To see the other types of publications on this topic, follow the link: Modeling of glottal pulse.
Dissertations / Theses on the topic 'Modeling of glottal pulse'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Modeling of glottal pulse.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Chytil, Pavel. "Detekce nemocí pomocí analýzy hlasu." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2008. http://www.nusl.cz/ntk/nusl-233419.
Full textAbstract:
Tato disertační práce je zaměřena na analýzu řečového signálu za učelem detekce nemocí ovlivňujících strukturu hlasových orgánů, obzvláště těch, které mění strukturální character hlasivek. Poskytnut je přehled současných technik. Dále jsou popsány zdroje použitých nahrávek pro zdravé a nemocné mlučí. Hlavním učelem této disertační práce je popsat vypočetní postup k odhadu parametrů modelu hlasového zdroje, které umožní následnou detekci a klasifikaci nemocí hlasivek. Poskytujeme detailní popis analýzy řečových signálů, které mohou být odvozeny z parametrických modelů hlasivek.
2
Plumpe, Michael David. "Modeling of the glottal flow derivative waveform with application to speaker identification." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/42591.
Full textAbstract:
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (p. 102-107).
by Michael David Plumpe.
M.S.
3
Stein, Gregory Joseph. "Modeling of nonlinear ultrashort optical pulse propagation." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/101475.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 97-100).
I present a numerical package, written in MATLAB, which provides a simplified scripting interface for simulating a host of ultrashort pulse propagation phenomena. With the proliferation of ultrashort laser technologies, the demand for efficient and accurate simulations has grown significantly. Here I introduce a linear-operator-based formalism for nonlinear pulse propagation beyond the slowly-varying-envelope approximation, which includes phenomena such as nonlinear wave mixing, plasma blue-shifting, and high harmonic generation. I also demonstrate the capabilities of our versatile simulation package, which can handle optical pulse propagation through a host of geometries and guiding structures. Finally, the simulation package is used to investigate a number of effects, particularly that of modulational instability in Kagome-type hollow-core photonic crystal fibers.
by Gregory Joseph Stein.
S.M.
4
Cheyne, Harold Arthur 1971. "Estimating glottal voicing source characteristics by measuring and modeling the acceleration of the skin on the neck." Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/27200.
Full textAbstract:
Thesis (Ph.D.)--Harvard--Massachusetts Institute of Technology Division of Health Sciences and Technology, 2002.Includes bibliographical references (p. 197-201).
This electronic version was scanned from a copy of the thesis on file at the Speech Communication Group. The certified thesis is available in the Institute Archives and Special Collections.
5
Hosnieh, Farahani Mehrdad. "Modeling of the human larynx with application to the influence of false vocal folds on the glottal flow." Diss., University of Iowa, 2013. https://ir.uiowa.edu/etd/4992.
Full textAbstract:
Human phonation is a complex phenomenon produced by multiphysics interaction of the fluid, tissue and acoustics fields. Despite recent advancement, little is known about the effect of false vocal folds on the fluid dynamics of the glottal flow. Recent investigations have hypothesized that this pair of tissue can affect the laryngeal flow during phonation. This hypothesis was tested both computationally and experimentally in this dissertation. The computations were performed using an incompressible solver developed in fixed Cartesian grid with a second order sharp immersed-boundary formulation while the experiments were carried out in a low-speed wind tunnel with physiologic speeds and dimensions. A parametric study was performed to understand the effect of false vocal folds geometry on the glottal flow dynamics and the flow structures in the laryngeal ventricle. The investigation was focused on three geometric features: the size of the false vocal fold gap, the height between the true and false vocal folds, and the width of the laryngeal ventricle. The computational simulations were used to study the flow structures of the glottal flow and pressure distribution on the surface of the larynx. The experimental pressure data served to validate the computational results and provided extended knowledge over a broad range of Reynolds numbers. It was found that the size of the false vocal fold gap has a significant effect on glottal flow aerodynamics; whereas the height between the true and false vocal folds and the width of the laryngeal ventricle were of lesser importance.
Due to lack of appreciation of the effect of real geometry of the larynx in the literature, a framework was discussed to extract the laryngeal geometry from the CT scan images. The image segmentation technique was utilized to extract the laryngeal geometries of a canine and a 45 years old female human larynx. Fully resolved three dimensional simulations of the laryngeal flow were conducted for physological Reynolds numbers in these realistic geometries to gain insight into the evolution of vortical structures in the larynx. It was shown that the glottal jet flow is highly three dimensional.
The two and three dimensional computational investigations revealed the presence of the rarely reported secondary vortices in the laryngeal ventricle known as rebound vortical structures. It was found that these vortical structures are formed due to the interaction between the starting vortex ring and the false vocal folds. Therefore, the small size of the false vocal folds gap was identified as an important factor in increasing the intensity of these vortical structures.
Finally, a novel high order Cartesian based moving least square finite volume solver was developed in this dissertation to model acoustic wave scattering at low Mach numbers flows. The computational aeroacoustic approach is based on incompressible viscous/acoustic splitting technique. In this solver, linearized perturbed compressible equations are solved on Cartesian grids and the boundaries are treated sharply using ghost fluid approach. The Cartesian grid framework is compatible with the incompressible solver and provides the flexibility of handling complex geometries. The acoustic solver was validated against several benchmark problems for which analytical solution is available.
6
Khayatian, Alireza. "Multirate and block methods for modeling and control of pulse modulated systems." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/13761.
Full text
7
Susa, Mirela. "Numerical Modeling of Pulse Thermography Experiments for Defect Characterisation Purposes." Thesis, Université Laval, 2009. http://www.theses.ulaval.ca/2009/26251/26251.pdf.
Full text
8
Özel, Feryal, Dimitrios Psaltis, Zaven Arzoumanian, Sharon Morsink, and Michi Bauböck. "MEASURING NEUTRON STAR RADII VIA PULSE PROFILE MODELING WITH NICER." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622456.
Full textAbstract:
The Neutron-star Interior Composition Explorer is an X-ray astrophysics payload that will be placed on the International Space Station. Its primary science goal is to measure with high accuracy the pulse profiles that arise from the non-uniform thermal surface emission of rotation-powered pulsars. Modeling general relativistic effects on the profiles will lead to measuring the radii of these neutron stars and to constraining their equation of state. Achieving this goal will depend, among other things, on accurate knowledge of the source, sky, and instrument backgrounds. We use here simple analytic estimates to quantify the level at which these backgrounds need to be known in order for the upcoming measurements to provide significant constraints on the properties of neutron stars. We show that, even in the minimal-information scenario, knowledge of the background at a few percent level for a background-to-source countrate ratio of 0.2 allows for a measurement of the neutron star compactness to better than 10% uncertainty for most of the parameter space. These constraints improve further when more realistic assumptions are made about the neutron star emission and spin, and when additional information about the source itself, such as its mass or distance, are incorporated.
9
Guerra, Aparecida de Cássia. "Estimação do sinal glotal para padrões acústicos de doenças da laringe." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/18/18133/tde-19052017-153430/.
