Thèses : « Spectral Doppler analysis »

1

Fan, Lingke. « Spectral and time-frequency analysis of ultrasonic Doppler signals ». Thesis, University of Leicester, 1994. http://hdl.handle.net/2381/34342.

Texte intégral

Résumé :

Spectral analysis of Doppler signals plays a very important role in non-invasive measurements of blood velocity distributions. Among the various spectral analysis methods available, the fast Fourier transform (FFT) is regarded as a "traditional" spectral analysis tool and is widely used in commercial, clinical, experimental and research equipment. Some drawbacks of this method, however, have imposed limitations on its use in some clinical cases. A numbers of spectral and time-frequency analysis methods have been studied in this dissertation. These include the traditional FFT, the autoregressive (AR) method, the Wigner-Ville distribution (WVD), and the Choi-Williams distribution (CWD). The advantages and disadvantages of each method have been studied and summarised. Efforts have been made to improve the temporal and frequency resolution of the results. New analysis methods such as the WVD and CWD have been interpreted physically, and some of their new properties have been explored. The results have suggested that the heights of the peaks in the AR spectra of narrow-band signals are not necessarily proportional to signal power, and should be used with caution in the context of Doppler signal processing. The results have also shown that it is appropriate to use the WVD or CWD to analyse signals when high temporal resolution is required. In practice, it is easier for the operator to handle the WVD, which usually produces reasonably good results. The above methods have been applied in practice. Considerable software and hardware development has been carried out, and a number of analysers have been implemented for use under different practical conditions. These analysers were also used to compare experimentally the analysis methods mentioned above, and to confirm the results of theoretical analyses. Some of these analysers have found applications in clinical practice.

Styles APA, Harvard, Vancouver, ISO, etc.

2

David, Jean-Yves. « Modern spectral analysis techniques for blood flow velocity and spectral measurements with a 20 MHZ pulsed doppler ultrasound catheter ». Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/17791.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

3

Sukkar, Ibrahim Hassan. « Non-invasive ultrasound Doppler spectral analysis in the assessment of aorto-iliac stenotic disease ». Thesis, Imperial College London, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299172.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

4

Graça, Cristo dos Santos Lopes Ruano Maria da. « Investigation of real-time spectral analysis techniques for use with pulsed ultrasonic Doppler blood flow detectors ». Thesis, Bangor University, 1992. https://research.bangor.ac.uk/portal/en/theses/investigation-of-realtime-spectral-analysis-techniques-for-use-with-pulsed-ultrasonic-doppler-blood-flow-detectors(f184d2a8-bde7-492a-b487-438704d3ea04).html.

Texte intégral

Résumé :

The goals of the work described here were the development of a method of selection of spectral estimation for use with pulsed Doppler ultrasonic blood flow instruments, and the use of this method to select an estimator and its implementation in a form suitable for real-time applications. A study of estimation accuracy of the mean frequency and bandwidth using a number of spectral estimators was carried out. Fourier based, parametric, and, minimum variance estimators were considered. A Doppler signal simulator was developed to allow the accuracy tests required. A method of selection of spectral estimators based on the accuracy of estimation of decisive signal parameters, under the constraint of low computational complexity has been proposed. This novel cost/benefit criterion, allows the possibility of weighting appropriate to estimator (mean frequency and bandwidth) and signal frequency importance (across the range of signal characteristics). For parametric spectral estimators, this criterion may also be used to select model order, leading to lower orders than FPE, AIC and CAT criteria. Its use led to the selection of a 4t' order modified covariance parametric method. A new version of the modified covariance method for spectral estimation of real signals was developed. This was created with a view to the parallel partitioning of the algorithm for parallel implementation on a transputer-based system, using OCCAM. A number of parallel topologies were implemented. Their performance was evaluated considering estimation of a single, and a sequence of Doppler signal segments, revealing the feasibility of these parallel implementations to be achieved in real-time.

Styles APA, Harvard, Vancouver, ISO, etc.

5

Yu, Yonghui. « MODEL STUDIES OF TIME-DEPENDENT DUCTING FOR HIGH-FREQUENCY GRAVITY WAVES AND ASSOCIATED AIRGLOW RESPONSES IN THE UPPER ATMOSPHER ». Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3623.

Texte intégral

Résumé :

