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1
De, Supinski Bronis R. "Logical time coherence maintenance." Full text, Acrobat Reader required, 1998. http://viva.lib.virginia.edu/etd/theses/supinski98.pdf.
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Abuhajar, Suhir. "Visualizing real time vasomotion in vivo using optical coherence tomography." Thesis, Lancaster University, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.659170.
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As blood vessel imaging techniques facilitate the fundamental understanding in vascular performance diagnosis and biomedical research improvement, we aimed to visualize and understand the blood vessels dynamics under human skin and their underlying mechanisms in real time. In this study, a noninvasive imaging system was selected to provide an investigation of the real time oscillation of blood vessels in vivo, using Spectral Radar Optical Coherence Tomography (SROCT). This main goal was achieved by evaluating the precision and confidence in recorded data by using a phantom made of Intralipid (IL) to mimic the physical properties of the skin. Then, we successfully managed to visualize for the first time the vasomotion under human skin using MatLab Image Processing Toolbox. After that, we explored mathematically the cyclic variations of the vascular area obtained from the images for a cohort of six participants. The Fourier and wavelet transforms were applied to identify the characteristic frequencies related to the oscillations in vascular cross sectional area. Finally, we investigated dynamical aspects of vasomotion, in response to temperature change, by using a Meleor Thermoelectric Temperature Controller (MTTC) to produce local heating in conjunction with Spectral Radar Optical Coherence Tomography (SROCT).
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GUIDOBONI, Greta. "Spin Coherence Time studies for the storage ring EDM search." Doctoral thesis, Università degli studi di Ferrara, 2013. http://hdl.handle.net/11392/2388878.
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This thesis is part of the feasibility studies for a search for an Electric
Dipole Moment (EDM) of charged particles in a storage ring. The evidence
for a non-vanishing EDM at the sensitivity of present or planned experiments
would clearly prove the existence of new CP violating meachanisms
beyond the Standard Model. The proposed solution to measure the EDM
of charged particles is the use of a storage ring where the polarized charged
particle beam can be kept circulating while interacting with a radial electric
field. Starting with a longitudinally polarized beam, the EDM signal
would be detected as a polarization precession starting from the horizontal
plane and rotating toward the vertical direction. A long horizontal polarization
lifetime, called spin coherence time, is required since it represents
the time available to observe the EDM signal. In order to have a sensitivity
about 10−29 e·cm to the deuteron EDM, the spin coherence time should
reach 1000 s while the measurement of a vertical polarization change should
detect angles as small as micro-radians.
The aim of this work is the analysis of the mechanisms which control
the spin coherence time in a storage ring. The measurements presented
here were made at the COSY (COoler SYnchrotron) ring located at the
Forschungszentrum-J¨ulich GmbH (Germany).
There are two set of measurements presented in this thesis: the first is a
study of a spin resonance induced by a radio-frequency (rf) solenoid and the
second shows the results from the first direct measurement of the horizontal
polarization as a function of time.
The first experiment sought to estimate the spin coherence time by measuring
the width of a deuteron spin resonance induced by an rf-solenoid.
Since the width of the resonance depends on the spin tune spread and thus
on particle momentum distribution, each mechanism that can change the
particle velocity in the beam could contribute to the spin tune spread. In
particular, these mechanisms are betatron oscillations related to the beam
emittance and synchrotron oscillations that are present only in a bunched
beam.
The experiment consisted in the measurement of the vertical polarization
measurements with the rf-solenoid running at fixed frequency on and
off resonance, for both uncooled and cooled bunched beam. In order to
interpret the data, a simple “no-lattice” model was developed based on two
rotation matrices for the spin precession about the vertical axis and the
solenoid kick about the longitudinal axis; synchrotron oscillations were included
as simple harmonic motion. The model demonstrated that the effect
of synchrotron oscillations on the induced spin resonance were large enough
to hide any dependence on emittance.
The second experiment was the direct measurement of the horizontal
polarization as a function of time. This task was accomplished through
the development of a dedicated data acquisition system synchronized with
the revolution frequency of the beam. By changing the horizontal beam
emittance with a white noise electric field, the measurements gave the first
experimental evidence of a dependence of the spin coherence time on the
horizontal beam size. The dependence is due to the path lengthening introduced
by betatron oscillations which forces the particles to go faster in order
to respect the isochronous condition in a bunched beam. A possible method
to correct for emittance effects is to use sextupole magnets. In fact the field
varies as the square of the radius from the center and provides an adjustment
to the particle orbit to remove the term driving the spin tune change.
It has been demonstrated that for a particular value of sextupole strength
the contribution from the horizontal emittance was canceled, reaching a
spin coherence time of a hundred seconds.
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Anglada, Sánchez Martí. "Exploiting frame coherence in real-time rendering for energy-efficient GPUs." Doctoral thesis, Universitat Politècnica de Catalunya, 2020. http://hdl.handle.net/10803/669210.
Full textAbstract:
The computation capabilities of mobile GPUs have greatly evolved in the last generations, allowing real-time rendering of realistic scenes. However, the desire for processing complex environments clashes with the battery-operated nature of smartphones, for which users expect long operating times per charge and a low-enough temperature to comfortably hold them. Consequently, improving the energy-efficiency of mobile GPUs is paramount to fulfill both performance and low-power goals. The work of the processors from within the GPU and their accesses to off-chip memory are the main sources of energy consumption in graphics workloads. Yet most of this energy is spent in redundant computations, as the frame rate required to produce animations results in a sequence of extremely similar images.
The goal of this thesis is to improve the energy-efficiency of mobile GPUs by designing micro-architectural mechanisms that leverage frame coherence in order to reduce the redundant computations and memory accesses inherent in graphics applications.
First, we focus on reducing redundant color computations. Mobile GPUs typically employ an architecture called Tile-Based Rendering, in which the screen is divided into tiles that are independently rendered in on-chip buffers. It is common that more than 80% of the tiles produce exactly the same output between consecutive frames. We propose Rendering Elimination (RE), a mechanism that accurately determines such occurrences by computing and storing signatures of the inputs of all the tiles in a frame. If the signatures of a tile across consecutive frames are the same, the colors computed in the preceding frame are reused, saving all computations and memory accesses associated to the rendering of the tile. We show that RE vastly outperforms related schemes found in the literature, achieving a reduction of energy consumption of 37% and execution time of 33% with minimal overheads.
Next, we focus on reducing redundant computations of fragments that will eventually not be visible. In real-time rendering, objects are processed in the order they are submitted to the GPU, which usually causes that the results of previously-computed objects are overwritten by new objects that turn occlude them. Consequently, whether or not a particular object will be occluded is not known until the entire scene has been processed. Based on the fact that visibility tends to remain constant across consecutive frames, we propose Early Visibility Resolution (EVR), a mechanism that predicts visibility based on information obtained in the preceding frame. EVR first computes and stores the depth of the farthest visible point after rendering each tile. Whenever a tile is rendered in the following frame, primitives that are farther from the observer than the stored depth are predicted to be occluded, and processed after the ones predicted to be visible. Additionally, this visibility prediction scheme is used to improve Rendering Elimination’s equal tile detection capabilities by not adding primitives predicted to be occluded in the signature. With minor hardware costs, EVR is shown to provide a reduction of energy consumption of 43% and execution time of 39%.
Finally, we focus on reducing computations in tiles with low spatial frequencies. GPUs produce pixel colors by sampling triangles once per pixel and performing computations on each sampling location. However, most screen regions do not include sufficient detail to require high sampling rates, leading to a significant amount of energy wasted computing the same color for neighboring pixels. Given that spatial frequencies are maintained across frames, we propose Dynamic Sampling Rate, a mechanism that analyzes the spatial frequencies of tiles and determines the best sampling rate for them, which is applied in the following frame. Results show that Dynamic Sampling Rate significantly reduces processor activity, yielding energy savings of 40% and execution time reductions of 35%.La capacitat de càlcul de les GPU mòbils ha augmentat en gran mesura en les darreres generacions, permetent el renderitzat de paisatges complexos en temps real. Nogensmenys, el desig de processar escenes cada vegada més realistes xoca amb el fet que aquests dispositius funcionen amb bateries, i els usuaris n’esperen llargues durades i una temperatura prou baixa com per a ser agafats còmodament. En conseqüència, millorar l’eficiència energètica de les GPU mòbils és essencial per a aconseguir els objectius de rendiment i baix consum. Els processadors de la GPU i els seus accessos a memòria són els principals consumidors d’energia en càrregues gràfiques, però molt d’aquest consum és malbaratat en càlculs redundants, ja que les animacions produïdes s¿aconsegueixen renderitzant una seqüència d’imatges molt similars. L’objectiu d’aquesta tesi és millorar l’eficiència energètica de les GPU mòbils mitjançant el disseny de mecanismes microarquitectònics que aprofitin la coherència entre imatges per a reduir els càlculs i accessos redundants inherents a les aplicacions gràfiques. Primerament, ens centrem en reduir càlculs redundants de colors. A les GPU mòbils, sovint s'empra una arquitectura anomenada Tile-Based Rendering, en què la pantalla es divideix en regions que es processen independentment dins del xip. És habitual que més del 80% de les regions de pantalla produeixin els mateixos colors entre imatges consecutives. Proposem Rendering Elimination (RE), un mecanisme que determina acuradament aquests casos computant una signatura de les entrades de totes les regions. Si les signatures de dues imatges són iguals, es reutilitzen els colors calculats a la imatge anterior, el que estalvia tots els càlculs i accessos a memòria de la regió. RE supera àmpliament propostes relacionades de la literatura, aconseguint una reducció del consum energètic del 37% i del temps d’execució del 33%. Seguidament, ens centrem en reduir càlculs redundants en fragments que eventualment no seran visibles. En aplicacions gràfiques, els objectes es processen en l’ordre en què son enviats a la GPU, el que sovint causa que resultats ja processats siguin sobreescrits per nous objectes que els oclouen. Per tant, no se sap si un objecte serà visible o no fins que tota l’escena ha estat processada. Fonamentats en el fet que la visibilitat tendeix a ser constant entre imatges, proposem Early Visibility Resolution (EVR), un mecanisme que prediu la visibilitat basat en informació obtinguda a la imatge anterior. EVR computa i emmagatzema la profunditat del punt visible més llunyà després de processar cada regió de pantalla. Quan es processa una regió a la imatge següent, es prediu que les primitives més llunyanes a el punt guardat seran ocloses i es processen després de les que es prediuen que seran visibles. Addicionalment, aquest esquema de predicció s’empra en millorar la detecció de regions redundants de RE al no afegir les primitives que es prediu que seran ocloses a les signatures. Amb un cost de maquinari mínim, EVR aconsegueix una millora del consum energètic del 43% i del temps d’execució del 39%. Finalment, ens centrem a reduir càlculs en regions de pantalla amb poca freqüència espacial. Les GPU actuals produeixen colors mostrejant els triangles una vegada per cada píxel i fent càlculs a cada localització mostrejada. Però la majoria de regions no tenen suficient detall per a necessitar altes freqüències de mostreig, el que implica un malbaratament d’energia en el càlcul del mateix color en píxels adjacents. Com les freqüències tendeixen a mantenir-se en el temps, proposem Dynamic Sampling Rate (DSR)¸ un mecanisme que analitza les freqüències de les regions una vegada han estat renderitzades i en determina la menor freqüència de mostreig a la que es poden processar, que s’aplica a la següent imatge...
