Basin bifurcations, oscillatory instability and rate-induced thresholds for AMOC in a global oceanic box model

The Atlantic Meridional Overturning Circulation (AMOC) transports substantial amounts of heat into the North Atlantic sector, and hence is of very high importance in regional climate projections. The AMOC has been observed to show multi-stability across a range of models of different complexity. The simplest models find a bifurcation associated with the AMOC `on' state losing stability that is a saddle node. Here we study a physically derived global oceanic model of Wood {\em et al} with five boxes, that is calibrated to runs of the FAMOUS coupled atmosphere-ocean general circulation model. We find the loss of stability of the `on' state is due to a subcritical Hopf for parameters from both pre-industrial and doubled CO${}_2$ atmospheres. This loss of stability via subcritical Hopf bifurcation has important consequences for the behaviour of the basin of attraction close to bifurcation. We consider various time-dependent profiles of freshwater forcing to the system, and find that rate-induced thresholds for tipping can appear, even for perturbations that do not cross the bifurcation. Understanding how such state transitions occur is important in determining allowable safe climate change mitigation pathways to avoid collapse of the AMOC.Comment: 18 figure

A Strong X-Ray Burst from the Low Mass X-Ray Binary EXO0748-676

We have observed an unusually strong X-ray burst as a part of our regular eclipse timing observations of the low mass binary system EXO0748-676. The burst peak flux was 5.2x10^-8 ergs cm^-2 s^-1, approximately five times the normal peak X-ray burst flux observed from this source by RXTE. Spectral fits to the data strongly suggest that photospheric radius expansion occurred during the burst. In this Letter we examine the properties of this X-ray burst, which is the first example of a radius expansion burst from EXO0748-676 observed by RXTE. We find no evidence for coherent burst oscillations. Assuming that the peak burst luminosity is the Eddington luminosity for a 1.4 solar mass neutron star we derive a distance to EXO0748-676 of 7.7 kpc for a helium-dominated burst photosphere and 5.9 kpc for a hydrogen-dominated burst photosphere.Comment: 15 pages including 2 figures and 1 table. Accepted for publication in the Astrophysical Journa

The Development of a Direct Homologous Radioimmunoassay for Serum Cortisol

Peer Reviewe

Report of the panel on volcanology, section 4

Two primary goals are identified as focal to NASA's research efforts in volcanology during the 1990s: to understand the eruption of lavas, gases, and aerosols from volcanoes, the dispersal of these materials on the Earth's surface and through the atmosphere, and the effects of these eruptions on the climate and environment; and to understand the physical processes that lead to the initiation of volcanic activity, that influence the styles of volcanic eruptions, and that dictate the morphology and evolution of volcanic landforms. Strategy and data requirements as well as research efforts are discussed

Vergleich dreier Ringversuche zur radioimmunologischen Thyrotropin-Bestimmung nach dem "Münchner Modell"

Peer Reviewe

Paper Session II-C - Commercial Space Initiatives

Traditionally, space technology has been developed and used primarily to meet the needs of civil and military government initiatives. In the future, it will be increasingly featured in two emerging trends: new space enterprises and the national drive to achieve a more competitive global economic position. To realize this potential, private sector initiatives and investment must adapt space technology and access to space to economically attractive, competitive ventures. While commercial development of space must be carried out in the private sector, it is clear that the Government has an important enabling role. NASA has established the Commercial Programs Advisory Committee (CPAC), to advise ftlASA on this and other aspects of the commercial development of space. CPAC, which is a standing committee of the NASA Advisory Council, is comprised of senior private sector executives and their university counterparts. The results of the first year of CPAC\u27s work has been published in the report Charting the Course: U.S. Space Enterprise and Space Industrial Competitiveness. This paper summarizes the CPAC report and examines promising space business sectors. Additionally, NASA\u27s initiatives which are supportive of commercial space are reviewed. Finally, an up-to-date look at the role of international cooperation in a highly competitive world is offered