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Dissertations / Theses on the topic 'Pulse dispersion'
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1
Chauhan, Vikrant Chauhan Kumar. "Pulse compression and dispersion control in ultrafast optics." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/37153.
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Pulse Compression and Dispersion Control in Ultrafast Optics
Vikrant K. Chauhan
116 Pages
Directed by Dr. Rick P. Trebino
In this thesis, we introduced novel pulse compressors that are easy to align and which also compensate for higher order dispersion terms. They use a single dispersive element or a combination of dispersive elements in single-element-geometry. They solve the problem of extra-cavity pulse compression by providing control of the pulse width in almost all of the experiments performed using ultrashort pulses, and they even compensate for higher order dispersion. We performed full spatiotemporal characterization of these compressors and demonstrated their performance. We also developed a theoretical simulation of pulse compressors which is based on a matrix based formalism. It models the full spatiotemporal characteristics of any dispersion control system. We also introduced a simple equation, in its most general form, to relate the total dispersion and magnification introduced by an arbitrary sequence of dispersive devices. Pulse compressor characterization was done using interferometric measurements in the experiments presented in this work, but we also developed a method to measure pulses that uses polarization gating FROG for measuring two unknown pulses. In the last part, we briefly discuss the designing of a high energy chirped pulse amplification system.
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Yanez, Mauricio. "Pulse narrowing in optical fibers with polarization mode dispersion." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0034/MQ65530.pdf.
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Arroyo, Marcos. "Pulse tests in soil samples." Thesis, University of Bristol, 2001. http://hdl.handle.net/1983/25e7e542-94f3-49f3-ba6f-36df35f5e0e2.
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Chou, Patrick Chien-pang 1970. "Optical pulse distortion and manipulation through polarization effects and chromatic dispersion." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/26886.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.<br>Includes bibliographical references (leaves 112-129).<br>Pulse distortion and shaping mechanisms play a significant role in optical fiber communication and sensing. In this thesis we shall investigate techniques which alleviate pulse deterioration due to polarization effects, and utilize large chromatic dispersion for system performance enhancement. We first demonstrate a method of mitigating polarization mode dispersion (PMD) in fiber optic communication systems. PMD has been a known effect for over a decade. However, it was not an impediment to system performance until recent advances in communication system bit rates. Today, with 10 Gb/s and 40 Gb/s channel rates appearing in new system equipment, PMD prohibits the use of many fiber cables already installed. Current PMD compensation techniques that require feedback control have difficulty meeting the speed and reliability requirements of telecom standards. In the first part of this thesis we investigate alternative compensation schemes which reduce the complexity of the feedback schemes. We next exploit the recent availability of ultra-long length chirped fiber Bragg gratings (FBG). Their enormous chromatic dispersion enables methods of improving current techniques in sensing and high speed optical sampling. In one experiment, we modulate the frequency of a standard distributed Bragg reflector (DBR) laser, and then apply the dispersion of the ultra-long FBG. Picosecond pulses are formed, whose repetition rate is independent of the laser cavity length. Since the gain of the laser is not modulated, the timing jitter is fundamentally limited only by the frequency noise of the laser. Finally, we again utilize the large delay of an ultra-long chirped FBG to implement arbitrary dynamic optical filtering of pulse spectra. In sensing applications such as fiber gyroscopes and optical coherence tomography (OCT), a wide Gaussian spectrum is ideal for low error in the gyro, and high image resolution in OCT. A modelocked fiber laser provides very wide spectra, but the shape can be irregular. We stretch the modelocked pulse temporally with an FBG, and access the frequency components in the time domain. We can then selectively suppress frequencies with an amplitude modulator to synthesize a Gaussian spectrum. Polarization effects and chromatic dispersion will inevitably appear in many optical systems. It is the goal of this thesis to show that their effects can be minimized or utilized for system performance enhancement.<br>by Patrick Chien-pang Chou.<br>Ph.D.
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Conlon, Patrick Joseph. "Ultra-short pulse generation with a Cr'4'+:YAG laser." Thesis, Imperial College London, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320180.
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Von, Eden Elric Omar. "Optical arbitrary waveform generation using chromatic dispersion in silica fibers." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/24780.
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Liu, Weilin. "Real-time Interrogation of Fiber Bragg Grating Sensors Based on Chirped Pulse Compression." Thèse, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/20289.
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Theoretical and experimental studies of real-time interrogation of fiber Bragg grating (FBG) sensors based on chirped pulse compression with increased interrogation resolution and signal-to-noise ratio are presented. Two interrogation systems are proposed in this thesis.
In the first interrogation system, a linearly chirped FBG (LCFBG) is employed as the sensing element. By incorporating the LCFBG in an optical interferometer as the sensor encoding system, employing wavelength-to-time mapping and chirped pulse compression technique, the correlation of output microwave waveform with a chirped reference waveform would provide an interrogation result with high speed and high resolution. The proposed system can provide an interrogation resolution as high as 0.25 μ at a speed of 48.6 MHz. The second interrogation system is designed to achieve simultaneous measurement of strain and temperature. In this system, a high-birefringence LCFBG (Hi-Bi LCFBG) is employed as a sensing element.
8
Hoffman, Mark Brandon. "Sub-picosecond pulse propagation in an erbium-doped fiber amplifier with ion-induced dispersion." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/14961.
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Khanolkar, Ankita Nayankumar. "Effect of Spectral Filtering on Pulse Dynamics of Ultrafast Fiber Oscillators at Normal Dispersion." University of Dayton / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1628171764933755.
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Chichkov, Nikolay B. [Verfasser]. "Pulse duration and energy scaling of femtosecond all-normal dispersion fiber oscillators / Nikolay B. Chichkov." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2012. http://d-nb.info/1024816354/34.
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Resan, Bojan. "DISPERSION-MANAGED BREATHING-MODE SEMICONDUCTOR MODE-LOCKED RING LASER." Doctoral diss., University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2907.
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A novel dispersion-managed breathing-mode semiconductor mode-locked ring laser is developed. The "breathing-mode" designation derives from the fact that intracavity pulses are alternately stretched and compressed as they circulate around the ring resonator. The pulses are stretched before entering the semiconductor gain medium to minimize the detrimental strong integrating self-phase modulation and to enable efficient pulse amplification. Subsequently compressed pulses facilitate bleaching the semiconductor saturable absorber. The intracavity pulse compression ratio is higher than 50. Down chirping when compared to up chirping allows broader mode-locked spectra and shorter pulse generation owing to temporal and spectral semiconductor gain dynamics. Pulses as short as 185 fs, with a peak power of ~230 w, and a focused intensity of ~4.6 gw/cm2 are generated by linear down chirp compensation and characterized by shg-frog method. To our knowledge, this is the highest peak power and the shortest pulse generation from an electrically pumped all-semiconductor system. The very good agreement between the simulated and the measured results verifies our understanding and ability to control the physical mechanisms involved in the pulse shaping within the ring cavity. Application trends such as continuum generation via a photonic crystal fiber, two-photon fluorescence imaging, and ultrafast pulse source for pump-probe experiments are demonstrated.<br>Ph.D.<br>Other<br>Optics and Photonics<br>Optics
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Rudhall, Andrew Peter. "Ultrashort laser pulse shaping for novel light fields and experimental biophysics." Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/3682.
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Broadband spectral content is required to support ultrashort pulses. However this broadband content is subject to dispersion and hence the pulse duration of corresponding ultrashort pulses may be stretched accordingly. I used a commercially-available adaptive ultrashort pulse shaper featuring multiphoton intrapulse interference phase scan technology to characterise and compensate for the dispersion of the optical system in situ and conducted experimental and theoretical studies in various inter-linked topics relating to the light-matter interaction. Firstly, I examined the role of broadband ultrashort pulses in novel light-matter interacting systems involving optically co-trapped particle systems in which inter-particle light scattering occurs between optically-bound particles. Secondly, I delivered dispersion-compensated broadband ultrashort pulses in a dispersive microscope system to investigate the role of pulse duration in a biological light-matter interaction involving laser-induced cell membrane permeabilisation through linear and nonlinear optical absorption. Finally, I examined some of the propagation characteristics of broadband ultrashort pulse propagation using a computer-controlled spatial light modulator. The propagation characteristics of ultrashort pulses is of paramount importance for defining the light-matter interaction in systems. The ability to control ultrashort pulse propagation by using adaptive dispersion compensation enables chirp-free ultrashort pulses to be used in experiments requiring the shortest possible pulses for a specified spectral bandwidth. Ultrashort pulsed beams may be configured to provide high peak intensities over long propagation lengths, for example, using novel beam shapes such as Bessel-type beams, which has applications in biological light-matter interactions including phototransfection based on laser-induced cell membrane permeabilisation. The need for precise positioning of the beam focus on the cell membrane becomes less strenuous by virtue of the spatial properties of the Bessel beam. Dispersion compensation can be used to control the temporal properties of ultrashort pulses thus permitting, for example, a high peak intensity to be maintained along the length of a Bessel beam, thereby reducing the pulse energy required to permeabilise the cell membrane and potentially reduce damage therein.