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Twengström, Mikael. "Time-reversal symmetry breaking and mixed coherence lengths in multicomponent superconductors." Thesis, KTH, Fysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-138163.
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Wojcik, Aleksander Karol. "Signal statistics of phase dependent optical time domain reflectometry." Texas A&M University, 2006. http://hdl.handle.net/1969.1/4873.
Full textAbstract:
The statistics of the phase dependent optical time-domain reflectometer have
been analyzed. The optical fiber is modeled by the use of a discrete set of reflectors
positioned randomly along the fiber. The statistics of the reflected light from
a traveling pulse are derived. The statistics of the signal are used to calculate the
characteristics of shot noise in the photodetector, and the probability that noise of
certain intensity will occur. An estimation of the backscattered power is made by calculating
the fraction of the backscattered power that is captured in a guiding mode.
Upper power limits are calculated by considering nonlinear optical effects. An estimation
of noise from thermally excited sound waves, amplified by Brillouin scattering,
is derived. This noise considers the parameters of a photodetector, giving a model
for the noise in the measurable photocurrent. Two models are used to describe the
fading probability of the signal. The first model, based on the Fabry-Perot interferometer
with a random phase perturbation in the middle, is used to calculate the
probability that the whole signal vanishes for any value of phase perturbation. The
second model, by calculating the correlation between two signals, one perturbed and
one unperturbed, predicts the fading of the signal of interest. The present work gives
the theoretical basis for the phase dependant Optical Time Domain Reflectometry,
allowing its optimization and setting the fundamental limitations to the performance of the system.
7
Panagos, Adam G., and Kurt Kosbar. "MIMO CHANNEL TIME VARIATION AS A FUNCTION OF MOBILE USER VELOCITY." International Foundation for Telemetering, 2004. http://hdl.handle.net/10150/605780.
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International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, CaliforniaThe analysis of multiple-input multiple-output (MIMO) communication systems often assumes a static, or quasi-static, environment. Platform motion and changes in the environment makes this an unreasonable assumption for many telemetry applications. This paper uses computer simulations to characterize the time variation of MIMO channel parameters when there is relative motion between the transmitter and receiver. These simulation results yield explicit time intervals over which a MIMO channel can be considered static for a given relative velocity and propagation environment. These results can be used to predict the practical limitations of proposed MIMO system algorithms.
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Chen, Jiajian. "Non-photorealistic rendering with coherence for augmented reality." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45749.
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A seamless blending of the real and virtual worlds is key to increased immersion and improved user experiences for augmented reality (AR). Photorealistic and non-photorealistic rendering (NPR) are two ways to achieve this goal. Non-photorealistic rendering creates an abstract and stylized version of both the real and virtual world, making them indistinguishable. This could be particularly useful in some applications (e.g., AR/VR aided machine repair, or for virtual medical surgery) or for certain AR games with artistic stylization.
Achieving temporal coherence is a key challenge for all NPR algorithms. Rendered results are temporally coherent when each frame smoothly and seamlessly transitions to the next one without visual flickering or artifacts that distract the eye from perceived smoothness. NPR algorithms with coherence are interesting in both general computer graphics and AR/VR areas. Rendering stylized AR without coherence processing causes the final results to be visually distracting. While various NPR algorithms with coherence support have been proposed in general graphics community for video processing, many of these algorithms require thorough analysis of all frames of the input video and cannot be directly applied to real-time AR applications. We have investigated existing NPR algorithms with coherence in both general graphics and AR/VR areas. These algorithms are divided into two categories: Model Space and Image Space. We present several NPR algorithms with coherence for AR: a watercolor inspired NPR algorithm, a painterly rendering algorithm, and NPR algorithms in the model space that can support several styling effects.
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Ansari, Zunaira. "Whole field, real time photorefractive holography for imaging through turbid media using sources of diverse spatial and temporal coherence." Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289853.
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Freiberger, Manuel. "A time domain optical coherence tomograph for laboratory investigations on phantoms and human skin." Thesis, Linköping University, Department of Biomedical Engineering, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-3852.
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Optical coherence tomography is an imaging modality with an outstanding resolution. During the project, a time domain OCT system based on a Michelson fibre interferometer was implemented and put into operation. A super-luminescent diode with a centre wavelength of 1295nm and a bandwidth of 45nm was selected as light source and a linear variable delay line as reference. Basic tests were made on phantoms constructed of filter foils and on gel-like agar slices with optical properties similar to human tissue. It was shown that the achievable resolution was at least 36um and can be increased. The system can easily be enhanced to create two-dimensional images.
Optische Kohärenztomographie ist ein bildgebendes Verfahren mit einer hervorragenden räumlichen Auflösung. Im Laufe des Projekts wurde ein OCT-System basierend auf einem faseroptischen Michelson-Interferometer implementiert und in Betrieb genommen. Als Lichtquelle wurde eine Superlumineszenzdiode mit einer Mittenwellenlänge von 1295nm und einer Bandbreite von 45nm gewählt. Eine variable optische Verzögerungsleitung diente als Referenz. Erste Messungen an Filterfolien und gelähnlichen Agarphantomen, die die optischen Eigenschaften von menschlichem Gewebe nachbildeten, lieferten eine räumliche Auflösung von mindestens 36um. Durch die modulare Bauweise ist das System leicht für zweidimensionale Aufnahmen erweiterbar.
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Ruggeri, Marco. "Extended Depth Optical Coherence Tomography for Anterior Segment and Accommodation Imaging in Real-Time." Scholarly Repository, 2011. http://scholarlyrepository.miami.edu/oa_dissertations/686.
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The changes in the human crystalline lens shape and its internal structure during accommodation and with aging are a fundamental component of the dynamic mechanism of accommodation and presbyopia, the loss of near vision with age. A better understanding of the crystalline lens changes during accommodation will help in developing new treatments to correct for presbyopia. The goal of this dissertation is to design and develop an imaging system to study the dynamic changes in lens shape during accommodative response. An imaging system based on spectral domain optical coherence tomography (SD-OCT) was developed with long axial range, high axial and lateral resolution and high speed for in vivo imaging the anterior segment along its entire length at video-rate. A slit-lamp mounted optical delivery scanning device for the extended depth SD-OCT system was developed. The delivery system was combined with a custom made unit that provides accommodation and disaccommodation step stimuli. A method to correct for the distortions of the OCT images was also developed that provides corrected two dimensional biometric data at different accommodative states.
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Clark, Ian George. "A unified approach to the study of asynchronous communication mechanisms in real-time systems." Thesis, King's College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326237.
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Zhang, Jinke. "Development of time-domain full-field optical coherence tomography as a non-destructive testing method." Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3015759/.
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Optical coherence tomography (OCT) serves as a non-destructive and non-invasive technique that is capable of imaging the inner structure of optical scattering samples with a high spatial resolution and deep penetration depth. Full-field time-domain OCT (FF-TD-OCT) is an extension of time-domain OCT (TD-OCT) which uses a two-dimensional (2D) detector to capture a series of en-face images to reconstruct the inner structure of samples in three-dimension (3D). In pharmaceutical industry, the pellet or tablet coating performs an important role in the release of active pharmaceutical ingredients (API) and controlling the desired API absorption rate in human body. Therefore, the accurate evaluation of coating thickness is vital to the pharmaceutical coating process. Our FF-TD-OCT system was developed in this research to image the pharmaceutical coating of small size pellets with a high axial resolution of 3.9μm and lateral resolution of 4.4μm. We characterized two pellet samples: a two-layer pellet with one clear coating layer and one drug-loaded layer, and a three-layer pellet with one clear coating layer and two drug-load layers. The mean thickness of a two-layer pellet was precisely determined automatically as 39.7±7.3μm and 49.1±7.0μm for the outer and inner layers respectively. The mean thickness of a three-layer pellet were 26.5±2.3μm, 20.6±3.4μm and 57.3±7.2μm respectively. In addition, the particles in the drug-loaded layer can be clearly resolved form the cross-section image. The precise and power information of the human corneal surface is of significant benefit in corneal corrective surgeries. Our developed FF-TD-OCT was combined with an average back-vertex focal length and average powercalculation algorithm in order to measure and calculate the individual power of the corneal surface. Meanwhile, the angle of incident light was considered as an important parameter and the errors introduced by the paraxial approximation was reduced. We managed to measure six formalin-fixed and two fresh corneas and map the surface power information of them. In addition, the cross-section image of cornea generated from our FF-TD-OCT system showed its structure including epithelium, Bowman’s layer and stroma clearly and the features of the stroma. For automotive paint system, the metallic flakes in base coat has a significant effect on the appearance of automotive bodies. Precise evaluation of the properties of these flakes is important in the automotive painting system in the purpose for quality assurance. Our FF-TD-OCT system was combined with a 3D variational segmentation method to measure and segment the individual flakes within the base coat of automotive paint system in 3D for the first time. The properties of flakes, including number, size and orientation in 3D space, were precisely calculated, which cannot be achieved by current commercial methods.
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Sorgenfrei, Florian [Verfasser]. "Time-Resolved Jitter-Free Experiments at FLASH: From Longitudinal Coherence Studies to Nonlinear Dynamics / Florian Sorgenfrei." München : Verlag Dr. Hut, 2013. http://d-nb.info/1042308047/34.
