Large scale gas sloshing out to half the virial radius in the strongest cool core REXCESS galaxy cluster, RXJ2014.8-2430

We search the cool core galaxy clusters in the REXCESS sample for evidence of large scale gas sloshing, and find clear evidence for sloshing in RXJ2014.8-2430, the strongest cool core cluster in the REXCESS cluster sample. The residuals of the surface brightness distribution from the azimuthal average for RXJ2014 show a prominent swirling excess feature extending out to an abrupt surface brightness discontinuity at 800 kpc from the cluster core (half the virial radius) to the south, which the XMM-Newton observations confirm to be cold, low entropy gas. The gas temperature is significantly higher outside this southern surface brightness discontinuity, indicating that this is a cold front 800 kpc from the cluster core. Chandra observations of the central 200 kpc show two clear younger cold fronts on opposite sides of the cluster. The scenario appears qualitatively consistent with simulations of gas sloshing due to minor mergers which raise cold, low entropy gas from the core to higher radius, resulting in a swirling distribution of opposing cold fronts at increasing radii. However the scale of the observed sloshing is much larger than that which has been simulated at present, and is similar to the large scale sloshing recently observed in the Perseus cluster and Abell 2142.Comment: 5 pages, 5 figures. Accepted for publication in MNRA

An XMM-Newton view of the merging activity in the Centaurus cluster

We report the results of XMM-Newton observations of the regions around the core of the Centaurus cluster where evidence for merging activity between the subgroup Cen 45 and the main Centaurus cluster has previously been observed using ASCA and ROSAT data. We confirm the ASCA findings of a temperature excess surrounding Cen 45. We find that this temperature excess can be explained using simple shock heating given the large line of sight velocity difference between Cen 45 and the surrounding main Centaurus cluster. We find that there is a statistically significant excess in metallicity around Cen 45, showing that Cen 45 has managed to retain its gas as it has interacted with the main Centaurus cluster. There is a pressure excess to the east in the direction of the merger, and there is also an entropy excess around the central galaxy of Cen 45. The metallicity between 50-100 kpc to the north of NGC 4696 is higher than to the south, which may be the result of the asymmetric distribution of metals due to previous sloshing of the core, or which may be associated with the filamentary structure we detect between NGC 4696 and NGC 4696B.Comment: 11 pages, 12 figures. Accepted for publication in MNRA

Constraining gas motions in the Centaurus cluster using X-ray surface brightness fluctuations and metal diffusion

We compare two different methods of constraining the characteristic velocity and spatial scales of gas motions in the X-ray bright, nearby Centaurus cluster, using new deep (760ks) Chandra observations. The power spectrum of excess surface brightness fluctuations in the 0.5-6.0 keV band in a sector to the west is measured and compared to theoretical expectations for Kolmogorov index fluctuations. The observed power spectrum is flatter than these expectations, and the surface brightness fluctuations are around the 8 percent level on length scales of 2 kpc. We convert the 2D power spectrum of fluctuations into a 3D power spectrum using the method of Churazov et al., and then convert this into constraints on the one-component velocity of the gas motions as a function of their length scale. We find one-component velocities in the range 100-150 km/s on spatial scales of 4-10 kpc. An independent constraint on the characteristic velocity and length scales of the gas motions is then found by considering the diffusion coefficient needed to explain the distribution of metals in the Centaurus cluster, combined with the need to balance the rate of gas cooling with the rate of heat dissipated by the gas motions. We find that these two methods of constraining the velocity and length scales of the gas motions are in good agreement.Comment: 8 pages, 7 figures. Accepted for publication in MNRA

Fluid mechanical model of the Helmholtz resonator

A semi-empirical fluid mechanical model of the acoustic behavior of Helmholtz resonators is presented which predicts impedance as a function of the amplitude and frequency of the incident sound pressure field and resonator geometry. The model assumes that the particle velocity approaches the orifice in a spherical manner. The incident and cavity sound fields are connected by solving the governing oscillating mass and momentum conservation equations. The model is in agreement with the Rayleigh slug-mass model at low values of incident sound pressure level. At high values, resistance is predicted to be independent of frequency, proportional to the square root of the amplitude of the incident sound pressure field, and virtually independent of resonator geometry. Reactance is predicted to depend in a very complicated way upon resonator geometry, incident sound pressure level, and frequency. Nondimensional parameters are defined that divide resonator impedance into three categories corresponding to low, moderately low, and intense incident sound pressure amplitudes. The two-microphone method was used to measure the impedance of a variety of resonators. The data were used to refine and verify the model

X-ray exploration of the outskirts of the nearby Centaurus cluster using Suzaku and Chandra

