Dissertations / Theses on the topic 'Radiations generation'
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Phillips, Richard J. "Monte Carlo generation of Cerenkov radiation." Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/26090.
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Corchia, Alessandra. "Generation of terahertz radiation from semiconductors." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620406.
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Winterfeldt, Carsten. "Generation and control of high-harmonic radiation." Doctoral thesis, [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=98219885X.
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Coffey, Katherine Leigh. "Next-Generation Earth Radiation Budget Instrument Concepts." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/35587.
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The current effort addresses two issues important to the research conducted by the Thermal Radiation Group at Virginia Tech. The first research topic involves the development of a method which can properly model the diffraction of radiation as it enters an instrument aperture. The second topic involves the study of a potential next-generation space-borne radiometric instrument concept.
Presented are multiple modeling efforts to describe the diffraction of monochromatic radiant energy passing through an aperture for use in the Monte-Carlo ray-trace environment. Described in detail is a deterministic model based upon Heisenberg's uncertainty principle and the particle theory of light. This method is applicable to either Fraunhofer or Fresnel diffraction situations, but is incapable of predicting the secondary fringes in a diffraction pattern. Also presented is a second diffraction model, based on the Huygens-Fresnel principle with a correcting obliquity factor. This model is useful for predicting Fraunhofer diffraction, and can predict the secondary fringes because it keeps track of phase.
NASA is planning for the next-generation of instruments to follow CERES (Clouds and the Earth's Radiant Energy System), an instrument which measures components of the Earth's radiant energy budget in three spectral bands. A potential next-generation concept involves modification of the current CERES instrument to measure in a larger number of wavelength bands. This increased spectral partitioning would be achieved by the addition of filters and detectors to the current CERES geometry. The capacity of the CERES telescope to serve for this purpose is addressed in this thesis.
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Lazzari, Cristiano. "Transistor level automatic generation of radiation-hardened circuits." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2007. http://hdl.handle.net/10183/15506.
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Tecnologias submicrônicas (DSM) têm inserido novos desafios ao projeto de circuitos devido a redução de geometrias, redução na tensão de alimentação, aumento da freqüência e aumento da densidade de lógica. Estas características reduzem significativamente a confiabilidade dos circuitos integrados devido a suscetibilidade a efeitos como crosstalk e acoplamento de substrato. Ainda, os efeitos da radiação são mais significantes devido as partículas com baixa energia começam a ser um problema em tecnologias DSM. Todas essas características enfatizam a necessidade de novas ferramentas de automação. Um dos objetivos desta tese é desenvolver novas ferramentas aptas a lidar com estes desafios. Esta tese é dividida em duas grandes contribuições. A primeira está relacionada com o desenvolvimento de uma nova metodologia com o objetivo de gerar circuitos otimizados em respeito ao atraso e ao consumo de potência. Um novo fluxo de projeto é apresentado na qual o circuito é otimizado no nível de transistor. Esta metodologia permite otimizar cada transistor de acordo com as capacitâncias associadas. Diferente da metodologia tradicional, o leiaute é gerado sob demanda depois do processo de otimização de transistores. Resultados mostram melhora de 11% em relação ao atraso dos circuitos e 30% de redução no consumo de potência em comparação à metodologia tradicional. A segunda contribuição está relacionada com o desenvolvimento de técnicas de geração de circuitos tolerantes a radiação. Uma técnica CWSP é usada para aplicar redundância temporal em elementos seqüenciais. Esta técnica apresenta baixa utilização de área, mas as penalidades no atraso estão totalmente relacionadas com a duração do pulso que se planeja atenuar. Além disso, uma nova metodologia de dimensionamento de transistores para falhas transientes é apresentada. A metodologia de dimensionamento é baseada em um modelo analítico. O modelo considera independente blocos de transistores PMOS e NMOS. Então, somente transistores diretamente relacionados à atenuação são dimensionados. Resultados mostram área, atraso e consumo de potência reduzido em comparação com as técnicas CWSP e TMR, permitindo o desenvolvimento de circuitos com alta freqüência.Deep submicron (DSM) technologies have increased the challenges in circuit designs due to geometry shrinking, power supply reduction, frequency increasing and high logic density. The reliability of integrated circuits is significantly reduced as a consequence of the susceptibility to crosstalk and substrate coupling. In addition, radiation effects are also more significant because particles with low energy, without importance in older technologies, start to be a problem in DSM technologies. All these characteristics emphasize the need for new Electronic Design Automation (EDA) tools. One of the goals of this thesis is to develop EDA tools able to cope with these DSM challenges. This thesis is divided in two major contributions. The first contribution is related to the development of a new methodology able to generate optimized circuits in respect to timing and power consumption. A new design flow is proposed in which the circuit is optimized at transistor level. This methodology allows the optimization of every single transistor according to the capacitances associated to it. Different from the traditional standard cell approach, the layout is generated on demand after a transistor level optimization process. Results show an average 11% delay improvement and more than 30% power saving in comparison with the traditional design flow. The second contribution of this thesis is related with the development of techniques for radiation-hardened circuits. The Code Word State Preserving (CWSP) technique is used to apply timing redundancy into latches and flipflops. This technique presents low area overhead, but timing penalties are totally related with the glitch duration is being attenuated. Further, a new transistor sizing methodology for Single Event Transient (SET) attenuation is proposed. The sizing method is based on an analytic model. The model considers independently pull-up and pull-down blocks. Thus, only transistors directly related to the SET attenuation are sized. Results show smaller area, timing and power consumption overhead in comparison with TMR and CWSP techniques allowing the development of high frequency circuits, with lower area and power overhead.
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Wüthrich, Stefan. "Generation and transport of 2,9 [my]m radiation /." Bern, 1991. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.
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Tempus, Martin. "Generation and coherent transmission of mid-infrared radiation /." Bern, 1993. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.
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Roberts, Daniel Rhys Griffin. "Semiconductor devices for generating terahertz radiation." Thesis, Bangor University, 2016. https://research.bangor.ac.uk/portal/en/theses/semiconductor-devices-for-generating-terahertz-radiation(ed1b94db-fa83-4508-9e04-14423e5338b7).html.
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This thesis will investigate different methods for realizing terahertz (THz) radiation. The work will look at the current state of the art in technologies for generating THz radiation using two types of semiconductor laser diodes, the vertical-cavity surface-emitting laser (VCSEL), and the vertical-external-cavity surface-emitting laser (VECSEL). The work starts by looking at designing a dual-wavelength laser inspired by work presented in the literature; with particular emphasis on reducing the wavelength spacing between the two wavelengths and improving the positions of the quantum-wells (QW) in order to reduce the residual absorption in the QWs. This naturally leads on to investigations into the effects of linewidth, and linewidth enhancement, on the performance of the device. It is found that linewidth enhancement is not a limiting factor in the design of dual-wavelength lasers. The thesis will then investigate the technique of injection locking, simulated by rate equations, in order to investigate, in detail, the various behavioural regions exhibited by such a scheme under varying injection rates and detuning frequencies. The scheme will consist of a two laser system approach, whereby both unidirectional and bidirectional injection locking will be investigated. The disadvantage to such a scheme is the fact that there will be a zero frequency separation between the lasers frequencies while operating in the locked condition, hence the injection locking scheme will provide a building block for a three laser locking system based on four-wave mixing (FWM). The interest in injection locking has been proven to be of great interest in the world of optics, ever since the Dutch scientist, Christiaan Huygens, discovered the phenomenon while confined to bed with illness during the 17th century. Such an approach has shown to be durable and efficient in improving the spectral and dynamic performance of directly modulated laser diodes. The scheme of injection locking will be utilized in order to build a system based on the FWM phenomenon with a nonzero frequency separation between the lasers’ frequencies. As with the injection locking scheme, the various behavioural patterns at varying injection rates and detuning frequencies will be thoroughly investigated. The resilience of the system to perturbations (modulation response) will then be investigated, and the performance of the three laser FWM system will be compared to that of an uncoupled laser, whereby the phasor difference between the first and the second laser is calculated. The amplitude of the resultant wave is then compared to the amplitude of the uncoupled wave in order to establish whether or not the three laser FWM system supresses any of the introduced perturbations. It is found that the more the injection rate is increased, the more the FWM system supresses the effect of the perturbations, where a maximum improvement of 44% over the uncoupled laser is observed. It is also found that the system shows the behaviour of a first order system in series with a second order system in its frequency response. The contributions made in this thesis include a new dual-wavelength VECSEL structure design, whereby the wavelength spacing between the two wavelengths has been significantly reduced, and the locations of the QWs have been improved. Also, a system has been modelled utilising the injection locking scheme, in order to produce a nonzero frequency difference between the coupled lasers. For the first time, a thorough investigation of the locking regions has been undertaken at varying injection rates and detuning frequencies, whereby the different behaviours exhibited by the system in each region has been explored. A detailed investigation on the resilience of this new system to introduced perturbations is also presented.
