774 research outputs found

    Through-the-Wall Imaging and Multipath Exploitation

    Get PDF
    We consider the problem of using electromagnetic sensing to estimate targets in complex environments, such as when they are hidden behind walls and other opaque objects. The often unknown electromagnetic interactions between the target and the surrounding area, make the problem challenging. To improve our results, we exploit information in the multipath of the objects surrounding both the target and the sensors. First, we estimate building layouts by using the jump-diffusion algorithm and employing prior knowledge about typical building layouts. We also take advantage of a detailed physical model that captures the scattering by the inner walls and efficiently utilizes the frequency bandwidth. We then localize targets hidden behind reinforced concrete walls. The sensing signals reflected from the targets are significantly distorted and attenuated by the embedded metal bars. Using the surface formulation of the method of moments, we model the response of the reinforced walls, and incorporate their transmission coefficients into the beamforming method to achieve better estimation accuracy. In a related effort, we utilize the sparsity constraint to improve electromagnetic imaging of hidden conducting targets, assuming that a set of equivalent sources can be substituted for the targets. We derive a linear measurement model and employ l1 regularization to identify the equivalent sources in the vicinity of the target surfaces. The proposed inverse method reconstructs the target shape in one or two steps, using single-frequency data. Our results are experimentally verified. Finally, we exploit the multipath from sensor-array platforms to facilitate direction finding. This in contrast to the usual approach, which utilizes the scattering close to the targets. We analyze the effect of the multipath in a statistical signal processing framework, and compute the Cramer-Rao bound to obtain the system resolution. We conduct experiments on a simple array platform to support our theoretical approach

    Study of a UAV with autonomous LIDAR navigation

    Get PDF
    The recent growth of Unmanned Aerial Vehicles has brought them to a wide variety of industries, from construction to film production or emergency services. These vehicles still depend on some part of human intervention and can only operate comfortably in very wide and open spaces. This is mainly due to the limited surrounding awareness that the UAVs have as they are equipped with very simple sensing equipment. In this research work, this issue will be tackled. This project focuses on the use of a solid-state LIDAR sensor module to perform obstacle avoidance. The integration is done in a Hummingbird multirotor platform where a path following algorithm has already been tested. The objective will be to integrate the system into the existing platform and validated it in real flight conditions. The Hummingbird UAV at the end of the project will be capable of autonomously navigating while at the same time being capable of performing obstacle avoidance manoeuvres around non-planned and static objects

    Decoupled controllers for power systems

    Get PDF
    Imperial Users onl

    Multi-source, multi-sensor approaches to diesel engine monitoring using acoustic emission

    Get PDF
    Abstract unavailable please refer to PD

    Quantum Computation

    Get PDF
    In the last few years, theoretical study of quantum systems serving as computational devices has achieved tremendous progress. We now have strong theoretical evidence that quantum computers, if built, might be used as a dramatically powerful computational tool. This review is about to tell the story of theoretical quantum computation. I left out the developing topic of experimental realizations of the model, and neglected other closely related topics which are quantum information and quantum communication. As a result of narrowing the scope of this paper, I hope it has gained the benefit of being an almost self contained introduction to the exciting field of quantum computation. The review begins with background on theoretical computer science, Turing machines and Boolean circuits. In light of these models, I define quantum computers, and discuss the issue of universal quantum gates. Quantum algorithms, including Shor's factorization algorithm and Grover's algorithm for searching databases, are explained. I will devote much attention to understanding what the origins of the quantum computational power are, and what the limits of this power are. Finally, I describe the recent theoretical results which show that quantum computers maintain their complexity power even in the presence of noise, inaccuracies and finite precision. I tried to put all results in their context, asking what the implications to other issues in computer science and physics are. In the end of this review I make these connections explicit, discussing the possible implications of quantum computation on fundamental physical questions, such as the transition from quantum to classical physics.Comment: 77 pages, figures included in the ps file. To appear in: Annual Reviews of Computational Physics, ed. Dietrich Stauffer, World Scientific, vol VI, 1998. The paper can be down loaded also from http://www.math.ias.edu/~doria

