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Ronga, Maria Grazia. "Study and modelling of very high energy electrons (VHEE) radiation therapy". Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPAST036.
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Le développement de méthodes innovantes susceptibles de réduire la sensibilité des tissus sains aux radiations, tout en maintenant l'efficacité du traitement sur la tumeur, est un aspect central de l'amélioration de l'efficacité de la radiothérapie pour le traitement du cancer. Parmi les développements et innovations méthodologiques possibles, la combinaison d'une irradiation à ultra-haut débit de dose (FLASH) et d'électrons de très haute énergie (VHEE) pourrait permettre d'exploiter les avantages radiobiologiques de l'effet FLASH pour le traitement des tumeurs profondes. En particulier, les VHEEs dans la gamme d'énergie de 100 à 250 MeV seraient particulièrement intéressants d'un point de vue balistique et biologique pour l'application des irradiations FLASH en radiothérapie. Cette thèse étudie donc l'utilisation possible des VHEEs en radiothérapie et en particulier leur utilisation à ultra-haut débit de dose, évaluant ainsi la faisabilité de la radiothérapie FLASH-VHEE. Bien que prometteuse, plusieurs aspects de cette technique doivent être étudiés avant qu'elle puisse être employée dans un contexte clinique. Une première partie du travail étudie les paramètres de la machine nécessaires pour répondre aux contraintes des irradiations FLASH. À cette fin, un modèle analytique de calcul de la dose basé sur la théorie de la diffusion multiple de Fermi-Eyges a été développé et testé. Ce modèle analytique a également été utilisé pour concevoir et optimiser un système de double diffusion pour la thérapie VHEE et ainsi obtenir des tailles de champ supérieures à 15x15 cm², et pour évaluer la possible adaptation des méthodes de conformation conventionnelles du faisceau de particules pour la thérapie FLASH-VHEE. La deuxième partie de ce travail porte sur la planification du traitement par VHEE et l'évaluation des plans cliniques. Quatre cas cliniques représentatifs ont été étudiés, pour lesquels des plans de traitement par balayage de mini-faisceau (PBS) et par double diffusion (DS) ont été calculés. L'influence de l'énergie du faisceau sur la qualité du plan a été étudiée et les techniques PBS et DS ont été comparées. Une description temporelle de l'irradiation a également été réalisée ainsi que l'incorporation d'un facteur de modification FLASH lors de l'évaluation du plan et de son effet sur les tissus sains en mode FLASH. Enfin, l'estimation des doses liées aux particules secondaires et les questions de radioprotection ont été abordées. Un calcul de la dose secondaire due aux photons de Bremsstrahlung et aux neutrons provenant des deux systèmes de délivrance de la dose a été développé dans l'eau. La dose dues aux particules secondaires reçues par divers organes a également été évaluée dans le cadre de traitements intracrâniens et afin de démontrer l'avantage des faisceaux VHEE par rapport aux faisceaux de protons en terme de dose neutrons hors champ. En résumé, les modèles analytiques accélérés et paramétrés dans cette étude permettent une estimation de la distribution de la dose produite par un système VHEE avec une bonne précision, ce qui fournit des informations importantes pour la conception éventuelle d'un système VHEE. Les résultats de ce travail pourraient soutenir le développement de la radiothérapie FLASH-VHEEThe development of innovative methods capable of reducing the sensitivity of healthy tissue to radiation, while maintaining the effectiveness of the treatment on the tumour, is a central aspect of improving the effectiveness of radiotherapy in the treatment of cancer. Among possible developments and methodological innovations, the combination of ultra-high dose rate irradiation (FLASH) and very high energy electrons (VHEE) could make it possible to exploit the radiobiological advantages of the FLASH effect for the treatment of deep tumours. In particular, VHEEs in the 100 to 250 MeV energy range would be particularly interesting from a ballistic and biological point of view for the application of FLASH irradiation in radiotherapy. This thesis therefore studies the possible use of VHEEs in radiotherapy, and in particular their use at ultra-high dose rates, thus assessing the feasibility of FLASH-VHEE radiotherapy. Although promising, several aspects of this technique need to be studied before it can be used in a clinical context. The first part of this work studies the machine parameters required to meet the constraints of FLASH irradiation. To this end, an analytical model for calculating the dose based on Fermi-Eyges multiple scattering theory was developed and tested. This analytical model has also been used to design and optimise a double-scattering system for VHEE therapy, in order to obtain field sizes greater than 15x15 cm², and to assess the possible adaptation of conventional particle beam conformation methods for FLASH-VHEE therapy. The second part of this work focuses on VHEE treatment planning and the evaluation of clinical plans. Four representative clinical cases were studied, for which pencil-beam scanning (PBS) and double scattering (DS) treatment plans were calculated. The influence of beam energy on plan quality was studied and the PBS and DS techniques were compared. A temporal description of the irradiation was also carried out, as well as the incorporation of a FLASH modification factor when evaluating the plan and its effect on healthy tissue in FLASH mode. Finally, the estimation of doses from secondary particles and radiation protection issues were addressed. A calculation of the secondary dose due to Bremsstrahlung photons and neutrons from the two dose delivery systems was developed in water. The secondary particle dose received by various organs was also assessed in the context of intracranial treatments and in order to demonstrate the advantage of VHEE beams over proton beams in terms of out-of-field neutron dose. In summary, the fast analytical models parameterised in this study allow the dose distribution produced by a VHEE system to be estimated with good accuracy, providing important information for the potential design of a VHEE system. The results of this work could support the development of FLASH-VHEE radiotherapy
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Mallot, Ann Kathrin. "The energy spectrum of cosmic electrons measured with the MAGIC telescopes". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2017. http://dx.doi.org/10.18452/17698.
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Die hier vorgestellte Analyse nutzt die MAGIC Teleskope, zwei abbildende Cherenkov-Teleskope, zum Vermessen des Elektronenflusses. Der Energiebereich dieser Teleskope überschneidet sich großflächig sowohl mit dem der Satellitenmissionen Fermi-LAT und AMS-02 als auch mit den hochenergetischen Messungen der Cherenkov-Teleskope VERITAS und H.E.S.S.. Diese Arbeit hat das Elektronenspektrum im Bereich von 135 GeV bis 4 TeV mittels der MAGIC Teleskope vermesssen. Das Spektrum lässt sich in diesem Bereich mit einem einfachen Potenzgesetz mit dem Index -3.14+-0.05(stat)+-0.5(syst) beschrieben werden. Die für diese Messung entwickelte Analyse weicht grundlegend von der Standardanalyse in MAGIC ab. Die Differenzierung von Signal und Untergrund kann nicht anhand der Richtung der eintreffenden Teilchen vorgenommen werden. Stattdessen basiert die Differenzierung auf einem Algorithmus für maschinelles Lernen, welcher eine Unterscheidung zwischen elektromagnetischen und hadronischen Luftschauern ermöglicht. Der Untergrund muss für diese Analyse anhand von Monte Carlo Simulationen geschätzt werden. Dafür wurden Protonen simuliert. Zudem liegt ein Schwerpunkt der Arbeit auf der Abschätzung systematischer Fehler und Unsicherheiten der neuen Analyse. Erwartungsgemäß sind die Unsicherheiten dieser indirekten Messmethode deutlich größer als bei direkten Messungen der Satellitenexperimente. Aufgrund der großen Unsicherheiten kann ein Bruch bei 800 GeV jedoch auch nicht ausgeschlossen werden. Die hier präsentierte Messung stimmt innerhalb der Fehler mit den Ergebnissen von AMS-02 und Fermi-LAT sowie innerhalb von zwei Standardabweichungen mit den Messungen von H.E.S.S. und VERITAS überein. Eine Interpretation des Elektronenflusses gestaltet sich aufgrund des großen Fehlers als schwierig. Im Endeffekt kann keine der potentiellen neuen Quellen kosmischer Elektronen ausgeschlossen werden.The measurement presented in this thesis seeks to provide an increased overlap of the Fermi-LAT and AMS-02 measurement, as well as the very-high-energy H.E.S.S. and VERITAS measurement. The MAGIC telescopes, a stereoscopic system of imaging air-shower Cherenkov telescopes, are a good candidate for such a measurement. They overlap largely with the Fermi-LAT energy range, down to 130 GeV, and extend into the energy range of the H.E.S.S. system, extending the measurement up to 4 TeV. The measurement performed in this thesis uses a non-standard method developed especially for this analysis. It is based on a machine-learning-algorithm which differentiates between hadronic and electro-magnetic air showers. The background needs to be simulated from Monte Carlo protons, which were produced in large quantities for this thesis. As this is an indirect detection method, the systematic uncertainties are much larger than those of the satellite missions. A detailed study of the systematic uncertainties was performed in the scope of this thesis, which prove to be much larger than the statistical uncertainties. The measured spectrum presented here extends from 135 GeV up to 4 TeV. It shows no clear break in the spectrum and is in line with an extension of the single power-law observed by Fermi-LAT and AMS-02. A broken power-law interpretation was disfavored when compared to the single power-law. The final spectrum has a powerlaw index of -3.14+-0.05(stat)+-0.5(syst). Due to the large uncertainties no definitive conclusion can be given at this point. Also, the cutoff seen by H.E.S.S. can not be ruled out. The result presented in this thesis is compatible with the Fermi-LAT and AMS-02 results, however there is minor tension with the H.E.S.S. and VERITAS results around 4 TeV. The limiting factor of the method is the large systematic uncertainty, making it impossible to distinguish between different electron sources for the results presented in this thesis.