This doctoral dissertation has mainly concentrated on modeling studies of shorter period acoustic-gravity waves propagating in the upper atmosphere. Several cases have been investigated in the literature, which are focusing on the propagation characteristics of high-frequency gravity wave packets. The dissertation consists of five main divisions of which each has its own significance to be addressed, and these five chapters are also bridged in order with each other to present a theme about gravity wave ducting dynamics, energetics, and airglows. The first chapter is served as an introduction of the general topic about atmospheric acoustic-gravity waves. Some of the historical backgrounds are provided as an interesting refreshment and also as a motivation reasoning this scientific research for decades. A new 2-D, time-dependent, and nonlinear model is introduced in the second chapter (the AGE-TIP model, acronymically named atmospheric gravity waves for the Earth plus tides and planetary waves). The model is developed during this entire doctoral study and has carried out almost all research results in this dissertation. The third chapter is a model application for shorter period gravity waves ducted in a thermally stratified atmosphere. In spite of mean winds the thermal ducting occurs because ducted waves are fairly common occurrences in airglow observations. One-dimensional Fourier analysis is applied to identify the ducted wave modes that reside within multiple thermal ducts. Besides, the vertical energy flux and the wave kinetic energy density are derived as wave diagnostic variables to better understand the time-resolved vertical transport of wave energy in the presence of multiple thermal ductings. The fourth chapter is also a model application for shorter period gravity waves, but it instead addresses the propagation of high-frequency gravity waves in the presence of mean background wind shears. The wind structure acts as a significant directional filter to the wave spectra and hence causes noticeable azimuthal variations at higher altitudes. In addition to the spectral analysis applied previously the wave action has been used to interpret the energy coupling between the waves and the mean flow among some atmospheric regions, where the waves are suspected to extract energy from the mean flow at some altitudes and release it to other altitudes. The fifth chapter is a concrete and substantial step connecting theoretical studies and realistic observations through nonlinearly coupling wave dynamic model with airglow chemical reactions. Simulated O (1S) (557.7 nm) airglow images are provided so that they can be compared with observational airglow images. These simulated airglow brightness variations response accordingly with minor species density fluctuations, which are due to propagating and ducting nonlinear gravity waves within related airglow layers. The thermal and wind structures plus the seasonal and geographical variabilities could significantly influence the observed airglow images. By control modeling studies the simulations can be used to collate with concurrent observed data, so that the incoherencies among them could be very useful to discover unknown physical processes behind the observed wave scenes.
Ph.D.
Department of Physics
Sciences
Physics PhD

Styles APA, Harvard, Vancouver, ISO, etc.

6

Kahyaoglu, Nazli Deniz. « Spectral And Statistical Analyses Of Experimental Radar Clutter Data ». Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612799/index.pdf.

Texte intégral

Résumé :

The performance of radar detection and imaging systems strongly depends on the characteristics of radar clutter. In order to improve the radar signal processing algorithms, successful analysis and modeling of radar clutter are required. For a successful model of radar clutter, both the spectral and statistical characteristics of the clutter should be revealed. Within the scope of this study, an experimental radar data acquisition system is established to analyze radar clutter. The hardware and the data processing system are first verified using generic signals and then a set of measurements is taken in the open terrain. In this thesis, the limitations and problems encountered during the establishment of the system are explained in detail. The spectral and statistical analyses performed on the recorded data are examined. The temporal and spatial behavior of the measured clutter data are explored. The hypothetical models proposed so far in the literature are tested on the experimental data and the fitting of models to the experimental data is confirmed using various goodness-of-fit tests. Finally, the results of the analyses are interpreted in the light of the radar system parameters and the characteristics of the illuminated terrain.

Styles APA, Harvard, Vancouver, ISO, etc.

7

Marques, Márcia Talita Amorim. « Obtenção da altura da camada limite planetária através da análise espectral do campo de vento do lidar Doppler ». Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-23022018-092958/.

Texte intégral

Résumé :

Este estudo explora a obtenção da altura da camada limite planetária a partir de diferentes métodos e equipamentos, com foco na análise espectral do campo de vento do lidar Doppler. Realizou-se uma campanha de medição por 80 dias com dois lidars Dopplers comerciais com diferentes alcances verticais. Para o lidar com maior alcance vertical e consequetemente uma medida direta da altura da camada limite planetária, foi aplicado o método da variância da razão sinal-ruído e os resultados foram comparados aos valores de altura estimados a partir de dados de radiossondagem através de dois métodos distintos, o método da parcela e o método do número de Richardson bulk, o qual apresentou melhores resultados. Para o lidar com menor alcance vertical, aplicou-se a análise espectral que forneceu valores de comprimento de onda dos picos espectrais, proporcionais à altura da camada limite planetária. A constante de proporcionalidade para obtenção dos valores da altura da camada foi calculada comparando-se os resultados aos valores de altura estimados pela radiossondagem através do método do número de Richardson bulk, obtendo-se um valor de constante de proporcionalidade próximo ao sugerido na literatura. Entretanto, o conjunto de dados que mostrou boas estimativas dos picos espectrais foi bastante restrito, limitando a comparação ao longo do período entre os lidars.
This study explores the obtaining of the planetary boundary layer height through different methods and equipment, focusing on the spectral analysis of the wind field from Doppler lidar. An 80-day measurement campaign was conducted with two commercial Doppler lidars with different vertical ranges. For the lidar with greater vertical range and consequently a direct measurement of the planetary boundary layer heigth, the method of signal-to-noise ratio variance was applied and the results were compared to the height values estimated from radiosonding data using two different methods, the parcel method and the bulk Richardson number method, which presented better results. For the lidar with a lower vertical range, spectral analysis was applied, which provided wavelength values of the spectral peak, proportional to the planetary boundary layer height. The proportionality constant, in order to obtain the boundary height values, were calculated by comparing the height values estimated from the radiosonding data, using the bulk Richardson number method. Proportionality constant value close to the one found in the literature were obtained. However, the set of data that showed good estimates of the spectral peaks was very restricted, limiting the comparison over the period between the lidars.

