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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
181

High energy emissions for astrophysical objects

Szabo, Anthony Paul. January 1992 (has links) (PDF)
Bibliography : leaves 1-6 of 2nd sequence
182

<i>NO</i><i>x</i> Production by Ionisation Processes in Air

Rahman, Mahbubur January 2005 (has links)
<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>
183

On the heliospheric diffusion tensor and its effect on 26-day recurrent cosmic-ray variations / N.E. Engelbrecht

Engelbrecht, Nicholas Eugéne January 2008 (has links)
Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2008.
184

Parametric Model for Astrophysical Proton-Proton Interactions and Applications

Karlsson, Niklas January 2007 (has links)
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
185

Atmospheric and Interstellar Cosmic Rays Measured With the CAPRICE98 Experiment

Mocchiutti, Emiliano January 2003 (has links)
No description available.
186

Studies of cosmic rays with the anticoincidence system of the PAMELA satellite experiment

Orsi, Silvio January 2007 (has links)
PAMELA is a satellite-borne experiment designed to study the charged component of the cosmic radiation of galactic, solar and trapped nature. The main scientific objective is the study of the antimatter component of cosmic rays over a wide range of energies (antiprotons: 80 MeV–190 GeV, positrons: 50 MeV–270 GeV). PAMELA is also searching for antinuclei with a precision ~10^−7 in anti-He/He measurements. PAMELA is mounted on the Resurs DK1 satellite that was launched on June 15th 2006 from the Baikonur cosmodrome and is now on a semipolar (69.9°) elliptical (350 × 600 km) orbit. The experiment has been acquiring data since July 11th 2006 and has a foreseen lifetime of at least 3 years. The PAMELA apparatus consists of a permanent magnet silicon spectrometer, an electromagnetic imaging calorimeter, a time of flight system, a scintillator-based anticoincidence (AC) system, a tail catcher scintillator and a neutron detector. The AC system can be used to reject particles not cleanly entering the PAMELA acceptance. Tests of the PAMELA instrument in its final flight configuration involved long duration acquisition runs with cosmic particles (mainly muons) on ground. A study of the functionality of the AC system during these runs is presented here with a set of selected muons. Studies of activity in the AC detectors as function of the rigidity of the muons and in correlation with the activity in the spectrometer and in the calorimeter are presented. A study of the AC system functionality during in-flight operations provides a map of the particle flux in orbit, and shows the anisotropy in the arrival direction of trapped particles in the Van Allen radiation belts. The singles rates indicate that the AC system saturates in the South Atlantic anomaly (SAA). Information from the AC system in the SAA is therefore not reliable for physics analysis. The timing and multiplicity of AC activity correlated to particle triggers has been studied. A dependence on orbital position was observed. An LED (Light Emitting Diode) based monitoring system was designed to determine the in-orbit behaviour of the AC system independently of the radiation environment and to compare it to the pre-launch behaviour. The LED system shows that the properties of the AC system are stable during flight and that no significant changes in performance occurred as a result of the launch. / QC 20100811
187

Gamma-Ray Emission from Galaxy Clusters : DARK MATTER AND COSMIC-RAYS

Pinzke, Anders January 2010 (has links)
The quest for the first detection of a galaxy cluster in the high energy gamma-ray regime is ongoing, and even though clusters are observed in several other wave-bands, there is still no firm detection in gamma-rays. To complement the observational efforts we estimate the gamma-ray contributions from both annihilating dark matter and cosmic-ray (CR) proton as well as CR electron induced emission. Using high-resolution simulations of galaxy clusters, we find a universal concave shaped CR proton spectrum independent of the simulated galaxy cluster. Specifically, the gamma-ray spectra from decaying neutral pions, which are produced by CR protons, dominate the cluster emission. Furthermore, based on our derived flux and luminosity functions, we identify the galaxy clusters with the brightest galaxy clusters in gamma-rays. While this emission is challenging to detect using the Fermi satellite, major observations with Cherenkov telescopes in the near future may put important constraints on the CR physics in clusters. To extend these predictions, we use a dark matter model that fits the recent electron and positron data from Fermi, PAMELA, and H.E.S.S. with remarkable precision, and make predictions about the expected gamma-ray flux from nearby clusters. In order to remain consistent with the EGRET upper limit on the gamma-ray emission from Virgo, we constrain the minimum mass of substructures for cold dark matter halos. In addition, we find comparable levels of gamma-ray emission from CR interactions and dark matter annihilations without Sommerfeld enhancement. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted.
188

Development of Cosmic Ray Simulation Program -- Earth Cosmic Ray Shower (ECRS)

Hakmana Witharana, Sampath S 04 May 2007 (has links)
ECRS is a program for the detailed simulation of extensive air shower initiated by high energy cosmic ray particles. In this dissertation work, a Geant4 based ECRS simulation was designed and developed to study secondary cosmic ray particle showers in the full range of Earth's atmosphere. A proper atmospheric air density and geomagnetic field are implemented in order to correctly simulate the charged particles interactions in the Earth's atmosphere. The initial simulation was done for the Atlanta (33.460 N , 84.250 W) region. Four different types of primary proton energies (109, 1010, 1011 and 1012 eV) were considered to determine the secondary particle distribution at the Earth's surface. The geomagnetic field and atmospheric air density have considerable effects on the muon particle distribution at the Earth's surface. The muon charge ratio at the Earth's surface was studied with ECRS simulation for two different geomagnetic locations: Atlanta, Georgia, USA and Lynn Lake, Manitoba, Canada. The simulation results are shown in excellent agreement with the data from NMSU-WIZARD/CAPRICE and BESS experiments at Lynn Lake. At low momentum, ground level muon charge ratios show latitude dependent geomagnetic effects for both Atlanta and Lynn Lake from the simulation. The simulated charge ratio is 1.20 ± 0.05 (without geomagnetic field), 1.12 ± 0.05 (with geomagnetic field) for Atlanta and 1.22 ± 0.04 (with geomagnetic field) for Lynn Lake. These types of studies are very important for analyzing secondary cosmic ray muon flux distribution at the Earth's surface and can be used to study the atmospheric neutrino oscillations.
189

Atmospheric and Interstellar Cosmic Rays Measured With the CAPRICE98 Experiment

Mocchiutti, Emiliano January 2003 (has links)
No description available.
190

Study of the inclusive cross sections in P-P collisions and their application to interstellar cosmic-ray calculation /

Tan, Lun-chang. January 1983 (has links)
Thesis--Ph. D., University of Hong Kong, 1983.

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