X-rays from Saturn: A study with XMM-Newton and Chandra over the years 2002-05

We present the results of the two most recent (2005) XMM-Newton observations of Saturn together with the re-analysis of an earlier (2002) observation from the XMM-Newton archive and of three Chandra observations in 2003 and 2004. While the XMM-Newton telescope resolution does not enable us to resolve spatially the contributions of the planet's disk and rings to the X-ray flux, we can estimate their strengths and their evolution over the years from spectral analysis, and compare them with those observed with Chandra. The spectrum of the X-ray emission is well fitted by an optically thin coronal model with an average temperature of 0.5 keV. The addition of a fluorescent oxygen emission line at ~0.53 keV improves the fits significantly. In accordance with earlier reports, we interpret the coronal component as emission from the planetary disk, produced by the scattering of solar X-rays in Saturn's upper atmosphere, and the line as originating from the Saturnian rings. The strength of the disk X-ray emission is seen to decrease over the period 2002 - 2005, following the decay of solar activity towards the current minimum in the solar cycle. By comparing the relative fluxes of the disk X-ray emission and the oxygen line, we suggest that the line strength does not vary over the years in the same fashion as the disk flux. We consider possible alternatives for the origin of the line. The connection between solar activity and the strength of Saturn's disk X-ray emission is investigated and compared with that of Jupiter. We also discuss the apparent lack of X-ray aurorae on Saturn and conclude that they are likely to lie below the sensitivity threshold of current Earth-bound observatories. A similar comparison for Uranus and Neptune leads to the same disappointing conclusion.Comment: 10 pages, 5 figures; to be published in 'Astronomy and Astrophysics

Neuroinflammation in Preclinical Alzheimer's Disease: A Review of Current Evidence

The pathology of sporadic Alzheimer’s disease (AD) may be present at mid-life and precede the prodromal and clinical dementia syndromes associated with the disorder by decades. Few successful therapeutic treatments exist and, as a result, attention is turning to the preclinical stages of the disease for the development of future intervention strategies. The success of such strategies will rely on well-defined biomarkers of preclinical disease to identify and monitor changes earlier in the disease course. Here, we consider whether immune function changes are potentially useful markers of preclinical disease. We have selected studies spanning epidemiological, animal, clinical and imaging research pertaining to the earliest stages of AD pathogenesis, as well as studies of non-demented adults at high AD risk. We examine changes in inflammatory markers, alongside changes in established biomarkers, to highlight their suitability as disease indicators across preclinical and prodromal stages. We conclude that further work surrounding this topic is required, calling for larger prospective epidemiological studies of preclinical disease that incorporate serial assessment designs with a wider range of inflammatory mediators. We anticipate that future benefits of work in this area include improved disease detection and modification, as well as diagnostic accuracy of trial participants, leading to more cost-effective observation and intervention studies

X-ray spectroscopy of the IP PQ Gem

Using RXTE and ASCA data, we investigate the roles played by occultation and absorption in the X-ray spin pulse profile of the intermediate polar PQ Gem. From the X-ray light curves and phase-resolved spectroscopy, we find that the intensity variations are the result of a combination of varying degrees of absorption and the accretion regions rotating behind the visible face of the white dwarf. These occultation and absorption effects are consistent with those expected from the accretion structures calculated from optical polarization data. We can reproduce the changes in absorber covering fraction either from geometrical effects, or by considering that the material in the leading edge of the accretion curtain is more finely fragmented than in other parts of the curtain. We determine a white dwarf mass of ∼ 1.2 using the RXTE data

Understanding the Impact of Childhood Maltreatment on Episstemic Trust, Learning and Psychopathology Throughout the Lifespan

Part 1presents a systematic literature review of 20 quantitative papers comparing maltreated and non-maltreated children’s performance on memory tasks involving varying degrees of interpersonal information. Findings suggest that children’s basic memory processes may be impaired when the to be remembered information contains more interpersonal content, however heterogeneity in terminology and methodology between studies impede the ability to draw firm conclusions. Part 2, which was part of a joint thesis project with MacGregor (2021), uses a novel retrospective measure of childhood maltreatment to explore the relationship between temporal characteristics of maltreatment subtypes and adult psychopathology symptomatology. The role of impaired social learning, as measured by a social learning task completed under one of four ostensive cue conditions, is also explored. Chronicity of maltreatment, and peer emotional bullying were identified as particular risk factors for adult psychopathology symptoms. Social learning was not found to mediate such associations. Part 3 provides a critical appraisal of the research process, considering the impact of completing this piece of work in the Covid-19 context, before moving on to consider the influence of previous personal clinical and research experience on the process. Implications of the research findings for future research, clinical practice, and my own career are considered

On the generation and characterisation of internal micro-architectures

Open cell micro-architectures are used in a large number of applications, ranging from medical, such as bone scaffolds, to industrial, such as heat transfer structures. Traditionally these structures are manufactured using foaming processes, however advances in additive manufacturing (AM) now allow such structures to be designed computationally and fabricated to a high degree of precision. In this thesis image-based methods are developed for the purpose of generating periodic micro-architectures based on implicit representations. The algorithms developed are shown to be efficient and robust, allowing for the creation of both surface and volume meshes. Methods are presented for the creation of functionally graded structures allowing for arbitrary variations in density between specifiable volume fractions. These algorithms are further extended for domain conforming applications as well as for internal structures in CAD models. By utilising a hybrid approach, imaging techniques can be exploited for the generation of internal structures in CAD models without de-featuring the original external geometry. The structures of interest are also shown to be manufacturable via selective laser melting (SLM). The issue of characterisation, for linear elastic properties, is addressed through the use of a novel homogenisation technique. Large multi-scale problems in irregular domains are divided into smaller sub-volumes using established tetrahedral volume meshing techniques. By performing a series of virtual tests on these macroelements their effective properties can be computed and subsequently used in macro-simulations. The technique is shown to yield results in excellent agreement with the often used kinematic uniform boundary conditions (KUBC). It is also shown how these properties may be used for visualising the distribution in properties over a domain.SimplewareEPSR

A fish farming experiment in Scottish sea lochs

The practice of stimulating dense growths of marine phytoplankton in laboratory cultures by the addition of nitrate and phosphate is now well established. Since in the sea the food chain leading ultimately to fish begins with inorganic nutrient salts, and passes through plankton and bottom fauna, it seemed feasible to attempt to stimulate the food cycle by the addition of artificial fertilizers to seawater areas. Nitrate and phosphate alone were considered since these are the nutrients in short supply in the sea

The nature and origin of Seyfert warm absorbers

We collate the results of recent high resolution X-ray spectroscopic observations of 23 AGN, and use the resulting information to try to provide answers to some of the main open questions about warm absorbers: where do they originate, what effect do they have on their host galaxies, and what is their importance within the energetics and dynamics of the AGN system as a whole? We find that the warm absorbers of nearby Seyferts and certain QSOs are most likely to originate in outflows from the dusty torus, and that the kinetic luminosity of these outflows accounts for well under 1% of the bolometric luminosities of the AGN. Our analysis supports, however, the view that the relativistic outflows recently observed in two PG quasars have their origin in accretion disc winds, although the energetic importance of these outflows is similar to that of the Seyfert warm absorbers. We find that the observed soft X-ray absorbing ionisation phases fill less than 10% of the available volume. Finally, we show that the amount of matter processed through an AGN outflow system, over the lifetime of the AGN, is probably large enough to have a significant influence on the evolution of the host galaxy and of the AGN itself