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Martin, Ian Peter Stephen. "Short pulse x-ray generation in synchrotron radiation sources." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:9ac0bcc2-bedb-46d0-b95c-22f4741f45a0.
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This thesis describes an investigation into the performance of different schemes for generating short x-rays pulses via synchrotron radiation emission. A review is given of the methods that have been previously proposed for this task. From this review, three leading schemes are selected for in-depth investigations, each of which explores the boundary of what is presently achievable in accelerator-based light sources. The first scheme generates short x-ray pulses by operating an electron storage ring in a quasi-isochronous state using a ‘low-alpha’ lattice. High and low emittance lattices are developed, studied through simulation and then implemented on the Diamond storage ring. Beam dynamics and bunch length measurements are presented for a variety of machine conditions, and an assessment is made of the minimum practically achievable bunch length for stable user operation. Radiation pulses of 1 ps r.m.s. are demonstrated using this scheme. The second and third schemes investigate performance limits for a linac-based light source through numerical simulations. The first of these generates ultra-short pulses by passing a highly compressed electron bunch through a long undulator to radiate in the ‘single-spike’ regime. A comparison is made with theoretical predictions for the required electron bunch length to operate in this way, which highlights the need for accurate start-to-end simulations. The final scheme generates ultra-short x-ray pulses through laser manipulation of the electron bunches. The modulated electrons pass through a long undulator with tapered gap, such that only the centre of the modulated portion experiences high free-electron laser (FEL) gain. A method to enhance the FEL output from this scheme using a wavelength filter and grating-compressor is investigated. The sensitivity of the two schemes to jitter sources is determined, and it is demonstrated both schemes are capable of generating GW-level, fully coherent sub-fs soft x-ray pulses. Such pulses would open up the development of time-resolved science to new regimes.
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Zhou, Jian Ying. "Generation of VUV radiation in xenon using dye lasers." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47323.
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Schneider, Tim. "Advancing the generation of proton minibeams for radiation therapy." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP069.
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Malgré d’importants progrès, la tolérance des tissus sains aux rayonnements demeure un facteur central en radiothérapie, limitant par exemple l’efficacité du traitement des gliomes de haute grade. La proton thérapie avec mini-faisceaux (proton minibeam radiation therapy, pMBRT) est une nouvelle stratégie thérapeutique qui a pour objectif d’améliorer la préservation des tissus sains en combinant les avantages balistiques des protons et le fractionnement spatial de la dose obtenu avec des faisceaux submillimétriques. Dans ce contexte, la pMBRT a déjà démontré sa capacité à augmenter l’index thérapeutique dans le traitement des tumeurs cérébrales de rats. Un défi important est la génération des mini-faisceaux dans un cadre clinique : contrairement à la radiothérapie conventionnelle qui utilise des faisceaux larges (diamètre d’environ 5 mm à plusieurs centimètres), les mini-faisceaux se caractérisent par un diamètre de moins d’un millimètre. Actuellement, la génération des mini-faisceaux de protons est réalisée à l’aide de collimateurs mécaniques (blocs en métal avec plusieurs fentes ou trous) ce qui comporte plusieurs inconvénients (notamment une très faible flexibilité, une réduction importante du débit de dose ainsi que la génération de particules secondaires indésirables). Une solution optimale pourrait être la génération des mini-faisceaux par focalisation magnétique. Il en découle la question principale traitée dans cette thèse : Comment la génération des mini-faisceaux de protons par focalisation magnétique peut-elle être réalisée dans un cadre clinique ? En utilisant le modèle numérique d’un pencil beam scanning nozzle (le "nozzle" est la dernière partie d’une ligne de faisceau clinique), il a été démontré que les nozzles actuels ne sont pas adéquats pour focaliser les faisceaux de protons à la taille requise, les principales raisons étant une distance focale trop grande et une présence d’air excessive. En partant de ces conclusions, un nouveau design de nozzle optimisé a été développé. Ce nouveau modèle est capable de générer des mini-faisceaux de protons par focalisation magnétique dans des conditions réalisables avec les technologies existantes. Une étude Monte Carlo a également été menée afin de comparer et de quantifier les différences entre la génération de mini-faisceaux par collimation mécanique et par focalisation magnétique. Dans un second temps, cette thèse présente une évaluation des ions d’hélium comme alternative aux protons pour la radiothérapie avec mini-faisceaux. Il a pu être démontré que les ions d’hélium peuvent être un bon compromis en offrant certains des avantages dosimétriques observés avec les ions lourds sans les risques de toxicité associésDespite major advances over the last decades, the dose tolerance of normal tissue continues to be a central problem in radiation therapy, limiting for example the effective treatment of hypoxic tumours and high-grade gliomas. Proton minibeam radiation therapy (pMBRT) is a novel therapeutic strategy, combining the improved ballistics of protons with the enhanced tissue sparing potential of submillimetric, spatially fractionated beams (minibeams), that has already demonstrated its ability to significantly improve the therapeutic index for brain cancers in rats. In contrast to conventional proton therapy which uses comparatively large beam diameters of five millimetres to several centimetres, minibeams require beam sizes of less than 1 mm which are challenging to create in a clinical context. So far, every implementation of pMBRT at clinically relevant beam energies could only be achieved with the help of mechanical collimators (metal blocks with thin slits or holes). However, this method is inefficient, inflexible and creates high levels of unwanted secondary particles. The optimal approach may therefore be the generation of minibeams through magnetic focussing.This thesis investigates how magnetically focussed proton minibeams can be realised in a clinical context. Starting from the computer model of a modern pencil beam scanning nozzle (the term "nozzle" describes the final elements of a clinical beamline), it could be shown that current nozzles will not be suitable for this task, since their large dimensions and the presence of too much air in the beam path make it impossible to focus the beam down to the required sizes. Instead, an optimised nozzle design has been developed and evaluated with clinical beam models. It could be demonstrated that this design allows the generation of proton minibeams through magnetic focussing and that the new nozzle can be used with already existing technology. Moreover, a Monte Carlo study was performed to compare and quantify the differences between magnetically focussed minibeams and mechanically collimated minibeams.Finally, as the second aspect of this thesis, helium ions were evaluated as a potential alternative to protons for minibeam radiation therapy. It could be shown that helium ions could present a good compromise exhibiting many of the dosimetric advantages of heavier ions without the risks related to normal tissue toxicities
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Chang, Juntao. "Characteristics of cooperative spontaneous radiation with applications to atom microscopy and coherent XUV radiation generation." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-3226.
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Hasaani, A. S. "Pulsed electron cyclotron maser experiments with different configurations." Thesis, University of Strathclyde, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381323.
