Clues from nearby galaxies to a better theory of cosmic evolution

The great advances in the network of cosmological tests show that the relativistic Big Bang theory is a good description of our expanding universe. But the properties of nearby galaxies that can be observed in greatest detail suggest a still better theory would more rapidly gather matter into galaxies and groups of galaxies. This happens in theoretical ideas now under discussion.Comment: published in Natur

Statistical mechanics of violent relaxation in stellar systems

We discuss the statistical mechanics of violent relaxation in stellar systems following the pioneering work of Lynden-Bell (1967). The solutions of the gravitational Vlasov-Poisson system develop finer and finer filaments so that a statistical description is appropriate to smooth out the small-scales and describe the ``coarse-grained'' dynamics. In a coarse-grained sense, the system is expected to reach an equilibrium state of a Fermi-Dirac type within a few dynamical times. We describe in detail the equilibrium phase diagram and the nature of phase transitions which occur in self-gravitating systems. Then, we introduce a small-scale parametrization of the Vlasov equation and propose a set of relaxation equations for the coarse-grained dynamics. These relaxation equations, of a generalized Fokker-Planck type, are derived from a Maximum Entropy Production Principle (MEPP). We make a link with the quasilinear theory of the Vlasov-Poisson system and derive a truncated model appropriate to collisionless systems subject to tidal forces. With the aid of this kinetic theory, we qualitatively discuss the concept of ``incomplete relaxation'' and the limitations of Lynden-Bell's theory

On the Origin of S0 Galaxies

I will review the basic properties of S0 galaxies in the local Universe in relation to both elliptical and spiral galaxies, their neighbours on the Hubble sequence, and also in relation to dwarf spheroidal (dSph) galaxies. This will include colours, luminosities, spectral features, information about the age and metallicity composition of their stellar populations and globular clusters, about their ISM content, as well as kinematic signatures and their implications for central black hole masses and past interaction events, and the number ratios of S0s to other galaxy types in relation to environmental galaxy density. I will point out some caveats as to their morphological discrimination against other classes of galaxies, discuss the role of dust and the wavelength dependence of bulge/disk light ratios. These effects are of importance for investigations into the redshift evolution of S0 galaxies -- both as individual objects and as a population. The various formation and transformation scenarios for S0 and dSph galaxies will be presented and confronted with the available observations.Comment: Invited Review, 18 pages, ``BARS 2004'' Conference, South Africa, June 2004, eds.: K. C. Freeman, D. L. Block, I. Puerari, R. Groess, Kluwer, in pres

Measuring sleep habits using the Sleep Timing Questionnaire: A validation study for school-age children

In 2003 Monk and colleagues published a single-administration replacement for a standard sleep diary, the Sleep Timing Questionnaire (STQ). Reliable and valid for adult participants, it offers advantages over existing methodologies in cost and convenience. It takes approximately 10 min to complete but can yield information equivalent to a week of actigraphy, or a 2-week sleep diary. This study sought to validate the STQ for school-age children. Sixty-five children (20 boys, 45 girls), aged 11-16 years participated in this study. The participants wore wrist actigraphs, completed a 1-week sleep diary and the STQ. Analyses tested convergent validity between the STQ and actigraphy, and the STQ and sleep diaries. Correlations between STQ and actigraphy (r = 0.45-0.76, P < 0.001), and STQ and sleep diaries (r = 0.42-0.86, P < 0.001), were positive and significant for sleep onset and wake times. Correlations between STQ and actigraphy for sleep latency and wake after sleep onset (WASO) were very low (r < 0.10). In contrast, sleep latency was moderately and significantly correlated between STQ and sleep diary (r = 0.42, P < 0.001), and the correlation for WASO was high and significant (r = 0.74, P < 0.001). Differences between the STQ and sleep diary were within acceptable limits for all sleep parameters, and the differences between STQ and actigraphy were acceptable for sleep onset and school day wake time. The STQ may be a valid indicator of sleep onset and wake time in school-age children. It can also produce measures of sleep latency and WASO with comparable accuracy to a standard sleep diary. © 2010 The Authors. Journal compilation © 2010 Japanese Society of Sleep Research