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Acharya, Megha N. "Speckle Reduction in an All Fiber Time Domain Common Path Optical Coherence Tomography by Frame Averaging." University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1353336847.
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Ullah, Saeed. "Optical control and detection of spin coherence in multilayer systems." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-10052017-163058/.
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Since a decade, spintronics and related physics have attracted considerable attention due to the massive research conducted in these areas. The main reason for growing interest in these fields is the expectation to use the electrons spin instead of or in addition to the charge for the applications in spin-based electronics, quantum information, and quantum computation. A prime concern for these spins to be possible candidates for carrying information is the ability to coherently control them on the time scales much faster than the decoherence times. This thesis reports on the spin dynamics in two-dimensional electron gases hosted in artificially grown III-V semiconductor quantum wells. Here we present a series of experiments utilizing the techniques to optically control the spin polarization triggered by either optical or electrical methods i.e. well known pump-probe technique and current-induced spin polarization. We investigated the spin coherence in high mobility dense two-dimensional electron gas confined in GaAs/AlGaAs double and triple quantum wells, and, it\'s dephasing on the experimental parameters like applied magnetic field, optical power, pump-probe delay and excitation wavelength. We have also studied the large spin relaxation anisotropy and the influence of sample temperature on the long-lived spin coherence in triple quantum well structure. The anisotropy was studied as a function sample temperature, pump-probe delay time, and excitation power, where, the coherent spin dynamics was measured in a broad range of temperature from 5 K up to 250 K using time-resolved Kerr rotation and resonant spin amplification. Additionally, the influence of Al concentration on the spin dynamics of AlGaAs/AlAs QWs was studied. Where, the composition engineering in the studied structures allows tuning of the spin dephasing time and electron g-factor. Finally, we studied the macroscopic transverse drift of long current-induced spin coherence using non-local Kerr rotation measurements, based on the optical resonant amplification of the electrically-induced polarization. Significant spatial variation of the electron g-factor and the coherence times in the nanosecond scale transported away half-millimeter distances in a direction transverse to the applied electric field was observed.Há uma década, a spintrônica e outras áreas relacionadas vêm atraindo considerável atenção, devido a enorme quantidade de pesquisa conduzidas por elas. A principal razão para o crescente interesse neste campo é a expectativa da aplicação do controle do spin do elétron no lugar ou em adição à carga, em dispositivos eletrônicos e informação e computação quânticas. A possibilidade destes spins carregarem informação depende, primeiramente, da habilidade de controlá-los coerentemente, em uma escala de tempo muito mais rápida do que o tempo de decoerência. Esta tese trata da dinâmica de spins em gases de elétrons bidimensionais, em poços quânticos de semicondutores III-V, crescidos artificialmente. Nós apresentamos uma série de experimentos, utilizando técnicas para o controle ótico da polarização de spin, desencadeadas por métodos óticos ou eletrônicos, ou seja, técnicas conhecidas de bombeio e prova e polarização de spin induzida por corrente. Nós investigamos a coerência de spin em gases bidimensionais, confinados em poços quânticos duplos e triplos de GaAs/AlGaAs e a dependência da defasagem com parâmetros experimentais, como campo magnético externo, potência ótica, tempo entre os pulsos de bombeio e prova e comprimento de onda da excitação. Também estudamos a grande anisotropia de relaxação de spin como função da temperatura da amostra, potência de excitação e defasagem entre bombeio e prova, medidos para uma vasta gama de temperatura, entre 5K e 250K, usando Rotação de Kerr com Resolução Temporal (TRKR) e Amplificação Ressonante de Spin (RSA). Além disso estudamos a influência da concentração de Al na dinâmica dos poços de AlGaAs/AlAs, para o qual a engenharia da composição da estrutura permite sintonizar o tempo de defasagem de spin e o fator $ g $ do elétron. Por fim, estudamos a deriva transversal macroscópica da longa coerência de spin induzida por corrente, através de medidas de Rotação de Kerr não-locais, baseadas na amplificação ressonante ótica da polarização eletricamente induzida. Observamos uma variação espacial significante do fator $ g $ e do tempo de vida da coerência, na escala de nanosegundos, deslocada distâncias de meio milímetro na direção transversa ao campo magnético aplicado.
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Lopes, Kim Samejima Mascarenhas. "Coerência parcial e aplicações." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/45/45133/tde-05112013-173150/.
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Neste trabalho foram estudadas algumas formas de relação entre séries temporais multivariadas. Discutiu-se, inicialmente, a função de coerência, uma função análoga a função de correlação(que é dada no domínio do tempo) calculada no domínio da freqüência. Foram estudadas também as funções de coerência parcial e coerência parcial direcionada. A função de coerência parcial mede a relação entre duas componentes de uma série multivariada, isolados os efeitos de outra série. Em linhas gerais, a Coerência Parcial Direcionada pode ser interpredata como a decomposição da coerência parcial a partir de modelos autoregressivos multivariados. Esse conceito pode ser interpretado como uma representação do conceito de causalidade de Granger no domínio da freqüência. Finalmente, foram aplicadas as funções acima em dois conjuntos de dados: um modelo VAR(1) trivariado simulado e dados de medições de eletroencefalograma.In this work we studied relationships between multivariate time series. We discussed the coherence function, a function similar to the correlation function(calculated in time domain) in frequency domain. Next, we discussed partial coherence and partial directed coherence. The partial coherence measures the relationship between two components of a multivariate time series, after removing the influence of another time series. Generally, the partial directed coherence can be interpreted as the decompositioin of the partial coherence from multivariate autoregressive models. We can interpret this function as a representation of the Granger causality concept in frequency domain. Finally, we applied these concepts in two situations: a simulated VAR(1) model and an electroencefalogram database.
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Khastehdel, Fumani Ahmad. "QUANTUM CONFINED STATES AND ROOM TEMPERATURE SPIN COHERENCE IN SEMICONDUCTOR NANOCRYSTAL QUANTUM DOTS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1449151739.
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Barsegov, Valeri Abulevich. "Quantum decoherence and time symmetry breaking : quantum-classical correspondence in non-adiabatic transitions /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004212.
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Baskin, John Spencer Zewail Ahmed H. Zewail Ahmed H. "Real-time observation and analysis of coherence and alignment in molecular systems : isolated molecules and chemical reactions /." Diss., Pasadena, Calif. : California Institute of Technology, 1990. http://resolver.caltech.edu/CaltechETD:etd-11252003-112746.
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Bäckström, Caroline A. "Professional and social support for first-time mothers and partners during childbearing." Doctoral thesis, Hälsohögskolan, Högskolan i Jönköping, HHJ. CHILD, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-38334.
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Background: Expecting a child and becoming a parent is one of life’s major events, during which the parents’ perspective on life and their couple relationship changes. For some parents, childbearing entails a decrease in parental couple relationship quality. The way in which parents are able to cope with childbearing may be connected with their Sense of Coherence; which is a person’s ability to perceive life as comprehensible, manageable and meaningful. For parents’ positive childbearing experiences, professional and social support have been proven to be valuable. However, far from all parents have access to social support; furthermore, professional support does not always meet the needs of expectant parents. Hence, more research is needed to increase knowledge about expectant parents’ experiences of professiona land social support. In addition, more research is needed to explore factors associated with quality of couple relationship among parents during childbearing. Aims: The overall aim of the thesis was to explore professional and social support for first-time mothers and partners during childbearing in relation toquality of couple relationship and Sense of Coherence. Methods: The study’s designs were explorative, prospective and longitudinal; both qualitative and quantitative methods were used. Specifically, explorative designs, qualitative methods and phenomenographic analysis were used to explore expectant first-time mothers’ (I) and partners’ perceptions of professional support (II). Furthermore, an explorative design, qualitative method and qualitative content analysis were used to explore expectant first-time mothers’ experiences of social support (III). Within Study IV, a prospective longitudinal design, descriptive statistics, non-parametric tests and multiple linear regression analysis were used to evaluate factors associated with quality of couple relationship among first-time mothers and partners, during pregnancy and the first six months of parenthood. Results: The overall results of the thesis revealed both similarities and differences between expectant first-time mothers’ and partners’ perceptions of professional support, effects from social support and associated factors with perceived quality of couple relationship. The similarities were; both mothers and partners perceived that professional support could facilitate partner involvement, influence their couple relationship and facilitate contacts with other expectant parents. According to first-time mothers’ experiences, their couple relationship with their partner was also strengthened by social support during pregnancy. Further, the results showed that both first-time mothers’ and partners’ higher perceived couple relationship quality six months after birth, was associated with their higher perceived social support. The results showed also that both mothers and partners perceived their quality of couple relationship to decrease and Sense of Coherence to increase six months after childbirth, compared to the pregnancy. Differences revealed were such as: higher Sense of Coherence was only associated with mothers’ higher perceived quality of couple relationship, and first-time mothers reported perceiving more social support compared to the partners both during pregnancy, first week and six months after childbirth. Conclusions: Professional and social support can strengthen first-time mothers and partners both individually and as a couple, in their abilities to cope with childbearing. On the individual basis, the expectant parents could be strengthened through professional and social support that contributed to their understanding and feeling of being prepared for childbirth and parenting, for instance. As a couple, the parents were strengthened by professional support that included the partner’s role, as well as higher perceived social support overall. In contrast, lack of support could have a negative influence on the expectant parents’ feeling of being prepared for childbirth and parenting. Besides this, the results indicates that childbearing has a positive effect on parents’ abilities to cope with life even though their quality of couple relationship decrease. Professionals can use these results in their further understanding about how to offer satisfactory support to first-time mothers and partners during childbearing.
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Thomas, Joshua Bryan. "Using the Coherence Function as a Means to Improve Frequency Domain Least Squares System Identification." Ohio University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1166476245.
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Zhao, Xiaowei. "MONITORING RADIOFREQUENCY ABLATION WITH POLARIZATION-SENSITIVE OPTICAL COHERENCE TOMOGRAPHY FOR THE TREATMENT OF ATRIAL FIBRILLATION." Case Western Reserve University School of Graduate Studies / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=case1619825666351729.
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Boussemaere, Luc. "Investigating off-axis digital holographic microscopy with a source of partial spatial coherence as a real-time sensor for cell cultures." Doctoral thesis, Universite Libre de Bruxelles, 2015. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209086.