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Sakata, M., S. Aoyagi, T. Ogura, and E. Nishibori. "Advanced Structural Analyses by Third Generation Synchrotron Radiation Powder Diffraction." American Institite of Physics, 2007. http://hdl.handle.net/2237/12008.
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Merkt, Frederic. "Generation and spectroscopic applications of coherent extreme ultraviolet (XUV) radiation." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240116.
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Ward, Barry. "Generation of acoustic waves by focused infrared neodymium-laser radiation." Thesis, Loughborough University, 1991. https://dspace.lboro.ac.uk/2134/10626.
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When the radiat Ion from a sufficient Iy powerful pulsed laser Is focused into transparent gaseous, liquid or solid media, dielectric breakdown may occur around the beam waist giving rise to a shortI ived high-temperature plasma which quickly heats the surrounding material. As a consequence of various energy-coupling mechanisms, this phenomenon causes the emission of one or more high-frequency ultrasonic acoustic waves whose speeds of propagation are dependent upon the physical propert les of the host medium. In the high-speed photographic studies described In this doctoral thesis, the 1.06-l'm near-Infrared radlat Ion from an 8-ns, lO-mJ Q-swl tched Nd:YAG laser Is focused In or onto a variety of fluid and solid materials. The rapid variations In density around the resulting plasma events are visualised using a Mach-Zehnder Interferometer with a sub-nanosecond dye-laser light source and a vldeo-Imaglng system. Calculat Ions of the corresponding transient pressure distributions are then enacted from the digitally-recorded Interferograms using a semi-automat Ic procedure under the control of a personal computer. Measurements of position. displacement and velocity are also carried out using the same opt ical apparatus In schlleren and focused shadowgraph highspeed photographic arrangements. The experimental work outlined In the following chapters is divided Into three broad fields of Interest. In the first of these, a study of the laser-generation of spherical shock waves· in atmospheric air is carried out. In the second, the neOdymium-laser beam Is focused onto different solid-fluid Interfaces resulting In the formation of bulk longitudinal and shear waves and surface acoustic waves. The Interactions of these waves with various obstacles and defects are Investigated with reference to their application to non-destructive test Ing. In the third and most important field, a detailed study of the dynamics of laser-Induced cavitation bubbles In water Is carried out. With regard to the associated phenomenon of cavitation erosion, particular attention Is paid to the formation of spherical acoustic waves by radlally-oscillatlng vapour cavities at various distances from transparent rigid boundaries.
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Holst, David. "DICOM Second Generation RT : An Analysis of New Radiation Concepts by way of First-Second Generation Conversion." Thesis, Uppsala universitet, Avdelningen för visuell information och interaktion, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-381978.
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The current DICOM communication standard for radiotherapy is outdated and has serious design issues. A new version of the standard, known as DICOM 2nd generation for Radiotherapy, has been introduced and this thesis examines new concepts relating to radiation delivery. Firstly, some background into the practice of radiotherapy is given, as well as a description of the DICOM standard. Secondly, the thesis describes the design issues of the current standard and how the 2nd generation aims to solve these. Thirdly, the thesis explores the conversion of a first generation C-Arm Photon/Electron treatment plan to the second generation RT Radiation and RT Radiation Set IODs. A converter is implemented based on a model proposed in a previous work. With some simplifications, the conversion of Basic Static and Arc treatment plans is shown to be successful. Conversion of further dynamic plan types is judged to be fairly simple to implement following the same methodology. The conversion model’s efficacy and testability are discussed and while the model is flexible and facilitates extension to further modalities some areas of improvement are suggested. Lastly, a GUI for the converter is demonstrated and the possibilities of user interaction during conversion are discussed.
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Urban, Michael Urban Matthias. "Third harmonic generation of high power far infrared radiation in semiconductors /." Lausanne : CRPP, [Centre de recherches en physique des plasmas], Ecole polytechnique fédérale, 1996. http://library.epfl.ch/theses/?nr=1492.
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Parnell, Nicholas Francis. "The generation and maintenance of diversity in a rapid adaptive radiation." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42743.
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The Lake Malawi cichlid fishes are a pre-eminent example of adaptive evolutionary radiation. The diversity of species (nearly 1000 extant) is mirrored by an array of variation in dozens of phenotypes (e.g. trophic morphology, tooth shape, color patterns, behavior, development). The unique characteristics of this system have produced unparalleled diversity with very little genetic differentiation between species. This dissertation is composed of four studies addressing different aspects of the variation in the LM cichlids and the mechanisms generating and maintaining this level of diversity at multiple biological levels.
Community-level diversity is investigated using null model analysis of species co-occurrence data. We detect signals of non-random community assembly at only the broadest and finest spatial scales. Based on the unique ecological and evolutionary characteristics of this assemblage we suggest that different mechanisms are responsible for these patterns. A core‟ group of species is posited to act as a foundation on which these diverse communities are created as a result of fine-scale species interactions. We identify both positive and negative depth-based correlations between species and suggest these interactions play an important role in species diversity in these fish.
The Lake Malawi cichlids exhibit an array of trophic morphologies which may play a role in the fine-scale species interactions described in chapter one. In the second chapter we build a genetic model to predict the evolution of jaw morphology and a complex functional jaw trait. We use a complex biomechanical system, the 4-bar jaw linkage, to simulate trait evolution during interspecific hybridizations. We find rampant transgression (trait values beyond parental distributions) in jaw function in a large proportion of potential crosses. This result is characterized by a lack of novel morphological components but rather is the result of recombinations of existing component traits thus producing functional novelty. In the third chapter we create a laboratory cross of one of the parental combinations suggested from the genetic model. The results of this study serve as a proof of principle to the simulations as we observe a large proportion of transgressive 4-bar function in the F2. As predicted this diversity is produced in the absence of transgressive morphology. We contrast these results between this complex system and data generated from several simple jaw lever traits and report differences in the patterns. Using quantitative trait locus (QTL) mapping approaches we examine the genetic basis for complex and simple jaw traits and discuss correlative patterns within and between systems.
Finally we examine the genetic architecture of sex-determination and color morphs in this hybrid cross. We find both ZW and XY sex systems segregating as well as linkage to sex-specific color patterns. Several loci and epistatic interactions are associated with sex-determination and color morphs in this cross. The orange-blotch (OB) color is found associated with ZW as predicted from previous work but a previously undescribed (in these species) male nuptial color (blue) is found associated with both ZW and XY genetic systems as well as other loci segregating for sex-determination. These results are discussed in the context of models of sex chromosome evolution as a result of sexual conflict and the potential importance of sexual selection in the diversification of Lake Malawi cichlids.
Overall we observe various mechanisms generating and maintaining diversity at different levels of biological organization. We use community co-occurrence analyses, genetic simulation, and QTL analysis of an F2 hybrid population to examine these mechanisms in this rapidly radiating assemblage. These results bolster our understanding of the origins of diversity and the interplay between variation and aspects of evolution in all biological systems.
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Chanwattana, Thakonwat. "Generation of short pulse THz radiation from accelerator based light sources." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:1e44dc39-7dbf-4ff1-bc0c-efd86a2e7ba3.
