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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.
1

Studies of dark matter in and around stars

Sivertsson, Sofia January 2012 (has links)
There is by now compelling evidence that most of the matter in the Universe is in the form of dark matter, a form of matter quite different from the matter we experience in every day life. The gravitational effects of this dark matter have been observed in many different ways but its true nature is still unknown. In most models, dark matter particles can annihilate with each other into standard model particles; the direct or indirect observation of such annihilation products could give important clues for the dark matter puzzle. For signals from dark matter annihilations to be detectable, typically high dark matter densities are required. Massive objects, such as stars, can increase the local dark matter density both via scattering off nucleons and by pulling in dark matter gravitationally as a star forms. Annihilations within this kind of dark matter population gravitationally bound to a star, like the Sun, give rise to a gamma ray flux. For a star which has a planetary system, dark matter can become gravitationally bound also through gravitational interactions with the planets. The interplay between the different dark matter populations in the solar system is analyzed, shedding new light on dark matter annihilations inside celestial bodies and improving the predicted experimental reach. Dark matter annihilations inside a star would also deposit energy in the star which, if abundant enough, could alter the stellar evolution. This is investigated for the very first stars in the Universe. Finally, there is a possibility for abundant small scale dark matter overdensities to have formed in the early Universe. Prospects of detecting gamma rays from such minihalos, which have survived until the present day, are discussed. / Kosmologiska observationer har visat att större delen av materian i universum består av mörk materia, en form av materia med helt andra egenskaper än den vi upplever i vardagslivet. Effekterna av denna mörka materia har observerats gravitationellt på många olika sätt men vad den egentligen består av är fortfarande okänt. I de flesta modeller kan mörk materia-partiklar annihilera med varandra till standardmodellpartiklar. Att direkt eller indirekt observera sådana annihilationsprodukter kan ge viktiga ledtrådar om vad den mörka materian består av. För att kunna detektera sådana signaler fordras typiskt höga densiteter av mörk materia. Stjärnor kan lokalt öka densiteten av mörk materia, både via spridning mot atomkärnor i stjärnan och genom den ökande gravitationskraften i samband med att en stjärna föds. Annihilationer inom en sådan mörk materia-population gravitationellt bunden till en stjärna, till exempel solen, ger upphov till ett flöde av gammastrålning, som beräknas. För en stjärna som har ett planetsystem kan mörk materia även bli infångad genom gravitationell växelverkan med planeterna. Samspelet mellan de två mörk materia-populationerna i solsystemet analyseras, vilket ger nya insikter om mörk materia-annihilationer inuti himlakroppar och förbättrar de experimentella möjligheterna att detektera dem. Mörk materia-annihilationer inuti en stjärna utgör också en extra energikälla för stjärnan, vilket kan påverka stjärnans utveckling om mörk materia-densiteten blir tillräckligt stor. Denna effekt undersöks för de allra första stjärnorna i universum. Slutligen finns det också en möjlighet att det i det tidiga universum skapades mörk materia-ansamlingar som fortfarande finns kvar idag. Utsikterna att upptäcka dessa genom mätning av gammastrålning diskuteras. / QC 20120130
2

Low energy solar neutrino analysis of the salt phase of the Sudbury neutrino observatory

