A problem solving system employing a formal approach to means

The thesis describes the theory and design of a general problem-solving system. The system uses a single general heuristic based on a formal definition of differences within the framework of means/ends analysis and employs tree search during problem solution. A comparison is made with two other systems using means/ends analysis. The conditions under which the system is capable of solving problems are investigated and the efficiency of the system is considered. The system has solved a variety of problems of varying complexity and the difference heuristic appears comparatively accurate for goal-directed search within certain limits

European support for the opposition to closer union of the Rhodesias and Nyasaland, with special reference to the period from 1945-1953

This dissertation is a study of the interplay of Imperial, Colonial and Settler politics in support of, and in opposition to the establishment of a united white ruled central Africa. Accordingly, consideration of African involvement arises only as it affected the other groups. This is not in any way to belittle the significance of African activity in the period - activity which has been studied in depth by other authors - it is simply a consequence of the aspect of the problem I have chosen to address

Re-estimation of argon isotope ratios leading to a revised estimate of the Boltzmann constant

In 2013, NPL, SUERC and Cranfield University published an estimate for the Boltzmann constant [1] based on a measurement of the limiting low-pressure speed of sound in argon gas. Subsequently, an extensive investigation by Yang et al [2] revealed that there was likely to have been an error in the estimate of the molar mass of the argon used in the experiment. Responding to [2], de Podesta et al revised their estimate of the molar mass [3]. The shift in the estimated molar mass, and of the estimate of kB, was large: -2.7 parts in 106, nearly four times the original uncertainty estimate. The work described here was undertaken to understand the cause of this shift and our conclusion is that the original samples were probably contaminated with argon from atmospheric air.
 In this work we have repeated the measurement reported in [1] on the same gas sample that was examined in [2, 3]. However in this work we have used a different technique for sampling the gas that has allowed us to eliminate the possibility of contamination of the argon samples. We have repeated the sampling procedure three times, and examined samples on two mass spectrometers. This procedure confirms the isotopic ratio estimates of Yang et al [2] but with lower uncertainty, particularly in the relative abundance ratio R38:36.
 Our new estimate of the molar mass of the argon used in Isotherm 5 in [1] is 39.947 727(15) g mol-1 which differs by +0.50 parts in 106 from the estimate 39.947 707(28) g mol-1 made in [3]. This new estimate of the molar mass leads to a revised estimate of the Boltzmann constant of kB = 1.380 648 60 (97) × 10−23 J K−1 which differs from the 2014 CODATA value by +0.05 parts in 106.&#13

EFFECTS OF IMPOSED CYCLE FREQUENCY TRAINING ON THE HEAVE AND PITCH PHASE RELATIONSHIPS IN UNDULATORY UNDERWATER SWIMMING

This study compared the effects of training at a self-selected preferred cycle frequency (PF) with an identical imposed cycle frequency (IF) on the heave and pitch phase relationship in undulatory underwater swimming (UUS), to examine the effects of frequency imposition on coordination. Kinematic data were recorded from 16 skilled swimmers performing maximal UUS prior to and during 4-weeks UUS training at either their PF or an IF set at their preferred frequency, with weekly testing sessions and final retest session 2-weeks post training. No differences in maximal swimming velocity were found. No differences were found in heave and pitch phase relationship between training groups. Further research is required to establish the efficacy of heave and pitch coupling as an effective measure of UUS behaviour in skilled swimmers

Significance of active site residues in the n-domain selectivity of angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is a zinc metallopeptidase that plays an important role in vascular function; with ACE inhibitors being clinically utilised in the treatment of cardiovascular disease and diabetic nephropathy. Somatic ACE consists of two homologous catalytically active domains (designated N- and C-domains) that share high overall sequence identity and structural topology. Despite the high degree of similarity between domains, each domain displays differences in substrate processing and inhibitor binding abilities. This suggests that active site residues differing between the two domains could provide unique interactions within the N-domain that allow for N-selective binding and processing. Literature reports of ACE crystal structures and studies with substrate and inhibitor analogues have implicated unique residues present in the S2 and S2' subsites in providing important interactions for N-selectivity

The geology and mineralogical zoning of the H.Y.C. Ag-Pb-Zn deposit, McArthur River, Northern Territory, Australia