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Bio-pharmaceutical industry is a vast growing market and recent recommendations of the Food and Drug Administration have put a large emphasis on the characterization of biological processes and models. As a consequence, there is a high incentive on developing modern sensors in order to more accurately monitor and control processes. In that way, Digital Holographic Microscopy (DHM) presents unique features thanks to the refocusing and quantitative phase contrast imaging capabilities. In this thesis we investigate the usage of DHM to monitor yeast cultures that are often used in both the bio-pharmaceutical and bread industries and lay the basis of a methodological framework for the study of in-line cell cultures in the context of process control. We begin with a description of Digital Holography and the microscopy setup used in the thesis as well as a detailed explanation of the image processing required to extract the holographic data and its implementation on GPU with some speed execution figures given for three popular programming paradigms. We then describe the flow setup used and infer the limitations on the dynamic range of the technique due to both Poisson statistics and overlapping phenomena. Finally, we describe an algorithm that extracts the cells position, count and morphological information such as the size, aspect ratio, circularity and refraction index. Some experimental results are presented for yeasts before drawing a general overview of the technology and its dependencies. We further end with some conclusions concerning the technology and a brief comparison with existing competitors.Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
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Muhammad, Rashed D. B. "Assessment of new real-time in-situ optical coherence tomography instrumentation and techniques for diagnosing and monitoring oral and cutaneous lesions." Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1471556/.
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Head and neck cancer is the sixth most common cancer worldwide, with 686,328 new cases per year. Most head and neck cancers are squamous cell carcinomas of the oral cavity and oropharynx, and are burdened by high mortality (50% at 5 years from diagnosis), notwithstanding recent progress in treatment methods. The vast majority of oro-pharyngeal cancers are late diagnosed, with significant adverse effects on cure, morbidity and prognosis. There is general consensus that earlier diagnosis contributes to better outcome measures. Current diagnostic standards consist of clinical examination and surgical biopsy, which are associated with delayed presentation, diagnosis and greater mortality. There is an unmet need for effective diagnostic techniques to aid early identification of cancers. Optical coherence tomography (OCT) is one of a number of non-invasive real-time imaging systems, introduced during the last two decades aiming to provide tissue information similar to conventional histopathological examination. The technique is similar to a B-mode ultrasound section, but employs a scanning near infrared light source rather than ultrasound waves, generating cross-sectional images of the sample tissue in an X-Z orientation. In this study, I investigated a modified OCT oral instrument (VivoSight® Michelson Diagnostics Ltd, Orpington, Kent, UK) with adapted probe for intraoral use. The new oral instrument was not CE marked, was uncalibrated and consequently a non-standard instrument. Therefore, prior to clinical application, the new instrument required calibration and comparison with the conventional instrument to assess and confirm performance in image quality and resolution in X, Y, and Z-planes. A series of laboratory engineering standards were created and compared by scanning with both instruments in X, Y & Z planes. A second series of experiments were conducted using porcine tissue as models for human tissue, confirming the similarities of fact and artefact observable when the two instruments were applied to challenging imaging scenarios, in particular, the effects of dissimilar target tissue refractive indices on the OCT image. The effects (tissue dimensional changes) of fixing samples in formal-incontaining media and tissue processing were also then investigated using this non-invasive measuring technique.
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Jansz, Paul V. "Characterising the effect of a novel optical delay line and light sources on the resolvability of time domain optical coherence tomography." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2015. https://ro.ecu.edu.au/theses/1755.
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Optical coherence tomography (OCT) is a reflection based imaging technique, with numerous applications, initially in medical diagnostics. Unlike ultrasound, another reflection imaging technique, OCT relies on light scattering in samples, low coherence near- infrared interferometry, and graphical image construction, to acquire 2D and 3D reflectogram images. OCT has resolution an order of magnitude greater than ultrasound, but its depth penetration is less than a few millimetres.
Axial resolution is a critical parameter in determining whether OCT can be used to resolve specific features in a sample image. Typically, measures of resolution have been attributed only to the light source’s characteristics, including its coherence length and the FWHM of its frequency spectrum’s inverse FT, or auto-correlogram. The need to cost effectively visualize the OCT-system-generated auto-correlograms, and OCT cross-correlograms (A-scan) (produced using many different OCT light sources), has necessitated the extrinsic-evolution of an OCT simulation model, presented in this thesis. This research indicated that empirical resolution in vivo is also strongly dependent on the optical characteristics of the tissue, including surface reflection. When the surface reflection is removed from the A-scan, the minimum stratum depth that can be resolved for the sub-surface strata, is significantly enhanced. Furthermore, this subtraction enhances the stratum depth resolution, so that it approaches more closely the light source’s resolution limit, compared to A-scans without the subtraction.
The time domain OCT’s optical delay line (ODL) and light source components were also reviewed to determine their affordability and functionality for engineering a portable, high resolution, but simple OCT modality. To this end, a stationary ODL, using a transmissive optical light valve array and a stepped mirrored structure (SMS), was characterised in ‘proof of principle’ experiments. Unfortunately, fabrication of the SMS, using four affordable techniques, proved unsuccessful; however, more promising techniques, based on the theoretical developments in this thesis, are envisaged. A stochastic pseudo-genetic algorithm (GAM), similar, but not exactly analogous to theoretical genetic intrinsic-evolution, was characterised and used to backwards-fit the solution set of strata depths and reflectivities of a selected OCT A-scan. Unfortunately, its speed in Matlab was not timely enough for e-medical application – though in c this GAM could run faster. This slowness is due to the GAM’s stochastic nature, prompting future investigation of other GAMs, which will eliminate the stochastic element so that more timely results can be achieved.
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Kinnunen, M. (Matti). "Comparison of optical coherence tomography, the pulsed photoacoustic technique, and the time-of-flight technique in glucose measurements in vitro." Doctoral thesis, University of Oulu, 2006. http://urn.fi/urn:isbn:9514281462.
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Abstract
The development of a non-invasive glucose monitoring technique is very important because it would tremendously diminish the need to puncture the skin when taking blood samples and help diabetic patients in controlling their blood glucose levels and in treating Diabetes Mellitus. The focus of this thesis is on measuring the effect of glucose on the light scattering properties of a tissue-simulating phantom and biological tissues in vitro. Optical coherence tomography (OCT), the pulsed photoacoustic (PA) technique, and the time-of-flight (TOF) technique are used in the measurements and their capabilities for detecting changes in the scattering properties are evaluated and compared with each other. The theoretical background of the techniques, light propagation and PA wave generation are briefly explained. The glucose-induced changes in light scattering are also reviewed.
The measurement results with the OCT and the PA technique from Intralipid, pig whole blood, and mouse skin tissue samples show that the glucose-induced changes are larger in the biological tissues than in the Intralipid phantom. The PA measurements show that although the PA signals are stronger at a wavelength of 532 nm than at 1064 nm, the glucose-induced change in the peak-to-peak value of the PA signal measured from pig whole blood is larger at a wavelength of 1064 nm than at 532 nm. The TOF measurements with a streak camera show that the scattering-related changes in the registered pulse shapes occur mainly in the rising part of the pulses. The utilization of fiber-optic measurement heads enabled the detection of back-scattered photons at different distances from the emitting fiber.
Although all the techniques are able to detect changes induced by large glucose concentrations (0–5000 mg/dl) in Intralipid, the effect of glucose on the scattering properties of Intralipid is so weak that the techniques failed to detect changes with lower (50–500 mg/dl) concentrations. The measurements of biological samples with the PA technique and with the OCT also demonstrate capabilities to measure glucose concentrations in the physiologically relevant range (18–450 mg/dl) as well. The results compare well with earlier literature and also confirm some earlier findings.
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Jakubisin, Daniel J. "Array Processing for Mobile Wireless Communication in the 60 GHz Band." Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/31130.
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In 2001, the Federal Communications Commission made available a large block of spectrum known as the 60 GHz band. The 60 GHz band is attractive because it provides the opportunity of multi-Gbps data rates with unlicensed commercial use. One of the main challenges facing the use of this band is poor propagation characteristics including high path loss and strong attenuation due to oxygen absorption. Antenna arrays have been proposed as a means of combating these effects. This thesis provides an analysis of array processing for communication systems operating in the 60 GHz band. Based on measurement campaigns at 60 GHz, deterministic modeling of the channel through ray tracing is proposed. We conduct a site-specific study using ray tracing to model an outdoor and an indoor environment on the Virginia Tech campus. Because arrays are required for antenna gain and adaptability, we explore the use of arrays as a form of equalization in the presence of channel-induced intersymbol interference. The first contribution of this thesis is to establish the expected performance achieved by arrays in the outdoor environment. The second contribution is to analyze the performance of adaptive algorithms applied to array processing in mobile indoor and outdoor environments.Master of Science
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Roden, John S., James A. Johnstone, and Todd E. Dawson. "Regional And Watershed-Scale Coherence In The Stable-Oxygen and Carbon Isotope Ratio Time Series in Tree Rings Of Coast Redwood (Sequoia Sempervirens)." Tree-Ring Society, 2011. http://hdl.handle.net/10150/622643.
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Coast redwood (Sequoia sempervirens) ecosystems are strongly influenced by the presence of
summer marine fog, and variation in fog frequency is closely linked to climate variation in the NE Pacific region. Because oxygen isotope composition (𝛿¹⁸O) of organic matter records distinct water sources (e.g. summertime fog vs. winter precipitation) and carbon isotopes (𝛿¹³C) are typically sensitive to humidity and water status, it then follows that inter-annual variation in tree-ring isotope ratios, which are coherent across multiple sites, should preserve a potentially powerful proxy for climate reconstruction. Here we present an analysis of a 50-year time series for both 𝛿¹⁸O and 𝛿¹³C values from subdivided tree rings obtained from multiple redwood trees at multiple sites. Within-site and between site correlations were highly significant (p < 0.01) for the 𝛿¹⁸O time series indicating a regionally coherent common forcing of 𝛿¹⁸O fractionation. Within-site and between-site correlation coefficients were lower for the 𝛿¹³C than for the 𝛿¹⁸O time series although most were still significant (at least to p < 0.05). The hypothesized reason for the differences in the correlation is that carbon isotope discrimination is more sensitive to microenvironmental and tree-level physiological variation than is 𝛿¹⁸O fractionation. Stable-isotope variation in tree-ring cellulose was similar between slope, gully and riparian micro-habitats within a single watershed, implying that minor topographic variation when sampling should not be a major concern. These results indicate that stable-isotope time series from
redwood tree rings are strongly influenced by regional climate drivers and potentially valuable proxies for Pacific coastal climate variability.