Kos, Mark Szymon 02 January 2008 (has links)
The neutrino fluxes from the neutral current (NC), charged current (CC), and elastic scattering (ES) neutrino interactions in the salt phase of SNO have been extracted. The signals were extracted above an energy threshold of 4MeV, which is the lowest energy threshold at which the neutrino signals have been extracted from SNO to date. To achieve this low energy threshold the internal and external radioactive background signals have also been measured. The $^{8}$B neutrino fluxes for the 4MeV threshold were found to be \begin{eqnarray*} \Phi_{CC} & = & 1.60 ~^{+0.04}_{-0.04}~(\mbox{stat}) ~^{+0.06}_{-0.06}~(\mbox{syst}) \times 10^6 \mbox{cm}^{-2} \mbox{sec}^{-1},\\ \Phi_{NC} & = & 4.84 ~^{+0.16}_{-0.16}~(\mbox{stat}) ~^{+0.29}_{-0.32}~(\mbox{syst}) \times 10^6 \mbox{cm}^{-2} \mbox{sec}^{-1},\\ \Phi_{ES} & = & 2.75 ~^{+0.23}_{-0.23}~(\mbox{stat}) ~^{+0.25}_{-0.26}~(\mbox{syst}) \times 10^6 \mbox{cm}^{-2} \mbox{sec}^{-1}. \end{eqnarray*} \noindent These results are in agreement with the values published in ~\cite{SNO3} and the NC flux is in agreement with the standard solar model calculation from ~\cite{bp2004}. The published fluxes were \begin{eqnarray*} \Phi_{CC} &= & 1.68 ~^{+0.06}_{-0.06}~(\mbox{stat}) ~^{+0.08}_{-0.09}~(\mbox{syst}) \times 10^6 \mbox{cm}^{-2} \mbox{sec}^{-1} , \\ \Phi_{NC} &= & 4.94 ~^{+0.21}_{-0.21}~(\mbox{stat}) ~^{+0.38}_{-0.34}~(\mbox{syst}) \times 10^6 \mbox{cm}^{-2} \mbox{sec}^{-1}, \\ \Phi_{ES} &= & 2.35 ~^{+0.22}_{-0.22}~(\mbox{stat}) ~^{+0.15}_{-0.15}~(\mbox{syst}) \times 10^6 \mbox{cm}^{-2} \mbox{sec}^{-1}. \end{eqnarray*} \noindent The uncertainties on the extracted NC and CC fluxes are significantly smaller than on the published values. A comparison of the total uncertainty from flux measurements presented here and those published are given below. \begin{table}[htp] \begin{center} \begin{tabular}{|c|c|c|} \hline & uncertainties presented here (\%) & uncertainties from ~\cite{SNO3} (\%) \\ \hline $\Phi_{CC}$ & $~^{+4.6}_{-4.4}$ & $~^{+5.9}_{-6.4}$ \\ \hline $\Phi_{NC}$ & $~^{+6.8}_{-7.4}$ & $~^{+8.9}_{-8.2}$ \\ \hline $\Phi_{ES}$ & $~^{+12.3}_{-12.6}$ & $~^{+11.3}_{-11.3}$ \\ \hline \end{tabular} \label{funcert1} \end{center} \end{table} The shape of the CC energy spectrum has also been extracted with the 4MeV energy threshold. The uncertainties on the extracted fluxes are smaller than what was previously published. The CC spectrum gives a measure of the neutrino energy shape distortion due to neutrino oscillations. The uncertainties on the lowest energy bins in the extracted CC spectrum are much larger than the predicted distortion. We are therefore not sensitive to the upturn in the neutrino survival probability at lower energies predicted by neutrino oscillations in the large mixing angle (LMA) region. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2007-12-19 13:58:16.601
3

Particle Astrophysics at the Galactic Center

Todd, Elizabeth January 2011 (has links)
The presence of turbulence in astrophysical magnetic fields can have a significant effect on the diffusion of particles and, therefore, should be taken into account when performing simulations involving particle propagation. After reviewing the constructionof the turbulent magnetic field component, we incorporate this feature in two separate projects. In the first, we consider the possible source(s) of hadronic cosmic rays thought to be responsible for the diffuse TeV gamma-ray emission in the vicinity ofthe Galactic center. Assuming a completely turbulent magnetic field with an average strength of 10-100microG, we find that relativistic protons do not travel far enough to produce gamma-rays spatially correlated with the giant molecular clouds, as seen by HESS,when injected into the interstellar medium by a single point source, such as the supermassive black hole Sagittarius A*. Increasing the number of point sources to five does improve the longitudinal extent of the emission but either shows only weak correlation with the molecular gas or highlights the source positions - both pictures areinconsistent with HESS observations. We conclude that protons must be accelerated throughout the Galactic center region via e.g. a second-order Fermi process in order to reproduce the HESS gamma-ray map if the magnetic field there is completely turbulent. Secondly, we examine the possible link between the asymmetric 511keV electron-positron annihilation emission from the inner Galactic disk and hard low mass X-ray binaries (LMXBs). Three different magnetic field configurations were considered: a completely turbulent field, a field in which the turbulent component has equal energy density as the mean component, and a strongly ordered field with little turbulence. Assuming the environment around each LMXB system is the same, we find that the LMXBs alone cannot account for all the positrons necessary to sufficiently fill the region regardless of the particular magnetic field structure chosen. Another transport mechanism (e.g. a galactic wind) in addition to the diffusive motion caused by the magnetic field fluctuations and/or allowing the LMXBs to be embedded in different phases of the interstellar medium is needed for the LMXB picture to remain a viable possibility.
4

