Third generation fermions as probes of new physics

This thesis concerns the properties of two particles, the top quark and the tau lepton, the heaviest of the quarks and leptons, respectively, in the standard model of elementary particle physics. After a chapter introducing the standard model, the second concerns the tau lepton. Amongst all the quarks and leptons, the tau has the unique property that its polarisation can readily be measured at high energy colliders. We propose and develop new methods of using this unique property to search for new physics, such as Higgs bosons, and also for making an accurate measurement of the polarisation of taus produced via Z decay leading to a precision determination of the electroweak coupling. The third chapter of this thesis concerns the top quark. We perform the complete one- loop radiative corrections to the helicity amplitudes within the standard model. Even though the radiative corrections to top quark production and decay have already been calculated separately, our work makes it possible to combine the sequence of events by keeping full information on the correlations among final state particles

Two nonlinear systems from mathematical physics

The dissertation is divided into two chapters. In the first one, we consider the 2-Vortex problem for two point vortices in a complex domain. The Hamiltonian of the system contains the regular part of a hydrodynamic Green’s function, the Robin function h and two coefficinets which are the strengths of the point vortices. We prove the existence of infinitely many periodic solutions with minimal period T which are a superposition of a slow motion of the center of vorticity along a level line of h and of a fast rotation of the two vortices around their center of vorticity. These vortices move in a prescribed subset of the domain that has to satisfy a geometric condition. The minimal period can be any T in a certain interval. Subsets to which our results apply can be found in any generic bounded domain. The proofs are based on a recent higher dimensional version of the Poincaré-Birkhoff theorem due to Fonda and Ureña. In the second part, we study bifurcations of a multi-component Schrödinger system. We construct a solution branch synchronized to a positive solution of a simpler system. From this branch, we find a sequence of local bifurcation values in the one dimensional case and also in the general case provided that the positive solution is nondegenerate

Disturbance maintains and promotes biodiversity in an artificial plant ecology

A model of plant growth, competition and reproduction in three dimensions was constructed using L-systems to simulate plant growth, ray tracing to simulate sunlight and shading, and a steady-state genetic algorithm to simulate evolution by natural selection. Simulated plant growth conformed to expected trade-os between, for instance, growing up and growing out. Simulated cohorts exhibited conventional population-level phenomena such as obeying the self-thinning law. Competition between species was simulated under various disturbance regimes. Undisturbed, a K-selected type of plant species dominated at equilibrium. However, under certain disturbance regimes, diverse life-history strategies were able to coexist at equilibrium, and even speciate

HCI for peace: from idealism to concrete steps

This panel will contribute diverse perspectives on the use of computer technology to promote peace and prevent armed conflict. These perspectives include: the use of social media to promote democracy and citizen participation, the role of computers in helping people communicate across division lines in zones of conflict, how persuasive technology can promote peace, and how interaction design can play a role in post-conflict reconciliation

Biodiversity in intensive grasslands: is a compromise possible?

Peer reviewe

New Opportunities for Automated Pedestrian Performance Measures

Pedestrian safety is an important concern when evaluating intersections. Previous literature has shown that exclusive pedestrian phases improve safety, but at the expense of imposing greater pedestrian and motorist delay. However, outside of crash data, there are no easily implementable performance measures for pedestrians at traffic signals. This study proposes two performance metrics: (1) a time-to-jaywalk measure, and (2) the Conflict Occupancy Ratio (COR) for evaluating concurrent pedestrian signal phasing with turning vehicles. The COR quantifies conflicts between turning vehicles and pedestrians in the crosswalk. The COR is based upon a commercially deployed video detection system that correctly identified the presence of pedestrians to within two per cycle in this study. This performance is likely sufficient for the current application, but as the technology matures it will provide a scalable screening tool to identify intersections that have opportunities for capacity adjustments or warrant further direct field investigation

Measuring straight time in elite short track speed skating relays

In short track speed skating, the relay exchange provides an additional strategic component to races by allowing a team to change the skater involved in the pack race. It is thought that during this period of the race, time can be gained or lost due to the execution of the relay exchange. However, the only temporal measurement reported in short track speed skating is lap time, of which the relay exchange accounts for less than 30 %. As such, a more appropriate measurement of relay exchange performance might be the time taken to complete the straight where the relay exchange was executed. The aim of this study, therefore, was to validate a method for measuring straight time during elite short track speed skating relays. The proposed method used a single HD camcorder to create virtual timing gates at the start and end of both straights. To validate the method, straight times measured using the single HD camcorder were compared to synchronised cameras located perpendicular to the virtual timing gates. The root mean square error for both near and far straight times was less than the temporal resolution of the camera. In addition, Bland-Altman plots showed that the single HD camcorder method was invariant to race speed. Collectively, these findings suggest that a single HD camcorder does provide a valid method for measuring straight times during elite short track speed skating relays