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Kashiyama, Kazumi. "Origins of High Energy Cosmic-Ray Electrons and Positrons". 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/157757.
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Carlton, Ashley Kelly. "Characterizing high-energy electrons in space using science imagers". Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120413.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 129-140).
Harsh radiation in the form of ionized, highly energetic particles is part of the space environment and can affect the operation, performance, and lifetime of spacecraft and their instruments. Jupiter has the largest and strongest magnetosphere of all of the planets in the solar system and it is dominated by high-energy electrons. Measuring and characterizing megaelectron volt (MeV) particles is fundamental for understanding the energetic processes powering the magnetosphere, interactions of the particles with surfaces of the Jovian satellites, and the effects of these particles on spacecraft near or in Jovian orbit. Electrons in Jupiter's magnetosphere can interact with spacecraft and lead to component failures, degradation of sensors and solar panels, and physical damage to materials. Dedicated instruments to monitor the radiation environment are not always included on spacecraft due to resource constraints. Measurements of the high-energy (>1 MeV) electron environment at Jupiter are currently spatially and temporally limited, predominantly coming from the Energetic Particle Detector (EPD) on the Galileo spacecraft. In this thesis, we develop ways to use existing hardware on spacecraft to measure the energetic particle environment. Solid-state detectors are commonly used as scientific imagers on spacecraft. In addition to being sensitive to incoming photons, semiconductor devices also are affected by incoming charged particles collected during integration and detector readout. These radiation hits from the space environment are typically considered "noise" at the detector. We develop a technique to extract quantitative high-energy electron environment information (energy and flux) from science imager radiation "noise". We use data from the Galileo spacecraft Solid-State Imaging (SSI) instrument, which is a silicon charge-coupled device (CCD). We post-process raw SSI images to obtain frames with only the radiation contribution. The camera settings are used to compute the energy deposited in each pixel, which corresponds to the intensity of the observed radiation hits. The energy deposited in the SSI pixels by incident particles from processed SSI images are compared with the results from 3D Monte Carlo transport simulations of the SSI using Geant4. Simulating the response of the SSI instrument to mono-energetic electron environments, we find that the SSI is capable of detecting >10 MeV electrons (>90% of <10 MeV particles are stopped with 95% confidence). Using geometric scaling factors computed for the SSI, we calculate the environment particle flux given a number of pixels with radiation hits. We compare the SSI results to measurements from the Galileo EPD, examining the electron fluxes from the >11 MeV integral flux channel. We find agreement with the EPD data within 3-sigma of the EPD data for 43 out of 43 (100%) of the SSI images evaluated. 62% of fluxes are also within 1-sigma of the EPD data. To demonstrate that the general technique is applicable to other imagers, we also analyze the Galileo Near-Infrared Mapping Spectrometer (NIMS). We find that NIMS is sensitive to >5 MeV electrons and the calculated fluxes are consistent with the EPD. This approach can be applied to other sets of imaging data (star trackers, etc.) in energetic electron environments, such as those found in geostationary Earth orbit. This thesis also includes a summary of required and recommended information (tests, models, etc.) for the use of science imagers as high-energy electron sensors.
by Ashley Kelly Carlton.
Ph. D.
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Aizatsky, N. I., N. P. Dikiy, A. N. Dovbnya, I. D. Fedorets, V. A. Kushnir, Yu V. Lyashko, D. V. Medvedev i in. "Properties of Zirconia Nanoceramics under High-Energy Electrons Irradiation". Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35622.
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Formation of radioactive isotopes is investigated under irradiation by relativistic electrons with energy
up to 100 MeV. Radioactive isotopes 87,88Y, 88,89,95Zr, 95Nb, 175Hf are registered after irradiation by
relativistic electrons with energy 47.2 MeV. The present data are necessary for the choice of a material for
a dielectric wakefield accelerator. The greatest danger at operation of accelerators represents 88Y.
Formation of radiation defects in nanoceramics is investigated. The various types of radiation defects are
found out at an irradiation by relativistic electrons with energy 47 MeV and 86 MeV. In UV VIS spectra
the absorption lines of radiation are registered at 402.2 nm and 635 nm, which correspond to the F and F'
centers of monocline lattices of zirconia. It is revealed, that krypton atoms are the centers of segregation of
point defects.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35622
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Dickinson, Hugh John. "Very high energy gamma-rays from binary systems". Thesis, Durham University, 2010. http://etheses.dur.ac.uk/290/.
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This thesis presents a study of the very high energy (VHE) gamma-ray emission from X-ray binary systems using the H.E.S.S. imaging atmospheric Cherenkov array. The historical background and basic principles of ground-based gamma-ray astronomy are briefly reviewed and an overview of the design and capabilities of the H.E.S.S. telescope system is presented. The broadband observational properties of X-ray binary systems and their relevance in a broader astrophysical context is also discussed. A review of the radiative emission mechanisms which relate to VHE gamma-ray emission in X-ray binaries is presented, with emphasis given to the leptonic emission processes of synchrotron radiation and inverse-Compton scattering. Intrinsic absorption processes which act to attenuate the emitted flux of VHE gamma-rays are also discussed. Three computer models are introduced which simulate aspects of the gamma-ray emission and absorption in X-ray binary systems. A detailed analysis of the VHE gamma-ray emission from the X-ray binary LS 5039 is presented and the relevant procedures for data selection, gamma-hadron separation and background estimation are discussed in some detail. Methods for the determination of detection significance and the calculation of gamma-ray fluxes are also reviewed and results are derived which apply specifically to LS 5039. A detailed temporal analysis of the gamma-ray signal from LS 5039 is presented, applying tests for secular, excess and periodic variability. Strong evidence is found for modulation of the observed gamma-ray flux on the orbital period of ~3.9 days. Following a brief discussion of the procedures required for spectral analysis of VHE gamma-ray data, results are presented for LS 5039 which reveal evidence for spectral variability which is correlated with the observed gamma-ray flux and therefore, the orbital phase of the binary system. The spectral and temporal characteristics of LS 5039 are then compared with the predictions of theoretical models in an attempt to explain the observed behaviour. Contemporaneous X-ray and VHE gamma-ray observations of three galactic microquasars using the Rossi X-ray Timing Explorer and H.E.S.S. are presented. Although no gamma-ray detections are reported, the observations permit the derivation of upper limits to the VHE gamma-ray flux which correspond to episodes of known X-ray behaviour. The X-ray characteristics of each target are compared with pre-existing observational data to infer the presence or otherwise of relativistic outflows at the H.E.S.S. observation epochs. The implications of the gamma-ray non-detections are then discussed in the context of these inferred system properties. The results of a survey of the VHE gamma-ray emission associated with the positions of 125 known X-ray binaries are presented. Although no conclusive detections were obtained, tentative indications were found for a population of faint, spectrally hard gamma-ray sources associated with high-mass X-ray binary systems. The inferred characteristics of the indicated population show broad agreement with the measured properties of known gamma-ray-emitting X-ray binary systems like LS 5039.
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Guillaud, Mathilde. "Neutrino oscillations at very high energy/matter density". Thesis, KTH, Fysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-292510.
