Mixed rectilinear sources localization under unknown mutual coupling

In this paper, a novel rectilinearity-based localization method for mixed near-field (NF) and far-field (FF) sources is proposed under unknown mutual coupling. The multiple parameters including direction of arrival (DOA), range and mutual coupling coefficient (MCC) are decoupled, thus only three one-dimensional (1-D) spectral searches are required to estimate the parameters of mixed rectilinear signals successively. Furthermore, the closed-form deterministic Cramer–Rao bound (CRB) of the concerned problem is also derived. Simulation results are provided to demonstrate the effectiveness of the proposed method for the classification and localization of mixed rectilinear sources

Stochastic Cramer-Rao bound for DOA estimation with a mixture of circular and noncircular signals

The Cramer-Rao bound (CRB) offers insights into the inherent performance benchmark of any unbiased estimator developed for a specific parametric model, which is an important tool to evaluate the performance of direction-of-arrival (DOA) estimation algorithms. In this paper, a closed-form stochastic CRB for a mixture of circular and noncircular uncorrelated Gaussian signals is derived. As a general one, it can be transformed into some existing representative results. The existence condition of the CRB is also analysed based on sparse arrays, which allows the number of signals to be more than the number of physical sensors. Finally, numerical comparisons are conducted in various scenarios to demonstrate the validity of the derived CRB

Theory and applications of free-electron vortex states

Both classical and quantum waves can form vortices: with helical phase fronts and azimuthal current densities. These features determine the intrinsic orbital angular momentum carried by localized vortex states. In the past 25 years, optical vortex beams have become an inherent part of modern optics, with many remarkable achievements and applications. In the past decade, it has been realized and demonstrated that such vortex beams or wavepackets can also appear in free electron waves, in particular, in electron microscopy. Interest in free-electron vortex states quickly spread over different areas of physics: from basic aspects of quantum mechanics, via applications for fine probing of matter (including individual atoms), to high-energy particle collision and radiation processes. Here we provide a comprehensive review of theoretical and experimental studies in this emerging field of research. We describe the main properties of electron vortex states, experimental achievements and possible applications within transmission electron microscopy, as well as the possible role of vortex electrons in relativistic and high-energy processes. We aim to provide a balanced description including a pedagogical introduction, solid theoretical basis, and a wide range of practical details. Special attention is paid to translate theoretical insights into suggestions for future experiments, in electron microscopy and beyond, in any situation where free electrons occur.Comment: 87 pages, 34 figure

Non-Radiative Calibration of Active Antenna Arrays

Antenna arrays offer significant benefits for modern wireless communication systems but they remain difficult and expensive to produce. One of the impediments of utilising them is to maintain knowledge of the precise amplitude and phase relationships between the elements of the array, which are sensitive to errors particularly when each element of the array is connected to its own transceiver. These errors arise from multiple sources such as manufacturing errors, mutual coupling between the elements, thermal effects, component aging and element location errors. The calibration problem of antenna arrays is primarily the identification of the amplitude and phase mismatch, and then using this information for correction. This thesis will present a novel measurement-based calibration approach, which uses a fixed structure allowing each element of the array to be measured. The measurement structure is based around multiple sensors, which are interleaved with the elements of the array to provide a scalable structure that provides multiple measurement paths to almost all of the elements of the array. This structure is utilised by comparison based calibration algorithms, so that each element of the array can be calibrated while mitigating the impact of the additional measurement hardware on the calibration accuracy. The calibration was proven in the investigation of the experimental test-bed, which represented a typical telecommunications basestation. Calibration accuracies of ±0.5dB and 5o were achieved for all but one amplitude outlier of 0.55dB. The performance is only limited by the quality of the coupler design. This calibration approach has also been demonstrated for wideband signal calibration

Instrumentation and development of a mass spectrometry system for the study of gas-phase biomolecular ion reactions

