Matthew G. Walker

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Cooperative robotic systems provide design and implementation challenges that are not easy to solve. This paper describes a parallel implementation for evolving cooperative robotic behaviour using an island model based genetic program on a cluster computer system. The application domain is robot soccer in which two robots must cooperate to avoid collisions(More)
The Milky Way has at least twenty-three known satellite galaxies that shine with luminosities ranging from about a thousand to a billion times that of the Sun. Half of these galaxies were discovered in the past few years in the Sloan Digital Sky Survey, and they are among the least luminous galaxies in the known Universe. A determination of the mass of(More)
This paper is a brief progress report on our work with two volunteers, each with 4 electrodes placed in his auditory nerve. We are performing stimulation studies to find out if multielectrode stimulation is more effective as a communication aid than single-electrode stimulation, and to gain insights on stimulus coding of environmental sound using(More)
We describe results from a new ground-based monitoring campaign on NGC 5548, the best-studied reverberation-mapped AGN. We find that it was in the lowest luminosity state yet recorded during a monitoring program, namely L 5100 ¼ 4:7 ; 10 42 ergs s À1. We determine a rest-frame time lag between flux variations in the continuum and the H line of 6:3 þ2:6 À2:3(More)
We present new observations leading to an improved black hole mass estimate for the Seyfert 1 galaxy NGC 4593 as part of a reverberation-mapping campaign conducted at the MDM Observatory. Cross-correlation analysis of the H emission-line light curve with the optical continuum light curve reveals an emission-line time delay of cent ¼ 3:73 AE 0:75 days. By(More)
We have undertaken a new ground-based monitoring campaign to improve the estimates of the mass of the central black hole in NGC 4151. We measure the lag time of the broad H line response compared to the optical continuum at 5100 8 and find a lag of 6:6 þ1:1 À0:8 days. We combine our data with the recent reanalysis of UVemission lines by Metzroth and(More)
In the standard cosmological model, the Universe consists mainly of two invisible substances: vacuum energy with constant mass-density ρv = Λ/(8πG) (where Λ is a 'cosmological constant' originally proposed by Einstein and G is Newton's gravitational constant) and cold dark matter (CDM) with mass density that is currently ρ DM,0 ∼ 0.3ρv. This 'ΛCDM' model(More)
Dark matter-only simulations of galaxy formation predict many more subhalos around a Milky Way-like galaxy than the number of observed satellites. Proposed solutions require the satellites to inhabit dark matter halos with masses 10(9)-10(10 )Msun at the time they fell into the Milky Way. Here we use a modelling approach, independent of cosmological(More)
The most common semiconductor diodes exhibiting transit-time negative resistance at microwave frequencies are those relying on avalanche breakdown at a reverse-biased p-n junction for carrier injection into a drift space. Recently, however, there has been considerable interest in the so-called BARITT (Barrier Injection Transit Time) diodes, which differ(More)
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