1,470 research outputs found
Deceleration without dark matter
In homogeneous isotropic cosmological models the angular size theta of a
standard measuring rod changes with redshift z in a manner that depends upon
the parameters of the model. It has been argued that as a population
ultracompact (milliarcsecond) radio sources measured by very long-baseline
interferometry (VLBI) do not evolve with cosmic epoch, and thus comprise a set
of standard objects, at least in a statistical sense. Here we examine the
angular-size/redshift relation for 256 ultracompact sources with z in the range
0.5 to 3.8 for cosmological models with two degrees of freedom (Omega_0 and
Lambda_0). The canonical inflationary cold dark matter model(Omega_0=1,
Lambda_0=0) appears to be ruled out by the observed relationship, whereas
low-density models with a cosmological constant of either sign are favoured.Comment: Although published (MNRAS 285, 806, 1997, submitted 1996 May 3), this
paper has not previously appeared on the arXive. Despite its title, a
prominent conclusion is that if the Universe is spatially flat, then the best
cosmological parameters are Omega_m=0.2, Omega_Lambda=0.8, with probable
range 0.1<Omega_m<0.3. It is the first in a series, the second being JCAP
0411(2004)007, astro-ph/0309390; the third is a recent preprint,
astro-ph/060506
Decelerating universes older than their Hubble times
Recent observations suggest that Hubble's constant is large, and hence that
the Universe appears to be younger than some of its constituents. The
traditional escape route, which assumes that the expansion is accelerating,
appears to be blocked by observations of Type 1a supernovae, which suggest(ed)
that the Universe is decelerating. These observations are reconciled in a model
in which the Universe has experienced an inflationary phase in the recent past,
driven by an ultra-light inflaton whose Compton wavelength is of the same order
as the Hubble radius.Comment: This paper, which predates the famous quintessence paper, has not
previously appeared on the e-Print archive. It is essentially a quintessence
model without eternal acceleration. Such models are now very topical in the
context of string theory. 9 pages, 5 figure
What's up prof? Current issues in the visual effects & post-production industry
We interviewed creative professionals at a number of London visual effects and post-production houses. We report on the key issues raised in those interviews: desirable new technologies, infrastructure challenges, personnel and process management
Influence of Dislocations in Thomson's Problem
We investigate Thomson's problem of charges on a sphere as an example of a
system with complex interactions. Assuming certain symmetries we can work with
a larger number of charges than before. We found that, when the number of
charges is large enough, the lowest energy states are not those with the
highest symmetry. As predicted previously by Dodgson and Moore, the complex
patterns in these states involve dislocation defects which screen the strains
of the twelve disclinations required to satisfy Euler's theorem.Comment: 9 pages, 4 figures in gif format. Original PS files can be obtained
in http://fermi.fcu.um.es/thomso
Can local NURBS refinement be achieved by modifying only the user interface?
NURBS patches have a serious restriction: they are constrained to a strict rectangular topology. This means that a request to insert a single new control point will cause a row of control points to appear across the NURBS patch, a global refinement of control. We investigate a method that can hide unwanted control points from the user so that the user’s interaction is with local, rather than global, refinement. Our method requires only straightforward modification of the user interface and the data structures that represent the control mesh, making it simpler than alternatives that use hierarchical or T-constructions. Our results show that our method is effective in many cases but has limitations where inserting a single new control point in certain cases will still cause a cascade of new control points to appear across the NURBS patch.Kosinka was supported by the Engineering and Physical Sciences Research Council [EP/H030115/1].This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.cad.2015.09.00
Re: Practice of breastfeeding and factors that affect breastfeeding in Hong Kong [2]
published_or_final_versio
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