Gas-phase reactions of biomolecular ions are highly relevant to the understanding of structures and functions of the biomolecules. Mass spectrometry is a powerful tool in investigating gas-phase ion chemistry. Various mass spectrometers have been developed to explore ion/molecule reactions, ion/ion reactions, ion/photon reactions, ion/radical reactions etc., both at atmospheric pressure and in vacuum. In-vacuum reactions have an advantage of involving pre-selecting the ions for the reactions using a mass analyzer. Over the decades, a variety of mass analyzers have been employed in the research of ion chemistry. Hybrid configurations, such as quadrupole ion trap with a time-of-flight and or a quadrupole ion trap tandem with an Orbitrap, have been utilized to improve the performances for both the reaction (in trapping mode) and the mass analysis (accurate mass measurements). Complicated instrument structures, including ion optics, multiple mass analyzers and differential pumping for high vacuum, are typically required for the mass spectrometers for gas phase ion chemistry study. An alternative approach is to simplify the instrumentation by using pulsed discontinuous atmospheric pressure interfaces for introducing ionic or neutral reactants and a single ion trap as both the reactor and the mass analyzer. Such a simple mass spectrometry system was set up and demonstrated using two discontinuous atmospheric pressure interfaces in the study for this thesis. It was capable of carrying out ion/molecule and ion/ion reactions at an elevated pressure without the needs of ion optics or differential pumping system. Together with a pyrolysis radical source, in-vacuum ion/radical reactions were performed and their associated chemistry was studied. Radicals are important intermediates related to biochemical processes and biological functions. There are very limited techniques to monitor the reactive intermediates in-situ during a multi-step reaction in aqueous phase. On the other hand, these intermediates can be cooled down and preserved into a single-step procedure in gas-phase reactions since they only occur via collisions. Therefore, the fundamental study of gas-phase radical ion chemistry will provide evidences of the reactivity, energetics, and structural information of biological radicals, which has the potential to solve puzzles of aging, disease biomarker identification, and enzymatic activities. Using the system described above, a new reaction between protonated alkyl amines and pyrolysis formed cyclopropenylidene carbene was discovered, as the first experimental evidence of the reactivity of cyclopropenylidene. Given the important role of cyclopropenylidene in the combustion chemistry, organic synthesis, and interstellar chemistry, it is highly desirable to establish a fundamental understanding of their physical and chemical properties. The amine/cyclopropenylidene reactions were systematically studied using both theoretical calculation and experimental evidences. A proton-bound dimer reaction mechanism was proposed, with the amine and the carbene sharing a proton to form a complex as the first step, which was closely related to the high gas-phase basicity of cyclopropenylidene. Subsequent unimolecular dissociation of the complex yielded three possible reaction pathways, including proton-transfer to the carbene, covalent product formation, and direct separation. These reactions were studied with a variety of alkyl amines of different gas-phase basicities. For the covalent complex formation, partial protonation on cyclopropenylidene within the dimer facilitates subsequent nucleophilic attack to the carbene carbon by the amine nitrogen and leads to a C-N bond formation. The highest yield of covalent complex was achieved with the gas-phase basicity of the amine slightly lower but comparable to cyclopropenylidene. The results demonstrated a new reaction pathway of cyclopropenylidene besides the formation of cyclopropenium, which has long been considered as a dead end in interstellar carbon chemistry. Further reactivity study of cyclopropenylidene towards biomolecular ions was also carried out for nucleobases, nucleosides, amino acids, peptides, proteins, and lipids. The reaction to form proton-bound dimer for protonated biomolecular ions remained as the dominant reaction pathway. Interestingly, other possible reaction pathways, such as modifications of thiyl group or disulfide bonds, double bond addition, and single bond insertion, were inhibited in gas-phase ion/carbene reactions. Such results inferred that the reactivity of neutral species was not directly applicable to ion reactions, with the proton involved in the gas-phase biomolecular ion reactions

Human Guidance Behavior Decomposition and Modeling

University of Minnesota Ph.D. dissertation. December 2017. Major: Aerospace Engineering. Advisor: Berenice Mettler. 1 computer file (PDF); x, 128 pages.Trained humans are capable of high performance, adaptable, and robust first-person dynamic motion guidance behavior. This behavior is exhibited in a wide variety of activities such as driving, piloting aircraft, skiing, biking, and many others. Human performance in such activities far exceeds the current capability of autonomous systems in terms of adaptability to new tasks, real-time motion planning, robustness, and trading safety for performance. The present work investigates the structure of human dynamic motion guidance that enables these performance qualities. This work uses a first-person experimental framework that presents a driving task to the subject, measuring control inputs, vehicle motion, and operator visual gaze movement. The resulting data is decomposed into subspace segment clusters that form primitive elements of action-perception interactive behavior. Subspace clusters are defined by both agent-environment system dynamic constraints and operator control strategies. A key contribution of this work is to define transitions between subspace cluster segments, or subgoals, as points where the set of active constraints, either system or operator defined, changes. This definition provides necessary conditions to determine transition points for a given task-environment scenario that allow a solution trajectory to be planned from known behavior elements. In addition, human gaze behavior during this task contains predictive behavior elements, indicating that the identified control modes are internally modeled. Based on these ideas, a generative, autonomous guidance framework is introduced that efficiently generates optimal dynamic motion behavior in new tasks. The new subgoal planning algorithm is shown to generate solutions to certain tasks more quickly than existing approaches currently used in robotics

Radar Imaging in Challenging Scenarios from Smart and Flexible Platforms

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Applications of Antenna Technology in Sensors

During the past few decades, information technologies have been evolving at a tremendous rate, causing profound changes to our world and to our ways of living. Emerging applications have opened u[ new routes and set new trends for antenna sensors. With the advent of the Internet of Things (IoT), the adaptation of antenna technologies for sensor and sensing applications has become more important. Now, the antennas must be reconfigurable, flexible, low profile, and low-cost, for applications from airborne and vehicles, to machine-to-machine, IoT, 5G, etc. This reprint aims to introduce and treat a series of advanced and emerging topics in the field of antenna sensors

Bio-Inspired Robotics

Modern robotic technologies have enabled robots to operate in a variety of unstructured and dynamically-changing environments, in addition to traditional structured environments. Robots have, thus, become an important element in our everyday lives. One key approach to develop such intelligent and autonomous robots is to draw inspiration from biological systems. Biological structure, mechanisms, and underlying principles have the potential to provide new ideas to support the improvement of conventional robotic designs and control. Such biological principles usually originate from animal or even plant models, for robots, which can sense, think, walk, swim, crawl, jump or even fly. Thus, it is believed that these bio-inspired methods are becoming increasingly important in the face of complex applications. Bio-inspired robotics is leading to the study of innovative structures and computing with sensory–motor coordination and learning to achieve intelligence, flexibility, stability, and adaptation for emergent robotic applications, such as manipulation, learning, and control. This Special Issue invites original papers of innovative ideas and concepts, new discoveries and improvements, and novel applications and business models relevant to the selected topics of ``Bio-Inspired Robotics''. Bio-Inspired Robotics is a broad topic and an ongoing expanding field. This Special Issue collates 30 papers that address some of the important challenges and opportunities in this broad and expanding field