32 research outputs found
HI in Local Group analogs: what does it tell us about galaxy formation?
We present the results of our HI survey of six loose groups of galaxies
analogous to the Local Group. The survey was conducted using the Parkes
telescope and the Australia Telescope Compact Array to produce a census of all
the gas-rich galaxies and potential analogs to the high-velocity clouds (HVCs)
within these groups down to M(HI)<10^7 M(sun) as a test of models of galaxy
formation. We present the HI mass function and halo mass function for these
analogous groups and compare them with the Local Group and other environments.
We also demonstrate that our non-detection of HVC analogs in these groups
implies that they must have low HI masses and be clustered tightly around
galaxies, including around our own Milky Way, and are not distributed
throughout the Local Group.Comment: 5 pages, To appear in ESO Astrophysics Symposia: "Groups of Galaxies
in the Nearby Universe
FUV and X-ray absorption in the Warm-Hot Intergalactic Medium
The Warm-Hot Intergalactic Medium (WHIM) arises from shock-heated gas
collapsing in large-scale filaments and probably harbours a substantial
fraction of the baryons in the local Universe. Absorption-line measurements in
the ultraviolet (UV) and in the X-ray band currently represent the best method
to study the WHIM at low redshifts. We here describe the physical properties of
the WHIM and the concepts behind WHIM absorption line measurements of H I and
high ions such as O VI, O VII, and O VIII in the far-ultraviolet and X-ray
band. We review results of recent WHIM absorption line studies carried out with
UV and X-ray satellites such as FUSE, HST, Chandra, and XMM-Newton and discuss
their implications for our knowledge of the WHIM.Comment: 26 pages, 9 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 3; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Maximum Lyapunov exponents as predictors of global gait stability: A modelling approach
To examine the stability of human walking, methods such as local dynamic stability have been adopted from dynamical systems theory. Local dynamic stability is calculated by estimating maximal finite time Lyapunov exponents (
The validity of stability measures: a modeling approach
Measures calculated from unperturbed walking patterns, such as variability measures and maximum Floquet multipliers, are often used to study the stability of walking. However, it is unknown if, and to what extent, these measures correlate to the probability of falling. We studied whether in a simple model of human walking, i.e., a passive dynamic walker, the probability of falling could be predicted from maximum Floquet multipliers, kinematic state variability, and step time variability. We used an extended version of the basic passive dynamic walker with arced feet and a hip spring. The probability of falling was manipulated by varying the foot radius and hip spring stiffness, or varying these factors while co-varying the slope to keep step length constant. The simulation data indicated that Floquet multipliers and kinematic state variability correlated inconsistently with probability of falling. Step time variability correlated well with probability of falling, but a more consistent correlation with the probability of falling was found by calculating the variability of the log transform of the step time. Our findings speak against the use of maximum Floquet multipliers and suggest instead that variability of critical variables may be a good predictor of the probability to fall
Tempo curves considered harmful
Contains fulltext :
74833.pdf (publisher's version ) (Open Access)In the literature of musicology, computer music research and the psychology of music, timing or tempo measurements are mostly presented in the form of continuous curves. The notion of these tempo curves is dangerous, despite its widespread use, because it lulls its users into the false impression that a continuous concept of temporal flow has an independent existence, a musical or psychological reality, and that time can be perceived independent of events carrying it. But if one bases a transformation or manipulation of timing on the implied characteristics of such a notion, one is doomed to fail.Special issue: J. D. Kramer (ed.), Time in contemporary musical though