RXTE and ASCA Constraints on Non-thermal Emission from the A2256 Galaxy Cluster

An 8.3 hour observation of the Abell 2256 galaxy cluster using the Rossi X-ray Timing Explorer proportional counter array produced a high quality spectrum in the 2 - 30 keV range. Joint fitting with the 0.7 - 11 keV spectrum obtained with the Advanced Satellite for Astrophysics and Cosmology gas imaging spectrometer gives an upperlimit of 2.3x10^-7 photons/cm^2/sec/keV for non-thermal emission at 30 keV. This yields a lower limit to the mean magnetic field of 0.36 micro Gauss (uG) and an upperlimit of 1.8x10^-13 ergs/cm^3 for the cosmic-ray electron energy density. The resulting lower limit to the central magnetic field is ~1 - 3 uG While a magnetic field of ~0.1 - 0.2 uG can be created by galaxy wakes, a magnetic field of several uG is usually associated with a cooling flow or, as in the case of the Coma cluster, a subcluster merger. However, for A2256, the evidence for a merger is weak and the main cluster shows no evidence of a cooling flow. Thus, there is presently no satisfactory hypothesis for the origin of an average cluster magnetic field as high as >0.36 uG in the A2256 cluster.Comment: 8 pages, Astrophysical Journal (in press

Radio jet refraction in galactic atmospheres with static pressure gradients

A theory of double radio sources which have a 'Z' or 'S' morphology is proposed, based on the refraction of radio jets in the extended atmosphere of an elliptical galaxy. The model describes a collimated jet of supersonic material bending self-consistently under the influence of external static pressure gradients. Gravity and magnetic fields are neglected in the simplest case except insofar as they determine the static pressure distribution. The calculation is a straightforward extension of a method used to calculate a ram-pressure model for twin radio trails ('C' morphology). It may also be described as a continuous-jet version of a buoyancy model proposed in 1973. The model has the added virtue of invoking a galactic atmosphere similar to those already indicated by X-ray measurements of some other radio galaxies and by models for the collimation of other radio jets

Precision Cosmology? Not Just Yet

The recent announcement from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite experiment combined with other recent advances in observational cosmology verifies key components of the standard cosmological model. However, we argue that there remain some significant open issues regarding the basic history and composition of the Universe and uncertainties in some of the most important parameters.Comment: 2 pages, 2 figures. Online journal version http://www.sciencemag.org/cgi/content/full/299/5612/153

The dangers of irreversibility in an age of increased uncertainty: revisiting plasticity in invertebrates

Plasticity in traits in response to environmental conditions can increase fitness, expanding the range of environments within which a genotype can generate viable and productive phenotypes, and therefore when and where populations can persist and diversify in ecological space. Adaptive forms of plasticity in invertebrates are diverse, ranging from polyphenism and diapause to behavioural thermoregulation and optimal foraging. Local patterns of environmental variation and developmental constraints will dictate which of these forms evolves. Here we review the core idea that the use of narrow developmental windows by invertebrates to attain specific types of phenotypic changes reduces their reversibility, while increasing their magnitude. These tradeoffs dictate the costs and effectiveness of plasticity in buffering environmental variation. In particular, plastic responses to narrow developmental or environmental windows increase fitness costs when predicted environmental challenges do not materialise, or when the environment changes in unpredictable ways. We then explore the converse idea that increasing trait reversibility depends on extending the period for which genotypes are sensitive to the environment, but also narrows the range of plastic phenotypes that can be generated. Considering these findings together, we would expect that the costs, benefits and constraints of reversible versus irreversible plasticity affect the rate and magnitude of adaptive responses to rapidly changing and novel environments. However, such predictions have rarely been tested or included in theoretical models. Identifying this knowledge gap leads us to propose new research directions to provide a deeper understanding of the evolution of plasticity in invertebrates and other organisms. We illustrate these possible directions through examples of Drosophila adapting to thermal stress

