472 research outputs found
Numerical modelling of lateral stress on integral abutments due to cyclic loading
The integral bridge concept eliminates problems associated with expansion joints and bearings used on conventional bridges. However, integral structures are not free from problems, and of particular concern is the magnitude of lateral soil stress which acts on the abutments. The cyclic nature of abutment displacement, caused by thermal loading of the deck, results in increased lateral soil stress from the granular backfill. Previous experiments investigated the fundamental behaviour of a granular soil element under integral bridge loading. No existing constitutive soil model replicated this behaviour, and therefore a soil model has been developed based upon this data. It was designed to account for the changes in secant stiffness and vertical strain due to the density and rolling/sliding behaviour of soil particles at the active state, found to be important in the previous research. The model was implemented into a finite difference method program, and initially validated by modelling the experimental triaxial tests. Subsequent modelling of centrifuge tests of bridge abutments, carried out by independent researchers, allowed the soil model to be validated at system level. After validation and testing, the model was considered suitable for predicting the lateral stress profile acting on integral bridge abutments and used in a parametric study. This highlighted that the value of wall friction coefficient is particularly significant in the system behaviour. The centrifuge test is an idealised system where only rotation/flexure is possible, so a spread base abutment was modelled to investigate the predicted stress profile for an in-service bridge. These were shown to be significantly different to those prescribed by BA42/96, both in shape and magnitude. Additionally, modelling daily cycles results in a different profile to yearly cycles. This research has shown that the soil model developed can provide good estimates of lateral soil stress. This can be used to further investigate soil loads acting on integral bridge abutments with the aim of improving the design of such structures
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The sensitivity of the colour of dust in MSG-SEVIRI Desert Dust infrared composite imagery to surface and atmospheric conditions
Infrared "Desert Dust" composite imagery taken by the Spinning Enhanced Visible and InfraRed Imager (SEVIRI), onboard the Meteosat Second Generation (MSG) series of satellites above the equatorial East Atlantic, has been widely used for more than a decade to identify and track the presence of dust storms from and over the Sahara Desert, the Middle East, and southern Africa. Dust is characterised by distinctive pink colours in the Desert Dust false-colour imagery; however, the precise colour is influenced by numerous environmental properties, such as the surface thermal emissivity and skin temperature, the atmospheric water vapour content, the quantity and height of dust in the atmosphere, and the infrared optical properties of the dust itself. For this paper, simulations of SEVIRI infrared measurements and imagery have been performed using a modelling system, which combines dust concentrations simulated by the aerosol transport model COSMO-MUSCAT (COSMO: COnsortium for Small-scale MOdelling; MUSCAT: MUltiScale Chemistry Aerosol Transport Model) with radiative transfer simulations from the RTTOV (Radiative Transfer for TOVS) model. Investigating the sensitivity of the synthetic infrared imagery to the environmental properties over a 6-month summertime period from 2011 to 2013, it is confirmed that water vapour is a major control on the apparent colour of dust, obscuring its presence when the moisture content is high. Of the three SEVIRI channels used in the imagery (8.7, 10.8, and 12.0 ÎŒm), the channel at 10.8 ÎŒm has the highest atmospheric transmittance and is therefore the most sensitive to the surface skin temperature. A direct consequence of this sensitivity is that the background desert surface exhibits a strong diurnal cycle in colour, with light blue colours possible during the day and purple hues prevalent at night. In dusty scenes, the clearest pink colours arise from high-altitude dust in dry atmospheres. Elevated dust influences the dust colour primarily by reducing the contrast in atmospheric transmittance above the dust layer between the SEVIRI channels at 10.8 and 12.0 ÎŒm, thereby boosting red and pink colours in the imagery. Hence, the higher the dust altitude, the higher the threshold column moisture needed for dust to be obscured in the imagery: for a sample of dust simulated to