836 research outputs found
Effect of aspect ratio on fire resistance of hollow core concrete floors
Previous studies have shown that the fire performance of hollowcore units is
significantly affected by the end support conditions, but it has not been clear how the fire
resistance of the overall floor system can be improved by providing side supports. The
previous studies used beam grillage and shell elements to separately model the hollowcore
units and the topping concrete slab using the platform of the non-linear finite element
program SAFIR. The modelling method required a lot of computational resources and is not
ideal to model a large floor area. This paper describes the effect of the side supports and the
aspect ratio of the floor on the predicted fire resistance. It also compares the efficiencies of
shell elements and short beam elements for finite element modelling of the topping concrete
in fire conditions. The results show that integrating the topping concrete slab into the beam
grillages reduces the complexity of the model and also provides satisfactory results. Side
supports can increase the fire performance of hollowcore floor slabs provided that the spacing
of the side supports does not greatly exceed the span length
Design of Steel Portal Frame Buildings for Fire Safety
This paper describes a study into the fire behaviour of steel portal frame buildings at elevated
temperatures using the finite element programme SAFIR. The finite element analysis carried
out in this report is three dimensional and covers different support conditions at the column
bases, the presence of axial restraints provided by the end walls, different fire severities
within the building, different levels of out-of-plane restraint to the columns and the effect of
concrete encasement to the columns. From a large number of analyses, it is shown that the
bases of the steel portal frames at the foundations must be designed and constructed with
some level of fixity to ensure that the structure will deform in an acceptable way during fire,
with no outwards collapse of the walls. The analyses also show that to avoid sidesway (i.e.
collapse outwards) it is not necessary for steel portal frame columns to be fire-protected
unless the designer wishes to ensure that the columns and the wall panels remain standing,
during and after the fire
Parametric study of modelling structural timber in fire with different software packages
In a bid to accurately model structural behaviour of timber buildings in fire, a number of obstacles have been identified which must be fully understood before advanced computer modelling can accurately be used to represent physical behaviour. This paper discusses the obstacles, with suggestions on how to mitigate them, incorporating the challenges of using general purpose finite element software. The paper examines modelling with ANSYS, SAFIR and ABAQUS and the individual and collective challenges related to thermal analyses of timber structures in fire conditions. It considers the effects various model parameters (thermal and structural) may have on physical interpretation of experimental data in comparison with the accuracy of numerical solutions. In detail, the study looks at the effects of 1D and 2D heat transfer analyses, finite element mesh sizes, time steps and different thermal property approaches on thermal models of timber members in fires. It further recommends how best to model these structures using the different finite element software packages
The SLICK hair locus derived from Senepol cattle confers thermotolerance to intensively managed lactating Holstein cows
AbstractThe SLICK haplotype (http://omia.angis.org.au/OMIA001372/9913/) in cattle confers animals with a short and sleek hair coat. Originally identified in Senepol cattle, the gene has been introduced into Holsteins. The objectives of the current study were to determine (1) whether lactating Holsteins with the slick hair phenotype have superior ability for thermoregulation compared with wild-type cows or relatives not inheriting the SLICK haplotype, and (2) whether seasonal depression in milk yield would be reduced in SLICK cows. In experiment 1, diurnal variation in vaginal temperature in the summer was monitored for cows housed in a freestall barn with fans and sprinklers. Vaginal temperatures were lower in slick-haired cows than in relatives and wild-type cows. In experiment 2, acute responses to heat stress were monitored after cows were moved to a dry lot in which the only heat abatement was shade cloth. The increases in rectal temperature and respiration rate caused by heat stress during the day were lower for slick cows than for relatives or wild-type cows. Moreover, sweating rate was higher for slick cows than for cows of the other 2 types. In experiment 3, effects of season of calving (summer vs. winter) on milk yield and composition were determined. Compared with milk yield of cows calving in winter, milk yield during the first 90 d in milk was lower for cows calving in the summer. However, this reduction was less pronounced for slick cows than for wild-type cows. In conclusion, Holsteins with slick hair have superior thermoregulatory ability compared with non-slick animals and experience a less drastic depression in milk yield during the summer
Comparison between chiral and meson-theoretic nucleon-nucleon potentials through (p,p') reactions
We use proton-nucleus reaction data at intermediate energies to test the
emerging new generation of chiral nucleon-nucleon (NN) potentials. Predictions
from a high quality one-boson-exchange (OBE) force are used for comparison and
evaluation. Both the chiral and OBE models fit NN phase shifts accurately, and
the differences between the two forces for proton-induced reactions are small.
