On the interaction of FR-II radio sources with the intracluster medium

The effect of the expansion of powerful FR-II radio sources into a cluster environment is discussed. The analysis considers both the thermal and temporal evolution of the ICM which has passed through the bow shock of the radio source and the effect of this swept-up gas on the dynamics of the radio source itself. The final state of the swept-up ICM is critcally dependent on the thermal conductivity of the gas. If the gas behind the bow shock expands adiabatically, and the source is expanding into a steeply falling atmosphere, then a narrow dense layer will form as the radio source lifts gas out of the cluster potential. This layer has a cooling time very much less than that of the gas just ahead of the radio source. This effect does not occur if the thermal conductivity of the gas is high, or if the cluster atmosphere is shallow. The swept-up gas also affects the dyamics of the radio source especially as it slows towards sub-sonic expansion. The preferential accumulation of the swept-up gas to the sides of the cocoon leads to the aspect ratio of the source increasing. Eventually the contact surface must become Rayleigh-Taylor unstable leading both to inflow of the swept-up ICM into the cavity created by the cocoon, but also substantial mixing of the cooler denser swept-up gas with the ambient ICM thereby creating a multi-phase ICM. The radio source is likely to have a marked effect on the cluster on timescales long compared to the age of the source.Comment: 12 pages, 3 figure

On principal hook length partitions and durfee sizes in skew characters

In this paper we construct for a given arbitrary skew diagram A all partitions nu with maximal principal hook lengths among all partitions with the character [nu] appearing in the skew character [A]. Furthermore we show that these are also partitions with minimal Durfee size. This we use to give the maximal Durfee size for [nu] appearing in [A] for the cases when A decays into two partitions and for some special cases of A. Also this gives conditions for two skew diagrams to represent the same skew character.Comment: 13 pages, minor changes from v1 to v2 as suggested by the referee, to appear in Annals. Com

A locally adaptive time-stepping algorithm for\ud petroleum reservoir simulations

An algorithm for locally adapting the step-size for large scale finite volume simulations of multi-phase flow in petroleum reservoirs is suggested which allows for an “all-in-one” implicit calculation of behaviour over a very large time scale. Some numerical results for simple two-phase flow in one space dimension illustrate the promise of the algorithm, which has also been applied to very simple 3D cases. A description of the algorithm is presented here along with early results. Further development of the technique is hoped to facilitate useful scaling properties

Mechanical Feedback from Active Galactic Nuclei in Galaxies, Groups, and Clusters

The radiative cooling timescales at the centers of hot atmospheres surrounding elliptical galaxies, groups, and clusters are much shorter than their ages. Therefore, hot atmospheres are expected to cool and to form stars. Cold gas and star formation are observed in central cluster galaxies but at levels below those expected from an unimpeded cooling flow. X-ray observations have shown that wholesale cooling is being offset by mechanical heating from radio active galactic nuclei. Feedback is widely considered to be an important and perhaps unavoidable consequence of the evolution of galaxies and supermassive black holes. We show that cooling X-ray atmospheres and the ensuing star formation and nuclear activity are probably coupled to a self-regulated feedback loop. While the energetics are now reasonably well understood, other aspects of feedback are not. We highlight the problems of atmospheric heating and transport processes, accretion, and nuclear activity, and we discuss the potential role of black hole spin. We discuss X-ray imagery showing that the chemical elements produced by central galaxies are being dispersed on large scales by outflows launched from the vicinity of supermassive black holes. Finally, we comment on the growing evidence for mechanical heating of distant cluster atmospheres by radio jets and its potential consequences for the excess entropy in hot halos and a possible decline in the number of distant cooling flows.Comment: Accepted for publication in New Journal of Physics Focus Issue on Clusters of Galaxie

Sow yards

THE sow is the production unit in the pig enterprise and she must be carefully managed and fed both when suckling and in the dry period. The use of a sow yard enables the management of the breeding herd to be closely controlled

Pigs have a place in the dairying areas

Pig-keeping could become a much more important feature on South-West dairy farms in the future with the enterprise as a definite farm-unit having a considerable effect on income. There are indications also that the collection of bulk skim milk and whey for pig feeding will increase in the future. This could make way for the efficient specialist operating large pig raising units close to the source of supply. In this article. Pig Husbandry Adviser P. McNamara, B.A. (Cantab.) examines pig-keeping in the South-West and makes suggestions on the part that pigs can play on the modem dairy farm