Ebola in Gorillas - How Vaccinations May Reduce Mortality Rates

Gorilla populations have been decimated by the Ebola virus, with as many as 5,000 casualties in a single outbreak. Studies estimate that 1/3 of total gorilla populations have been wiped out by the virus since the 1990’s. Being marked as Critically Endangered on the IUCN Red List, Ebola poses as a significant threat to their future. The 2014 West Africa Ebola epidemic took the lives of over 11,000 human individuals. Gorillas and humans have a 95% and 50% Ebola mortality rate, respectively. Ebola haemorrhagic fever causes both internal and external bleeding. Transmission occurs through bodily fluids, making the gorillas particularly susceptible due to their social nature. Corpses remain infected for days, adding to the overall spread of the disease. As humans and gorillas come into contact with each other via illegal poaching, deforestation, the illegal wildlife trade, and tourism, it is imperative that preventive measures are taken to avoid future outbreaks. Vaccinations have proven to be successful in eliminating various fatal diseases in the past, making them an ideal candidate for Ebola prevention. There have been successful trials done on chimpanzees; however ethical reasons have prevented further development of a vaccination. The vaccine could be given to wild populations of gorillas through oral administration, allowing for some to develop immunity to the disease. Gorillas are a keystone species as they transport large seeds and pollen throughout the forest. Because of this, it is vital to prevent the spread of the disease to protect the biodiversity of the ecosystem

Effects Of The Space Environment On The Performance Of SMILE SXI CCDs

This thesis investigates the effects of the hazardous space environment on the performance of SMILE SXI CCDs, split between the roles of radiation and micrometeoroid damage. The radiation damage work focuses on developing an analytical technique to guide experimental CCD charge transfer optimisation, which is often a significantly time-consuming process. The technique is initially used to inform SXI CCD optimal clocking speeds and subsequently used to predict in-orbit performance benefits of different CCD operation modes. The first key result was the predicted charge transfer performance improvement from implementing tri-level clocking in the SMILE CCDs being less than 7%, which led to the decision to not implement it in the drive electronics. The second key result, related to radiation damage in a cryogenically irradiated CCD280, was the analysis of an unstable defect found to have a half-life of approximately 4 hours. The final key result is that the thermal cycling of SXI in-orbit will not have a noticeable effect on the defect landscape and hence CTI during the 3-year science lifetime. The micrometeoroid work focuses on development of a framework to quantify the effects of micrometeoroid impacts in CCD-based soft X-ray space telescopes. The work is tailored specifically for SMILE SXI but can be used in future CCD-based soft X-ray space missions, or any mission that will use silicon micropore optics. The key result of the analysis was the prediction that between 20 and 100 micrometeoroids of a least 1×10-6 m diameter will strike the CCDs of SMILE SXI over 3 years. Additional analysis was carried out using crater damage equations to estimate the number of pixels affected by the number of micrometeoroid impacts stated above. Finally, a bespoke experimental setup was built and tested by the author, in preparation for a micrometeoroid experiment testing campaign

Monte Carlo simulations of hyper-velocity particulate mechanics within silicon micropore optics

The focal planes of X-ray astronomy missions are at risk of particulate impacts from both micrometeoroids and orbital debris due to the open aperture of the narrow-angle incidence optics. Silicon micro-pore optics (sMPOs) have seen significant development due to their wide-angle observing capabilities and are planned for use in future X-ray space missions such as SMILE and THESEUS. Although previous space missions have seen sporadic and disruptive events in detectors which are attributed to particulate impacts, the number of particulates that can traverse the new sMPO and affect detector performance is not currently known, preventing the quantification of damage on focal planes. Work carried out on nested shell X-ray optics suggested that hyper-velocity particulates could scatter from the polished inner-mirrors and be focused on the focal plane of an instrument. By assuming that this basic scattering mechanic is present in sMPO, along with the natural clear path from space to the focal plane, the overall transmission rate of particulates through such an optic can be calculated using the Monte Carlo simulation methodology. By using the simulation presented here, along with known micrometeoroid flux models and so-called damage equations, the risk to focal planes of large-scale space missions due to hyper-velocity particulate impacts can for the first time be quantified. As such, the work presented here has many applications and uses across a wide range of fields

Ionising radiation effects in a soft X-ray CMOS image sensor

CIS221-X is a prototype monolithic CMOS image sensor, optimised for soft X-ray astronomy and developed for the proposed ESA THESEUS mission. A significant advantage of CMOS technology is its resistance to radiation damage. To assess this resistance, four backside-illuminated CIS221-X detectors have been irradiated up to a total ionising dose of 113 krad at the ESA ESTEC 60Co facility. Using unirradiated readout electronics, the performance of each sensor has been measured before and after irradiation. The gain, readout noise and dark current are shown to increase, while the image lag remains unchanged. These measurements are compared to that of similar CMOS image sensors and a possible physical explanation is provided for each result

SMILE soft X-ray Imager flight model CCD370 pre-flight device characterisation

Throughout the SMILE mission the satellite will be bombarded by radiation which gradually damages the focal plane devices and degrades their performance. In order to understand the changes of the CCD370s within the soft X-ray Imager, an initial characterisation of the devices has been carried out to give a baseline performance level. Three CCDs have been characterised, the two flight devices and the flight spare. This has been carried out at the Open University in a bespoke cleanroom measurement facility. The results show that there is a cluster of bright pixels in the flight spare which increases in size with temperature. However at the nominal operating temperature (−120 °C) it is within the procurement specifications. Overall, the devices meet the specifications when operating at −120 °C in 6 × 6 binned frame transfer science mode. The serial charge transfer inefficiency degrades with temperature in full frame mode. However any charge losses are recovered when binning/frame transfer is implemented

Effects of temperature anneal cycling on a cryogenically proton irradiated CCD

Throughout a typical Earth orbit a satellite is constantly bombarded by radiation with trapped and solar protons being of particular concern as they gradually damage the focal plane devices throughout the mission and degrade their performance. To understand the impact the damage has on CCDs and how it varies with their thermal history a proton radiation campaign has been carried out using a CCD280. The CCD is irradiated at 153 K and gradually warmed to 188 K in 5 K increments with Fe55 X-ray, dark current and trap pumping images taken at 153 K after each anneal step. The results show that despite the trap landscape changing throughout the anneal it has little impact on parallel charge transfer inefficiency. This is thought to be because most traps are unaffected and a lot of those that do anneal only move from the continuum between distinct trap species and into a nearby divacancy trap “peak” whose emission time constant is similar enough to still impact the CTI. In terms of using a CCD280 or similar devices in a mission the CTI being unaffected by thermal annealing up to 188 K means that any CTI correction needed as the radiation damage builds up does not have to take into account the thermal history of the focal plane. However, it is possible that a significant amount of annealing will occur at temperatures greater than 188 K and care should be taken when a mission is operating in this range to gather accurate pre-flight data