Full textAbstract:
Muitas pesquisas tem sido feitas em processamento digital de sinais (PDS) na tentativa de se avaliar o sinal de fala para diagnosticar doenças da laringe. Medidas acústicas têm sido propostas de forma a avaliar indiretamente o trato glotal por meio do sinal de voz coletado através de microfone convencional. Para isso, o modelo paramétrico Liljencrants-Fant (LF) foi desenvolvido para representar o sinal glotal em condições normais e patológicas. Tais parâmetros apresentam vantagens sobre medidas acústicas por possuírem características fisiológicas reais das pregas vocais. Assim, podendo ser empregados para identificação de doenças da laringe. Além da estimação dos parâmetros LF, no domínio do tempo (parâmetros T), a forma de onda da derivativa glotal também pôde ser quantificada através dos parâmetros identificados na literatura por parâmetros R (Rd, Ra, Rk e Rg), parâmetros quocientes Q (SQ, OQ, CQ, AQ e NAQ), parâmetros B1 e B2 que são as extensões de bandas do pulso derivativo LF, e o parâmetro ece, que relaciona os parâmetros β e Ta. Os parâmetros B1 e B2 e ece apesar de serem propostos na literatura, não são encontrados resultados diferentes a essas duas medidas. Os resultados mostraram que os parâmetros B não foram confiáveis na discriminação entre as vozes, por outro lado, o parâmetro ece mostrou-se ser opção na discriminação entre as vozes normais, nódulo e Reinke. O objetivo deste trabalho é direcionar a atenção sobre o sinal glotal, estimando-o automaticamente mediante técnicas de PDS aplicadas ao sinal de fala, visando extrair parâmetros que identifiquem as condições normais e patológicas da laringe. Por fim foram propostos os parâmetros TRp e TRs, visando dissociar os efeitos de primeira ordem dos de ordem superior na fase de retorno do pulso glotal com a finalidade de estimar a real não-linearidade do sub-sistema glotal, retratando as condições normais e patológicas da laringe. Por fim foram propostos os parâmetros TRp e TRs, visando dissociar os efeitos de primeira ordem dos de ordem superior na fase de retorno do pulso glotal com a finalidade de estimar a real não-linearidade do sub-sistema glotal, retratando as condições fisiológicas do movimento das pregas vocais. Com um nível de confiança de 95%, o parâmetro de primeira ordem (TRp) é efetivo na discriminação do Edema de Reinke, porém mostrou-se ineficaz na detecção do nódulo. Em relação ao parâmetro de ordem superior, conclui-se que o TRs é um excelente detetor de vozes patológicas (nódulo e Edema de Reinke), porém não é capaz de discriminar as patologias.Many researches has been conducted in digital signal processing (DSP) atempting to evaluate the physiological conditions of larynx. Acoustical parameters have been proposed to evaluate the glotal tract from voice signal. One technique proposed is the Liljencrants-Fant model (LF) developed to represent normal and pathologic conditions of the larynx. Those parameters compare favourably as far as real physiologic characteristic of vocal folds is concerned. So, a primary use of the model is the larynx pathologic identification. Beyond LF parameters estimation, (T parameters in the time domain), the waveform of glotal pulse derivative also can be quantified through, R parameters (Rd, Ra, Rk and Rg), quocient parameters (SQ, OQ, CQ, AQ and NAQ), B parameters (B1 and B2) that are band extension of the LF glotal pulse derivative and the ece parameter that in fact, is a relationship between β and Ta. Although proposed in the literature, no results are found, related to B and ece parameters. Our founds show that B parameters do not present good results in voice discrimination, however, ece parameter seems to be good option to discriminate normal voice, nodulo and Reinke edema. The main purpose of this work is to estimate the glotal signal from the voice signal using DSP techniques in order to obtain parameters that identifies the physiological larynx condition. In order to estimate the shape of return phase of glotal pulse, twoparameters have been proposed in this work. The first one evaluates the pulse (TRp, in other words, the first order component of the return phase. The second is responsible to evaluate superior orders components of the return phase (TRs), i.e, the non-linear component of the glotal pulse. With 95% of confidence level, TRp is effective in Reinke edema discrimination however it is inefficient for nodule e dection. By the other hand, the TRs parameter works well to detect pathologic voice however is unable to discriminated them.
10
Al-Numay, Mohammed Saleh. "Discrete-time modeling and tracking control of pulse-width modulated systems." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/15387.
Full text
11
Westreich, Eric Lex. "Modeling pulse transmission in the Monterey Bay using parabolic equation methods." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/27138.
Full textAbstract:
Approved for public release; distribution is unlimitedAcoustic tomography signal transmissions in the Monterey Bay is modelled using the time-domain parabolic equation method of Collins and Westwood (1991). Comparison of the model output with the measured arrival structures obtained in Monterey Bay in 1988 shows that this Fourier synthesis can produce good agreement with data. Furthermore, identification of the measured modal arrivals is possible by decomposing the PE model output into individual normal modes. Modal identification provides for the application of tomography in shallow water.
12
Mattsson, Per. "Pulse-modulated feedback in mathematical modeling and estimation of endocrine systems." Licentiate thesis, Uppsala universitet, Avdelningen för systemteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-231908.
Full textAbstract:
The research field of systems biology has gained a lot of interest during the last decades. Systems biology can be seen as the systematic study of complex interactions in biological systems, mainly by methods from dynamical systems theory. This thesis mainly deals with the testosterone (Te) regulation in the human male, but techniques developed here might be useful for studying other parts of the endocrine system too. The contribution of the thesis can be divided into two parts: one covering mathematical models of Te regulation and another suggesting and validating identification techniques for those models. Regarding modeling, existing models of testosterone regulation have been extended with time delays and nonlinear dynamics, with the purpose of achieving better fit to clinical data. The identification part treats the estimation of unknown model parameters, and estimation of signals that cannot be measured in a noninvasive way.
13
Tinsley, Carl Terrie III. "Modeling of Multi-Pulse Transformer/Rectifier Units in Power Distribution Systems." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/34655.
Full textAbstract:
Multi-pulse transformer/rectifier systems are becoming increasingly popular in power distribution systems. These topologies can be found in aircraft power systems, motor drives, and other applications that require low total harmonic distortion (THD) of the input line current. This increase in the use of multi-pulse transformer topologies has led to the need to study large systems composed of said units and their interactions within the system. There is also an interest in developing small-signal models so that stability issues can be studied.
This thesis presents a procedure for the average model of multi-pulse transformer/rectifier topologies. The dq rotating reference frame was used to develop the average model and parameter estimation is incorporated through the use of polynomial fits. The average model is composed of nonlinear dependent sources and linear passive components. A direct benefit from this approach is a reduction in simulation time by two orders of magnitude. The average model concept demonstrates that it accurately predicts the dynamics of the system being studied. In particular, two specific topologies are studied, the 12-pulse hexagon transformer/rectifier (hex t/r) and the 18-pulse autotransformer rectifier unit (ATRU). In both cases, detailed switching model results are used to verify the operation of the average model. In the case of the hex t/r, the average model is further validated with experimental data from an 11 kVA prototype. The hex t/r output impedance, obtained from the linearized average model, has also been verified experimentally.Master of Science
14
RUSSELL, ALEX. "Modeling Ultrashort Pulse Laser Damage with the Particle in Cell Method." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1552154386797503.
