1,947 research outputs found
“The most philosophically of all the sciences”: Karl Popper and physical cosmology
No full textProblems of scientific cosmology only rarely occur in the works of Karl Popper. Nevertheless, it was a subject that interested him and which he occasionally commented on. What is more important, his general claim of falsifiability as a criterion that demarcates science from non-science has played a significant role in periods of the development of modern physical cosmology. The paper examines the historical contexts of the interaction between cosmology and Popperian philosophy of science. Apart from covering Popper’s inspiration from Einstein and his views on questions of cosmology, it focuses on the impact of his thoughts in two periods of controversy of modern cosmology, the one related to the steady state theory and the other to the recent multiverse proposal. It turns out that the impact has been considerable, and continues to be so, but also that the versions of Popperian methodology discussed by cosmologists are sometimes far from what Popper actually thought and wrote
Differentiation of the brain vasculature : the answer came blowing by the Wnt
No full textVascularization of the vertebrate brain takes place during embryonic development from a preformed perineural vascular plexus. As a consequence of the intimate contact with neuroectodermal cells the vessels, which are entering the brain exclusively via sprouting angiogenesis, acquire and maintain unique barrier properties known as the blood-brain barrier (BBB). The endothelial BBB depends upon the close association of endothelial cells with pericytes, astrocytes, neurons and microglia, which are summarized in the term neuro-vascular unit. Although it is known since decades that the CNS tissue provides the cues for BBB induction and differentiation in endothelial cells, the molecular mechanism remained obscure. Only recently, the canonical Wnt/beta-catenin pathway and the Wnt7a/7b growth factors have been implicated in brain angiogenesis on the one hand and in BBB induction on the other. This breakthrough in understanding the differentiation of the brain vasculature prompted us to review these findings embedded in the emerging concepts of Wnt signaling in the vasculature. In particular, interactions with other pathways that are crucial for vascular development such as VEGF, Notch, angiopoietins and Sonic hedgehog are discussed. Finally, we considered the potential role of the Wnt pathway in vascular brain pathologies in which BBB function is hampered, as for example in glioma, stroke and Alzheimer's disease
Numerical computation for parallel plate thermoacoustic heat exchangers in standing wave oscillatory flow
No full textA simplified computational method for studying the heat transfer characteristics of parallel plate thermoacoustic heat exchangers is presented. The model integrates the thermoacoustic equations of the standard linear theory into an energy balance-based numerical calculus scheme. Details of the time-averaged temperature and heat flux density distributions within a representative domain of the heat exchangers
and adjoining stack are given. The effect of operation conditions and geometrical parameters on the heat exchanger performance is investigated and main conclusions relevant for HX design are drawn as far as fin length, fin spacing, blockage ratio, gas and secondary fluid-side heat transfer coefficients are concerned. Most relevant is that
the fin length and spacing affect in conjunction the heat exchanger behaviour and have to be simultaneously optimized to minimize thermal losses localized at the HX-stack
junctions. Model predictions fit experimental data found in literature within 36% and 49% respectively at moderate and high acoustic Reynolds numbers
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Jetting, In-Nozzle Meniscus Motion and Nozzle-Plate Flooding in An Industrial Drop-on-Demand Print Head
No full textThe state of the ink film at and near the nozzles of a drop-ondemand(DoD) print head during jetting has a direct impact on
printing performance and reliability. We have developed highspeed imaging apparatus and analytical techniques to investigate
the ink film dynamics on an industrial print head nozzle-plate in real-time. In addition to a direct correlation between the jet
emergence velocity and drive voltage, drive-dependent variations in the oscillation of the ink meniscus in adjacent nozzles were also observed. Using a ray-tracing model to analyze the meniscus shape, the meniscus oscillations for both printing and nonprinting nozzles were found to be complex and involve elements such as pre-oscillation and high-order surface waves. The flooding of non-firing nozzles, deliberately caused by the application of maximum drive voltage to a neighboring nozzle, has been recorded and analyzed dynamically. The build-up of fluid in an annulus around the nozzle (flooding rate) has been characterized and compared with models for the net ink flow
through the nozzle
Cracking and tension field action in composite beams
No full textTwo aspects of the behaviour of uncased composite 'T' beams of steel
and concrete are considered.
Flexural cracking in the reinforced concrete slab was studied by
subjecting seven 350-mm deep composite beams to hogging bending moment.
Measured strains were found to exceed those calculated from an elastic
analysis ignoring concrete in tension. Also, the first cracks to form in
the slab were much wider than expected. Both of these effects are shown
to be due to drying shrinkage in the slab of the composite beam. A
formula for calculating the mean surface strain in the slab, which allows
for both drying shrinkage and tension stiffening, is proposed.
Consideration of the parameters which affect cracking leads to a
formula for predicting crack widths in composite beams. Comparison with
experimental results shows that it is sufficiently accurate for design
purposes.
