Non-contact Vital Signs Monitor

An apparatus for measuring simultaneous physiological parameters such as heart rate and respiration without physically connecting electrodes or other sensors to the body. A beam of frequency modulated continuous wave radio frequency energy is directed towards the body of a subject. The reflected signal contains phase information representing the movement of the surface of the body, from which respiration and heartbeat information can be obtained. The reflected phase modulated energy is received and demodulated by the apparatus using synchronous quadrature detection. The quadrature signals so obtained are then signal processed to obtain the heartbeat and respiratory information of interest.Georgia Tech Research Corporatio

Generation of terahertz-modulated optical signals using AlGaAs/GaAs laser diodes

The Thesis reports on the research activities carried out under the Semiconductor-Laser Terahertz-Frequency Converters Project at the Department of Electronics and Electrical Engineering, University of Glasgow. The Thesis presents the work leading to the demonstration of reproducible harmonic modelocked operation from a novel design of monolithic semiconductor laser, comprising a compound cavity formed by a 1-D photonic-bandgap (PBG) mirror. Modelocking was achieved at a harmonic of the fundamental round-trip frequency with pulse repetition rates from 131 GHz up to a record-high frequency of 2.1 THz. The devices were fabricated from GaAs/AlGaAs material emitting at a wavelength of 860 nm and incorporated two gain sections with an etched PBG reflector between them, and a saturable absorber section. Autocorrelation studies are reported, which allow the device behaviour for different modelocking frequencies, compound cavity ratios, and type and number of intra-cavity reflectors to be analyzed. The highly reflective PBG microstructures are shown to be essential for subharmonic-free modelocking operation of the high-frequency devices. It was also demonstrated that the multi-slot PBG reflector can be replaced with two separate slots with smaller reflectivity. Some work was also done on the realisation of a dual-wavelength source using a broad-area laser diode in an external grating-loaded cavity. However, the source failed to deliver the spectrally-narrow lines required for optical heterodyning applications. Photomixer devices incorporating a terahertz antenna for optical-to microwave down-conversion were fabricated, however, no down-conversion experiments were attempted. Finally, novel device designs are proposed that exploit the remarkable spectral and modelocking properties of compound-cavity lasers. The ultrafast laser diodes demonstrated in this Project can be developed for applications in terahertz imaging, medicine, ultrafast optical links and atmospheric sensing

A novel harmonic klystron configuration for high power microwave frequency conversion

A new frequency converter, operating at significantly higher power and efficiency than previous devices, is described in this paper. The proposed device is implemented as a klystron structure where a new design principle is used. New analytical formulas and a specific design procedure are proposed. The klystron frequency multiplier can be suitable for telecommunications and non-lethal weapon, scientific and medical particle accelerators while the most interested exploitations are in the field of high gradient particle acceleration and FEL devices for which no performant sources exist. The advanced klystron multiplier can replace all the low level circuitry for frequency multiplication as a less expensive alternative. Efficiencies in the range of 60% in the K-band range with power levels of 30 MW are possible without phase noise, sideband generation, jitter or chirp effects. The presented design principle is applicable to other bands or power levels.Comment: 14 pages, 12 figure

On timing in time-frequency analysis of speech signals

The objective of this paper is to demonstrate the importance of position of the analysis time window in time-frequency analysis of speech signals. Speech signals contain information about the time varying characteristics of the excitation source and the vocal tract system. Resolution in both the temporal and spectral domains is essential for extracting the source and system characteristics from speech signals. It is not only the resolution, as determined by the analysis window in the time domain, but also the position of the window with respect to the production characteristics that is important for accurate analysis of speech signals. In this context, we propose an event-based approach for speech signals. We define the occurrence of events at the instants corresponding to significant excitation of the vocal tract system. Knowledge of these instants enable us to place the analysis window suitably for extracting the characteristics of the excitation source and the vocal tract system even from short segments of data. We present a method of extracting the instants of significant excitation from speech signals. We show that with the knowledge of these instants it is possible to perform prosodic manipulation of speech and also an accurate analysis of speech for extracting the source and system characteristics