Full text
15
Whitfield, Jason A. "Pressures and Flows for a Convergent and Divergent Oblique Glottis of 15 Degrees." Bowling Green State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1333486868.
Full text
16
Namuq, Mohammed Ali. "Simulation and modeling of pressure pulse propagation in fluids inside drill strings." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2013. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-107969.
Full textAbstract:
Modern bottom-hole assemblies are equipped with various sensors which measure the geological and directional information of the borehole while drilling. It is very crucial to get the measured downhole information to the surface in real time in order to be able to monitor, steer and optimize the drilling process while drilling. The transmission of the information to the surface is most commonly carried out by coded pressure pulses (the technology called mud pulse telemetry) which propagate through the drilling mud inside the drill string towards the surface. However, hardly any specific experimental research on the hydraulic data transmission can be found in the literature. Moreover, it is essential to use a reliable model/simulation tool which can more accurately simulate the pressure pulse propagation in fluids inside drill strings under various drilling operation conditions in order to improve the performance of the data transmission process. The aims of this study are to develop and test a laboratory experimental setup, a simulation model and a novel method for detecting and decoding of measurement while drilling pressure pulse propagation in fluids inside drill strings.
This thesis presents a laboratory experimental setup for investigating the process of data transmission in boreholes by mud pulse telemetry. The test facility includes a flow loop, a centrifugal pump, a positive mud pulser or alternatively a mud siren, pressure transducers at four different locations along the flow loop and a data collection system. Moreover, it includes an “actuator system” for the simulation of typical noise patterns created by the common duplex or triplex mud pumps. This laboratory setup with great capabilities opens the way for testing and developing new concepts for data transmission.
A theoretical model using ANSYS CFX11 (Computational Fluid Dynamics (CFD) commercial code) was successfully developed to simulate dynamic pressure pulse transmission behavior in the fluid inside the flow loop. The collected laboratory data which simulate various data transmission processes in boreholes were used to verify and calibrate the theoretical method. A pretty good agreement is achieved between the predicted and measured pressure pulses at different locations along the flow loop for positive pulses with various durations using different flow rates and for continuous pressure pulses using different carrier frequencies.
A novel approach (continuous wavelet transformation) for detecting and decoding the received continuous pressure pulses in a noisy environment was applied to various simulated drilling operation conditions for data transmission in boreholes in the laboratory. The concept was registered at the German Patent and Trade Mark Office (DPMA) for a patent in 2011. The results indicate that the continuous wavelet transformation can be used to clearly identify and better detect the continuous pressure pulse periods, frequencies and discontinuity positions in the time domain compared to the conventional method (Fourier transformation). This method will contribute to the possibility of transmitting the data at higher rates and over longer distances.
A concept for developing an innovative pulser using electrical discharge or acoustic sources for inducing pulses keeping the drill strings fully open (eliminating the problem of plugging the pulser by pumped lost circulation materials) and without any mechanical moving parts (eliminating the failure related to the pulser moving parts) was also registered at the German Patent and Trade Mark Office (DPMA) for a patent in 2012. With this pulser, it is expected that it would be possible to transmit the data over longer distances and at higher rates. Realizing the concept of the new pulser and using continuous wavelet transformation for detecting and decoding the pulser signal are recommended for future work.
17
Wan, Li. "Modeling and optimal design of annular array based ultrasound pulse-echo system." Link to electronic thesis, 2001. http://www.wpi.edu/Pubs/ETD/Available/etd-0418101-100413/.
Full textAbstract:
Thesis (M.S.)--Worcester Polytechnic Institute.Title from title screen. Keywords: optimal design; modeling; object identification; ultrasound pulse-echo system; annular array. Includes bibliographical references (p. 159-162).
18
Siomacco, Edward Michael. "Parametric modeling and estimation of pulse propagation on microwave integrated circuit interconnections." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA232465.
Full textAbstract:
Dissertation (Ph.D. in Electrical Engineering)--Naval Postgraduate School, June 1990.Dissertation supervisor(s): Tummala., Murali. "June 1990." Description based on title page as viewed on October 16, 2009. DTIC Identifier(s): Lossy lines, Dispersive lines, Circuit interconnections, Pulse propagation, Energy transmission lines, Integrated circuits, Theses. Author(s) subject terms: Microstrip, ARMA, Parametic Modeling, Parameter Estimation. Includes bibliographical references (p. 136-140). Also available online.
19
WAN, Li. "Modeling and Optimal Design of Annular Array Based Ultrasound Pulse-Echo System." Digital WPI, 2001. https://digitalcommons.wpi.edu/etd-theses/219.
Full textAbstract:
The ability to numerically determine the received signal in an ultrasound pulse-echo system is very important for the development of new ultrasound applications, such as tissue characterization, complex object recognition, and identification of surface topology. The output signal from an ultrasound pulse-echo system depends on the transducer geometry, reflector shape, location and orientation, among others, therefore, only by numerical modeling can the output signal for a given measurement configuration be predicted. This thesis concerns about the numerical modeling and optimal design of annular array based ultrasound pulse-echo system for object recognition. Two numerical modeling methods have been implemented and evaluated for calculating received signal in a pulse-echo system. One is the simple, but computationally demanding Huygens Method and the other one is the computationally more efficient Diffraction Response for Extended Area Method (DREAM). The modeling concept is further extended for pulse-echo system with planar annular array. The optimal design of the ultrasound pulse-echo system is based on annular array transducer that gives us the flexibility to create a wide variety of insonifying fields and receiver characteristics. As the first step towards solving the optimization problem for general conditions, the problem of optimally identifying two specific reflectors is investigated. Two optimization methods, the straightforward, but computationally intensive Global Search Method and the efficient Waveform Alignment Method, have been investigated and compared.
20
Pathak, Kedar A. "Computational Modeling of Plume Dynamics in Multiple Pulse Laser Ablation of Carbon." University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1216317908.
Full text
21
Nadkarni, Aditya. "Reflector geometry specific modeling of an annular array based ultrasound pulse-echo system." Link to electronic thesis, 2007. http://www.wpi.edu/Pubs/ETD/Available/etd-091207-114218/.
Full text
22
Bakula, Casey J. "LOW-POWER PULSE-SHAPING FILTER DESIGN USING HARDWARE-SPECIFIC POWER MODELING AND OPTIMIZATION." University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1204743997.
Full text
23
Olsen, Jesse Eric Burle. "Flood pulse influences on exploited fish populations of the Central Amazon." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/83864.