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Neutrino oscillations in matter can be studied in different regimes, depending on the energy of the incoming neutrinos and the matter density of the medium. In this thesis we investigate neutrino oscillations in dense matter at very high energy (TeV-PeV range), taking into account the absorption that the neutrinos may undergo in such dense media. This absorption phenomenon is relevant for neutrino telescope measurements of astrophysical neutrinos. We begin with a brief reminder on neutrino oscillations in vacuum and the construction of the PMNS matrix. Then, we proceed with calculations for dense matter. We then explore the accuracy of the resulting effective 2-neutrino mixing formulas. They present a good accuracy for Earth-like densities in our range of energies. We develop the calculations for oscillation probabilities in dense matter with absorption through charged-current inelastic scattering for both the two-neutrino and three-neutrino case. We find that in dense media, astrophysical neutrinos indeed undergoabsorption, which reduces signicantly the fluxes for each flavor, with a resonant absorption of electron-anti-neutrinos around E_{res}\simeq 6.3PeV. We discuss the impact of neutrino absorption in the Earth for neutrino telescopes measurements. We find that solar and lunar shadowing is not problematic for current telescopes but could be a good angular resolution indicator for new telescopes to come.Neutrinooscillationer i materia kan studeras i olika regimer beroende på inkommande neutrinernas energi och densiteten hos det bakomliggande mediet. I detta examensarbete undersöker vi neutrinooscillationer i gränsen av tät materia och mycket hög energi (TeV-PeV-intervall), och tar hänsyn till den absorption av neutriner som då kan inträffa i sådant materia. Detta absorptionsfenomen är relevant för neutrino-teleskopmätningar av astrofysiska neutriner. Vi börjar med att kort påminna oss om neutrinooscillationer i vakuum och konstruktionen av PMNS-matrisen. Vi försätter sedan med beräkningar av neutrinooscillationer i tät materia. Vi undersöker noggrannheten i resulterande effektiva 2-neutrino-blandningsformlerna. De uppvisar en god noggrannhet i jordlika materieprofiler i vårt intervall av energier. Vi utvecklar beräkningarna av oscillationssannolikheterna i tät materia inklusive absorption genom laddad ström oelastisk spridning i båda två- och tresmaksfallen. Vi finner att astrofysiska neutriner i tät materia absorberas, vilket minskar betydligt flödena för varje smak, med en resonansabsorption av elektron-antineutrino omkring E_res\simeq 6.3PeV. Vi diskuterar sedan effekterna av neutrinoabsorption på jorden för neutrino-teleskopmätningar. Vi finner att sol- och månskuggning är inte problematisk för nuvarande teleskop och kunde vara en bra vinkelupplösningsindikator för kommande teeskop.
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Sritragool, Kunlapaporn. "Modification of Rubber Particle filled Thermoplastic with High Energy Electrons". Doctoral thesis, Universitätsbibliothek Chemnitz, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-201000954.
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In present study, high energy electrons were used to modify blends based on RP and PP under two conditions: stationary and in-stationary conditions. Modification of blend under stationary condition is a process which is established in industrial application and where required absorbed dose is applied to form parts (after molding) at room temperature and in solid state. On the contrary, the modification of blend with high energy electrons under in-stationary condition is a new process (electron induced reactive processing) where required absorbed dose is applied to a molten state during melt mixing process. The modification of blend based on RP and PP under stationary condition resulted in slightly enhancement of tensile properties while the modification of this blend under in-stationary condition resulted in deterioration of tensile properties due to degradation of the PP matrix. Thus, special grafting agent (GA) is required for improving the tensile properties. The effect of different GAs on tensile, thermal, dynamic mechanical as well as morphological properties and melt flow properties of blends based on RP and PP were determined. The optimum absorbed dose for modification of blend based on RP and PP under both conditions was evaluated. In addition, the effect of treatment parameters of electron induced reactive processing was investigated.
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Williams, Andrew James. "A water calorimeter for high energy x-rays and electrons". Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394541.
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Lemieux, François 1979. "Are inflationary predictions sensitive to very high energy physics?" Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=80316.
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It was recently proposed that modifications to physics at trans-Planckian energies could lead to a non-adiabatic evolution of the scalar fluctuations responsible for the temperature anisotropy of the cosmological microwave background. If such a possibility was to be confirmed, it would provide us the first possibility to ever get experimental measurements of the physics near the Planck scale. This work investigates the physicality of such non-adiabatic evolutions, by avoiding the introduction of any exotic physics, by working well below the Planck scale. Simple 'hybrid-like' models of inflation composed of an inflaton field coupled to another heavy scalar will be used. It will be shown that small oscillations in the heavy scalar field can generate a non-adiabatic evolution of the inflationary vacuum leading to new features in the power spectrum that could eventually be observed. The naturalness of this non-adiabaticity is also studied, leading to a constraint about the maximum duration of inflation if these effects are to be big enough to ever be detectable.
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Schroedter, Martin. "The very high energy gamma-ray spectra of AGN". Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/290128.
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A total of six extragalactic objects have been detected so far at very high energies (VHE). They are BL Lac objects, a sub-group of active galactic nuclei characterized by intense nonthermal radiation. The VHE spectra of two of these, 1ES 1959 + 650 and 1ES 2344 + 514, were measured in this work. Similar to the other four BL Lacs detected, their VHE spectrum and flux level is highly variable and shows a broadband spectrum characterized by two emission peaks: one in X-ray, the other at GeV to TeV energies. For one of these, 1ES 1959 + 650, simultaneous observations were carried out at other wavelengths and for the first time, a VHE flare without increased X-ray flux level was recorded. For the other object, 1ES 2344 + 514, no simultaneous X-ray observations were taken, making further modeling impossible. VHE gamma-ray astronomy can establish important upper limits on the density of the extragalactic background light (EBL). If one can somehow guess what the source spectrum is, then one can infer the EBL density from the measured attenuation in the spectra. As the VHE spectra of BL Lac object are very similar, the zeroth order assumption was made (and justified) in this work that they are actually the same; differences in attenuation arising solely due to the different distances to the objects. The upper limits derived here are not very constraining, but they do question one particular set of EBL measurements that are very high in the near infrared waveband. Galaxy formation models are typically not able to reproduce this high density. The analysis of VHE spectra is still being developed; in part because of the new array of four telescopes, VERITAS, being built at the moment. Monte-Carlo simulations are used in this work and changes in the simulation software had not seen a comparison to the previous version until this work. Differences were identified that impact the energy reconstruction. A method was developed to calibrate the absolute energy scale by automatically identifying cosmic-ray muons recorded by the telescope.
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Dickinson, Mark R. "Very high energy gamma ray observations of southern hemisphere blazars". Thesis, Durham University, 1997. http://etheses.dur.ac.uk/4705/.
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This thesis is concerned with very high energy γ-ray observations of blazars observable from the southern hemisphere. The data presented were obtained using the recently deployed University of Durham Mark 6 high sensitivity Čerenkov telescope. Chapters 1 and 2 are introductory; the subjects of γ-ray astronomy, extensive air showers, Čerenkov light production, the development of the atmospheric Čerenkov technique and the current status of TeV astronomy are discussed. Chapter 3 introduces the telescopes operated by the University of Durham. The Mark 6 telescope, designed to have a low threshold energy and a high resolution imaging system, is discussed in detail. Chapter 4 presents the calibration and analysis techniques routinely applied to data obtained with the Mark 6 telescope. The chapter concludes with a set of moment parameter selections designed to reject a significant fraction of the cosmic ray cascades, while retaining the majority of γ-rays cascades. These selections have resulted in a 5σ detection of PSR 1706-44. Chapter 5 discusses active galactic nuclei and in particular blazars. Topics included are recent high energy observations; the differences between the radio/X-ray selected BL Lacs and flat spectrum radio quasars; the infrared background; high energy flux variability and γ-ray production mechanisms within these objects. The chapter concludes with a list of possible very high energy γ-ray emitting blazars observable with the Mark 6 Čerenkov telescope. Chapter 6 presents the results from four of these very high-energy γ-ray blazar candidates; PKS 0548-322, PKS 1514-24, PKS 2005-489 and PKS 2155-304. There is no evidence for γ-ray emission from these sources, either in the form of a steady flux or variable activity. Three sigma integral flux upper limits above 300 GeV are produced for these objects and the implications of these observations are discussed. The conclusions are presented in Chapter 7 as well as ideas for future work.
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Mak, Wai-ying, i 麥偉瑩. "Very high energy gamma-ray emission from active galactic nuclei". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31221464.
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Mak, Wai-ying. "Very high energy gamma-ray emission from active galactic nuclei /". Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B20567492.
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Xiao, Dan. "Development and Investigation of High-Performance Fire Retardant Polypropylene Nanocomposites via High Energy Electrons". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-229650.
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Polypropylene (PP) has excellent mechanical and chemical properties. Thus, it is used in a wide range of applications. However, like for most polymers, the high flammability of PP limits its application in various fields requiring specific flame-retardant standards. Some of halogenated flame retardants are restricted by European Community directives ROHs, WEEE and REACH. Now metallic hydroxides flame retardants are widely used in industry, but the high loading (about 60 wt %) seriously destroys the mechanical properties of polymeric materials. To improve the performance of flame retardant polymers, an environment-friendly electron beam (EB) technology has been successfully used in modifying flame retardant and polymer matrix.
In this work, high efficient functional intumescent flame retardants and functional surfactant are designed and prepared for EB technology. In-depth studies the thermal stability, fire behavior and mechanical properties of these flame retardant PP composites have been studied. The possible graft-linking and cross-linking mechanisms of such EB modified composites can be well established. Specially, it is shown that the novel surfactant has better thermal stability in comparison to traditionally used modifiers.