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

Asymmetry of jets, lobe size and spectral index in radio galaxies and quasars

We investigate the correlations between spectral index, jet side and extent of the radio lobes for a sample of nearby FRII radio galaxies. In Dennett-Thorpe et al. (1997) we studied a sample of quasars and found that the high surface brightness regions had flatter spectra on the jet side (explicable as a result of Doppler beaming) whilst the extended regions had spectral asymmetries dependent on lobe length. Unified schemes predict that asymmetries due to beaming will be much smaller in narrow-line radio galaxies than in quasars: we therefore investigate in a similar manner, a sample of radio galaxies with detected jets. We find that spectral asymmetries in these objects are uncorrelated with jet sidedness at all brightness levels, but depend on relative lobe volume. Our results are not in conflict with unified schemes, but suggest that the differences between the two samples are due primarily to power or redshift, rather than to orientation. We also show directly that hotspot spectra steepen as a function of radio power or redshift. Whilst a shift in observed frequency due to the redshift may account for some of the steepening, it cannot account for all of it, and a dependence on radio power is required.Comment: accepted for publication in MNRAS, 10 pages; typos/minor correctio

Model wine solutions: Colour and composition changes during ageing

The interaction between malvidin 3-glucoside, the main anthocyanin in red wine made from Vitis vinifera grapes, and (+)-catechin and the effect on this interaction of ferric ions and acetaldehyde was examined. In the models not containing acetaldehyde losses of malvidin 3-glucoside were observed, but there were only negligible losses of catechin; no new compounds were observed. In the presence of acetaldehyde the formation of new compounds was determined by high performance liquid chromatography; this formation coincided with rapid losses in the concentrations of malvidin 3-glucoside and catechin. A molecular ion at m/z 809 was determined by FAB MS, corresponding to a dimer consisting of malvidin 3-glucoside linked to catechin by an acetaldehyde bridge, according to a mechanism previously suggested by TIMBER-LAKE and BRIDLE (1976). Concurrent with the losses in anthocyanins, qualitative and quantitative changes in visible colour were also observed, consisting of changes in the wavelength of maximum absorbance (λmax) and in maximum absorbance intensity (Amax). Models containing malvidin 3-glucoside plus catechin or catechin plus ferric ions showed a marked decrease in their λmax from 525 nm to 440 nm; there was little net effect of the ferric ions on these changes. The model containing acetaldehyde showed a large increase in Amax while the λmax showed a bathochromic shift from 524 nm to 557 nm; colour decreased after achieving a maximum and the λmax decreased slightly. Changes in colour monitored by measuring hue angle, chroma and L* value are also reported

Model wine solutions: Effect of sulphur dioxide on colour and composition during ageing

The effect of sulphur dioxide and acetaldehyde on the interaction between malvidin 3-glucoside, the main anthocyanin in red wine made from Vitis vinifera grapes, and (+)-catechin was examined. In all model wines the molar losses of malvidin 3-glucoside were significantly greater than the losses of catechin. The concentration of malvidin 3-glucoside decreased fastest in the presence of acetaldehyde while the most rapid loss of catechin occurred in the model containing malvidin 3-glucoside and catechin only. In the presence of sulphur dioxide, these losses still occurred, but much more slowly, indicating that condensation reactions may take place even in the presence of sulphur dioxide. Polymerisation was most prominent in the model containing malvidin 3-glucoside, catechin and acetaldehyde. Concurrent with the losses in anthocyanin and catechin, qualitative and quantitative changes in visible colour were also observed. Changes in colour monitored by measuring hue angle and chroma are also reported

Improving Search through A3C Reinforcement Learning based Conversational Agent

We develop a reinforcement learning based search assistant which can assist users through a set of actions and sequence of interactions to enable them realize their intent. Our approach caters to subjective search where the user is seeking digital assets such as images which is fundamentally different from the tasks which have objective and limited search modalities. Labeled conversational data is generally not available in such search tasks and training the agent through human interactions can be time consuming. We propose a stochastic virtual user which impersonates a real user and can be used to sample user behavior efficiently to train the agent which accelerates the bootstrapping of the agent. We develop A3C algorithm based context preserving architecture which enables the agent to provide contextual assistance to the user. We compare the A3C agent with Q-learning and evaluate its performance on average rewards and state values it obtains with the virtual user in validation episodes. Our experiments show that the agent learns to achieve higher rewards and better states.Comment: 17 pages, 7 figure

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