Full textAbstract:
Seasonally fluctuating water levels, known as flood pulses, influence the population dynamics and catches of fishes from river-floodplains. Although different measures of flood pulses, here called flood pulse variables, have been correlated to changes in catches of river-floodplain fishes, the flood pulse variables that have the strongest relationships to catches have not been identified. Furthermore, it is unclear if flood pulses influence catches of river-floodplain fishes with different life history strategies in different ways. Catches of 21 taxa from approximately 18,000 fishing trips were modeled as a function of fishing effort, gear type, seasonal flood pulse variables, and interannual flood pulse variables. These models were analyzed to understand which flood pulse variables had the strongest relationships to catches, and evaluate different flood pulse influences among taxa with different life history strategies. High water flood pulse variables generally had positive influences on catches in future years, while low water flood pulse variables generally had negative influences on catches in future years. Flood pulses generally had stronger influences on the catches of fishes with high fecundities and smaller eggs than on catches of fishes with low fecundities and larger eggs. Variation was observed in strengths and directions of flood pulse influences on catches of fishes with similar and different life history strategies. While my results were generally consistent with prevailing knowledge of how flood pulses influence catches of fishes, other biological factors of specific fish populations may further explain population responses to flood pulses.Master of Science
24
Mitchell, Robert Andrew III. "Understanding Femtosecond-Pulse Laser Damage through Fundamental Physics Simulations." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440411512.
Full text
25
Petersson, Marcus. "Computational Modeling of Deep Brain Stimulation." Thesis, Linköping University, Department of Biomedical Engineering, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-9512.
Full textAbstract:
Deep brain stimulation (DBS) is a surgical treatment technique, which involves application of electrical pulses via electrodes inserted into the brain. Neurons, typically located in the basal ganglia network, are stimulated by the electrical field. DBS is currently widely used for symptomatically treating Parkinson’s disease patients and could potentially be used for a number of neurological diseases. In this study, computational modeling was used to simulate the electrical activity of neurons being affected by the electrical field, to gain better understanding of the mechanisms of DBS. The spatial and temporal distribution of the electrical field was coupled to a cable model representing a human myelinated axon. A passing fiber with ends infinitely far away was simulated. Results show that excitation threshold is highly dependent on the diameter of the fiber and the influence (threshold-distance and threshold-diameter relations) can be controlled to some extent, using charge-balanced biphasic pulses.
26
Hutcheson, Patrick D. "Design, modeling and performance of a split path JP-10/Air Pulse Detonation engine." Thesis, Monterey, Calif. : Naval Postgraduate School, 2006. http://bosun.nps.edu/uhtbin/hyperion.exe/06Dec%5FHutcheson.pdf.
Full textAbstract:
Thesis (M.S. in Mechanical Engineering and Mechanical Engineer)--Naval Postgraduate School, December 2006.Thesis Advisor(s): Christopher M. Brophy. "December 2006." Includes bibliographical references (p. 97-98). Also available in print.
27
KENNEDY, BRIDGET ROSE. "MODELING PULSE PROPAGATION IN LOSS COMPENSATED MATERIALS THAT EXHIBIT THE NEGATIVE REFRACTIVE INDEX PROPERTY." Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/193641.
Full textAbstract:
Rapid development in nanofabrication has led to the design of new materials with very unusual properties. The exhibition of negative and zero indices of refraction are among the most striking properties of these materials, which have become the focus of intensive research worldwide. The potential for applications that is possible due to the new light manipulation capabilities of these materials has been the driving force behind this research. Most of the research in this field has primarily been experimental while the theoretical studies have mainly been limited to computer modeling, which in itself is a challenging problem. This research requires considerable computational resources and the development of new computer algorithms.The origin of the unusual properties in these materials comes from the combination of dielectric host materials with metallic nanosructures. These materials are often referred to as nanocomposite metamaterials. The plasmonic resonance in properly engineered metallic nanostructures gives rise to the resonant interaction of the incident electromagnetic field with metamaterials in such a way as to stimulate a magnetic permeability and an electric permittivity with negative real parts. The resonant nature of this phenomenon leads to considerable losses in metamaterials, which has made the study of loss compensation one of the key subjects in this field.The two techniques of loss compensation in metamaterials are considered in this dissertation. One of these techniques consists of doping the host material with active atoms. In the second technique, loss compensation is achieved by embedding these active atomic inclusions directly into the nanostructures. This dissertation presents the derivation of the systems of governing equations and studies the coherent pulse amplification for both cases.
28
Hollander, Henrik. "Modeling of an IGBT and a Gate Unit." Thesis, KTH, Elektrisk energiomvandling, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-124545.
Full textAbstract:
The purpose of this master thesis was to create a model of an IGBT in a single pulse test circuit and connect this model to a model of a Gate Unit. The IGBT model and the single pulse test circuit were both implemented in MATLAB and the Gate Unit was implemented in Simulink. The purpose of this model was to test the actions of the gate unit, so that the initial tuning could be done before going to the lab. Since no tests were performed in the lab, it was not possible to see how much of the testing that could have been done by simulations. However, the actions of the IGBT model much resembled the actions of the real component, even though some drawbacks were clear, such as the lack of tail current and tail voltage. These comparisons could be made between simulated characteristics and recordings from a previous test with the same component.
29
Cooley, James Hamilton. "Modeling laser pulse evolution in ionizing gas and plasma with application to laser wakefield acceleration." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/1770.
Full textAbstract:
Thesis (Ph. D.) -- University of Maryland, College Park, 2004.Thesis research directed by: Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
30
Deutschmann-Olek, Andreas [Verfasser]. "Modeling and Control of Optical Pulse Amplifiers for Ultra-Short Laser Pulses / Andreas Deutschmann-Olek." Düren : Shaker, 2021. http://d-nb.info/1233547895/34.
Full text
31
Baregheh, Mandana. "High performance numerical modeling of ultra-short laser pulse propagation based on multithreaded parallel hardware." Thesis, Aston University, 2013. http://publications.aston.ac.uk/19300/.
Full textAbstract:
The focus of this study is development of parallelised version of severely sequential and iterative numerical algorithms based on multi-threaded parallel platform such as a graphics processing unit. This requires design and development of a platform-specific numerical solution that can benefit from the parallel capabilities of the chosen platform. Graphics processing unit was chosen as a parallel platform for design and development of a numerical solution for a specific physical model in non-linear optics. This problem appears in describing ultra-short pulse propagation in bulk transparent media that has recently been subject to several theoretical and numerical studies. The mathematical model describing this phenomenon is a challenging and complex problem and its numerical modeling limited on current modern workstations. Numerical modeling of this problem requires a parallelisation of an essentially serial algorithms and elimination of numerical bottlenecks. The main challenge to overcome is parallelisation of the globally non-local mathematical model. This thesis presents a numerical solution for elimination of numerical bottleneck associated with the non-local nature of the mathematical model. The accuracy and performance of the parallel code is identified by back-to-back testing with a similar serial version.
32
John, Malte [Verfasser]. "Frequency-domain modeling of harmonic interactions in pulse-width modulated voltage-source inverter drives / Malte John." Hannover : Gottfried Wilhelm Leibniz Universität Hannover, 2019. http://d-nb.info/1183907060/34.
Full text
33
Almér, Stefan. "Control and Analysis of Pulse-Modulated Systems." Doctoral thesis, KTH, Optimeringslära och systemteori, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4713.