Styles APA, Harvard, Vancouver, ISO, etc.

8

Himes, Benjamin John. « Development and Analysis of a Vibration Based Sleep Improvement Device ». BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/9168.

Texte intégral

Résumé :

Many research studies have analyzed the effect that whole-body vibration (WBV) has on sleep, and some have sought to use vibration to treat sleep disorders such as insomnia. It has been shown that low frequencies (f < 2Hz) are generally sleep inducing, but oscillations of this frequency are typically difficult to achieve using electromagnetic vibration drives. In the research that has been performed, optimal vibration parameters have not been determined, and the effects of multiple vibration sources vibrating at different frequencies to induce a low frequency traveling wave have not been explored. Insomnia affects millions of people worldwide, and non-pharmacological treatment options are limited. A bed excited with multiple vibration sources was used to explore beat frequency vibration as a non-pharmacological treatment for insomnia. A repeated measures design pilot study of 14 participants with mild-moderate insomnia symptom severity was conducted to determine the effects of beat frequency vibration, and traditional standing wave vibration on sleep latency and quality. Participants were monitored using high-density electroencephalography (HD-EEG). Sleep latency was compared between treatment conditions. Trends of a decrease in sleep latency due to beat frequency vibration were found (p ≤ 0.181 for AASM latency, and p ≤ 0.068 for unequivocal sleep latency). Neural complexity during wake, N1, and N2 stages were compared using Multi-Scale Sample Entropy (MSE), which demonstrated significantly lower MSE between wake and N2 stages (p ≤ 0.002). Lower MSE was found in the transition from wake to N1 stage sleep but did not reach significance (p ≤ 0.300). During N2 sleep, beat frequency vibration shows lower MSE than the control session in the left frontoparietal region. This indicates that beat frequency vibration may lead to a decrease of conscious awareness during deeper stages of sleep. Standing wave vibration caused reduced Alpha activity and increased Delta activity during wake. Beat frequency vibration caused increased Delta activity during N2 sleep. These preliminary results suggest that beat frequency vibration may help individuals with insomnia symptoms by decreasing sleep latency, by reducing their conscious awareness, and by increasing sleep drive expression during deeper stages of sleep. Standing wave vibration may be beneficial for decreasing expression of arousal and increasing expression of sleep drive during wake, implying that a dynamic vibration treatment may be beneficial. The application of vibration treatment as part of a heuristic sleep model is discussed.

Styles APA, Harvard, Vancouver, ISO, etc.

9

Ho, King-fung. « Some studies in deconvoluting Coincidence Doppler Broadening spectra / ». Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B23621953.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

10

Kurt, Mustafa. « Time Resolved Spectroscopy Of Laser Induced Air Plasma ». Phd thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608985/index.pdf.

Texte intégral

Résumé :

The laser beam interaction with matter and the plasma generation have been studied for many years. In some applications what is really important is to understand the composition and the temporal evolution of the species in the interested medium. In this thesis, time resolved optical spectroscopy was employed to understand the evolution of the plasma which is produced by interaction of Infrared (1.064 µ
m) laser beam with air. In this thesis, a new technique is suggested to analyze the time evolution of laser induced breakdown spectroscopy. The suggested method and the instrumentation of the setup are tested with a single gas (He). After the tests, we analyzed time sequence spectra of Laser Induced Air Breakdown. The suggested method is based on triggering the laser and the spectrometer at different time and applying the spectrometer trigger time by adding the time delay (&
#916
t) between them by using the pulse generator. The results show that the decay rates are slowing down microseconds after the excitation of the plasma. The results of the time-resolved measurements of the line spectra show that different component of the air has different decay rate, and lifetime. The lifetime of helium is 20 µ
s, and the decay start 5 µ
s after the initiation of plasma. Air has 12 µ
s lifetime, and the decay start 3 µ
s after the initiation of the plasma. Also, the decay rate and the lifetime depend on the state. We also calculate Doppler velocity for different component and different emission states. Doppler velocities show that the component which has great mass has small velocity, the component which has small mass has high velocity.

Styles APA, Harvard, Vancouver, ISO, etc.

11

Ho, King-fung, et 何競豐. « Some studies in deconvoluting Coincidence Doppler Broadening spectra ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B29773726.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

12

Whitfield, Melinda D. « Doppler-Broadening of Light Nuclei Gamma-Ray Spectra ». TopSCHOLAR®, 2010. http://digitalcommons.wku.edu/theses/1075.

Texte intégral

Résumé :

Non-destructive methods of material interrogation are used to locate hidden explosives and thwart terrorism attempts. In one such method materials are bombarded with neutrons which react with the nuclei of the atoms within causing a de-excitation process emitting a gamma-ray. The spectrum displayed by the collection of these gamma-rays gives valuable information regarding the material’s elemental make-up. It has been hypothesized that gamma-rays from neutron-induced gamma-ray reactions on light elements with atomic numbers less than 20, including most of the gamma-rays of interest in explosives detection, are Doppler-broadened. This thesis focuses on the gamma ray spectra from the 4438 keV gamma ray in the 12C (n, n’γ) reaction wherein Doppler broadening was investigated. A graphite sample was exposed to 14 MeV neutrons and the 12C gamma ray spectra collected using an HPGe detector positioned at four different angles with respect to the neutron beam; near 00, 450, 900 and 1350. No other experimental parameter was changed. The resultant gamma ray spectra indicated Doppler broadening had occurred.

