Comptonisation of Cosmic Microwave Background Photons in Dwarf Spheroidal Galaxies

We present theoretical modelling of the electron distribution produced by annihilating neutralino dark matter in dwarf spheroidal galaxies (dSphs). In particular, we follow up the idea of Colafrancesco (2004) and find that such electrons distort the cosmic microwave background (CMB) by the Sunyaev-Zeldovich effect. For an assumed neutralino mass of 10 GeV and beam size of 1'', the SZ temperature decrement is of the order of nano-Kelvin for dSph models with a soft core. By contrast, it is of the order of micro-Kelvin for the strongly cusped dSph models favoured by some cosmological simulations. Although this is out of reach of current instruments, it may well be detectable by future mm telescopes, such as ALMA. We also show that the upscattered CMB photons have energies within reach of upcoming X-ray observatories, but that the flux of such photons is too small to be detectable soon. Nonetheless, we conclude that searching for the dark matter induced Sunyaev-Zeldovich effect is a promising way of constraining the dark distribution in dSphs, especially if the particles are light.Comment: 10 pages, 5 figures, MNRAS, in pres

Theory of forward stimulated Brillouin scattering in dual-mode single-core fibres

Recently, stimulated Brillouin scattering in a forward direction (FSBS) in a dual-mode single-core optical fiber was reported for the first time. Frequency shifts on the order of 17 MHz were seen in fiber supporting LP01 and LP11 modes at 514.5 nm. The phenomenon is examined here in more detail, and the governing differential equations of the three-wave parametric process (involving laser pump, Brillouin signal, and acoustic flexural-wave phonon) are derived and solved. FSBS is possible because although the overlap integral between a flexural fiber mode and the light is small, the phonon lifetime is much longer than in conventional SBS. FSBS may also be the first example of a nonlinear effect which is enhanced by increasing the optical mode area at constant pump power

Application of artificial neural networks to weighted interval Kalman filtering

The interval Kalman filter is a variant of the traditional Kalman filter for systems with bounded parametric uncertainty. For such systems, modelled in terms of intervals, the interval Kalman filter provides estimates of the system state also in the form of intervals, guaranteed to contain the Kalman filter estimates of all point-valued systems contained in the interval model. However, for practical purposes, a single, point-valued estimate of the system state is often required. This point value can be seen as a weighted average of the interval bounds provided by the interval Kalman filter. This article proposes a methodology based on the application of artificial neural networks by which an adequate weight can be computed at each time step, whereby the weighted average of the interval bounds approximates the optimal estimate or estimate which would be obtained using a Kalman filter if no parametric uncertainty was present in the system model, even when this is not the case. The practical applicability and robustness of the method are demonstrated through its application to the navigation of an uninhabited surface vehicle. © IMechE 2014

On the application of a hybrid ellipsoidal-rectangular interval arithmetic algorithm to interval Kalman filtering for state estimation of uncertain systems

Modelling uncertainty is a key limitation to the applicability of the classical Kalman filter for state estimation of dynamic systems. For such systems with bounded modelling uncertainty, the interval Kalman filter (IKF) is a direct extension of the former to interval systems. However, its usage is not yet widespread owing to the over-conservatism of interval arithmetic bounds. In this paper, the IKF equations are adapted to use an ellipsoidal arithmetic that, in some cases, provides tighter bounds than direct, rectangular interval arithmetic. In order for the IKF to be useful, it must be able to provide reasonable enclosures under all circumstances. To this end, a hybrid ellipsoidal-rectangular enclosure algorithm is proposed, and its robustness is evidenced by its application to two characteristically different systems for which it provides stable estimate bounds, whereas the rectangular and ellipsoidal approaches fail to accomplish this in either one or the other case

All fibre polariser using a null coupler

We report a new fibre polariser based on a twisted null taper coupler. The best extinction ratio observed so far is 15dB

An Instrument for Rapid Mesozooplankton Monitoring at Ocean Basin Scale

The development and testing of a new imaging and classification system for mesozooplankton sampling over very large spatial and temporal scales is reported. The system has been evaluated on the Atlantic Meridional Transect (AMT), acquiring nearly one million images of planktonic particles over a transect of 13,500km. These images have been acquired at a flow rate of 12.5L per minute, in near-continuous underway mode from the ships seawater supply and in discrete mode using integrated vertical net haul samples. The aim of this development is to produce an instrument capable of delivering autonomously acquired and processed data on the biomass and taxonomic distribution of mesozooplankton over ocean-basin scales, in or near real-time, so that data are immediately available without the need for significant amounts of post-cruise processing and analysis. The hardware and image acquisition and processing software system implemented to support this development, together with some preliminary results from AMT21, are described. The images acquired during this Atlantic cruise comprise microplankton, mesoplankton, fish larvae and sampling artefacts (air bubbles, detritus, etc.), and were classified to one of 7 pre-defined taxonomic classes with 67% success