In a second series of tests, three 900-mm deep composite plate girders
with slender webs were subjected to combined shear and bending to study
their ultimate load behaviour. Failure was due to the formation of a
plastic collapse mechanism which closely resembles that observed in plain
steel girders under similar loading. The addition of a concrete slab
acting compositely with the girder increased the ultimate strength of the
beam, but variations in the size of the slab and the strength of the
shear connection had negligible effect on the beam's strength.
An idealised collapse model, based on the experimental observations,
is described and is used in the development of a method to calculate the
ultimate strength of composite plate girders. It is shown that a design
method for plain steel girders in the draft Part 3, BS5400 may, with
small modifications, be applied to composite plate girders
Centrifuge modelling of plate bearing tests
No full textCurrent guidance given on plate bearing testing of granular soils suggests that the plate be at least five times the nominal size of the coarsest material. However this limiting ratio can have a huge influence on the reaction load required from plant and resources when conducted to confirm strength parameters used in the design of the sub grade and platform materials of working piling platforms. The aim of the research presented in this paper was to investigate the effect of particle to plate size to establish, if any correlation which would allow the use of a smaller plate size and plant on site to allow more economical plate testing of the platform for design purposes. Different sized model plate bearing tests were carried out in a centrifuge on a large, coarse grained Devonian Limestone. The results from the test series reported show a good similarity in the bearing stress against displacement behaviour between the different sized plate sizes
Catalogue de l'oeuvre lithographieÌ et graveÌ de H. Daumier /
No full text"TireÌ aÌ 100 exemplaires numeÌroteÌs"--P. [2].The plate was etched in sections by Alfred TaieÌe, Harpignies, FeÌlicien Rops, and Daumier at a soireÌe in 1872; see p. 47. The printer is given on the plate as Cadart, Paris.Mode of access: Internet.Library's copy bound in gray paper backed with vellum, the original paper cover included. Author, title and date written on spine. Slipcase.Library's copy is no. 73, initialed by the publishers H. Heymann and J. Perois
Moist Rayleigh-Benard Convection
No full textWe report the observations from turbulent thermal Rayleigh-Benard convection experiment with a two-phase liquid-vapor binary mixture. Evaporation/condensation processes in a turbulent convection are accompanied by the formation of cloud like structures above the liquid-vapor interface. We also found that a liquid film condensation on the underside of the top plate results in regular hexagonal patterns of falling droplets
Optimum Jet-to-Plate Spacing of Inline Impingement Heat Transfer for Different Crossflow Schemes
No full textA nine-by-nine jet array impinging on a flat plate at Reynolds numbers from 15,000 to 35,000 has been studied by the transient liquid crystal method. The spacing between the impingement plate and target plate is adjusted to be 1, 2, 3, 4, and 5 jet diameters. The effect of jet-to-plate spacing has been investigated for three jet-induced crossflow schemes, referred as minimum, medium, and maximum crossflow, correspondingly. The local air jet temperature is measured at several positions on the impingement plate to account for an appropriate reference temperature of the heat transfer coefficient. The jet-to-plate spacing, H/d - 3, is found to be better than the others for all the crossflow schemes. Jet-to-plate spacings H/d = 1 and H/d = 2 result in a sudden decrease in the stagnation zone. The large jet-to-plate spacings H/d = 4 and H/d = 5 could not provide higher heat transfer performance with higher crossflow
Scientometric portrait of Nobel laureate Leland H. Hartwell
No full textLeland H. Hartwell was honoured with the Nobel Prize in Physiology or Medicine (2001) at his 62 years age and at 41 years of research publishing career. The first contribution of the author was in 1961 at the age of 22. The number of his contributions in a year peaked in 1997 when it touched 8. He had 108 publications during 1961 – 2001 in domains: Molecular Biology of Cell Cycle Regulation (43), Genetics of Cell Division (48), Genomic Re-arrangement and DNA Repair (9), Molecular Genetics of Yeast Cell Fission (5), and Drug Target Interaction (3) which were analysed for authorship pattern with his 101 collaborators. Most active researchers having number of publications with Leland H. Hartwell were : Weinert, T. A. (10), Garvik, B. M. (8), McLaughlin, C. S. (8), Jenness, D. D. (5). His productivity coefficient was 0.76 which clearly indicates that his productivity increased after 50 percentile age. Highest collaboration coefficient (1) for Leland H. Hartwell was found during 1963-1965, 1968-1969, 1977, 1981-1983, 1985-1990, 1996 and 1998-2001. Journals have been the most preferred channel of communication where, as many as 96 papers out of 108 have been published. The core journals publishing his papers were: Cell (14), Genetics (12), Mol. Cell Biol. (8), J. Bactariol. (7), J. Cell Biol. ( 7), Science (7) J. Mol. Biol.(6), Exp. Cell Res. (5), and Proc. Nat. Acad. Sci.(5). Publication density is 2.63 and Publication concentration is 14.63. Most prolific keywords in titles of publications were: Saccharomyces cerevisiae , Yeast , Cell division cycle , RAD9, DNA Damage , Genes , Cell cycle, Genetic control , Check point (s) , Cell division , Mutant of Yeast
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