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Harris, John. "Structural coherence in early anthologies of French prose short stories : a study of the unframed collections compiled at the time of François I." Thesis, Royal Holloway, University of London, 1987. http://repository.royalholloway.ac.uk/items/2e430c40-9caa-4261-a000-45303faea6b4/1/.
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Four anthologies of sixteenth-century French prose contes are examined, with the aim of elucidating the processes which informed their compilation and the reading strategies which they imply, and the relationship between the structural coherence of unframed anthologies and that of collections incorporating a frame-story structure.'Framed' collections and their structures have served as the yardstick against which unframed anthologies have been measured, and judged to be loose compilations whose component tales may be read in any order. Though the view of framed collections implied by this comparison may also be questioned, this study con-centrates on the structural aspects of four anthologies - those by Philippe de Vigneulles and Bonaventure Des P6riers, and the anonymous Parangon de Nouvelles and Parolles Joyeuses - while yet noting the major points of similarity and dissimilarity with framed collections. Evidence for the methods of construction involved and for the reading strategies which were envisaged are sought in the prolegomena, and in the general or particular structural ties made explicit or especially prominent in the stories. This search is extended through a survey of the deeper and implicit levels of consonance between stories, where related elements may be considered to have played an important part in thejuxtaposition of particular narratives or the construction of the whole text and may also influence the ways in which they will be read. Finally, the closure of each anthology is examined and the contribution of its terminal structures evaluated. The evidence of the features identified and classified leads to the conclusion that in each anthology there is a strong linear structure which, while it cannot prevent other reading strategies, encourages a predominantly sequential approach to the stories.
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Avena, Anna. "Analyzing brain connectivity of disorder of consciousness patients with a multi-variate, time-dependent and adaptive arma model." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/20409/.
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Nell'ambito delle neuroscienze vengono effettuati sempre più studi al fine di comprendere meglio le reti cerebrali e le loro dinamiche. La comunità scientifica ha condotto numerosi studi ed esperimenti sulle normali funzioni cerebrali umane, ma solo recentemente un discreto numero di ricercatori ha rivolto la propria attenzione all'analisi di diversi disturbi cerebrali, tra cui i disturbi della coscienza (Disorders of Consciousness o DoC).
Un DoC è uno stato in cui viene meno la capacità psichica e cognitiva della persona e quest'ultima non mostra segni di veglia e/o di consapevolezza.
Questa tesi mira a sviluppare un modello che consente di analizzare la connettività neurale tra le diverse aree cerebrali e fare inferenze sullo stato dei pazienti affetti da DOC al fine di supportare e affiancare gli attuali criteri diagnostici e migliorare così il processo decisionale medico.
L'approccio utilizzato per raggiungere questo obiettivo si basa sul concetto di causalità di Granger (G-causality). Questo metodo permette l'identificazione delle interazioni causali all'interno del cervello e può essere tracciato attraverso un modello autoregressivo a media mobile (ARMA) basato sull'algoritmo delle trasformazioni di Fourier (FT).
In particolare, in questa tesi è stata implementata una peculiare normalizzazione della G-causality denominata coerenza parziale diretta (PDC).
La PDC mira a stimare la connettività tra coppie di neuroni e i risultati mostrano quanto siano forti tali connessioni, permettendo così l'identificazione di pattern e la comparazione fra i diversi stati tipici dei disturbi della coscienza.
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Stevens, Christopher E. "Study of Transition Metal Dichalcogenides Via Linear and Non-Linear Spectroscopy." Scholar Commons, 2019. https://scholarcommons.usf.edu/etd/7955.
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Beginning with the discovery of graphene, two-dimensional materials have amassed a strong interest. Like graphene, transition metal dichalcogenides (TMDs) can be coaxed into atomically thin sheets which have some impressive properties. Unlike graphene, TMDs also has a change in their electronic band structure causing an indirect band gap to a direct gap transition in its monolayer form. Additionally, these materials lose their inversion symmetry as a monolayer. These unique properties make TMDs a strong candidate for being used in optoelectronic and valleytronic devices. In order for these devices to be successful, the optical properties of TMDs must be thoroughly understood. Due to this class of material's strong Coulomb interaction, the optical properties are dominated by excitons, a quasiparticle made up of an electron-hole pair. Therefore, the success of these devices relies, in part, on understanding and manipulating excitons. One key parameter of excitons is their dephasing rate which characterizes the lifetime of the coherent superposition of two states (i.e. how the coherence decays which is caused by excitons interacting with their environment). In this work, two optical properties are investigated: (1) How the linear absorption of the TMDs A-exciton peak varies as the material increases in thickness. By looking at how the absorption varies by sample thickness, the interaction between emitters can be understood. Experimental results for the diamagnetic shift are presented which are used to determine the lateral excitonic size. Through theoretical calculations, based on the semiconductor Maxwell-Bloch equations, additional insight into the radiative coupling of the systems are obtained. (2) How the coherence prole of the exciton changes in the presence of an external magnetic eld and specic valley excitation. By varying the polarization scheme in the four wave mixing measurement, specic valley excitation can be selected, allowing for insight into the dephasing mechanisms. By applying an external magnetic eld, the energy levels of the electron and hole can be discretized and the corresponding eects on the system's coherence seen. In conjunction with time-dependent density function theory calculations and the experimental results, a deeper understanding of exciton dynamics and multi-exciton complexes was obtained. Finally, a new system is proposed in which complex spectroscopic techniques can be performed on micron sized samples as well as devices in the presence of an external magnetic eld at cryogen temperatures. This system will allow for the investigation of the optical properties of stacked monolayers (heterostructures) as well as devices.
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Maraun, Douglas. "What can we learn from climate data? : Methods for fluctuation, time/scale and phase analysis." Phd thesis, [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=981698980.
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Klimeš, Petr. "Stanovení vzájemných vazeb mezi mozkovými strukturami." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2017. http://www.nusl.cz/ntk/nusl-263416.
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The Human brain consists of mutually connected neuronal populations that build anatomically and functionally separated structures. To understand human brain activity and connectivity, it is crucial to describe how these structures are connected and how information is spread. Commonly used methods often work with data from scalp EEG, with a limited number of contacts, and are incapable of observing dynamic changes during cognitive processes or different behavioural states. In addition, connectivity studies almost never analyse pathological parts of the brain, which can have a crucial impact on pathology research and treatment. The aim of this work is connectivity analysis and its evolution in time during cognitive tasks using data from intracranial EEG. Physiological processes in cognitive stimulation and the local connectivity of pathology in the epileptic brain during wake and sleep were analysed. The results provide new insight into human brain physiology research. This was achieved by an innovative approach which combines connectivity methods with EEG spectral power calculation. The second part of this work focuses on seizure onset zone (SOZ) connectivity in the epileptic brain. The results describe the functional isolation of the SOZ from the surrounding tissue, which may contribute to clinical research and epilepsy treatment.
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Takahashi, Daniel Yasumasa. "Medidas de fluxo de informação com aplicação em neurociência." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/95/95131/tde-07062011-115256/.
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Inferência da força de interação nos fenômenos físicos/biológicos é objetivo comum a diversas áreas da ciência. Em particular, nas neurociências tem-se assistido a uma mudança no paradigma experimental em que a atenção tem-se voltado à compreensão da interação entre grupamentos neuronais. Em vista desta demanda surgiram naturalmente diversos métodos estatísticos de medida de dependência entre grupamentos neurais. Alguns foram desenhados para inferência de fluxo de informação, sem contudo precisar o que se entende por fluxo de informação, gerando consequentemente controvérsias na literatura. O principal objetivo deste trabalho é aplicar os conceitos da Teoria da Informação na análise de processos estacionários de segunda ordem para precisar as idéias de fluxo de informação utilizadas na literatura de forma ad hoc e obter um melhor entendimento da relação existente entre as diferentes medidas de dependência propostas.We study the relationship between different measures of causality or information flow. We show that the concept of partial measures of dependence are related to the definition of inverse random variables.
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Pyon, Okmin. "The data processing to detect correlated movement of Cerebral Palsy patient in early phase." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/64776.
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The early diagnosis of CP (Cerebral Palsy) in infants is important for developing meaningful interventions. One of the major symptoms of the CP is lack of the coordinated movements of a baby. The bilateral coordinated movement (BCM) is that a baby shows in the early development stage. Each limb movement shows various ranges of speed and angle with fluency in a normal infant. When a baby has CP the movements are cramped and more synchronized.
A quantitative method is needed to diagnose the BCM. Data is collected from 3-axis accelerometers, which are connected, to each limb of the baby. Signal processing the collected data using short time Fourier transforms, along with the formation of time-dependent transfer functions and the coherence property is the key to the diagnostic approach. Combinations of each limb's movement and their relationship can represent the correlated movement. Data collected from a normal baby is used to develop the technique for identifying the fidgety movement. Time histories and the resulting diagnostic tool are presented to show the regions of the described movement. The evaluation of the transduction approach and the analysis is discussed in detail.
The application of the quantitative tool for the early diagnosis of CP offers clinicians the opportunity to provide interventions that may reduce the debilitating impact this condition has on children. Tools such as this can also be used to assess motor development in infants and lead to the identification and early intervention for other conditions.Master of Science
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Khoshnavaz, Mohammad Javad. "Coherency based time-domain imaging algorithms." Thesis, Curtin University, 2016. http://hdl.handle.net/20.500.11937/54048.
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Seismic time-domain imaging is one of the most robust tools in seismic data processing. Compared with depth imaging, time-domain imaging employs a reduced number of parameters by taking effective approximations for wave propagation in the subsurface. Accurate time-domain seismic imaging as applied in very complex environments (e.g., hard rock environments) requires a novel critical thinking. In this thesis, several efficient time-domain imaging techniques have been developed and successfully applied to different seismic data sets.
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Gustafsson, Amanda, and Pia Lindgren. "Faktorer för att upprätthålla psykosocial hälsa : -en studie utifrån socialsekreterares egna upplevelser." Thesis, Linnéuniversitetet, Institutionen för socialt arbete (SA), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-29595.