Another part of this work deals with the exploration of novel allylamine polyphosphate (AAPP) as flame retardant crosslinker for PP by electron beam (EB) treatment. Multifunctional AAPP showed unique efficient intumescent flame retardant properties. The limiting oxygen index (LOI) value and the effective melt drop resistance in UL-94 test of multifunctional flame retardant PP composites is greatly enhanced. In the cone calorimeter test, a reduction of peak heat release rate, total heat release and smoke production is achieved. Moreover, EB treatment increased the thermal stability of these designed flame retardant PP composites. Furthermore, AAPP provided an excellent quality of char residue in the combustion stage due to P−N−C and P−O−C structure. In addition, synergistic mechanism of AAPP with montmorillonite (MMT) was explored.
Finally, different EB parameters have been used to modify fire retardant polymer nanocomposites. The effects of EB treatment on thermal stability, fire behavior and mechanical properties of fire retardant PP nanocomposites have been discussed. The heat release, the production of toxic gases and the mass loss of EB modified fire retardant PP nanocomposites are delayed in accordance to the result of cone calorimeter test. Based on these results high performance fire retardant polymer nanocomposites can be developed for industrial applications such as insulated material of wire, cable, etc.
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Robinson, D. "A study of high transverse momentum electrons produced in high energy proton-antiproton collisions". Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47230.
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Elgammal, Sherif. "Detection of high energy electrons in the CMS detector at the LHC". Doctoral thesis, Universite Libre de Bruxelles, 2009. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210208.
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Détection et identification de la réaction quark + anti-quark -> e+ + e- à l'aide du détecteur CMS (Compact Muon Solenoid) auprès du Grand Collisionneur de Hadrons du CERN, le LHC. Cette réaction permet de tester avec précision le Modèle Standard et de rechercher d'éventuelles nouvelles particules (Z') prédites par les théories de grande unification (GUT) et par les modèles à dimensions spatiales supplémentaires.Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Wolfe, Gregory John. "Effects of Large Doses of High Energy Electrons on a YBa2Cu3O6 + delta High Temperature Superconductors". Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/25879.
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Pallassini, Renato. "A study of very high energy γ-ray emission from blazars". Thesis, University of Leeds, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.441185.
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Cheesebrough, Alistair. "The search for very high energy γ-rays from misaligned AGN". Thesis, Durham University, 2013. http://etheses.dur.ac.uk/7717/.
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The aim of this work is to study the potential for emission at very high energies (100 GeV) by misaligned active galactic nuclei (AGN) and the future prospects for observations of these objects with the next generation imaging atmospheric Cherenkov telescope, the Cherenkov Telescope Array (CTA). Initially, data collected by the H.E.S.S. array was used to study fourteen Seyfert galaxies and two other AGN with Seyfert-like properties and no new detections were reported. For each object upper limits were calculated, assuming a similar spectral shape to M87. Further work focused on modelling the GeV spectra of misaligned AGN (AGN with angles of inclination to the line of sight 5◦ ) detected in 2010 with the Fermi Space Telescope. The modelling was carried out using a multiblob model that had previously been used to model the very high energy emission of M87 and Centaurus A. This work was used to investigate the capacity of the model to reproduce the high energy spectra observed for each object, while also allowing predictions of the potential very high energy fluxes to be produced. In each case the multiblob model was able to reproduce the observed GeV spectrum. The spectral energy distributions produced were then compared to predicted sensitivity curves for a number of possible CTA configurations to determine the likelihood of detection of these misaligned AGN with the array. It was found that detection of the objects within 50 hours of observations with CTA using standard Durham analysis is unlikely, but that 3C 111 may be detectable using the Paris analysis method.
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Kwok, Ping Wai. "Very high-energy gamma rays from the Crab nebula and pulsar". Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184863.
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This project is to search for Very High Energy (VHE) (10¹¹ eV to 10¹⁴ eV) gamma rays from the Crab nebula and pulsar using the atmospheric Cherenkov imaging technique. The technique uses an array of 37 photomultiplier tubes to record the images of the Cherenkov light pulses generated by energetic particles in the air showers initiated by VHE gamma rays or charged cosmic rays. Gamma-ray-like events are selected from numerous cosmic-ray events based on the predicted properties of the image, such as the size, shape, and orientation with respect to the axis of the detector. A steady weak flux of VHE gamma rays from the Crab is detected at high statistical significance (9 sigma), which is not usually achieved in VHE gamma-ray astronomy. No strong evidence of pulsed emission is found when the same data is folded at the Crab pulsar's radio ephemeris. The angular resolution of the technique cannot separate the emission coming from the nebula from that from the pulsar. Although it is generally believed that the unpulsed emission is coming from the nebula, there may be an unpulsed component coming at only a couple of light cylinder radii away from the pulsar too. Using the outer gap model of pulsar, the spectrum is derived and is found to be compatible with the observations.
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Fegan, Stephen. "A very high energy gamma-ray survey of unidentified EGRET sources". Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/280605.
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A survey of unidentified 100 MeV γ-ray sources is undertaken, with the Whipple 10m telescope, with the objective of detecting very high energy (>350 GeV) γ-ray emission. The survey consists of nineteen sets of observations of sources detected by the EGRET instrument on the Compton Gamma-Ray Observatory between 1991 and 1995. Results for 21 EGRET sources are reported; in some cases two EGRET sources are close enough to be viewed in a single observation. For each EGRET source, candidate associations are listed and the implications of each candidate for VHE emission discussed. Finally, a study of the performance of a next-generation ground based instrument, VERITAS, using simulations is presented. The implications of the increased sensitivity of such an instrument for suture gamma-ray surveys is briefly discussed.
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Hu, Hsiu-Lien. "Quantum transport of energetic electrons in ballistic nanostructures". Virtual Press, 2000. http://liblink.bsu.edu/uhtbin/catkey/1178341.
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The various electronic phenomena of electrons in the quasi-one-dimensional semiconducotor heterostructures have been largely investigated in the past research, due to its importance both on the theoretical understanding and the design of nanodevices. In particular, most research is currently based on the GaAs-AIGaAs material system with a 2-DEG interface. From the study of Hua Wu, following the Bohm's interpretation of quantum mechanics, energetic electrons approximately approach the classical behavior. The goal of this theoretical study is to investigate how the flow of energetic electrons may be controlled by the use of a tunable reflector. When encountering hard potential walls, energetic electrons in the nanostructure nearly follow the law of reflection. In addition, if the hard potential walls function as a reflector, the bouncing ball trajectory is also predicted. In this project, the fact that energetic electrons demonstrate semi-classical periodical flow motion is conceptually verified.The quantum wire (QW) with a tab and a notch nanostructure is selected as the practical model to achieve the project's goal. The resonant properties of the QW with a tab and the QW with a notch are individually investigated. The tight-binding recursive Green's function method is the theory underlying the numerical computation of the conductance in a nanodevice.Department of Physics and Astronomy
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Schlenker, Stefan. "Very high energy gamma rays from the binary pulsar PSR B1259-63". Doctoral thesis, [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=976502267.
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Rayner, Stephen Mark. "Very high energy gamma rays from isolated pulsars and non-pulsating objects". Thesis, Durham University, 1989. http://etheses.dur.ac.uk/6458/.
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This thesis is concerned with the detection of very high energy 7-rays from isolated pulsars and objects that are not known to emit pulsed radiation, using the atmospheric Cerenkov technique. The first chapter summarises the processes by which celestial 7-rays can be generated and absorbed. A discussion of the criteria for selecting objects for study is given. The second chapter describes the atmospheric Cerenkov technique and gives a brief outline of its historical development. Details of the design and operation of the current Durham university V.H.E. 7- ray telescopes are given. The third chapter describes the standard analysis techniques used to search for pulsed and unpulsed emission. The fourth chapter presents results of new observations of four isolated pulsars. Upper limits to the V.H.E. 7-ray flux are derived for each pulsar. A summary of the results is given and conclusions drawn regarding the consequences of the observations for the most popular pulsar model. The fifth chapter deals with new analysis techniques that have been developed to test data for the presence of a signal which is not necessarily periodic. A number of different approaches is described. The results of these techniques when applied to simulated data are presented and conclusions are drawn regarding the relative effectiveness of the tests. The sixth chapter applies the most successful test to data from three objects. Upper limits to the flux from Centaurus A and SN1987aare derived from our observations. Evidence for V.H.E. 7-ray emission from Scorpius X-1 is presented, together with evidence that this emission is modulated with the period of the binary orbit of this system. The final chapter summarises the preceding results and conclusions and indicates areas where current research may lead to substantial improvements in telescope design and analysis techniques.
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Chadwick, Mary Paula. "Very high energy cosmic gamma rays from radio and X-ray pulsars". Thesis, Durham University, 1987. http://etheses.dur.ac.uk/6720/.
