Cette thèse de cosmologie est consacrée à l'étude de l'empreinte de l'énergie noire sur la formation des structures de l'Univers. Je défini et introduit les régions cosmiques compensées comme l'environnement à grande échelle autour des extrema locaux dans le champ de densité. Dans le cas d'un minimum central, cette région peut être identifiée aux vides cosmiques usuels. A l'aide de simulations numériques, je montre que ces régions présentent des propriétés de formes particulières et qu'elles dépendent de la cosmologie. Je montre que la forme moyenne de ces profils de densité ainsi que leur propriétés statistiques peuvent être calculée analytiquement dans l'Univers primordial. En utilisant une dynamique appropriée, je montre qu'il est possible de suivre précisément l'évolution non linéaire de ces structures. Il devient alors possible de reconstruire les profils de matières observés aujourd'hui à partir les profils théoriques primordiaux évolués selon une dynamique appropriée. J’exhibe une propriété fondamentale de ces régions qui maintient constant une taille particulière, le rayon de compensation. Autour de ce point, l'évolution non linéaire du champ de matière peut être suivie analytiquement. En étudiant l'effondrement gravitationnel dans des théories étendues de gravité, je montre qu'il est possible de contraindre efficacement la nature de la gravité et de la cosmologie à partir de l'étude de certaines propriétés spécifiques à ces régions. Ce travail permet à la fois de donner une origine aux profils de matière sur les très grandes échelles cosmiques mais aussi de définir de nouvelles sondes cosmologiques pour tester la nature de notre Univers. / This thesis is devoted to the study of the imprints of dark energy on the formation of the large scale structures in the Universe. I define the spherically compensated cosmic regions as the large-scale environment around local extrema in the density field. For central minimum, this region can be identified with standard cosmic voids. Using numerical simulations, I show that these regions, once properly identified, can be used efficiently to distinguish competitive cosmological models. I show that the average shape of these density profiles and their statistical properties can be analytically computed in the primordial Universe. Using an appropriate dynamical formalism, I show that it is possible to follow the nonlinear evolution of these structures until today. This allows to reconstruct the shape of such large scale regions from first principles. I exhibit a fundamental property of these regions which maintains constant a particular size : the compensation radius. Around this radius, the nonlinear evolution of the matter field can be analytically derived. By studying the gravitational collapse in gravity models beyond General Relativity, I show that it is possible to constrain efficiently both cosmology and the nature of gravity. Beside giving a physically motivated model for both shape and statistical properties of such large scale matter profile, this work also define new cosmological probes that could be used to test the nature of our Universe.

This work aims to contribute to the study of the origins of cosmic rays, and broadly, to the advancement of both data analysis methods and instrumentation for very-high-energy γ-ray astronomy. First, reviewing the state of γ-ray astronomy, we show how gains in sensitivity can be achieved through sophisticated data analyses and improved instrumental designs. We then develop such an improved analysis method for the Very Energetic Radiation Imaging Telescope Array System (VERITAS) by combining Image Template Method (ITM) with Boosted Decision Trees (BDT), and study its performance, attaining a 30-50% improvement in integral sensitivity over the instrument’s standard analysis. Systematic issues in spectral reconstruction that the analysis displays are resolved satisfactorily by imposing a more stringent condition on the selection of its energy threshold. We employ the newly developed analysis to measure the γ-ray energy spectrum of the starburst galaxy M82, and combining our result with a measurement from the Fermi Large Area Telescope (Fermi-LAT), we find that a single power law fits the spectrum well between 100 GeV and 10 TeV, with no evidence for a spectral break or a cutoff. We conclude that this is in line with the current understanding that M82 is not a good proton calorimeter. Finally, we detail the design, implementation, and performance of the optical alignment system of the prototypeSchwarzschild-Couder Telescope (pSCT) for the Cherenkov Telescope Array (CTA), a novel two-mirror design that addresses many shortcomings of current instruments.