Styles APA, Harvard, Vancouver, ISO, etc.

13

程曦敏 et Hei-man Anita Ching. « Detector noise reduction in positron doppler broadening related spectroscopy systems ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31225846.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

14

Ching, Hei-man Anita. « Detector noise reduction in positron doppler broadening related spectroscopy systems / ». Hong Kong : University of Hong Kong, 2002. http://sunzi.lib.hku.hk/hkuto/record.jsp?B25212114.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

15

Woo, Kee-tsz, et 胡紀慈. « Some mathematical studies in least square deconvolution of positron doppler broadening spectra using Huber regularization ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2003. http://hub.hku.hk/bib/B29468553.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

16

Zhang, Jingdong. « Development of optimized deconvoluted coincidence doppler broadening spectroscopy and deep level transient spectroscopies with applications to various semiconductor materials ». Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B38279010.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

17

Kakuschke, Chris. « Entwicklung alternativer Auswerteverfahren für Mikrowellendopplersignale bei der Geschwindigkeitsbestimmung im Bahnverkehr ». Doctoral thesis, Universitätsbibliothek Chemnitz, 2004. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200400877.

Texte intégral

Résumé :

To measure the speed of a vehicle, the revolution of a wheel or a rigid axle is traditionally used. Therefore non corrigible systematic errors occur which are caused by slip, spin and by the change of wheel diameter due to fretting. Train control and traction systems require new robust as well as precise methods of speed measurement. Because of their physical properties, Doppler-radar-sensors attached to the vehicle and measuring ground speed are first choice for this range of applications. Currently used sensors cannot fulfil the high demands under all operating conditions, because they are unable to completely compensate the various interferences and systematic deviations. This is the starting point of this dissertation. Two independent diverse methods with optimised reliability and accuracy must be used to meet all requirements. Limited resources of the embedded digital signal processor system under real-time conditions have to be taken into account. According to the boundary conditions, the introductory chapters critically discuss the frequency analysis methods currently used and describe starting points for further development. This leads to the design of a new, robust, wide-band spectral analysis which combines techniques of the dyadic wavelet transformation with the fast Fourier transformation. At the same time a new frame procedure and general model for the estimation of motion parameters is developed which features short delays. The disadvantages of the block-based discrete spectral analysis applied over continuous approaches are extensively compensated. The block structure of spectral data enables the selective use of new knowledge-based spectral filters for the compensation of the remaining intense interferences which are typical of this kind of application
Die Fahrzeuggeschwindigkeitsmessung über die Drehzahl eines Rades weist in Schlupf- und Schleuderzuständen erhebliche systematische Abweichungen auf. Deshalb erfordern Zugbeeinflussungs- und Antriebssysteme neue gleichzeitig robuste und präzise Geschwindigkeitsmessmethoden. Die Mikrowellensensorik unter Nutzung des Dopplereffekts zwischen Fahrzeug und Gleisbett wird wegen ihrer physikalischen Eigenschaften für dieses Einsatzgebiet favorisiert. Bisherige Sensorapplikationen erfüllen aber die hohen Ansprüche nicht in allen Betriebszuständen. Hier setzt die in dieser Arbeit beschriebene Sensorentwicklung auf. Zwei getrennt hergeleitete und nach Zuverlässigkeit und Genauigkeit optimierte neue Verfahren können bei gleichzeitiger Anwendung die gestellten Anforderungen erfüllen. Dabei müssen auch die beschränkten Ressourcen des eingebetteten digitalen Signalverarbeitungssystems unter Echtzeitbedingungen berücksichtigt werden. Entsprechend dieser Randbedingungen findet einleitend eine kritische Betrachtung bestehender Frequenzanalysemethoden statt und Ansätze für die Weiterentwicklung werden herausgearbeitet. Einerseits führt dies zur Konstruktion einer neuen störunempfindlichen Weitbereichsspektralzerlegung, welche Ansätze der dyadischen Wavelettransformation mit der Diskreten Fourier-Transformation verbindet. Andererseits wird ein neues Rahmenverfahren für die verzögerungsarme Schätzung der Bewegungsparameter des Fahrzeuges aufgrund seines physikalischen Bewegungsmodells hergeleitet und mit einem hochgenauen Frequenzauswerteverfahren kombiniert. Beide Verfahren basieren auf blockweisen diskreten Spektralzerlegungen, deren prinzipielle Nachteile gegenüber kontinuierlichen Ansätzen weitgehend kompensiert werden können. Durch die Blockorganisation lassen sich neuartige wissensbasierte Spektralfilter selektiv zur Unterdrückung starker bahnanwendungstypischer Störeinflüsse einsetzen

Styles APA, Harvard, Vancouver, ISO, etc.

