A study of possible temporal and latitudinal variations in the properties of the solar tachocline

Temporal variations of the structure and the rotation rate of the solar tachocline region are studied using helioseismic data from the Global Oscillation Network Group (GONG) and the Michelson Doppler Imager (MDI) obtained during the period 1995--2000. We do not find any significant temporal variation in the depth of the convection zone, the position of the tachocline or the extent of overshoot below the convection zone. No systematic variation in any other properties of the tachocline, like width, etc., is found either. Possibility of periodic variations in these properties is also investigated. Time-averaged results show that the tachocline is prolate with a variation by about 0.02R_sun in its position. The depth of the convection zone or the extent of overshoot does not show any significant variation with latitude.Comment: To appear in MNRA

“One More for Luck”: The Destruction of U971 by HMCS Haida and HMS Eskimo, 24 June 1944

On the evening of 23 June 1944, HMCS Haida and HMS Eskimo set out from Plymouth, operational base of the 10th Destroyer Flotilla (10th DF), to conduct a sweep of the Western Approaches to the English Channel. Their role was to assist in securing these waters for the ongoing delivery of supplies and reinforcements to the Normandy bridgehead. Across the Channel to the southest, American, British and Canadian forces were now in their third week of fighting across the fields and hedgerows of Normandy. Operation OVERLORD had been the largest amphibious invasion in history and, dependent as it was on the unimpeded use of the sea, required an intensive concentration of air and naval forces to protect Allied supply convoys. This naval counterpart of OVERLORD was Operation NEPTUNE, and it was as part of this massive undertaken that Haida and Eskimo now steamed out of Plymouth

A grounded theory analysis of the occupational impact of caring for a partner who has multiple sclerosis

Chronic progressive conditions such as multiple sclerosis impact engagement in and orchestration of daily occupations by people with the condition, and their family members. This qualitative study addressed the way in which multiple sclerosis can affect family life, particularly exploring how it affects the occupations of the partner of a person with the condition. The study involved in-depth interviewing and grounded theory analysis to explore the occupational nature of being a partner of someone who has multiple sclerosis. Findings reveal how partners’ occupations are affected over time, with occupational opportunities inspired by multiple sclerosis and occupational constraints provoked by the disorder, including nostalgia for an multiple sclerosis free existence, the transition to being a carer and an occupationally uncertain future

Using learned action models in execution monitoring

Planners reason with abstracted models of the behaviours they use to construct plans. When plans are turned into the instructions that drive an executive, the real behaviours interacting with the unpredictable uncertainties of the environment can lead to failure. One of the challenges for intelligent autonomy is to recognise when the actual execution of a behaviour has diverged so far from the expected behaviour that it can be considered to be a failure. In this paper we present further developments of the work described in (Fox et al. 2006), where models of behaviours were learned as Hidden Markov Models. Execution of behaviours is monitored by tracking the most likely trajectory through such a learned model, while possible failures in execution are identified as deviations from common patterns of trajectories within the learned models. We present results for our experiments with a model learned for a robot behaviour

Information Equation of State

Landauer's principle is applied to information in the universe. Once stars began forming, the increasing proportion of matter at high stellar temperatures compensated for the expanding universe to provide a near constant information energy density. The information equation of state was close to the dark energy value, w = -1, for a wide range of redshifts, 10> z >0.8, over one half of cosmic time. A reasonable universe information bit content of only 10^87 bits is sufficient for information energy to account for all dark energy. A time varying equation of state with a direct link between dark energy and matter, and linked to star formation in particular, is clearly relevant to the cosmic coincidence problem.In answering the "Why now?" question we wonder "What next?" as we expect the information equation of state to tend towards w = 0 in the future.Comment: 10 pages, 2 figure

On the magnetic field required for driving the observed angular-velocity variations in the solar convection zone

A putative temporally varying circulation-free magnetic-field configuration is inferred in an equatorial segment of the solar convection zone from the helioseismologically inferred angular-velocity variation, assuming that the predominant dynamics is angular acceleration produced by the azimuthal Maxwell stress exerted by a field whose surface values are consistent with photospheric line-of-sight measurements.Comment: to appear in MNRA

On electrostatic screening of ions in astrophysical plasmas

There has been some controversy over the expression for the so-called `interaction energy' due to screening of charged particles in a plasma. Even in the relatively simple case of weak screening, first discussed in the context of astrophysical plasmas by Salpeter (1954), there is disagreement. In particular, Shaviv and Shaviv (1996) have claimed recently that by not considering explicitly in his calculation the complete screening cloud, Salpeter obtained a result for the interaction energy between two nuclei separated by a distance $r$ which in the limit $r \to 0$ is only 2/3 the correct value. It appears that this claim has arisen from a fundamental misconception concerning the dynamics of the interaction. We rectify this misconception, and show that Salpeter's formula is indeed correct.Comment: 17 pages, no figures, AAS Latex, to appear in The Astrophysical Journa

Experimental Study of Diamond Like Carbon (DLC) Coated Electrodes for Pulsed High Gradient Electron Gun

For the SwissFEL Free Electron Laser project at the Paul Scherrer Institute, a pulsed High Gradient (HG) electron gun was used to study low emittance electron sources. Different metals and surface treatments for the cathode and anode were studied for their HG suitability. Diamond Like Carbon (DLC) coatings are found to perform exceptionally well for vacuum gap insulation. A set of DLC coated electrodes with different coating parameters were tested for both vacuum breakdown and photo electron emission. Surface electric fields over 250MV/m (350 - 400kV, pulsed) were achieved without breakdown. From the same surface, it was possible to photo-emit an electron beam at gradients up to 150MV/m. The test setup and the experimental results are presentedComment: 4 pages, 14 figures, IPMHVC 2010 : IEEE International Power Modulator and High Voltage Conferenc