Full textAbstract:
The thesis consists of an introduction and four appended papers. In the introduction we give an overview of pulse-modulated systems and provide a few examples of such systems. Furthermore, we introduce the so-called dynamic phasor model which is used as a basis for analysis in two of the appended papers. We also introduce the harmonic transfer function and finally we provide a summary of the appended papers. The first paper considers stability analysis of a class of pulse-width modulated systems based on a discrete time model. The systems considered typically have periodic solutions. Stability of a periodic solution is equivalent to stability of a fixed point of a discrete time model of the system dynamics. Conditions for global and local exponential stability of the discrete time model are derived using quadratic and piecewise quadratic Lyapunov functions. A griding procedure is used to develop a systematic method to search for the Lyapunov functions. The second paper considers the dynamic phasor model as a tool for stability analysis of a general class of pulse-modulated systems. The analysis covers both linear time periodic systems and systems where the pulse modulation is controlled by feedback. The dynamic phasor model provides an $\textbf{L}_2$-equivalent description of the system dynamics in terms of an infinite dimensional dynamic system. The infinite dimensional phasor system is approximated via a skew truncation. The truncated system is used to derive a systematic method to compute time periodic quadratic Lyapunov functions. The third paper considers the dynamic phasor model as a tool for harmonic analysis of a class of pulse-width modulated systems. The analysis covers both linear time periodic systems and non-periodic systems where the switching is controlled by feedback. As in the second paper of the thesis, we represent the switching system using the L_2-equivalent infinite dimensional system provided by the phasor model. It is shown that there is a connection between the dynamic phasor model and the harmonic transfer function of a linear time periodic system and this connection is used to extend the notion of harmonic transfer function to describe periodic solutions of non-periodic systems. The infinite dimensional phasor system is approximated via a square truncation. We assume that the response of the truncated system to a periodic disturbance is also periodic and we consider the corresponding harmonic balance equations. An approximate solution of these equations is stated in terms of a harmonic transfer function which is analogous to the harmonic transfer function of a linear time periodic system. The aforementioned assumption is proved to hold for small disturbances by proving the existence of a solution to a fixed point equation. The proof implies that for small disturbances, the approximation is good. Finally, the fourth paper considers control synthesis for switched mode DC-DC converters. The synthesis is based on a sampled data model of the system dynamics. The sampled data model gives an exact description of the converter state at the switching instances, but also includes a lifted signal which represents the inter-sampling behavior. Within the sampled data framework we consider H-infinity control design to achieve robustness to disturbances and load variations. The suggested controller is applied to two benchmark examples; a step-down and a step-up converter. Performance is verified in both simulations and in experiments.QC 20100628
34
Pels, Andreas [Verfasser], Sebastian [Akademischer Betreuer] Schöps, and Sabariego Ruth [Akademischer Betreuer] V. "Multirate modeling and simulation of pulse-width modulated power converters / Andreas Pels ; Sebastian Schöps, Ruth V. Sabariego." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2020. http://d-nb.info/1204201129/34.
Full text
35
Atkinson, Terry. "Modeling of magnetic optic for the short pulse mode operation of Energy Recovery Linac based light sources." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2015. http://dx.doi.org/10.18452/17300.
Full textAbstract:
Das Forschungsfeld der Synchrotronstrahlungsquellen hat sich in den letzen Jahren entscheidend weiterentwickelt. Alle Zukunftsideen, unabhängig von ihrer Komplexität, haben dennoch eines gemeinsam: die Erzeugung kurzer Pulse. Die Naturwissenschaften haben die Spitzenbrillanz, die mit Hilfe kürzester Pulse produziert werden kann, als neues Schlüsselwerkzeug entdeckt. Die Nutzergemeinschaft verlangt nicht mehr nur ein statisches Bild, sondern vielmehr eine Reihe von bewegten Aufnahmen atomarer Substrukturen und den dazugehöringen Prozessen. Existierende dritte Generation Synchrotronstrahlungsquellen werden an die neuen Herausforderungen angepasst: Verbesserungen an der Magnet-Optik sowie der Einbau modernster Beschleunigertechnologie ermöglichen die Erzeugung kürzester Pulse mit höchster Brillanz für zeitaufgelöste Experimente. Ein möglicher Kandidat für die Lichtquelle der nächsten Generation ist ein Linear-Beschleuniger mit Energierückgewinnung. Durch die Verwendung langer Beschleunigungsstrukturen kann es, selbst bei hohen Energien, nicht zur Ausbildung des Emittanzgleichgewichts wie in Speicherringen kommen. Durch die Verwendung Impulsabhängiger-Umlaufbahnen und der Rückgewinnung der Strahlenergie ist es mit `Energy Recovery Linac'' (ERL)-basierten Quellen energieeffizient möglich, hochenergetische Elektronen-Pulse im Femtosekundenbereich zu erzeugen. Die longitudinale Elekronstrahldynamik solcher ERLs ist eines der Hauptthemen dieser Arbeit. Umfangreiche Simulationen über die gesamte Maschine wurden im Rahmen der `Femto-Science Factory'' Lichtquellen Studie durchgeführt. Die Begrenzungen des Kurzpulsmodus Betriebes wurden untersucht und mit den Erwartungen verglichen. Besondere Aufmerksamkeit lag dabei auf den 6D Elektronenstrahleigenschaften, insbesondere auf der Vermeidung von Strahlaufweitungen, die mit der Erzeugung von Ultra-Kurzpulsen einhergehen können.Synchrotron light sources are entering a new era. No matter how elaborate, all the next generation proposals share a common necessity; the production of ultra-short electron bunches. There is an evolution in the field of science under investigation using the high peak brilliance generated from such bunches. The user community is demanding not just pictures but videos of atomic substructures and the processes that define them. Existing 3rd generation facilities are modifying their magnetic lattices and upgrading the acceleration schemes in order to keep up with this trend of generating short pulses with ultimate brilliance for time resolved experiments. A possible candidate for the next generation light source is one based on ERL technology. Using long linacs to accelerate to high energies overcomes the present limitation of emittance equilibrium in storage rings. By implementing independent arcs for acceleration and deceleration while recuperating the beams energy, ERL based sources are theoretically capable of efficiently producing high energy femtosecond long bunch lengths. The study of the longitudinal motion of the beam through single pass magnetic optic in combination with linacs is the main topic of this thesis. Dedicated start-to-end simulations in the framework of the Femto-Science Factory large scale light source are undertaken. The expectations and restrictions on the short pulse mode (SPM) operation are comprehensively examined in this work. Particular attention is given to the 6D electron beam properties and with it the beam degradation caused by the production of ultra-short bunches.
36
Yin, Zhiyao. "Fuel Oxidation and Ignition by Nanosecond Pulse Discharges at Elevated Temperatures." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1373812880.
Full text
37
Lindell, Adam. "Pulse Repetition Interval Time Series Modeling for Radar Waves using Long Short-Term Memory Artificial Recurrent Neural Networks." Thesis, Uppsala universitet, Avdelningen för beräkningsvetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-377865.