18

Zhang, Jingdong, et 張敬東. « Development of optimized deconvoluted coincidence doppler broadening spectroscopy and deep level transient spectroscopies with applicationsto various semiconductor materials ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B38279010.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

19

Coutinho, Fábio Rizental. « Um novo método ultrassônico para detecção da posição da interface em escoamentos bifásicos ar-água ». Universidade Tecnológica Federal do Paraná, 2014. http://repositorio.utfpr.edu.br/jspui/handle/1/972.

Texte intégral

Résumé :

IBP; FINEP
Técnicas de medição de velocidade baseadas em ultrassom vem sendo muito utilizadas atualmente para o estudo de escoamentos de fluidos devido ao seu caráter não intrusivo. Em escoamentos bifásicos ar-água, a grande dificuldade na aplicação dessa metodologia é resolver a que fase pertence a velocidade medida. Esse problema envolve a tarefa de determinar a posição da interface líquido-gás. O algoritmo de estimação de velocidade denominado de Velocity Matched Spectrum (VMS) se diferencia dos demais por apresentar como resultado um espectro de velocidades para cada volume amostral interrogado. Neste trabalho um método baseado no formato dessa curva espectral da velocidade é utilizado para gerar um mapeamento espaço-temporal, o qual, após aplicação de filtros espaciais, resulta na detecção acurada da posição da interface água-ar. Para isso, um sistema de medição que utiliza o estimador VMS foi desenvolvido e validado através de um experimento de escoamento em cilindro girante e de um escoamento horizontal monofásico turbulento. A ascensão de bolhas em líquido estagnado apresenta dificuldades na detecção da fronteira água-ar devido às mudanças abruptas na inclinação da interface da bolha no seu movimento de subida. É mostrado que a técnica proposta apresenta um erro RMS entre 1,71 a 3,39 e uma probabilidade de falha na detecção e de falsa detecção entre 0,89% a 11,9% na determinação da posição espaço-temporal da interface água-ar de um escoamento externo de ascensão de bolhas em líquido estagnado. Mostra-se que a exatidão na determinação é mantida mesmo no caso de um transdutor obstruído por uma chapa metálica, ou então, emitindo externamente a uma tubulação de acrílico.
Ultrasonic measurement techniques for velocity estimation are currently widely used in flow study due to its non-intrusive nature. The difficulty on the application of this methodology to a two-phase air-water flow is in deciding from which phase the velocity data measured comes from. This problem involves the task of evaluating gas-liquid interface position. The algorithm known as Velocity Matched Spectrum (VMS) is a velocity estimator that stands out from other methods by returning a spectrum of velocities for each interrogated volume sample. In this work a method based on velocity spectrum curve shape is used to generate a spatial-temporal mapping, which, after spatial filtering, yields an accurate contour of the air-water interface. Therefore, a measurement system that implements VMS estimator was developed and validated through a rotating cylinder and a horizontal single-phase pipe turbulent flow experiments. Interface detection of free-rising bubbles in quiescent liquid presents some difficulties for interface detection due to abrupt changes in interface inclination. It is showed that the proposed technique yields a RMS error between 1.71 to 3.39 and a probability of detection failure or false detection between 0.89% to 11.9% in determining the spatial-temporal gas-liquid interface position in the flow of free rising bubbles in stagnant liquid. This result is valid for both free path and with transducer emitting through a metallic plate or a Plexiglas pipe.

Styles APA, Harvard, Vancouver, ISO, etc.

20

Dellacherie, Stéphane. « Contribution à l'analyse et à la simulation numériques des équations cinétiques décrivant un plasma chaud ». Phd thesis, Université Paris-Diderot - Paris VII, 1998. http://tel.archives-ouvertes.fr/tel-00479816.

Texte intégral

Résumé :

Lors de la formation du point chaud dans une expérience de Fusion par Confinement Inertiel, le plasma au centre de la sphère de deutérium-tritium peut être loin de l'équilibre thermodynamique local. Dans la première partie, on décrit donc un modèle cinétique ionique de type Vlasov-Fokker-Planck susceptible de prendre en compte ces déséquilibres. Après avoir rappelé les grandes étapes pour résoudre numériquement le système obtenu, on introduit la notion de moyenne entropique pour définir un nouveau schéma numérique traitant les collisions ion-électron homogènes en espace. Ce schéma est conservatif, stable et entropique sous un critère de type CFL dans sa version explicite. Dans sa version semi-implicite, on établit que ce schéma conserve l'équilibre thermodynamique. Le temps de calcul pour résoudre les équations cinétiques étant très important, il est nécessaire d'étudier la possibilité de ne résoudre ces équations que là où c'est nécessaire c'est à dire principalement au centre de la sphère de deutérium-tritium. Dans la seconde partie, on propose donc une technique de couplage cinétique-fluide, la formation du point chaud étant traitée avec le modèle cinétique, le reste avec les équations d'Euler à deux températures (températures ionique et électronique). Les ions deutérium et tritium pouvant ne pas être à l'équilibre thermodynamique, on s'est ensuite posé la question de la validité des formules analytiques donnant le taux de réaction nucléaire, formules établies en supposant que le plasma est à l'équilibre thermodynamique. Dans la troisième partie, on propose donc une méthode de type Monte-Carlo pour résoudre numériquement les équations cinétiques de type Boltzmann qui décrivent les réactions de fusion thermonucléaire et on montre qu'effectivement, les déséquilibres thermodynamiques rencontrés lors de la formation du point chaud peuvent invalider les formules usuelles.

