3,170 research outputs found
Reducing Urban Pollution Exposure from Road Transport(RUPERT)
This paper presents the preliminary results of a two-year study on reducing urban pollution exposure from road transport (RUPERT). The main aim of this project
is to develop a new modelling framework for nitrogen dioxide, carbon monoxide and particulate matter to simulate exposures of different population groups
across a city, and to assess the impact of roadside concentrations on these exposures. This will be achieved by modelling the frequency distribution of
personal exposures (PEFDs) as a function of urban background and roadside concentrations, under different traffic conditions. The modelling approach combines new and existing models relating traffic and air pollution data, with particular emphasis of the impact of congestion, and the probabilistic modelling framework of personal exposure. Modelling of roadside concentrations consists of two main elements, namely the analysis of concentrations patterns at different roadside sites and of the relationship between traffic conditions and added
roadside pollution. Roadside concentrations are predicted using empirically derived relationships; statistical models, novel statistics and artificial neural
networks namely feed forward neural network and radial basis neural network. The exposure modelling is carried out by linking two models: the INDAIR model, which is designed to simulate probabilistically diurnal profiles of air pollutant concentrations in a range of microenvironments, and the EXPAIR model, which is designed to simulate population exposure patterns based on
population time-activity patterns and a library of micro-environmental concentrations derived from the INDAIR model
A Dense Packing of Regular Tetrahedra
We construct a dense packing of regular tetrahedra, with packing density .Comment: full color versio
Atomic X-ray Spectroscopy of Accreting Black Holes
Current astrophysical research suggests that the most persistently luminous
objects in the Universe are powered by the flow of matter through accretion
disks onto black holes. Accretion disk systems are observed to emit copious
radiation across the electromagnetic spectrum, each energy band providing
access to rather distinct regimes of physical conditions and geometric scale.
X-ray emission probes the innermost regions of the accretion disk, where
relativistic effects prevail. While this has been known for decades, it also
has been acknowledged that inferring physical conditions in the relativistic
regime from the behavior of the X-ray continuum is problematic and not
satisfactorily constraining. With the discovery in the 1990s of iron X-ray
lines bearing signatures of relativistic distortion came the hope that such
emission would more firmly constrain models of disk accretion near black holes,
as well as provide observational criteria by which to test general relativity
in the strong field limit. Here we provide an introduction to this phenomenon.
While the presentation is intended to be primarily tutorial in nature, we aim
also to acquaint the reader with trends in current research. To achieve these
ends, we present the basic applications of general relativity that pertain to
X-ray spectroscopic observations of black hole accretion disk systems, focusing
on the Schwarzschild and Kerr solutions to the Einstein field equations. To
this we add treatments of the fundamental concepts associated with the
theoretical and modeling aspects of accretion disks, as well as relevant topics
from observational and theoretical X-ray spectroscopy.Comment: 63 pages, 21 figures, Einstein Centennial Review Article, Canadian
Journal of Physics, in pres
Layer dynamics of a freely standing smectic-A film
We study the hydrodynamics of a freely-standing smectic-A film in the
isothermal, incompressible limit theoretically by analyzing the linearized
hydrodynamic equations of motion with proper boundary conditions. The dynamic
properties for the system can be obtained from the response functions for the
free surfaces. Permeation is included and its importance near the free surfaces
is discussed. The hydrodynamic mode structure for the dynamics of the system is
compared with that of bulk systems. We show that to describe the dynamic
correlation functions for the system, in general, it is necessary to consider
the smectic layer displacement and the velocity normal to the layers,
, together. Finally, our analysis also provides a basis for the
theoretical study of the off-equilibrium dynamics of freely-standing smectic-A
films.Comment: 22 pages, 4 figure
The Coupled Cluster Method in Hamiltonian Lattice Field Theory: SU(2) Glueballs
The glueball spectrum within the Hamiltonian formulation of lattice gauge
theory (without fermions) is calculated for the gauge group SU(2) and for two
spatial dimensions.
The Hilbert space of gauge-invariant functions of the gauge field is
generated by its parallel-transporters on closed paths along the links of the
spatial lattice. The coupled cluster method is used to determine the spectrum
of the Kogut-Susskind Hamiltonian in a truncated basis. The quality of the
description is studied by computing results from various truncations, lattice
regularisations and with an improved Hamiltonian.
