Modalités de la compétition larvaire intraspécifique chez Bruchus affinis (Coleoptera, Bruchidae) dans les graines de Lathyrus sylvestris (Leguminosae, Fabaceae)

Summary. — In spring, a high concentration of Bruchus affinis eggs laid on the first appearing pods of Lathyrus sylvestris is responsible for an important intraspecific larval competition during the colonization of growing ovules. A single adult emerges from the seed, even if the seed has been infested by several larvae. We studied the patterns of this competition. Growth and development of B. affinis larvae are concommitent with the ones of infested ovules, and two main characteristics can be pointed out : a first larval ecdysis after the colonization of a growing ovule and a larval tendency to settle down in the center of cotyledons. Larval competition is closely related to a noticeable territorial behaviour of the larvae. Meetings of larvae moving towards the centre turn them in a situation of agression. When a larva casually meets another one from the side or the rear, it can hurt it with its mouth parts and kill it. Nevertheless, a larva which is already in the center of a wider gallery shows a greater mobility and kills more easily an approaching larva. The bigger (or older) larva is not necessarily the «winner» of the competition even if it is generally favoured by its central position and greater mobility.Résumé. — Au printemps, la forte concentration des pontes de Bruchus affinis sur les premières gousses formées de Lathyrus sylvestris est à l'origine d'une importante compétition larvaire intra-spécifique au moment de la colonisation des ovules en croissance. Un seul adulte émerge de la graine même si celle-ci a été colonisée par plusieurs larves. L'analyse des modalités de cette compétition est abordée. La croissance et le développement des larves de B. affinis sont concomitants de ceux des ovules colonisés et deux caractéristiques se dégagent : première mue larvaire après occupation d'un ovule en croissance et tendance larvaire à occuper le centre des cotylédons. La compétition larvaire est en relation étroite avec un comportement territorial très marqué de la larve. Les rencontres fortuites par recoupement des galeries larvaires lors de la progression vers le centre mettent les larves en situation de compétition. Lorsque'une larve en rejoint fortuitement une autre sur le côté ou par derrière, elle peut la blesser avec ses pièces buccales et l'éliminer. Mais une larve, déjà au centre dans une galerie plus large, a une mobilité plus grande et élimine plus facilement toute autre larve tentant de la rejoindre. La larve la plus grosse (ou la plus âgée) n'est pas nécessairement le «vainqueur» de la compétition, bien qu'elle soit en général plus favorisée par sa position au centre et sa meilleure mobilité.N'diaye Saliou, Fabres Gérard, Labeyrie Vincent. Modalités de la compétition larvaire intraspécifique chez Bruchus affinis (Coleoptera, Bruchidae) dans les graines de Lathyrus sylvestris (Leguminosae, Fabaceae). In: Bulletin de la Société entomologique de France, volume 97 (2), juin 1992. pp. 135-144

Femtolens Imaging of a Quasar Central Engine Using a Dwarf Star Telescope

We show that it is possible to image the structure of a distant quasar on scales of $\sim 1\,$AU by constructing a telescope which uses a nearby dwarf star as its ``primary lens'' together with a satellite-borne ``secondary''. The image produced by the primary is magnified by $\sim 10^5$ in one direction but is contracted by 0.5 in the other, and therefore contains highly degenerate one-dimensional information about the two-dimensional source. We discuss various methods for extracting information about the second dimension including ``femtolens interferometry'' where one measures the interference between different parts of the one-dimensional image with each other. Assuming that the satellite could be dispatched to a position along a star-quasar line of sight at a distance $r$ from the Sun, the nearest available dwarf-star primary is likely to be at \sim 15\,\pc\,(r/40\,\rm AU)^{-2}. The secondary should consist of a one-dimensional array of mirrors extending $\sim 700\,$m to achieve 1 AU resolution, or $\sim 100\,$m to achieve 4 AU resolution.Comment: 12 pages including 3 embedded figure