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High power and short pulse THz radiation has become increasingly important in the investigation of dynamics of organic and chemical molecules. Such radiation can be effectively generated with accelerator-based light sources. This thesis reports a series of studies on the generation of short pulse THz radiation from storage rings and from compact accelerators that can be based in University sized laboratories. The first part of this thesis reviews THz radiation, synchrotron radiation and free electron laser (FEL). The second part presents the studies of short pulse THz radiation generated from the Diamond storage ring in a new operating mode known as ultra-low alpha mode to extend spectrum of coherent radiation to higher THz frequency. The numerical simulations of a single bunch dynamics show qualitative agreements with the measurements taken at the Diamond storage ring. The third part is dedicated to the design of a compact RF linac-based THz radiation source for producing short pulse THz self-amplified spontaneous emission (SASE) FEL with an undulator and THz coherent synchrotron radiation (CSR) with a bending magnet. Start-to-end simulations of SASE FEL and CSR were performed to analyse the beam dynamics and the generation of THz radiation. The SASE FEL reaches saturation within the undulator length of 5 m, whereas the CSR spectrum covers frequency below 16 THz. In the fourth part, we investigated a THz/IR radiation source driven by a Laser Plasma Wakefield Accelerator (LPWA). Extensive 2D particle-in-cell (PIC) simulations were done to generate an ultra-short electron bunch from self-injection in a nonlinear bubble regime. The 60-MeV electron bunch was obtained with 6% energy spread and 18 mrad beam divergence. The self-injected electron beam was used to drive the SASE FEL using a normal undulator and a transverse gradient undulator (TGU) to exploit the electron bunch with large energy spread. The results show that the energy spread of 6% is too large even for the TGU. Although the energy spread is reduced to 1%, the FEL saturation cannot be reached because the bunch length of the LPWA driven beam is shorter than the FEL cooperation length. The last part of this thesis discusses the Accelerator Science Laboratory (ASL) project at the University of Oxford. The designs of THz radiation sources driven by the RF linac and the LPWA previously presented were considered as potential options for the ASL. The radiation shielding for the ASL was investigated with Monte Carlo simulations to design a proper beam dump and shielding covering the beam dump.
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Hu, Wen 1968. "Generation of coherent high-power microwave radiation with relativisitic electron beams." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/28102.
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Wootton, Mark J. "Radiation damage in advanced materials for next generation nuclear power plants." Thesis, Loughborough University, 2017. https://dspace.lboro.ac.uk/2134/26781.
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The ageing state of the world's nuclear power infrastructure, and the need to reduce humanity s dependency on fossil fuels, requires that this electrical energy generating capacity is replaced. Economic factors, and its physical and chemical properties, make high purity iron-chromium binary alloys a strong candidate for use in the construction of the pressure vessels of the next generation of nuclear reactors. This relatively inexpensive metal retains the oxidation resistance property of so-called stainless steel alloys, and has demonstrated dimensional stability and low degradation under harsh experimental environments of temperature and radiation. In this work, we consider radiation induced interstitial damage to the atomic lattices of iron-chromium binary alloys using the atomistic modelling methods, Molecular Dynamics and Adaptive Kinetic Monte Carlo, simulating collision cascade sequences, and the migration of defects in the aftermath. Variations in chromium content does not effect the initial damage production in terms of the number of Frenkel pairs produced, but iron and chromium atoms are not evenly distributed in defect atoms with respect to the bulk concentration. In simulations conducted at low temperature, chromium is under-represented, and at high temperature, a greater proportion of interstitial atoms are chromium than in the lattice overall. The latter phenomena is most strongly pronounced in systems of low bulk chromium content. During the simulation of post-cascade defect migration, interstitials atoms are observed to form temporary clusters and vacancies align along adjacent lattice sites, with the two types of defect also migrating to annihilate by recombination. Calculating the energy spectra of cascade events corresponding to an example experimental configuration using the SRIM package, we investigated the evolution of lattice systems in which a sequence of multiple cascade events occurred, both with and without a physically representative time gap between events. These simulations gave us the opportunity to observe the behaviour of cascades in the proximity of damage remaining from previous events, such as the promotion of defect clustering when this occurs.
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Kotak, Yash Satish. "Solar PV generation enhancement using radiation augmentation from improved reflectance horizons." Thesis, Heriot-Watt University, 2017. http://hdl.handle.net/10399/3310.
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The total incident irradiation on a surface such as a photovoltaic (PV) module is the sum of beam, sky-diffuse and ground reflected radiation. Ground albedo or ground reflectance is defined as the ratio between the ground reflected radiation and the global incident radiation. A constant albedo value of 0.2 for bare ground and 0.5 for dry tropical localities is widely accepted and is used in the modelling of PV systems. The real albedo values of foreground surfaces are different and hence using a constant value may be unsuitable to accurately predict the output of PV systems. This research investigated the real albedo values of various foreground surfaces and how it is affected by the factors such as ageing, solar altitude, rain and cloud cover (sky conditions). To investigate the impact of such factors, an experiment was setup to measure the albedo of conventional foreground materials (grass, sand and cement) and non-conventional materials (white pebbles, white paint, white tiles and aluminium foil). These materials were selected based on the type of PV applications such as solar farms and Building Applied Photovoltaic. The measured average albedo values of grass, sand, cement, white pebbles, white paint, white tiles and aluminium foil were 0.20, 0.36, 0.56, 0.15, 0.70, 0.61 and 0.73 respectively. Research has shown that non-conventional materials, increased the slope irradiation and ultimately the energy generation of PV modules. These results were further validated using the long-term data from the Garston and Edinburgh database. Lastly, a new computational tool was developed, which considers various albedo values of foreground materials simultaneously for any tilt angle of a PV module to compute the ground-reflected component.
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Lago, Daniel E. "Benchmarking the coarse mesh radiation transport (COMET) method." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52957.
Full textAbstract:
This thesis presents a whole-core benchmark of the European Pressurized Reactor
(EPR) using multiple transport methods. The core specifications were taken directly from
the Final Safety Analysis Report (FSAR) submitted to the Nuclear Regulatory
Commission (NRC) and the reactor was modeled in a stylized manner while maintaining
full heterogeneity at the pin and assembly level. The geometry and material specifications
are given as well as problem-specific cross sections for 2, 4, and 8 energy group
calculations. Cross sections were generated using HELIOS, a lattice depletion code based
on the Collision Probability Method (CPM). The multi-group cross sections were utilized
in the reference calculation, COMET calculation, and response function generation. The
reference solution was obtained via an MCNP model identical to the one implemented in
COMET. Specific steps towards constructing and running a COMET calculation are
outlined. Detailed results including assembly eigenvalues, core eigenvalues, and pin
fission densities are presented.
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Francoeur, Mathieu. "NEAR-FIELD RADIATIVE TRANSFER: THERMAL RADIATION, THERMOPHOTOVOLTAIC POWER GENERATION AND OPTICAL CHARACTERIZATION." UKnowledge, 2010. http://uknowledge.uky.edu/gradschool_diss/58.
Full textAbstract:
This dissertation focuses on near-field radiative transfer, which can be defined as the discipline concerned with energy transfer via electromagnetic waves at sub-wavelength distances. Three specific subjects related to this discipline are investigated, namely nearfield thermal radiation, nanoscale-gap thermophotovoltaic (nano-TPV) power generation and optical characterization. An algorithm for the solution of near-field thermal radiation problems in one-dimensional layered media is developed, and several tests are performed showing the accuracy, consistency and versatility of the procedure. The possibility of tuning near-field radiative heat transfer via thin films supporting surface phononpolaritons (SPhPs) in the infrared is afterwards investigated via the computation of the local density of electromagnetic states and the radiative heat flux between two films. Results reveal that due to SPhP coupling, fine tuning of near-field radiative heat transfer is possible by solely varying the structure of the system, the structure being the film thicknesses and their distance of separation. The coexistence of two regimes of near-field thermal radiation between two thin films of silicon carbide is demonstrated via numerical simulations and an asymptotic analysis of the radiative heat transfer coefficient. The impacts of thermal effects on the performances of nano-TPV power generators are investigated via the solution of the coupled near-field thermal radiation, charge and heat transport problem. The viability of nano-TPV devices proposed so far in the literature, based on a tungsten radiator at 2000 K and indium gallium antimonide cell, is questioned due to excessive heating of the junction converting thermal radiation into electricity. Using a convective thermal management system, a heat transfer coefficient as high as 105 Wm-2K-1 is required to maintain the junction at room temperature. The possibility of characterizing non-intrusively, and potentially in real-time, nanoparticles from 5 nm to 100 nm in size via scattered surface wave is explored. The feasibility of the characterization framework is theoretically demonstrated via a sensitivity analysis of the scattering matrix elements. Measurements of the scattering matrix elements for 200 nm and 50 nm gold spherical particles show the great sensitivity of the characterization tool, although an ultimate calibration is difficult with the current version of the experimental set-up.