have an aerosol optical depth (AOD) at 550 nm of 2-3 at an altitude of 3-4 km, the characteristic colour of the dust may only be impaired when the total column water vapour is particularly moist ('39 mm). Meanwhile, dust close to the surface (altitude < 1 km) is only likely to be apparent when the atmosphere is particularly dry and when the surface is particularly hot, requiring column moisture/13 mm and skin temperatures '314 K, and is highly unlikely to be apparent when the skin temperature is/300 K. Such low-altitude dust will regularly be almost invisible within the imagery, since it will usually be beneath much of the atmospheric water vapour column. It is clear that the interpretation of satellite-derived dust imagery is greatly aided by knowledge of the background environment
Regression equation for Ar3 temperature for coarse grained as-cast steels
A regression equation for the Ar3 temperature for as-cast ferrite/pearlite steels has been
obtained. At these coarse grain sizes, very little influence of grain size on the Ar3 is observed. Out of all the elements examined, C, Mn and Nb had the major influence in decreasing the
Ar3. A change in cooling rate from 10 to 200K/min results in only a small decrease of around
25oC. Of particular interest is the very marked effect of Nb in reducing the Ar3, an addition of
0.03%Nb causing a decrease in the Ar3 of 55oC
Production, Collection and Utilization of Very Long-Lived Heavy Charged Leptons
If a fourth generation of leptons exists, both the neutrino and its charged
partner must be heavier than 45 GeV. We suppose that the neutrino is the
heavier of the two, and that a global or discrete symmetry prohibits
intergenerational mixing. In that case, non-renormalizable Planck scale
interactions will induce a very small mixing; dimension five interactions will
lead to a lifetime for the heavy charged lepton of years. Production
of such particles is discussed, and it is shown that a few thousands can be
produced and collected at a linear collider. The possible uses of these heavy
leptons is also briefly discussed.Comment: 9 pages Late
(No) Eternal Inflation and Precision Higgs Physics
Even if nothing but a light Higgs is observed at the LHC, suggesting that the
Standard Model is unmodified up to scales far above the weak scale, Higgs
physics can yield surprises of fundamental significance for cosmology. As has
long been known, the Standard Model vacuum may be metastable for low enough
Higgs mass, but a specific value of the decay rate holds special significance:
for a very narrow window of parameters, our Universe has not yet decayed but
the current inflationary period can not be future eternal. Determining whether
we are in this window requires exquisite but achievable experimental precision,
with a measurement of the Higgs mass to 0.1 GeV at the LHC, the top mass to 60
MeV at a linear collider, as well as an improved determination of alpha_s by an
order of magnitude on the lattice. If the parameters are observed to lie in
this special range, particle physics will establish that the future of our
Universe is a global big crunch, without harboring pockets of eternal
inflation, strongly suggesting that eternal inflation is censored by the
fundamental theory. This conclusion could be drawn even more sharply if
metastability with the appropriate decay rate is found in the MSSM, where the
physics governing the instability can be directly probed at the TeV scale.Comment: 25 pages, 3 figures. v2: updated value of top mass, added references,
JHEP published versio
Comparing plasma and faecal measures of steroid hormones in Adelie penguins Pygoscelis adeliae
Physiological measurements of both stress and sex hormones are often used to estimate the consequences of natural or human-induced change in ecological studies of various animals. Different methods of hormone measurement exist, potentially explaining variation in results across studies; methods should be cross-validated to ensure that they correlate. We directly compared faecal and plasma hormone measurements for the first time in a wild free-living species, the Adelie penguin (Pygoscelis adeliae). Blood and faecal samples were simultaneously collected from individual penguins for comparison and assayed for testosterone and corticosterone (or their metabolites). Sex differences and variability within each measure, and correlation of values across measures were compared. For both hormones, plasma samples showed greater variation than faecal samples. Males had higher mean corticosterone concentrations than females, but the difference was only statistically significant in faecal samples. Plasma testosterone, but not faecal testosterone, was significantly higher in males