409 research outputs found
Radioluminescence des milieux organiques III. Ătude expĂ©rimentale des solutions aromatiques liquides
L'Ă©tude du dĂ©clin de la scintillation Ă©mise par des solutions aromatiques liquides irradiĂ©es par un rayonnement ÎČ a permis de montrer que la composante diffĂ©rĂ©e est due Ă une interaction entre deux Ă©tats triplets du solutĂ© excitĂ©s par capture de l'Ă©nergie du solvant. La constante de Stern-Volmer de la rĂ©action de transfert de l'Ă©nergie des Ă©tats triplets du solvant au solutĂ© (α-NPO) a Ă©tĂ© estimĂ©e Ă 350 M -1 pour les solutions de benzĂšne et de toluĂšne. La durĂ©e de vie de l'Ă©tat triplet le plus bas du solvant est infĂ©rieure Ă une vingtaine de ns. Par ailleurs, on a Ă©valuĂ© Ă environ 40 Ă
le rayon des zones cylindriques de forte densité d'activation dans lesquelles a lieu la réaction d'annihilation bimoléculaire des états triplets
Material screening and selection for XENON100
Results of the extensive radioactivity screening campaign to identify
materials for the construction of XENON100 are reported. This Dark Matter
search experiment is operated underground at Laboratori Nazionali del Gran
Sasso (LNGS), Italy. Several ultra sensitive High Purity Germanium detectors
(HPGe) have been used for gamma ray spectrometry. Mass spectrometry has been
applied for a few low mass plastic samples. Detailed tables with the
radioactive contaminations of all screened samples are presented, together with
the implications for XENON100.Comment: 8 pages, 1 figur
Oval Domes: History, Geometry and Mechanics
An oval dome may be defined as a dome whose plan or profile (or both) has an oval form. The word Aoval@ comes from the latin Aovum@, egg. Then, an oval dome has an egg-shaped geometry. The first buildings with oval plans were built without a predetermined form, just trying to close an space in the most economical form. Eventually, the geometry was defined by using arcs of circle with common tangents in the points of change of curvature. Later the oval acquired a more regular form with two axis of symmetry. Therefore, an âovalâ may be defined as an egg-shaped form, doubly symmetric, constructed with arcs of circle; an oval needs a minimum of four centres, but it is possible also to build polycentric ovals.
The above definition corresponds with the origin and the use of oval forms in building and may be applied without problem until, say, the XVIIIth century. Since then, the teaching of conics in the elementary courses of geometry made the cultivated people to define the oval as an approximation to the ellipse, an âimperfect ellipseâ: an oval was, then, a curve formed with arcs of circles which tries to approximate to the ellipse of the same axes. As we shall see, the ellipse has very rarely been used in building.
Finally, in modern geometrical textbooks an oval is defined as a smooth closed convex curve, a more general definition which embraces the two previous, but which is of no particular use in the study of the employment of oval forms in building.
The present paper contains the following parts: 1) an outline the origin and application of the oval in historical architecture; 2) a discussion of the spatial geometry of oval domes, i. e., the different methods employed to trace them; 3) a brief exposition of the mechanics of oval arches and domes; and 4) a final discussion of the role of Geometry in oval arch and dome design
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