Interstellar dust plays an important role in the physics of the interstellar medium, as well as the formation and evolution of stars. The presence of dust is often indicated in optical images by dark lanes which bisect spiral galaxies, or seen directly as reflection nebulosity around stars or emission nebulosity if sufficient heating is present. Of interest in this thesis is the dust that is associated with bipolar outflow sources. Bipolar outflows can occur in either evolved stars or in young stellar objects, and are so named because they consist of two lobes which are thought to be due to out-flowing dust and gas, with a dark lane between them due to thick dust in a circumstellar disk or shell which often blocks the light from the central star. The spatial distribution of the properties of dust around bipolar outflow sources has been examined using a combination of theoretical and observational techniques. To aid the interpretation of observations of bipolar outflow sources, we have modelled the wavelength dependence of light from 0.36 to 22\um, scattered by dust particles with varying characteristics. The results were then presented in the form of colour excess ratios. These model ratios can be applied to observations if the contribution due to the central star is able to be removed, such that all that remains in the image is the effect of the dust particles. The scattering of light by dust particles was modelled by varying six different characteristics: grain material, size (particle radius from 0.002 to 0.75\um), mantle temperatures and thicknesses, shape, and orientation. Of those characteristics, the largest variation in the colour excess ratios resulted from varying grain composition and size. Different scattering angles also produce a noticeable variation in the colour excess ratios, however the effect is difficult to distinguish from the general extinction due to dust around the source. Water ice mantles were also found to significantly change the colour excess ratios. Grain shape and orientation produced only small variations in the colour excess ratios. Three bipolar outflow sources were studied as part of this thesis, two evolved objects, OH~231.8+4.2 and Mz\,3, and the young T-Tauri object Rno\,91. The observations involved multi-wavelength imaging in the infrared, from which colours and colour excess ratios were obtained at various points of the bipolar outflows and then compared to the predictions made in the modelling. The most extensive data set analysed was seven images of the object OH~231.8+4.2 which were used in a multi-wavelength study in the infrared H to N bands (1.25--12\um). The central source position of the object has been confined to less than an arcsec using the longer wavelength images and an L--M colour image. The two peaks which dominate the lobes in the shorter wavelength images were found to be scattering peaks where the light from the central source is scattered from the walls of the lobes. The spatial distribution of water ice in the nebula has also been constrained to the circumstellar disk which has a torus or disk shape rather than being a spherical shell. The colour excess ratios derived for the nebula from the images also suggest slightly different dust properties between the circumstellar disk, lobe walls and within the lobe cavities. The young T-Tauri star Rno\,91 also contains ice, and was observed between J and L. The central star which illuminates the nebula was shown to be coincident with the brightest point in these images. Using colour excess ratio results for various parts of the nebula, it was shown that the dust close to the central star is likely to contain larger grains than the diffuse ISM, but with a similar composition. Moving away from the central star, the dust becomes more like that observed in the diffuse ISM. The presence of water ice on dust close to the central star was confirmed using images centred in the ice band. The protoplanetary bipolar outflow source Mz\,3 is slightly more evolved than OH 231.8+4.2, and does not have evidence of any water ice in the circumstellar disk. Images of this object were obtained between J and 10\um. The presence of warm dust throughout the inner bipolar lobes of this object is noticeable by the brightness of the lobes in the image at 10\um. Line profiles through the position of the central source of the 10\um\ image demonstrate that there is a circumstellar shell close to the central source which has an inner radius of $\lta\,375$\,AU. Colour excess ratio results for the bipolar lobes suggest that the dust associated with Mz\,3 is generally smaller than that found in the diffuse ISM. The properties of the dust in the bipolar lobes were also observed to be different to the dust closer to the central source and lying in the circumstellar disk. The small sizes for dust in Mz\,3 is consistent with the high velocity outflows that have been associated with the object.

