Circulating Subbeam Systems and the Physics of Pulsar Emission

The purpose of this paper is to suggest how detailed single-pulse observations of ``slow'' radio pulsars may be utilized to construct an empirical model for their emission. It links the observational synthesis developed in a series of papers by Rankin starting in the 1980s to the more recent empirical feedback model of Wright (2003a) by regarding the entire pulsar magnetosphere as a non-steady, non-linear interactive system with a natural built-in delay. It is argued that the enhanced role of the outer gap in such a system indicates an evolutionary link to younger pulsars, in which this region is thought to be highly active, and that pulsar magnetospheres should no longer be seen as being ``driven'' by events on the neutron star's polar cap, but as having more in common with planetary magnetospheres and auroral phenomena.Comment: 15 pages, 3 figure

Improved laboratory gradiometer can be a field survey instrument

Improvements made to quartz gradiometer minimize or eliminate disturbing effects from known error sources and permit sensitivity of + or - 1 times 10 to the minus 9th power/sec sq or better and measuring accuracy of + or - 5 times 10 to the minus 9th power/sec sq

The `Periodic Nulls' of Radio Pulsar J1819+1305

We present a single-pulse study of the four-component pulsar J1819+1305, whose ``null'' pulses bunch at periodic intervals of around 57 times the rotation period. The emission bursts between the null bunches exhibit characteristic modulations at two shorter periodicities of approximately 6.2 and 3 times the rotation period, the former found largely in the two outer components, and the latter only in the first component. Many bursts commence with bright emission in second component, exhibit positive six-period drift across the full profile width, and end with 3-period modulation in the leading component. The 57-period cycle can be modelled geometrically as a sparsely filled subbeam carousel with nulls appearing whenever our line of sight intersects a circulating empty region. This interpretation is compatible with other recent evidence for periodic, carousel-related nulling and appears to support the physics of a polar-gap emission model for ``drifting'' subpulses, but the subtle structure of the emission bursts defies an easy explanation.Comment: 8 pages, 9 figure

The effect of milk on recovery from repeat-sprint cycling in female team-sport athletes

The consumption of milk post-eccentric exercise attenuates the effects of muscle damage in team-sport athletes. However, participation in team sport involves both concentric-eccentric loading and metabolic stress. Therefore, the aim of this study was to investigate the effects of post-exercise milk consumption on recovery from a cycling protocol designed to simulate the metabolic demands of team sport. Ten female team-sport athletes participated in a randomised cross-over investigation. Upon completion of the protocol participants consumed 500ml of milk (MILK) or 500ml of an energy-matched carbohydrate (CHO) drink. Muscle function (peak torque, rate of force development (RFD), countermovement jump (CMJ), 20m sprint, muscle soreness and tiredness, serum creatine kinase (CK), (high-sensitivity C reactive protein (hsCRP) and measures of oxidative stress (protein carbonyls (PC) and GSH:GSSG (oxidized glutathione:reduced glutathione) ratio) were determined pre-, 24h, 48h and 72h post-exercise. MILK had a possible beneficial effect in attenuating losses in peak torque (180 s) from baseline to 24h (3.2±7.8% v -6.2±7.5%, MILK v CHO) and a possible beneficial effect in minimising soreness (baseline-48h; baseline-72h) and tiredness (baseline-24h; baseline-72h). There was no change in oxidative stress following the exercise protocol, though a likely benefit of milk was observed for GSH:GSSH ratio at baseline-24h (0.369 x/÷ 1.89, 1.103 x/÷ 3.96, MILK v CHO). MILK had an unclear effect on all other variables. Consumption of 500ml milk post-repeat sprint cycling had little to no benefit in minimising losses in peak torque, or minimising increases in soreness and tiredness and had no effect on serum markers of muscle damage and inflammation

Drifting, moding, and nulling: another look at pulsar B1918+19

Arecibo observations of the conal triple pulsar B1918+19 at 0.327- and 1.4-GHz are used to analyse its subpulse behaviour in detail. We confirm the presence of three distinct drift modes (A,B,C) plus a disordered mode (N) and show that they follow one another in specific cycles. Interpreting the pulsar's profile as resulting from a sightline traverse which cuts across an outer cone and tangentially grazes an inner cone, we demonstrate that the phase modulation of the inner cone is locked to the amplitude modulation of the outer cone in all the drift modes. The 9% nulls are found to be largely confined to the dominant B and N modes, and, in the N mode, create alternating bunches of nulls and emission in a quasi-periodic manner with an averaged fluctuation rate of about 12 rotation periods ($P_1$). We explore the assumption that the apparent drift is the first alias of a faster drift of subbeams equally spaced around the cones. This is shown to imply that all modes A, B and C have a common circulation time of 12 $P_1$ and differ only in the number of subbeams. This timescale is on the same order as predicted by the classic {\bf E}$\times${\bf B} drift and also coincides with the N-mode modulation. We therefore arrive at a picture where the circulation speed remains roughly invariant while the subbeams progressively diminish in number from modes A to B to C, and are then re-established during the N mode. We suggest that aliasing combined with subbeam loss may be responsible for apparently dramatic changes in drift rates in other pulsars