Wildlife-friendly farming increases crop yield: evidence for ecological intensification

Ecological intensification has been promoted as a means to achieve environmentally sustainable increases in crop yields by enhancing ecosystem functions that regulate and support production. There is, however, little direct evidence of yield benefits from ecological intensification on commercial farms growing globally important foodstuffs (grains, oilseeds and pulses). We replicated two treatments removing 3 or 8% of land at the field edge from production to create wildlife habitat in 50–60 ha patches over a 900 ha commercial arable farm in central England, and compared these to a business as usual control (no land removed). In the control fields, crop yields were reduced by as much as 38% at the field edge. Habitat creation in these lower yielding areas led to increased yield in the cropped areas of the fields, and this positive effect became more pronounced over 6 years. As a consequence, yields at the field scale were maintained—and, indeed, enhanced for some crops—despite the loss of cropland for habitat creation. These results suggested that over a 5-year crop rotation, there would be no adverse impact on overall yield in terms of monetary value or nutritional energy. This study provides a clear demonstration that wildlife-friendly management which supports ecosystem services is compatible with, and can even increase, crop yields

Impacts of neonicotinoid use on long-term population changes in wild bees in England

Wild bee declines have been ascribed in part to neonicotinoid insecticides. While short-term laboratory studies on commercially-bred species (principally honeybees and bumblebees) have identified sub-lethal effects, there is no strong evidence linking these insecticides to losses of the majority of wild bee species. We relate 18 years of UK national wild bee distribution data for 62 species to amounts of neonicotinoid use in oilseed rape. Using a multi-species dynamic Bayesian occupancy analysis, we find evidence of increased population extinction rates in response to neonicotinoid seed treatment use on oilseed rape. Species foraging on oilseed rape benefit from the cover of this crop, but were on average three times more negatively affected by exposure to neonicotinoids than non-crop foragers. Our results suggest that sub-lethal effects of neonicotinoids could scale-up to cause losses of bee biodiversity. Restrictions on neonicotinoid use may reduce population declines

Muscle recruitment patterns during the prone leg extension

BACKGROUND: The prone leg extension (PLE) is a clinical test used to evaluate the function of the lumbopelvis. It has been theorized that a normal and consistent pattern of muscle activation exists. Previous research has found two contradictory patterns of muscle activation during PLE in normal individuals. One study shows an almost simultaneous activation of the lower erector spinae and hamstring muscle group with a delayed activation of the gluteus maximus, while the second describes the order of activation being ipsilateral erector spinae (to the leg being extended), hamstrings, contralateral erector spinae and gluteus maximus. Due to the different conclusions from these two studies and the lack of quantified muscle onset times, expressed in absolute time this study attempted to quantify the muscle onset times (in milliseconds) during the prone leg extension, while noting if a consistent order of activation exists and whether a timing relationship also exists between the gluteus maximus and contralateral latissimus dorsi. METHODS: 10 asymptomatic males (Average height: 175.2 cm (SD 6.5), Average Weight 75.9 kg (SD 6.5), Average Age: 27.1(SD 1.28)) and 4 asymptomatic females (Average height 164.5 (SD 2.9), weight: 56.2 (SD 8.9), Average Age: 25 (SD 1)) performed the prone leg extension task while the myoelectric signal was recorded from the bilateral lower erector spinae, gluteus maximus and hamstring muscle groups. Activation onsets were determined from the rectified EMG signal relative to the onset of the hamstrings muscle group. RESULTS: No consistent recruitment patterns were detected for prone leg extension among the hamstring muscle group and the erector spinae. However, a consistent delay in the Gluteus Maximus firing of approximately 370 ms after the first muscle activated was found. Five out of 14 asymptomatic subjects showed a delay in gluteus maximus firing exceeding the average delay found in previous research of subjects considered to have a dysfunctional firing pattern. CONCLUSION: A consistent pattern of activation was not found. Variability was seen across subjects. These findings suggest the PLE is not sufficient for a diagnostic test due to the notable physiological variation. An overlap between normal and potentially abnormal activation patterns may exist