406 research outputs found
Nonassociative geometry: Towards discrete structure of spacetime
In the framework of nonassociative geometry (hep-th/0003238) a unified
description of continuum and discrete spacetime is proposed. In our approach at
the Planck scales the spacetime is described as a so-called "diodular discrete
structure" which at large spacetime scales `looks like' a differentiable
manifold. After a brief review of foundations of nonassociative geometry,we
discuss the nonassociative smooth and discrete de Sitter spacetimes.Comment: RevTex file, 5 pages, typos correcte
Nitrosamine degradation by UV light in post-combustion CO2 capture: Effect of solvent matrix
AbstractPotential production and emission of nitrosamines during post-combustion CO2 capture has drawn some attention due to their toxicity and potential carcinogenicity. One of the possible ways to reduce the concentration of nitrosamines is irradiation of the liquid streams of the capture plant with UV light. This paper shows experimental results of the degradation of nitrosamines such as N-nitroso-diethanolamine (NDELA) and N-mononitroso-piperazine (MNPZ) in different solvent matrices. These solvent matrices include water and laboratory grade monoethanolamine (MEA) aqueous solutions, as well as aqueous MEA solution and wash water that had been used in a CO2 capture pilot plant connected to a coal-fired power plant. Experiments were conducted in dedicated batch set-ups and in a continuous mini CO2 capture plant. Results show that the UV absorbance of impurities (degradation products and/or dissolved metals) present in MEA solvent that had been used in a pilot plant significantly reduces the UV degradation rate of nitrosamines. Furthermore, UV light seems to accelerate the degradation of the capture solvent itself. For these reasons, if UV light treatment is to be used in full-scale post-combustion CO2 capture plants, suitable locations would be the absorber's washing section or the stripper's condensate. At these locations, less interference of degradation products can occur and there is less solvent to be degraded
Integrable discrete nets in Grassmannians
We consider discrete nets in Grassmannians which generalize
Q-nets (maps with planar elementary
quadrilaterals) and Darboux nets (-valued maps defined on the
edges of such that quadruples of points corresponding to
elementary squares are all collinear). We give a geometric proof of
integrability (multidimensional consistency) of these novel nets, and show that
they are analytically described by the noncommutative discrete Darboux system.Comment: 10 p
The role of the North Atlantic Oscillation in controlling U.K. butterfly population size and phenology
Copyright @ 2012 The Authors. This article can be accessed from the links below.This article has been made available through the Brunel Open Access Publishing Fund.1. The North Atlantic Oscillation (NAO) exerts considerable control on U.K. weather. This study investigates the impact of the NAO on butterfly abundance and phenology using 34 years of data from the U.K. Butterfly Monitoring Scheme (UKBMS). 2. The study uses a multi-species indicator to show that the NAO does not affect overall U.K. butterfly population size. However, the abundance of bivoltine butterfly species, which have longer flight seasons, were found to be more likely to respond positively to the NAO compared with univoltine species, which show little or a negative response. 3. A positive winter NAO index is associated with warmer weather and earlier flight dates for Anthocharis cardamines (Lepidoptera: Pieridae), Melanargia galathea (Lepidoptera: Nymphalidae), Aphantopus hyperantus (Lepidoptera: Nymphalidae), Pyronia tithonus (Lepidoptera: Nymphalidae), Lasiommata megera (Lepidoptera: Nymphalidae) and Polyommatus icarus (Lepidoptera: Lycaenidae). In bivoltine species, the NAO affects the phenology of the first generation, the timing of which indirectly controls the timing of the second generation. 4. The NAO influences the timing of U.K. butterfly flight seasons more strongly than it influences population size.This study was supported by a multi-agency consortium led by the U.K. Department for Environment, Food and Rural Affairs (Defra), including the Countryside Council for Wales, the Joint Nature Conservation Committee, the Forestry Commission, Natural England, the Natural Environment Research Council, the Northern Ireland Environment Agency and Scottish Natural Heritage. This article is made available through the Brunel Open Access Publishing Fund
Chair and Bed Rise Performance in ADL‐Impaired Congregate Housing Residents
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111141/1/j.1532-5415.2000.tb04999.x.pd
Scalar cosmological perturbations from inflationary black holes
We study the correction to the scale invariant power spectrum of a scalar
field on de Sitter space from small black holes that formed during a
pre-inflationary matter dominated era. The formation probability of such black
holes is estimated from primordial Gaussian density fluctuations. We determine
the correction to the spectrum by first deriving the Keldysh propagator for a
massless scalar field on Schwarzschild-de Sitter space. Our results suggest
that the effect is strong enough to be tested -- and possibly even ruled out --
by observations.Comment: 41 pages, 11 figures, published versio
Mechanically induced current and quantum evaporation from Luttinger liquids
We investigate transport through a tunnelling junction between an
uncorrelated metallic lead and a Luttinger liquid when the latter is subjected
to a time dependent perturbation. The tunnelling current as well as the
electron energy distribution function are found to be strongly affected by the
perturbation due to generation of harmonics in the density oscillations. Using
a semiconducting lead instead of a metallic one results in electrons being
injected into the lead even without applied voltage. Some applications to
carbon nanotubes are discussed.Comment: 7 pages, 2 figures (eps files
The Bose-Einstein correlation function from a Quantum Field Theory point of view
We show that a recently proposed derivation of Bose-Einstein correlations
(BEC) by means of a specific version of thermal Quantum Field Theory (QFT),
supplemented by operator-field evolution of the Langevin type, allows for a
deeper understanding of the possible coherent behaviour of the emitting source
and a clear identification of the origin of the observed shape of the BEC
function . Previous conjectures in this matter obtained by other
approaches are confirmed and have received complementary explanation.Comment: Some misprints corrected. To be publishe in Phys. Rev.
Nonlinear QCD Evolution: Saturation without Unitarization
We consider the perturbative description of saturation based on the nonlinear
QCD evolution equation of Balitsky and Kovchegov (BK). Although the nonlinear
corrections lead to saturation of the scattering amplitude locally in impact
parameter space, we show that they do not unitarize the total cross section.
The total cross section for the scattering of a strongly interacting probe on a
hadronic target is found to grow exponentially with rapidity. The origin of
this violation of unitarity is the presence of long range Coulomb fields away
from the saturation region. The growth of these fields with rapidity is not
tempered by the nonlinearity of the BK equation.Comment: 4 pages, RevTe
Symmetry justification of Lorenz' maximum simplification
In 1960 Edward Lorenz (1917-2008) published a pioneering work on the `maximum
simplification' of the barotropic vorticity equation. He derived a coupled
three-mode system and interpreted it as the minimum core of large-scale fluid
mechanics on a `finite but unbounded' domain. The model was obtained in a
heuristic way, without giving a rigorous justification for the chosen selection
of modes. In this paper, it is shown that one can legitimate Lorenz' choice by
using symmetry transformations of the spectral form of the vorticity equation.
The Lorenz three-mode model arises as the final step in a hierarchy of models
constructed via the component reduction by means of symmetries. In this sense,
the Lorenz model is indeed the `maximum simplification' of the vorticity
equation.Comment: 8 pages, minor correction
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