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This thesis is concerned with the detection of very high energy cosmic gamma-rays from isolated pulsars and X-ray binary sources using the atmospheric Cerenkov technique. A general introduction to gamma ray detection techniques is followed by adscription of the properties of atmospheric Cerenkov radiation and a discussion of the principles of the atmospheric Cerenkov technique. The Mark I and Mark II gamma-ray telescopes operated in Dugway, Utah by the University of Durham between 1981 and 1984 are briefly described. There follows a discussion of the results from observations at many different wavelengths of Cygnus X-3. This object was observed by the Durham group between 1981 and 1983 in Dugway Utah and also in Durham during autumn 1985. The detection in the Dugway data of the 4.8 hr X-ray period and the possible detection of a19.2 day intensity variation are considered. The discovery of a 12.59 ms pulsar in data taken on Cygnus X-3 in 1983 is described. Evidence is presented which suggests this periodicity is also present at a weaker level in earlier data and also in the data taken in Durham in 1985.Results from observations of PSR1937+21 , PSR1953+29and six radio pulsars , are presented. The design and construction of the Mark III telescope, now operating in Narrabri , N.S.W. , is described in detail. Preliminary results from observations with the Mark III telescope of three objects, LMC X-4, the Vela pulsar and CentaurusX-3, are presented, with particular reference to periodicities inherent in the sources. An observation of the supernova in the Large Magellanic Cloud is discussed. A brief discussion of the mechanisms by which V.H.E. gamma-rays may be produced in isolated pulsars and X-ray binary pulsars is given, followed by a description of the future prospects for the Mark III and Mark IV telescopes.
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Vasileiou, Vlasios. "A search for bursts of very high energy gamma rays with milagro". College Park, Md.: University of Maryland, 2008. http://hdl.handle.net/1903/8570.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2008.Thesis research directed by: Dept. of Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Gajdus, Michael. "The Vela pulsar in very high energy gamma-rays with H.E.S.S. II". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17610.
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Die vorliegende Dissertation analysiert Beobachtungen des Vela-Pulsars mit dem H.E.S.S.-Observatorium und präsentiert damit den ersten Nachweis gepulster Strahlung mit H.E.S.S. Die signifikante Detektion (11.4 s) oberhalb einer bis jetzt unerreichten Energieschwelle von lediglich 15 GeV wurde mittels von 24 h Beobachtungsdaten erzielt, die mit dem im Jahr 2012 in Betrieb genommenen CT5-Teleskop aufgezeichnet wurden. Nach dem Krebs-Pulsar ist damit der Vela-Pulsar der zweite Pulsar, von dem sehr hochenergetische Gammastrahlung nachgewiesen wurde. Die Spektren von Pulsaren im Bereich der sehr hochenergetischen Gammastrahlung sind von besonderem Interesse, da sie Einblicke in einen bisher fast komplett unerforschten Energiebereich erlauben. Der experimentelle Nachweis stellt eine besondere Herausforderung dar, da die Rate der Gammastrahlen gemäß einem Potenzgesetz mit der Energie abfällt und die resultierenden Zählraten klein sind. Daher werden neue gewichtete Testgrößen eingeführt, um die Sensitivität für den Nachweis schwacher Pulsationen für zukünftige Beobachtungen von Pulsaren zu verbessern. Die Testgrößen sind Erweiterungen von bereits existierenden ungewichteten Verfahren und anwendbar auf beliebige diskrete Daten, in denen ein Puls oder mehrere Pulse erwartet werden. Sie sind leistungsfähig für den Fall unbekannter Phasenprofile und erzielen bei Standardgewichtung eine 10 %-ige Steigerung der Detektionssignifikanz. Die optimierte Analysekette wurde zur Detektion des Vela-Pulsars im Energiebereich von 15 GeV bis 125 GeV eingesetzt. Der phasengemittelte integrierte Energiefluss beträgt 4.29_(-1.02)^(+1.14)_stat _(-3.31)^(+5.50)_sys × 10^(-11) erg cm^(-2) s^(-1) und wird durch einen einzelnen Puls verursacht. Das Profil des Pulses kann durch eine asymmetrischen Lorentz-Funktion mit einer schmaleren abfallenden Flanke beschrieben werden. Der Photonfluß fällt gemäß einem Potenzgesetz mit Index -5.39 mit der Energie ab. Dies ist in guter Übereinstimmung mit einem theoretischen Annular-Gap-Emissionsmodell.The analysis of the first pulsar to be detected with the H.E.S.S. array is presented. The high significance detection at the 11.4 s level down to a hitherto unachievable 15 GeV energy threshold is a result of 24 h of observations of the Vela pulsar with the new CT5 telescope introduced into the array in 2012. This is only the second pulsar to be detected in the very high energy (VHE) ?-ray regime. Of particular interest are the VHE spectra of pulsars as this is an almost completely unexplored energy domain. This does however entail smaller signals as the rate of ?-rays generally drops according to a power law function. New weighted statistical tests are introduced to improve the sensitivity to weak pulsations for use with future observations of pulsars. These tests are modifications of currently used tests and are applicable to any discrete data in which a single or many pulses are expected; they are powerful when the phase profile is unknown and with a basic weighting provide up to a 10 % boost in detection significance. An optimised analysis chain contributed to the detection of the Vela pulsar with phase averaged energy flux in the energy range (15,125) GeV of 4.29_(-1.02)^(+1.14)_stat _(-3.31)^(+5.50)_sys × 10^(-11) erg cm^(-2) s^(-1). The single pulse is characterised with an asymmetric Lorentzian function with a narrower trailing edge. The photon flux falls as a power law with index -5.39 which is moderately consistent with an Angular Gap emission model but represents a steeper drop in emission than that measured with the Fermi-LAT. The emission efficiency of the Vela pulsar in the VHE band is evaluated as 0.0025 %, which is comparable to that of the Crab pulsar in the same energy regime measured with the MAGIC telescope array. Comparisons to other candidate VHE pulsars are also drawn. A weak constraint is placed on the energy at which Lorentz invariance violation occurs in terms of the Planck energy as E_LIV>10^(-4) E_P.
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Wagner, Robert M. "Very High Blazar Astrophysics : Measurement of Very High Energy Gamma-Ray Emission from Four Blazars Using the MAGIC Telescope and a Comparative Blazar Study /". Fischbachtal, Odenw : HARLAND media, 2007. http://deposit.d-nb.de/cgi-bin/dokserv?id=3001678&prov=M&dok_var=1&dok_ext=htm.
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Hoffmann, Agnes Irene Dorothee. "Analysis of hard X-ray emission from selected very high energy g-ray". Reutlingen, Bruno-Matzke-Str.15 A. Hoffmann, 2009. http://d-nb.info/999640429/34.
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Noyes, David Carl. "A search for short duration very high energy emission from gamma-ray bursts". College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2910.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2005.Thesis research directed by: Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Hayashida, Masaaki. "Observation of Very-High-Energy Gamma-Rays from Blazars with the MAGIC Telescope". Diss., lmu, 2008. http://nbn-resolving.de/urn:nbn:de:bvb:19-82911.
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Hinman, Roderick Thornton. "Recovered energy logic--a logic family and power supply featuring very high efficiency". Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/12015.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1994.Includes bibliographical references (p. 215-220).
by Roderick Thornton Hinman.
Ph.D.
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Tsirou, Michelle. "Study of Pulsar Wind Nebulae in Very-High-Energy gamma-rays with H.E.S.S". Thesis, Montpellier, 2019. http://www.theses.fr/2019MONTS096.