Full textAbstract:
This project is a performance study of Long Short-Term Memory artificial neural networks in the context of a specific time series prediction problem consisting of radar pulse trains. The network is tested both in terms of accuracy on a regular time series but also on an incomplete time series where values have been removed in order to test its robustness/resistance to small errors. The results indicate that the network can perform very well when no values are removed and can be trained relatively quickly using the parameters set in this project, although the robustness of the network seems to be quite low using this particular implementation.
38
Feng, Ruimin. "LABORATORY-SCALE INVESTIGATION OF PERMEABILITY AND FLOW MODELING FOR HIGHLY STRESSED COALBED METHANE RESEROVIRS USING PULSE DECAY METHOD." OpenSIUC, 2017. https://opensiuc.lib.siu.edu/dissertations/1477.
Full textAbstract:
The steady flow method (SFM), most commonly used for permeability measurement in the laboratory, is not applicable for tight rocks, higher rank coals and coals under highly stressed condition because of the difficulty in measuring steady-state gas flowrates resulting from the tight rock structure of. However, accurate estimation of permeability of highly stressed coals is pivotal in coalbed methane (CBM) operations in order to precisely and effectively model and project long-term gas production. A fast and accurate permeability measurement technique is, therefore, required to investigate gas flow behavior of CBM reservoirs. The pulse-decay method (PDM) of permeability measurement is believed to be better suited for low-permeability rocks. In this study, application of the currently used pulse-decay laboratory permeability measurement techniques for highly stressed coals were evaluated. Considering the limitations of these techniques in permeability measurement of unconventional gas reservoirs, such as coal and gas shales, the conventional PDM was optimized by adjusting the experimental apparatus and procedures. Furthermore, the applicability of an optimized PDM was verified numerically and experimentally. This dissertation is composed of five chapters. To complete the research objectives as discussed above, it is necessary to have a profound understanding of the basic theories, such as, gas storage mechanism, gas migration, and permeability evolution during gas depletion in coalbed reservoirs. In Chapter 1, a brief discussion regarding the basic knowledge of reservoir properties and transport mechanisms is presented. The chapter also provides the appropriate background and rationale for the theoretical and experimental work conducted in this study. Chapter 2 presents the transient pressure-decay technique in permeability measurement of highly stressed coals and verifies the validity of Brace et al.’s solution (1968) by comparing it with Dicker and Smits’s solution (1988) and Cui et al.’s solution. The differences between these three solutions are discussed in detail. Based on the established permeability trends from these different solutions, a persuasive suggestion is presented for selection of the best alternative when testing coal permeability. Furthermore, permeability is regarded as a coupled parameter, resulting from the combined effects of mechanical compression and “matrix shrinkage” caused by desorption of gas. To isolate the role of gas desorption from the coupled result, a series of experiments were carried out under constant effective stress condition and a stress-dependent permeability trend was established. Chapter 3 proposes an optimized experimental design in order to improve the accuracy of the calculated permeability for sorptive rocks. In order to verify the optimized design theoretically, a modified mathematical model is presented and describes the one-dimensional fluid flow in porous media by a partial differential equation. The numerical solutions of the model are presented graphically to evaluate the fluid flow behavior in porous media. Finally, the validity of Brace et al.’s solution when testing sorptive rocks, without the need of consideration on the compressive storage and sorption effect, is elucidated. Chapter 4 demonstrates the efficiency and applicability of the optimized PDM through its direct application to experimental work designed to establish the permeability trend under best replicated in situ conditions. In this chapter, CO2 was used as the test fluid to profile and characterize the pulse decay plots due to its higher affinity towards coal than methane, and then establish the stress-dependent-permeability trend for highly-stressed CBM reservoirs. In this chapter, Brace et al.’s solution was also verified by comparing the laboratory data and computer simulated results obtained from the optimized mathematical model proposed in Chapter 3. The experimental work demonstrates that the optimized technique can be used for permeability tests of sorptive rocks without the need to carry out additional experimental work required to measure rock porosities and sorption isotherms. Finally, a summary and future research perspectives are presented in Chapter 5.
39
Sterkhova, Anna. "Modelling of Pulse Propagation in Nonlinear Photonic Structures." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-234225.
Full textAbstract:
V současnosti jsme svědky stále zvyšujících se nároku na rychlost přenosu a zpracování signálu a kapacitu pamet’ových zařízení. Proto se pozornost výzkumných pracovníku zaměřuje k plně optickým zařízením, která by mohla splnit zmíněné požadavky. Jednou z intenzívně zkoumaných možností je využití mikroprstencových optických rezonátoru. Při výzkumu je nutné využít numerických metod, které simulují šíření optického záření v dané struktuře. K tomuto účelu existuje celá rada metod, které se liší v efektivitě výpočtu, použitých aproximacích, i možnostech použití. Cílem této práce bylo vyvinout dvě jednoduché a praktické numerické metody pro modelování šíření pulzního záření v nelineárních vlnovodných strukturách. Přítom bylo požadováno, aby, na rozdíl od obecně známé a často využívané metody konečných diferencí v časové oblasti (FD-TD), bylo možné metody snadno aplikovat při studiu nelineárních struktur založených na mikroprstencových rezonátorech. Proto vyvinuté metody používají některé aproximace, zejména aproximaci pomalu proměnné obálky. Výhodou metod je vysoká rychlost a skromné požadavky na výpočetní zdroje. Obě metody vycházejí ze zkutečnosti, že naprostá většina nelineárních struktur založených na mikroprstencových rezonátorech se skládá ze dvou základních prvku: obyčejných vlnovodu a vlnovodných vazebních clenu. První metoda řeší vázané parciální diferenciální rovnice, které popisují šíření obálky pulzu ve struktuře. Přitom je použito tzv. „up-wind“ schéma vhodné pro parciální diferenciální rovnice popisující šíření vln. Druhá metoda vychází z první; rozdíl je v popisu vazby mezi dvěma vlnovody. Pokud se v první metodě uvažuje realistická vazba rozložená na určité délce, pak druhá metoda je založena na představě vazby nacházející se v jednom místě. Díky tomu je možné integrovat příslušné rovnice a dosáhnout výrazného urychlení výpočtu. Kvazianalytický charakter druhé metody umožňuje dále snadnou klasifikaci různých typu ustálených řešení. Vzhledem k těmto vlastnostem byla druhá metoda využita k výzkumu samovolné generace optických pulzu ve strukturách skládajících se z vázaných prstencových rezonátoru. Obě metody, které byly vyvinuty během této práce, představují rychlé a fyzikálně názorné alternativy k metodě FD-TD, a tak lze očekávat, že mohou hrát důležitou roli při výzkumu nelineárních vlnovodných struktur.
40
Jiang, Hao. "Numerical Modeling and Analysis of Micro-structuring on Silicon on Insulator (SOI) Film under Localized Single Pulse Laser Irradiation." University of Toledo / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1302280541.
Full text
41
Yang, Jin. "Modeling of HVDC IGBT in Pspice : Serving an ultimate goal for converter station EMC studies." Thesis, KTH, Elektroteknisk teori och konstruktion, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-176859.
