29 research outputs found
Origin and Evolution of Saturn's Ring System
The origin and long-term evolution of Saturn's rings is still an unsolved
problem in modern planetary science. In this chapter we review the current
state of our knowledge on this long-standing question for the main rings (A,
Cassini Division, B, C), the F Ring, and the diffuse rings (E and G). During
the Voyager era, models of evolutionary processes affecting the rings on long
time scales (erosion, viscous spreading, accretion, ballistic transport, etc.)
had suggested that Saturn's rings are not older than 100 My. In addition,
Saturn's large system of diffuse rings has been thought to be the result of
material loss from one or more of Saturn's satellites. In the Cassini era, high
spatial and spectral resolution data have allowed progress to be made on some
of these questions. Discoveries such as the ''propellers'' in the A ring, the
shape of ring-embedded moonlets, the clumps in the F Ring, and Enceladus' plume
provide new constraints on evolutionary processes in Saturn's rings. At the
same time, advances in numerical simulations over the last 20 years have opened
the way to realistic models of the rings's fine scale structure, and progress
in our understanding of the formation of the Solar System provides a
better-defined historical context in which to understand ring formation. All
these elements have important implications for the origin and long-term
evolution of Saturn's rings. They strengthen the idea that Saturn's rings are
very dynamical and rapidly evolving, while new arguments suggest that the rings
could be older than previously believed, provided that they are regularly
renewed. Key evolutionary processes, timescales and possible scenarios for the
rings's origin are reviewed in the light of tComment: Chapter 17 of the book ''Saturn After Cassini-Huygens'' Saturn from
Cassini-Huygens, Dougherty, M.K.; Esposito, L.W.; Krimigis, S.M. (Ed.) (2009)
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Evaluation of changes in myocardial perfusion and function on exercise in patients with coronary artery disease by gated MIBI scintigraphy.
Asthma Programme in Finland: Did the use of secondary care resources become more rational?
SummaryObjectivesThe aims were to evaluate the profile of newly diagnosed adult asthma cases and the approach adopted to the secondary care management at the launch of the Finnish asthma programme in 1994 and seven years later, in 2001.MethodsA retrospective medical record audit was made of non-acutely referred patients with asthma in 1994 (n=165) and in 2001 (n=133). Clinical profile data, numbers of out-patient visits and periods of in-patient care before and after asthma diagnosis were gathered from referral letters and secondary care records.ResultsThe newly diagnosed asthma patients in 2001 were older, more obese and had more co-morbidities. The main asthma symptoms, such as dyspnoea, wheezing and cough, occurred equally in both years but were more often periodic than daily in 2001. Wheezing during auscultation was significantly less common in 2001. The diagnostic process was associated to a history of asthma in first-degree relatives (OR 5.34, 95% CI 1.12–24.49) in 1994 and a visit to a nurse prior to that to a physician (OR 3.13, 95% CI 1.17–8.37) in 2001. Secondary care visits per new case of asthma (7.3 in 1994 vs. 5.4 in 2001) and days in hospital (3.6 in 1994 vs. 0.95 in 2001) decreased significantly.ConclusionsThe profile of asthma diagnosed in secondary care indicates milder disease with more co-morbidities in 2001 than in 1994.Trends towards assigning a more active role on the part of primary care physicians and more rational use of secondary care resources in the management of asthma were found