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Clark, Jeffrey. "Double Negative Metamaterials in Dielectric Waveguide Configurations." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/28708.
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With the recent resurgence of interest in double negative (DNG) materials and the reported construction of a metamaterial with DNG characteristics, applications of these materials become feasible and examination of the behavior of systems and devices a potentially fruitful topic. The most promising area of research, upon inquiry into past work related to DNG materials, proves to be dielectric waveguides. The present investigation, then, focuses on the inclusion of DNG materials in various planar dielectric waveguide configurations. These waveguides involve a core region surrounded by various numbers of symmetrically-placed cladding layers.
The present investigation involves the review of the electromagnetic properties of DNG materials by a thorough analysis based on Maxwell's equations. The use of a negative index of refraction for these materials is justified. These results are then used to perform a frequency domain analysis of an N-layer formulation for dielectric waveguides which is general for any combination of DNG and double positive (DPS) materials. This N-layer formulation allows for the derivation of the characteristic equation, which relates the operating frequency and the propagation constant solutions, along with the cutoff conditions and field distributions. A causal material model which obeys the Kramers-Kronig relations and which is based on measurements of a realized metamaterial is studied and used in the investigation in order to produce realistic results.
The N-layer formulation is then applied to the three-layer (slab) waveguide and known results are reviewed. A new interpretation of intramodal degeneracy is given, whereby degenerate modes are split into two separate modes, one with positive phase velocity and one with negative phase velocity but both with a causal positive group (energy) velocity. Next, the formulation is applied to the five-layer waveguide. New behaviors are observed in this case which are not seen for the three-layer waveguide, including the return of the fundamental mode in some cases, whereas it is never present for the three-layer guide, the absence of certain higher-order modes in some situations and the appearance of new modes. Additionally, for some configurations the order of the even and odd modes in the DNG frequency range is found to be reversed from that of conventional waveguides.
The photonic crystal waveguide, which involves an infinite number of periodically placed cladding layers, is next studied using ray analysis, and a slight variation of the N-layer formulation is used to compare these results with those of the pseudo-photonic crystal waveguide. The pseudo-photonic crystal waveguide is identical to the photonic crystal waveguide with the exception that it has only large but finite number of layers. It is seen that the results of these two cases are similar for conventional modes, but the photonic crystal waveguide allows for new modes called photonic crystal modes which are inaccessible through conventional waveguides. Interesting phenomena such as mode crossings among the photonic crystal modes are observed and discussed.
Using the results from the frequency domain analysis of the five-layer waveguide, a Fourier transform technique is used to study pulse propagation in a waveguide containing DNG materials. A Gaussian pulse is launched in the waveguide over the frequency range covering a portion of the positive- and negative-phase-velocity fundamental transverse electric (TE) modes. Splitting of the input pulse into two separate pulses is observed, where both of these new pulses have a causal, positive energy velocity. The interpretation of intramodal degeneracy given in previous discussions is buttressed with evidence from this portion of the investigation, thus completing the analysis and bringing the present study to its conclusion.<br>Ph. D.
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Mota, Achiles Fontana da. "Análise de propagação de pulso em meios metamateriais." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/18/18155/tde-26032015-084251/.
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Este trabalho tem por objetivo o estudo de dispersão de pulsos ultracurtos em estruturas metamateriais para a faixa de micro-ondas. Como é bem sabido, os metamateriais são estruturas altamente dispersivas em qualquer faixa de frequências. Essas características dispersivas são normalmente tratadas como deletérias para a propagação de pulsos. Entretanto, nesta dissertação é demonstrado que essas mesmas características podem produzir efeitos benéficos em certas aplicações. Para isso é realizada uma análise teórica detalhada das características de dispersão de células metamateriais de diferentes geometrias. Adicionalmente, é investigada a propagação de um pulso gaussiano em meios metamateriais infinitos com o objetivo de melhor compreender fenomenologia por trás dos efeitos de dispersão nesses materiais. É também apresentado um novo procedimento de homogeneização de metamateriais que permite descrever estes meios de maneira mais precisa e com menor custo computacional que métodos encontrados na literatura. Esse método é baseado em modelos materiais conhecidos, como os de Lorentz e Drude. Este trabalho também apresenta uma nova abordagem para compressão de pulsos e compensação de dispersão por meio da propagação de pulsos de micro-ondas chirpados em metamateriais no regime de refração negativa. Para conseguir esse efeito, são investigadas placas de metamateriais com espessuras de 1, 3, 5 e 7 células metamateriais utilizando o método das diferenças finitas no domínio do tempo (FDTD) juntamente com técnicas de extração de parâmetros. É demonstrado que com o controle do chirp inicial do pulso, em associação com a densidade/geometria das células metamateriais e de sua resposta em frequência, é possível não só compensar o alargamento temporal desses pulsos devido à dispersão cromática como também realizar a compressão temporal por um fator de 2.<br>The goal of this work is to study the dispersion of ultra-short microwave pulses in metamaterials structures. It is well known that metamaterials are highly dispersive structures in any frequency range. These dispersive characteristics are normally treated as deleterious to pulse propagation. However, in this dissertation it is demonstrated that these characteristics can produce beneficial effects in certain applications. This assertion is addressed through a theoretical analysis of the dispersion of metamaterials cells of different geometries. In addition, it is investigated the propagation of a gaussian pulse through an infinite homogeneous metamaterial structure aiming at improving our understanding of the phenomenology behind dispersion effects in such media. It is also presented a new homogenization procedure for metamaterials that allows these media to be described in a more realistic manner and with computational cost lower than those currently found in the literature. This procedure is based on well known material models, such as Drude and Lorentz models. This work also introduces an efficient technique for pulse compression and dispersion compensation via propagation of chirped microwave pulses through metamaterials in the negative refraction regime. To accomplish this, it is investigated infinitely wide metamaterial slabs with thicknesses of 1, 3, 5, and 7 cells with a finite difference in time domain method together with a parameter extraction technique. It is demonstrated that by controlling the chirp of the initial pulse, in association with the metamaterial cell density/geometry and frequency response, it is possible not only to compress the pulse (by a factor of 2), but also to compensate pulse broadening due to chromatic dispersion.
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Zaukevičius, Audrius. "The use of angular dispersion for formation of high peak power and ultrashort pulsed light beams in nonlinear interactions." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2012. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20121227_090300-84220.
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This thesis is aimed to provide an extensive picture of the phenomena encountered in optical parametric amplification of pulsed light beams. The particular attention is paid for the spatio-temporal dynamics of the pulsed light beams being amplified. All the research has been done by means of numerical methods. The equations used in the model were derived from the Maxwell’s equations and the assumptions made along the derivation of equations were discussed. Using the presented model it has been numerically demonstrated, that in noncollinear optical parametric amplifier, when pulse fronts of pump and signal are not matched, the signal pulse becomes tilted and aside from angular dispersion acquires a spatial chirp. It has been shown, that the magnitudes of the induced spatial and angular dispersions decrease at different rates with the increase of the signal pulse temporal chirp. The main results of this study were verified experimentally. Additionally, in this thesis we have proposed a novel and versatile method for pulsed conical wave parametric amplification with subsequent spatio-temporal compression during propagation in free space. It allows to form ultra-intense and propagation invariant wave-packets capable to propagate over many Rayleigh range in the desired material. In contrast to ordinary chirped-pulse amplification technique it does not require a pulse compressor, thus greatly facilitates the parametric amplification of few-cycle light pulses.<br>Disertacija yra skirta išnagrinėti ir paaiškinti impulsinių šviesos pluoštų parametrinio stiprinimo metu vykstančius reiškinius. Ypatingas dėmesys yra skiriamas erdvinei-laikinei impulsinio šviesos pluošto dinamikai stiprinimo metu. Visi nagrinėjamų reiškinių tyrimai buvo atliekami taikant skaitmeninio modeliavimo metodus. Modelyje panaudotos lygtys buvo išvestos iš Maksvelo lygčių, išsamiai aptariant lygčių išvedimo metu daromas prielaidas. Naudojantis pateiktu modeliu buvo gauti skaitmeniniai rezultatai, kurie parodė, jog nekolineariame parametriniame stiprintuve, kuomet kaupinimo ir signalinio impulsų frontai nėra sutapatinti, signalinis impulsas tampa pakrypęs ir be kampinės dispersijos taip pat įgyja ir erdvinį čirpą. Nustatyta, kad indukuotų erdvinės ir kampinės dispersijų mažėjimo sparta, didinant signalinio impulso laikinį čirpą, yra skirtinga. Pagrindiniai šio teorinio tyrimo rezultatai buvo patvirtinti eksperimentiškai. Taip pat šioje disertacijoje yra pristatomas naujas ir universalus impulsinių kūginių bangų parametrinio stiprinimo metodas, kuriame sustiprinti impulsai patys susispaudžia laike ir erdvėje paprasčiausiai sklisdami laisvoje erdvėje. Šis metodas leidžia formuoti didelio smailinio intensyvumo invariantiškus bangų paketus, galinčius nusklisti daugelį Relėjaus nuotolių norimoje medžiagoje. Priešingai nei įprastame čirpuotų impulsų stiprinimo metode, šis metodas nereikalauja impulsų spaustuvo, o tai žymiai palengvina parametrinį kelių optinių ciklų... [toliau žr. visą tekstą]
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Kobayashi, Wataru [Verfasser], and Helmut [Akademischer Betreuer] Zacharias. "Development of a high-repetition-rate intense ultrashort optical parametric chirped-pulse amplifier system with a global dispersion management / Wataru Kobayashi. Betreuer: Helmut Zacharias." Münster : Universitäts- und Landesbibliothek der Westfälischen Wilhelms-Universität, 2012. http://d-nb.info/1027027881/34.