Styles APA, Harvard, Vancouver, ISO, etc.

21

Zabihian, B. « Spectral analysis of coronary bypass doppler blood flow signals ». Master's thesis, 2011. http://hdl.handle.net/10400.1/3773.

Texte intégral

Résumé :

Dissertação de mest., Engenharia Electrónica e Telecomunicações, Faculdade de Ciências e Tecnologia, Univ. do Algarve, 2011
The pulsed Doppler ultrasound (DU) is one of the important tools in the study of vessel diseases and the investigation of flow conditions. Due to its non-invasive nature, it has been increasingly used in medicine in the last few decades. Accurate estimation of DU spectral center frequency and bandwidth parameters are extremely important for blood flow diagnostic purposes. Under real-time data acquisition conditions the DU signal is generally corrupted with different types of noise. In these situations the identification of signal components solely belonging to the blood flow signal is a difficult task. This thesis was aimed to study spectral techniques to enhance spectral parameter estimation, in particular the center frequency. Spectral estimates were obtained using the Short Time Fourier Transform (STFT) and Continuous Wavelet Transform (CWT). STFT was applied to short duration data segments, respecting signals’ stationary properties. Two CWT functions have been studied: varying bandwidth filter and fixed bandwidth filter. Since different filter bandwidth values yield different results, bandwidths for fixed bandwidth filter were investigate and the most proper one has been used on the performance comparative studies. To enhance the blood flow signal content of noise-embedded clinical Doppler signals, a STFT-based technique was proposed to reduce the signals’ noise components. Quantitative evaluation of the spectral methods was primarily performed on simulated signals with deterministic center frequency and bandwidth. Different signal to noise ratio signals were simulated. It has been observed that STFT spectral center frequency and bandwidth estimators were less biased than the CWT ones, although the last ones were less sensitive to the center frequency variations. Applying the proposed noise cancellation technique to simulated signals reduces the spectral estimators’ errors. As an example, a typical noisy signal with 10dbSNR, a reduction of 88% and 97% was obtained on the RMS bias of the estimation of the center frequency and bandwidth estimators respectively.

Styles APA, Harvard, Vancouver, ISO, etc.

22

ZHAN, XIAO-LONG, et 詹曉龍. « Spectral analysis of heart murmurs:relations of frequency parameters and doppler blood velocities ». Thesis, 1990. http://ndltd.ncl.edu.tw/handle/06910611560281356112.

Texte intégral

Styles APA, Harvard, Vancouver, ISO, etc.

23

Tsai, Chi-Lin, et 蔡季霖. « The Development of Ultrasound Blood Flow Analysis Model and Determination of Doppler Spectral Threshold for Doppler Angle Estimations ». Thesis, 2001. http://ndltd.ncl.edu.tw/handle/52220536915534449152.

Texte intégral

Résumé :

碩士
國立陽明大學
醫學工程研究所
89
Ultrasound image system bears non-invasive and real-time characteristics, using the Doppler principle to identify the blood flow velocity. In order to obtain the blood velocity quantitatively, it is necessary to acquire the Doppler angle in advance. Doctors always use 2D ultrasound image to find the longitudinal cross-section image of blood vessel for Doppler angle estimations. In recent years, many approaches based on axial velocity (projected on sound field axial axis) have been proposed. Due to the difficulty acquirement of baseband and RF signals, it’s hard to develop velocity algorithms and analysis approaches. Simulation using a computer program to develop blood model and to simulate blood situation in vessel is made in this research, using the echo signal from the scatterers to form RF signals. Moreover, optimal threshold setting algorithm and model for automatic Doppler velocity measurement are created. The accurate Doppler spectral threshold value is matched with the Doppler angle and blood flow velocity. The result of this research based on the optimal algorithm shows that it is a beneficial application for measuring blood flow velocity in the body small vessels etc. This simulation method also has the potentially beneficial for detail study of flow imaging system.

Styles APA, Harvard, Vancouver, ISO, etc.

24

Liu, Yung-Chi, et 劉榮啟. « Effect of Gender and Development on Fetal Heart Rate Variability --- Spectral Analysis by Doppler Ultrasound ». Thesis, 2003. http://ndltd.ncl.edu.tw/handle/59996658321293652825.