We find consistency for the mass ratio predictions within a scaling region
where we obtain good agreement with standard lattice Monte Carlo results.Comment: 13 pages, 7 figure
Modern nuclear force predictions for the neutron-deuteron scattering lengths
The nd doublet and quartet scattering lengths have been calculated based on
the modern NN and 3N interactions. We also studied the effect of the
electromagnetic interactions in the form introduced in AV18. Switching them off
for the various nuclear force models leads to shifts of up to +0.04 fm for
doublet scattering length, which is significant for present day standards. The
electromagnetic effects have also a noticeable effect on quartet scattering
length, which otherwise is extremely stable under the exchange of the nuclear
forces. For the current nuclear force models there is a strong scatter of the
3H binding energy and the doublet scattering length values around an averaged
straight line (Phillips line). This allows to use doublet scattering length and
the 3H binding energy as independent low energy observables.Comment: 16 pages, 1 table, 4 ps figure
Normal Cones and Thompson Metric
The aim of this paper is to study the basic properties of the Thompson metric
in the general case of a real linear space ordered by a cone . We
show that has monotonicity properties which make it compatible with the
linear structure. We also prove several convexity properties of and some
results concerning the topology of , including a brief study of the
-convergence of monotone sequences. It is shown most of the results are
true without any assumption of an Archimedean-type property for . One
considers various completeness properties and one studies the relations between
them. Since is defined in the context of a generic ordered linear space,
with no need of an underlying topological structure, one expects to express its
completeness in terms of properties of the ordering, with respect to the linear
structure. This is done in this paper and, to the best of our knowledge, this
has not been done yet. The Thompson metric and order-unit (semi)norms
are strongly related and share important properties, as both are
defined in terms of the ordered linear structure. Although and
are only topological (and not metrical) equivalent on , we
prove that the completeness is a common feature. One proves the completeness of
the Thompson metric on a sequentially complete normal cone in a locally convex
space. At the end of the paper, it is shown that, in the case of a Banach
space, the normality of the cone is also necessary for the completeness of the
Thompson metric.Comment: 36 page
Neutron scattering and molecular correlations in a supercooled liquid
We show that the intermediate scattering function for neutron
scattering (ns) can be expanded naturely with respect to a set of molecular
correlation functions that give a complete description of the translational and
orientational two-point correlations in the liquid. The general properties of
this expansion are discussed with special focus on the -dependence and hints
for a (partial) determination of the molecular correlation functions from
neutron scattering results are given. The resulting representation of the
static structure factor is studied in detail for a model system using
data from a molecular dynamics simulation of a supercooled liquid of rigid
diatomic molecules. The comparison between the exact result for and
different approximations that result from a truncation of the series
representation demonstrates its good convergence for the given model system. On
the other hand it shows explicitly that the coupling between translational
(TDOF) and orientational degrees of freedom (ODOF) of each molecule and
rotational motion of different molecules can not be neglected in the
supercooled regime.Further we report the existence of a prepeak in the
ns-static structure factor of the examined fragile glassformer, demonstrating
that prepeaks can occur even in the most simple molecular liquids. Besides
examining the dependence of the prepeak on the scattering length and the
temperature we use the expansion of into molecular correlation
functions to point out intermediate range orientational order as its principle
origin.Comment: 13 pages, 7 figure
Nonleptonic two-body charmless B decays involving a tensor meson in ISGW2 model
Nonleptonic charmless B decays into a pseudoscalar (P) or a vector (V) meson
accompanying a tensor (T) meson are re-analyzed. We scrutinize the hadronic
uncertainties and ambiguities of the form factors which appear in the
literature. The Isgur-Scora-Grinstein-Wise updated model (ISGW2) is adopted to
evaluate the relevant hadronic matrix elements. We calculate the branching
ratios and CP asymmetries for various decay processes. With the
ISGW2 model, the branching ratios are enhanced by about an order of magnitude
compared to the previous estimates. We show that the ratios \calB(B\to
VT)/\calB(B\to PT) for some strangeness-changing processes are very sensitive
to the CKM angle ().Comment: 23 pages, REVTEX; minor clarifications included; to appear in Phys.
Rev.
Protective Effect of Ocotillol, the Derivate of Ocotillol-Type Saponins in Panax Genus, against Acetic Acid-Induced Gastric Ulcer in Rats Based on Untargeted Metabolomics
Gastric ulcer (GU), a prevalent digestive disease, has a high incidence and is seriously harmful to human health. Finding a natural drug with a gastroprotective effect is needed. Ocotillol, the derivate of ocotillol-type saponins in the Panax genus, possesses good anti-inflammatory activity. The study aimed to investigate the gastroprotective effect of ocotillol on acetic acid-induced GU rats. The serum levels of endothelin-1 (ET-1) and nitric oxide (NO), the gastric mucosa levels of epidermal growth factor, superoxide dismutase and NO were assessed. Hematoxylin and eosin staining of gastric mucosa for pathological changes and immunohistochemical staining of ET-1, epidermal growth factor receptors and inducible nitric oxide synthase were evaluated. A UPLC-QTOF-MS-based serum metabolomics approach was applied to explore the latent mechanism. A total of 21 potential metabolites involved in 7 metabolic pathways were identified. The study helps us to understand the pathogenesis of GU and to provide a potential natural anti-ulcer agent
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