Browsing by Author "Adams, Patrick"

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    An investigation into the ergonomics of standing
    (1996) Whistance, Rosemary Simpson; Bridger, Robert; Adams, Patrick
    This section examines the literature on standing and attempts to build up a comprehensive picture of what happens when a human being stands upright. The review starts by exploring those changes to the skeleton and musculature which have enabled homo sapiens to be erect. This is followed by a look at how humans maintain upright posture through postural control and the role of the 'anti-gravity muscles'. Postural sway is inherent to standing and this is examined in some detail along with the concepts of centre of foot pressure and effective foot base. Attention is drawn to the fact that the subtleties of the upright posture_ are largely determined by culture and background. Foot position largely determines the quality of upright posture and this concept is explored in some detail. There are quantifiable physiological changes which occur when going from a supine position to an upright position and the review covers a comprehensive examination of these. In addition, the phenomenon of postural stress is also discussed. Besides postural sway, people move while standing and various reasons for changing postures are presented. The review also examines asymmetry, an inherent aspect of standing. Finally, research on standing in the wor~place is discussed. It is clear that the area is under-researched. Much work on standing was done earlier in the early part of the century and then again 40 and 50 years ago. Very little of this early research has penetrated ergonomics. By contrast, there is a vast body of accepted research on seating which is applied in ergonomics. This review seeks to present knowledge about standing which may be applied in the context of ergonomics. The preceding review underscores the importance of focusing on the standing worker who must simultaneously contend with multiple variables like gravity, culture, workplace constraints, physiological changes and bodies which have not evolved for many of the postures imposed on them.
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    Cio-cio-san no Yūutsu: memoirs of magnetogenesis and Turbulent Dynamo Theory
    (2013) Adams, Patrick; Osano, Bob
    The origins of cosmic magnetic fields are not as yet well understood. In this dissertation we investigate, via direct numerical simulation, the temporal evolution and behaviour of magnetic fields that are generated from absolute zero initial conditions via a thermal battery term in the Induction Equations (i.e. the Magnetogenesis problem), whilst making use of the Ideal- and Chaplygin Gas equations of state, in turn, to model the relationship between pressure and density. The dependence of the onset of dynamo action on various values of the magnetic Reynolds- and Prandtl numbers for the cases of the Roberts Flow kinematic dynamo and a flow that, in turn, incorporates both a non-helical and helical forcing function that introduces turbulence into the system is also considered via direct numerical simulation. For the purposes of the simulation work conducted, we make use of the PENCIL CODE, which is a high-order finite-difference Magnetohydrodynamical code capable of performing simulation runs in parallel using the Message Passing Interface (MPI) system for parallel processing. Theoretical results relevant to the simulations conducted are partially recovered and discussed in detail. These include, and are not limited to, the emergence of the thermal battery term in the General Ohm's Law as a consequence of the two-fluid approximation of a plasma, derivation of the Induction Equations incorporating the aforementioned battery term, introduction and discussion of the Chaplygin Gas and its place in the field of Cosmology, energetics governing the flow of kinetic- and magnetic energy during the dynamo process, the Zel'dovich stretch-twist-fold dynamo as an example of both a fast dynamo and a cornerstone underlying the operation of all dynamos and, finally, the Kazantsev Theory for small-scale, turbulent dynamos. For our magnetogenesis simulations, it is found that the magnetic fields produced undergo two distinct growth phases (the first, classified as an initial """"upshoot"""" that is possibly due to the battery term and the second, classified as an exponential growth phase), as well as two distinct phases of decay in strength, which is attributed to the effects of magnetic diffusion. This behaviour is observed for fields generated using both the Ideal- and Chaplygin Gas equations of state in turn and it is noted that the Chaplygin Gas equation of state produces magnetic fields that are of comparable strength to those produced by the Ideal Gas equation of state. Dynamo action simulations confirm the existence of a critical magnetic Reynolds number, beyond which, an initial prescribed magnetic field will grow exponentially in strength. In the case of the forced turbulence simulations, it is noted that the use of a helical forcing function greatly lowers the value of the critical magnetic Reynolds number required for the onset of guaranteed dynamo action and also produces stronger magnetic fields when compared to University of Cape Town the cases that used a non-helical forcing function. In both cases of the forced turbulence, the magnetic field is observed to saturate when its kinematic (i.e. exponential growth) phase is complete, provided that the magnetic Reynolds number is above the aforementioned critical threshold. Results of the magnetogenesis simulations are also investigated for dynamo action, and it is concluded that a type of """"kinematic dynamo"""" phase was most probably present when these fields underwent the observed phase of exponential growth.