10,631 research outputs found
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
Development of a channel measurement system for Multiple-Input Multiple-Output (MIMO) applications
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
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