2,943 research outputs found
The time dependence of muon spin relaxation spectra and spin correlation functions
The existing theory of the microscopic interpretation of the dynamical
contribution to zero-field muon depolarization spectra in a longitudinal
geometry is developed. The predicted relaxation of the muon depolarization is
calculated from two forms of the spin correlation function. First, when the
spin correlation function has an exponential form with a single wave vector
dependent relaxation rate is considered, it is shown that this form of the spin
correlation function reproduces the slow and fast fluctuation limits of
stochastic spin theory regardless of the choice of microscopic spin model.
Second, if the spin correlation function is a homogeneous scaling function
(such as a power-law decay with time), as suggested by the mode-coupling theory
of spin dynamics, this results in a stretched exponential relaxation of the
muon spectra. For simple spin diffusion, the muon spectra are shown to be relax
with a root-exponential form.Comment: 5 pages, 1 figur
From k-essence to generalised Galileons
We determine the most general scalar field theories which have an action that
depends on derivatives of order two or less, and have equations of motion that
stay second order and lower on flat space-time. We show that those theories can
all be obtained from linear combinations of Lagrangians made by multiplying a
particular form of the Galileon Lagrangian by an arbitrary scalar function of
the scalar field and its first derivatives. We also obtain curved space-time
extensions of those theories which have second order field equations for both
the metric and the scalar field. This provide the most general extension, under
the condition that field equations stay second order, of k-essence, Galileons,
k-Mouflage as well as of the kinetically braided scalars. It also gives the
most general action for a scalar classicalizer, which has second order field
equations. We discuss the relation between our construction and the Euler
hierachies of Fairlie et al, showing in particular that Euler hierachies allow
one to obtain the most general theory when the latter is shift symmetric. As a
simple application of our formalism, we give the covariantized version of the
conformal Galileon.Comment: 25 page
Demand side management within a regional electricity company
The work presented in this thesis concerns itself with the application of Demand Side Management (DSM) by industrial subsector as applied to the UK electricity industry. A review of the origins of DSM in the US and the relevance of experience gained to the UK electricity industry is made. Reviews are also made of the current status of the UK electricity industry, the regulatory system, and the potential role of DSM within the prevalent industry environment. A financial appraisal of DSM in respect of the distribution business of a Regional Electricity Company (REC) is also made. This financial appraisal highlights the economic viability of DSM within the context of the current UK electricity industry. The background of the work presented above is then followed by the construction of a framework detailing the necessary requirements for expanding the commercial role of DSM to encompass benefits for the supply business of a REC. The derived framework is then applied, in part, to the UK ceramics manufacturing industry, and in full to the UK sanitaryware manufacturing industry. The application of the framework to the UK sanitaryware manufacturing industry has required the undertaking of a unique first-order energy audit of every such manufacturing site in the UK. As such the audit has revealed previously unknown data on the timings and magnitude of electricity demand and consumption attributable to end-use manufacturing technologies and processes. The audit also served to reveal the disparity in the attitudes toward energy services, and thus by implication towards DSM, of manufacturers within the same Standard Industrial Classification (SIC) code. In response to this, attempt is made to identify the underlying drivers which could cause this variation in attitude. A novel approach to the market segmentation of the companies within the UK ceramics manufacturing sector has been utilised to classify these companies in terms of their likelihood to participate in DSM programmes through the derived Energy Services approach. The market segmentation technique, although requiring further development to progress from a research based concept, highlights the necessity to look beyond the purely energy based needs of manufacturing industries when considering the utilisation of the Energy Services approach to facilitate DSM programs
Light from Cosmic Strings
The time-dependent metric of a cosmic string leads to an effective
interaction between the string and photons - the "gravitational Aharonov-Bohm"
effect -- and causes cosmic strings to emit light. We evaluate the radiation of
pairs of photons from cosmic strings and find that the emission from cusps,
kinks and kink-kink collisions occurs with a flat spectrum at all frequencies
up to the string scale. Further, cusps emit a beam of photons, kinks emit along
a curve, and the emission at a kink-kink collision is in all directions. The
emission of light from cosmic strings could provide an important new
observational signature of cosmic strings that is within reach of current
experiments for a range of string tensions.Comment: 8 pages, 1 figur
Prospective surveillance of invasive group a streptococcal disease, Fiji, 2005-2007.
We undertook a prospective active surveillance study of invasive group A streptococcal (GAS) disease in Fiji over a 23-month period, 2005-2007. We identified 64 cases of invasive GAS disease, which represents an average annualized all-ages incidence of 9.9 cases/100,000 population per year (95% confidence interval [CI] 7.6-12.6). Rates were highest in those >65 years of age and in those <5 years, particularly in infants, for whom the incidence was 44.9/100,000 (95% CI 18.1-92.5). The case-fatality rate was 32% and was associated with increasing age and underlying coexisting disease, including diabetes and renal disease. Fifty-five of the GAS isolates underwent emm sequence typing; the types were highly diverse, with 38 different emm subtypes and no particular dominant type. Our data support the view that invasive GAS disease is common in developing countries and deserves increased public health attention
Collisions of strings with Y junctions
We study the dynamics of Nambu--Goto strings with junctions at which three
strings meet. In particular, we exhibit one simple exact solution and examine
the process of intercommuting of two straight strings, in which they exchange
partners but become joined by a third string. We show that there are important
kinematical constraints on this process. The exchange cannot occur if the
strings meet with very large relative velocity. This may have important
implications for the evolution of cosmic superstring networks and non-abelian
string networks.Comment: 4 pages, 1 figure, uses revtex 4. Clarifying comments added to
correct a conceptual error, reference updated. Version accepted by Phys Rev
Letters, with additional references and minor change
Chiral Superconducting Membranes
We develop the dynamics of the chiral superconducting membranes (with null
current) in an alternative geometric approach either making a Lagrangian
description and a Hamiltonian point of view. Besides of this, we show the
equivalence of the resulting descriptions to the one known Dirac-Nambu-Goto
(DNG) case. Integrability for chiral string model is obtained using a proposed
light-cone gauge. In a similar way, domain walls are integrated by means of a
simple ansatz. We compare the results with recently works appeared in the
literature.Comment: Latex file, 17 pages, no figures. Improved version, typos corrected,
Comments and references adde
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