Gamma/hadron discrimination using composite cherenkov telescopes

The Durham University Mk6 Ground Based Gamma Ray Telescope is a sensitive detector in the Very High Energy (VHE) band (~100GeV-10TeV). It is a 'composite' Cherenkov telescope consisting of three 42m(^2) mirrors, each of which is viewed by a Cherenkov photon detector. Together the three detectors provide the basis for a sophisticated coincidence trigger that gives the telescope its low energy threshold of ~300GeV. Analysis of high resolution Cherenkov images from the central detector allows gamma rays to be identified from the hadronic background. The Left and Right detectors also record two independent, medium resolution, Cherenkov images. This thesis has investigated the use of the images from the Left and Right detectors to provide extra gamma/hadron discrimination power. Two measurements, represented by the parameters dDist and LRconc, have been identified that are capable of improving current VHE source detection significance by 20-30%.In Chapter 1 some of the motivations behind the field of VHE gamma ray astronomy are discussed, along with brief explanations of VHE gamma ray production mechanisms. Potential astronomical sources of VHE photons are outlined in Chapter 2. In Chapter 3 the phenomenon of Cherenkov radiation emitted in the atmosphere from Extensive Air Showers (EAS) is introduced. The construction of Atmospheric Cherenkov Telescopes is considered in Chapter 4 and the Durham Mk6 telescope is detailed in Chapter 5. The moments method of analysing Cherenkov images is given in Chapter 6. Chapter 7 investigates the measurements that that could be made using data from the Left and Right detectors to identify gamma ray EAS from the hadron background. The effects on these measurements of various aspects of the Mk6 telescope's performance are also researched here and in further detail in Chapter 8. Finally a summary and some suggestions for future work are given in Chapter 9

Simplifying Bayesian experimental design for multivariate partially exchangeable systems

We adopt a Bayes linear approach to tackle design problems with many variables cross-classified in many ways. We investigate designs where we wish to sample individuals belonging to different groups, exploiting the powerful properties of the adjustment of infinitely second-order exchangeable vectors. The types of information we gain by sampling are identified with the orthogonal canonical directions. We show how we may express these directions in terms of the different factors of the model. This allows us to solve a series of lower dimensional problems, through which we may identify the different aspects of our adjusted beliefs with the different aspects of the choice of design, leading both to qualitative insights and quantitative guidance for the optimal choice of design. These subproblems have an interpretable form in terms of adjustment upon subspaces of the full problem and remain valid when we consider adjusting the underlying population structure and also for predicting future observables from past observation. We then examine the adjustment of finitely second-order exchangeable vectors, and show that the adjustment shares the same powerful properties as the adjustment in the infinite case. We show how if the finite sequence of vectors is extendible, then the differences in the adjustment of the sequence is quantitatively the same for all sequence lengths and it is easy to compare the qualitative differences. Extending to an infinite sequence allows us to draw comparisons between the finite and infinite modelling. Such comparisons may also be made when we consider sampling individuals belonging to different groups, where each group contains only a finite number of individuals

Survival analysis of DNA mutation motifs with penalized proportional hazards

Antibodies, an essential part of our immune system, develop through an intricate process to bind a wide array of pathogens. This process involves randomly mutating DNA sequences encoding these antibodies to find variants with improved binding, though mutations are not distributed uniformly across sequence sites. Immunologists observe this nonuniformity to be consistent with "mutation motifs", which are short DNA subsequences that affect how likely a given site is to experience a mutation. Quantifying the effect of motifs on mutation rates is challenging: a large number of possible motifs makes this statistical problem high dimensional, while the unobserved history of the mutation process leads to a nontrivial missing data problem. We introduce an $\ell_1$-penalized proportional hazards model to infer mutation motifs and their effects. In order to estimate model parameters, our method uses a Monte Carlo EM algorithm to marginalize over the unknown ordering of mutations. We show that our method performs better on simulated data compared to current methods and leads to more parsimonious models. The application of proportional hazards to mutation processes is, to our knowledge, novel and formalizes the current methods in a statistical framework that can be easily extended to analyze the effect of other biological features on mutation rates

Megalyridia capensis (Hymenoptera: Megalyridae: Megalyridiini) a relict species endemic to South Africa

Numerous further specimens of the monotypical megalyrid species Megalyridia capensis Hedqvist have recently been collected from diverse habitats encompassing a distributional range of more than 800 km in South Africa. The male of M. capensisis recorded for the first time. We provide high-quality Numerous further specimens of the monotypical megalyrid species Megalyridia capensis Hedqvist have recently been collected from diverse habitats encompassing a distributional range of more than 800 km in South Africa. The male of M. capensisis recorded for the first time. We provide high-quality images of both sexes and a key to genera of Megalyridae occurring in the Afrotropical region. Online keys are available at: http://www.waspweb. org/Megalyroidea/Megalyridae/Keys/index.htm. The biogeography of this relict species is discussed

Competitive formation of spiro and ansa derivatives in the reactions of tetrafluorobutane-1,4-diol with hexachlorocyclotriphosphazene: a comparison with butane-1,4-diol

Reaction of hexachlorocyclotriphosphazene, N3P3Cl6 (1), in two stoichiometries (1:1.2 and 1:3) with the sodium derivative of the fluorinated diol, 2,2,3,3-tetrafluorobutane-1,4-diol, (2), in THF solution at room temperature afforded six products, whose structures have been characterized by X-ray crystallography and 1H, 19F and 31P NMR spectroscopy: the mono-spiro compound, N3P3Cl4(OCH2CF2CF2CH2O), (3), its ansa isomer, (4), a di-spiro derivative N3P3Cl2(OCH2CF2CF2CH2O)2, (5), its spiro-ansa (6) and non-gem cis bis-ansa (7) isomers and a tri-spiro compound N3P3(OCH2CF2CF2CH2O)3, (8). The tri-spiro derivative (8) was also formed in the reaction of the ansa compound (4) with diol (2) in a 1:3 ratio in THF at room temperature. The reactions of (1) with step-wise additions of (2) were also investigated at low temperature (-780C) to give the same range of products as at room temperature. The results of all reactions are compared with previous work on the reactions of (1) with butane-1,4-diol/pyridine mixtures and with the reaction of hexafluorocyclotriphosphazene, N3P3F6 (9), with the silyl derivative of the diol (2), (Me3SiOCH2CF2)2, in a 1:0.4 mole ratio in the same solvent, THF

Youth and Crime: Centennial Reflections on the Children Act 1908

Guest Editoria