Multiple imaging by gravitational waves

Gravitational waves act like lenses for the light propagating through them. This phenomenon is described using the vector formalism employed for ordinary gravitational lenses, which was proved to be applicable also to a non-stationary spacetime, with the appropriate modifications. In order to have multiple imaging, an approximate condition analogous to that for ordinary gravitational lenses must be satisfied. Certain astrophysical sources of gravitational waves satisfy this condition, while the gravitational wave background, on average, does not. Multiple imaging by gravitational waves is, in principle, possible, but the probability of observing such a phenomenon is extremely low.Comment: 23 pages, LaTeX, no figures, to appear in Int. J. Mod. Phys.

Large Faraday rotation of resonant light in a cold atomic cloud

We experimentally studied the Faraday rotation of resonant light in an optically-thick cloud of laser-cooled rubidium atoms. Measurements yield a large Verdet constant in the range of 200 000 degrees/T/mm and a maximal polarization rotation of 150 degrees. A complete analysis of the polarization state of the transmitted light was necessary to account for the role of the probe laser's spectrum

Speckle Statistics in Adaptively Corrected Images

(abridged) Imaging observations are generally affected by a fluctuating background of speckles, a particular problem when detecting faint stellar companions at small angular separations. Knowing the distribution of the speckle intensities at a given location in the image plane is important for understanding the noise limits of companion detection. The speckle noise limit in a long-exposure image is characterized by the intensity variance and the speckle lifetime. In this paper we address the former quantity through the distribution function of speckle intensity. Previous theoretical work has predicted a form for this distribution function at a single location in the image plane. We developed a fast readout mode to take short exposures of stellar images corrected by adaptive optics at the ground-based UCO/Lick Observatory, with integration times of 5 ms and a time between successive frames of 14.5 ms ($\lambda=2.2$ $\mu$m). These observations temporally oversample and spatially Nyquist sample the observed speckle patterns. We show, for various locations in the image plane, the observed distribution of speckle intensities is consistent with the predicted form. Additionally, we demonstrate a method by which $I_c$ and $I_s$ can be mapped over the image plane. As the quantity $I_c$ is proportional to the PSF of the telescope free of random atmospheric aberrations, this method can be used for PSF calibration and reconstruction.Comment: 7 pages, 4 figures, ApJ accepte

Shortcuts to adiabaticity for trapped ultracold gases

We study, experimentally and theoretically, the controlled transfer of harmonically trapped ultracold gases between different quantum states. In particular we experimentally demonstrate a fast decompression and displacement of both a non-interacting gas and an interacting Bose-Einstein condensate which are initially at equilibrium. The decompression parameters are engineered such that the final state is identical to that obtained after a perfectly adiabatic transformation despite the fact that the fast decompression is performed in the strongly non-adiabatic regime. During the transfer the atomic sample goes through strongly out-of-equilibrium states while the external confinement is modified until the system reaches the desired stationary state. The scheme is theoretically based on the invariants of motion and scaling equations techniques and can be generalized to decompression trajectories including an arbitrary deformation of the trap. It is also directly applicable to arbitrary initial non-equilibrium states.Comment: 36 pages, 14 figure

The EMCCD-Based Speckle Interferometer of the BTA 6-m Telescope: Description and First Results

The description is given for the speckle interferometer of the BTA 6-m telescope of the SAO RAS based on a new detector with an electron multiplication CCD. The main components of the instrument are microscope objectives, interference filters and atmospheric dispersion correction prisms. The PhotonMAX-512B CCD camera using a back-illuminated CCD97 allows up to 20 speckle images (with 512$\times$512 pix resolution) per second storage on the hard drive. Due to high quantum efficiency (93% in the maximum at 550 nm), and high transmission of its optical elements, the new camera can be used for diffraction-limited (0.02$''$) image reconstruction of $15^{m}$ stars under good seeing conditions. The main advantages of the new system over the previous generation BTA speckle interferometer are examined.Comment: 18 pages, 14 figure