Bibliography: p. 157-167. / ii, 180 p. : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Presents results of searches made with the Buckland Park and SUGAR data sets for Ultra High Energy gamma-ray emission from certain astrophysical objects. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1994

Bibliography : leaves 1-6 of 2nd sequence

<p>Nuclear particles hitting the silicon in a electronic device can cause a change in the data in a memory bit cell or in a flip-flop. The device is still working, but the data is corrupted and this is called a soft error. A soft error caused by a single nuclear particle is called a single event upset and is a growing problem. Research is ongoing at Saab aiming at how susceptible random access memories are to protons and neutrons.</p><p>This thesis describes the development of equipment for measuring cosmic-ray effects on DRAM in laboratories. The system is built on existing hardware with a FPGA as the core unit. A short history of soft errors is also given and what causes it. How a DRAM works and basic operation is explained and the difference between a SRAM. The result is a working system ready to be used.</p>

<p>The study presented in this thesis was motivated by the large uncertainty on the concentration of atmospheric electrical discharges to the global nitrogen budget. This uncertainty is partly due to the fact that information concerning the <i>NO</i><i>x</i> production efficiency of electrical discharges having current signatures similar to those of lightning flashes is not available in the literature. Another reason for this uncertainty is the fact that energy is used as a figure of merit in evaluating <i>NO</i><i>x</i> production from lightning flashes even though insufficient knowledge is available concerning the energy dissipation in lightning flashes. The third reason for this uncertainty is the lack of knowledge concerning the contribution of discharge processes other than return strokes to the <i>NO</i><i>x</i> production in the atmosphere. Lightning is not the only process in the atmosphere that causes ionisation and dissociation of atmospheric air. Cosmic rays continuously bombard the Earth with high energetic particles and radiation causing ionization and dissociation of air leading to the production of <i>NO</i><i>x</i> in the atmosphere. The work carried out in this thesis is an attempt to improve the current knowledge on the way in which these processes contribute to the global <i>NO</i><i>x</i> production. Experiments have been conducted in this thesis to estimate the <i>NO</i><i>x</i> production efficiency of streamer discharges, laser-induced plasma, laboratory sparks having current signatures similar to those of lightning flashes, alpha particle impact in air and finally with the lightning flash itself. The results obtained from laboratory electrical discharges show the following: (a) The <i>NO</i><i>x</i> production efficiency, in terms of energy, of positive streamer discharges is more or less similar to those of hot discharges. (b) The <i>NO</i><i>x</i> production efficiency of an electrical discharge depends not only on the energy but also on the peak and the shape of the current waveform. (c) The current signature is a better figure of merit in evaluating the <i>NO</i><i>x</i> yield of electrical discharges. As a part of this thesis work a direct measurement of <i>NO</i><i>x</i> generated by lightning flashes was conducted and the results show that slow discharge processes such as continuing currents could be the main source of <i>NO</i><i>x</i> in lightning flashes. Concerning <i>NO</i><i>x</i> production by other ionisation processes such as alpha particle impacts in the atmosphere, the data gathered in this thesis show that each ionising event in air leads to the creation of one <i>NO</i><i>x</i> molecule. In terms of energy the <i>NO</i><i>x</i> production efficiency of alpha particles is similar to that of electrical discharges. The theoretical studies conducted within this thesis indicate that M-components contribute more than the return strokes to the <i>NO</i><i>x</i> production. The calculations also show that the contribution to the global <i>NO</i><i>x</i> budget by return stroke is not as high as that assumed in the current literature.</p>

