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The connection between X-ray Clusters and Star Formation
The properties of X-ray clusters of galaxies can be well understood in terms
of a competition between shock heating and adiabatic compression. Strong shocks
are expected to be important for massive clusters, while adiabatic compression
is dominant for small clusters and groups. The scale of the shock/adiabatic
transition is marked by a change of slope of the L-T relation and in the global
properties of the emitting plasma. This scale is connected to star formation
processes. Two quantities are crucial: the average energy injected in the IGM
from stars and SNe, and the epoch of the energy injection. We show how these
quantities can be synthesized in terms of specific entropy, which ultimately
determines the X-ray emission from groups and clusters.Comment: 4 pages, including 2 figures, LaTex2e. To be published in the
Proceedings of the ``VLT Opening Symposium'', Antofagasta (Chile), 1-4 March
1999. Typos changed in eq. (3
Electronic trading on futures exchanges
Although the open outcry method is still the best way to trade highly active contracts on futures exchanges, electronic systems can improve the efficiency and cost effectiveness of trading some types of futures and options. In recent years, the volume of electronic trades on futures exchanges has more than doubled, and it should continue to grow rapidly.Futures
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