Narrow-band single-photon emission in the near infrared for quantum key distribution

We report on the observation of single colour centers in natural diamond samples emitting in the near infrared region when optically excited. Photoluminescence of these single emitters have several striking features, such as a narrow-band fully polarized emission (FWHM 2 nm) around 780 nm, a short excited-state lifetime of about 2 ns, and perfect photostability at room temperature under our excitation conditions. We present a detailed study of their photophysical properties. Development of a triggered single-photon source relying on this single colour centre is discussed in the prospect of its application to quantum key distribution.Comment: 9 page

Experimental realization of Wheeler's delayed-choice GedankenExperiment

The quantum "mystery which cannot go away" (in Feynman's words) of wave-particle duality is illustrated in a striking way by Wheeler's delayed-choice GedankenExperiment. In this experiment, the configuration of a two-path interferometer is chosen after a single-photon pulse has entered it : either the interferometer is \textit{closed} (\textit{i.e.} the two paths are recombined) and the interference is observed, or the interferometer remains \textit{open} and the path followed by the photon is measured. We report an almost ideal realization of that GedankenExperiment, where the light pulses are true single photons, allowing unambiguous which-way measurements, and the interferometer, which has two spatially separated paths, produces high visibility interference. The choice between measuring either the 'open' or 'closed' configuration is made by a quantum random number generator, and is space-like separated -- in the relativistic sense -- from the entering of the photon into the interferometer. Measurements in the closed configuration show interference with a visibility of 94%, while measurements in the open configuration allow us to determine the followed path with an error probability lower than 1%

Wheeler's delayed-choice thought experiment: Experimental realization and theoretical analysis

Wheeler has strikingly illustrated the wave-particle duality by the delayed-choice thought experiment, in which the configuration of a 2-path interferometer is chosen after a single-photon light-pulsed has entered it. We present a quantitative theoretical analysis of an experimental realization of Wheeler's proposal

Thermocapillary valve for droplet production and sorting

Droplets are natural candidates for use as microfluidic reactors, if active control of their formation and transport can be achieved. We show here that localized heating from a laser can block the motion of a water-oil interface, acting as a microfluidic valve for two-phase flows. A theoretical model is developed to explain the forces acting on a drop due to thermocapillary flow, predicting a scaling law which favors miniaturization. Finally, we show how the laser forcing can be applied to sorting drops, thus demonstrating how it may be integrated in complex droplet microfluidic systems.Comment: Five pages, four figure

Contacts homme-eau et schistosomiase urinaire dans un village mauritanien = Water contact and urinary schistosomiasis in a Mauritanian village

Huit jours d'observations directes, de septembre à décembre 1985, dans un village d'endémie bilharzienne à #S. haematobium$ situé en zone sahélienne ont permis d'enregistrer 1226 contacts homme-eau dans la mare du village et d'analyser la responsabilité des diverses activités dans la transmission. Un indice d'exposition, intégrant la durée du contact, la surface corporelle exposée et la probabilité de présence de cercaires dans l'eau a été calculé pour chaque contact. Les activités domestiques, essentiellement féminines, ont représenté 62 % des contacts mais seulement 15 % de l'exposition totale. La situation est inverse pour les activités récréatives qui, impliquant principalement de jeunes garçons, n'étaient responsables que de 14 % des contacts mais de 70 % de l'exposition totale. Entre 6 et 20 ans l'exposition moyenne par contact est plus importante pour le sexe masculin. Une politique de prévention de la maladie par une action sur les contacts semble irréaliste dans le contexte étudié et le traitement sélectif des enfants ou des sujets fortement infectés apparaît comme la stratégie de lutte la mieux adaptée. (Résumé d'auteur

Keck Spectroscopy of Two Young Globular Clusters in the Merger Remnant NGC 3921

Low-resolution UV-to-visual spectra of two candidate globular clusters in the merger remnant NGC 3921 are presented. These two clusters of apparent magnitude V = 22.2 (Mv = -12.5) lie at projected distances of ~5 kpc from the center and move with halo-type radial velocities relative to the local galaxy background. Their spectra show strong Balmer absorption lines indicative of main-sequence turnoffs dominated by A-type stars. Comparisons with model-cluster spectra computed by Bruzual & Charlot and others yield cluster ages in the range of 200-530 Myr, and metallicities about solar to within a factor of three. Given their small half-light radii (Reff < 5 pc) and ages corresponding to ~100 core- crossing times, these clusters are gravitationally bound and, hence, indeed young globulars. Assuming that they had Chabrier-type initial mass functions, their estimated current masses are 2.3(+-0.1)x10^6 Msun and 1.5(+-0.1)x10^6 Msun, respectively, or roughly half the mass of omegaCen. Since NGC 3921 itself shows many signs of being a 0.7(+-0.3) Gyr old protoelliptical, these two young globulars of roughly solar metallicity and their many counterparts observed with the Hubble Space Telescope provide supporting evidence that, in the process of forming elliptical-like remnants, major mergers of gas-rich disks can also increase the number of metal-rich globular clusters. (Abridged)Comment: 22 pages, 6 figures, accepted for publication in AJ, July 200

\u3ci\u3eArcola malloi\u3c/i\u3e (Pastrana), the alligatorweed stemborer, a new synonym of \u3ci\u3eMacrorrhinia endonephele\u3c/i\u3e (Hampson) (Lepidoptera: Pyralidae: Phycitinae)

Arcola malloi (Pastrana, 1961) is a junior subjective synonym of Macrorrhinia endonephele (Hampson, 1918) syn. nov. (Lepidoptera: Pyralidae). The species is a biological control agent introduced in United States and Australia to control alligatorweed, Alternanthera philoxeroides (Mart.) Griseb. (Amaranthaceae). The synonymy is recognized by comparison of type specimens, genitalic dissections, and DNA COI barcoding. Vogtia Pastrana, 1961 syn. nov. and Arcola Shaffer, 1995 syn. nov. are synonymized with Macrorrhinia Ragonot, 1887. Macror­rhinia megajuxta (Neunzig and Goodson, 1992) comb. nov. is transferred from Ocala Hulst, 1892. Lectotypes are designated for Divitiaca ochrella Barnes and McDunnough, 1913, and Divitiaca simulella Barnes and Mc­Dunnough, 1913