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Pulsar wind nebulae consist of magnetised clouds of positrons and electrons accelerated to very high energies through the action of a central pulsar, often embedded within a host supernova remnant. They are the largest population of firmly identified sources of TeV gamma-rays within the Galaxy and are thought to be contributors to the leptonic Galactic cosmic-ray spectrum,and thus viable source candidates in the quest to interpret the origin of the cosmic-ray positron fraction excess. Their very-high-energy gamma-ray emission is of particular interest for spectral models, as their dominant radiation process is inverse Compton scattering on target photons present in interstellar radiation fields such as the visible, near and far infrared ambient photons in addition to the Cosmic Microwave Background.In this thesis dissertation I present the scope of my research work, which lies on pulsar wind nebula morphology and understanding their very-high-energy radiation.I report the latest morphological and spectral studies of the pulsar wind nebula within the MSH 15-52 composite supernova remnant through High Energy Stereoscopic System (H.E.S.S.) observations.In this phenomenological study I have conducted a fit of the very-high-energy emission morphology beyond ~ 0.3 TeV detected in HESS-I data using a template X-ray synchrotron map in the 4–7 keV band based on archival Chandra observations. In the model of the emission, the gamma-ray emission produced by inverse Compton scattering is thought to ensue from the same leptonic population responsible for the observed synchrotron emission, and thus the X-ray template represents the spatial distribution of these electrons and positrons, convolved with the spatial dependence of the magnetic field. Our best-fit results yield an additional extended TeV component located on the south-eastern region of the nebula, centered at ∼4 pc from the position of the associated pulsar PSR B1509-58, with an intrinsic radius of ∼7′(or 9 pc). We also detect a significant steepening in the spectral shape of the total emission from the pulsar wind nebula, occurring above∼10 TeV. This coincides with a shrinking of the emission observed in the sky map, as revealed by our energy-dependent morphological analyses. Several scenarii are presented so as to explain our morphological and spectral results concerning the emission originating from MSH 15-52. Based on the Galactic radiation field characteristics derived from published models, the gamma-ray emission is well described by leptons scattering on the far infrared and cosmic microwave backgrounds, respectively at lower and higher energies than the detected spectral steepening energy, which suggests an interpretation of the energy dependence as a consequence of Klein-Nishina effects in the cross-section.During the last year of my thesis I have worked with collaborators on a study of drivers behind the observed significant offsets of TeV-emitting pulsar wind nebulae with respect to their pulsar. We performed relativistic (magneto)-hydrodynamical numerical simulations and tested physical setups in one-dimensional studies and are pursuing an ongoing two-dimensional investigation to quantify the effect of the pulsar proper motion in comparison to ambient medium density gradients so as to derive constrains on these physical factors leading to asymmetrical evolution in pulsar wind nebulaePulsar wind nebulae consist of magnetised clouds of positrons and electrons accelerated to very high energies through the action of a central pulsar, often embedded within a host supernova remnant. They are the largest population of firmly identified sources of TeV gamma-rays within the Galaxy and are thought to be contributors to the leptonic Galactic cosmic-ray spectrum,and thus viable source candidates in the quest to interpret the origin of the cosmic-ray positron fraction excess. Their very-high-energy gamma-ray emission is of particular interest for spectral models, as their dominant radiation process is inverse Compton scattering on target photons present in interstellar radiation fields such as the visible, near and far infrared ambient photons in addition to the Cosmic Microwave Background.In this thesis dissertation I present the scope of my research work, which lies on pulsar wind nebula morphology and understanding their very-high-energy radiation.I report the latest morphological and spectral studies of the pulsar wind nebula within the MSH 15-52 composite supernova remnant through High Energy Stereoscopic System (H.E.S.S.) observations.In this phenomenological study I have conducted a fit of the very-high-energy emission morphology beyond ~ 0.3 TeV detected in HESS-I data using a template X-ray synchrotron map in the 4–7 keV band based on archival Chandra observations. In the model of the emission, the gamma-ray emission produced by inverse Compton scattering is thought to ensue from the same leptonic population responsible for the observed synchrotron emission, and thus the X-ray template represents the spatial distribution of these electrons and positrons, convolved with the spatial dependence of the magnetic field. Our best-fit results yield an additional extended TeV component located on the south-eastern region of the nebula, centered at ∼4 pc from the position of the associated pulsar PSR B1509-58, with an intrinsic radius of ∼7′(or 9 pc). We also detect a significant steepening in the spectral shape of the total emission from the pulsar wind nebula, occurring above∼10 TeV. This coincides with a shrinking of the emission observed in the sky map, as revealed by our energy-dependent morphological analyses. Several scenarii are presented so as to explain our morphological and spectral results concerning the emission originating from MSH 15-52. Based on the Galactic radiation field characteristics derived from published models, the gamma-ray emission is well described by leptons scattering on the far infrared and cosmic microwave backgrounds, respectively at lower and higher energies than the detected spectral steepening energy, which suggests an interpretation of the energy dependence as a consequence of Klein-Nishina effects in the cross-section.During the last year of my thesis I have worked with collaborators on a study of drivers behind the observed significant offsets of TeV-emitting pulsar wind nebulae with respect to their pulsar. We performed relativistic (magneto)-hydrodynamical numerical simulations and tested physical setups in one-dimensional studies and are pursuing an ongoing two-dimensional investigation to quantify the effect of the pulsar proper motion in comparison to ambient medium density gradients so as to derive constrains on these physical factors leading to asymmetrical evolution in pulsar wind nebulae
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Theiling, Mark. "Observations of very high energy gamma ray emission from supernova remnants with VERITAS". Connect to this title online, 2009. http://etd.lib.clemson.edu/documents/1263397351/.
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Chandril, Sandeep. "In situ structural and compositional analysis using RHEED electrons induced x-rays". Morgantown, W. Va. : [West Virginia University Libraries], 2009. http://hdl.handle.net/10450/10641.
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Thesis (Ph. D.)--West Virginia University, 2009.Title from document title page. Document formatted into pages; contains ix, 97 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 95-97).
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Clark, Michelle Susan. "Improving the feasibility of energy disaggregation in very high- and low-rate sampling scenarios". Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/54873.
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Given the world's urgent need to reduce greenhouse gas emissions in order to avoid the most disastrous effects of climate change, efforts must be made to reduce these emissions in every way possible. A large share of these emissions come from the energy consumption in buildings and there are significant opportunities to reduce this consumption through energy saving measures. Energy disaggregation or non-intrusive load monitoring (NILM) is a useful tool that infers the energy consumption of individual appliances or equipment within a building from detailed measurements of the building's total energy consumption. This method is very attractive for providing a detailed breakdown of building energy consumption because it is less expensive and more convenient than measuring the energy use of each appliance individually. A wide variety of NILM methods have been proposed and in this thesis we focus on improving the feasibility of two different classes of NILM methods. We first explore the use of random filtering and random demodulation, two methods closely related to the new and developing field of compressed sensing (CS), to acquire and manage very-high-rate electrical measurements used for NILM. We show that these methods allow us to reduce the required sampling rate and volume of data collected while retaining valuable signal information required for NILM. Second, we switch to the analysis of very-low-rate data for NILM and develop a method to detect interesting patterns in the very-low-rate aggregate consumption signal. These patterns are shown to be responsible for a significant share of the total energy consumption in some buildings and are also related to the outdoor air temperature in some cases. Taken together, the two parts of this thesis allow us to contribute to the field of NILM by improving its feasibility and helping to facilitate its widespread use.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
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Bartko, Hendrik. "Observation of Galactic Sources of Very High Energy Gamma-Rays with the MAGIC Telescope". Diss., Lichtenberg (Odw.) : Harland Media, 2007. http://deposit.d-nb.de/cgi-bin/dokserv?id=3001679&prov=M&dok_var=1&dok_ext=htm.
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Keogh, Dominic Robert. "The search for pulsar wind nebulae in the very high energy gamma-ray regime". Thesis, Durham University, 2010. http://etheses.dur.ac.uk/776/.
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The aim of this Thesis is to study the development of pulsar wind nebulae in the TeV regime and in doing so uncover more sources which have as yet not been observed at these wavelengths. It is found that the extent of pulsar wind nebula in the TeV gamma-ray increases with its age while no developmental relationship is seen concerning the luminosity or spectral index of the nebulae when observed in the TeV gamma-ray regime due to uncertainties in the measurements available. TeV gamma-ray upper limits are calculated for several nebulae observed in the X-ray regime allowing the strength of their magnetic fields to be constrained but only one new source, which was previously confused with its companion, was discovered, the Eel Nebula. Predictions of the fluxes of many of the sources for which upper limits are derived in this work have been calculated from observations of their emission in X-rays and some of these sources should be uncovered with the next generation CTA instrument.
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MacRae, John Hamish Kenneth. "The detection of very high energy cosmic gamma rays using the atmospheric Cerenkov technique". Thesis, Durham University, 1985. http://etheses.dur.ac.uk/7854/.
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This thesis is concerned with the detection of very high energy cosmic gamma rays using the atmospheric Cerenkov technique. A general introduction to gamma ray detection techniques is followed by a detailed discussion of the principles of the atmospheric Cerenkov technique and the history of its use prior to this work. The design and operation of the University of Durham facility in Dugway, Utah is described in depth. Monte Carlo computer simulations have been developed to assist in both the understanding of the equipment and the analysis of the results for the Durham facility. The variation of the response of the array with zenith angle and detector threshold has been investigated and the aperture function of a single telescope calculated. The latter has been found to be a complicated function of both zenith angle and detector threshold. Computer simulations have also been developed to aid in the design of a camera to record two-dimensional Cerenkov light images from small extensive air showers, and to provide a means of testing analysis routines; these are discussed. The camera is located at the F.L. Whipple Observatory in Arizona. The techniques employed in the analysis of data recorded by the Dugway facility are discussed, and a computer package developed to aid in the routine aspects of the analysis is described. Results of observations from two sources, Cygnus X-3 and PSR0531, are presented, with particular reference to periodicities inherent in the sources and to bursts of gamma ray emission. The discussion of the results includes a review of the various models which have been proposed for Cygnus X-3.
