Optimising Structured P2P Networks for Complex Queries

With network enabled consumer devices becoming increasingly popular, the number of connected devices and available services is growing considerably - with the number of connected devices es- timated to surpass 15 billion devices by 2015. In this increasingly large and dynamic environment it is important that users have a comprehensive, yet efficient, mechanism to discover services. Many existing wide-area service discovery mechanisms are centralised and do not scale to large numbers of users. Additionally, centralised services suffer from issues such as a single point of failure, high maintenance costs, and difficulty of management. As such, this Thesis seeks a Peer to Peer (P2P) approach. Distributed Hash Tables (DHTs) are well known for their high scalability, financially low barrier of entry, and ability to self manage. They can be used to provide not just a platform on which peers can offer and consume services, but also as a means for users to discover such services. Traditionally DHTs provide a distributed key-value store, with no search functionality. In recent years many P2P systems have been proposed providing support for a sub-set of complex query types, such as keyword search, range queries, and semantic search. This Thesis presents a novel algorithm for performing any type of complex query, from keyword search, to complex regular expressions, to full-text search, over any structured P2P overlay. This is achieved by efficiently broadcasting the search query, allowing each peer to process the query locally, and then efficiently routing responses back to the originating peer. Through experimentation, this technique is shown to be successful when the network is stable, however performance degrades under high levels of network churn. To address the issue of network churn, this Thesis proposes a number of enhancements which can be made to existing P2P overlays in order to improve the performance of both the existing DHT and the proposed algorithm. Through two case studies these enhancements are shown to improve not only the performance of the proposed algorithm under churn, but also the performance of traditional lookup operations in these networks

Studies on the breeding biology and population dynamics of the great skua (catharacta skua brűnnich)

The history and breeding biology of the-North Atlantic Great Skua Catharacta skua skua Brűnnich was examined to determine its status in seabird communities, and to find reasons for current population increases. A variety of colony census methods are critically compared. Changes in colony sizes in Iceland, Faroe and Britain, which appear to be genetically isolated populations, are documented in detail. Evidence is presented suggesting that the Great Skua first colonised the northern hemisphere around 1500 AD. Ringing- recoveries are analysed to examine movements of known-age birds through the year. Causes of mortality are examined in relation to age and area of recovery. Attendance of prebreeders is described. A computer model is used to estimate energy requirements of Great Skua and other seabird populations. Model precision is examined using sensitivity analyses and a Monte Carlo method. Seasonal variations in Great Skua diet were examined by analyses of pellets and regurgitates. Time budgets of breeders and prebreeders were compared, and food preferences determined. The relative importance of predation and kleptoparasitism as feeding techniques, and their effects on other species are discussed. Methods were developed to classify eggs into first or second laid, and to estimate hatching dates from egg densities. Rates of chick growth were studied in relation to hatching status and date. Conversion tables were prepared to age chicks and to determine an index of body condition from measurements. Pesticide and pollutant concentrations were examined in adults and eggs, as were the influences of these, of age, experience, nest density and food-availability, on breeding success. Effects of interactions with nesting Arctic Skuas were investigated, and factors influencing success of kleptoparasitic chases by both species were determined. Adult and first year survival rates were estimated and rates of colony increase compared. Future population changes are discussed speculatively

A view from above : changing seas, seabirds and food sources

In this review we summarize what is known about mechanisms by which climate change may be affecting the populations of seabirds around the UK. Breeding success and adult survival are the key factors affecting changes in seabird populations, and food intake is implicated as a major determinant of both. The diet of most UK seabird species is almost exclusively sandeels, small clupeoid fish or zooplankton and it is clear that the marine pelagic food web is the key ecological system determining food supply. Hence, we develop the review by first considering how climate changes may affect primary production, and then examine how this propagates through the food web to zooplankton and fish culminating in fluctuations in seabird numbers. A trend of increasing numbers of many seabird species since 1970, particularly puffins, guillemots and razorbills, appears to have been reversed since 2000. The proximate cause of the recent declines seems to be a succession of 5 years of low breeding success for a range of species due to a shortage of food, especially sandeels. However, the connection with climate change remains uncertain, though there are indications that declines in the productivity of sandeel populations may be linked in some complex way to warming sea temperatures. The main conclusion is that no part of the marine food web, including fisheries, can be considered in isolation when trying to understand and predict the consequences of climate change for seabirds. Impacts can be expected in all parts of the system, and all parts of the system are interconnected

