723 research outputs found
'Kill a kid and get a house': rationality versus retribution in the case of Robert Thompson and Jon Venables, 1993-2001.
No full textFrom Thatcher’s Grandchildren? Politics and Childhood in the Twenty-First Century, Stephen Wagg and Jane Pilcher (eds), Palgrave 2014, pp. 1-26
Local and Global Models for Articulated Motion Analysis
No full textVision is likely the most important of the senses employed by humans in understanding their environment, but computer systems are still sorely lacking in this respect. The number of potential applications for visually capable computer systems is huge; this thesis focuses on the field of motion capture, in particular dealing with the problems encountered when analysing the motion of articulated or jointed targets, such as people. Joint articulation greatly increases the complexity of a target object, and increases the incidence of self-occlusion (one body part obscuring another). These problems are compounded in typical outdoor scenes by the clutter and noise generated by other objects. This thesis presents a model-based approach to automated extraction of walking people from video data, under indoor and outdoor capture conditions. Local and global modelling strategies are employed in an iterative process, similar to the Generalised Expectation-Maximisation algorithm. Prior knowledge of human shape, gait motion and self-occlusion is used to guide this extraction process. The extracted shape and motion information is applied to construct a gait signature, sufficient for recognition purposes. Results are presented demonstrating the success of this approach on the Southampton Gait Database, comprising 4820 sequences from 115 subjects. A recognition rate of 98.6% is achieved on clean indoor data, comparing favourably with other published approaches. This recognition rate is reduced to 87.1% under the more difficult outdoor capture conditions. Additional analyses are presented examining the discriminative potential of model features. It is shown that the majority of discriminative potential is contained within body shape features and gait frequency, although motion dynamics also make a significant contribution
Supporting brace sizing in structures with added linear viscous fluid dampers: A filter design solution
No full textViscous fluid dampers have proved to be effective in suppressing unwanted vibrations in a range of engineering structures. When dampers are fitted in a structure, a brace is typically used to attach them to the main structure. The stiffness of this brace can significantly alter the effectiveness of the damper, and in structures with multiple dampers, this can be a complex scenario to model. In this paper, we demonstrate that the effects of the brace compliance on the damper performance can be modelled by way of a first-order filter. We use this result to formulate a procedure that calculates the stiffness required by the supporting brace to provide a specified effectiveness of the damping action. The proposed procedure assumes that viscous dampers have been sized in a previous design step based on any optimal methodology in which, as is usually the case, the presence of supporting braces and their dynamic effects were neglected. Firstly considering a one degree-of-freedom system, we show that the proposed method ensures a desired level of damper efficiency for all frequencies within a selected bandwidth. Then the analysis is extended to the case of multi-degree-of-freedom systems to show that the design criteria can be applied in a straightforward and successful manner to more complex structures
Bifurcations of backbone curves for systems of coupled nonlinear two mass oscillator
No full textThis paper considers the dynamic response of coupled, forced and lightly damped nonlinear oscillators with two degree-of-freedom. For these systems, backbone curves define the resonant peaks in the frequency-displacement plane and give valuable information on the prediction of the frequency response of the system. Previously, it has been shown that bifurcations can occur in the backbone curves. In this paper, we present an analytical method enabling the identification of the conditions under which such bifurcations occur. The method, based on second-order nonlinear normal forms, is also able to provide information on the nature of the bifurcations and how they affect the characteristics of the response. This approach is applied to a two-degree-of-freedom mass, spring, damper system with cubic hardening springs. We use the second-order normal form method to transform the system coordinates and identify which parameter values will lead to resonant interactions and bifurcations of the backbone curves. Furthermore, the relationship between the backbone curves and the complex dynamics of the forced system is shown.</p
Automated Markerless Extraction of Walking People Using Deformable Contour Models