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Research on psychosocial health in social work isn't developed enough. Instead, there's much more research on psychosocial unhealth. What about social workers, the unhealth is often related to the situation at work and the work environment. The aim of this study was to "during interviews understand the factors which social workers experience as important to maintain their own psychosocial health in the life situations". With hermeneutic method the particular interest was directed on how the participants experienced and explained their psychosocial health on the basis of their life situations, and the results was analyzed with Antonovsky's (1991/2005) perspective directed on health and Sense of Coherence (SOC). In the study, we used a qualitative form of interviews which allowed our participants to answer with their own words and from how they interpreted the questions. We have made interviews with eight social workers in a average municipality in Sweden. The results are shown qualitatively in current text. With our interest in social workers´ psychosocial health, we have understood that it's complicated to make a partition line between the life at work and the private life when it comes to the social workers´ experiences of factors that helps to maintain psychosocial health. Instead, it's about to understand the social worker's psychosocial health as a whole, on the basis of the work as well as the private life. In comparison to research on psychosocial unhealth, our participants said that it's especially the private life, rather than the life at work, that influences and sometimes even controls the psychosocial health in general. Nevertheless, there were plural factors at work which were experienced as especially important to maintain the psychosocial health, for example a "good director", "good colleagues", "ability to let go of the liability for clients" and a working situation where you "work two together" plus "experience and knowledge" from the whole life situations. In private life, and in addition to work, the experiences were about "enriching leisure time", social support from friends and family and the ability to make "reasonable demands and limits for yourself" in private life as well as at work.
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Lopes, Kim Samejima Mascarenhas. "Directed wavelet covariance for locally stationary processes." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/45/45133/tde-14032018-174950/.
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The main goal of this study is to propose a methodology that measures directed relations between locally stationary processes. Unlike stationary processes, locally stationary processes may present sudden pattern changes and have local characteristics in specific intervals. This behavior causes instability in measures based on Fourier transforms. The relevance of this study relies on considering these processes and propose robust methodologies that are not affected by outliers, sudden pattern changes or local behavior. We start reviewing the Partial Directed Coherence (PDC) and the Wavelet Coherence. PDC measures the directed relation between components of a multivariate stationary Vector Autoregressive (VAR) model in the frequency domain, while Wavelet Coherence is based on complex wavelets decomposition. We then propose a causal wavelet decomposition of the covariance structure for bivariate locally stationary processes: the Directed Wavelet Covariance (DWC). Compared to Fourier-based quantities, wavelet-based estimators are more appropriate for non-stationary processes and processes with local patterns, outliers and rapid regime changes like in EEG experiments with the introduction of stimuli. We then propose its estimators and calculate its expectation and analyze its variance. Next we propose a decomposition for the variance of multivariate processes with more than two components: the Partial Directed Wavelet Covariance (pDWC). Considering a N-variate locally stationary process, the pDWC calculates the Directed Wavelet Covariance of X_1(t) with X_2(t) eliminating the effect of the other components X_3(t), ... ,X_N(t). We propose two approaches to this situation. First we filter the multivariate process to remove all the exogenous influences and then we calculate the directed relation between the components. In the second case, as in Partial Directed Coherence, we consider the multivariate process as a time-varying Vector Autoregressive Model (tv-VAR) and use its coefficients in the decomposition of the covariance function to isolate the effects of the other components. We also compare results of the PDC, Wavelet Coherence and Directed Wavelet Covariance with simulated data. Finally, we present an application of the proposed Directed Wavelet Covariance and Partial Directed Wavelet Covariance on EEG data. Simulation results show that the proposed measures capture the simulated relations. The pDWC with linear filter has shown more stable estimations than the proposed pDWC considering the tv-VAR. Future studies will discuss the DWC\'s and pDWC\'s asymptotic distributions and significance tests. The proposed Directed Wavelet Covariance decomposition is a different approach to deal with non-stationary processes in the context of causality. The use of wavelets is a gain and adds to the number of studies that can be addressed when Fourier transform does not apply. The pDWC is an alternative for multivariate processes and it removes linear influences from observed external components.O objetivo deste trabalho é propor uma metodologia para mensurar o impacto direcionado entre processos localmente estacionários. Diferente de processos estacionários, processos localmente estacionários podem apresentar mudanças bruscas e características específicas em determinados intervalos. Tal comportamento pode causar instabilidade em medidas baseadas na transformada de Fourier. A importância deste estudo se dá em englobar processos com tais características, propondo metodologias robustas que não são afetadas pela existência de mudanças bruscas, pontos discrepantes e comportamentos locais. Inicialmente apresentamos conceitos já existentes na literatura, como a Coerência Parcial Direcionada (PDC) e a Coerência de Ondaletas. A PDC mede o impacto direcionado entre componentes de um modelo vetorial autoregressivo (VAR) no domínio da frequência. A coerência de ondaletas é baseada em transformadas complexas de ondaletas. Propomos então uma decomposição no domínio de ondaletas para a estrutura de covariância de processos bivariados localmente estacionários: a Covariância Direcionada de Ondaletas (DWC). Em comparação com as quantidades baseadas na tranformada Fourier, os estimadores baseados em ondaletas são mais apropriados para processos não estacionários com padrões locais, pontos discrepantes ou mudanças rápidas de regime, como em experimentos de eletroencefalograma (EEG) com a introdução de estímulo. Ainda, propomos um estimador para a DWC, calculamos a esperança deste estimador e avaliamos sua variância. Em seguida, propomos uma quantidade análoga à DWC para processos multivariados com mais de duas componentes: a Covariância Parcial Direcionada de Ondaletas (pDWC). Considerando um processo N-variado localmente estacionário, a pDWC calcula a Covariância Direcionada de Ondaletas entre X_1(t) e X_2(t) eliminando o efeito das outras componentes X_3(t), ... , X_N(t). Propomos duas abordagens para a pDWC: na primeira, a pDWC é calculada após a aplicação de um filtro linear que remove o efeito das variáveis exógenas. No segundo caso, a exemplo da Coerência Parcial Direcionada, consideramos o processo multivariado como um Modelo Autoregressivo de Vetorial variante no tempo (tv-VAR) e usamos seus coeficientes na decomposição da função de covariância para isolar os efeitos das demais componentes. Também comparamos os resultados da PDC, Coerência de Ondaletas e Covariância Direcionada de Ondaletas com dados simulados. Por fim, apresentamos uma aplicação da DWC e da pDWC em dados de EEG. Identificamos nas simulações que tanto as medidas já existentes na literatura quanto as quantidades propostas identificaram as relações simuladas. A pDWC proposta com filtros lineares apresentou estimações mais estáveis do que a pDWC considerando os modelos tv-VAR. Estudos futuros discutirão as propriedades assintóticas e testes de significância da DWC e pDWC.
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García, Arellano Guadalupe. "Influence of the concentration and temperature on the spin relaxation time of donor-bound electrons immersed in a CdTe quantum well." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS109.
Full textAbstract:
Ce travail présente une étude de l'influence de la concentration de dopage, de la température et du champ magnétique longitudinal sur le temps de relaxation de spin des électrons liés aux donneurs immergés au milieu d'un puits quantique (PQ) de CdTe. En insérant les donneurs dans un PQ, les règles de sélection optique de la lumière polarisée circulairement sont purifiées, ce qui permet un meilleur degré d'orientation optique des spins des électrons que dans les cristaux 3D. En utilisant une technique de rotation Faraday photo-induite, nous mesurons d’abord le temps de relaxation de spin des électrons liés aux donneurs pour différentes concentrations de dopage à basse température dans le régime isolant. Ensuite, pour évaluer les mécanismes de relaxation de spin dans notre système, nous calculons l'énergie d'échange d'une paire d'électrons liés aux donneurs immergés au milieu d'un PQ infini, pour toute distance inter-donneur et différentes épaisseurs. En utilisant ce calcul, nous expliquons le comportement expérimental comme une interaction de deux mécanismes : l’interaction hyperfine et l’anisotrope d’échange. De plus, nous déterminons la constante spin-orbite dans CdTe αso = 0.079. Ensuite, nous présentons le développement d’une expérience pompe-sonde étendue permettant de mesurer les temps de relaxation de spin à l’échelle microseconde. Nous discutons brièvement des premiers résultats expérimentaux pour le temps de relaxation de spin longitudinal d'électrons liés aux donneurs immergés dans un PQ de CdTe avec différentes concentrations de dopage. Enfin, nous étudions l'évolution en température de la relaxation de spin de 10 à 80 K. On explique le comportement expérimental en invoquant l'échange de spin entre les électrons localisés et le spin d'électrons promus en états de conduction. Le spin des électrons localisés subit l’effet des interactions hyperfine et anisotrope, le mécanisme de D’yakonov-Perel’ régit la relaxation de spin des électrons de conductionThis work presents a study of the influence of doping concentration, temperature and longitudinal magnetic field on the spin relaxation time of donor-bound electrons immersed in the middle of a CdTe quantum well (QW). By inserting the donors in a QW, the optical selection rules for circularly polarized light are purified, allowing a higher degree of optical orientation of the electron spins than in 3D crystals. By using a photo-induced Faraday rotation technique, we first measure the spin relaxation time of donor-bound electrons for different doping concentrations at low temperature in the insulating regime. Then, in order to evaluate the spin relaxation mechanisms in our system, we calculate the exchange energy of a pair of donor-bound electrons immersed in the middle of an infinite QW, for any inter-donor distance and for different thicknesses. By using this calculation, we explain the experimental behavior as an interplay of two mechanisms: hyperfine and anisotropic exchange interactions. Moreover we determine the CdTe spin-orbit constant: αso = 0.079. Afterwards we present the development of an extended pump-probe experiment allowing to measure spin relaxation times at the microsecond scale. We briefly discuss the first experimental results for the longitudinal spin relaxation time of donor-bound electrons immersed in a CdTe QW with different doping concentrations. Finally, we investigate the temperature evolution of the spin relaxation in the range 10-80 K. The experimental behavior is explained by invoking spin exchange between electron spins localized on donors and the spin of electrons promoted to conduction states. The spin of localized electrons undergoes the effect of hyperfine and anisotropic exchange interactions, the D’yakonov-Perel’ mechanism governs the spin relaxation of the conduction electrons
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Locquet, Alexandre Daniel. "Chaotic optical communications using delayed feedback systems." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10431.
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Chaotic dynamics produced by optical delay systems have interesting applications in telecommunications. Optical chaos can be used to transmit secretly, in real-time, a message between an emitter and a receiver. The noise-like appearance of chaos is used to conceal the message, and the synchronization of the receiver with the chaotic emitter is used to decode the message. This work focuses on the study of two crucial topics in the field of chaotic optical communications.