The geology of the Barbon and Middleton Fells, near Kirkby Lonsdale, Westmorland

The results of stratigraphical, palaeontological, petrographical, and sedimentological investigations into the Silurian strata of the Barbon and Middleton Fells, east of the Lune Valley Westmorland, are described,and compared with strata of a similar age in other parts of the country.A detailed stratigraphical succession has been erected for the first time, the strata having been sub-divided on a lithological basis into the Coniston Grits and Bannisdale Slates. Zoning of this succession by means of the graptolite faunas reveals that the lundgreni, nilssoni-scanicus, leintwardinensis incipiens and leintwardinensis leintwardinensis zones are present in the area. The lundgreni fauna which is indicative of the upper part of the Wenlock Series, is restricted almost entirely to the southern extremity of the area. The remainder of the strata fall within the Ludlow Series.Statistical investigations into the petrography of the coarse sediments have shown that they may be classified as fine grained greywackes, which have been derived from the northern part of the Southern Uplands. Consideration of sedimentary structures and changes in thickness and grain size of the sediments in adjacent areas supports this conclusion. This indicates that there is little evidence in favour of the Lake District and Southern Uplands areas of deposition being separated by a border land mass in Ludlovian times.The coarse grained sediments are shown to have been brought into the area from the north-west, by comparatively vigorous turbidity currents. Finer grained sediments, however, are considered to represent deposition from low grade currents during quiescent periods which become more and more dominant in the higher parts of the succession. Pyritic films in these finer sediments suggest that deposition took place under anaerobic conditions.Consideration of the structure has revealed that during the Caledonian orogeny the sediments were folded and faulted along WNW-ESE axes, to produce two large open synclines on which minor folding is superimposed. The effect of the later Hercynian orogeny was to introduce a set of N-S and NE-SW trending faults into the area, and to tilt the strata slightly to the north-west

Feeding and foraging ecology of Trindade petrels Pterodroma arminjoniana during the breeding period in the South Atlantic Ocean

Seabirds breeding in tropical environments experience high energetic demands, when foraging in an oligotrophic environment. The globally threatened Trindade petrel Pterodroma arminjoniana has its largest colony in Trindade Island (20°30′S–29°19′W) inside the oligotrophic South Atlantic Subtropical Gyre. Diet sampling methods, geolocator tracking and stable isotope analysis were used to describe its diet, compare foraging trips and distributions, and assess temporal variations in the trophic niche throughout the breeding period. Diet consisted mainly of squid and fish. The high species diversity and wide range of prey sizes consumed suggests the use of multiple foraging techniques. Stable isotope mixing models confirm that Trindade petrels rely mainly on squid throughout the breeding period. Its broad isotopic niche seems to reflect both a diverse diet and foraging range, since birds can reach up to 3335 km from the colony. Isotopic niche showed limited variation even in an 8-year interval, apparently due to oceanographic stability, although changes in the isotopic niche have demonstrated an adjustment to different conditions in different seasons. Petrels change foraging areas and prey during the breeding period: pre-incubating birds use more productive areas west of Trindade Island and obtain low trophic position prey; incubating petrels perform longer trips southward to consume prey of high trophic position; and chick-rearing petrels use areas around the island. These results demonstrate that to deal with high demand breeding in a colony surrounded by oligotrophic waters, Trindade petrels need to explore wide foraging areas and utilize a diverse diet, besides adjusting trophic niche according to breeding stage

UK rail workers' perceptions of accident risk factors: An exploratory study

Although non-fatal injuries remain a frequent occurrence in Rail work, very few studies have attempted to identify the perceived factors contributing to accident risk using qualitative research methods. This paper presents the results from a thematic analysis of ten interviews with On Track Machine (OTM) operatives. The inductive methodological approach generated five themes, of which two are discussed here in detail, ‘Pressure and fatigue’, and ‘Decision making and errors’. It is concluded that for companies committed to proactive accident risk reduction, irrespective of current injury rates, the collection and analysis of worker narratives and broader psychological data across safety-critical job roles may prove beneficial

Dual energy X-ray absorptiometry positioning protocols in assessing body composition: A systematic review of the literature:A systematic review of the literature

OBJECTIVES: To systematically identify and assess methods and protocols used to reduce technical and biological errors in published studies that have investigated reliability of dual energy X-ray absorptiometry (DXA) for assessing body composition. DESIGN: Systematic review. METHODS: Systematic searches of five databases were used to identify studies of DXA reliability. Two independent reviewers used a modified critical appraisal tool to assess their methodological quality. Data was extracted and synthesised using a level of evidence approach. Further analysis was then undertaken of methods used to decrease DXA errors (technical and biological) and so enhance DXA reliability. RESULTS: Twelve studies met eligibility criteria. Four of the articles were deemed high quality. Quality articles considered biological and technical errors when preparing participants for DXA scanning. The Nana positioning protocol was assessed to have a strong level of evidence. The studies providing this evidence indicated very high test–retest reliability (ICC 0.90–1.00 or less than 1% change in mean) of the Nana positioning protocol. The National Health and Nutrition Examination Survey (NHANES) positioning protocol was deemed to have a moderate level of evidence due to lack of high quality studies. However, the available studies found the NHANES positioning protocol had very high test–retest reliability. Evidence is limited and reported reliability has varied in papers where no specific positioning protocol was used or reported. CONCLUSIONS: Due to the strong level of evidence of excellent test–retest reliability that supports use of the Nana positioning protocol, it is recommended as the first choice for clinicians when using DXA to assess body composition

Structure and Innervation of the Extrahepatic Biliary System in the Australian Possum, Trichosurus Vulpecula

The morphology, microanatomy and innervation of the biliary tree of the Australian possum, Trichosurus vulpecula, was examined. The gross morphology of the gallbladder, hepatic and cystic ducts, and the course of the common bile duct, conforms to those of other species. The sphincter of Oddi has an extraduodenal segment that extends 15mm from the duodenal wall; within this segment the pancreatic and common bile ducts are ensheathed together by sphincter muscle. Their lumens unite to form a common channel within the terminal intraduodenal segment