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Carraminana, Alberto. "Very high energy gamma ray astronomy and non pulsating low mass X-ray binaries". Thesis, Durham University, 1991. http://etheses.dur.ac.uk/6241/.
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This thesis is concerned with non pulsating Low Mass X-Ray Binaries as Very High Energy γ-ray sources, in particular Scorpius X-1; the brightest of these objects in X-rays, and the most likely to be detectable at energies above 250 GeV. After a first introductory chapter, experimental techniques presently used in Very High Energy γ-ray Astronomy are reviewed. In the third chapter statistical techniques used to quantify count rate excesses and orbital modulations are described and applied to data from Scorpius X-1. Data taken in 1988 and 1989 showing a 3cr count excess, reported previously elsewhere, are found to show orbital modulation at the 3% statistical level. The analysis of data taken on 1990 shows no signal. Periodicity tests, in particular the Rayleigh test, are also described. The principles of a segmented fast algorithm for period searches in Cerenkov data using memory limited, but relatively fast, micro-computers are shown in the fourth chapter. Various of these machines can be used simultaneously in order to achieve a large efficiency. A method to perform various trials per independent frequency is also presented. The results of period searches in data from three selected objects (Scorpius X-1, GX 5-1 and Supernova 1987A) are presented. No periodicity is found at significant level in these data. The complete power spectrum of four segments of data from Cygnus X-3 showing a signal near to 12.59 ms are also shown. The final chapter considers theoretical models developed previously for more massive systems accounting for the different physical scenario of these low mass systems. The process of pair production between high energy photons and the radiation field of the accretion disc appears as the tightest constraint on how close to the neutron star high energy photons can be produced.
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Tomarchio, Salvatore Gaspare. "Power Switching Converters with very low power consumption and high efficiency for energy savings". Doctoral thesis, Università di Catania, 2013. http://hdl.handle.net/10761/1311.
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The objective of this research is the analysis of power switching converters with targets of very low power consumption and high efficiency for being used in new system for energy savings.
Typically, they are implemented as Switching Mode Power Supply (SMPS) modules in different type of applications in both consumer and energy businesses .
In particular have been considered power supply systems with output power in the class of low and medium power, in the range from few watts up to hundreds watts.
Referring to consumer business, the main fields of application are lighting and home appliances where in the last years the international Agencies and Governments have been focused their attention to ask for reducing the continuous energy waste.
Therefore, more restricted and challenging constraints have been fixed in order to reduce the energy waste and to improve the level of performances of new products, that pushed the introduction of new technologies and new design solutions.
In particular in the lighting applications the improvement in LED technologies is leading to the development of LED lamps with higher light efficiency and lower power consumption.
The analysis will start making a overview of the principal topologies of switching converters used to drive the LED bulbs. Advantages and disadvantages will be shown for each topology. Then the flyback topology will be analyzed and discussed in more details, since it is considered the most promising one. Finally, an alternative schematic will be proposed in order to increase the electrical performance of the whole power conversion system.
On the other side in the home appliance applications there are conditions where the energy is consumed by the device when this does not work or does not perform its main functions and that happens without the final user realizing it. One condition is when the device is put in standby status.
For this case the analysis of the commonly used techniques for reducing power consumption in the switching converter is discussed and a new technique for reducing power during the inactivity state of the appliance system is proposed.
The proposed solution works on the feedback network, introducing a perturbation on the feedback signal: in this way the main power transistor, in the converter, is switched off and the output voltage of the converter is settled to zero. This solution allows an important reduction of the effective power consumption of the system.
In order to confirm this solution an auxiliary SMPS with output power of 5 W to supply the user interface of a washing machine has been designed, and the converter topology used is a Flyback converter, compliant with the current regulations of the home appliance applications.
In addition a prototype is realized and then simulations in PSpice, thermal and electrical measurements are performed in order to verify the operations of the converter in different environmental and electrical conditions.
Looking at the business of energy conversion, in the design of applications of high power systems an important issue is to provide low voltages, in the range of tens of Volt, tapping from high voltage input line, which is usually in the range between hundreds of Volt to kilovolt, by means of switching power supplies. Low voltages are needed to supply the logic control circuits and the power semiconductors driving the applications. The supply system has to deal, consequently, with both wide input voltage range and electrical insulation. The evaluation of the operative conditions of a driving system for IGCT devices, used in a transmission system application with wide input voltage range, is described. The design of a 100 W supply converter is shown considering all the issues related with the series connection of power devices and the needs of insulation.
Converter design, modelling and experimental results are shown together with the evaluation of the efficiency of the proposed solution.
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Ergin, Tülün. "The energy spectrum of very high energy gamma rays from the Crab Nebula as measured by the H.E.S.S. array". [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=979099897.
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Ergin, Tülün. "The energy spectrum of very high energy gamma rays from the Crab Nebula as measured by the H.E.S.S. array". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2006. http://dx.doi.org/10.18452/15435.
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Das Thema dieser Arbeit ist die fuer das HEGRA Experiment entwickelte Rekonstruktions-Algoritmen, die Geometry und Energie von hochenergetischen kosmischen Gamma-Strahlen zu rekonstruieren, in die H.E.S.S. software Umgebung zu implementieren und das nicht-gepulste Energie-Spektrum des Krebsnebels zwischen Energien von 300 GeV und 20 TeV zu bestimmen. Dafuer wurden die ersten stereoskopischen Daten von Oktober und November 2003 mit einer 3 Teleskope-Konfiguration des H.E.S.S. Systems der Phase-I verwendet. Die Phase-I des H.E.S.S. Systems wurde im Dezember 2003 fertiggestellt, nachdem das vierte Teleskop in Betrieb genommen wurde. Die Rekonstruktionsalgorithmen wurden mit Monte Carlo Simulationen fuer die vollstaendige Phase-I des Teleskop-Systems getestet. Die Aufloesung fuer die rekonstruierte Richtung und Energie der einzelnen gamma-Ereignisse sind 0.15 Grad und 14 Prozent bei 45 Grad Zenitwinkel. Die Daten des Krebsnebels, die eine Wobble-Versetzung von +-0.5 Grad and +-1.0 Grad haben und die im Zenitwinkel-Bereich von 45 Grad bis 50 Grad fuer 4 Stunden beobachtet wurden, geben ein Signal von 50 Standardabweichungen. Das differentielle Energiespektrum des Krebsnebels zwischen 450 GeV und 20 TeV nach den Schnitten ist (dN / dE) = (3.37+-0.47)*10^{-11}*E^{-2.59+-0.12} cm^{-2} s^{-1} TeV^{-1}. Der integrierte Fluss oberhalb 1 TeV ist (2.11+-0.29)*10^{-11} cm^{-2} s^{-1}. Diese Resultate sind konsistent mit Messungen anderer Experimente, speziell von HEGRA und Whipple. Die Resultate stimmen mit den Erwartungen der synchroton self-Compton Modelle fuer den TeV Emissionbereich ueberein. Das magnetische Feld in der Region, wo die TeV gamma-Strahlen vermutlich entstehen, wird zu 0.18+-0.01 mG bestimmt. Die Resultate dieser Arbeit zeigen die Leistungsfaehigkeit des H.E.S.S. Teleskop-Systems.The goal of this thesis is to implement the methods developed for the HEGRA experiment to reconstruct the geometry and energy of the air-showers induced by the cosmic high-energy gamma rays into the software environment of the H.E.S.S. experiment. Furthermore, using the implemented algorithms, a search for the unpulsed emission is aimed in the energy range between 300 GeV and 20 TeV from the Crab Nebula using the first stereoscopic data taken during October and November 2003 with the 3 telescope configuration of the H.E.S.S. array in Phase-I. The Phase-I of the H.E.S.S. array was completed in December 2003 by the addition of the fourth telescope. By testing the reconstruction algorithms of a complete Phase-I H.E.S.S. array with Monte Carlo simulations, it is found that the resolution of the reconstructed direction and energy of a gamma-ray event from a zenith angle of 45 degrees is around 0.15 degrees and 14 percent, respectively. The data on the Crab Nebula including runs with wobble offset of +-0.5 degrees and +-1.0 degrees is collected at zenith angles from 45 degrees to 50 degrees for a total of 4 hours and gives a background subtracted signal of about 50 standard deviations. The differential energy spectrum of the unpulsed gamma-ray emission from the Crab Nebula is found to be (dN / dE) = (3.37+-0.47)*10^{-11}*E^{-2.59+-0.12} cm^{-2} s^{-1} TeV^{-1} between 450 GeV and 20 TeV after all cuts. The integral flux above 1 TeV is (2.11+-0.29)*10^{-11} cm^{-2} s^{-1}. These results are consistent with the results published by other experiments, in particular HEGRA and Whipple. The results agree well with the expectation from synchrotron self-Compton models for TeV emission range. The magnetic field in the region, where TeV gamma rays are produced, is found to be 0.18+-0.01 mG. This result agrees with the magnetic field values deduced by the models. The results obtained for the Crab Nebula in this thesis demonstrate the performance of the H.E.S.S. array.