Full textAbstract:
An IGBT/diode model with more accurate characteristics than simple switchis required to serve for EMC issues from converter valve. The purpose of thismaster thesis is to develop an IGBT and diode model to achieve both accuratetransient behavior and fast simulation time during single pulse switchingtest circuit for the 4:5 kV and 2:0 kA StakPakTM IGBT module. A gate unitwhich resembles the ABB gate unit is implemented to obtain a good agreementbetween simulation and measurement. For demonstration and verication, theIGBT/diode model is applied in a simplied arm simulation of full scale ABBGeneration 4 HVDC-VSC converter station and capable of a half cell consistingof 8 series-connected IGBTs and their anti-paralleled diodes. The arm simulationresults are analyzed further for converter station EMC studies.Convergence issue is the most important problem in the whole process of modelimplementation and application. To guarantee the convergence in simulationsome characteristics such as the tail voltage at the end of turn-o is disregarded.But overall, the model is validated and adopted successfully.En IGBT-/diodmodell med mer exakta egenskaper an en enkel switch kravs foratt hantera EMC-problem fran omvandlarventilen. Syftet med denna magisteruppsatsar att utveckla en IGBT- och diodmodell for att uppna bade noggrantovergaende beteende och snabb simuleringstid under enkelpulsomkopplingstestkretsfor 4,5 kV och 2,0 kA-StakPak IGBT-modulen. En grindenhetsom liknar ABB-grindenheten implementeras for att fa god overensstammelsemellan simulering och matning. For demonstration och veriering, tillampasIGBT-/diodmodellen i en forenklad armsimulering av en fullskalig ABB Generation4 HVDC-VSC-omvandlarstation och med kapacitet for en halvcell bestaendeav 8 seriekopplade IGBT och deras anti-parallellkopplade dioder. Resultatenfran armsimuleringen analyseras vidare for EMC-studier av omvandlarstationen.Konvergensfragan ar det viktigaste problemet i hela processen for modellimplementeringoch -tillampning. For att garantera konvergensen i simulering ignorerasvissa egenskaper sasom svansspanningen vid slutet av avstangning. Mentotalt sett, valideras och antas modellen framgangsrikt.
42
Forouzanfar, Mohamad. "A Modeling Approach for Coefficient-Free Oscillometric Blood Pressure Estimation." Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31213.
Full textAbstract:
Oscillometry is the most common measurement method used in automatic blood pressure (BP) monitors. However, most of the oscillometric algorithms are without physiological and theoretical foundation, and rely on empirically derived coefficients for systolic and diastolic pressure evaluation which affects the reliability of the technique. In this thesis, the oscillometric BP estimation problem is addressed using a comprehensive modeling approach, based on which coefficient-free estimation of BP becomes possible. A feature-based neural network approach is developed to find an implicit relationship between BP and the oscillometric waveform (OMW). The modeling approach is then extended by developing a mathematical model for the OMW as a function of the arterial blood pressure, cuff pressure, and cuff-arm-artery system parameters. Based on the developed model, the explicit relationship between the OMW and the systolic and diastolic pressures is found and a new coefficient-free oscillometric BP estimation method using the trust region reflective algorithm is proposed. In order to improve the reliability of BP estimates, the electrocardiogram signal is recorded simultaneously with the OMW, as another independent source of information. The electrocardiogram signal is used to identify the true oscillometric pulses and calculate the pulse transit time (PTT). By combining our developed model of oscillomtery with an existing model of the pulse wave velocity, a new mathematical model is derived for the PTT during the cuff deflation. The derived model is incorporated to study the PTT-cuff pressure dependence, based on which a new coefficient-free BP estimation method is proposed. In order to obtain accurate and robust estimates of BP, the proposed model-based BP estimation method sare fused by computing the weighted arithmetic mean of their estimates. With fusion of the proposed methods, it is observed that the mean absolute error (MAE) in estimation of systolic and diastolic pressures is 4.40 and 3.00 mmHg, respectively, relative to the Food and Drug Administration-approved Omron monitor. In addition, the proposed feature-based neural network was compared with auscultatory measurements by trained observers giving MAE of 6.28 and 5.73 mmHg in estimation of systolic and diastolic pressures, respectively. The proposed models thus show promise toward developing robust BP estimation methods.
43
Ghotikar, Miheer S. "Aortic valve analysis and area prediction using bayesian modeling." [Tampa, Fla.] : University of South Florida, 2005. http://purl.fcla.edu/fcla/etd/SFE0001369.
Full text
44
Thévenet, Maxence. "Modeling the interaction between a few-cycle relativistic laser pulse and a plasma mirror : from electron acceleration to harmonic generation." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX112/document.
Full textAbstract:
Lorsqu'une impulsion laser est focalisée à une intensité relativiste sur une cible solide, le matériau est instantanément ionisé et forme un miroir plasma, c'est-à-dire un plasma surdense présentant un court gradient de densité sur sa face avant. La réflexion de l'impulsion laser génère alors des harmoniques élevées dans l'impulsion réfléchie, et des électrons peuvent être accélérés hors de la cible. Si la génération d'harmoniques est bien comprise, l'accélération des électrons reste, à ce jour, mal expliquée. Basée sur des résultats expérimentaux obtenus sur deux lasers femtosecondes ultraintenses (le laser "Salle Noire" au LOA et le laser UHI100 au CEA), cette thèse théorique et numérique porte sur le mécanisme d'accélération des électrons en suivant trois axes de recherche. Premièrement, à l'aide de simulations numériques de type particle-in-cell, nous identifions le mécanisme d'éjection des électrons de la surface qui a lieu à l'échelle du cycle optique. En particulier, le rôle déterminant des champs à l'intérieur du plasma a été mis en évidence, et ce travail montre que la longueur caractéristique du gradient de densité est un paramètre fondamental de cette interaction. Deuxièmement, après l'éjection du plasma, les électrons peuvent être accélérés par les champs laser de l'impulsion réfléchie. Ce processus, appelé "accélération laser dans le vide", avait été peu étudié expérimentalement en raison de la difficulté d'injecter des électrons directement au centre d'une impulsion laser intense. Le miroir plasma constitue une solution à ce problème, servant d'injecteur à électrons. Grâce à un modèle présenté dans cette thèse, nous avons pu interpréter les résultats expérimentaux obtenus sur le laser UHI100 du CEA. En particulier, nous démontrons que ces expériences ont conduit pour la première fois à l'accélération dans le vide d'un faisceau d'électrons de charge élevée (3 nC) jusqu'à des énergies relativistes (10 MeV). Enfin, la génération d'harmoniques lors de cette interaction peut se produire suivant deux mécanismes : l'accélération cohérente de sillage à faible intensité et le miroir oscillant relativiste à haute intensité. La comparaison entre l'éjection d'électrons et chacun de ces mécanismes apporte de nouvelles informations sur la dynamique à l'échelle nanométrique de la surface plasmaWhen a laser pulse with a relativistic intensity is focused onto a solid target, the material is instantly ionized and forms a plasma mirror, namely an overdense plasma with a short density gradient on its front side. During the laser pulse reflection, high harmonics are generated in the reflected pulse, and electrons can be accelerated out of the target. While the mechanisms for high harmonic generation are well-known, the acceleration of electrons remained unclear. Based on experimental results from two ultraintense femtosecond laser systems (the "Salle Noire" laser at LOA and the UHI100 laser at CEA), this theoretical and numerical thesis unravels the mechanisms for ejection and acceleration of electrons, following three research lines. First, using particle-in-cell numerical simulations, we identify the ejection mechanism occuring during every laser period at the plasma surface. In particular, the role of the fields inside the plasma is highlighted, and the scale length of the plasma density gradient is shown to be a key parameter. Second, after being ejected from the plasma surface, electrons can be accelerated by the laser fields in the reflected pulse. This so-called "vacuum laser acceleration" had not been studied extensively in experiments, the biggest hurdle being to inject electrons directly inside an ultraintense laser pulse. Plasma mirrors offer an answer to this question and serve as electron injectors. In this thesis, we develop a model to interpret experimental results obtained on the UHI100 laser at CEA. In particular, we show that these experiments lead to the first observation of vacuum laser acceleration of a high-charge (3 nC) electron beam to relativistic energies (10 MeV). Finally, high harmonic generation may occur via two mechanisms: coherent wake emission at low intensity and the relativistic oscillating mirror effect at high intensity. Comparing electron ejection with each of these mechanisms brought new insights into the nanoscale dynamics of the plasma surface
45
Li, Yinyun. "Computational Modeling of Slow Axonal Transport of Neurofilaments." Ohio University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1373290973.