A theoretical study of ultrafast phenomena in complex atoms

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química. Fecha de lectura: 15-11-2019Esta tesis tiene embargado el acceso al texto completo hasta el 15-05-2021The ultrafast movement of electrons is a driving force of chemical reactions, making it a highly desirable avenue for study. This thesis studies such movements, making use of pump-probe methods such as attosecond transient absorption spectroscopy (ATAS) and reconstruction of attosecond beatings by interference of two-photon transitions (RABITT), in complex atomic systems. The main approach used to solve the time-dependent Schr¨odinger equation (TDSE) was exact, attosecond, full-electron, ab-initio calculations. Firstly, helium was probed above the second ionisation threshold, where severalionisationchannelsareopen, usingaccurateab-initiocalculations. Here, the ATAS method was employed to predict beatings between the autoionising 3snp1Po resonances and nearby 1Se and 1De states. More surprisingly, twophoton beatings between the doubly-excited 3s3p state and the 1Po continuum werealsoobserved,demonstratingcontrolofthecorrelated,two-electron,multichannel wave packet. Secondly, two studies of neon were carried out below the second ionisation threshold. The first makes use of ATAS calculations to probe beatings between the autoionising neon states. Using a two-colour, mixed extreme-ultraviolet (XUV) near-infrared (NIR) pump, one-photon beatings between the 2s−13p1Po and the nearby 2s−13s1Se and 2s−13d1De resonances are observed. Further, oneand two-photonbeatings between the autoionising 2s−13`, `∈{0,1}and the 1Po continuum are predicted. The second uses the RABITT method to probe the atomic phase in the vicinity of multiple resonances. This is far from trivial, and interferometric methods have until now been restricted to simpler energy-regions, due to the difficulty of accurately describing the electron correlation associated with the more complex case, making accurate ab-initio calculations needed to guide experiments unavailable. Despite the complex energy-dependence of the phase when several resonances are present, presented results from experiment and abinitiotheoryareinexcellentagreement. Further,usingasimpleextensionofthe Fano model for resonant continua, the contributions of the different involved resonances are disentangled. Such simple models are highly desirable in more advanced systems, where accurate ab-initio calculations are inaccessible. The ab-initio results of both neon studies were carried out using the newly developed XCHEM methodology, which is thus further validated by the excellent agreement with presented experiments and previous studies. Finally,aRABITTstudyofargoninthevicinityofthe3s−1n` resonanceswas performed. Angularly resolved, experimental results are presented, showing the anisotropy of the atomic phase in smooth continua as well as the vicinity of resonances. Due to the complexity of the system,no ab-initio results a represent. Instead, simpler interferometric models are used to successfully explain the anisotropic behaviour of the phaseEl movimiento ultrarrápido de electrones es la fuerza motriz de las reacciones químicas, por lo cual su estudio resulta muy atractivo. Esta tesis se dedica al estudio de ese tipo de movimientos, utilizando métodos de bombeo y sonda, como espectroscopia de absorción transitoria de attosegundos (ATAS) y reconstrucción de ”beatings” de attosegundo por interferencia de transiciones de dos fotones (RABITT), en átomos complejos. El método principal utilizado para resolver de la ecuación de Schrödinger dependiente del tiempo fue la propagación exacta (ab-initio) considerando todos los electrones. En primer lugar, se investigó el átomo de helio por encima del segundo umbral de ionización, donde existen varios canales de ionización. Aquí, el método de ATAS se empleó para predecir beatings entre las resonancias 3snp1Po y estados 1Se y 1De cercanos. Sorprendentemente, también se observaron beatings de dos fotones, lo cual muestra control del paquete de ondas correlacionado multicanal de dos electrones. En segundo lugar, dos estudios por debajo del segundo umbral de ionización del neón se llevaron a cabo. El primero utiliza cálculos de ATAS para investigar los beatings entre estados auto ionizantes de neón. Utilizando un bombeo de dos colores, radiación ultravioleta extrema (XUV) mezclada con radiación infrarrojo cercano (NIR), es posible observar beatings entre la resonancia del 2s−13p1Po y las 2s−13s1Se y 2s−13d1De. Además, se predicen beatings de uno y dos fotones entre las resonancias auto ionizantes 2s−13`, `∈{0,1}y el continuo 1Po. El segundo usa el método de RABITT para estudiar la fase atómica en las cercanías de las resonancias múltiples. Hasta ahora, los métodos interferométricos han estado restringidos a regiones de energía de hasta una resonancia, a causa de las dificultades en llevar a cabo propagaciones exactas (ab-initio), las cuales dependen de la correlación electrónica para describir bien los experimentos. A pesar de la complejidad de la dependencia de la energíac con la fase, debido a la presencia de varias resonancias, los resultados teóricos obtenidos comparan muy bien con los resultados experimentales presentados. Además, usando una extensión del modelo de Fano para continuos resonantes, las contribuciones de las distintas resonancias se han podido resolver. Modelos más simples son necesarios en sistemas más avanzados, donde cálculos ab-initio son inaccesibles. Los resultados ab-initio presentados en ambos estudios se realizaron con el método XCHEM recientemente propuesto, dando así validez al método. Finalmente, se realizó un estudio RABITT cerca de las resonancias 3s−1n` del argón. Se presentan experimentos mostrando la dependencia angular de la fase atómica, tanto en continuos suaves como en las cercanías de resonancias. Debido a la complejidad del sistema, no se presentan resultados ab-initio. En cambio, mediante modelos interferométricos se ha podido explicar el comportamiento anisótropo de la fas

