Measuring the coefficient of restitution for all six degrees of freedom

The coefficient of restitution is a cornerstone empirical parameter of any model where energy is dissipated by particle collisions. However, completely determining this parameter experimentally is challenging, as upon collision, a particle’s material properties (such as roughness, sphericity and shape) or minor imperfections, can cause energy to be shifted to other translational or rotational components. When all degrees of freedom are not resolved, these shifts in energy can easily be mistaken for dissipated energy, affecting the derivation of the coefficient of restitution. In the past, these challenges have been highlighted by a large scatter in values of experimental data for the restitution coefficient. In the present study, a novel experimental procedure is presented, determining all six degrees of freedom of a single, spherical, nylon particle, dropped on a glass plate. This study highlights that only by using all six degrees of freedom, can a single reliable and consistent coefficient of restitution be obtained for all cases and between subsequent collisions

Supercurrent diode effect in thin film Nb tracks

We demonstrate nonreciprocal critical current in 65 nm thick polycrystalline and epitaxial Nb thin films patterned into tracks. The nonreciprocal behavior gives a supercurrent diode effect, where the current passed in one direction is a supercurrent and the other direction is a normal state (resistive) current. We study the variation of the diode effect with temperature and magnetic field, and find an unexpected dependence with the width of the Nb tracks from 2-10 $\mu$m. For both polycrystalline and epitaxial samples, we find that tracks of width 4 $\mu$m provides the largest supercurrent diode efficiency of up to $\approx30\%$, with the effect reducing or disappearing in the widest tracks of 10 $\mu$m. It is anticipated that the supercurrent diode will become a ubiquitous component of the superconducting computer.Comment: 15 pages, 4 figure

Modification of perpendicular magnetic anisotropy and domain wall velocity in Pt/Co/Pt by voltage-induced strain

The perpendicular magnetic anisotropy Keff, magnetization reversal, and field-driven domain wall velocity in the creep regime are modified in Pt/Co(0.85–1.0 nm)/Pt thin films by strain applied via piezoelectric transducers. Keff, measured by the extraordinary Hall effect, is reduced by 10 kJ/m3 by tensile strain out-of-plane ez5931024, independently of the film thickness, indicating a dominant volume contribution to the magnetostriction. The same strain reduces the coercive field by 2–4 Oe, and increases the domain wall velocity measured by wide-field Kerr microscopy by 30-100%, with larger changes observed for thicker Co layers. We consider how strain-induced changes in the perpendicular magnetic anisotropy can modify the coercive field and domain wall velocity

The Risk Game: a critical discourse perspective on the construction and transference of pensions risk

Financial retirement risk is one of the biggest dilemmas faced by individuals and societies in late modernity. It is an unintended consequence of over fifty years of social, scientific and economic development. These have produced ageing citizens, who spend too much and save too little. In response, economists argue that more of the State's pension risk must be transferred to the individual. To achieve this, the UK Government introduced auto-enrolment workplace pension policy to 'nudge' spenders into becoming savers. In this thesis, I use this change in legislation to explore what happens when the libertarian paternalism, implicit in behavioural economic theory, enters the real world. Adopting a sociological approach through critical discourse analysis, I explore the different interpretations of financial risk constituted by the State, media, employers and employees. The study traces how the State has attempted to transfer financial risks onto individuals through a process labelled the risk game. This involves constructing and legitimising discourses of winners versus losers, spenders versus savers and experts versus lay people. However, the risk game is not straightforward. Other participants, such as the press, employees and employers, play with the discourses government set in motion and through their discursive reinterpretations, they attempt to transfer the risk onto the other players, including the government. The discursive strategies adopted include: the passive matching effect, used by employees to pass the responsibility to the employer; and the avoidance effect, where employees return the risk to the State in a new form. Other employees actively choose to play by different rules, using the operative visualization of risk, through discourses of long-term vision and self-reflexive action. Understood as the risk game, this thesis reveals flaws in the implementation of the government's auto-enrolment pension policy. Informed by Beck’s theories, the thesis concludes that rather than nudging individuals, the State can only transfer responsibility for risk through coercion or with the recipient’s understanding and active engagement. This has implications for pension policy and the pensions industry and casts doubt on the prevailing economic theory that spenders can be nudged into becoming savers

Convergence of the Generalized Volume Averaging Method on a Convection-Diffusion Problem: A Spectral Perspective

