La mesure de la vitesse de la lumière à Nice par Henri Joseph Anastase Perrotin

Article de vulgarisation paru dans "Reflets de la Physique" (volume 26)National audienceEntre 1898 et 1904, Perrotin, directeur du nouvel Observatoire de Nice, entreprend de mesurer la vitesse de la lumière avec une précision record, qui entrera dans l'histoire. Cette entreprise, quasiment oubliée aujourd'hui, a pourtant donné un résultat cité comme référence pendant des décennies. Les archives de l'Observatoire de la Côte d'Azur permettent de revivre au jour le jour ce projet, assez audacieux, et de redécouvrir cet homme déterminé qui avait accepté de présider à la destinée de ce " palais astronomique et physique " pour la gloire de la " Science française "

Torsional stiffness as an influence parameter on arch stability

Arch bridge springs can be connected to concrete abutments either by prestressing bars or by connectors. In both options, the torsional stiffness is substantially reduced, compared to the full arch cross sectional area. The influence of this lack of torsional stiffness on arch buckling is being researched, both numerically and experimentally. To reduce any residual stress during tests, wooden rods that simulate the arch were submerged in water and subsequently bent to the desired shape. Imperfections of the arch samples are measured. Two unequal concentrated loads are applied to the samples, thus simulating the effect of movable loads across half of the arch span. During loading, lateral deflections were measured until elastic buckling occurred. The simulation of more flexible rotation of the springs required replacing the cross section by thin equivalent side plates. Since all parameters have not been isolated, the results are limited yet. However, comparing the failure load of similar conditions, the reduction of torsion stiffness by 81.48% reduces the failure load by 26.3%. This indicates that total prevention of axial rotation may not be imperative for arch bridges

Experimental verification of buckling of curved web close steel section

Senzori igraju važnu ulogu u izvedbi modernih elektroničkih sustava u vozilu. U ovom radu dan je uvid u razvoj inteligentnih senzora koji se ugrađuju u vozila. Senzori poput senzora temperature i tlaka u gumama se primjenjuju u svrhu detektiranja stanja sustava unutar vozila, a senzori kao što su radarski ili video senzori služe prepoznavanju okoline kako bi se obavljale bezbrojne funkcije praćenja i kontrole. Kako bi se objasnila bit samih senzora, obrađeni su i neki sustavi poput ACC (engl. Adaptive Cruise Control) sustava, čime bi se olakšalo razumijevanje rada senzora. Razvoj senzora i sigurnosnih sustava u budućnosti omogućiti će vozilu „osjetiti“ okolinu, prepoznati potencijalno opasne situacije i osigurati unaprijed određenu razinu potpore i sigurnosti vozaču

Experimental verification of buckling of curved web close steel section

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PoGOLite - A High Sensitivity Balloon-Borne Soft Gamma-ray Polarimeter

We describe a new balloon-borne instrument (PoGOLite) capable of detecting 10% polarisation from 200mCrab point-like sources between 25 and 80keV in one 6 hour flight. Polarisation measurements in the soft gamma-ray band are expected to provide a powerful probe into high-energy emission mechanisms as well as the distribution of magnetic fields, radiation fields and interstellar matter. At present, only exploratory polarisation measurements have been carried out in the soft gamma-ray band. Reduction of the large background produced by cosmic-ray particles has been the biggest challenge. PoGOLite uses Compton scattering and photo-absorption in an array of 217 well-type phoswich detector cells made of plastic and BGO scintillators surrounded by a BGO anticoincidence shield and a thick polyethylene neutron shield. The narrow FOV (1.25msr) obtained with well-type phoswich detector technology and the use of thick background shields enhance the detected S/N ratio. Event selections based on recorded phototube waveforms and Compton kinematics reduce the background to that expected for a 40-100mCrab source between 25 and 50keV. A 6 hour observation on the Crab will differentiate between the Polar Cap/Slot Gap, Outer Gap, and Caustic models with greater than 5 sigma; and also cleanly identify the Compton reflection component in the Cygnus X-1 hard state. The first flight is planned for 2010 and long-duration flights from Sweden to Northern Canada are foreseen thereafter.Comment: 11 pages, 11 figures, 2 table