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Pistore, Valentino. "Modelocking of THz quantum cascade lasers : dispersion control and non-linearities." Electronic Thesis or Diss., Sorbonne université, 2019. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2019SORUS302.pdf.
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Les LCQ THz sont aujourd'hui considérés comme une plate-forme prometteuse pour la génération d’impulsions THz intenses et ultracourtes. En raison de leur temps de récupération du gain rapide, le verrouillage en mode passif des LCQ THz s'est jusqu'à présent révélé difficile. Au contraire, le verrouillage de mode actif avec une modulation hyperfréquence a été appliqué avec succès. La durée du pouls a cependant été difficile à réduire malgré des années de recherche. En 2017, notre groupe a généré des impulsions THz de 4ps grâce à l'application d'une structure intégrée (un GTI) visant à réduire la dispersion chromatique. La recherche dans cette thèse commence à partir de ce point. Je présente notamment l'ingénierie de dispersion dans les LCQ THz afin d'obtenir des impulsions très courtes, même à partir de dispositifs à bande relativement étroite. Ceci est réalisé en utilisant des méthodes de modulation actives éprouvées qui peuvent ajuster l’émission de LCQ d’un régime de dispersion élevé à faible. Je montre également que les LCQ THz peuvent présenter une forte modulation d'amplitude de leur profil d'émission et qu'ils peuvent émettre spontanément des impulsions à la suite d'un mécanisme d’auto-verrouillage. En conséquence, cela indique que le temps de récupération de gain rapide n'est pas un facteur limitant pour la génération d'impulsions. Je montre également ce schéma passif dans le cadre des premières démonstrations du verrouillage en mode harmonique de LCQ THz. Enfin, un nouveau phénomène est présenté où les modes d’une LCQ THz peuvent battre ensemble pour générer une émission de micro-ondes dans l’espace libre<br>THz QCLs are nowadays considered a promising platform for the generation of intense and ultrashort THz pulses. Owing to their fast gain recovery time, passive modelocking of THz QCLs has so far proved to be difficult. On the contrary, active modelocking with a microwave modulation has been successfully applied. The pulse duration, however, has been arduous to reduce despite years of research. In 2017, THz pulses as short as 4ps have been generated by our group with the application of an integrated structure (a GTI) aiming to reduce the chromatic dispersion. The research in this thesis starts from this point.In particular, I present dispersion engineering in THz QCLs in order to obtain very short pulses even from relatively narrow-band devices. This is achieved using proven active modulation methods that can tune the QCL emission from high to low dispersion regimes. I also show that THz QCLs can present a strong amplitude modulation of their emission profile and that they can spontaneously emit pulses as a result of a self-locking mechanism, contrary to the expected frequency modulated response. As a consequence, this indicates that the fast gain recovery time is not a limiting factor for the generation of pulses. I also show this passive self-locking scheme for passive pulse generation in the framework of the first demonstrations of harmonic modelocking of THz QCLs. Finally, a new phenomenon is presented where the modes of a free running THz QCL can beat together to generate free space microwave emission
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Lobry, Emeline. "Batch to continuous vinyl chloride suspension polymerization process : a feasibility study." Phd thesis, Toulouse, INPT, 2012. http://oatao.univ-toulouse.fr/11498/1/lobry.pdf.
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Continuous processes present the benefit to be safer and more cost saving than batch processes. Many researches have been carried out in fine chemistry but few contributions refer to polymerization. We focus on the vinyl chloride suspension polymerization. This process has been extensively studied in batch with lots of improvement regarding the formulation and the technologies. This polymerization process is highly complex due to the toxic nature of the monomer, the good manage of heat transfer and stirring. Moreover the reaction step remains the only batch step of the PVC production. According to the PVC grain formation, the process can be divided into three steps (i) a liquid-liquid dispersion step in which the monomer droplet (30-50 µm) are generated and stabilized, (ii) a controlled agglomeration step of the reacting droplets exhibiting a sticky behaviour, (iii) a reaction step until the conversion rate is around 80-90% and the particles size is stable. In this study, the different technologies suitable for the different steps are pointed out. Based on the state of the art of the grain behaviour depending on the reaction conversion and on the literature concerning polymerization continuous process, static mixers and different co-current pulsed columns are proposed. Three technologies with different model system were chosen to study the liquid-liquid dispersion step. Static mixers allow the control of the droplet size under turbulent flow. In the range of the operating conditions, the dispersed phase concentration does not have a significant effect on the droplet size. The interfacial tension appears to be the most significant physico-chemical parameters. Correlation to predict the mean droplet size is proposed depending on different dimensionless numbers based on the hydrodynamics and on the systems: the Reynolds and Weber numbers. Given the promising results, static mixers are implemented at pilot scale to load the batch prior to polymerization. Their use demonstrates a noticeable reduction of the loading time and a better homogenisation of the different suspending agents and initiator inside the PVC grain. The two co-current pulsed columns design studied are the discs and doughnuts pulsed column and the COBR (continuous oscillatory baffled reactor, Nitech). For the first one, the effect of the packing materials (type and height), of the physico-chemical parameters (dispersed phase concentration, surfactant) and of hydrodynamic parameters (flowrate and oscillation conditions) on the droplet size are investigated where as for the second one the study is limited to the hydrodynamic parameters. A mean droplet size correlation is proposed based on the characteristic dimensionless numbers. The three continuous contactors used for liquid-liquid dispersion are compared in term of energy dissipation rate. The reaction is carried out in a continuous tubular reactor (the pulsed column). The column is suitable to transport solid-liquid suspension. Vinyl acetate suspension polymerization is performed to demonstrate the feasibility and particularly to study the encrusting and fouling problem. The first results are very promising.
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Zhu, S. "Digital communications over dispersive channels using pre-transmission pulse shaping." Thesis, University of Essex, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374731.
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Shane, Janelle. "Optical micromanipulation using dispersion-compensated and phase-shaped ultrashort pulsed lasers /." St Andrews, 2009. http://hdl.handle.net/10023/730.
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Coleman, William F. "Pulse-splitting and AM-FM conversion in a nonlinear dispersive medium." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA277041.
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Thesis (M.S. in Physics) Naval Postgraduate School, December 1993.<br>Thesis advisor(s): Andrés Larraza ; Anthony A. Atchley. "December 1993." Includes bibliographical references. Also available online.
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Okoye, Raphael. "Manipulation of short pulses." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/85576.
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Thesis (MSc)--Stellenbosch University, 2013.<br>ENGLISH ABSTRACT: An ultra-fast laser pulse can be described in the time or frequency domain. If the timebandwidth
product of an ultra-fast pulse is not satisfied, then the pulse is stretched. Stretching
can be described in the time or frequency domain. In the time domain, it is called a chirp and
in the frequency domain, it is known as the group delay dispersion GDD. Various techniques
can be used to stretch and compress laser pulses. In this project, a prism pulse compressor used
for compressing stretched pulses was built. A 200nm supercontinnum generated in an all normal
dispersion photonic crystal fibre (ANDi-PCF) was compressed using the prism pulse compressor
from 2ps to 140fs. The experiment and physical interpretation presented in this project suggest
that a shorter pulse duration less than the measured 140fs of the compressed supercontinnum
can be obtained.<br>AFRIKAANSE OPSOMMING: 'n Ultra-vinnige laser puls kan beskryf word in tyd of frekwensie. As die tyd-bandwydte produk
van ‘n ultra-vinnige puls nie bevredig is nie, dan is die puls uitgerek. Hierdie uitrekking kan
beskryf word in tyd of frekwensie. In tyd word dit tjirp genoem en in frekwensie groep vertraging
dispersie. Verskeie tegnieke kan gebruik word om ‘n laser puls te rek of saam te pers. In
hierdie projek is ‘n prisma puls kompressor gebou om uitgerekte pulse saam te pers. ‘n 200nm
bre e bandwydte puls (“supercontinuum”) is gegenereer in ‘n fotoniese kristal optiese vesel wat
uitsluitlik normale dispersie toon (ANDI-PCF) en die puls is toe saamgepers met behulp van die
prisma puls kompressor van‘n oorspronklike 2ps na 140fs. Die eksperiment en fisiese interpretasie
wat in hierdie projek aangebied word dui daarop dat ‘n nog korter puls, minder as die gemete
140 fs, verkry kan word deur die bre e bandwydte puls verder saam te pers.