Extraction of Structural Metrics from Crossing Fiber Models

Diffusion MRI (dMRI) measurements allow us to infer the microstructural properties of white matter and to reconstruct fiber pathways in-vivo. High angular diffusion imaging (HARDI) allows for the creation of more and more complex local models connecting the microstructure to the measured signal. One of the challenges is the derivation of meaningful metrics describing the underlying structure from the local models. The aim hereby is to increase the specificity of the widely used metric fractional anisotropy (FA) by using the additional information contained within the HARDI data. A local model which is connected directly to the underlying microstructure through the model of a single fiber population is spherical deconvolution. It produces a fiber orientation density function (fODF), which can often be interpreted as superposition of multiple peaks, each associated to one relatively coherent fiber population (bundle). Parameterizing these peaks one is able to disentangle and characterize these bundles. In this work, the fODF peaks are approximated by Bingham distributions, capturing first and second order statistics of the fiber orientations, from which metrics for the parametric quantification of fiber bundles are derived. Meaningful relationships between these measures and the underlying microstructural properties are proposed. The focus lies on metrics derived directly from properties of the Bingham distribution, such as peak length, peak direction, peak spread, integral over the peak, as well as a metric derived from the comparison of the largest peaks, which probes the complexity of the underlying microstructure. These metrics are compared to the conventionally used fractional anisotropy (FA) and it is shown how they may help to increase the specificity of the characterization of microstructural properties. Visualization of the micro-structural arrangement is another application of dMRI. This is done by using tractography to propagate the fiber layout, extracted from the local model, in each voxel. In practice most tractography algorithms use little of the additional information gained from HARDI based local models aside from the reconstructed fiber bundle directions. In this work an approach to tractography based on the Bingham parameterization of the fODF is introduced. For each of the fiber populations present in a voxel the diffusion signal and tensor are computed. Then tensor deflection tractography is performed. This allows incorporating the complete bundle information, performing local interpolation as well as using multiple directions per voxel for generating tracts. Another aspect of this work is the investigation of the spherical harmonic representation which is used most commonly for the fODF by means of the parameters derived from the Bingham distribution fit. Here a strong connection between the approximation errors in the spherical representation of the Dirac delta function and the distribution of crossing angles recovered from the fODF was discovered. The final aspect of this work is the application of the metrics derived from the Bingham fit to a number of fetal datasets for quantifying the brain’s development. This is done by introducing the Gini-coefficient as a metric describing the brain’s age

Ultrafast carrier and structural dynamics in graphite detected via attosecond soft X-ray absorption spectroscopy

