322 research outputs found
Planar manipulation of magneto-tactic bacteria using unidirectional magnetic fields
We show for the first time that an alternating unidirectional magnetic field generated by a magnetic erase head allows planar manipulation of magneto-tactic bacteria (MTB), and is not restricted to parallel directions only. We used squared-shaped magnetic fields of approximately 4 mT while sweeping from 0.25 to 10 Hz, and found that at frequencies of over 3 Hz the mean orthogonal velocity becomes constant. The erase head offers a significant reduction in size and complexity over conventional manipulators
Modélisation de critères de localisation : prédiction de l'orientation des bandes de localisation et tracé de courbes limites de formage
Différentes approches de modélisations ont
été proposées pour prédire les phénomènes de localisation lors d’opérations de mise en
forme de tôles métalliques par emboutissage. Des exemples de ces approches sont le
principe de force maximum, les critères à deux zones et les analyses de bifurcation ou
de stabilité. En l’absence de consensus relatif à leur choix et à l’étendu de leur
domaine de validité, la présente étude se propose de formuler ces modélisations dans un
cadre unifié, de mettre en évidence les liens théoriques pouvant exister entre elles et
ensuite de valider ces observations par le tracé de courbes limites de formage et par la
comparaison de l’orientation des bandes de localisation
Protection against ultraviolet radiation by commercial summer clothing: need for standardised testing and labelling
BACKGROUND: The use of clothing as a means of sun protection has been recommended in recent education campaigns. Contrary to popular opinion, however, some fabrics provide insufficient ultraviolet (UV) protection. MATERIAL AND METHODS: We investigated 236 apparel textiles of the spring/summer collections 2000 and 2001. In accordance with the forthcoming European standard the UV protection factor (UPF) of the fabrics was determined spectrophotometrically. RESULTS: Seventy-eight (33%) fabrics had UPF < 15, 45 (19%) had UPF = or > 15 and < 30, and 113 (48%) had UPF = or > 30 (30+). More than 70% of the wool, polyester, and fabric blends, and only less than 30% of the cotton, linen, and viscose fabrics had UPF values of 30+. Fabrics with black, navy-blue, white, green, or beige colours provided most frequently UPF values of 30+. CONCLUSIONS: It is difficult for the sun-aware consumer to choose the 'right' garment, with a third of summer clothing providing insufficient UV protection and only half of the fabrics having UPF 30+, the UPF recommended by the European standard. Therefore, apparel summer fabrics should be measured and labelled in accordance with a standard document
Spatial and Temporal Hadron Correlators below and above the Chiral Phase Transition
Hadronic correlation functions at finite temperature in QCD, with four
flavours of dynamical quarks, have been analyzed both above and below the
chiral symmetry restoration temperature. We have used both point and extended
sources for spatial as well as temporal correlators. The effect of periodic
temporal boundary conditions for the valence quarks on the spatial meson
correlators has also been investigated. All our results are consistent with the
existence of individual quarks at high temperatures. A measurement of the
residual interaction between the quarks is presented.Comment: 19 pages HLRZ 54/93, BI-TP 93/76, TIFR/TH/94-1
Improvement of the Staggered Fermion Operators
We present a complete and detailed derivation of the finite lattice spacing
corrections to staggered fermion matrix elements. Expanding upon arguments of
Sharpe, we explicitly implement the Symanzik improvement program demonstrating
the absence of order terms in the Symanzik improved action. We propose a
general program to improve fermion operators to remove corrections from
their matrix elements, and demonstrate this program for the examples of matrix
elements of fermion bilinears and . We find the former does have
corrections while the latter does not.Comment: 16 pages, latex, 1 figur
Fertile Prototaxites taiti: a basal ascomycete with inoperculate, polysporous asci lacking croziers
The affinities of Prototaxites have been debated ever since its fossils, some attaining tree-trunk proportions, were discovered in Canadian Lower Devonian rocks in 1859. Putative assignations include conifers, red and brown algae, liverworts and fungi (some lichenised). Detailed anatomical investigation led to the reconstruction of the type species, P. logani, as a giant sporophore (basidioma) of an agaricomycete (= holobasidiomycete), but evidence for its reproduction remained elusive. Tissues associated with P. taiti in the Rhynie chert plus charcoalified fragments from southern Britain are investigated here to describe the reproductive characters and hence affinities of Prototaxites. Thin sections and peels (Pragian Rhynie chert, Aberdeenshire) were examined using light and confocal microscopy; Přídolí and Lochkovian charcoalified samples (Welsh Borderland) were liberated from the rock and examined with scanning electron microscopy. Prototaxites taiti possessed a superficial hymenium comprising an epihymenial layer, delicate septate paraphyses, inoperculate polysporic asci lacking croziers and a subhymenial layer composed predominantly of thin-walled hyphae and occasional larger hyphae. Prototaxites taiti combines features of extant Taphrinomycotina (Neolectomycetes lacking croziers) and Pezizomycotina (epihymenial layer secreted by paraphyses) but is not an ancestor of the latter. Brief consideration is given to its nutrition and potential position in the phylogeny of the Ascomycota
Strongly coupled compact lattice QED with staggered fermions
We explore the compact U(1) lattice gauge theory with staggered fermions and
gauge field action -\sum_P [\beta \cos(\Theta_P) + \gamma \cos(2\Theta_P)],
both for dynamical fermions and in the quenched approximation. (\Theta_P
denotes the plaquette angle.) In simulations with dynamical fermions at various
\gamma \le -0.2 on 6^4 lattices we find the energy gap at the phase transition
of a size comparable to the pure gauge theory for \gamma \le 0 on the same
lattice, diminishing with decreasing \gamma. This suggests a second order
transition in the thermodynamic limit of the theory with fermions for \gamma
below some finite negative value. Studying the theory on large lattices at
\gamma = -0.2 in the quenched approximation by means of the equation of state
we find non-Gaussian values of the critical exponents associated with the
chiral condensate, \beta \simeq 0.32 and \delta \simeq 1.8, and determine the
scaling function. Furthermore, we evaluate the meson spectrum and study the
PCAC relation.Comment: 21 page
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