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Tehrani, Mehran. "Next Generation Multifunctional Composites for Impact, Vibration and Electromagnetic Radiation Hazard Mitigation." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/49547.
Full textAbstract:
For many decades, fiber reinforced polymers (FRPs) have been extensively utilized in load-bearing structures. Their formability and superior in-plane mechanical properties have made them a viable replacement for conventional structural materials. A major drawback to FRPs is their weak interlaminar properties (e.g., interlaminar fracture toughness). The need for lightweight multifunctional structures has become vital for many applications and hence alleviating the out-of-plane mechanical (i.e., quasi-static, vibration, and impact) and electrical properties of FRPs while retaining minimal weight is the subject of many ongoing studies. The primary objective of this dissertation is to investigate the fundamental processes for developing hybrid, multifunctional composites based on surface grown carbon nanotubes (CNTs) on carbon fibers\' yarns. This study embraces the development of a novel low temperature synthesis technique to grow CNTs on virtually any substrate. The developed method graphitic structures by design (GSD) offers the opportunity to place CNTs in advantageous areas of the composite (e.g., at the ply interface) where conventional fiber architectures are inadequate. The relatively low temperature of the GSD (i.e. 550 C) suppresses the undesired damage to the substrate fibers. GSD carries the advantage of growing uniform and almost aligned CNTs at pre-designated locations and thus eliminates the agglomeration and dispersion problems associated with incorporating CNTs in polymeric composites. The temperature regime utilized in GSD is less than those utilized by other synthesis techniques such as catalytic chemical vapor deposition (CCVD) where growing CNTs requires temperature not less than 700 C.It is of great importance to comprehend the reasons for and against using the methods involving mixing of the CNTs directly with the polymer matrix, to either fabricate nanocomposites or three-phase FRPs. Hence, chapter 2 is devoted to the characterization of CNTs-epoxy nanocomposites at different thermo-mechanical environments via the nanoindentation technique. Improvements in hardness and stiffness of the CNTs-reinforced epoxy are reported. Long duration (45 mins) nanocreep tests were conducted to study the viscoelastic behavior of the CNT-nanocomposites. Finally, the energy absorption of these nanocomposites is measured via novel nanoimpact testing module.
Chapter 3 elucidates a study on the fabrication and characterization of a three phase CNT-epoxy system reinforced with woven carbon fibers. Tensile test, high velocity impact (~100 ms-1), and dynamic mechanical analysis (DMA) were employed to examine the response of the hybrid composite and compare it with the reference CFRP with no CNTs. Quasi-static shear punch tests (QSSPTs) were also performed to determine the toughening and damage mechanisms of both the CNTs-modified and the reference CFRP composites during transverse impact loading.
The synthesis of CNTs at 550 C via GSD is the focus of chapter 4. The GSD technique was adjusted to grow Palladium-catalyzed carbon filaments over carbon fibers. However, these filaments were revealed to be amorphous (turbostratic) carbon. Plasma sputtering was utilized to sputter nickel nano-films on the surface of the substrate carbon fibers. These films were later fragmented into nano-sized nickel islands from which CNTs were grown utilizing the GSD technique. The structure and morphology of the CNTs are evaluated and compared to CNTs grown via catalytic chemical vapor deposition (CCVD) over the same carbon fibers.
Chapter 5 embodies the mechanical characterization of composites based on carbon fibers with various surface treatments including, but not limited to, surface grown CNTs. Fibers with and without sizing were subjected to different treatments such as heat treatment similar to those encountered during the GSD process, growing CNTs on fabrics via GSD and CCVD techniques, sputtering of the fibers with a thin thermal shield film of SiO2 prior to CNT growth, selective growth of CNTs following checkerboard patterns, etc.
The effects of the various surface treatments (at the ply interfaces) on the on-axis and off-axis tensile properties of the corresponding composites are discussed in this chapter. In addition, the DMA and impact resistance of the hybrid CNT-CFRP composites are measured and compared to the values obtained for the reference CFRP samples. While the GSD grown CNTs accounted for only 0.05 wt% of the composites, the results of this chapter contrasts the advantages of the GSD technique over other methods that incorporate CNTs into a CFRP (i.e. direct growth via CCVD and mixing of CNTs with the matrix).
Understanding the behavior of the thin CFRPs under impact loadings and the ability to model their response under ballistic impact is essential for designing CFRP structures. A precise simulation of impact phenomenon should account for progressive damage and strain rate dependent behavior of the CFRPs. In chapter 6, a novel procedure to calibrate the state-of-the-art MAT162 material model of the LS-DYNA finite element simulation package is proposed. Quasi-static tensile, compression, through thickness tension, and in-plane Isopescu shear tests along with quasi-static shear punch tests (QSSPTs) employing flat cylindrical and spherical punches were performed on the composite samples to find 28 input parameters of MAT162. Finally, the capability of this material model to simulate a transverse ballistic impact of a spherical impactor with the thin 5-layers CFRP is demonstrated.
It is hypothesized that the high electrical conductivities of CNTs will span the multifunctionality of the hybrid composites by facilitating electromagnetic interference (EMI) shielding. Chapter 6 is devoted to characterizing the electrical properties of hybrid CNT-fiberglass FRPs modified via GSD method. Using a slightly modified version of the GSD, denser and longer CNTs were grown on fiberglass fabrics. The EMI shielding performance of the composites based on these fabrics was shown to be superior to that for reference composites based on fiberglass and epoxy. To better apprehend the effect of the surface grown CNTs on the electrical properties of the resulting composites, the electrical resistivities of the hybrid and the reference composites were measured along different directions and some interesting results are highlighted herein.
The work outlined in this dissertation will enable significant advancement in protection methods against different hazards including impact, vibrations and EMI events.
Ph. D.
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Radtke, Hanna. "Surface properties of quantum dots for next generation solar cells." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/surface-properties-of-quantum-dots-for-next-generation-solar-cells(9712421f-aec1-4ac6-aa1b-840f40b6b9fc).html.
