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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.
11

UHECR flux from SHDM annihilation in GC-like substructures

Wunderle, Kai Erik 14 February 2006
The objective of this thesis is to outline a relation between the measured Ultra High Energy Cosmic Ray (UHECR) flux and theoretical models for Super Heavy Dark Matter (SHDM) annihilation in Globular Cluster (GC)-like substructures in our Galaxy. Thus a possible solution for these two puzzling phenomena in present day astroparticle physics is presented. <p>A possible connection between GC-like substructures and UHECR sources was identified by combining the theoretical results for the annihilation of SHDM with the core densities derived from Dark Matter (DM)-profile fits to the GC data by Harris. The annihilation fluxes were derived for the Navarro, Frenk, and White-profile, the Moore-profile and a new constant density core approach. To compute the core densities of the GC-like substructures the GC-data by Harris were fitted to the most commonly used DM-profiles as well as to a more general DM-profile with variable inner power law index. The core densities were then calculated by making assumptions on the distribution of the masses in the GC-like substructure system as well as on the relation between the substructure mass and the core density. <p>Numerical simulations for the constant density core approach show that it is possible to reproduce the amount of substructure of the GC system of our Galaxy by choosing the mass fraction of the clumped dark matter to xi = 0.1 and the fraction of the heaviest substructure to eta = 0.01 xi, which corresponds to a mass of 10^9 M_odot for the most massive substructure. These simulation parameters then predict a product of the s-wave unitary bound with the fraction of the density of the Sun of zeta u approx 10^{-4}. Fits of the GC data to the DM-profiles reveal that all commonly used DM-profiles have to be rejected. Instead the profile with variable inner power law index is in good agreement with the GC data. The core densities are then calculated to range from 10^2 M_odot pc^{-3} to 10^8 M_odot pc^{-3}. <p>Therefore it can be concluded that SHDM annihilation in GC-like subclumps in our Galaxy presents a promising possibility to explain the measured UHECR flux.
12

UHECR flux from SHDM annihilation in GC-like substructures

Wunderle, Kai Erik 14 February 2006 (has links)
The objective of this thesis is to outline a relation between the measured Ultra High Energy Cosmic Ray (UHECR) flux and theoretical models for Super Heavy Dark Matter (SHDM) annihilation in Globular Cluster (GC)-like substructures in our Galaxy. Thus a possible solution for these two puzzling phenomena in present day astroparticle physics is presented. <p>A possible connection between GC-like substructures and UHECR sources was identified by combining the theoretical results for the annihilation of SHDM with the core densities derived from Dark Matter (DM)-profile fits to the GC data by Harris. The annihilation fluxes were derived for the Navarro, Frenk, and White-profile, the Moore-profile and a new constant density core approach. To compute the core densities of the GC-like substructures the GC-data by Harris were fitted to the most commonly used DM-profiles as well as to a more general DM-profile with variable inner power law index. The core densities were then calculated by making assumptions on the distribution of the masses in the GC-like substructure system as well as on the relation between the substructure mass and the core density. <p>Numerical simulations for the constant density core approach show that it is possible to reproduce the amount of substructure of the GC system of our Galaxy by choosing the mass fraction of the clumped dark matter to xi = 0.1 and the fraction of the heaviest substructure to eta = 0.01 xi, which corresponds to a mass of 10^9 M_odot for the most massive substructure. These simulation parameters then predict a product of the s-wave unitary bound with the fraction of the density of the Sun of zeta u approx 10^{-4}. Fits of the GC data to the DM-profiles reveal that all commonly used DM-profiles have to be rejected. Instead the profile with variable inner power law index is in good agreement with the GC data. The core densities are then calculated to range from 10^2 M_odot pc^{-3} to 10^8 M_odot pc^{-3}. <p>Therefore it can be concluded that SHDM annihilation in GC-like subclumps in our Galaxy presents a promising possibility to explain the measured UHECR flux.
13

Implementing variable energy positron lifetime spectroscopy based on secondary electron timing from thin carbon foil in transmission geometry

Ng, Cheuk-kwong, 吳卓光 January 2014 (has links)
abstract / Physics / Doctoral / Doctor of Philosophy
14

Positron beam studies on the electric field at metal-semiinsulating GaAs interfaces

胡一帆, Hu, Yi-fan. January 1997 (has links)
published_or_final_version / Chemistry / Master / Master of Philosophy
15

Positron lifetime and mobility studies of SiC

張秀霞, Cheung, Sau-ha. January 1998 (has links)
published_or_final_version / Physics / Master / Master of Philosophy
16

Slow positron annihilation spectroscopy applied to the analysis of the semiconductor, silicide, and titanium nitride structures

Frost, Robert Lewis 08 1900 (has links)
No description available.
17

Characterization of polymeric thin film by using positron annihilation spectroscopy

Zhang, Junjie, Jean, Y. C. January 2005 (has links)
Thesis (Ph. D.)--Dept. of Chemistry and School of Computing and Engineering. University of Missouri--Kansas City, 2005. / "A dissertation in chemistry and computer networking." Advisor: Yan-Ching Jean. Typescript. Vita. Description based on contents viewed Nov. 12, 2007; title from "catalog record" of the print edition. Includes bibliographical references (leaves 162-174). Online version of the print edition.
18

Study of radiation effects on polyurethanes by positron annihilation techniques

Yang, Duanjie. January 2007 (has links)
Thesis (Ph. D.)--University of Hong Kong, 2008. / Also available in print.
19

Positron lifetime and mobility studies of SiC /

Cheung, Sau-ha. January 1998 (has links)
Thesis (M. Phil.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 80-81).
20

Positron beam studies on the electric field at metal-semiinsulating GaAs interfaces /

Hu, Yi-fan. January 1997 (has links)
Thesis (M. Phil.)--University of Hong Kong, 1998. / Includes bibliographical references.

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