Why do tall herbs rarely dominate Tasmanian alpine vegetation? Evidence from islands in the Ouse River system

Tall alpine herb field is largely absent from the Tasmanian alpine zone. This absence has been attributed to marsupial grazing. Small islands in the upper Ouse River valley are partly dominated by Craspedia paludicola, a showy tall alpine herb. The herbs dominate on the upstream ends of the islands. The surrounding vegetation on the banks is mainly grassland. The tall herbs are a very minor element of the shore vegetation, occurring on the undercut banks. Grassy islands close to the river banks are grazed and few tall herbs are found there. Craspedia paludicola also occurs in small numbers in damp areas on grassy heaths at other grazed locations, largely within bushes with pungent leaves. The distribution of Craspedia paludicola suggests that it is highly palatable and can thus only survive in larger numbers away from the influence of vertebrate grazers (rabbits and marsupials). It appears that this species requires both disturbance and a lack of grazing to dominate an area

Synchrotron brightness distribution of turbulent radio jets

Radio jets are considered as turbulent mixing regions and it is proposed that the essential small scale viscous dissipation in these jets is by emission of MHD waves and by their subsequent strong damping due, at least partly, to gyro-resonant acceleration of supra-thermal particles. A formula relating the synchrotron surface brightness of a radio jet to the turbulent power input is deduced from physical postulates, and is tested against the data for NGC315 and 3C31 (NGC383). The predicted brightness depends essentially on the collimation behavior of the jet, and, to a lesser extent, on the CH picture of a 'high' nozzle with accelerating flow. The conditions for forming a large scale jet at a high nozzle from a much smaller scale jet are discussed. The effect of entrainment on the prediction is discussed with the use of similarity solutions. Although entrainment is inevitably associated with the turbulent jet, it may or may not be a dominant factor depending on the ambient density profile

Homoeopathy

Homoeopathy is a system of treating patients using very low dose preparations according to the principle: "like should be cured with like". This paper summarises the research evidence presented in a recent issue of Effective Health Care on the effectiveness of homoeopathy. Increasing numbers of patients are seeking information on complementary medicines from NHS health professionals. Results of a 1998 survey of use and expenditure on complementary medicine in England suggested that 28% of respondents had either visited a complementary therapist or had purchased an over the counter herbal or homoeopathic remedy in the past year. From this survey it was estimated that there could be over 470 000 recent users of homoeopathic remedies in England

A Comprehensive Radio and Optical Study of Abell 2256: Activity from an Infalling Group

Abell 2256 is a nearby (z~0.06), rich cluster of galaxies with fascinating observed properties across a range of wavelengths. Long believed to represent a cluster merger, recent X-ray and optical results have suggested that in addition to the primary cluster and subcluster there is evidence for a third, poorer system. We present wide-field, high sensitivity 1.4 GHz VLA radio observations of Abell 2256 in conjunction with optical imaging and additional spectroscopy. Over 40 cluster radio galaxies are identified, with optical spectroscopy indicating the emission source (star formation or AGN) for most of them. While the overall fraction of galaxies exhibiting radio emission is consistent with a large sample of other nearby clusters, we find an increase in the activity level of galaxies belonging to the third system (hereafter, the ``Group''). Specifically, the Group has relatively more star formation than both the primary cluster and main subcluster. The position of the Group is also coincident with the observed cluster radio relic. We suggest that the Group recently (~0.3 Gyr) merged with the primary cluster and that this merger, not the ongoing merger of the primary and the main subcluster, might be responsible for many of the unusual radio properties of Abell 2256. Furthermore, the greater star formation activity of the Group suggests that the infall of groups is an important driver of galaxy evolution in clusters.Comment: 21 pages plus 13 JPEG figures; to appear in the Astronomical Journa

Neutrino production through hadronic cascades in AGN accretion disks

We consider the production of neutrinos in active galactic nuclei (AGN) through hadronic cascades. The initial, high energy nucleons are accelerated in a source above the accretion disk around the central black hole. From the source, the particles diffuse back to the disk and initiate hadronic cascades. The observable output from the cascade are electromagnetic radiation and neutrinos. We use the observed diffuse background X-ray luminosity, which presumably results {}from this process, to predict the diffuse neutrino flux close to existing limits from the Frejus experiment. The resulting neutrino spectrum is $E^{-2}$ down to the \GeV region. We discuss modifications of this scenario which reduce the predicted neutrino flux.Comment: 12 Pages, LaTeX, TK 92 0

A new list of extra-galactic radio jets

A catalogue of extra-galactic jets is very useful both in observational and theoretical studies of active galaxies. With the use of new powerful radio instruments, the detailed structures of very compact or weak radio sources are investigated observationally and many new radio jets are detected. In this paper, we give a list of 661 radio sources with detected radio jets known to us prior to the end of December 2000. All references are collected for the observations of jets in radio, IR, optical, UV and X-ray wave-bands.Comment: 43 pages, 1 figur

Density Evolution in the New Modified Chaplygin Gas Model

In this paper, we have considered new modified Chaplygin gas (NMCG) model which interpolates between radiation at early stage and $\Lambda$CDM at late stage. This model is regarded as a unification of dark energy and dark matter (with general form of matter). We have derived the density parameters from the equation of motion for the interaction between dark energy and dark matter. Also we have studied the evolution of the various components of density parameters.Comment: 6 Latex pages, 4 figures, RevTex styl

Weak gravitational lensing with the Square Kilometre Array

We investigate the capabilities of various stages of the SKA to perform world-leading weak gravitational lensing surveys. We outline a way forward to develop the tools needed for pursuing weak lensing in the radio band. We identify the key analysis challenges and the key pathfinder experiments that will allow us to address them in the run up to the SKA. We identify and summarize the unique and potentially very powerful aspects of radio weak lensing surveys, facilitated by the SKA, that can solve major challenges in the field of weak lensing. These include the use of polarization and rotational velocity information to control intrinsic alignments, and the new area of weak lensing using intensity mapping experiments. We show how the SKA lensing surveys will both complement and enhance corresponding efforts in the optical wavebands through cross-correlation techniques and by way of extending the reach of weak lensing to high redshift.Comment: 19 pages, 6 figures. Cosmology Chapter, Advancing Astrophysics with the SKA (AASKA14) Conference, Giardini Naxos (Italy), June 9th-13th 201

Scattering in the vicinity of relativistic jets: a method for constraining jet parameters

Relativistic jets of radio loud active galactic nuclei (AGN) produce highly directed, intense beams of radiation. A fraction of this beamed radiation scatters on the thermal plasma generally surrounding an AGN. The morphology of the scattered emission can thus provide constraints on the physical properties of the jet. We present a model to study the feasibility of constraining the parameters of a jet, especially its inclination angle and bulk Lorentz factor in this way. We apply our model to the well studied jet of M87 and the surrounding diffuse gas and find that the observational limits of the surface brightness measured in the region of the putative counterjet provide the tightest constraints on the jet parameters consistent with constraints derived by other methods. We briefly discuss the applicability of our model to other sources exhibiting relativistic motionsComment: 17 pages, 15 figures, to appear in A&A, 420, 33 (2004