PERFORMANCE EVALUATION OF SIGNAL CONDITIONING BOARDS AND SIMULATION OF THE IMPACT OF ELECTRONICS NOISE ON THE DEAP-3600 DARK MATTER DETECTOR

Chouinard, Rhys Timon Unknown Date
No description available.
5

Development and Performance of Detectors for the Cryogenic Dark Matter Search Experiment with an Increased Sensitivity Based on a Maximum Likelihood Analysis of Beta Contamination

Driscoll, Donald D., Jr. 14 January 2004 (has links)
No description available.
6

THE LUX DARK MATTER EXPERIMENT: DETECTOR PERFORMANCE AND ENERGY CALIBRATION

Phelps, Patrick 02 September 2014 (has links)
No description available.
7

Search for high energy GRB neutrinos in IceCube

Casey, James David 21 September 2015 (has links)
The IceCube Neutrino Observatory has reported the observation of 35 neutrino events above 30 TeV with evidence for an astrophysical neutrino flux using data collected from May 2010 to May 2013. These events provide the first high-energy astrophysical neutrino flux ever observed. The sources of these events are currently unknown. IceCube has looked for correlations between these events and a list of TeV photon sources including a catalog of 36 galactic sources and 42 extragalactic sources, correlations with the galactic plane and center, and spatial and temporal clustering. These searches have shown no significant correlations. The isotropic distribution of the event directions gives indications that the events could be extragalactic in nature and therefore may originate in the same processes that generate ultra-high-energy cosmic rays (UHECRs). The sources of these UHECRs are still unknown; however, gamma-ray bursts (GRBs) have been proposed as one possible source class. By determining the source of these high-energy neutrinos, it may be possible to determine the sources of UHECRs as well. This study is a search for directional and temporal correlation between 856 GRBs and the astrophysical neutrino flux observed by IceCube. Nearly 10,000 expanding time windows centered on the earliest reported time of the burst were examined. The time windows start at ±10 s and extend to ±15 days. We find no evidence of correlations for these time windows and set an upper limit on the fraction of the astrophysical flux that can be attributed to the observed GRBs as a function of the time window. GRBs can contribute at most 12% of the astrophysical neutrino flux if the neutrino-GRB correlation time is less than ≈20 hours, and no more than 38% of the astrophysical neutrino flux can be attributed to the known GRBs at time scales up to 15 days. We conclude that GRBs observable by satellites are not solely responsible for IceCube’s astrophysical neutrino flux, even if very long correlation time scales are assumed.
8

LUX Thermosyphon Cryogenics and Radon-Related Backgrounds for the First WIMP Result

Bradley, Adam Wade 11 June 2014 (has links)
No description available.
9

Implementação de uma sequência de ensino e aprendizagem sobre tópicos de astrofísica de partículas para o ensino médio / Implementation of a teaching and learning sequence for particle astrophysics topics in High School