The first topic is the synchronization of chaotic external-cavity laser diodes, which are among the most promising chaotic emitters for secure communications. It is shown that, for edge-emitting lasers, two drastically different synchronization regimes are possible. The regimes differ in terms of the delay time in the synchronization and in terms of the robustness of the synchronization with respect to parameter mismatches between the emitter and the receiver. In vertical-cavity surface-emitting lasers, the two linearly-polarized components of the electric field also exhibit isochronous and anticipating synchronization when the coupling between the lasers is isotropic. When the coupling is polarized, the linearly-polarized component that is parallel to the injected polarization tends to synchronize isochronously with the injected optical field, while the other component tends to be suppressed, but it can also be antisynchronized.
The second topic is the analysis of time series produced by optical chaotic emitters subjected to a delayed feedback. First, we verify with experimental data that chaos produced by optical delay systems is highly complex. This high complexity is demonstrated by estimating chaos dimension and entropy from experimental time series and from models of optical delay systems. Second, by analyzing chaotic time series, it is shown that the value of the delay of a single-delay system can always be identified, independently of the type of system used and of its complexity. Unfortunately, an eavesdropper can use this information on the delay value to break the cryptosystem. We propose a new cryptosystem with two delayed feedback loops that increases the difficulty of the delay identification problem.
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Silva, Tiago Sanches da. "Plataforma de estudo para determinação de conectividade cerebral embarcada e em tempo real." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/3/3142/tde-30062016-075729/.
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A presente dissertação examina um método de determinação da conectividade cerebral cujo uso vem se tornando popular nos últimos anos, o partial direct coherence (PDC), que se destaca dentre outros métodos por possibilitar a verificação das relações imediatas de sinais multivariados. Este método representa a conectividade cerebral no domínio da frequência e tem íntima relação com a noção de \"causalidade\" de Granger (GRANGER, 1969), que possibilita quantificar a influência mútua entre séries temporais observadas. De um ponto de vista computacional, o referido método faz uso de modelos de séries temporais que hoje têm implementação bastante eficiente em termos de algoritmos off-line, mas cujo sucesso depende da presunção de estacionariedade dos dados, fato que é somente verdadeiro em trechos relativamente curtos de sinais de origem cerebral, como no caso do EEG (Eletroencefalograma). O objetivo deste trabalho é criar um sistema que calcule o PDC, continuamente, em tempo real e que possua a mesma precisão do método off-line, além de ser uma plataforma de estudos para implementações e testes de métodos de determinação da conectividade neural em tempo real. A plataforma desenvolvida é modular, incentivando futuros trabalhos na mesma, e mostrouse eficaz quanto a precisão numérica dos resultados do cálculo do PDC. As características de tempo real foram atingidas com algumas restrições, que dependem da configuração do usuário e do número de canais que um sinal possui.This thesis examines a method of determination of brain connectivity whose use becomes popular in recent years, the partial direct coherence (PDC) that stands out in comparison with other methods for making possible the verification of immediate relations of multivariate signal. This method represents the brain connectivity in the frequency domain and has a close relationship with the notion of Granger causality (GRANGER, 1969) that makes it possible to quantify the mutual influence between observed time series. From a computational perspective, the above method makes use of time series models, which today has very efficient implementation in terms of off-line algorithm, but whose success depends on presume that the data is stationary, a fact that is only true in relatively short stretches of cerebral signals, especially in the case of EEG. The objective of this thesis is to create a system that calculates the PDC continuously and in real time maintaining the same precision of the off-line method. Furthermore being a research platform for implementations and tests of new methods for determining neural connectivity in real time. The developed platform is modular encouraging future work on it, and was effective in the numerical accuracy of the PDC calculation results. The real time characteristics were achieved with some restrictions that depend of the user configuration and the number of channels that the signal has.
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Fauvet, Maxime. "Mécanismes centraux de contrôle de la motricité saine et altérée : rôle fonctionnel de la dynamique des couplages cortico-musculaires." Thesis, Toulouse 3, 2022. http://www.theses.fr/2022TOU30065.
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Le contrôle de l'activité motrice volontaire est un point de discussion important pour les personnes intéressées par le mouvement des êtres humains et qui est partagé entre le domaine de la biomécanique et celui du contrôle moteur exercé au niveau central. Il existe des théories valides qui modélisent les mécanismes mis en jeu, que ce soit au niveau de l'encéphale, de la moelle épinière ou des muscles, pour les deux approches. Cependant, il manque encore à ce jour une théorie unificatrice qui relierait les différents niveaux d'observation en un modèle global du contrôle moteur. C'est dans l'objectif de contribuer à la construction d'une telle théorie que ce projet de thèse a été réalisé en s'appuyant sur l'analyse de la connectivité entre les différentes structures intervenant dans la réalisation d'un mouvement pour mettre en évidence les communications au sein du réseau moteur. Ainsi, les principaux objectifs de ce travail ont été i) de développer une méthode d'analyse de la dynamique de la connectivité, ii) d'appliquer cette méthode à l'étude de la connectivité fonctionnelle à partir de mouvements du coude chez le sujet sain et le patient AVC et iii) d'approfondir les données issues de la connectivité fonctionnelle par des analyses de la dynamique de la connectivité effective. Ce projet de thèse est donc pluridisciplinaire, en se situant au croisement des neurosciences, de la biomécanique et du traitement du signal. Nos résultats montrent que la méthode développée permet l'analyse de la dynamique de la connectivité dans un contexte de variabilité inter et intra-individuelle importante. L'étude comparée des sujets sains et des patients AVC révèle une altération de la connectivité fonctionnelle entre le cortex moteur et les muscles antagonistes au mouvement chez les patients ainsi que des niveaux variables de connectivité au cours du mouvement. Enfin, le développement des méthodes de connectivité effective et la sélection des différents paramètres à appliquer laissent supposer que leur application permettra d'étudier les sens des différents échanges d'informations qui ont lieu pendant un mouvement. L'ensemble des résultats de ce travail révèle que l'inclusion des analyses de la dynamique de la connectivité peut représenter un apport majeur aux théories du contrôle moteur existantes et peut même servir de base à la constitution d'un modèle dynamique reflétant les communications qui relient les différentes structures impliquées dans la génération d'un mouvementThe control of voluntary movement is a most discussed issue for those people interested in how the human locomotion or other daily acts are controlled and find answers in two apparently separate fields of research: biomechanics on the one hand and motor control on the other. Verified theories, which model some of the mechanisms involved in motor control at either muscles or brain levels, exist in both fields. However, we still miss a unifying theory that would bridge the gap existing between biomechanics and motor control and would offer a model including all levels of observation: from central nervous system to muscle activity. The present work has been actually designed to partly answer this issue: we propose to study the dynamics of communications occurring during a movement between the different nodes of the motor network through connectivity analyses. Hence, we pursued three main goals: i) develop a dynamic analysis of connectivity measures, ii) apply this analysis to the comparison of functional connectivity between healthy subjects and stroke patients performing elbow extensions and iii) complete the previous analyses with effective connectivity studies of the same paradigm. Thus, this is a multidisciplinary work involving neurosciences, biomechanics and signal processing. Our results show that high inter-variability and intra-variability are less influential in connectivity analysis with our method. Compared analyses between healthy subjects and stroke patients reveal a specific alteration of functional connectivity between antagonist muscles and motor cortex in stroke patients and varying levels of connectivity measures during movement. Finally, the development of effective connectivity analyses and the associated parameters selection will allow us to figure out the direction of communications within the motor network during movement. The overall results of this work show that the analyses of connectivity dynamics can complete existing motor control theories and provide a basis for the constitution of a new dynamic model including the communications between the nodes of the motor network involved in movement control and finally reunite biomechanics and motor control
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Duran, Denise, and Julia Ottosson. "Det gemensamma hälsofrämjande arbetet : En studie om hur det hälsofrämjande arbetet kan stärkas genom samverkan mellan elevhälsoteamet och fritidshemmet." Thesis, Högskolan i Gävle, Pedagogik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-32705.
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Syftet med denna studie var att undersöka hur fritidshemmet och skolans elevhälsoteam arbetar utifrån ett hälsofrämjande perspektiv. Det för att synliggöra om ett behov av samverkan mellan fritidshemspersonal och elevhälsoteamet fanns och hur det gemensamma uppdraget kan verka stärkande för det hälsofrämjande uppdraget. Studiens frågeställningar löd: Hur beskrivs samverkan mellan fritidshemmets personal och skolans elevhälsoteam? På vilket sätt kan samverkan mellan fritidshem och elevhälsoteamet bidra till ett gemensamt hälsofrämjande arbete och verksamhet? Studien baserades på en online-enkätundersökning bestående av kvalitativ forskningsmetod med endast öppna frågor av kvalitativ art. Online-enkäten publicerades och distribuerades till 18 personer som var verksamma inom fritidshem samt elevhälsoteam. Av de 13 respondenter som deltog i studien var fem fritidslärare, tre skolkuratorer och fem skolsköterskor. De som deltog i studien arbetar på olika grundskolor i tre medelstora kommuner. Studiens empiri analyserades genom Aaron Antonovskys salutogena perspektiv och känsla av sammanhang (KASAM). Genom tematiserade kategoriseringar utifrån ett nulägesperspektiv och ett framåtsyftande perspektiv, presenterades resultatet. Resultatet synliggjorde brister inom samverkansuppdraget mellan fritidshemmet och elevhälsan samt att det hälsofrämjande arbetet fortfarande är åsidosatt gentemot det tidigare åtgärdsbaserade arbetet. Resultatet visade också en önskan och tes från professionerna om att samverkan mellan dessa parter kan stärka det gemensamma hälsofrämjande arbetet. Slutsatsen visar på att studiens resultat överensstämmer med vad litteratur och forskning framhåller angående om att en samsyn ska finnas för att ett samverkansarbete ska kunna etableras.
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Kaphle, Manindra R. "Analysis of acoustic emission data for accurate damage assessment for structural health monitoring applications." Thesis, Queensland University of Technology, 2012. https://eprints.qut.edu.au/53201/1/Manindra_Kaphle_Thesis.pdf.