Our Solar system contains a large amount of dust, containing valuable information about our close cosmic environment. If created in a planet's system, the particles stay predominantly in its vicinity and can form extended dust envelopes, tori or rings around them. A fascinating example of these complexes are Saturnian rings containing a wide range of particles sizes from house-size objects in the main rings up to micron-sized grains constituting the E ring. Other example are ring systems in general, containing a large fraction of dust or also the putative dust-tori surrounding the planet Mars. The dynamical life'' of such circumplanetary dust populations is the main subject of our study. In this thesis a general model of creation, dynamics and death'' of circumplanetary dust is developed. Endogenic and exogenic processes creating dust at atmosphereless bodies are presented. Then, we describe the main forces influencing the particle dynamics and study dynamical responses induced by stochastic fluctuations. In order to estimate the properties of steady-state population of considered dust complex, the grain mean lifetime as a result of a balance of dust creation, life'' and loss mechanisms is determined. The latter strongly depends on the surrounding environment, the particle properties and its dynamical history. The presented model can be readily applied to study any circumplanetary dust complex. As an example we study dynamics of two dust populations in the Solar system. First we explore the dynamics of particles, ejected from Martian moon Deimos by impacts of micrometeoroids, which should form a putative tori along the orbit of the moon. The long-term influence of indirect component of radiation pressure, the Poynting-Robertson drag gives rise in significant change of torus geometry. Furthermore, the action of radiation pressure on rotating non-spherical dust particles results in stochastic dispersion of initially confined ensemble of particles, which causes decrease of particle number densities and corresponding optical depth of the torus. Second, we investigate the dust dynamics in the vicinity of Saturnian moon Enceladus. During three flybys of the Cassini spacecraft with Enceladus, the on-board dust detector registered a micron-sized dust population around the moon. Surprisingly, the peak of the measured impact rate occurred 1 minute before the closest approach of the spacecraft to the moon. This asymmetry of the measured rate can be associated with locally enhanced dust production near Enceladus south pole. Other Cassini instruments also detected evidence of geophysical activity in the south polar region of the moon: high surface temperature and extended plumes of gas and dust leaving the surface. Comparison of our results with this in situ measurements reveals that the south polar ejecta may provide the dominant source of particles sustaining the Saturn's E ring. / In unserem Sonnensystem befindet sich eine große Menge an Staub, der viele Informationen über unseren Kosmos enthält. Wird der Staub im System um den Planeten gebildet, bleibt er vorwiegend in dessen Nähe und bildet Staubhüllen, -tori oder -ringe um ihn. Ein faszinierendes Beispiel eines solchen Komplexes sind die Saturnringe, in denen von mikrometergroßen Partikeln bis zu hausgroßen Körpern alle Partikelgrößen vertreten sind. Weitere Beispiele sind Ringsysteme im Allgemeinen, sowie der vermutete Staubring um Mars. Das dynamische Verhalten einer solchen Staubpopulation ist Hauptthema dieser Dissertation. In dieser Arbeit wurde ein allgemeines Modell zur Erzeugung, Dynamik und Vernichtung von planetarem Staub entwickelt. Endogene und exogene Mechanismen zur Produktion von Staub an atmosphärenlosen Körpern werden vorgestellt. Desweiteren werden die wichtigsten Kräfte welche die Teilchendynamik beeinflussen, sowie die Auswirkung von stochastischen Fluktuationen untersucht. Die Lebenszeiten der Staubkörner als Bilanz zwischen Staubproduktion und -vernichtung werden bestimmt, um den stationären Zustand der Staubkonfiguration abzuschätzen. Die Lebenszeit des Staubes hängt stark von den Eigenschaften der Umgebung und der Teilchen sowie von deren dynamischer Vergangenheit ab. Das vorgestellte Modell kann auf alle planetaren Systeme angewandt werden. Als Beispiel wurden zwei Staubpopulationen in unserem Sonnensystem studiert. Zuerst wurde die Dynamik des Staubes untersucht, welcher durch Mikrometeorideneinschläge auf dem Marsmond Deimos produziert wird und die vermuteten Marstori erzeugt. Der Poynting-Robertson-Effekt, als indirekter Einfluss des Strahlungsdruckes, bewirkt eine signifikante Langzeitänderung der Torusgeometrie. Desweiteren verursacht der Strahlungsdruck eine stochastische Dispersion des nichtsphärischen Staubteilchenensembles, was eine Verringerung der Teilchenzahldichten beziehungsweise der entsprechenden optischen Tiefen im Torus bewirkt. Weiterhin wurde die Staubdynamik in der Umgebung des Saturnmondes Enceladus untersucht. Während des Vorbeifluges der Raumsonde Cassini registrierte der Staubdetektor eine Staubpopulation von mikrometergroßen Teilchen um den Mond. Überraschenderweise wurde die maximal registrierte Staubrate eine Minute vor der größten Annäherung an den Mond gemessen. Diese Asymmetrie der Messung kann, wie in dieser Arbeit demonstriert, mit einer lokalen Staubquelle am Südpol des Mondes erklärt werden. Andere Instrumente der Cassini - Sonde belegen die geophysikalische Aktivität der Südpolregion des Mondes in Form einer erhöhten Oberflächentemperatur und Fontänen von Gas und Staub an der Südpolumgebung. Der Vergleich der numerischen Simulationen mit den in - situ - Messungen zeigt, dass die Südpolquelle die voraussichtlich wichtigste Quelle von E-Ringteilchen ist.

