Quasi-periodic oscillations and noise in neutron star and black-hole X-ray binaries

Before the launch of the Rossi X-ray Timing Explorer (RXTE) satellite, the differences in the rapid X-ray variability between the two main types of neutron star binaries (i.e., the Z and atoll sources) could be explained by invoking different mass accretion rates and magnetic field strengths. However, the results obtained with RXTE now show that these systems are more similar than previously thought and although differences in mass accretion rate are still likely, the differences in the magnetic field strength have become questionable. The great similarities between the neutron star systems and the black-hole candidates at low mass accretion rates also point towards a similar origin of their timing phenomena indicating that the presence or absence of a solid surface, a magnetic field, or an event horizon do not play a significant role in the production mechanisms for the rapid X-ray variability.Comment: Talk presented at the 33rd COSPAR Scientific Assembly, Warsaw, Poland, 16-23 July 2000. Submitted for publication in Advances in Space Researc

Equity and Patterns of Library Governance

published or submitted for publicatio

A sustainable model for ICT capacity building in developing countries

System administrators are often asked to apply their professional expertise in unusual situations, or under tight resource constraints. What happens, though, when the “situation” is a foreign country with only basic technical infrastructure, and the task is to bauild systems which are able to survive and grow in these over-constrained environments? In this paper we report on our experiences in two very different countries – Cuba and Ethiopia – where we ran a number of ICT projects. In those projects we assisted local universities to upgrade their ICT infrastructure and services. This included skills and process building for local system administrators. Based on our experiences we formulate a model for sustainable ICT capacity building. We hope this model will be useful for other organizations doing similar projects

Nodal separators of holomorphic foliations

We study a special kind of local invariant sets of singular holomorphic foliations called nodal separators. We define notions of equisingularity and topological equivalence for nodal separators as intrinsic objects and, in analogy with the celebrated theorem of Zariski for analytic curves, we prove the equivalence of these notions. We give some applications in the study of topological equivalences of holomorphic foliations. In particular, we show that the nodal singularities and its eigenvalues in the resolution of a generalized curve are topological invariants

The crust cooling curve of the neutron star in MXB 1659-29

We have monitored the quasi-persistent neutron-star X-ray transient MXB 1659-29 in quiescence using Chandra. The purpose of our observations was to monitor the quiescent behavior of the source after its last prolonged outburst episode and to study the cooling curve of the neutron star in this system. We discuss the results obtained and how they constrain the properties of the neutron star in MXB 1659-29Comment: To appear in Proceedings of IAU Colloquium 194 "Compact binaries in the Galaxy and beyond" (Rev. Mex. A&A Conf. Series), eds. G. Tovmassian and E. Sio