than females. Correlation between sample types was poor overall, and weaker in females than in males, perhaps because measures from plasma represent hormones that are both free and bound to globulins, whereas measures from faeces represent only the free portion. Faecal samples also represent a cumulative measure of hormones over time, as opposed to a plasma âsnapshotâ concentration. Our data indicate that faecal sampling appears more suitable for assessing baseline hormone concentrations, whilst plasma sampling may best define immediate responses to environmental events. Consequently, future studies should ensure that they select the most appropriate matrix and method of hormone measurement to answer their research questions
Anti-Periodic Boundary Conditions in Supersymmetric DLCQ
It is of considerable importance to have a numerical method for solving
supersymmetric theories that can support a non-zero central charge. The central
charge in supersymmetric theories is in general a boundary integral and
therefore vanishes when one uses periodic boundary conditions. One is therefore
prevented from studying BPS states in the standard supersymmetric formulation
of DLCQ (SDLCQ). We present a novel formulation of SDLCQ where the fields
satisfy anti-periodic boundary conditions. The Hamiltonian is written as the
anti-commutator of two charges, as in SDLCQ. The anti-periodic SDLCQ we
consider breaks supersymmetry at finite resolution, but requires no
renormalization and becomes supersymmetric in the continuum limit. In
principle, this method could be used to study BPS states. However, we find its
convergence to be disappointingly slow.Comment: 9pp, 2 figure
Self Excitation of the Tunneling Scalar Field in False Vacuum Decay
A method to determine the quantum state of a scalar field after
-symmetric bubble nucleation has been developed recently. The method has
an advantage that it concisely gives us a clear picture of the resultant
quantum state. In particular, one may interpret the excitations as a particle
creation phenomenon just as in the case of particle creation in curved
spacetime. As an application, we investigate in detail the spectrum of quantum
excitations of the tunneling field when it undergoes false vacuum decay. We
consider a tunneling potential which is piece-wise quadratic, hence is simple
enough to allow us an analytical treatment. We find a strong dependence of the
excitation spectrum upon the shape of the potential on the true vacuum side. We
then discuss features of the excitation spectrum common to general tunneling
potentials not restricted to our simple model.Comment: 24 pages, uuencoded compressed postscript fil
A Matrix Big Bang
The light-like linear dilaton background represents a particularly simple
time-dependent 1/2 BPS solution of critical type IIA superstring theory in ten
dimensions. Its lift to M-theory, as well as its Einstein frame metric, are
singular in the sense that the geometry is geodesically incomplete and the
Riemann tensor diverges along a light-like subspace of codimension one. We
study this background as a model for a big bang type singularity in string
theory/M-theory. We construct the dual Matrix theory description in terms of a
(1+1)-d supersymmetric Yang-Mills theory on a time-dependent world-sheet given
by the Milne orbifold of (1+1)-d Minkowski space. Our model provides a
framework in which the physics of the singularity appears to be under control.Comment: 25 pages, LaTeX; v2: discussion of singularity of Einstein frame
metric added, references adde
Unconventional low-energy SUSY from warped geometry
Supersymmetric models with a warped fifth spatial dimension can solve the
hierarchy problem, avoiding some shortcomings of non-supersymmetric
constructions, and predict a plethora of new phenomena at typical scales Lambda
not far from the electroweak scale (Lambda ~ a few TeV). In this paper we
derive the low-energy effective theories of these models, valid at energies
below Lambda. We find that, in general, such effective theories can deviate
significantly from the Minimal Supersymmetric Standard Model (MSSM) or other
popular extensions of it, like the NMSSM: they have non-minimal Kaehler
potentials (even in the Mp -> \infty limit), and the radion is coupled to the
visible fields, both in the superpotential and the Kaehler potential, in a
non-trivial (and quite model-independent) fashion. The corresponding
phenomenology is pretty unconventional, in particular the electroweak breaking
occurs in a non-radiative way, with tan beta \simeq 1 as a quite robust
prediction, while the mass of the lightest Higgs boson can be as high as ~ 700
GeV.Comment: 53 pages, 2 ps figure
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