Full text
46
Castro, Bolinaga Celso Francisco. "Numerical Simulation of the Propagation of Fine-Grained Sediment Pulses in Alluvial Rivers." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/82348.
Full textAbstract:
Sediment pulses are defined as large amounts of loose sediment that are suddenly deposited in river corridors due to the action of external factors or processes of natural or anthropogenic origin. Such factors and processes include landslides, debris flows from tributaries, volcanic eruptions, dam removal projects, and mining-related activities. Their occurrence is associated with a surplus in sediment load to downstream reaches, and therefore, with severe channel aggradation and degradation, significant floodplain deposition, increase in flood frequency, damage of infrastructure, and impairment of aquatic habitats. The main objective of this research is to develop a better understanding of the fundamental mechanisms that govern the propagation of these sediment-flow hazards in alluvial sand-bed rivers. Specifically, the study presented herein is divided into three separate parts to achieve this overarching goal. First, a component intended to improve the numerical modeling of morphodynamic processes in alluvial sand-bed rivers by proposing a novel solution methodology that applies either the decoupled or the coupled modeling approach based on local flow and sediment transport conditions. Secondly, a detailed numerical analysis to characterize the behavior of fine-grained sediment pulses (i.e. composed of granular material in the sand size range) in alluvial sand-bed rives by identifying the properties of these types of pulses, as well as the characteristics of riverine environments, that are most relevant to their downstream migration. And lastly, a case study application to assess the effect of the magnitude, duration, and frequency of severe hydrologic events on the overall propagation behavior of fine-grained sediment pulses in alluvial sand-bed rivers. Ultimately, this research aims to contribute towards reducing the uncertainty associated with the impact of these phenomena, and hence, improving the resilience of rivers corridors.Ph. D.
47
RAGHUPATHY, ARUN PRAKASH. "A NUMERICAL STUDY OF DETONATION AND PLUME DYNAMICS IN A PULSED DETONATION ENGINE." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1123290677.
Full text
48
Ayachit, Agasthya. "Steady-State and Small-Signal Modeling of A-Source Converter." Wright State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=wright1534187954423628.
Full text
49
Qin, Zhenpeng. "Modeling of Ion Transport for Micro/Nano Size Particles in Coulter Counter Application." University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1240858653.
Full text
50
Slavinskis, Nerijus. "Short pulse q-switched longitudinally diode pumped solid state minilasers: generation, characterization and application." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2011. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2011~D_20110630_134119-87467.
Full textAbstract:
The dissertation is dedicated to the detailed numerical modelling of generation dynamics of actively and/or passively Q-switched diode laser longitudinally pumped solid-state lasers, characterization of spatial and temporal laser properties and for the demonstration of application possibility of created minilasers. A detailed theoretical model for the description of generation dynamics using travelling wave approach is presented. In this model more parameters of active laser medium, pump sources and resonator architecture are taken into account. In this thesis the results which show the principal difference between results obtained using the laser travelling wave model and point laser model are presented. Using point laser model the problems of generated pulse timing jitter in passively Q-switched lasers are described and its lowering possibilities using different pumping methods are suggested. In this thesis new, based by the second order moment, laser beam characterisation by knife-edge method is presented. Also laser pulse compression possibilities in tetrachloride CCL4 medium are described. It is showed that using seed signal it is possible to obtain shorter (< 60 ps) and more stable optical pulses. In this thesis application possibilities of created minilasers are presented: the experimental results of the Z-scan measurements obtained using pulses with different pulse shapes for fused silica are presented; also experiments, in which, created minilasers for paper cleaning... [to full text]Disertacija skirta diodais kaupinamų kietojo kūno lazerių su aktyviąja ir pasyviąja kokybės moduliacija generacijos dinamikos detalesnei skaitmeninei analizei, lazerio impulsų laikinių ir erdvinių parametrų charakterizavimui ir sukurtų minilazerių panaudojimo galimybių demonstracijai. Generacijos dinamikos detalesniai skaitmeniniai analizei, darbe pristatomas sukurtas bėgančiųjų bangų modelis, kuriame atsižvelgiama ne tik į daugelį procesų vykstančių lazerio aktyviajame elemente, bet ir į rezonatoriaus konfigūraciją bei kaupinimo šaltino parametrus. Pateikiami skaitinio modeliavimo rezultatai demonstruojantys šio modelio privalumus lyginant su dažniausiai naudojamu taškiniu lazerio modeliu. Naudojant taškinį lazerio modelį yra nagrinėjama generuojamų impulsų laikinio tirtėjimo problema pasyvios kokybės moduliacijos lazeriuose ir pasiūlyti mažinimo būdai naudojant skirtingus kaupinimo būdus. Darbe taip pat pateiktas naujas, antraisiais momentais pagrįstas, pluošto charakterizavimo judančiu peiliu metodas. Nagrinėjamos lazerių impulsų spūdos galimybės tetrachlorido CCL4 skystyje ir pademonstruota, kad naudojant užkrato signalą galima gauti trumpesnius (< 60 ps) ir stabilesnius optinius impulsus. Darbe pademonstruotos sukurtų minilazerių pritaikymo galimybės: aprašomas netiesinio lūžio rodiklio kvarciniame stikle matavimas Z-skenavimo metodu ir gautų duomenų apdorojimo procedūra įskaitant naudojamų impulsų erdvinę ir laikinę formą; aprašomi eksperimentai, kuriuose sukurti... [toliau žr. visą tekstą]