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Zaukevičius, Audrius. "Kampinės dispersijos panaudojimas galingų ir ultratrumpų impulsinių šviesos pluoštų formavimui netiesinių sąveikų metu." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2012. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20121227_090243-44723.
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Disertacija yra skirta išnagrinėti ir paaiškinti impulsinių šviesos pluoštų parametrinio stiprinimo metu vykstančius reiškinius. Ypatingas dėmesys yra skiriamas erdvinei-laikinei impulsinio šviesos pluošto dinamikai stiprinimo metu. Visi nagrinėjamų reiškinių tyrimai buvo atliekami taikant skaitmeninio modeliavimo metodus. Modelyje panaudotos lygtys buvo išvestos iš Maksvelo lygčių, išsamiai aptariant lygčių išvedimo metu daromas prielaidas. Naudojantis pateiktu modeliu buvo gauti skaitmeniniai rezultatai, kurie parodė, jog nekolineariame parametriniame stiprintuve, kuomet kaupinimo ir signalinio impulsų frontai nėra sutapatinti, signalinis impulsas tampa pakrypęs ir be kampinės dispersijos taip pat įgyja ir erdvinį čirpą. Nustatyta, kad indukuotų erdvinės ir kampinės dispersijų mažėjimo sparta, didinant signalinio impulso laikinį čirpą, yra skirtinga. Pagrindiniai šio teorinio tyrimo rezultatai buvo patvirtinti eksperimentiškai. Taip pat šioje disertacijoje yra pristatomas naujas ir universalus impulsinių kūginių bangų parametrinio stiprinimo metodas, kuriame sustiprinti impulsai patys susispaudžia laike ir erdvėje paprasčiausiai sklisdami laisvoje erdvėje. Šis metodas leidžia formuoti didelio smailinio intensyvumo invariantiškus bangų paketus, galinčius nusklisti daugelį Relėjaus nuotolių norimoje medžiagoje. Priešingai nei įprastame čirpuotų impulsų stiprinimo metode, šis metodas nereikalauja impulsų spaustuvo, o tai žymiai palengvina parametrinį kelių optinių ciklų... [toliau žr. visą tekstą]<br>This thesis is aimed to provide an extensive picture of the phenomena encountered in optical parametric amplification of pulsed light beams. The particular attention is paid for the spatio-temporal dynamics of the pulsed light beams being amplified. All the research has been done by means of numerical methods. The equations used in the model were derived from the Maxwell’s equations and the assumptions made along the derivation of equations were discussed. Using the presented model it has been numerically demonstrated, that in noncollinear optical parametric amplifier, when pulse fronts of pump and signal are not matched, the signal pulse becomes tilted and aside from angular dispersion acquires a spatial chirp. It has been shown, that the magnitudes of the induced spatial and angular dispersions decrease at different rates with the increase of the signal pulse temporal chirp. The main results of this study were verified experimentally. Additionally, in this thesis we have proposed a novel and versatile method for pulsed conical wave parametric amplification with subsequent spatio-temporal compression during propagation in free space. It allows to form ultra-intense and propagation invariant wave-packets capable to propagate over many Rayleigh range in the desired material. In contrast to ordinary chirped-pulse amplification technique it does not require a pulse compressor, thus greatly facilitates the parametric amplification of few-cycle light pulses.
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Bell, Matthew Richard. "Versatile high resolution dispersion measurements in semiconductor photonic nanostructures using ultrashort pulses." Thesis, St Andrews, 2007. http://hdl.handle.net/10023/339.
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Calvo, David C. (David Christopher). "Dyanmics of nonlinear pulses near the zero-dispersion wavelength in optical fibers." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/42676.
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Chouli, Souad. "Structures optiques dissipatives en cavité laser à fibre." Phd thesis, Université de Bourgogne, 2011. http://tel.archives-ouvertes.fr/tel-00692049.
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Cette thèse concerne l'étude de la dynamique des structures optiques dissipatives observées dans une cavité à gestion de dispersion utilisant l'évolution non linéaire de la polarisation comme technique de blocage de modes. Nous avons montré expérimentalement l'existence d'une transition graduelle entre le régime de fonctionnement continu et le régime de fonctionnement multi-impulsionnel. Nous nous sommes intéressés à l'état intermédiaire où il nous a été possible d'obtenir divers régimes inédits et d'étudier ainsi le comportement collectif des solitons dissipatifs en présence d'un fond continu. La dynamique de "la pluie de solitons" est une manifestation complexe et fascinante constituée de trois composantes de champ : le fond continu, les solitons de dérive et la phase condensée. Elle s'accompagne d'une circulation d'énergie à travers ces trois composantes. Le mouvement relatif des solitons de dérive ainsi que l'asymétrie temporelle présentent les caractéristiques majeures qui distinguent cette dynamique des autres. D'autres types d'auto-organisation ont été observés et étudiés, comme "le relargage des solitons de la phase condensée" ou bien encore "la vobulation du train de solitons". Nous nous sommes intéressés aussi à la propagation d'une seule impulsion dans la cavité. Pour la première fois, une importante dynamique de respiration spectrale a été prédite dans une cavité à gestion de la dispersion. Nous avons montré qu'une compression temporelle de l'impulsion est accompagnée d'un élargissement spectral d'une grande ampleur dans la partie passive de la cavité et que la largeur de l'impulsion peut dépasser la largeur de la bande passante du milieu amplificateur. Nous avons étudié la dynamique de la respiration spectrale, l'extraction et l'optimisation du signal laser en fonction des paramètres de la cavité et nous avons présenté les caractéristiques d'une cavité qui permet la génération d'une impulsion dont sa largeur spectrale est supérieure à la largeur de la bande passante de l'amplificateur d'un facteur de 2.4. Les dynamiques présentées dans cette thèse témoignent de la complexité et de la richesse de la dynamique dissipative des lasers à fibre fonctionnant en régime de blocage de modes passif par évolution non linéaire de la polarisation.
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Eliasson, Peder. "Emittance preservation and luminosity tuning in future linear colliders." Doctoral thesis, Uppsala University, Department of Physics and Astronomy, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8576.
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<p>The future International Linear Collider (ILC) and Compact Linear Collider (CLIC) are intended for precision measurements of phenomena discovered at the Large Hadron Collider (LHC) and also for the discovery of new physics. In order to offer optimal conditions for such experiments, the new colliders must produce very-high-luminosity collisions at energies in the TeV regime.</p><p>Emittance growth caused by imperfections in the main linacs is one of the factors limiting the luminosity of CLIC and ILC. In this thesis, various emittance preservation and luminosity tuning techniques have been tested and developed in order to meet the challenging luminosity requirements.</p><p>Beam-based alignment was shown to be insufficient for reduction of emittance growth. Emittance tuning bumps provide an additional powerful preservation tool. After initial studies of tuning bumps designed to treat certain imperfections, a general strategy for design of optimised bumps was developed. The new bumps are optimal both in terms of emittance reduction performance and convergence speed. They were clearly faster than previous bumps and reduced emittance growth by nearly two orders of magnitude both for CLIC and ILC.</p><p>Time-dependent imperfections such as ground motion and magnet vibrations also limit the performance of the colliders. This type of imperfections was studied in detail, and a new feedback system for optimal reduction of emittance growth was developed and shown to be approximately ten times more efficient than standard trajectory feedbacks.</p><p>The emittance tuning bumps require fast and accurate diagnostics. The possibility of measuring emittance using a wide laserwire was introduced and simulated with promising results. While luminosity cannot be directly measured fast enough, it was shown that a beamstrahlung tuning signal could be used for efficient optimisation of a number of collision parameters using tuning bumps in the Final Focus System.</p><p>Complete simulations of CLIC emittance tuning bumps, including static and dynamic imperfections and realistic tuning and emittance measurement procedures, showed that an emittance growth six times lower than that required may be obtained using these methods.</p>
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Demircan, Ayhan [Verfasser]. "Control of ultrashort pulses in nonlinear dispersive media / Ayhan Demircan." Hannover : Technische Informationsbibliothek (TIB), 2016. http://d-nb.info/1108820948/34.
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Brunet, Léna. "Conception d'un nouveau type de colonne pulsée appliquée au contact solide-liquide." Toulouse, INPT, 2005. https://hal.science/tel-04582776.
