Millisecond Pulsars, their Evolution and Applications

Millisecond pulsars (MSPs) are short-period pulsars that are distinguished from "normal" pulsars, not only by their short period, but also by their very small spin-down rates and high probability of being in a binary system. These properties are consistent with MSPs having a different evolutionary history to normal pulsars, viz., neutron-star formation in an evolving binary system and spin-up due to accretion from the binary companion. Their very stable periods make MSPs nearly ideal probes of a wide variety of astrophysical phenomena. For example, they have been used to detect planets around pulsars, to test the accuracy of gravitational theories, to set limits on the low-frequency gravitational-wave background in the Universe, and to establish pulsar-based timescales that rival the best atomic-clock timescales in long-term stability. MSPs also provide a window into stellar and binary evolution, often suggesting exotic pathways to the observed systems. The X-ray accretion-powered MSPs, and especially those that transition between an accreting X-ray MSP and a non-accreting radio MSP, give important insight into the physics of accretion on to highly magnetised neutron stars.Comment: Has appeared in Journal of Astrophysics and Astronomy special issue on 'Physics of Neutron Stars and Related Objects', celebrating the 75th birth-year of G. Srinivasa

Top Quark Spin Correlations at the Tevatron

Recent measurements of the correlation between the spin of the top and the spin of the anti-top quark produced in proton anti-proton scattering at a centre of mass energy of 1.96 TeV by the CDF and D0 collaborations are discussed. Using up to 4.3 fb^-1 of data taken with the CDF and D0 detectors the spin correlation parameter C, the degree to which the spins are correlated, is measured in dileptonic and semileptonic final states. The measurements are found to be in agreement with Standard Model predictions.Comment: 8 pages, 5 figures, talk presented at TOP2010, Bruges, Belgiu

Real-Time Planning with Primitives for Dynamic Walking over Uneven Terrain

We present an algorithm for receding-horizon motion planning using a finite family of motion primitives for underactuated dynamic walking over uneven terrain. The motion primitives are defined as virtual holonomic constraints, and the special structure of underactuated mechanical systems operating subject to virtual constraints is used to construct closed-form solutions and a special binary search tree that dramatically speed up motion planning. We propose a greedy depth-first search and discuss improvement using energy-based heuristics. The resulting algorithm can plan several footsteps ahead in a fraction of a second for both the compass-gait walker and a planar 7-Degree-of-freedom/five-link walker.Comment: Conference submissio

A re-evaluation of M. prototuberculosis

It has been suggested that a group of smooth tubercle bacilli, isolated from patients with tuberculosis and associated with Djibouti, East Africa, along with the seven species and subspecies that are traditional members of the Mycobacterium tuberculosis complex, should be considered a single species. This suggestion is based on the sequence similarity of the16S rRNA and segments of six housekeeping genes. The very concept of bacterial species is now subject to debate, and I follow the lead of Maynard Smith, who, in a review of the bacterial species concept, suggested that using genetic distance to define bacterial species was “arbitrary and of little merit”. If defining a species by sequence diversity alone is controversial, then it is important to carefully examine the recent claim that strains of M. tuberculosis are descendants and members of a much more ancient and large bacterial species called Mycobacterium prototuberculosis. Furthermore, given the importance of M. tuberculosis as a human pathogen and the implications for research, it is important to verify the claim that our remote hominid ancestors may have suffered from tuberculosis and that the tubercle bacilli originated in Africa