6,539 research outputs found
String mediated phase transitions
It is demonstrated from first principles how the existence of string-like structures can cause a system to undergo a phase transition. In particular, the role of topologically stable cosmic string in the restoration of spontaneously broken symmetries is emphasized. How the thermodynamic properties of strings alter when stiffness and nearest neighbor string-string interactions are included is discussed
Fanny Copeland and the geographical imagination
Raised in Scotland, married and divorced in the English south, an adopted Slovene, Fanny Copeland (1872 – 1970) occupied the intersection of a number of complex spatial and temporal conjunctures. A Slavophile, she played a part in the formation of what subsequently became the Kingdom of Yugoslavia that emerged from the First World War. Living in Ljubljana, she facilitated the first ‘foreign visit’ (in 1932) of the newly formed Le Play Society (a precursor of the Institute of British Geographers) and guided its studies of Solčava (a then ‘remote’ Alpine valley system) which, led by Dudley Stamp and commended by Halford Mackinder, were subsequently hailed as a model for regional studies elsewhere. Arrested by the Gestapo and interned in Italy during the Second World War, she eventually returned to a socialist Yugoslavia, a celebrated figure. An accomplished musician, linguist, and mountaineer, she became an authority on (and populist for) the Julian Alps and was instrumental in the establishment of the Triglav National Park. Copeland’s role as participant observer (and protagonist) enriches our understanding of the particularities of her time and place and illuminates some inter-war relationships within G/geography, inside and outside the academy, suggesting their relative autonomy in the production of geographical knowledge
New type scalar fields for cosmic acceleration
We present a model where a non-conventional scalar field may act like dark
energy leading to cosmic acceleration. The latter is driven by an appropriate
field configuration, which result in an effective cosmological constant. The
potential role of such a scalar in the cosmological constant problem is also
discussed.Comment: 6 page
On the reliability of inflaton potential reconstruction
If primordial scalar and tensor perturbation spectra can be inferred from
observations of the cosmic background radiation and large-scale structure, then
one might hope to reconstruct a unique single-field inflaton potential capable
of generating the observed spectra. In this paper we examine conditions under
which such a potential can be reliably reconstructed. For it to be possible at
all, the spectra must be well fit by a Taylor series expansion. A complete
reconstruction requires a statistically-significant tensor mode to be measured
in the microwave background. We find that the observational uncertainties
dominate the theoretical error from use of the slow-roll approximation, and
conclude that the reconstruction procedure will never insidiously lead to an
irrelevant potential.Comment: 16 page LaTeX file with eight postscript figures embedded with epsf;
no special macros neede
String Dilaton Fluid Cosmology
We investigate -dimensional string-dilaton cosmology with effective
dilaton potential in presence of perfect-fluid matter.We get exact solutions
parametrized by the constant \gam of the state equation p=(\gam-1)\rho, the
spatial dimension number , the bulk of matter, and the spatial curvature
constant . Several interesting cosmological behaviours are selected. Finally
we discuss the recovering of ordinary Einstein gravity starting from string
dominated regime and a sort of asymptotic freedom due to string effective
coupling.Comment: 16 pages, Latex, submitted to Int. Jou. Mod. Phys.
wormholes and topological charge
I investigate solutions to the Euclidean Einstein-matter field equations with
topology in a theory with a massless periodic scalar
field and electromagnetism. These solutions carry winding number of the
periodic scalar as well as magnetic flux. They induce violations of a
quasi-topological conservation law which conserves the product of magnetic flux
and winding number on the background spacetime. I extend these solutions to a
model with stable loops of superconducting cosmic string, and interpret them as
contributing to the decay of such loops.Comment: 18 pages (includes 6 figs.), harvmac and epsf, CU-TP-62
A formative review of physical activity interventions for minority ethnic populations in England
Background: Physical activity (PA) levels are lower among some UK minority ethnic groups than the
majority White British population. Barriers to participation have been examined and a variety of
tailored interventions have emerged. This study documents the characteristics and logic of local
adaptations; a vital first step in evaluating such innovations.
Methods: 58 PA interventions from an English PA dataset were examined to establish the
characteristics of programmes focussed on minority ethnic populations. From these 58, three case
studies were examined to reveal the nature of tailoring and the logic underpinning it; employing
documentary analysis and qualitative interviews.
Results: Interventions typically aimed to improve both health and social outcomes, were largely
publically and charitably funded and sought to engage the most inactive groups. Tailoring was based
on six principles including using community resources to promote the intervention and
accommodating varying degrees of cultural identification. Additionally, tailoring interventions were
intended to build capacity for sustainability.
Conclusions: PA interventions tailored to the needs of minority ethnic groups reflect their largely
disadvantaged position in society and focus on addressing inactivity. Tailoring PA with the six
principles in mind could be used as a useful framework for developing, designing and evaluating
interventions for minority ethnic populations
Scaling configurations of cosmic superstring networks and their cosmological implications
We study the cosmic microwave background temperature and polarisation spectra
sourced by multi-tension cosmic superstring networks. First we obtain solutions
for the characteristic length scales and velocities associated with the
evolution of a network of F-D strings, allowing for the formation of junctions
between strings of different tensions. We find two distinct regimes describing
the resulting scaling distributions for the relative densities of the different
types of strings, depending on the magnitude of the fundamental string coupling
g_s. In one of them, corresponding to the value of the coupling being of order
unity, the network's stress-energy power spectrum is dominated by populous
light F and D strings, while the other regime, at smaller values of g_s, has
the spectrum dominated by rare heavy D strings. These regimes are seen in the
CMB anisotropies associated with the network. We focus on the dependence of the
shape of the B-mode polarisation spectrum on g_s and show that measuring the
peak position of the B-mode spectrum can point to a particular value of the
string coupling. Finally, we assess how this result, along with pulsar bounds
on the production of gravitational waves from strings, can be used to constrain
a combination of g_s and the fundamental string tension mu_F. Since CMB and
pulsar bounds constrain different combinations of the string tensions and
densities, they result in distinct shapes of bounding contours in the (mu_F,
g_s) parameter plane, thus providing complementary constraints on the
properties of cosmic superstrings.Comment: 23 pages, 8 figures, 3 tables; V2: matches published version (PRD
Dependence of Inflationary Reconstruction upon Cosmological Parameters
The inflationary potential and its derivatives determine the spectrum of
scalar and tensor metric perturbations that arise from quantum fluctuations
during inflation. The CBR anisotropy offers a promising means of determining
the spectra of metric perturbations and thereby a means of constraining the
inflationary potential. The relation between the metric perturbations and CBR
anisotropy depends upon cosmological parameters -- most notably the possibility
of a cosmological constant. Motivated by some observational evidence for a
cosmological constant (large-scale structure, cluster-baryon fraction,
measurements of the Hubble constant and age of the Universe) we derive the
reconstruction equations and consistency relation to second order in the
presence of a cosmological constant. We also clarify previous notation and
discuss alternative schemes for reconstruction.Comment: 15 pages, LaTeX, 3 postscript figures (included with epsf), submitted
to Phys. Rev.
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