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Cette étude porte sur la conception d'une nouvelle technologie de colonne pulsée appliquée au contact solide/liquide. L'originalité du concept développé réside dans l'introduction d'internes et d'un mode de pulsation qui permettent de contrôler le temps de séjour solide indépendamment de celui du liquide. La faisabilité du concept et la caractérisation du comportement hydrodynamique des deux phases ont été étudiées sur un pilote semi-industriel, en réalisant des DTS sur des systèmes modèles. Un cas réel a ensuite été mis en oeuvre dans la colonne, afin d'illustrer les avantages du nouveau procédé en termes d'efficacité du transfert de matière. Il apparaît, au final, que le dispositif permet de réduire sensiblement la dispersion granulométrique et de prolonger le temps de séjour du solide, tout en réduisant la consommation en solvant. Les qualités de la nouvelle colonne conçue en font un appareil particulièrement adapté aux systèmes solide/liquide nécessitant un temps de contact prolongé. Grâce à une technologie innovante et à un réglage fin des paramètres opératoires, il est ainsi rendu possible d'intensifier le contact solide/liquide<br>This work deals with a novel type of pulsed column used as a solid/liquid contactor. An evolution in the design of the internals and in the shape of the pulsation has been set up. The initial objectives were to achieve a contactor of much longer solid residence time, independently of the liquid phase behaviour. Phase contacting is carried out countercurrently, solid is fed in at the bottom of the column and flows upwardly, regardless of the density difference between both phases. First, the technical feasibility was demonstrated. Then, the behaviour of solid and liquid phases was investigated through the analysis of residence times distributions. And, mass transfer efficiency has been evaluated with an industrial case. It was found that the column could enhance solid residence times, reduce granulometric segregation and solvent consumption. The new contactor seems to be particularly suitable for cases where a long contact between both phases is needed. Thanks to innovative internals and to an optimal tuning of the operating conditions, intensification of solid/liquid contacting was finally achieved
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Boscolo, Sonia A. "Mathematical and numerical modelling of dispersion-managed solitons, autosolitons and self-similar optical pulses." Thesis, Aston University, 2002. http://publications.aston.ac.uk/7997/.
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Firstly, dispersion-managed (DM) solitons in fibre lines employing a weak dispersion map are analysed by means of a perturbation approach. In the case of small dispersion map strengths the average pulse dynamics is described by a perturbation approach (NLS) equation. Applying a perturbation theory, based on the Inverse Scattering Transform method, an analytic expression for the envelope of the DM soliton is derived. This expression correctly predicts the power enhancement arising from the dispersion management. Secondly, autosoliton transmission in DM fibre systems with periodical in-line deployment of nonlinear optical loop mirrors (NOLMs) is investigated. The use of in-line NOLMs is addressed as a general technique for all-optical passive 2R regeneration of return-to-zero data in high speed transmission system with strong dispersion management. By system optimisation, the feasibility of ultra-long single-channel and wavelength-division multiplexed data transmission at bit-rates ³ 40 Gbit s-1 in standard fibre-based systems is demonstrated. The tolerance limits of the results are defined. Thirdly, solutions of the NLS equation with gain and normal dispersion, that describes optical pulse propagation in an amplifying medium, are examined. A self-similar parabolic solution in the energy-containing core of the pulse is matched through Painlevé functions to the linear low-amplitude tails. The analysis provides a full description of the features of high-power pulses generated in an amplifying medium.
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Nikolaidis, Konstantinos. "An investigation of an optical multiple pulse position modulation link over a dispersive optical channel." Thesis, University of Huddersfield, 2008. http://eprints.hud.ac.uk/id/eprint/6980/.
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Digital Pulse Position Modulation (digital PPM) is a modulation format that codes n bits of PCM into a single pulse that occupies one of 2n time slots. Various studies over the last three decades have shown that such a scheme can offer an improvement in receiver sensitivity of 5-11 dB when compared to Pulse Code Modulation (PCM). Such an increase in sensitivity can be exploited beneficially in both long haul applications and the multi-user environment. However, this improvement results in a considerable increase in the final data rate of the original PCM, and this makes implementation difficult. Alternative methods have been proposed, such as multiple PPM, dicode PPM, differential PPM and overlapping PPM, that reduce transmission bandwidth while maintaining an increased sensitivity. Dicode and multiple PPM (MPPM) are the most bandwidth efficient of these formats and MPPM, the subject of this thesis, offers the best sensitivity without the large bandwidth increase. In this scheme, multiple pulses per frame are used, with the pulse positions being determined by the original PCM word. The main concern of this thesis is a full and detailed investigation of an Optical MPPM link operating over a dispersive optical channel. As the analysis of any (X/Y) multiple PPM system, in which X denotes the number of data slots and Y the number of pulses, is extremely time-consuming, a novel automated solution was designed to predict the equivalent PCM error rates of specific sequences and simplify the task. An original mathematical formulation is developed using the Maximum Likelihood Sequence Detection (MLSD) scheme. Using the equivalent PCM error rates of specific sequences generated from software, a full simulation of an MPPM optical link can be produced and the results show the effectiveness of the MPPM format over PPM. A measure of coding quality is proposed that accounts for efficiency of coding and bandwidth expansion. Original results are presented for a (12/Y) MPPM system, considered as very efficient and examined by many authors, showing that the most efficient systems are in the middle of the family. A methodology to predict the Bit Error Rate (BER) of any MPPM system is also proposed. The results obtained confirmed the results obtained from the full mathematical analysis. The effects of linear increment, linear decrement, Gray code and random mapping of data on ther performance of a (12/Y) multiple PPM system are also examined. Simulations show that the Gray code is the most effective as it minimizes the Hamming distance between adjacent multiple PPM words. Further experiments showed that system performance can be obtained exclusively with the use of software making the analysis simpler and minimizing the time consumption. A novel algorithm is presented and results obtained using this method, agree with those obtained using a full mathematical model. Certain mappings can either enhance or degrade the final total error probability of the system and hence affect the sensitivity of the MLSD scheme. In this thesis the author also suggests a methodology of how to predict and generate an optimum or close to optimum mapping. The methodology is based on minimizing the occurrence of dominant error sequences. Detailed results show the effectiveness of this mapping routine. For the first time also, high order MPPM codes are considered for analysis. All the experiments completed for the (12/Y) MPPM system are repeated for a range of MPPM systems (with 4, 7, 15, 17, 22, 28 and 33 slots operating over a plastic optical fibre (POF) channel showing again that the most efficient systems are in the middle of the family. Close to optimum mappings are also presented for these MPPM systems. The estimated mappings were found to be far superior to the efficient Gray codes, linear coding and a series of random mappings. To measure these optimum mappings a very efficient mapping is also considered. This mapping minimises the Hamming distance between all MPPM codewords. This mapping allows repetitions of MPPM codewords and cannot be used in a MLSD scheme. Therefore, it is only used for comparisons with the (close to) optimum mappings. It is shown that the optimum mappings are close to ideal. Other correlation techniques are also considered for optimised detection in the MLSD scheme. Results obtained showed that raised cosine filtering can enhance detection.
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Šeděnka, Vladimír. "Numerická řešení problematiky EMC malých letadel." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2013. http://www.nusl.cz/ntk/nusl-233594.
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Disertace popisuje současné problémy v certifikaci malých letadel, které by se měly v budoucnu řešit numerickým modelováním. Tento postup má zefektivnit návrh a zlevnit certifikaci letadel. Práce je úzce spjata s projektem HIRF-SE, který se problematikou certifikace letadel numerickými metodami zabývá. Podstatná část práce je věnována popisu dvou modulů pro platformu HIRF-SE: řešič BUTFE založený na metodě konečných prvků v časové oblasti a budicí nástroj BUTFE_EXC. Práce popisuje řešení pohlcujících okrajových podmínek, modelování disperzních a anizotropních materiálů a aproximaci tenkých drátů. Speciální pozornost je věnována řešení aproximace tenkých drátů s ostrými ohyby, jejíž současná formulace způsobuje překryvy mezi jednotlivými segmenty drátu.
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Drikas, Zachary Benjamin. "New Techniques for Time-Reversal-Based Ultra-wideband Microwave Pulse Compression in Reverberant Cavities." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/100998.