The H.Y.C. Pyritic Shale Member is composed of interbedded potassic bituminous pyritic shale, sedimentary breccia and tuff. The shales contain dolomite nodules, dolomite concretions and black chert globules. The H. Y. C. Pb-Zn deposit, a sedimentary stratiform sulfide deposit, occurs at the base of the member in the H. Y. C. sub-basin. It is postulated that the member was deposited in a saline lacustrine environment, which was subject to oscillations in water level. During periods of low water level the area was emergent. The Cooley Dolomite Member, adjacent to the H.Y.C. sub-basin, is a fault bounded block (the Western Fault Block) of Mara Dolomite. Between the Western Fault Block and the H.Y.C. sub-basin it is suggested that a talus breccia was deposited, composed of dolomite clasts derived from the Western Fault Block. The contact between the Western Fault Block and the talus breccia is delineated by a major syndepositonal fault, the Western Fault. The tu££ beds and shale in the H.Y.C. sub-basin are composed of quartz, ferroan dolomite, K-feldspar, albite, calcite, illite, kaolinite, chlorite and sulfides. The non-sulfide minerals outline a mineral halo above the tt. Y. C. deposit. The halo is recognized by changes with increasing distance from the H.Y.C. deposit and Cooley Dolomite, by decreases in the: (a) K-feldspar to albite ratio (b) dolomite to calcite ratio (c) crystallinity of illite (d) percentage alteration of feldspar: to clay The mineral halo is consistent with solutions which travelled from east to west across the sub-basin, and with falling temperatures away from the H.Y.C. deposit. The chalcophile elements in the H. Y. C. deposit and in the shales above the deposit are zoned with respect to the ratios Pb/Zn, Cq/(Pb+Zn), . Cu/Zn, Ag/Pb, Fe/(Pb+Zn), As/Fe, Co/Spy (where Spy is the amount of sulfur in pyrite), Cd/Zn and Tl/Spy. The zonal distribution of the base metal sulfides in the lower orebodies is consistent with mineralization having formed from solutions which entered the H.Y.C. sub-basin at its northeastern corner and travelled in a southwestern direction. The zonal distribution in the upper orebodies and the shales above the deposit, is consistent with mineralization having formed from solutions which entered the sub-basin along its eastern margin and travelled from east to west across the sub-basin. The zonal distribution and mineral textures of the sulfide and non-sulfide minerals in the H. Y. C. sub-basin indicate that they formed during an extended time period and/or from several pulses of solution with varying chemical compositions. The sulfide minerals are postulated to have formed during diagenesis below, but within about 100 meters of the sediment-water interface, and the non-sulfide minerals during diagenesis and also after deposition of the entire H.Y.C. Pyritic Shale Member. The chemical composition of the solutions and the minerals in equilibrium with the solutions, both in time and space, changed as the solutions travelled across the sub-basin away from the Cooley Dolomite. The major chemical changes in the solution(s) as they moved across the sub-basin were: (a) a decrease in the Cu/(Pb+Zn) ratio (b) a decrease in the Pb/Zn ratio (c) a decrease in the K/Na ratio (d) a decrease in the Mg/Ca ratio (e) an increase in the K⁺/H⁺ ratio. The formation of the sulfide and non-sulfide minerals in the H.Y.C. sub-basin were integral parts of a multistage hydrothermal history, in which solutions discharged intermittently from the Emu Fault Zone and/or Cooley Dolomite over the time period encompassing the deposition of almost all of the ll.Y.C. Pyritic Sha],e Hember exposed in the !LY.C. sub-basin

Framing energetic top-quark pair production at the LHC

Top-quark pair production is central to many facets of LHC physics. At leading order, the top and anti-top are produced in a back-to-back topology, however this topology accounts only for a minority of $t \bar t$ events with TeV-scale momentum transfer. The remaining events instead involve the splitting of an initial or final-state gluon to $t \bar t$. We provide simple quantitative arguments that explain why this is the case and examine the interplay between different topologies and a range of variables that characterise the event hardness. We then develop a method to classify the topologies of individual events and use it to illustrate our findings in the context of simulated events, using both top partons and suitably defined fiducial tops. For events with large $t \bar t$ invariant mass, we comment on additional features that have important experimental and theoretical implications.Comment: 23 pages + 2 appendice

Not just in man’s best friend: a review of Staphylococcus pseudintermedius host range and human zoonosis.

Staphylococcus pseudintermedius is one species in the commensal staphylococcal population in dogs. While it is commonly carried on healthy companion dogs it is also an opportunistic pathogen associated with a range of skin, ear, wound and other infections. While adapted to dogs, it is not restricted to them, and we have reviewed its host range, including increasing reports of human colonisation and infections. Despite its association with pet dogs, S. pseudintermedius is found widely in animals, covering companion, livestock and free-living species of birds and mammals. Human infections, typically in immunocompromised individuals, are increasingly being recognised, in part due to improved diagnosis. Colonisation, infection, and antimicrobial resistance, including frequent multidrug resistance, among S. pseudintermedius isolates represent important One Health challenge

Risk of hospitalisation or death in households with a case of COVID-19 in England: an analysis using the HOSTED dataset

Objective: To determine whether household contacts of confirmed cases of COVID-19 have an increased risk of hospitalisation or death. Methods: We used the HOSTED dataset of index cases of COVID-19 in England between June and November 2020, linked to Secondary Uses Service data on hospital episodes and Office for National Statistics’ mortality data. Multivariable logistic regression models of the odds of household contacts being hospitalised or dying within six weeks of an index case, adjusted for case type, age, sex and calendar month were calculated. Excess risk was determined by comparing the first six weeks after the index case with 6-12 weeks after the index case in a survival analysis framework. Results: Index cases were more likely to be hospitalised or die than either secondary cases or non-cases, having adjusted for age and sex. There was an increased risk of hospitalisation for non-cases (adjusted hazard ratio (aHR) 1.10 (95% CI 1.04, 1.16)) and of death (aHR 1.57 (95% CI 1.14, 2.16)) in the first six weeks after an index case, compared to 6-12 weeks after. Conclusion: Risks of hospitalisation and mortality are predictably higher in cases compared to non-cases. The short-term increase in risks for non-case contacts following diagnosis of the index case may suggest incomplete case ascertainment among contacts, although this was relatively small