    Geophysical techniques for urban environment monitoring

    Get PDF
    The research activities conducted in this thesis contributes, through the application of geophysical techniques, to the mitigation of seismic risk with the twofold objective of studying the interaction between the urban subsoil and the overlying-built heritage and carrying out a modal characterisation of a strategic infrastructure. The former objective was pursued by producing a map of the double soil-structure resonance levels of the Matera urban area, while the latter was achieved by setting up and applying an innovative multi-methodological geophysical approach on the Gravina Bridge. As part of the first study, I performed 230 single-station ambient seismic noise measurements on the main lithologies (134) and on the main typology of buildings (96) in reinforced concrete (RC) and unreinforced load-bearing masonry buildings (URM) of the Matera urban area. The ambient seismic noise recorded on the soil 12 min time duration and on buildings 14 min time duration was recorded with a compact digital seismometer and processed using a non-reference site method, the Horizontal-to-vertical noise spectral ratio technique, HVNSR. The measurements taken on the ground and buildings allowed the resonance frequencies and relative amplitudes of the fundamental peaks of the soil and the first elastic frequency of vibration of the buildings to be estimated. A deterministic interpolator (Inverse Distance Weight, IDW) was used in GIS environment to derive the iso-frequency and iso-amplitude maps of the urban area by using as variables the resonance frequencies and amplitudes of the soil HV ratios. A linear period-to-height relationship for the buildings was derived from the experimental results, allowing the fundamental elastic frequency to be estimated for all buildings in the study area. An intersection approach between soil and building frequency bands was used for the first time to derive a map of double soil-structure resonance levels in the linear elastic domain for the whole urban area. Matera represents an important case study since the elastic frequency of vibration for most of the buildings is quite close to that of the foundation soils. In the study area, 21% of the buildings show a high susceptibility to the effect of double soil-building resonance, 63% of the buildings could be characterised by a medium level of double resonance, while 16% could exhibit a zero or very low resonance level. The proposed approach also makes it possible to locate the areas of the city characterised by these different levels of double resonance. Therefore, the first part of the thesis work provided a contribution in assessing the soil – structure interaction effect (SSI, influence of built structures in modifying the ground motion during earthquake shaking) between urban soil and all the overlying buildings in the city of Matera by characterising all the foundation soils of the urban area and all the overlying buildings. A geo-database, the CLARA WebGIS portal (available at this link: https://smartcities-matera-clara.imaa.cnr.it/), for storing and sharing the data and results collected during my PhD activity has been implemented with 488 pre-existing geological, geotechnical, geophysical data. CLARA WebGIS is the first useful tool for predicting which and how many buildings could suffer higher damage due to the double soil-building resonance effect and is the first open geo-platform that shares the results of the double soil-building resonance from experimental data for an entire urban area. CLARA WebGIS addresses a wide range of end-users (local administrations, engineers, geologists, etc.) as support for the implementation of seismic risk mitigation strategies in terms of urban planning, seismic retrofit, and post-earthquake crisis management. The knowledge of the spatial distribution of the site effects (modifications of the ground motions due to changes in the shallow geological layers) in terms of amplification effect, the primary characteristics of buildings, and of soil-building resonance levels estimations, a three-part objective have been achieved: (i) through CLARA's WebGIS every citizen is aware of the characteristics of buildings and foundation soils, so this knowledge makes each individual citizen more resilient to the effects of a seismic event; (ii) preventing the potential losses in economic and social terms; (iii) reducing recovering phase time to facilitate the return of the urban system to equilibrium pre-existing conditions. A deepening of this first study was made by specialising the linear period-height relationship derived from the experimental results as a function of the construction typology and foundation soil for unreinforced load-bearing masonry buildings (URM) founded on rigid soil (Gravina calcarenite characterised by flat HVNSR curves). This relationship is more representative of the condition of a fixed-base masonry building. Variations in the dynamic response of masonry buildings due to soil-foundation-structure interaction at urban scale can be evaluated by simplified analytical approaches based on the traditional compliant-base oscillator model and on simplified assumptions about the geometry and mechanical properties of the soil and foundations. The experimental period-height relationship for URM buildings founded on Gravina calcarenite were integrated in a simplified analytical procedure extended to complex and more realistic stratified soils and irregular foundation geometry. The modified simplified procedure were applied at an urban scale to predict the fundamental period of seven masonry buildings studied in the historic centre of Matera, for which all soil and structural data necessary for the analytical model were available. The comparison of the fundamental periods obtained with the three approaches, traditional, simplified-modified, and experimental, shown that the adoption of the simplified-modified approach significantly improved the agreement between the experimental and analytical periods. This part of the thesis work therefore appears promising to encourage an extended application of the analytical and experimental techniques to other historic urban area characterised by similar characteristics of the built heritage and soil stratification. In the second study of the thesis, has been implemented a multi-methodological approach that allowed to estimate the main modal parameters of the Gravina bridge by analysing short duration ambient noise signals (less than two hours) recorded by low-cost and non-invasive sensors and by performing dynamic tests. The Gravina is an arch bridge located on outcropping limestone in the city of Matera and spans 144 m along a steel-concrete deck suspended by two tubular steel arches. Ambient seismic noise was recorded using two acquisition configurations on the deck and inside the arch. The noise signal data were processed by applying: the standard spectral analysis (FFT), to examine frequencies and energy content distribution, a spectral ratio method with reference station, the Standard Spectral Ratio (SSR) technique, to check and validate eigenfrequencies, the Operational Modal Analysis (OMA) technique, i.e., the Frequency Domain Decomposition (FDD) method, to derive eigenfrequencies and mode shapes, and a seismic interferometric method, the Ambient Noise Deconvolution Interferometry (ANDI), to derive the propagation velocity of ambient noise in the infrastructure. Six eigenfrequencies have been estimated on the deck. The examination of the energy content distribution played a key role for the interpretation of the mode shapes. The variation of the eigenfrequencies of the infrastructure with the seasons as a function of temperature (°C) were monitored: the frequency variations are less than 5% and the behaviour of the structure do not exhibit degradation since the Gravina Bridge is a newly constructed road infrastructure. Deconvolution interferometry has been applied on the ambient noise signals recorded on the deck deriving the wave propagation velocity on the infrastructure. The results presented showed that the ANDI method is sensitive to the distribution of infrastructure stiffness. The multi-methodological approach used in this part of the thesis is promising for (i) evaluating the behaviour of standard structure like buildings and critical infrastructure like a bridge at different scales (global and local), (ii) examining variation of eigenfrequencies, mode shapes and ambient noise waves propagation velocities as a result of aging, degradation, and/or occurrence of potential damage, (iii) controlling and validating outcomes comparing the results obtained from different techniques, (iv) supporting at an early stage as a quick, non-invasive, low-cost tool applied without either diverting, blocking the traffic flow, or stopping the infrastructure service

    Master index volumes 31–40

    Get PDF
    • …
    corecore