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Generation of high-peak power, microwave ultra-short pulses (USPs) is desirable for ultra-wideband communications and remote sensing. A variety of microwave USP generators exist today, or are described in the literature, and have benefits and limitations depending on application. A new class of pulse compressors for generating USPs using electromagnetic time reversal (TR) techniques have been developed in the last decade, and are the topic of this dissertation. This dissertation presents a compact TR microwave pulse-compression cavity that has ultra-wide bandwidth (5 GHz – 18 GHz), and employs waveguide feeds for high-peak power output over the entire band. The system uses a time-reversal-based pulse compression scheme with one-bit processing (OBTR) to achieve high compression gain. Results from full-wave simulations are presented as well as measurements showing compression gain exceeding 21.2 dB, 22% efficiency, and measured instantaneous peak output powers reaching 39.2 kW. These are all record results for this type of pulse compressor. Additionally presented is new analysis of variation in compression gain due to impulse response recording time and bandwidth variation, new experimental work on the effect of mode stirrer position on compression gain, and a novel RF switch-based technique for reducing time-sidelobes while using OBTR. Finally, a new technique is presented that uses a reverberant cavity with only one feed connected to an ultra-wideband circulator (6.5 GHz to 17 GHz) to perform TRPC. Prior to this work, TRPC has only been demonstrated in electromagnetics using two or more feeds and a reverberant cavity acting as the time-reversal mirror. This new 1-port technique is demonstrated in both simulation and measurement. The proposed system achieves up to a measured 3 dB increase in compression gain and increased efficiency. Also, a novel application of the random coupling model (RCM) to calculate compression gain is presented. The cavity eigenfrequencies are modeled after eigenvalues of random matrices satisfying the Gaussian orthogonal ensembles (GOE) condition. Cavity transfer functions are generated using Monte Carlo simulations, and used to compute the compression gains for many different cavity realizations.<br>Doctor of Philosophy<br>Generation of high-peak power, microwave ultra-short pulses (USPs) is desirable for ultra-wideband communications and remote sensing. A variety of microwave USP generators exist today, or are described in the literature, and have benefits and limitations depending on application. A new class of pulse compressors for generating USPs using electromagnetic time reversal (TR) techniques have been developed in the last decade, and are the topic of this dissertation. This dissertation presents a compact TR-based microwave pulse-compression cavity that has unique features that make it optimal for high-power operations, with results from simulations as well as measurements showing improved performance over other similar cavities published in the literature with a record demonstrated peak output power of 39.2 kW. Additionally, new analysis on the operation and optimization of this cavity for increased performance is also presented. Finally, a new technique is presented that uses a cavity with only one feed that acts as both the input and output. This 1-port technique is demonstrated in both simulation and measurement. The proposed system achieves a two-times increase in compression gain over its 2-port counterpart. In conjunction with these measurements and simulations, a novel technique for predicting the performance of these cavities using Monte Carlo simulation is also presented.
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LE, GARREC STEPHANE. "Modelisation et simulation numerique de l'ecoulement et de la dispersion d'un contaminant dans une colonne pulsee." Paris, CNAM, 1993. http://www.theses.fr/1993CNAM0167.
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Les simulations numeriques d'ecoulements oscillants pour lesquels la vitesse debitante varie de facon sinusoidale dans le temps, a mis en evidence divers regimes d'ecoulement dans une gamme etendue d'amplitude et de frequence. Aux plus basses valeurs de ces parametres, des recirculations sont alternativement detruites par l'ecoulement moyen puis remplacees tandis que des recirculations perpetuelles sont observees aux amplitudes et aux frequences plus elevees. La simulation de la dispersion d'un contaminant a mis en evidence deux mecanismes de melange associes a l'inertie des recirculations. Le contaminant se disperse sous l'action unique de l'ecoulement moyen lorsque les recirculations sont periodiquement detruites et generees a chaque cycle de pulsation. Lorsque des recirculations perpetuelles ont suffisamment d'inertie pour maintenir un niveau de vitesse eleve, la dispersion s'effectue sous les effets des actions conjuguees de l'ecoulement moyen et des recirculations. Par ailleurs, l'ecoulement parietal du a l'espace entre les couronnes et le cylindre de la colonne ainsi que l'application d'une pulsation en forme de creneau contribuent a la reduction de la dispersion longitudinale
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Bhonsle, Suyashree P. "Non-linearity and Dispersion Effects in Tissue Impedance during Application of High Frequency Electroporation-Inducing Pulsed Electric Fields." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/91904.
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Since its conception in 2005, irreversible electroporation (IRE), a non-thermal tumor ablation modality, was investigated for safety and efficacy in clinical applications concerning different organs. IRE utilizes high voltage (~3kV), short duration (~100us) pulses to create transient nanoscale defects in the plasma membrane to cause cell death due to irreversible defects, osmotic imbalances and ATP loss. More recently, high-frequency irreversible electroporation (H-FIRE), which employs narrow bipolar pulses (~0.5-10us) delivered in bursts (on time ~100us), was invented to provide benefits such as the mitigation of intense muscle contractions associated with IRE-based treatments. Furthermore, H-FIRE exhibits the potential to improve lesion predictability in homogeneous and heterogeneous tissue masses.
Therapeutic IRE and H-FIRE utilize source and sink electrodes inserted into or around the tumor to deliver the treatment. Prediction of the ablation size, for a set of parameters, can be achieved by the use of pre-treatment planning algorithms that calculate the induced electric field distribution in the target tissue. An electric field above a certain threshold induces cell death and parameters are tuned to ensure complete tumor coverage while sparing the nearby healthy tissue. IRE studies have shown that the underlying field is influenced by the increase in tissue conductivity due to enhanced membrane permeability, and treatment outcome can be improved when this nonlinearity is accounted for in numerical models.
Since IRE pulses far exceed the time constant of the cell (~1us), the tissue response can be treated as essentially DC a static approximation can be used to predict the field distribution. Alternately, as H-FIRE pulses are on the order of the time constant of the membrane, the tissue response can no longer be treated as DC. The complexity of the H-FIRE-induced field distribution is further enhanced due to the dispersion and non-linearity in biological tissue impedance during treatment.
In this dissertation, we have studied the electromagnetic fields induced in tissue during H-FIRE using several experimental and modeling techniques. In addition, we have characterized the nonlinearity and dispersion in tissue impedance during H-FIRE treatments and proposed simpler methods to predict the field distribution to enable easier translation to the clinic.<br>Ph. D.
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Li, Ji. "Modèle dans le domaine temporel et la validation expérimentale d’un scanner ultrasonore à ondes de surface sans contact." Thesis, Ecole centrale de Lille, 2017. http://www.theses.fr/2017ECLI0026/document.
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Ce travail de recherche propose l’algorithme de calcul pour la modélisation d’un scanner ultrasonore sans contact à ondes de surface. L’approche proposée permet de prendre en compte l’ouverture finie du récepteur, l’atténuation d’air et la réponse électrique he de l’ensemble émetteur-récepteur. Le milieu avec l’atténuation (air et milieu testé) est modélisé dans le domaine temporel à l’aide de la fonction de Green causale permettant la caractérisation large bande. Le réponse he est déterminée de manière expérimentale en utilisant la procédure spatialement développée, incluant la déconvolution des effets d’atténuation. Le modèle est implémenté numériquement en utilisant l’approche de la Représentation Discrète et les résultats obtenus sont validés expérimentalement. La technique chirp est utilisée afin d’améliorer le rapport signal/bruit. Il est démontré que lorsque l’atténuation dans l’air, la dimension de récepteur et la réponse he reconstituée avec précision sont correctement pris en compte, la réponse impulsionnelle du système peut être prédite avec l’erreur de 2-5 %. L’introduction de la taille du récepteur est essentielle pour la prédiction dans le champ proche. Le temps de calcul obtenu est considérablement plus court que le temps nécessaire pour les méthodes FEM. A l’aide de ce modèle l’influence des réglages du scanner est étudiée. Les résultats obtenus permettent de formuler des recommandations pour les réglages optimaux<br>In this research the time-domain model for the prediction of an acoustic field in an air-coupled, non-contact, surface wave scanner is proposed. The model takes into account the finite size of the aperture receiver, attenuation in air, and the electric response he of the emitter-receiver set he. The attenuation is characterized by a causal time-domain Green’s function, allowing the wideband attenuation of a lossy medium (air and solid tested sample) obeying the power law to be modelled. The response he is recovered experimentally using an original especially developed procedure which includes the deconvolution of air absorption effects. The model is implemented numerically using a Discrete Representation approach and validated experimentally. In order to improve the signal to noise ratio the chirp technique is used. It is shown that when the attenuation in air, the receiver size, and the accurately recovered response he, are correctly taken into account, the model allows the system’s impulse response to be very accurately predicted, with errors ranging between 2-5%. Inclusion of the size of the receiver dimension in the model appears to be crucial to the accuracy of the near field predictions. The obtained computation efficiency is much better that efficiency of FEM methods. The influence of typical user defined settings has been investigated. The obtained conclusions will be used as the recommendations for further use
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Pathak, Mihir Gaurang. "Periodic flow physics in porous media of regenerative cryocoolers." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49056.
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Pulse tube cryocoolers (PTC) are a class of rugged and high-endurance refrigeration systems that operate without moving parts at their low temperature ends, and are capable of reaching temperatures down to and below 123 K. PTCs are particularly suitable for applications in space, guiding systems, cryosurgery, medicine preservation, superconducting electronics, magnetic resonance imaging, weather observation, and liquefaction of gases. Applications of these cryocoolers span across many industries including defense, aerospace, biomedical, energy, and high tech. Among the challenges facing the PTC research community is the improvement of system efficiency, which is a direct function of the regenerator component performance. A PTC implements the theory of oscillatory compression and expansion of the gas within a closed volume to achieve desired refrigeration. An important deficiency with respect to the state of art models dealing with PTCs is the limited understanding of the hydrodynamic and thermal transport parameters associated with periodic flow of a cryogenic fluid in micro-porous structures. In view of the above, the goals of this investigation include: 1) experimentally measuring and correlating the steady and periodic flow Darcy permeability and Forchheimer’s inertial hydrodynamic parameters for available rare-Earth ErPr regenerator filler; 2) employing a CFD-assisted methodology for the unambiguous quantification of the Darcy permeability and Forchheimer’s inertial hydrodynamic parameters, based on experimentally measured steady and periodic flow pressure drops in porous structures representing recently developed regenerator fillers; and 3) performing a direct numerical pore-level investigation for steady and periodic flows in a generic porous medium in order to elucidate the flow and transport processes, and quantify the solid-fluid hydrodynamic and heat transfer parameters. These hydrodynamic resistances parameters were found to be significantly different for steady and oscillatory flows.