A comparison to a chiral model with a less accurate NN description sets the
scale for the ability of such models to work for nuclear reactions.Comment: 6 pages, revtex, 4 eps-figure
Come back Marshall, all is forgiven? : Complexity, evolution, mathematics and Marshallian exceptionalism
Marshall was the great synthesiser of neoclassical economics. Yet with his qualified assumption of self-interest, his emphasis on variation in economic evolution and his cautious attitude to the use of mathematics, Marshall differs fundamentally from other leading neoclassical contemporaries. Metaphors inspire more specific analogies and ontological assumptions, and Marshall used the guiding metaphor of Spencerian evolution. But unfortunately, the further development of a Marshallian evolutionary approach was undermined in part by theoretical problems within Spencer's theory. Yet some things can be salvaged from the Marshallian evolutionary vision. They may even be placed in a more viable Darwinian framework.Peer reviewedFinal Accepted Versio
Dimensionless cosmology
Although it is well known that any consideration of the variations of
fundamental constants should be restricted to their dimensionless combinations,
the literature on variations of the gravitational constant is entirely
dimensionful. To illustrate applications of this to cosmology, we explicitly
give a dimensionless version of the parameters of the standard cosmological
model, and describe the physics of Big Bang Neucleosynthesis and recombination
in a dimensionless manner. The issue that appears to have been missed in many
studies is that in cosmology the strength of gravity is bound up in the
cosmological equations, and the epoch at which we live is a crucial part of the
model. We argue that it is useful to consider the hypothetical situation of
communicating with another civilization (with entirely different units),
comparing only dimensionless constants, in order to decide if we live in a
Universe governed by precisely the same physical laws. In this thought
experiment, we would also have to compare epochs, which can be defined by
giving the value of any {\it one} of the evolving cosmological parameters. By
setting things up carefully in this way one can avoid inconsistent results when
considering variable constants, caused by effectively fixing more than one
parameter today. We show examples of this effect by considering microwave
background anisotropies, being careful to maintain dimensionlessness
throughout. We present Fisher matrix calculations to estimate how well the fine
structure constants for electromagnetism and gravity can be determined with
future microwave background experiments. We highlight how one can be misled by
simply adding to the usual cosmological parameter set
'Education, education, education' : legal, moral and clinical
This article brings together Professor Donald Nicolson's intellectual interest in professional legal ethics and his long-standing involvement with law clinics both as an advisor at the University of Cape Town and Director of the University of Bristol Law Clinic and the University of Strathclyde Law Clinic. In this article he looks at how legal education may help start this process of character development, arguing that the best means is through student involvement in voluntary law clinics. And here he builds upon his recent article which argues for voluntary, community service oriented law clinics over those which emphasise the education of students
Current status of turbulent dynamo theory: From large-scale to small-scale dynamos
Several recent advances in turbulent dynamo theory are reviewed. High
resolution simulations of small-scale and large-scale dynamo action in periodic
domains are compared with each other and contrasted with similar results at low
magnetic Prandtl numbers. It is argued that all the different cases show
similarities at intermediate length scales. On the other hand, in the presence
of helicity of the turbulence, power develops on large scales, which is not
present in non-helical small-scale turbulent dynamos. At small length scales,
differences occur in connection with the dissipation cutoff scales associated
with the respective value of the magnetic Prandtl number. These differences are
found to be independent of whether or not there is large-scale dynamo action.
However, large-scale dynamos in homogeneous systems are shown to suffer from
resistive slow-down even at intermediate length scales. The results from
simulations are connected to mean field theory and its applications. Recent
work on helicity fluxes to alleviate large-scale dynamo quenching, shear
dynamos, nonlocal effects and magnetic structures from strong density
stratification are highlighted. Several insights which arise from analytic
considerations of small-scale dynamos are discussed.Comment: 36 pages, 11 figures, Spa. Sci. Rev., submitted to the special issue
"Magnetism in the Universe" (ed. A. Balogh
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