Full textAbstract:
Colloidal quantum dots (QDs) are promising candidates for the next generation of solar cells due to their tunable band gaps, solution processability and the potential for multiple exciton generation. However their stability and the reduction of surface defects are big challenges and effective surface passivation is needed. Passivations via organic ligands have been shown to be imperfect and hinder the charge transfer in devices. Three different QD systems, chosen as exemplars of different approaches to surface passivation, have been investigated with synchrotron-radiation (SR) depth- profiling X-ray photoelectron spectroscopy (XPS). With this technique the chemical composition of the top few nanometres of a sample can be studied with depth. The study of CdTe QDs with and without a chloride treatment revealed the presence of stoichiometric particles prior to, and the likely coexistence of Cl atoms and organic ligands on the surfaces of the QDs after the treatment. The chloride treatment led to a better surface passivation of the QDs resulting in photoluminescence quantum yields of up to 97.2%. Shell thickness estimations using a core/shell/shell model were performed of the chloride treated sample and XPS highlighted the complexity of the structure of the sample. CdTe QDs passivated by a thick CdSe shell were investigated. Indications for an improvement of the stability of the QDs against oxidation were found. The Se:Te ratio was equivalent to a CdSe shell of 0.3-0.4 nm which was significantly smaller than intended, indicating that the butylamine ligand exchange and/or the washing of the sample reduced the thickness of the CdSe shell drastically. The third system studied was PbS QDs that were passivated with a thin CdS shell. XPS of the thoroughly washed QDs confirmed the presence of Cd in an amount equivalent to a 0.13-0.18 nm thick shell. This is thicker than the 0.05 nm shell expected from absorption spectroscopy. A study of ageing of the PbS/CdS QDs revealed that oxidation took place on the surface of the QDs. It was found that sulfur oxidised in stages leading to highly oxidised SO4^2- components. Upon long-term ageing Pb oxidised more rapidly than S, and either some Pb and/or Cd migration or some decomposition of the QDs occurred. The PbS/CdS nanoparticles were more stable than a comparable PbS colloidal quantum dot sample from the literature. The study of the PbS/CdS QDs prior to and after the second wash- ing cycle after a mercaptopropionic acid (MPA) ligand exchange revealed, amongst other things, the removal of MPA and a reduction of the Cd:Pb ratio indicating that (parts of) the QDs decomposed through the ligand exchange or the washing. In addition to the results of the nanoparticles studied some limitations of the study of colloidal QDs with SR depth-profiling XPS are discussed.
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Cliffe, Matthew. "Generation of longitudinally polarised terahertz radiation for the energy manipulation of relativistic electron beams." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/generation-of-longitudinally-polarised-terahertz-radiation-for-the-energy-manipulation-of-relativistic-electron-beams(5ea447a5-bd46-4d87-8a62-5c7c01f5b8e4).html.
Full textAbstract:
The acceleration of charged particles with ultrafast terahertz electromagnetic radiation could enable new, and improve many of aspects of, accelerator applications. These include providing shorter electron bunches for ultrafast time-resolved pump-probe spectroscopy, enabling complex longitudinal profiles to be imparted onto charged particle bunches and significantly improving the ability to synchronise an accelerator to an external laser. In this thesis I present investigations into terahertz radiation sources that enabled the generation of terahertz radiation with attractive properties for accelerator based applications. Specific attention has been paid to temporally tunable sources that generate strong longitudinally polarised electric field components as these enable a free-space co-linear interaction geometry to be implemented. A simulation describing the propagation of radiation from such sources has been developed. Terahertz sources have been designed and the radiation generated characterised via electro optic detection. These include a radially biased photoconductive antenna (PCA) based source of which the longitudinally polarised terahertz electric field component was found to have an amplitude of 2.22 kVcm-1 as well as a near-single cycle temporal profile. This radially biased PCA was used in conjunction with the Accelerators and Lasers in Combined Experiments (ALICE) energy recovery linear accelerator at the Daresbury Laboratory in an electron acceleration experiment. To enable higher longitudinally polarised terahertz electric field strengths to be obtained, as well as the ability to temporally tune the terahertz radiation, generation within non-linear optical crystals was investigated. Magnesium-oxide doped stoichiometric lithium niobate (MgO:SLN) was investigated as a possible candidate due to its high non-linear susceptibility tensor and reported ability to impose temporal tuning directly from the pump laser beam. A scheme consisting of two MgO:SLN crystals each generating a separate linear polarised terahertz pulse which were then combined via a lens was designed and built. Electro optic detection techniques were used to characterise the radiation generated from this source. Peak terahertz electric fields amplitudes of 11.6 kVcm-1 and 47 kVcm-1 were measured for both the longitudinally and transversely polarised field components respectively. Temporal profiles measured from both the longitudinally and transversely polarised electric field components showed electric field periods of approximately 300 fs. This method of generating terahertz radiation employed a pulse-front tilt technique. Allowing for the same scaling as recently reported in the literature for MgO:SLN generation techniques, which will in principle allow this method to scale to longitudinally polarised terahertz electric field profiles in excess of 1 MVcm-1.
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Rogl, Andreas. "High-frequency driven semiconductor superlattice oscillators for generation of subterahertz and terahertz radiation." Regensburg Univ.-Verl. Regensburg, 2009. http://d-nb.info/999590391/34.
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Stephanos, Cyril [Verfasser], and Jochen [Akademischer Betreuer] Mannhart. "Thermoelectronic Power Generation from Solar Radiation and Heat / Cyril Stephanos. Betreuer: Jochen Mannhart." Augsburg : Universität Augsburg, 2013. http://d-nb.info/107770254X/34.
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Pollitt, David Frederic. "Performance evaluation of a second generation metaphase finder for chromosome-based radiation dosimetry." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0009/MQ32550.pdf.
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Vockerodt, Tobias [Verfasser]. "Generation of harmonic radiation in self-guided filaments in gaseous media / Tobias Vockerodt." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2012. http://d-nb.info/1027563538/34.
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Pechhacker, Roman. "Particle acceleration with associated generation and absorption of electromagnetic radiation in solar plasmas." Thesis, Queen Mary, University of London, 2014. http://qmro.qmul.ac.uk/xmlui/handle/123456789/8843.
Full textAbstract:
The heating of solar chromospheric internetwork regions is investigated by means of the absorption of electromagnetic (EM) waves that originate from the photospheric black body radiation. It is studied in the framework of a plasma slab model. The absorption is provided by the electron-neutral collisions in which electrons oscillate in the EM wave field and electron-neutral collisions damp the EM wave. It is shown that for plausible physical parameters, the absorbed heating flux is between 20% and 45% of the chromospheric radiative loss flux requirement. Further, 1.5D particle-in-cell simulations of a hot, low density electron beam injected into magnetized, Maxwellian plasma were used to further explore the alternative non-gyrotropic beam driven EM emission mechanism, which was first studied in Ref.[83]. Variation of beam injection angle and background density gradient showed that the emission is caused by the perpendicular component of the beam injection current, whereas the parallel component only produces Langmuir waves, which play no role in the generation of EM waves in our mechanism. When the beam is injected perpendicularly to the background magnetic field, any electrostatic wave generation is turned off and a purely EM signal is left. Finally, a possible solution to the unexplained high intensity hard x-ray emission observable during solar flares was investigated via 3D particle-in-cell simulations. A beam of accelerated electrons was injected into a magnetised, Maxwellian, homogeneous and inhomogeneous background plasma. The electron distribution function was unstable to the beam-plasma instability and was shown to generate Langmuir waves, while relaxing to plateau formation. Three different background plasma density gradients were investigated. The strong gradient case produced the largest fraction of electrons beyond 15vth. Further, Langmuir wave power is shown to drift to smaller wavenumbers, as found in previous quasi-linear simulations.
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Debnath, Sree Bash Chandra. "New generation X-ray detector for radiation therapy and instrumentation for surface physics." Thesis, Aix-Marseille, 2020. http://www.theses.fr/2020AIXM0252.