Correa, Roger Willians 05 February 2015 (has links)
Este trabalho tem como objetivo investigar a implementação de uma sequência de ensino e aprendizagem sobre tópicos de Astrofísica de Partículas para o Ensino Médio. Buscou-se determinar o ponto de impacto e a direção de chegada de um raio cósmico primário ao solo, utilizando dados do Observatório Pierre Auger. A fim de identificar elementos relevantes dessa sequência, analisamos a maneira como os estudantes interagiram e realizamos refinamentos progressivos a fim de aperfeiçoá-la. No refinamento da sequência de ensino, a análise dos dados obtidos desempenhou um importante papel, já que indicou os caminhos a serem tomados para que a atividade desenvolvida fizesse parte do repertório de conhecimentos do aluno. Esperou-se que esse conhecimento, longe de ser mecânico e passageiro, fosse significativo ao aluno no sentido de que os conteúdos tratados se entrelaçassem a conhecimentos prévios e se transformassem em conhecimento mais estáveis e ricos em significados. Por este viés, a Teoria da Aprendizagem Significativa de Ausubel norteou a escolha do método de avaliação e interpretação dos dados coletados neste estudo. Assim, de acordo com o referencial teórico adotado, os mapas conceituais apresentaram-se como forma de análise e serviram de avaliação do conhecimento obtido pelos estudantes e, por conseguinte, da sequência didática proposta. Conforme indicou a análise dos mapas conceituais, a maior parte das informações relacionadas com a dinâmica de determinação do ponto de impacto e da direção de chegada de um raio cósmico primário começou a ter significado na estrutura de conhecimentos dos alunos. Assim, o conteúdo raios cósmicos mostrou-se possível de ser ensinado na sala de aula do Ensino Médio. / This paper aims at investigating the implementation of a teaching and learning sequence for particle Astrophysics topics in High School. Our aim is to determine the impact point and direction of a primary cosmic ray to the ground, using the Pierre Auger Observatory data. To identify the relevant elements of this sequence, we analyzed the way in which students interacted and then implemented progressive refinements to improve it. The data analysis played an important role in refining the teaching sequence, enabling the results to form part of the students\' knowledge. It is hoped the knowledge gained has been significant for the students and when added to previous knowledge has helped them develop a more stable and rich understanding of the subject. Ausubel\'s theory guided the choice of the evaluation method and interpretation of data collected in this study. According to the theoretical approach, the conceptual maps were presented as a way of analyzing and evaluate the knowledge gained by students and therefore the proposed didactic sequence. As indicated by analysis of the conceptual maps, most of the information related to the dynamics of determination of the impact point and the direction of arrival of a primary cosmic ray began to have meaning in students\' knowledge structure. Along these lines, the content cosmic rays proved possible to be taught in the high school classroom.
10

Implementação de uma sequência de ensino e aprendizagem sobre tópicos de astrofísica de partículas para o ensino médio / Implementation of a teaching and learning sequence for particle astrophysics topics in High School

Roger Willians Correa 05 February 2015 (has links)
Este trabalho tem como objetivo investigar a implementação de uma sequência de ensino e aprendizagem sobre tópicos de Astrofísica de Partículas para o Ensino Médio. Buscou-se determinar o ponto de impacto e a direção de chegada de um raio cósmico primário ao solo, utilizando dados do Observatório Pierre Auger. A fim de identificar elementos relevantes dessa sequência, analisamos a maneira como os estudantes interagiram e realizamos refinamentos progressivos a fim de aperfeiçoá-la. No refinamento da sequência de ensino, a análise dos dados obtidos desempenhou um importante papel, já que indicou os caminhos a serem tomados para que a atividade desenvolvida fizesse parte do repertório de conhecimentos do aluno. Esperou-se que esse conhecimento, longe de ser mecânico e passageiro, fosse significativo ao aluno no sentido de que os conteúdos tratados se entrelaçassem a conhecimentos prévios e se transformassem em conhecimento mais estáveis e ricos em significados. Por este viés, a Teoria da Aprendizagem Significativa de Ausubel norteou a escolha do método de avaliação e interpretação dos dados coletados neste estudo. Assim, de acordo com o referencial teórico adotado, os mapas conceituais apresentaram-se como forma de análise e serviram de avaliação do conhecimento obtido pelos estudantes e, por conseguinte, da sequência didática proposta. Conforme indicou a análise dos mapas conceituais, a maior parte das informações relacionadas com a dinâmica de determinação do ponto de impacto e da direção de chegada de um raio cósmico primário começou a ter significado na estrutura de conhecimentos dos alunos. Assim, o conteúdo raios cósmicos mostrou-se possível de ser ensinado na sala de aula do Ensino Médio. / This paper aims at investigating the implementation of a teaching and learning sequence for particle Astrophysics topics in High School. Our aim is to determine the impact point and direction of a primary cosmic ray to the ground, using the Pierre Auger Observatory data. To identify the relevant elements of this sequence, we analyzed the way in which students interacted and then implemented progressive refinements to improve it. The data analysis played an important role in refining the teaching sequence, enabling the results to form part of the students\' knowledge. It is hoped the knowledge gained has been significant for the students and when added to previous knowledge has helped them develop a more stable and rich understanding of the subject. Ausubel\'s theory guided the choice of the evaluation method and interpretation of data collected in this study. According to the theoretical approach, the conceptual maps were presented as a way of analyzing and evaluate the knowledge gained by students and therefore the proposed didactic sequence. As indicated by analysis of the conceptual maps, most of the information related to the dynamics of determination of the impact point and the direction of arrival of a primary cosmic ray began to have meaning in students\' knowledge structure. Along these lines, the content cosmic rays proved possible to be taught in the high school classroom.

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