12,106 research outputs found
A search for evidence of large body Earth impacts associated with biological crisis zones in the fossil record
The natural history of the Earth, how the present plant and animal species developed, how others completely died out, etc., was studied. The rock strata sampled and studied were at the time of deposition at sea bottom. It was found that, exactly at the stratigraphic level corresponding to the extinction, a thin clay layer was greatly enriched in the the rare element iridium. It was hypothesized that the excess irridium at the boundary came from a large steroid like object that hit the earth, and that the impact of this object threw up a dust cloud dense enough and long lasting enough to bring about the extinction of a wide variety of plants and animals, producing the unique break in in the fossil record, the cretaceous-tertiary boundary. The same iridium and platinum metals enrichement are found in a thin clay layer that corresponds with the boundary as difined by sudden radical changes in plant populations. The irridium enrichement is confirmed at other fresh water origin rites in the Raton Basin
Astrometric Effects of Gravitational Wave Backgrounds with non-Luminal Propagation Speeds
A passing gravitational wave causes a deflection in the apparent astrometric positions of distant stars. The effect of the speed of the gravitational wave on this astrometric shift is discussed. A stochastic background of gravitational waves would result in a pattern of astrometric deflections which are correlated on large angular scales. These correlations are quantified and investigated for backgrounds of gravitational waves with sub- and super-luminal group velocities. The statistical properties of the correlations are depicted in two equivalent and related ways: as correlation curves and as angular power spectra. Sub-(super-)luminal gravitational wave backgrounds have the effect of enhancing (suppressing) the power in low-order angular modes. Analytical representations of the redshift-redshift and redshift-astrometry correlations are also derived. The potential for using this effect for constraining the speed of gravity is discussed
Developing an embedded nursing service within a homeless shelter: Client's perspectives
This phenomenological case study of a newly developed nursing service, embedded within a homeless shelter in the South East of England, uses semi-structured to elicit experiences and perceptions of clients within the service. Participants ( = 6) were interviewed using a semi-structured approach and identified three broad themes: impact of previous healthcare experiences, benefits of embedding healthcare within the shelter, and future service development. The study illuminates the diversity and complexity of healthcare needs of homeless people, as well as offers a unique insight into the service user's perception of the service
Sports psychology in the English Premier League: ‘It feels precarious and is precarious’
This is the author accepted manuscript. The final version is available from SAGE Publications via the DOI in this record.This article gives a rare account of the working life of a sports psychologist in the
English Premier League (EPL), the elite division in English professional football. It
shows how members of emerging professions such as sports psychology are a new
precariat. Martin is more successful than many sports psychologists, but his job
security is dependent on his continued ability to navigate managerial change: using
his skills as a psychologist in the defence of his own employment but simultaneously
keeping the (potentially sensitive) ‘psychology’ label of the work he does hidden until
circumstances are propitious
Generalized coherent states are unique Bell states of quantum systems with Lie group symmetries
We consider quantum systems, whose dynamical symmetry groups are semisimple
Lie groups, which can be split or decay into two subsystems of the same
symmetry. We prove that the only states of such a system that factorize upon
splitting are the generalized coherent states. Since Bell's inequality is never
violated by the direct product state, when the system prepared in the
generalized coherent state is split, no quantum correlations are created.
Therefore, the generalized coherent states are the unique Bell states, i.e.,
the pure quantum states preserving the fundamental classical property of
satisfying Bell's inequality upon splitting.Comment: 4 pages, REVTeX, amssymb style. More information on
http://www.technion.ac.il/~brif/science.htm
First Clear Signature of an Extended Dark Matter Halo in the Draco Dwarf Spheroidal
We present the first clear evidence for an extended dark matter halo in the
Draco dwarf spheroidal galaxy based on a sample of new radial velocities for
159 giant stars out to large projected radii. Using a two parameter family of
halo models spanning a range of density profiles and velocity anisotropies, we
are able to rule out (at about the 2.5 sigma confidence level) haloes in which
mass follows light. The data strongly favor models in which the dark matter is
significantly more extended than the visible dwarf. However, haloes with
harmonic cores larger than the light distribution are also excluded. When
combined with existing measurements of the proper motion of Draco, our data
strongly suggest that Draco has not been tidally truncated within ~1 kpc. We
also show that the rising velocity dispersion at large radii represents a
serious problem for modified gravity (MOND).Comment: to be published in ApJL; 5 pages, 4 figure
The Influence of Binary Stars on Dwarf Spheroidal Galaxy Kinematics
We have completed a Monte-Carlo simulation to estimate the effect of binary
star orbits on the measured velocity dispersion in dwarf spheroidal galaxies.
This paper analyses previous attempts at this calculation, and explains the
simulations which were performed with mass, period and ellipticity
distributions similar to that measured for the solar neighbourhood. The
conclusion is that with functions such as these, the contribution of binary
stars to the velocity dispersion is small. The distributions are consistent
with the percentage of binaries detected by observations, although this is
quite dependent on the measuring errors and on the number of years over which
measurements have been taken. For binaries to be making a significant
contribution to the dispersion measured in dSph galaxies, the distributions of
the orbital parameters would need to be very different from those of stars in
the solar neighbourhood. In particular more smaller period orbits with higher
mass secondaries would be required. The shape of the velocity distribution may
help to resolve this issue when more data becomes available. In general, the
scenarios producing a larger apparent dispersion have a velocity distribution
which deviates more clearly from Gaussian.Comment: MNRAS in press, uuencoded ps fil
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