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Structural health monitoring (SHM) refers to the procedure used to assess the condition of structures so that their performance can be monitored and any damage can be detected early. Early detection of damage and appropriate retrofitting will aid in preventing failure of the structure and save money spent on maintenance or replacement and ensure the structure operates safely and efficiently during its whole intended life. Though visual inspection and other techniques such as vibration based ones are available for SHM of structures such as bridges, the use of acoustic emission (AE) technique is an attractive option and is increasing in use. AE waves are high frequency stress waves generated by rapid release of energy from localised sources within a material, such as crack initiation and growth. AE technique involves recording these waves by means of sensors attached on the surface and then analysing the signals to extract information about the nature of the source. High sensitivity to crack growth, ability to locate source, passive nature (no need to supply energy from outside, but energy from damage source itself is utilised) and possibility to perform real time monitoring (detecting crack as it occurs or grows) are some of the attractive features of AE technique.
In spite of these advantages, challenges still exist in using AE technique for monitoring applications, especially in the area of analysis of recorded AE data, as large volumes of data are usually generated during monitoring. The need for effective data analysis can be linked with three main aims of monitoring: (a) accurately locating the source of damage; (b) identifying and discriminating signals from different sources of acoustic emission and (c) quantifying the level of damage of AE source for severity assessment.
In AE technique, the location of the emission source is usually calculated using the times of arrival and velocities of the AE signals recorded by a number of sensors. But complications arise as AE waves can travel in a structure in a number of different modes that have different velocities and frequencies. Hence, to accurately locate a source it is necessary to identify the modes recorded by the sensors. This study has proposed and tested the use of time-frequency analysis tools such as short time Fourier transform to identify the modes and the use of the velocities of these modes to achieve very accurate results. Further, this study has explored the possibility of reducing the number of sensors needed for data capture by using the velocities of modes captured by a single sensor for source localization.
A major problem in practical use of AE technique is the presence of sources of AE other than crack related, such as rubbing and impacts between different components of a structure. These spurious AE signals often mask the signals from the crack activity; hence discrimination of signals to identify the sources is very important. This work developed a model that uses different signal processing tools such as cross-correlation, magnitude squared coherence and energy distribution in different frequency bands as well as modal analysis (comparing amplitudes of identified modes) for accurately differentiating signals from different simulated AE sources.
Quantification tools to assess the severity of the damage sources are highly desirable in practical applications. Though different damage quantification methods have been proposed in AE technique, not all have achieved universal approval or have been approved as suitable for all situations. The b-value analysis, which involves the study of distribution of amplitudes of AE signals, and its modified form (known as improved b-value analysis), was investigated for suitability for damage quantification purposes in ductile materials such as steel. This was found to give encouraging results for analysis of data from laboratory, thereby extending the possibility of its use for real life structures.
By addressing these primary issues, it is believed that this thesis has helped improve the effectiveness of AE technique for structural health monitoring of civil infrastructures such as bridges.
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Camp, Howard Alan. "Measurements of the time evolution of coherent excitation." Diss., Manhattan, Kan. : Kansas State University, 2005. http://hdl.handle.net/2097/73.
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Sugiura, Shinya. "Coherent versus non-coherent space-time shift keying for co-located and distributed MIMO systems." Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/165759/.
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In this thesis, we propose the novel Space-Time Coding (STC) concept of Space-Time Shift Keying (STSK) and explore its characteristics in the contexts of both co-located and cooperative Multiple-Input Multiple-Output (MIMO) systems using both coherent and non-coherent detection. Furthermore, we conceive new serially-concatenated turbo-coding assisted STSK arrangements for the sake of approaching the channel capacity limit, which are designed with the aid of EXtrinsic Information Transfer (EXIT) charts. The basic STSK concept is first proposed for the family of co-located MIMO systems employing coherent detection. More specifically, in order to generate space-time codewords, these Coherent STSK (CSTSK) encoding schemes activate one out of Q dispersion matrices. The CSTSK scheme is capable of striking an attractive tradeoff between the achievable diversity gain and the transmission rate, hence having the potential of outperforming other classic MIMO arrangements. Since no inter-channel interference is imposed at the CSTSK receiver, the employment of single-stream-based Maximum Likelihood (ML) detection becomes realistic. Furthermore, for the sake of achieving an infinitesimally low Bit-Error Ratio (BER) at low SNRs, we conceive a three-stage concatenated turbo CSTSK scheme. In order to mitigate the effects of potential Channel State Information (CSI) estimation errors as well as the high pilot overhead, the Differentially-encoded STSK (DSTSK) philosophy is conceived with the aid of the Cayley transform and differential unitary space-time modulation. The DSTSK receiver benefits from low-complexity non-coherent single-streambased ML detection, while retaining the CSTSK scheme’s fundamental benefits. In order to create further flexible STSK architecture, the above-mentioned co-located CSTSK scheme is generalized so that P out of Q dispersion matrices are activated during each space-time block interval. Owing to its highly flexible structure, this generalized STSK scheme subsumes diverse other MIMO arrangements. Finally, the STSK concept is combined with cooperative MIMO techniques, which are capable of attaining the maximum achievable diversity gain by eliminating the undesired performance limitations imposed by uncorrelated fading. More specifically, considering the usual twin-phase cooperative transmission regime constituted by a broadcast phase and by a cooperative phase, the CSTSK and DSTSK schemes developed for co-located MIMO systems are employed during the cooperative transmission phase.
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Jerebtsov, Serguei Nikolaevich. "Femtosecond time-resolved spectroscopy of coherent oscillations in nanomaterials." [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1358.
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Pestov, Dmitry Sergeyevich. "Detection of bacterial endospores by means of ultrafast coherent raman spectroscopy." Texas A&M University, 2008. http://hdl.handle.net/1969.1/85958.
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This work is devoted to formulation and development of a laser spectroscopic technique
for rapid detection of biohazards, such as Bacillus anthracis spores. Coherent anti-Stokes
Raman scattering (CARS) is used as an underlying process for active retrieval of
species-specific characteristics of an analyte. Vibrational modes of constituent molecules
are Raman-excited by a pair of ultrashort, femtosecond laser pulses, and then probed
through inelastic scattering of a third, time-delayed laser field.
We first employ the already known time-resolved CARS technique. We apply it
to the spectroscopy of easy-to-handle methanol-water mixtures, and then continue
building our expertise on solutions of dipicolinic acid (DPA) and its salts, which happen
to be marker molecules for bacterial spores. Various acquisition schemes are evaluated,
and the preference is given to multi-channel frequency-resolved detection, when the
whole CARS spectrum is recorded as a function of the probe pulse delay. We
demonstrate a simple detection algorithm that manages to differentiate DPA solution
from common interferents. We investigate experimentally the advantages and
disadvantages of near-resonant probing of the excited molecular coherence, and finally
observe the indicative backscattered CARS signal from DPA and NaDPA powders. The possibility of selective Raman excitation via pulse shaping of the preparation pulses is
also demonstrated.
The analysis of time-resolved CARS experiments on powders and B. subtilis
spores, a harmless surrogate for B. anthracis, facilitates the formulation of a new
approach, where we take full advantage of the multi-channel frequency-resolved
acquisition and spectrally discriminate the Raman-resonant CARS signal from the
background due to other instantaneous four-wave mixing (FWM) processes. Using
narrowband probing, we decrease the magnitude of the nonresonant FWM, which is
further suppressed by the timing of the laser pulses. The devised technique, referred to as
hybrid CARS, leads to a single-shot detection of as few as 104 bacterial spores, bringing
CARS spectroscopy to the forefront of potential candidates for real-time biohazard
detection. It also gives promise to many other applications of CARS, hindered so far by
the presence of the overwhelming nonresonant FWM background, mentioned above.
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Charissou, Camille. "Etude de la contribution du couplage intermusculaire au contrôle de l’activité des muscles synergistes agonistes et antagonistes lors de contractions isométriques volontaires." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0122/document.
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Le corps humain possède une grande redondance musculo-squelettique, se traduisant par une infinité de coordinations musculaires possibles pour produire un effort résultant. Lors d'un mouvement, le système nerveux central est confronté à la gestion de cette redondance. A travers l’analyse de cohérence entre les signaux électromyographiques, ce travail de thèse étudie le rôle fonctionnel du couplage intermusculaire et explore la contribution des mécanismes nerveux impliqués dans la régulation de la redondance musculaire en termes de contrôle de l’activité des muscles agonistes, et antagonistes impliqués dans le phénomène de co-contraction. Nos résultats ont révélé que le couplage intermusculaire entre deux muscles agonistes est modulé en présence de fatigue et en fonction de l’expertise sportive. De plus, le couplage entre muscles agonistes et antagonistes dépend des contraintes mécaniques et du rôle fonctionnel des muscles, et semble directement lié au niveau de co-contraction. La cohérence intermusculaire est modulée dans plusieurs bandes de fréquence, témoignant de l’implication de différentes commandes centrales communes d’origines spinales et supra-spinales. Nos conclusions amènent à penser que la coordination musculaire est en partie contrôlée par des commandes nerveuses communes dont la contribution est modulée suivant les propriétés fonctionnelles des muscles concernées, pour s’adapter de manière optimale aux contraintes internes ou externes de la tâche. Les travaux déjà engagés proposent de contribuer à une meilleure compréhension des mécanismes sous-jacents l’altération de la fonction motrice chez des patients cérébro-lésésThe human motor system is characterized by high musculoskeletal redundancy, implying that a given resultant effort can result from infinity of feasible muscle coordinations. During a movement, the central nervous system has to manage such redundancy. Through coherence analysis between electromyographic signals, this thesis work aims at investigating the functional role of intermuscular coupling and at better understanding the contribution of central nervous mechanisms responsible for the regulation of muscle redundancy, in terms of agonist muscle activity and also antagonist muscles activity involved in co-contraction. Our results revealed that intermuscular coupling between agonist muscles is modulated according to both the fatigue level and the training status. We also showed that the coupling between agonist and antagonist muscles depends on the mechanical configuration and functional role of muscle pairs, and seems directly related to co-contraction. The modulation of intermuscular coherence occurs in several frequency bands, suggesting the involvement of different common central drives of spinal and supra-spinal origins according to task constraints. Taken together, our results lead us to conclude that common neural drives take part in the control of muscular coordination, with different relative contribution according to the functional properties of recruited muscles, in order to optimally adapt to both internal and external task contraints. Work already undertaken proposes to provide a better understanding of the mechanisms underlying impairment of motor function in brain-injured patients