Observations of gamma-rays have been made from celestial sources such as active galaxies, gamma-ray bursts and supernova remnants as well as the Galactic ridge. The study of gamma rays can provide information about production mechanisms and cosmic-ray acceleration. In the high-energy regime, one of the dominant mechanisms for gamma-ray production is the decay of neutral pions produced in interactions of ultra-relativistic cosmic-ray nuclei and interstellar matter. Presented here is a parametric model for calculations of inclusive cross sections and transverse momentum distributions for secondary particles - gamma rays, elecrons, positrons, electron neutrinos, electron antineutrinos, muon neutrinos and muon antineutrinos - produced in proton-proton interactions. This parametric model is derived on the proton-proton interaction model proposed by Kamae et al.; it includes the diffraction dissociation process, Feynman-scaling violation and the logarithmically rising inelastic proton-proton cross section. To improve fidelity to experimental data for lower energies, two baryon resonance excitation processes were added; one representing the Delta(1232) and the other multiple resonances with masses around 1600 MeV/c^2. The model predicts the power-law spectral index for all secondary particles to be about 0.05 lower in absolute value than that of the incident proton and their inclusive cross sections to be larger than those predicted by previous models based on the Feynman-scaling hypothesis. The applications of the presented model in astrophysics are plentiful. It has been implemented into the Galprop code to calculate the contribution due to pion decays in the Galactic plane. The model has also been used to estimate the cosmic-ray flux in the Large Magellanic Cloud based on HI, CO and gamma-ray observations. The transverse momentum distributions enable calculations when the proton distribution is anisotropic. It is shown that the gamma-ray spectrum and flux due to a pencil beam of protons varies drastically with viewing angle. A fanned proton jet with a Gaussian intensity profile impinging on surrounding material is given as a more realistic example. As the observer is moved off the jet axis, the peak of the spectrum is moved to lower energies. / QC 20100803

Cosmic reionization was most likely initiated by star forming dwarf galaxies. Little is known about the physical mechanisms allowing ionizing Lyman continuum (LyC) photons to escape from galaxies, but to learn more we can study local galaxies in detail. Until now, there has however only been one claim of a local LyC leaking galaxy, the disputed case of Haro 11. The lack of local detections could in part be a combined effect of technical problems and search strategies. Re-examining the FUSE (Far Ultraviolet Spectroscopic Explorer) data of Haro 11 led us to develop a new model for the spectral reduction, by which we could confirm an escape fraction of LyC photons (fesc) of 3.3±0.7%. In addition, eight more galaxies from the FUSE archive were examined leading to a new detection, Tol 1247-232, with fesc = 2.4±0.5%. The low value derived from the stacked spectrum of the whole sample, fesc = 1.4±0.4%, could be an indication of an evolving fesc scenario and/or an effect of probing the wrong targets. Local LyC candidates are normally selected among starburst galaxies with high equivalent widths in Hα. This can however give preference to ionization bounded H II regions with low escape fractions. In an attempt to overcome this selection bias, we developed a novel method to select LyC leaking galaxies. The selection is based on a blue continuum and weak emission lines, properties that in combination can be explained only by models with very high fesc. Using these criteria, we selected a sample of leaking candidates at z≈0.03 to be observed in Hα and Johnson B filters. The sample galaxies have properties that strongly favour leakage. Among these are clear signs of mergers and interaction with neighbouring galaxies, off-centre major star forming regions and spectral properties indicating previous starburst activity. The Lyman-alpha (Lyα) line is often used as a tracer for the distant galaxies believed to have reionized the universe. Here, for the first time local face-on spiral galaxies are studied in Lyα imaging. All three galaxies are emitting Lyα photons in the polar direction far out in the spiral arms, in clear contrast to previously studied irregular galaxies where strong emission is seen from the nuclei. If the small sample studied here is representative, it will have implications for detecting Lyα galaxies at high redshifts as it would depend strongly on the viewing angle.