774 research outputs found
Through-the-Wall Imaging and Multipath Exploitation
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
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
Imperial Users onl
Multi-source, multi-sensor approaches to diesel engine monitoring using acoustic emission
Abstract unavailable please refer to PD
Quantum Computation
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
Recommended from our members
Fermionic Quantum Information in Surface Acoustic Waves
Quantum computers are on the verge of revolutionising modern technology by providing scientists with unparalleled computational resources. With quantum-mechanical phenomena such as the superposition principle and entanglement, these computers could solve certain computational problems that are otherwise impossible for even the most powerful classical supercomputers. One of the major challenges standing in the way of this computing revolution is the accurate control of quantum bits. Quantum systems are extremely fragile and, by their nature, cannot be measured without destroying their quantum state.
I wrote a numerical program to solve the time-dependent Schrödinger equation, the differential equation that describes the evolution of wave functions. The advantage of my code over other solvers is its speed. I used graphics processing units (GPUs), a technology that has only recently matured, to accelerate high-performance computing. Hardware- acceleration allows me to solve complex time-evolution problems within days rather than years. Such an exceptional speedup has enabled me to calculate the behaviour of single electrons in semiconductor devices. Electrons are particularly interesting because they are ubiquitous in modern technology, as well as being fundamental quantum particles. Using the simulations produced by my code, I track the time evolution of an electron wave function as it propagates along quantum circuits. By animating the evolution of the wave function, I am able to visualise the wave function of electrons propagating in space and time. This is a remarkable tool for studying the behaviour of quantum particles in nanodevices. I focused my thesis on the realistic modelling of devices that are readily available in a laboratory or on designs that could be fabricated in the near future. I began by modelling single electrons as quantum bits. I provide a definition for an optimal qubit and lay out the set of operations required to manipulate the quantum information carried by the electron.
In all my simulations, I aim to model experimentally realistic devices. I calculated the electrostatic potential of a real nanodevice and simulated the time-evolution of a single electron. I show that it is possible to create a single-electron beam splitter by tuning the voltages applied to various parts of the device and I calculate the range of voltages in which quantum information is preserved and manipulated accurately. These results were verified experimentally by collaborators at the Institut Néel and were published in Nature Communications 10, 4557 (2019).
Using my code, I developed a framework for general measurements of electron qubits and provided a design for a semiconductor device capable of performing positive-operator valued measures (POVMs). A POVM is a powerful measurement technique in quantum mechanics that allows quantum information to be manipulated in interesting ways. The proposed setup is suggested as an implementation of entanglement distillation, which is a useful error correction tool that transforms an arbitrary entangled state into a pure Bell pair. Entanglement is one of the most fascinating aspects of quantum mechanics and it remains a challenge to generate perfectly entangled particle pairs. An experimentally viable method for distilling – or perfecting – entanglement is crucial for the design of quantum computers or quantum communication systems. Using this design, I introduced a protocol to use electrons, rather than photons, in quantum-optics-like systems. These results were published in Phys. Rev. A 96, 052305 (2017).
Going beyond single-particle behaviour, I compare different methods for generating entanglement between electron-spin qubits using the power-of-SWAP operation. By using realistic experimental parameters in my simulations, I demonstrate that generating entan- glement via electron-electron collisions in a harmonic channel cannot be implemented for multidimensional systems. These findings go against what researchers thought was possible and put forward the need for new solutions to particle entanglement. I provide an alternative by demonstrating that a method based on the exchange energy is more viable than previously thought. I present a semiconductor device structure and an electrostatic potential that experi- mental groups can use in order to obtain the most efficient entangling quantum logic gates. These findings were published in Phys. Rev. A 101, 022329 (2020).
The results presented in this thesis provide a comprehensive description of the control of single electrons in a surface-acoustic-wave-based quantum circuit. However, work in this field is far from over. I present various research paths for future projects. These include going beyond the time-dependent Schrödinger equation to capture more complicated dynamics, using different hardware solutions to further accelerate numerical problem solving, and studying new systems of interest to extend this project beyond semiconductor physics.In all my simulations, I aim to model experimentally realistic devices. I calculated the electrostatic potential of a real nanodevice and simulated the time-evolution of a single electron. I show that it is possible to create a single-electron beam splitter by tuning the voltages applied to various parts of the device and I calculate the range of voltages in which quantum information is preserved and manipulated accurately. These results were verified experimentally by collaborators at the Institut Néel and were published in Nature Communications 10, 4557 (2019).
Using my code, I developed a framework for general measurements of electron qubits and provided a design for a semiconductor device capable of performing positive-operator valued measures (POVMs). A POVM is a powerful measurement technique in quantum mechanics that allows quantum information to be manipulated in interesting ways. The proposed setup is suggested as an implementation of entanglement distillation, which is a useful error correction tool that transforms an arbitrary entangled state into a pure Bell pair. Entanglement is one of the most fascinating aspects of quantum mechanics and it remains a challenge to generate perfectly entangled particle pairs. An experimentally viable method for distilling – or perfecting – entanglement is crucial for the design of quantum computers or quantum communication systems. Using this design, I introduced a protocol to use electrons, rather than photons, in quantum-optics-like systems. These results were published in Phys. Rev. A 96, 052305 (2017).
Going beyond single-particle behaviour, I compare different methods for generating entanglement between electron-spin qubits using the power-of-SWAP operation. By using realistic experimental parameters in my simulations, I demonstrate that generating entan- glement via electron-electron collisions in a harmonic channel cannot be implemented for multidimensional systems. These findings go against what researchers thought was possible and put forward the need for new solutions to particle entanglement. I provide an alternative by demonstrating that a method based on the exchange energy is more viable than previously thought. I present a semiconductor device structure and an electrostatic potential that experi- mental groups can use in order to obtain the most efficient entangling quantum logic gates. These findings were published in Phys. Rev. A 101, 022329 (2020).
The results presented in this thesis provide a comprehensive description of the control of single electrons in a surface-acoustic-wave-based quantum circuit. However, work in this field is far from over. I present various research paths for future projects. These include going beyond the time-dependent Schrödinger equation to capture more complicated dynamics, using different hardware solutions to further accelerate numerical problem solving, and studying new systems of interest to extend this project beyond semiconductor physics.The Institute of Physics
Horizon 2020 Marie Skłodowska Curie Actions
Fonds de Recherche du Québec – Nature et technologies
St Edmund’s College, Cambridge
Canadian Imperial Bank of Commerce
Canadian Centennial Scholarship Fund
Institute of Engineering and Technolog
Geophysical techniques for urban environment monitoring
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
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