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Prichard, Leslie Stephen. "Studies of reversal processes in particulate recording media using pulsed field magnetometry." Thesis, Bangor University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311392.
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Castellano, Simone. "Multiscale study and modeling of dispersion properties relevant for liquid-liquid extraction : adaptation of breakup and coalescence kernels to industrial processes." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1243.
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Ce projet de thèse porte sur l'étude de l'hydrodynamique des dispersions dans les extracteurs liquide-liquide utilisés dans l'industrie du recyclage nucléaire. Dans la première partie du projet, un modèle de bilan de population homogène (0D-PBM), basé sur l'évaluation des taux moyens en volume de coalescence et de rupture, est proposé. La méthode tient compte des inhomogénéités spatiales dans le mélange, notamment de la fonction de densité de probabilité de la dissipation de l’énergie cinétique turbulente dans l’appareil. Le modèle est capable de reproduire les expériences de dispersion liquide-liquide turbulentes à faible viscosité. Dans la deuxième partie de cette étude, un modèle généralisé pour les noyaux de rupture et coalescence, valable pour l’ensemble du spectre de la turbulence, est proposé et validé. La plupart des noyaux disponibles dans la littérature sont basés sur la fonction de structure de second-ordre de Kolmogorov, qui n'est valable que dans le domaine inertiel. Cependant, dans des nombreuses situations rencontrées au niveau industriel, la plupart des gouttes peuvent avoir une taille dans le domaine dissipatif, où la fonction de structure de second-ordre de Kolmogorov ne s'applique pas. Le modèle généralisé est basé sur la fonction de structure de second ordre de Davidson, valable dans tout le spectre de la turbulence. Dans la dernière partie de l'étude, un modèle permettant de simuler le comportement hydrodynamique d'une colonne pulsée est proposé. Le modèle est basé sur un bilan de population 1D, dont les termes source ont été modélisés à l'aide des noyaux de Coulaloglou et Tavlarides généralisés. Les inhomogénéités turbulentes dans la colonne pulsée ont été prises en compte par la fonction de densité de probabilité du taux de dissipation turbulent. Un bon accord modèle-expérience est obtenu en ce qui concerne le diamètre et la concentration moyenne des gouttes dans un compartiment<br>This PhD project deals with the study of the hydrodynamics of the dispersions in the liquid-liquid extractors employed in the nuclear recycle industry. In the first part of the project, a zero-dimensional homogenous Population Balance Model (0D-PBM), based on the evaluation of the volume-averaged coalescence and breakup rates, is adopted to fit low-viscosity turbulent liquid-liquid dispersion experiments. The method accounts for the spatial inhomogeneities in mixing, namely for the probability density function of the turbulent kinetic energy dissipation in the apparatus. In the second part of this study, a generalized model for the breakage and coalescence kernels, valid for the entire spectrum of turbulence, is proposed and validated. Most of the available kernels in literature indeed are based on the Kolmogorov second-order structure function, which is only valid in the inertial subrange. However, in many industrially encountered situations, most of the droplets may have size in the dissipation range, where the Kolmogorov second-order structure function does not apply. The generalized model is based on the Davidson second-order structure function, valid in the entire spectrum of turbulence. In the last part of the study, a model that allows to simulate the hydrodynamic behavior of a pulsed column is proposed. The model is based on a 1D Population Balance Equation (1D-PBE), whose source terms were modeled through the generalized Coulaloglou and Tavlarides kernels. The turbulent inhomogeneities in the pulsed column were accounted through the probability density function of the turbulent dissipation rate. The model well reproduces the experimental Sauter mean diameters and the dispersed phase volume fractions in a compartment of the pulsed column
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Zhang, Runtong. "Measurement of effective diffusivity : chromatographic method (pellets & monoliths)." Thesis, University of Bath, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608352.
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This thesis aims to find out the effective diffusivity (Deff) of a porous material – γ-alumina, using an unsteady state method with two inert gases at ambient condition with no reactions. For porous materials, Deff is important because it determines the amount of reactants that transfers to the surface of pores. When Deff is known, the apparent tortuosity factor of γ-alumina is calculated using the parallel pore model. The apparent tortuosity factor is important because: (a) it can be used to back-calculate Deff at reacting conditions; (b) once Deff with reactions is known, the Thiele modulus can be calculated and hence the global reaction rate can be found; (c) apparent tortuosity factor is also important for modelling purposes (e.g. modelling a packed-bed column or a catalytic combustion reactor packed with porous γ-alumina in various shapes and monoliths). Experimental measurements were performed to determine the effective diffusivity of a binary pair of non-reacting gases (He in N2, and N2 in He) in spherical γ-alumina pellets (1 mm diameter), and in γ-alumina washcoated monoliths (washcoat thickness 20 to 60 µm, on 400 cpsi (cells per square inch) cordierite support). The method used is based on the chromatographic technique, where a gas flows through a tube, which is packed with the sample to be tested. A pulse of tracer gas is injected (e.g. using sample loops: 0.1, 0.2, 0.5 ml) and by using an on-line mass spectrometer the response in the outlet of the packed bed is monitored over time. For the spherical pellets, the tube i.d. = 13.8 mm and the packed bed depths were 200 and 400 mm. For monoliths the tube i.d. = 7 mm and the packed lengths were 500 and 1000 mm. When the chromatographic technique was applied to the monoliths, it was observed that experimental errors can be significant, and it is very difficult to interpret the data. However, the technique worked well with the spherical pellets, and the effective diffusivity of He in N2 was 0.75 – 1.38 × 10-7 m2 s-1, and for N2 in He was 1.81 – 3.10 × 10-7 m2 s-1. Using the parallel pore model to back-calculate the apparent tortuosity factor, then a value between 5 to 9.5 was found for the pellets.
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Wei, Fanli. "Temporal Manipulation of Spatiotemporal Optical Vortex Via Temporal Airy Profile." University of Dayton / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1628123176895496.
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Habel, Florian [Verfasser], and Ferenc [Akademischer Betreuer] Krausz. "Advanced dispersive mirrors for ultrashort laser pulses from the near-UV to the mid-IR spectral range / Florian Habel ; Betreuer: Ferenc Krausz." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2017. http://d-nb.info/1126968331/34.
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Bethge, Jens. "Novel designs and applications of photonic crystal fibers." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2012. http://dx.doi.org/10.18452/16470.
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Zuerst wird die Idee einer gechirpten photonischen Kristallfaser vorgestellt. Aus einem stark vereinfachten Modell, die qualitativen Eigenschaften dieses neuen Fasertyps abgeleitet. Hier gelingt es, alle wichtigen Designparameter zu bestimmen. Die hervorragenden Leitungseigenschaften dieser Fasern werden dann in Experimenten demonstriert. Ohne jegliche Dispersionskompensation wird die Übertragung eines 25 fs Impulses in einer 1 Meter langen Faser gezeigt. Wird zusätzlich eine Dispersionskompensation verwendet, lassen sich sogar Impulse mit weniger als 20 fs Dauer übertragen. Im Anschluss daran wird eine photonische Kristallfaser untersucht, die mit einer Flüssigkeit gefüllt ist. Die hergestellte Faser ist dahingehend optimiert, einen hoch effizienten Soliton-Fission Mechanismus zu ermöglichen, der zur Erzeugung von Weißlicht genutzt wird. Diese Weißlicht-Impulse haben eine mit Soliton-Fission bisher noch nie erreichte Energie von 390 nJ. Auf Grundlage einer guten Übereinstimmung mit den experimentellen Resultaten lässt sich aus numerischen Simulationen der zugrunde liegende Effekt bestimmen. Abschließend wird über ein Experiment berichtet, das die nichtlineare Wechselwirkung zwischen zwei Impulsen verschiedener Wellenlänge ausnutzt, um einen optischen Schalter zu verwirklichen. Dieses Experiment erfordert genaueste Kontrolle der Dispersion und der Nichtlinearität in der Faser. Bei der gleichzeitigen Propagation von zwei Impulsen wird ein neuartiger Schalteffekt beobachtet. Beide Impulse haben nahezu die gleiche Gruppengeschwindigkeit, und ihre nichtlineare Wechselwirkung basierend auf Kreuz-Phasen-Modulation wird dadurch deutlich verstärkt. Hiermit wird ein voll funktionsfähiger optischer Transistor mit gutem Schaltkontrast experimentell demonstriert, der insbesondere einen schwachen Impuls einen stärkeren Impuls schalten lässt.<br>First, the concept of a novel chirped photonic crystal fiber is introduced. The qualitative dispersion and loss properties of this new fiber are theoretically derived. The calculated results agree excellently with experimental data obtained from fabricated fiber samples. The superior guiding properties of this new photonic fiber are demonstrated in two experiments. The delivery of 25 fs pulses over a 1 meter distance is realized without any dispersion compensation. Moreover, using dispersion compensation, the delivery of even sub-20-fs pulses becomes possible. Subsequently, a photonic crystal fiber with a liquid core is investigated, work presents effective methods for the preparation and explains a scheme for successfully reducing the insertion loss. The fiber is optimized to support the highly efficient soliton-fission mechanism at unprecedented pulse energies in white-light supercontinuum generation. Because of the liquid core, the supercontinuum generation scheme can be scaled beyond the peak-power limitations of solid-core fibers. The generation of a two-octave spanning supercontinuum with 390 nJ pulse energy is demonstrated. The experimental results are compared to a numerical simulation and the underlying mechanism is identified. Finally, an experiment is presented that exploits strong nonlinear interaction of two pulses inside a photonic crystal fiber for all-optical switching. A novel effect is observed during the co-propagation of two ultrashort pulses with different wavelengths. Because of the dispersion properties in the chosen fiber, these pulses are propagating at nearly identical group velocities, which dramatically increases the nonlinear interaction via cross-phase modulation between the two pulses. Based on this interaction, a fully functional optical transistor is experimentally demonstrated with good switching contrast. In particular, the demonstrated optical transistor enables switching of a strong pulse by a much weaker pulse.