Understanding most of the physical and chemical phenomena determining the world around us requires the possibility to interrogate their main characters on their natural scale in space and time. The insulating or conductive behavior of matter, its magnetic properties or the nature of chemical bonds are strongly dependent on the nuclear and electronic structure of the atoms, molecules or solids considered. Hence, tools are needed to probe electrons and nuclei directly at the atomic scale with a temporal resolution allowing the observation of electron dynamics (on the attosecond-to-femtosecond timescale) and structural dynamics (on the femtosecond-to-picosecond timescale) in real time. Attosecond science offers unique opportunities to investigate electronic and structural dynamics at the heart of important processes in atomic, molecular and solid-state physics. The generation of attosecond bursts of light, in the form of train of pulses or of isolated pulses, has been achieved on table-top sources by exploiting the high-order harmonic generation (HHG) process. The photons constituting the attosecond emission have energies that range from the extreme ultra-violet (XUV) up to the soft X-ray (SXR) region of the spectrum, allowing to interrogate the electronic structure of the probed material directly at the level of the inner electronic shells. Because of this property of accessing the characteristic electronic structure of the elements constituting the target, XUV and, especially, SXR spectroscopy are considered element-specific techniques. Attosecond pulses have already proven to be able to observe ultrafast phenomena in atoms, molecules or solids previously inaccessible. In this thesis, the application of time-resolved X-ray absorption fine-structure (XAFS) spectroscopy using attosecond SXR pulses to the study of carrier and structural dynamics in graphite is reported. In chapter 1, an introduction to the field of attoscience and the presentation of the state of the art of ultrafast dynamics in graphite are given. The established technique to generate attosecond pulses is described and a review of the most significant application of attosecond pulses to the study of electron dynamics is presented. The electronic and structural properties of graphite are then discussed, highlighting some of the most representative experiments detecting electron and lattice dynamics. The experimental setup developed at ICFO in the group of Prof. Dr. Jens Biegert and used for this Ph.D. thesis project is described in details in chapter 2. The system needed for the generation, propagation and detection of the attosecond SXR radiation is presented. The performances of the SXR source in terms of spectral tunability, photon flux and stability are discussed. The implementation of a IR pump - SXR probe scheme is reported, allowing beams' recombination in both collinear and non-collinear fashion. To conclude, the results of an attosecond streaking experiment are presented, through which a temporal characterization of the HHG emission has been achieved. A discussion on the spectroscopic capabilities of XAFS technique to interrogate the electronic and lattice structure of the observed material is presented in chapter 3. The potential of this technique has been demonstrated with an experimental investigation of a graphite thin film, with the results showing the possibility to probe the first unoccupied electronic bands and the characteristic distances defining the lattice structure. Finally, the XAFS capabilities have been exploited in a time-resolved experimental study of graphite to observe light-induced carrier and lattice dynamics, presented in chapter 4. The interpretation of the experimental data reveals insights on the ultrafast interaction of the pump laser field with charge carriers and on the effects of carrier-carrier and carrier-phonon scattering following photoexcitation.Comprender la mayoría de los fenómenos físicos y químicos que determinan el mundo que nos rodea requiere interrogar a sus personajes principales - los átomos, moléculas o sólidos - en el espacio y en el tiempo. Por lo tanto, se necesitan herramientas para investigar el movimiento de los electrones y núcleos atómicos que los componen en tiempo real. Para ello, necesitamos trabajar directamente en su escala natural, es decir, con una resolución temporal de attosegundos en el caso de los electrones y de femtosegundos a picosegundos en el caso de los núcleos. La Attociencia ofrece oportunidades únicas para investigar dinámicas electrónicas y estructurales en el corazón de procesos importantes en física atómica, molecular y del estado sólido. La generación de pulsos de luz de attosegundos se ha logrado en fuentes láseres de laboratorio explotando la generación de armónicos de alto orden (HHG). Los fotones que constituyen las emisiones de as tienen energías que van desde el ultravioleta extremo (XUV) hasta la región de rayos X blandos (SXR) del espectro, lo que permite examinar los niveles electrónicos internos. Los pulsos de attosegundos ya han demostrado ser capaces de observar fenómenos ultrarrápidos y previamente inaccesibles en átomos, moléculas o sólidos. En esta tesis se presenta la aplicación de la espectroscopía de absorción de rayos X (XAFS) resuelta en el tiempo usando pulsos SXR de as para el estudio de dinámicas electrónicas y estructurales en grafito. El capítulo 1 incluye una introducción al campo de la Attociencia y la presentación del estado del arte de las dinámicas ultrarrápidas en grafito. Asimismo, se describe la técnica establecida para generar pulsos de attosegundos y se presenta una revisión de las aplicaciones más significativas de estos pulsos al estudio de las dinámicas electrónicas. A continuación, se explican las propiedades electrónicas y estructurales del grafito, destacando algunos de los experimentos más representativos en detección de dinámicas electrónicas y vibracionales. En el capítulo 2 se describe la metodología experimental desarrollada en el grupo del Prof. Jens Biegert en ICFO y utilizada en esta tesis doctoral. En concreto, se presenta el sistema láser empleado para el proceso HHG para producir la radiación SXR de attosegundos así como el sistema utilizado para la generación, propagación y detección de la radiación. De igual modo, se discuten las propiedades de la fuente SXR en términos de afinación espectral, flujo de fotones y estabilidad. También se presenta la implementación de un sistema “pump-probe” con un pulso de bomba infrarrojo y una sonda SXR, lo que permite la recombinación de haces de manera colineal y no colineal. En último lugar, se presentan los resultados de un experimento de caracterización temporal de la emisión de HHG. A continuación, en el capítulo 3 se presenta una discusión sobre las capacidades espectroscópicas de la técnica XAFS para interrogar la estructura electrónica y vibracional del material en estudio. El potencial de esta técnica se ha demostrado con una investigación experimental sobre grafito, con los resultados que muestran la posibilidad de estudiar las primeras bandas electrónicas desocupadas y las distancias características que definen la estructura del cristal. Finalmente, las capacidades de XAFS han sido utilizadas en un estudio experimental sobre grafito para observar dinámicas electrónicas y vibracionales, desde la escala sub-fs hasta el ps, y se presenta en el capítulo 4. La interpretación de los datos experimentales revela ideas sobre la interacción ultrarrápida del campo eléctrico del láser con electrones, los efectos de dispersión electrón-electrón y electrón-fonón después de la foto-excitación, con el último inducido por el fuerte acoplamiento electrón-fonón en el caso del grafito