Texte intégral

Résumé :

碩士
慈濟大學
神經科學研究所
91
Fetal heart rate variability (FHRV) is the most important parameter of fetal well-being. To date, visual inspection is a more popular method to analyze FHRV, but it is relatively subjective and qualitative. To develop a non-invasive and quantitative method to detect the fetal heart rate, we recorded the fetal heart sounds of the normal pregnancy women who visiting the OPD of Yu Li Veterans Hospital for prenatal care. Fetal heart sounds were recorded for 2.5 minutes with supine position in a quite room. Fetal heart sounds were detected from a mini-microphone in conjunction with abdominal ultrasound, ultrasound fetoscope, and fetal monitor. The off-line data was analyzed by self-designed program software with fast Fourier transform and spectral analysis. Frequency domain analysis of beat-to-beat intervals including very low frequency power (VLF, 0.003-0.04 Hz), low frequency power (LF, 0.04-0.15 Hz), high frequency power (HF, 0.15-0.4 Hz) and the ratio of LF to HF (LF/HF) were performed. Ninety-four recording trials from 76 pregnancy women were recorded in this study and 48 were selected to be quantitatively analyzed. Three groups were defined: 1st trimester (gestational age of 9-14 week, N = 5); 2nd trimester (gestational age of 15-28 weeks, N = 18) and 3rd trimester (gestational age of 29-41 weeks, N = 25). The results showed that fetal heart rate was decreased by gestational age significantly. VLF, LF, HF and TP were increased significantly and LF/HF decreased in the 3rd trimester. Heart rate of male fetus was significantly higher than female only in the 3rd trimester. We concluded that Power spectral analysis of FHRV is a non-invasive, convenient method and spectral analysis of fetal heart rate variability by Doppler ultrasound is feasible. The heart rate of male fetus was higher than female significantly in the third trimester. It seems that the parasympathetic activity of fetal autonomic state was increased significantly in the 3rd trimester. And the decrease of LF/HF may be the indicator of maturity of autonomic nervous system in fetal development.

Styles APA, Harvard, Vancouver, ISO, etc.

25

Rossi, Stefano, et Piero Tortoli. « Development and validation of novel approaches for real-time ultrasound vector velocity measurements ». Doctoral thesis, 2021. http://hdl.handle.net/2158/1239650.

Texte intégral

Résumé :

Ultrasound imaging techniques have become increasingly successful in the medical field as they provide relatively low cost and totally safe diagnosis. Doppler methods focus on blood flow for the diagnosis and follow-up of cardiovascular diseases. First Doppler methods only measured the axial component of the motion. More recently, advanced methods have solved this problem, by estimating two or even all three velocity components. In this context, high frame rate (HFR) imaging techniques, based on the transmission of plane waves (PW), lead to the reconstruction of 2-D and 3-D vector maps of blood velocity distribution. The aim of this Ph.D. project was to develop novel acquisition schemes and processing methods for advanced ultrasound Doppler systems. Each development step was based on simulations and experimental tests. Simulations were based on Field II©, while experiments were conducted by using the ULA OP 256 open scanner. In particular, the recently proposed 2-D HFR vector flow imaging (VFI) method (DOI: 10.1109/TUFFC.2014.3064), based on the frequency domain for displacement estimation, was thoroughly investigated. Three main issues were addressed: the high underestimation of blood flow velocity observed when examining vessels at great depths, the high computational load, which hindered any real-time implementation and the lack of information about the third velocity component. Specifically, the progressive broadening of the transmitted beam on the elevation plane due to the acoustic lens was demonstrated to be responsible for the underestimation. The computational cost was reduced by processing demodulated and down-sampled baseband data instead of radiofrequency data, and a preliminary real time version of the 2-D VFI method was implemented. It was also found that a more efficient implementation could be obtained by exploiting parallel computing and graphic processing units (GPUs). An expansion circuit board for the ULA-OP 256 hardware, which allocates GPU resources, was thus designed and built. This new system architecture may allow the implementation of even more complex algorithms, such as the 3-D VFI methods. In particular, it will be possible to implement the novel method for 3D VFI that was developed and tested during this Ph.D. project. Such method suitably extended the 2D VFI approach by proposing an efficient estimation strategy that considerably limits the overall computational load.

Styles APA, Harvard, Vancouver, ISO, etc.

26

Yen, Nan-Yang, et 顏楠源. « PN Synchronization Performance Analysis of Direct-Sequence Spread-Spectrum Communication System in the Presence of Doppler Shift ». Thesis, 1997. http://ndltd.ncl.edu.tw/handle/47587343241026882128.

Texte intégral

Résumé :

博士
國立成功大學
電機工程學系研究所
85
The use of direct-sequence spread-spectrum (DS-SS) in communication systems is considered a promising technique to obtain higher bandwidth efficiency and power efficiency, in addition to its well-knownmerits in the field of secure communications. However, the efficiency of a spread-spectrum system is highly dependent on the capability of the receiver to obtain accurate and fast synchronization between the received and the locally generated PN codes. In severe Doppler environm ent, such asthe low-earth-orbit (LEO) satellite communication, the effectsof D oppler include not only the carrier frequency shift, but alsothe PN code chip rate offset, which may result in the PN code synchronization to be hard to accomplish. Thus, we shall investi gate the effects of Doppler shift on the PNcode synchronization, including the combined acquisition-trackingsynchronization loops and the digital delay lock loops (DDLL). Moreover, we intend to findsome simple and feasible designs to diminish the influencesof Doppler effect. In this thesis, we first analyze the overall acquisition performanceof the combined acqu isition-tracking synchronization loopsin the presence of Doppler shift. Both t he change of effectivesearch rate and the impact onthe detection probability d ue to Doppler are taken into account. Furthermore, the influence of the DDLL acquiring capability on the complete acquisition process is investi gated and some numerical results are presented to demonstratethe acquisition performance of this combined loop whichare quite di fferent from the previous reports. The delay lock loop is a we ll-known technique to track the PN codes for DS-SS system. This thesis considers discrete time analys es of thefirst- and second-order digital delay lock loops (DDLL), and pre sents the results of an investigation concerning the performance degradation d ue to Doppler. The performance measures eva luated include the pull-in capability, the steady-state timing error probability density function (pdf),and the mean time to lose lock (MTLL). The linear approximations are also providedand confirmed by computer simulations.