Full textAbstract:
Le traitement moderne par radiothérapie est motivé par la demande constante d'un détecteur dosimétrique approprié. Plus récemment, seuls quelques détecteurs se sont montrés prometteurs dans ce sens, mais ils présentent plusieurs obstacles lors de leur mise en œuvre, tant pour les applications à forte dose de rayonnement que pour celles à faible dose. Les dosimètres à rayons X développés industriellement sont encore limités par l'exigence de taille importante, l'effet de moyennage de volume, le manque de sensibilité et le faible rapport signal/bruit, etc. Dans ce contexte, ce travail de thèse est consacré à la conception et à la fabrication d'un nouveau détecteur de rayons X extrêmement compact, en temps réel et très sensible. Le principe du dispositif est basé sur des clusters scintillantes qui sont greffées à l'extrémité d'une petite fibre centrale. Sous irradiation aux rayons X, les clusters émettent de la lumière visible qui est collectée par un compteur de photons à travers la fibre optique. Le détecteur développé a été testé pour la caractérisation de petits champs (inférieurs à 0,5 x 0,5 cm²) en radiothérapie et également en brachythérapie. Dans les deux cas, le détecteur présente d'excellentes performances.En outre, un détecteur similaire à tête nanométrique a été mis en œuvre pour la physique des surfaces au moyen d'une nouvelle technique à double sonde (STM/Fibre). Ainsi, les résultats de cette recherche explorent la dosimétrie des rayonnements miniaturisés avec l'amélioration des traitements des tumeurs de stade précoce. En outre, dans le domaine de l'imagerie des surfaces, une nouvelle technique de caractérisation des matériaux sera mise au pointThe modern radiation therapy treatment is driven by the everlasting demand of a suitable dosimetric detector. Most recently, only a few detectors have shown promise in this direction, but exhibiting several barriers while implementing both in high and low radiation dose applications. The industrially developed X-ray dosimeters/detectors are still limited by the significant size requirement, volume averaging effect, lack of sensitivity, and low signal-to-noise ratio, etc. In this context, this thesis work is devoted to the design and fabrication of a novel extremely compact, small-scale, real-time, dynamic, and highly sensitive X-ray detector. The device principle is based on scintillating clusters that are grafted at the extremity of a small core fiber. Under X-ray irradiation, clusters emit visible light that is collected by a photon counter through the optical fiber. The developed detector was tested for small (lower than 0.5 x 0.5 cm²) field characterization in radiotherapy. It also allows characterizing radiation dosimetry in brachytherapy. In both cases, the detector demonstrates excellent performances when compared to the existing dosimeters and MC simulation.In addition, a similar detector with nano-metric head was implemented for the application in surface physics by means of a novel dual-probe (STM/Fiber) technique. Thus, the outcomes of this research explore miniaturized radiation dosimetry and will disclose the path of enhancing early-stage tumor treatments through real-time dosimetry. Moreover, the performance of the probe in surface imaging will open the path of novel material characterization technique allowing simultaneous sample imaging
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Rogl, Andreas. "High frequency driven semiconductor superlattice oscillators for generation of subterahertz and terahertz radiation." Regensburg Univ.-Verl. Regensburg, 2007. http://d-nb.info/994208251/04.
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Cook, Alan Matthew. "Generation of narrow-band terahertz coherent Cherenkov radiation in a dielectric wakefield structure." Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1905663081&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Matlack, Kathryn H. "Nonlinear ultrasound for radiation damage detection." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51965.
Full textAbstract:
Radiation damage occurs in reactor pressure vessel (RPV) steel, causing microstructural changes such as point defect clusters, interstitial loops, vacancy-solute clusters, and precipitates, that cause material embrittlement. Radiation damage is a crucial concern in the nuclear industry since many nuclear plants throughout the US are entering the first period of life extension and older plants are currently undergoing assessment of technical basis to operate beyond 60 years. The result of extended operation is that the RPV and other components will be exposed to higher levels of neutron radiation than they were originally designed to withstand. There is currently no nondestructive evaluation technique that can unambiguously assess the amount of radiation damage in RPV steels. Nonlinear ultrasound (NLU) is a nondestructive evaluation technique that is sensitive to microstructural features such as dislocations, precipitates, and their interactions in metallic materials. The physical effect monitored by NLU is the generation of higher harmonic frequencies in an initially monochromatic ultrasonic wave, arising from the interaction of the ultrasonic wave with microstructural features. This effect is quantified with the measurable acoustic nonlinearity parameter, beta. In this work, nonlinear ultrasound is used to characterize radiation damage in reactor pressure vessel steels over a range of fluence levels, irradiation temperatures, and material composition. Experimental results are presented and interpreted with newly developed analytical models that combine different irradiation-induced microstructural contributions to the acoustic nonlinearity parameter.
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Yeh, Ka-Lo. "The generation of high field terahertz radiation and its application in terahertz nonlinear spectroscopy." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/49748.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2009.Includes bibliographical references (p. 147-155).
In this thesis research, I implemented a terahertz generation scheme that enables high-field near-single-cycle terahertz (THz) pulse generation via optical rectification in a LiNbO3 (LN) crystal. I also developed a method for the non reconfigurable generation of high-intensity multiple-cycle THz fields aimed to more efficiently deliver THz energy to resonant samples. A novel free-space THz-pump/THz-probe setup enabled time-resolved measurement of ultrafast nonlinear electronic responses in doped bulk semiconductor samples. The ability to spectrally and temporally resolve the response of the semiconductor sample using a THz probe allowed us to uncover both the dynamics of impact ionization and interesting phonon-plasma interactions in indium antimonide (InSb) for the first time. Nonlinear vibrational responses in LN were ob-served first in a dual THz beam setup on an integrated LN waveguide platform with optical probing to reveal the generation of terahertz second harmonic signals and also in THz transmission measurements in cooled LN where THz intensity-dependent self-phase modulation and harmonic generation were observed. An outlook and preliminary results toward implementation and observation of high-field THz-driven responses in ferroelectric materials are given in the final chapter of this thesis.
by Ka-Lo Yeh.
Ph.D.
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Yang, Hongyu S. M. Massachusetts Institute of Technology. "High energy femtosecond fiber laser at 1018 nm and high power Cherenkov radiation generation." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/93055.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 51-54).
Two novel laser systems for ultrafast applications have been designed and built. For the seeding of a high energy cryogenically cooled Yb:YLF laser, a novel 1018 nm fiber laser system is demonstrated. It produces >35 nJ pulse energy and 5 nm spectral bandwidth. A double-cladd amplifier and an appropriate filter to optimize the system for the amplifier seeding application were employed. This is the highest pulse energy with narrow spectrum at 1018 nm. For a photonic analog-to-digital conversion system operating at 1250 nm, a fiber laser system generating 4 W of femtosecond Cherenkov radiation at that wavelength was built. The characteristics of the Cherenkov radiation were well studied.
by Hongyu Yang.
S.M.
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Upadhya, Prasanth Chandrashekara. "Coherent generation and detection of Terahertz radiation : time domain Terahertz spectroscopy of molecular crystals." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614771.
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AlHajDarwish, Mustafa Yousef. "Studies of current induced magnetization reversal and generation of GHz radiation in magnetic nanopillars." Diss., Connect to online resource - MSU authorized users, 2008.
Find full textAbstract:
Thesis (Ph. D.)--Michigan State University. Dept. of Physics and Astronomy, 2008.Title from PDF t.p. (viewed on July 23, 2009) Includes bibliographical references (p. 50-52). Also issued in print.
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Rogl, Andreas [Verfasser]. "High-frequency driven semiconductor superlattice oscillators for generation of subterahertz and terahertz radiation / Andreas Rogl." Regensburg : Univ.-Verl. Regensburg, 2009. http://d-nb.info/999590391/34.
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Qian, Ximei. "Applications of third generation synchrotron radiation in vacuum ultra-violet (VUV) photoionization spectroscopy and dynamics /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2003. http://uclibs.org/PID/11984.
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Holcomb, Andrew M. "Development of a graphical user interface for the coarse mesh radiation transport code COMET and cross section generation with HELIOS." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52952.
Full textAbstract:
The coarse mesh radiation transport (COMET) code uses response functions to solve the neutron transport equation. Most nuclear codes used today have a very steep learning curve; COMET is no exception. To ease the user's onus of learning how to create correctly formatted COMET input-files, a graphical user interface (GUI) was created. The GUI allows the user to select values for all the relevant variables while simultaneously minimizing the errors a typical new user would make. To this end, the GUI creates all of the input files required to run COMET. The GUI also provides a visualization tool that the user may use to check the problem geometry before running COMET. The GUI is also responsible for post-processing the COMET output for visualization with TecPlot.
