GPS Ionospheric mapping and tomography: A case of study in a geomagnetic storm

The ionosphere has been normally detected by traditional instruments, such as ionosonde, scatter radars, topside sounders onboard satellites and in situ rocket. However, most instruments are expensive and also restricted to either the bottomside ionosphere or the lower part of the topside ionosphere (usually lower than 800 km), such as ground based radar measurements. Nowadays, GPS satellites in high altitude orbits (~20,200 km) are capable of providing details on the structure of the entire ionosphere, even the plasmasphere. In this paper, a Regional Ionospheric Mapping and Tomography (RIMT) tool was developed, which can be used to retrieve 2-D TEC and 3-D ionospheric electron density profiles using ground-based or space-borne GPS measurements. Some results are presented from the RIMT tool using regional GPS networks in South Korea and validated using the independent ionosonde. GPS can provide time-varying ionospheric profiles and information at any specified grid related to ionospheric activities and states, including the electron density response at the F2-layer peak (the NmF2) during geomagnetic storms.Comment: Proceeding of IEEE International Geoscience and Remote Sensing Symposium (IGARSS), 24-29 July, 2011, Vancouver, Canad

Investigating the Operating Mechanisms of Polymer Light Emitting Diodes

This work uses a broad range of optoelectronic characterisation techniques to understand – at a fundamental level – the operating mechanisms of PLEDs. The electromodulation (EM) technique particularly provides a straightforward means of determining the electric field strength inside operational devices, and is used here to investigate the improved device performance due to the insertion of an interlayer between the anode and the emissive layer. The effects of different interlayer materials (hole-transporting polymeric materials and one crosslinkable material) are studied in red, green and blue PLEDs. Interlayer devices yield better efficiencies and longer lifetimes, which can be attributed to charge accumulation near the anode/interlayer and (or) interlayer/emissive layer interfaces indicated by EM measurements. A promising alternative anode material – vapour phase polymerised poly(3,4- ethylenedioxy thiophene)] (VPP-PEDOT) is another major focus of this thesis. Together with poly(3,4-ethylenedioxythiophene-styrenesulfonate) (PEDOT:PSS), VPP-PEDOT is a viable alternative anode to indium tin oxide (ITO), capable of yielding superior efficiencies in otherwise identical PLEDs. Finally, a simulation code is developed for organic semiconductor devices to systematically study the charge and electric field distributions in model devices. This code, based on drift-diffusion model, can be used to study light-emitting electrochemical cells (LECs). The simulation results indicate that there are high electric fields at both electrodes due to ionic charge distribution, which in turn facilitates electronic charge injection and thus leads to high recombination rates and luminous efficiencies

A three-loop radiative neutrino mass model with dark matter

We present a model that generates small neutrino masses at three-loop level due to the existence of Majorana fermionic dark matter, which is stabilized by a Z2 symmetry. The model predicts that the lightest neutrino is massless. We show a prototypical parameter choice allowed by relevant experimental data, which favors the case of normal neutrino mass spectrum and the dark matter with m \sim 50-135 GeV and a sizable Yukawa coupling. It means that new particles can be searched for in future e+e- collisions.Comment: 7 pages, 3 figure