228 research outputs found
Probing Dark Matter
Recent novel observations have probed the baryonic fraction of the galactic
dark matter that has eluded astronomers for decades. Late in 1993, the MACHO
and EROS collaborations announced in this journal the detection of transient
and achromatic brightenings of a handful of stars in the Large Magellanic Cloud
that are best interpreted as gravitational microlensing by low-mass foreground
objects (MACHOS). This tantalized astronomers, for it implied that the
population of cool, compact objects these lenses represent could be the elusive
dark matter of our galactic halo. A year later in 1994, Sackett et al. reported
the discovery of a red halo in the galaxy NGC 5907 that seems to follow the
inferred radial distribution of its dark matter. This suggested that dwarf
stars could constitute its missing component. Since NGC 5907 is similar to the
Milky Way in type and radius, some surmised that the solution of the galactic
dark matter problem was an abundance of ordinary low-mass stars. Now Bahcall et
al., using the Wide-Field Camera of the recently repaired Hubble Space
Telescope, have dashed this hope.Comment: 3 pages, Plain TeX, no figures, published as a News and Views in
Nature 373, 191 (1995
Functional analysis of altered Tenascin isoform expression in breast cancer
Background:
Cellular interactions with the extracellular matrix (ECM) control many aspects of cell function. The complex ECM protein Tenascin-C (TN), which exists as multiple isoforms, is upregulated in breast cancer. We previously have identified a change in the TN isoform profile in breast cancer, with detection of two additional isoforms — TN16 and TN14/16 — not seen in normal breast [1]. The purpose of this study was to investigate directly the effects of these tumour-associated TNC isoforms on breast cancer cell behaviour
Austerity, personalisation and the degradation of voluntary sector employment conditions
This qualitative study of two social care organisations, explores how public sector austerity and policies to personalise social care services through introducing individual budgets in the UK combine to reshape employment conditions. It further explores how these new market relations impact on staff morale and commitment. The individual case summaries reveal a remarkable degree of similarity in terms of employment outcomes, with social care workers experiencing an erosion of the standard employment relationship. Workers experience greater insecurity in areas of pay and conditions, working time, training and development, career prospects, along with work intensification. Worker morale appeared vulnerable as employees struggled to cope with worsening working conditions, but also expressed concerns with quality of care in an era of austerity
Measuring our universe from galaxy redshift surveys
Galaxy redshift surveys have achieved significant progress over the last
couple of decades. Those surveys tell us in the most straightforward way what
our local universe looks like. While the galaxy distribution traces the bright
side of the universe, detailed quantitative analyses of the data have even
revealed the dark side of the universe dominated by non-baryonic dark matter as
well as more mysterious dark energy (or Einstein's cosmological constant). We
describe several methodologies of using galaxy redshift surveys as cosmological
probes, and then summarize the recent results from the existing surveys.
Finally we present our views on the future of redshift surveys in the era of
Precision Cosmology.Comment: 82 pages, 31 figures, invited review article published in Living
Reviews in Relativity, http://www.livingreviews.org/lrr-2004-
The MACHO Project Large Magellanic Cloud Variable Star Inventory. VIII. The Recent Star Formation History of the LMC from the Cepheid Period Distribution
We present an analysis of the period distribution of Cepheids in the Large Magellanic Cloud, based on data obtained by the MACHO microlensing experiment and on a previous catalogue by Payne-Gaposchkin. Using stellar evolution and pulsation models, we construct theoretical period-frequency distributions that are compared to the observations. These models reveal that a significant burst of star formation has occurred recently in the LMC ( years). We also show that during the last years, the main center of star formation has been propagating from SE to NW along the bar. We find that the evolutionary masses of Cepheids are still smaller than pulsation masses by % and that the red edge of the Cepheid instability strip could be slightly bluer than indicated by theory. There are Cepheids with periods below days cannot be explained by evolution theory. We suggest that they are anomalous Cepheids; a number of these stars are double-mode Cepheids
The Cosmological Constant
This is a review of the physics and cosmology of the cosmological constant.
Focusing on recent developments, I present a pedagogical overview of cosmology
in the presence of a cosmological constant, observational constraints on its
magnitude, and the physics of a small (and potentially nonzero) vacuum energy.Comment: 50 pages. Submitted to Living Reviews in Relativity
(http://www.livingreviews.org/), December 199
Multiscale models for movement in oriented environments and their application to hilltopping in butterflies
Hilltopping butterflies direct their movement in response to topography, facilitating mating encounters via accumulation at summits. In this paper, we take hilltopping as a case study to explore the impact of complex orienteering cues on population dynamics. The modelling employs a standard multiscale framework, in which an individual's movement path is described as a stochastic 'velocity-jump' process and scaling applied to generate a macroscopic model capable of simulating large populations in landscapes. In this manner, the terms and parameters of the macroscopic model directly relate to statistical inputs of the individual-level model (mean speeds, turning rates and turning distributions). Applied to hilltopping in butterflies, we demonstrate how hilltopping acts to aggregate populations at summits, optimising mating for low-density species. However, for abundant populations, hilltopping is not only less effective but also possibly disadvantageous, with hilltopping males recording a lower mating rate than their non-hilltopping competitors. © 2013 Springer Science+Business Media Dordrecht
Formation of Supermassive Black Holes
Evidence shows that massive black holes reside in most local galaxies.
Studies have also established a number of relations between the MBH mass and
properties of the host galaxy such as bulge mass and velocity dispersion. These
results suggest that central MBHs, while much less massive than the host (~
0.1%), are linked to the evolution of galactic structure. In hierarchical
cosmologies, a single big galaxy today can be traced back to the stage when it
was split up in hundreds of smaller components. Did MBH seeds form with the
same efficiency in small proto-galaxies, or did their formation had to await
the buildup of substantial galaxies with deeper potential wells? I briefly
review here some of the physical processes that are conducive to the evolution
of the massive black hole population. I will discuss black hole formation
processes for `seed' black holes that are likely to place at early cosmic
epochs, and possible observational tests of these scenarios.Comment: To appear in The Astronomy and Astrophysics Review. The final
publication is available at http://www.springerlink.co
Physics, Astrophysics and Cosmology with Gravitational Waves
Gravitational wave detectors are already operating at interesting sensitivity
levels, and they have an upgrade path that should result in secure detections
by 2014. We review the physics of gravitational waves, how they interact with
detectors (bars and interferometers), and how these detectors operate. We study
the most likely sources of gravitational waves and review the data analysis
methods that are used to extract their signals from detector noise. Then we
consider the consequences of gravitational wave detections and observations for
physics, astrophysics, and cosmology.Comment: 137 pages, 16 figures, Published version
<http://www.livingreviews.org/lrr-2009-2
Risk factors associated with experienced stigma among people diagnosed with mental ill-health: a cross-sectional study
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