338 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
Analysis of different preferences for the EU's regulatory options forendocrine disruptor identification criteria using argumentation theory
What criteria are most suitable to identify endocrine disrupting substances (EDSs) for regulatory purposes in the EU? The results of the European Commission's public consultation, as part of the process to establish identification criteria for EDSs, show that different regulatory options are supported. Some respondents prefer an option including hazard characterization considerations, whereas others prefer an option that avoids these considerations and introduces several hazard-identification based weight-of-evidence categories. In this study, the argumentation underlying the different preferences for identification criteria are analyzed and compared using pragma-dialectical argumentation theory (PDAT). All responses of non-anonymous, national governments that submitted a response in English (n = 17) were included. Responses of other stakeholder organizations were included if a Google News search returned an opinionated presence in the media on the subject (n = 9). Five topical themes and 21 underlying issues were identified. The themes are 1) mechanistic understanding of EDSs, 2) regulatory considerations related to the identification of EDSs, 3) consistency with existing regulatory frameworks, and 4) evaluations of specific issues related to a category approach and 5) related to including potency. We argue that two overarching (implicit) ‘advocacy coalitions’ can be discerned, that adopted contrasting positions towards the identified themes and issues. Among these ‘coalitions’, there appears to be consensus about the necessity of having ‘science-based’ criteria, though different perspectives exist as to what the most accurate mechanistic understanding of EDSs entails. To move the discussion forward, we argue that a societal dialogue would be beneficial, where EDS science and regulation are discussed as interrelated themes
Early reconstitution of effector memory CD4+ CMV-specific T cells protects against CMV reactivation following allogeneic SCT.
Reactivation of CMV is a common complication following allogeneic haematopoietic SCT and is associated with significant morbidity and mortality. The relative importance of the CD4+ and CD8+ components of the CMV-specific immune response in protection from reactivation is unclear. The CMV-specific CD4+ and CD8+ immune response was measured at serial time points in 32 patients following allogeneic HSCT. Intracellular cytokine staining following CMV lysate stimulation and HLA-peptide tetramers were used to determine CMV-specific CD4+ and CD8+ responses, respectively. A deficient CMV-specific CD4+ T-cell immune response within the first 30-50 days post transplant was associated with high risk of viral reactivation. Patients with combined impairment of the CD4+ and CD8+ immune response within the first 100 days were susceptible to late viral reactivation. The frequency of CMV-specific CD4+ T cells correlated with CMV-specific CD8+ T cells, comprising 10% of the whole T-cell repertoire. Early CMV-specific CD4+ T-cell reconstitution was dominated by effector memory cells with normal levels of IL-2 resuming 6 months following transplantation. In summary, both CD4 and CD8 CMV-specific immune reconstitution is required for protection from recurrent activation. Measurement of the magnitude of the CMV-specific CD4+ immune response is useful in managing viral reactivation following HSCT
Scalar perturbation spectra from warm inflation
We present a numerical integration of the cosmological scalar perturbation
equations in warm inflation. The initial conditions are provided by a
discussion of the thermal fluctuations of an inflaton field and thermal
radiation using a combination of thermal field theory and thermodynamics. The
perturbation equations include the effects of a damping coefficient
and a thermodynamic potential . We give an analytic expression for the
spectral index of scalar fluctuations in terms of a new slow-roll parameter
constructed from . A series of toy models, inspired by spontaneous
symmetry breaking and a known form of the damping coefficient, lead to a
spectrum with on large scales and on small scales.Comment: 12 pages, 5 figures, RevTeX 4, revised with extra figure
Aging-related defects in macrophage function are driven by MYC and USF1 transcriptional programs
Macrophages are central innate immune cells whose function declines with age. The molecular mechanisms underlying age-related changes remain poorly understood, particularly in human macrophages. We report a substantial reduction in phagocytosis, migration, and chemotaxis in human monocyte-derived macrophages (MDMs) from older (>50 years old) compared with younger (18–30 years old) donors, alongside downregulation of transcription factors MYC and USF1. In MDMs from young donors, knockdown of MYC or USF1 decreases phagocytosis and chemotaxis and alters the expression of associated genes, alongside adhesion and extracellular matrix remodeling. A concordant dysregulation of MYC and USF1 target genes is also seen in MDMs from older donors. Furthermore, older age and loss of either MYC or USF1 in MDMs leads to an increased cell size, altered morphology, and reduced actin content. Together, these results define MYC and USF1 as key drivers of MDM age-related functional decline and identify downstream targets to improve macrophage function in aging
Metal enrichment processes
There are many processes that can transport gas from the galaxies to their
environment and enrich the environment in this way with metals. These metal
enrichment processes have a large influence on the evolution of both the
galaxies and their environment. Various processes can contribute to the gas
transfer: ram-pressure stripping, galactic winds, AGN outflows, galaxy-galaxy
interactions and others. We review their observational evidence, corresponding
simulations, their efficiencies, and their time scales as far as they are known
to date. It seems that all processes can contribute to the enrichment. There is
not a single process that always dominates the enrichment, because the
efficiencies of the processes vary strongly with galaxy and environmental
properties.Comment: 18 pages, 8 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 17; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Classical Yang-Mills Black hole hair in anti-de Sitter space
The properties of hairy black holes in Einstein–Yang–Mills (EYM) theory are reviewed, focusing on spherically symmetric solutions. In particular, in asymptotically anti-de Sitter space (adS) stable black hole hair is known to exist for frak su(2) EYM. We review recent work in which it is shown that stable hair also exists in frak su(N) EYM for arbitrary N, so that there is no upper limit on how much stable hair a black hole in adS can possess
Magnetic Field Generation in Stars
Enormous progress has been made on observing stellar magnetism in stars from
the main sequence through to compact objects. Recent data have thrown into
sharper relief the vexed question of the origin of stellar magnetic fields,
which remains one of the main unanswered questions in astrophysics. In this
chapter we review recent work in this area of research. In particular, we look
at the fossil field hypothesis which links magnetism in compact stars to
magnetism in main sequence and pre-main sequence stars and we consider why its
feasibility has now been questioned particularly in the context of highly
magnetic white dwarfs. We also review the fossil versus dynamo debate in the
context of neutron stars and the roles played by key physical processes such as
buoyancy, helicity, and superfluid turbulence,in the generation and stability
of neutron star fields.
Independent information on the internal magnetic field of neutron stars will
come from future gravitational wave detections. Thus we maybe at the dawn of a
new era of exciting discoveries in compact star magnetism driven by the opening
of a new, non-electromagnetic observational window.
We also review recent advances in the theory and computation of
magnetohydrodynamic turbulence as it applies to stellar magnetism and dynamo
theory. These advances offer insight into the action of stellar dynamos as well
as processes whichcontrol the diffusive magnetic flux transport in stars.Comment: 41 pages, 7 figures. Invited review chapter on on magnetic field
generation in stars to appear in Space Science Reviews, Springe
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