Radiation Mechanism of the Soft Gamma-ray Pulsar PSR B1509-58

The outer gap model is used here to explain the spectrum and the energy dependent light curves of the X-ray and soft gamma-ray radiations of the spin-down powered pulsar PSR B1509-58.In the outer gap model, most pairs inside the gap are created around the null charge surface and the gap's electric field separates the two charges to move in opposite directions. Consequently, the region from the null charge surface to the light cylinder is dominated by the outflow of particles and that from the null charge surface to the star is dominated by the inflow of particles. The inflow and outflow of particles move along the magnetic field lines and emit curvature photons, and the incoming curvature photons are converted to pairs by the strong magnetic field of the star. These pairs emit synchrotron photons. We suggest that the X-rays and soft gamma-rays of PSR B1509-58 result from the synchrotron radiation of these pairs, and the viewing angle of PSR B1509-58 only receives the inflow radiation. The magnetic pair creation requires a large pitch angle, which makes the pulse profile of the synchrotron radiation distinct from that of the curvature radiation. We carefully trace the pulse profiles of the synchrotron radiation with different pitch angles. We find that the differences between the light curves of different energy bands are due to the different pitch angles of the secondary pairs, and the second peak appearing at E>10MeV comes from the region near the star, where the stronger magnetic field allows the pair creation to happen with a smaller pitch angle.Comment: 5 pages, 8 figures, 2012 Fermi Symposium proceedings - eConf C12102

Factors contributing to biofilm formation of Yersinia enterocolitica : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology, Massey University, Palmerston North, New Zealand

Content removed from thesis due to copyright reasons: Wang H., Palmer J., & Flint S. (2015). A rapid method for the nonselective enumeration of Yersinia enterocolitica, a foodborne pathogen associated with pork. Meat Science, 113: 59–61. doi:10.1016/j.meatsci.2015.11.005; Wang H., Tay M., Palmer J., Flint S. (2016) Biofilm formation of Yersinia enterocolitica and its persistence following treatment with different sanitation agents. Food Control, 73, 433-437. doi:10.1016/j.foodcont.2016.08.033Biofilms of pathogenic bacteria are recognised as a threat to food safety. The aim of the present study was to investigate the potential of Yersinia enterocolitica to form biofilms in the pork processing environment and identify the resistance of these biofilms to sanitation. The biofilm formation by Y. enterocolitica was monitored at conditions simulating pork processing environment under daily cleaning routine using an impedance method established in this study. Results showed that Y. enterocolitica had the potential to form biofilm and become resistant to sanitation in a pork processing environment. An investigation into the factors influencing biofilm formation of Y. enterocolitica indicated that the Ca2+ ion increased the level of biofilm formation. In addition, the presence of the virulence plasmid pYV is essential for the biofilm Ca2+ response. Further analysis of the bacterial cell surface properties and extracellular polymeric substance (EPS) composition suggested that the pYV+ cell surfaces are more negatively charged and more hydrophobic than the pYV- cells although no significant difference was observed with the addition of Ca2+. The pYV+ cells appear to produce more exopolysaccharide than the pYV- cells regardless of Ca2+ concentration. Ca2+ was able to increase the yield of extracellular DNA while the presence of pYV appeared to be dispensable in terms of extracellular DNA release. Analysis of cell wall protein revealed one protein expressed in the pYV+ cells but absent in the pYV- cells