Styles APA, Harvard, Vancouver, ISO, etc.

27

CHIEN, WEI-CHE, et 簡偉哲. « A Study of Exercise Training Effect by Spectrum Analysis and Feature Extraction of Doppler Ultrasound at Carotid Artery Site ». Thesis, 2017. http://ndltd.ncl.edu.tw/handle/m4hjgw.

Texte intégral

Résumé :

碩士
國立中正大學
資訊工程研究所
105
Cardiovascular and cerebrovascular diseases are often in the list of top ten causes of death in Taiwan, and has high mortality rate. The site where carotid artery splits into internal and external carotid artery is usually the place arteriosclerosis (ASC) starts to occur. Internal carotid artery delivers blood to the brain, so its ASC-induced occlusion often causes stroke. The external carotid artery supplies oxygen to the facial skin, so its ASC occlusion leads to facial paralysis. Carotid ASC has huge impact to our life. Ultrasound imaging is a non-invasive and economic examination method to check the carotid condition. In the past, researchers used the vessel diameter change between systolic and diastolic states to assess atherosclerosis. Some of them calculate the pulsatility index or resistance index from the spectral Doppler waveforms. Our research analyzes the raw acoustic data of the Doppler ultrasound. First, we use Hilbert-Huang transform (HHT) to decompose the sound into signals in several frequency components. Then we transformed signals into spectrograms. After the observation, components with the interference were removed to contrast useful information. Finally, we calculate approximate entropy (ApEn) from the processed signals, and also extract features from its spectrogram to find the change in spectrum power. ApEn and spectrum power are two measures of interest to characterize ASC. Experimental results show that heartbeat signal significantly affects the ApEn calculation in normal people under exercise training. HHT effectively extracts the heartbeat signal from the raw data, so the ApEn will not change too much before and after exercise. The spectral power is lower after exercise. We infer that the blood density increases after exercise, and causes less flow-induced Doppler shift in the signal. Further experiments are required to confirm our conjecture.

Styles APA, Harvard, Vancouver, ISO, etc.

28

Jia, Huang Hsin, et 黃信嘉. « Evaluating the Effect of Exercise on Shoulder and Lower Extremities Microcirculation Using the Spectrum Analysis on Laser Doppler Signals ». Thesis, 2016. http://ndltd.ncl.edu.tw/handle/22329462529227330150.

Texte intégral

Résumé :

碩士
逢甲大學
生醫資訊暨生醫工程碩士學程
104
Many modern illnesses are attributed by society changes and faster pace of daily life, therefore, preventive medicine should be addressed because “prevention is better than cure”. Exercise is one of the best preventive medicine. Exercise can relieve muscle tension and calm nerves of the workers under circumstances of high stress over a long period of time. It can also avoid poor circulation, muscle ache and stiffness. The aim of this study is to explore the physiological indexes for evaluating the exercise effect via analyzing the microcirculatory signals. This study uses the spectrum analysis technique on the microcirculatory signals detected using the Laser Doppler Flowmetry in five frequency bands: Endothelial, Neurogenic, Myogenic, Respiratory, and Heartbeat. By comparing the energy difference of the flexibility exercise and the strengthening exercise in the case of before and after the training in the five bands, the effect of exercise on human microcirculation are discussed. Clinical studies include: 1. Implementation of the shrugging motion on healthy subjects and discussion of the effects of strengthening exercise. 2. Implementation of the ankle joint flexion and extension on the healthy subjects and discussion of the effects of flexibility exercise. 3. Implementation of standard exercise prescription on the subjects with neck and shoulder pain and discussion of the effects of the exercise treatment. The results showed that standard exercise prescription can decrease the neck perfusion dramatically. In frequency domain, the energy of Endothelial band decreased significantly, while the energy of Myogenic band increased significantly. Shrugging exercise can dramatically increase neck perfusion. In frequency domain, the energy of Endothelial band rose up significantly, while the energy of Myogenic band decreased significantly. When performing the lower extremities stretching, the energy of Endothelial and Neurogenic bands increased significantly, however, the energy of Myogenic, Respiratory, and Heartbeat bands decreased significantly. Lower extremities passive dorsiflexion can increase blood flow significantly. Our results reveal that the analysis technique in frequency domain can analyze the difference of microcirculation impact according to different exercises. In the future, it can be used to evaluate the effectiveness of the exercise in the health promotion and the preventive medicine fields.

Styles APA, Harvard, Vancouver, ISO, etc.

Thèses sur le sujet « Spectral Doppler analysis »

Créez une référence correcte selon les styles APA, MLA, Chicago, Harvard et plusieurs autres