Spinor algebra and null solutions of the wave equation

In this paper we exploit the ideas and formalisms of twistor theory, to show how, on Minkowski space, given a null solution of the wave equation, there are precisely two null directions in $\ker df$, at least one of which is a shear-free ray congruence

Weierstrass representations for harmonic morphisms on Euclidean spaces and spheres

We construct large families of harmonic morphisms which are holomorphic with respect to Hermitian structures by finding heierarchies of Weierstrass-type representations. This enables us to find new examples of complex-valued harmonic morphisms from Euclidean spaces and spheres.Comment: Minor revision adding example. Latex 2.09. 14 page

Twistor theory on a finite graph

We show how the description of a shear-free ray congruence in Minkowski space as an evolving family of semi-conformal mappings can naturally be formulated on a finite graph. For this, we introduce the notion of holomorphic function on a graph. On a regular coloured graph of degree three, we recover the space-time picture. In the spirit of twistor theory, where a light ray is the more fundamental object from which space-time points should be derived, the line graph, whose points are the edges of the original graph, should be considered as the basic object. The Penrose twistor correspondence is discussed in this context

A Survey of Ring Baffle Damping in Cylindrical Tanks

Survey of Miles method for determination of damping by ring baffles in cylindrical tank

Characterising and Testing Deep UV LEDs for Use in Space Applications

Deep ultraviolet (DUV) light sources are used to neutralise isolated test masses in highly sensitive space-based gravitational experiments. An example is the LISA Pathfinder charge management system, which uses low-pressure mercury lamps. A future gravitational-wave observatory such as eLISA will use UV light-emitting diodes (UV LEDs), which offer numerous advantages over traditional discharge lamps. Such devices have limited space heritage but are are now available from a number of commercial suppliers. Here we report on a test campaign that was carried out to quantify the general properties of three types of commercially available UV LEDs and demonstrate their suitability for use in space. Testing included general electrical and UV output measurements, spectral stability, pulsed performance, temperature dependence as well as thermal vacuum, radiation and vibration survivability

Friends with Benefits: Other Regard in Epicurean Ethics

Friendship and hedonism are both major components of Epicureanism. I attempt to relieve the tension that seems to follow from endorsing both of these. I argue that Epicurean friendships require valuing a friend’s well-being in the same way as one’s own and that embarking on such friendships is what David Schmidtz terms a maieutic end – one that is achieved by taking on a new set of ends. This conception fits with other-regarding concern that is espoused throughout the Epicurean texts discussing friendship and, as I argue, remains consistent with other psychological and ethical commitments of Epicureanism