We present Suzaku observations of the Centaurus cluster out to 0.95r200, taken along a strip to the north west. We have also used congruent Chandra observations of the outskirts to resolve point sources down to a threshold flux around 7 times lower than that achievable with just Suzaku data, considerably reducing the systematic uncertainties in the cosmic X-ray background emission in the outskirts. We find that the temperature decreases by a factor of 2 from the peak temperature to the outskirts. The entropy profile demonstrates a central excess (within 0.5r200) over the baseline entropy profile predicted by simulations of purely gravitational hierarchical structure formation. In the outskirts the entropy profile is in reasonable agreement with the baseline entropy profile from Voit et al., but lies slightly below it. We find that the pressure profile agrees with the universal pressure profile of Arnaud et al. but lies slightly above it in the outskirts. The excess pressure and decrement in entropy in the outskirts appear to be the result of an excess in the measured gas density, possible due to gas clumping biasing the density measurements high. The gas mass fraction rises and reaches the mean cosmic baryon fraction at the largest radius studied. The clumping corrected gas mass fraction agrees with the expected hot gas fraction and with the simulations of Young et al. We further the analysis of Walker et al. which studied the shapes of the entropy profiles of the clusters so far explored in the outskirts with Suzaku. When scaled by the self similar entropy the Suzaku entropy profiles demonstrate a central excess over the baseline entropy profile, and are consistent with it at around r500 . However outside r500 the entropy profiles tend to lie below the baseline entropy profile.Comment: 17 pages, 15 figures. Accepted for publication in MNRA

Control of common scab without the use of water

The most effective way to control common scab is by irrigating a potato crop at tuber initiation. With the introduction of legislation such as the Water Framework Directive this will become increasingly difficult. In this field experiment, we assessed the potential of a number of non-water measures for controlling this disease. Common scab on daughter tubers at harvest was reduced by applying rapeseed meal at 1 t ha-1 to the beds and then incorporating it into the soil, and adding a mixture of Trichoderma viride isolates into the furrow at planting. None of these treatments was as effective as using water

Evidence from Rb–Sr mineral ages for multiple orogenic events in the Caledonides of Shetland, Scotland

Shetland occupies a unique central location within the North Atlantic Caledonides. Thirty-three new high-precision Rb–Sr mineral ages indicate a polyorogenic history. Ages of 723–702 Ma obtained from the vicinity of the Wester Keolka Shear Zone indicate a Neoproterozoic (Knoydartian) age and preclude its correlation with the Silurian Moine Thrust. Ordovician ages of c. 480–443 Ma obtained from the Yell Sound Group and the East Mainland Succession constrain deformation fabrics and metamorphic assemblages to have formed during Grampian accretionary orogenic events, broadly contemporaneously with orogenesis of the Dalradian Supergroup in Ireland and mainland Scotland. The relative paucity of Silurian ages is attributed to a likely location at a high structural level in the Scandian nappe pile relative to mainland Scotland. Ages of c. 416 and c. 411 Ma for the Uyea Shear Zone suggest a late orogenic evolution that has more in common with East Greenland and Norway than with northern mainland Scotland

What fraction of the density fluctuations in the Perseus cluster core is due to gas sloshing rather than AGN feedback?

Deep Chandra observations of the core of the Perseus cluster show a plethora of complex structure. It has been found that when the observed density fluctuations in the intracluster medium are converted into constraints on AGN induced turbulence, the resulting turbulent heating rates are sufficient to balance cooling locally throughout the central 220kpc. However while the signatures of AGN feedback (inflated bubbles) dominate the central 60kpc in X-ray images, beyond this radius the intracluster medium is increasingly shaped by the effects of gas sloshing, which can also produce subtle variations in X-ray surface brightness. We use mock Chandra observations of gas sloshing simulations to investigate what fraction of the observed density fluctuations in the core of the Perseus galaxy cluster may originate from sloshing rather than AGN induced feedback. Outside 60kpc, we find that the observed level of the density fluctuations is broadly consistent with being produced by sloshing alone. If this is the case, AGN-generated turbulence is likely to be insufficient in combating cooling outside 60kpc.Comment: 9 pages, 5 figures, accepted for publication in MNRA

Ca2+ transients are not required as signals for long-term neurite outgrowth from cultured sympathetic neurons

A method for clamping cytosolic free Ca2+ ([Ca2+]i) in cultures of rat sympathetic neurons at or below resting levels for several days was devised to determine whether Ca2+ signals are required for neurite outgrowth from neurons that depend on Nerve Growth Factor (NGF) for their growth and survival. To control [Ca2+]i, normal Ca2+ influx was eliminated by titration of extracellular Ca2+ with EGTA and reinstated through voltage-sensitive Ca2+ channels. The rate of neurite outgrowth and the number of neurites thus became dependent on the extent of depolarization by KCl, and withdrawal of KCl caused an immediate cessation of growth. Neurite outgrowth was completely blocked by the L type Ca2+ channel antagonists nifedipine, nitrendipine, D600, or diltiazem at sub- or micromolar concentrations. Measurement of [Ca2+]i in cell bodies using the fluorescent Ca2+ indicator fura-2 established that optimal growth, similar to that seen in normal medium, was obtained when [Ca2+]i was clamped at resting levels. These levels of [Ca2+]i were set by serum, which elevated [Ca2+]i by integral of 30 nM, whereas the addition of NGF had no effect on [Ca2+]i. The reduction of [Ca2+]o prevented neurite fasciculation but this had no effect on the rate of neurite elongation or on the number of extending neurites. These results show that neurite outgrowth from NGF-dependent neurons occurs over long periods in the complete absence of Ca2+ signals, suggesting that Ca2+ signals are not necessary for operating the basic machinery of neurite outgrowth