No full textWe develop a new automated markerless motion capture system for the analysis of walking people. We employ global evidence gathering techniques guided by biomechanical analysis to robustly extract articulated motion. This forms a basis for new deformable contour models, using local image cues to capture shape and motion at a more detailed level. We extend the greedy snake formulation to include temporal constraints and occlusion modelling, increasing the capability of this technique when dealing with cluttered and self-occluding extraction targets. This approach is evaluated on a large database of indoor and outdoor video data, demonstrating fast and autonomous motion capture for walking people
A noniterative design procedure for supplemental brace–damper systems in single-degree-of-freedom systems
No full textIn this paper, a method for designing supplemental brace–damper systems in single-degree-of-freedom (SDOF) structures is presented. We include the effects of the supporting brace stiffness in the dynamic response by using a viscoelastic Maxwell model. On the basis of the study of an SDOF under ground excitation, we propose a noniterative design procedure for simultaneously specifying both the damper and the brace while assuring a desired structural performance. It is shown that to increase the damper size beyond the value delivered by the proposed criteria will not provide any improvement but actually worsen the structural response. The design method presented here shows excellent agreement with the FEMA 273 design approach but offers solutions closer to optimality
Sieber etal, Control-based continuation of unstable periodic orbits, ASME 2011
No full text<p>J. Sieber, B. Krauskopf, D. Wagg, S. Neild, A. Gonzalez-Buelga, Control-based continuation of unstable periodic orbits.<br>ASME Journal of Computational and Nonlinear Dynamics 6(1) 011005, 2011.</p>
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Resolving discs and mergers in z ∼ 2 heavily reddened quasars and their companion galaxies with ALMA
No full textWe present sub-arcsecond resolution Atacama Large Millimeter Array imaging of the CO(3–2) emission in two z ∼ 2.5 heavily reddened quasars (HRQs) – ULASJ1234+0907 and ULASJ2315+0143 – and their companion galaxies. Dynamical modelling of the resolved velocity fields enables us to constrain the molecular gas morphologies and host galaxy masses. Combining the new data with extensive multiwavelength observations, we are able to study the relative kinematics of different molecular emission lines, the molecular gas fractions, and the locations of the quasars on the MBH–Mgal relation. Despite having similar black hole properties, the two HRQs display markedly different host galaxy properties and local environments. J1234 has a very massive host – Mdyn ∼ 5 × 1011 M⊙ and two companion galaxies that are similarly massive located within 200 kpc of the quasar. The molecular gas fraction is low (∼6 per cent). The significant ongoing star formation in the host galaxy is entirely obscured at rest-frame ultraviolet (UV) and optical wavelengths. J2315 is resolved into a close-separation major merger (Δr = 15 kpc; Δv = 170 km s−1) with a ∼1:2 mass ratio. The total dynamical mass is estimated to be ≲1011 M⊙ and the molecular gas fraction is high (>45 per cent). A new HSC image of the galaxy shows unobscured UV-luminous star-forming regions co-incident with the extended reservoir of cold molecular gas in the merger. We use the outputs from the Illustris simulations to track the growth of such massive black holes from z ∼ 6 to the present day. While J1234 is consistent with the simulated z ∼ 2 relation, J2315 has a black hole that is overmassive relative to its host galaxy
Nonlinear Modal Decomposition Using Normal Form Transformations
No full textIn this paper we discuss a technique for decomposing multi-degree-of-freedom weakly nonlinear systems into a simpler form. This type of decomposition technique is an established cornerstone of linear modal analysis. Extending this type of technique to nonlinear multi-degree-of-freedom systems has been an important area of research in recent years. The key result in this work is that a theoretical transformation process is used to reveal both the linear and nonlinear system resonances. For each resonance, the parameters which characterise the backbone curves and higher harmonic components of the response, can be obtained. The underlying mathematical technique is based on a near identity normal form transformation for systems of equations written in second-order form. This is a natural approach for structural dynamics where the governing equations of motion are written in this form as standard practice. The example is a system with cubic nonlinearities, and shows how the transformed equations can be used to obtain a time independent representation of the system response. It is shown that when the natural frequencies are close to an integer multiple of each other, the backbone curve bifurcates. Examples of the predicted responses are compared to time-stepping simulations to demonstrate the accuracy of the technique
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