In addition to the GUI, multi-group cross section libraries were generated as part of the MHTGR-350 (Modular High Temperature Gas Reactor) benchmark problem under development at Georgia Tech. This project aims to couple COMET with a thermal hydraulics code to best model the true physics of the reactor design. In order for this goal to be actualized, six-group cross sections were generated over the operational temperature range of the MHTGR using the current coupling and collision probability code HELIOS.
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McLenaghan, Joanna Siân. "Negative frequency waves in optics : control and investigation of their generation and evolution." Thesis, University of St Andrews, 2014. http://hdl.handle.net/10023/6532.
Full textAbstract:
This thesis is concerned with various methods for the control and investigation of pulse dynamics in a Photonic Crystal Fibre (PCF) and of the radiation driven by a short pulse. In particular the focus is on pulses in the anomalous dispersion region which would form solitons in the absence of higher order effects. Several different types of radiation can be driven by such pulses if they are perturbed by higher order dispersive and non-linear effects - for example Resonant Radiation (RR) and Negative Resonant Radiation (NRR) two dispersive waves which gain energy at the expense of the pulse. The feature of NRR which is of particular importance is that it is the first observed example of a coupling between positive and negative frequencies in optics. This has only been possible due to recent advances in fields such as PCFs, lasers and analogue systems. As with many scientific discoveries, NRR was found by bringing together ideas and techniques from these different fields. Both the pulse and the driven radiation are investigated using a number of different pulse and PCF parameters. These include power, chirp, polarisation and PCF dispersion. These are used to vary the wavelengths at which the driven radiation occurs as well as its generation efficiency. Furthermore the power and chirp are used to vary where in the PCF the driven radiation is generated by controlling where the driving pulse compresses and spectrally expands. This property is used to investigate different stages in the evolution of the pulse and driven radiation as well as to optimise the generation efficiency of the driven radiation.
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Cantono, Giada. "Relativistic Plasmonics for Ultra-Short Radiation Sources." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS353/document.
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La plasmonique étudie le couplage entre le rayonnement électromagnétique et les oscillations collectives des électrons dans un matériel. Les plasmons de surface (SPs), notamment, ont la capacité de concentrer le champ électromagnétique sur des distances micrométriques, ce qui les rend intéressants pour le développement des dispositifs photoniques les plus novateurs. 'Etendre l'excitation de SPs au régime de champs élevés, où les électrons oscillent à des vitesses relativistes, ouvre des perspectives stimulantes pour la manipulation de la lumière laser ultra-intense et le développement de sources de rayonnement énergétiques et à courte durée. En fait, l'excitation de modes résonnants du plasma est l'une des stratégies possibles pour transférer efficacement l'énergie d'une impulsion laser ultra-puissante à une cible solide, cela étant parmi les défis actuels dans la physique de l’interaction laser-matière à haute intensité. Dans le cadre de ces deux sujets, ce travail de thèse démontre la possibilité d'exciter de façon résonnante des plasmons de surface avec des impulsions laser ultra-intenses. Elle étudie comment ces ondes peuvent à la fois accélérer de paquets d'électrons relativistes le long de la surface de la cible mais aussi augmenter la génération d'harmoniques d'ordre élevé de la fréquence laser. Ces deux processus ont été caractérisés avec de nombreuses expériences et simulations numériques. En utilisant un schéma d’interaction standard de la plasmonique classique, les SPs sont excités sur des cibles dont la surface présente une modulation périodique régulière à l'échelle micrométrique (cibles réseau). Dans ce cas, les propriétés de l'émission d'électrons tout comme celles des harmoniques permettent d’envisager leur utilisation dans des application pratiques. En réussissant à dépasser les principaux problèmes conceptuels et techniques qui jusqu'au présent avaient empêché l'application d'effets plasmoniques dans le régime de champs élevés, ces résultats apportent un intérêt nouveau à l'exploration de la Plasmonique RelativistePlasmonics studies how the electromagnetic radiation couples with the collective oscillations of the electrons within a medium. Surface plasmons (SPs), in particular, have a well-established role in the development of forefront photonic devices, as they allow for strong enhancement of the local EM field over sub-micrometric dimensions. Promoting the SP excitation to the high-field regime, where the electrons quiver at relativistic velocities, would open stimulating perspectives for the both the manipulation of ultra-intense laser light and the development of energetic, short radiation sources. Indeed, the excitation of resonant plasma modes is a possible strategy to efficiently deliver the energy of a high-power laser to a solid target, this being among the current challenges in the physics of highly-intense laser-matter interaction. Gathering these topics, this thesis demonstrates the opportunity of resonant surface plasmon excitation at ultra-high laser intensities by studying how such waves accelerate bunches of relativistic electrons along the target surface and how they enhance the generation of high-order harmonics of the laser frequency. Both these processes have been investigated with numerous experiments and extensive numerical simulations. Adopting a standard configuration from classical plasmonics, SPs are excited on solid, wavelength-scale grating targets. In their presence, both electron and harmonic emissions exhibit remarkable features that support the conception of practical applications. Putting aside some major technical and conceptual issues discouraging the applicability of plasmonic effects in the high-field regime, these results are expected to mark new promises to the exploration of Relativistic Plasmonics
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Catalano, Sarah L. "Transport Imaging developing an optical technique to characterize bulk semiconductor materials for next generation radiation detectors." Thesis, Monterey, Calif. : Naval Postgraduate School, 2009. http://edocs.nps.edu/npspubs/scholarly/theses/2009/Jun/09Jun%5FCatalano.pdf.
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Thesis (M.S. in Physics)--Naval Postgraduate School, June 2009.Thesis Advisor(s): Haegel, Nancy M. "June 2009." Description based on title screen as viewed on July 10, 2009. Author(s) subject terms: Cathodoluminescence, Diffusion, Drift, Mobility, Lifetime, Bismuth Ferrite, BiFeO3 , Semiconductor, Transport Imaging. Includes bibliographical references (p. 61-62). Also available in print.
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Abdukadyrova, I. Kh. "Influence of high reactor irradiation on some parameters of Al203 crystals and process generation of a several points nanodefects." Thesis, Sumy State University, 2011. http://essuir.sumdu.edu.ua/handle/123456789/20873.
Full textAbstract:
In this connection the peculiarities of radiation effect on lattice parameters, form
and position of several reflections, reflection coefficient and frequency of valence and
deformation oscillations of Al-O bonds, optical characteristics of the oxide aluminium
Al2O3 were studied with techniques of X-diffraction, absortion-luminescenke and IRreflection
spectroscopy. The characteristic features of the process of radiation-defect
formation and generation of some points nanodefects, change in the structural, optical
properties of Al2O3 crystals exposed to gamma and reactor radiation have been investigated
by spectroscopic methods. The dose dependence’s of the generation in crystals
the color and luminescence centers, nanodefects - type F- and F-aggregate, change of the
structural parameters was determined. For example, in work presented of temperaturedose
dependence on the intensity of the 330, 420 nm bands in FL and GL spectrum of
crystals. As the T= 600-7000C and fluence 1.1016 cm-2 - 1.1019 cm-2 of intensity this
bands increasing (nanodefects - F+ centers) was can see. In this paper was given dose
dependence of generation on the oxide in the absorption spectra a bands 257 and 358 nm
(nanodefects of a type F- and F-aggregate defects). The possible mechanism of damage
structure of a samples irradiated in a reactor is discussed.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/20873
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Carlsson, Fredrik. "Utilizing Problem Structure in Optimization of Radiation Therapy." Doctoral thesis, Stockholm : Matematik, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4689.
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Christian, Lea Rajeshkumar. "Xeroderma Pigmentosum A Deficiency Results in Increased Generation of Microvesicle Particles in Response to Ultraviolet B Radiation." Wright State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=wright1621875551264658.
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