A mixed formulation is proposed and analyzed mathematically for coupled convection-diffusion in heterogeneous medias. Transfer in solid parts driven by pure diffusion is coupled with convection-diffusion transfer in fluid parts. This study is carried out for translation-invariant geometries (general infinite cylinders) and unidirectional flows. This formulation brings to the fore a new convection-diffusion operator, the properties of which are mathematically studied: its symmetry is first shown using a suitable scalar product. It is proved to be self-adjoint with compact resolvent on a simple Hilbert space. Its spectrum is characterized as being composed of a double set of eigenvalues: one converging towards −∞ and the other towards +∞, thus resulting in a nonsectorial operator. The decomposition of the convection-diffusion problem into a generalized eigenvalue problem permits the reduction of the original three-dimensional problem into a two-dimensional one. Despite the operator being nonsectorial, a complete solution on the infinite cylinder, associated to a step change of the wall temperature at the origin, is exhibited with the help of the operator’s two sets of eigenvalues/eigenfunctions. On the computational point of view, a mixed variational formulation is naturally associated to the eigenvalue problem. Numerical illustrations are provided for axisymmetrical situations, the convergence of which is found to be consistent with the numerical discretization

The Risk Game: a critical discourse perspective on the construction and transference of pensions risk

Financial retirement risk is one of the biggest dilemmas faced by individuals and societies in late modernity. It is an unintended consequence of over fifty years of social, scientific and economic development. These have produced ageing citizens, who spend too much and save too little. In response, economists argue that more of the State's pension risk must be transferred to the individual. To achieve this, the UK Government introduced auto-enrolment workplace pension policy to 'nudge' spenders into becoming savers. In this thesis, I use this change in legislation to explore what happens when the libertarian paternalism, implicit in behavioural economic theory, enters the real world. Adopting a sociological approach through critical discourse analysis, I explore the different interpretations of financial risk constituted by the State, media, employers and employees. The study traces how the State has attempted to transfer financial risks onto individuals through a process labelled the risk game. This involves constructing and legitimising discourses of winners versus losers, spenders versus savers and experts versus lay people. However, the risk game is not straightforward. Other participants, such as the press, employees and employers, play with the discourses government set in motion and through their discursive reinterpretations, they attempt to transfer the risk onto the other players, including the government. The discursive strategies adopted include: the passive matching effect, used by employees to pass the responsibility to the employer; and the avoidance effect, where employees return the risk to the State in a new form. Other employees actively choose to play by different rules, using the operative visualization of risk, through discourses of long-term vision and self-reflexive action. Understood as the risk game, this thesis reveals flaws in the implementation of the government's auto-enrolment pension policy. Informed by Beck’s theories, the thesis concludes that rather than nudging individuals, the State can only transfer responsibility for risk through coercion or with the recipient’s understanding and active engagement. This has implications for pension policy and the pensions industry and casts doubt on the prevailing economic theory that spenders can be nudged into becoming savers

The abstract boundary---a new approach to singularities of manifolds

A new scheme is proposed for dealing with the problem of singularities in General Relativity. The proposal is, however, much more general than this. It can be used to deal with manifolds of any dimension which are endowed with nothing more than an affine connection, and requires a family \calc\ of curves satisfying a {\em bounded parameter property} to be specified at the outset. All affinely parametrised geodesics are usually included in this family, but different choices of family \calc\ will in general lead to different singularity structures. Our key notion is the {\em abstract boundary\/} or {\em $a$-boundary\/} of a manifold, which is defined for any manifold \calm\ and is independent of both the affine connection and the chosen family \calc\ of curves. The $a$-boundary is made up of equivalence classes of boundary points of \calm\ in all possible open embeddings. It is shown that for a pseudo-Riemannian manifold (\calm,g) with a specified family \calc\ of curves, the abstract boundary points can then be split up into four main categories---regular, points at infinity, unapproachable points and singularities. Precise definitions are also provided for the notions of a {\em removable singularity} and a {\em directional singularity}. The pseudo-Riemannian manifold will be said to be singularity-free if its abstract boundary contains no singularities. The scheme passes a number of tests required of any theory of singularities. For instance, it is shown that all compact manifolds are singularity-free, irrespective of the metric and chosen family \calc.Comment: 40 pages (amslatex) + 5 uuencoded figures (A postscript version is also available on http://einstein.anu.edu.au/), CMA Maths. Research Report No. MRR028-9