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Spa, Carvajal Carlos. "Time-domain numerical methods in room acoustics simulations." Doctoral thesis, Universitat Pompeu Fabra, 2009. http://hdl.handle.net/10803/7565.
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L'acústica de sales s'encarrega de l'estudi del comportament de les ones sonores en espais tancats.La informació acústica de qualsevol entorn, coneguda com la resposta impulsional, pot ser expressada en termes del camp acústic com una funció de l'espai i el temps. En general, és impossible obtenir solucions analítiques de funcions resposta en habitacions reals. Per tant, en aquests últims anys, l'ús d'ordinadors per resoldre aquest tipus de problemes ha emergit com una solució adecuada per calcular respostes impulsionals.<br/>En aquesta Tesi hem centrat el nostre anàlisis en els mètodes basats en el comportament ondulatori dins del domini temporal. Més concretament, estudiem en detall les formulacions més importants del mètode de Diferències Finites, el qual s'utilitza en moltes aplicacions d'acústica de sales, i el recentment proposat mètode PseudoEspectral de Fourier. Ambdós mètodes es basen en la formulació discreta de les equacions analítiques que descriuen els fenòmens acústics en espais tancats.<br/>Aquesta obra contribueix en els aspectes més importants en el càlcul numèric de respostes impulsionals: la propagació del so, la generació de fonts i les condicions de contorn de reactància local.<br>Room acoustics is the science concerned to study the behavior of sound waves in enclosed rooms. The acoustic information of any room, the so called impulse response, is expressed in terms of the acoustic field as a function of space and time. In general terms, it is nearly impossible to find analytical impulse responses of real rooms. Therefore, in the recent years, the use of computers for solving this type of problems has emerged as a proper alternative to calculate the impulse responses. <br/>In this Thesis we focus on the analysis of the wavebased methods in the timedomain. More concretely, we study in detail the main formulations of FiniteDifference methods, which have been used in many room acoustics applications, and the recently proposed Fourier PseudoSpectral methods. Both methods are based on the discrete formulations of the analytical equations that describe the sound phenomena in enclosed rooms. <br/>This work contributes to the main aspects in the computation of impulse responses: the wave propagation, the source generation and the locallyreacting boundary conditions.
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Power, Christian. "Caracterización de nano materiales de CdSe, CdTe y Cd0. 5Mn0. 5Te formados por ciclos de presión." Toulouse 3, 2006. http://www.theses.fr/2006TOU30265.
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La présente étude a pour objet la formation et caractérisation structurale et morphologique de nanoparticules semi-conductrices de CdSe, CdTe y Cd0. 5Mn0. 5Te, à partir de la phase solide monocristalline, par application de cycles de pression, à T=300K, (schéma Top Down). Les pressions maximales appliquées sur les échantillons sont inférieures à 11GPa, elles furent obtenues par l'utilisation d'une cellule de grand volume type Paris-Edimbourg. Les échantillons récupérés furent caractérisés par diffraction de rayons X, microscopie électronique en transmission, diffraction électronique et dispersion Raman et nous avons pu déterminer que nos nano matériaux ainsi formés sont approximativement sphériques de diamètre inférieur à 50nm. Nos mesures magnétiques obtenues par magnétomètre SQUID et sous champ magnétique pulsé montrent qu'à basses températures le comportement de nos nanoparticules de Cd0. 5Mn0. 5Te, est régit par une contribution ferromagnétique des spins de surface, se superposant au comportement spin glass<br>This research propose the formation and structural and morphologic characterization of nanoparticles semiconductors of CdSe, CdTe and Cd0. 5Mn0. 5Te, from your solid phase mono crystal in bulk, for the cycles of pressure applications to T=300K (way Top Down). The maximum pressures applied are under of 11GPa, using the cell of great volume type Paris-Edinburgh. The sample recovers were characterized using diffraction of X–rays, electronic microscopic of transmission, diffraction electrons and Raman dispersion, and it achieve to determine that they are spherical nanoparticles with average diameter lower 50nm. With the SQUID Magnetometer and magnetization in the High Magnetic Field Pulsed, we determined the behavior of the nanoparticles of Cd0. 5Mn0. 5Te to low temperatures and this is guided by ferromagnetic contribution of the spin of surface, that put on top on behavior of spin glass
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ZENG, RUI-ZHEN, and 曾瑞珍. "Gaussian pulse dispersion over coherent fiber optical communication system." Thesis, 1992. http://ndltd.ncl.edu.tw/handle/55514872205908361090.
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楊展昇. "An Assessment of Pulse Dispersion in Ionospheric Propagation Channels." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/16081071357522565517.
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碩士<br>國立中山大學<br>電機工程研究所<br>85<br>Ionospheric propagation, unlike the line-of-sight path which is limited by the curvature of the earth, is capable of long-distance communication. The propagation mode is known as the sky wave. It is found that the HF band (3-30 MHz) is particularly suitable for the ionospheric propagation. In this band, the properties of the ionosphere dominates the characteristics and quality of the channel, among which the dispersion is most noticeable. The ionospheric dispersion has been studied by assuming a quadratic phase channel. Other attempt using the ionospheric transfer function has also been carried out. In the thesis the effect of the third-order derivative of the phase with respect to the carrier frequency is included. In addition, the influence of the possible horizontal gradient of the electron density is also studied. It is found that the quadratic phase channel assumption is adequate under practical situations.
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Hsu, Chia-Jen, and 徐家仁. "Dispersion Compensation in a Ten-Terawatt Ultrashort Pulse Laser System." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/39920584077993545066.
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碩士<br>國立臺灣大學<br>光電工程學研究所<br>89<br>In this thesis, I discuss in detail the design issues of dispersion compensation in a high peak-power ultrashort
pulse laser system.
I also describe how to construct some of the crucial components of this laser system including pulse stretcher,
regenerative amplifier, and pulse compressor. By using the chirped-pulse amplification technique, combined with the use of
broad-bandwidth laser gain media such as Ti:sapphire, we've successfully built a tabletop high peak-power ultrashort
pulse laser system. The temporal and spatial characteristics of the output pulse of this laser system is carefully
measured by using some of the latest pulse diagnostic techniques.
Laser peak intensities of $10^{19}$ W/cm$^2$ can be generated by properly focusing the output pulse of this laser
system. Such high laser intensities can be utilized to conduct various kinds of laser-plasma interaction experiments.
Preliminary results of several laser-plasma interaction experiments show that our system is good enough to be used to do
research in high field sciences.
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駒井, 慎一, Shin'ichi Komai, 義輝 矢澤, et al. "Determination of Metal Dispersion of Pt/CeO2 Catalyst by CO-pulse Method." 2005. http://hdl.handle.net/2237/14010.
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Salimi, Elham. "Nanosecond pulse electroporation of biological cells: The effect of membrane dielectric relaxation." 2011. http://hdl.handle.net/1993/4460.
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Nanosecond pulse electroporation of biological cells is gaining significant interest due to its ability to influence intracellular structures. In nanosecond pulse electroporation of biological cells nanosecond duration pulses with high frequency spectral content are applied to the cell. In this research we show that accurate modeling of the nanosecond pulse electroporation process requires considering the effect of the membrane dielectric relaxation on the electric potential across the membrane. We describe the dielectric relaxation of the membrane as dispersion in the time-domain and incorporate it into the nonlinear asymptotic model of electroporation. Our nonlinear dispersive model of a biological cell is solved using finite element method in 3-D space enabling arbitrary cell structures and internal organelles to be modeled. The simulation results demonstrate two essential differences between dispersive and non-dispersive membrane models: the process of electroporation occurs faster when the membrane dispersion is considered, and the minimum required electric field to electroporate the cell is significantly reduced for the dispersive model.