter extraction, target detection over tracking and classification technologies. Topic area 4: “Radar Subsystems and Components” consists of design technology of radar subsystem components like antenna design or waveform design

    Online learning of physics during a pandemic: A report from an academic experience in Italy

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    The arrival of the Sars-Cov II has opened a new window on teaching physics in academia. Frontal lectures have left space for online teaching, teachers have been faced with a new way of spreading knowledge, adapting contents and modalities of their courses. Students have faced up with a new way of learning physics, which relies on free access to materials and their informatics knowledge. We decided to investigate how online didactics has influenced students’ assessments, motivation, and satisfaction in learning physics during the pandemic in 2020. The research has involved bachelor (n = 53) and master (n = 27) students of the Physics Department at the University of Cagliari (N = 80, 47 male; 33 female). The MANOVA supported significant mean differences about gender and university level with higher values for girls and master students in almost all variables investigated. The path analysis showed that student-student, student-teacher interaction, and the organization of the courses significantly influenced satisfaction and motivation in learning physics. The results of this study can be used to improve the standards of teaching in physics at the University of Cagliar

    3D full-wave computation of RF modes in magnetised plasmas

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    An Approximate PML Applied to Cylindrical and Spherical Coordinate Sectors

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    This letter proposes an approximate perfectly matched layer (PML) that is applicable to cylindrical and spherical coordinate sectors. The proposed PML is based on complex coordinate stretching, which enables the truncation of finite-difference time-domain (FDTD) grids, not only at the ρ- and r-coordinates but also at the φ- and Ξ-coordinates. The absorption performance of the PML is demonstrated through numerical simulations

    Numerical Modeling of a Wind Turbine Blade Deflection Sensing System Using the Moving Frame FDTD Method

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    Characteristics of Upward Lightning Flashes

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    In addition to the general aims of lightning research such as lightning physics and meteorology, the study of upward lightning is of particular importance in protection of tall objects such as wind turbines and telecommunication towers. It also helps us in better understanding the lightning initiation process and its role in the earth- atmosphere electrical balance. Within this context, this thesis presents an analysis on various aspects of upward lightning discharge (negative, positive, bipolar) using experimental observation and theoretical modeling for better understanding of its initial stage, the propagation of its electromagnetic field along irregular terrain and its interaction with the ionosphere. Our investigation on the superimposed impulsive components of the initial stage of upward negative flashes revealed that they can transfer net negative charges to ground by both M-component and return stroke modes of charge transfer, which can be distinguished by their associated electric field signature. Moreover, we investigated the ability of Lightning Location Systems (LLSs) to locate and detect upward negative flashes. Different aspects of upward negative flashes which might affect the evaluation performance of LLSs were discussed. It is found that LLSs tend to overestimate the peak current values of RS pulses of upward negative flashes. Using full-wave numerical simulation, it is demonstrated that this overestimation is mainly due to electric field enhancement by wave propagation along mountainous terrain around SĂ€ntis Tower. Using simultaneous channel-base current and electric field records of upward positive flashes, we observed that two types of pulsations can be distinguished during the course of progression of upward negative leaders which are very similar to ÂżClassical PBPsÂż and ÂżNarrow PBPsÂż of the initial stage of downward negative leaders suggesting a general similarity between upward and downward negative leaders. We present and discuss current waveforms associated with 13 bipolar flashes recorded at the SĂ€ntis Tower during the period from June 2010 to January 2015. We have found two flashes of our data base each characterized by a sequence of two upward leaders of opposite polarity within the same flash, a scenario that has never been reported from previous observations at instrumented towers. The obtained results suggest that the traditional classification of bipolar flashes should be revisited. We present simultaneous channel-base current and wideband electric field waveforms at 380 km distance from the strike point associated with upward flashes initiated from the SĂ€ntis Tower. The dataset presented in this study represents, to the best of the AuthorÂżs knowledge, the first simultaneous records of lightning currents and distant fields associated with natural upward flashes featuring ionospheric reflections. The data are used to infer the characteristics of the ionospheric layers. We present a full-wave 2D FDTD analysis of the field propagation including the effect of the ionospheric reflections and the results are compared with the experimental data. Furthermore, we present a novel semi-analytical simplified approach based on the ray tracing concept to estimate radiated electric fields associated with lightning return strokes, taking into account ionospheric reflections

    Abstracts on Radio Direction Finding (1899 - 1995)

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    The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion

    Doctor of Philosophy

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