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Ernst, Darin R. (Darin Richard) 1965. "Momentum transport, radial electric field, and ion thermal energy confinement in very high temperature plasmas". Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50337.
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Krygier, Andrew. "On The Origin of Super-Hot Electrons in Intense Laser-Plasma Interactions". The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1365724528.
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Zackrisson, Björn. "Biological effects of high energy radiation and ultra high dose rates". Doctoral thesis, Umeå universitet, Onkologisk radiobiologi, 1991. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-96889.
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Recently a powerful electron accelerator, 50 MeV race-track microtron, has been taken into clinical use. This gives the opportunity to treat patients with higher x-ray and electron energies than before. Furthermore, treatments can be performed were the entire fractional dose can be delivered in parts of a second. The relative biological effectiveness (RBE) of high energy photons (up to 50 MV) was studied in vitro and in vivo. Oxygen enhancement ratio (OER) of 50 MV photons and RBE of 50 MeV electrons were investigated in vitro. Single-fraction experiments, in vitro, using V-79 Chinese hamster fibroblasts showed an RBE for 50 MV x-rays of approximately 1.1 at surviving fraction 0.01, with reference to the response to 4 MV x- rays. No significant difference in OER could be demonstrated. Fractionation experiments were carried out to establish the RBE at the clinically relevant dose level, 2 Gy. The RBE calculated for the 2 Gy/fraction experiments was 1.17. The RBEs for 20 MV x-rays and 50 MeV electrons were equal to one. In order to investigate the validity of these results, the jejunal crypt microcolony assay in mice was used to determine the RBE of 50 MV x-rays. The RBE for 50 MV x-rays in this case was estimated to be 1.06 at crypt surviving fraction 0.1. Photonuclear processes are proposed as one possible explanation to the higher RBE for 50 MV x-rays. Several studies of biological response to ionizing radiation of high absorbed dose rates have been performed, often with conflicting results. With the aim of investigating whether a difference in effect between irradiation at high dose rates and at conventional dose rates could be verified, pulsed 50 MeV electrons from a clinical accelerator were used for experiments with ultra high dose rates (mean dose rate: 3.8 x 10^ Gy/s) in comparison to conventional (mean dose rate: 9.6 x 10"^ Gy/s). V-79 cells were irradiated in vitro under both oxic and anoxic conditions. No significant difference in relative biological effectiveness (RBE) or oxygen enhancement ratio (OER) was observed for ultra high dose rates compared to conventional dose rates. A central issue in clinical radiobiological research is the prediction of responses to different radiation qualities. The choice of cell survival and dose response model greatly influences the results. In this context the relationship between theory and model is emphasized. Generally, the interpretations of experimental data are dependent on the model. Cell survival models are systematized with respect to their relations to radiobiological theories of cell kill. The growing knowledge of biological, physical, and chemical mechanisms is reflected in the formulation of new models. This study shows that recent modelling has been more oriented towards the stochastic fluctuations connected to radiation energy deposition. This implies that the traditional cell survival models ought to be complemented by models of stochastic energy deposition processes at the intracellular level.S. 1-44: sammanfattning, s. 47-130: 5 uppsatser
digitalisering@umu
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Brown, Anthony Murray. "Very high energy emission and multi-wavelength campaigns of the BL Lac object PKS 2155-304". Thesis, Durham University, 2006. http://etheses.dur.ac.uk/919/.
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This thesis is concerned with multi-wavelength observations of the prominent southern hemisphere high energy BL Lac object, (HBL), PKS 2155-304. After a general introduction covering the particulars of Active Galactic Nuclei, the pysical processes and models that are believed to play an important role in the observations and ground based γ-ray astronomy, the results and interpretation of four individual multi-wavelength campaigns on PKS 2155-304 are presented. Lead by observations of the High Energy Stereoscopic System (H.E.S.S.), these campaigns include observations with RXTE, NTT at ESO, ROTSE, Spitzer, JCMT and the NRT. During all these campaigns, the source appeared to be in a quiescent state, allowing us to probe the jet paramaters and emission models for a quiescent HBL for the first time. The models for VHE emission from HBLs have evolved over the last 14 years since Mkn 421 was detected as a VHE emitter. However, the sensitivity of the past generations of VHE telescopes has only been sufficient to observe VHE emission from HBLs during apparent active states. These evolved models are therefore essentially high active state emission models. Since the sensitivity of H.E.S.S. now allows us to detect these objects in a quiescent state , the obvious question is, do the 'active state' models still accurately predict the SED and in particular the VHE emission?
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Seglar-Arroyo, Monica. "Studying the origin of cosmic-rays : Multi-messenger studies with very-high-energy gamma-ray instruments". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS260.
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Les phénomènes explosifs qui se produisent dans l'Univers à haute énergie sont capables d'accélérer les particules jusqu'aux énergies les plus élevées. Ces processus produisent des particules secondaires de nature différente, c'est-à-dire des photons et des neutrinos. Dans des cas particuliers, ces événements induisent des perturbations sur l'espace-temps, c'est-à-dire des ondes gravitationnelles détectables par des interféromètres sur Terre. La combinaison des informations complémentaires fournies par ces messagers cosmiques peuvent permettre de répondre à des questions ouvertes en astrophysique. Parmi les événements les plus violents qui produisent de tels signaux figurent la fusion des deux objets les plus denses, comme les étoiles à neutrons et les trous noirs ou l'activité accréatrice dans les galaxies sur un trou noir supermassif. Dans ce travail, nous nous concentrons sur les photons à très haute énergie que produisent ces événements extrêmes, et sur la connexion avec les autres contreparties, afin de fournir une image globale multi-messagers qui permet l'étude des mécanismes physiques en place. Les défis inhérents à l'astronomie multi-messager dans le domaine temporel, ce qui implique un effort mondial coordonné et simultané entre les installations et les disciplines astronomiques, sont discutés et abordés. Une nouvelle stratégie d'observation optimisée du suivi de l'eau souterraine pour les petits et moyens instruments de FoV comme le H.E.S.S. et le futur CTA, capable d'apporter une réponse rapide aux alertes, qui prend en compte les risques caractéristiques de l'événement GW et maximise les chances de détecter la contrepartie électromagnétique, sera présentée. Cette stratégie s'est avérée fructueuse lors d'observations de suivi avec les télescopes H.E.S.S., et en particulier dans le cas de la première detection de la fusion d'une binaire d'étoiles à neutrons, GW170817. Dans le cadre du réseau AMON, une analyse multi-messagers qui combine des événements d'ondes gravitationnelles avec des données HAWC a été développée dans le but d'identifier les coïncidences astrophysiques à partir d'événements indépendants. De plus, la découverte par H.E.S.S. en très hautes énergies du noyau galactique actif OT 081, lors d'un état de flux élevé en juillet 2016, sera présentéeThe explosive phenomena occurring in the high-energy Universe are able to accelerate particles up to the highest energies. These processes produce secondary particles of different nature, i.e. photons and neutrinos. In special cases, these events induce perturbations on the space-time, i.e. gravitational waves detectable by interferometers on Earth. The combination and the complementary information provided by these cosmic messengers may allow to answer open questions in astrophysics, as the origin of cosmic rays. Amongst the most violent events producing such signals are the merge of the two densest objects, as neutron stars and black holes or the accretion activity in galaxies onto a supermassive black hole. In this work, we focus on the very-high energy photons that these extreme events produce, and the connection with the other counterparts, in order to provide a broad multi-messenger picture which enables the study of the physical mechanisms in place. The challenges inherent to time-domain multi-messenger astronomy are discussed and tackled, which involves simultaneous coordinated worldwide effort across facilities and astronomical disciplines. A novel, optimized GW follow-up observation strategy for small/mid- FoV instruments as H.E.S.S. and the future CTA, able to perform a rapid response to alerts, which considers the characteristics of the GW event and maximizes the chances to detect the electromagnetic counterpart will be presented. This strategy was proven successful in follow-up observations with the H.E.S.S. telescopes and in particular in the case of the first ever detected binary neutron star merger, GW170817. In the context of the AMON network, a multi-messenger analysis that combines gravitational wave events with HAWC data, with the aim to identify astrophysical coincidences out of independent events, has been developed. In addition, the discovery by H.E.S.S. in very-high energies of the active galactic nucleus OT 081, during a flaring episode in July 2016, will be presented
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Collins, William James. "A measurement of the forward-backward asymmetry of e'+e'- -> Z'0 -> bb using electrons at OPAL". Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309334.
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