47,822 research outputs found
The New World species of Ataenius Harold, 1867 : 5. Revision of the A. strigatus group (Scarabaeidae: Aphodiinae: Eupariini)
The strigatus group of the New World species of Ataenius Harold is revised. Seventeen species are recognized including two species described as new: Ataenius ecruensis sp. nov. from the United States and A. oaxacaensis sp. nov. from Mexico. Fifteen previously used names are considered valid, three new synonyms are proposed: A. liogaster Bates (= A. edwardsi Chapin syn. nov. = A. hoguei Cartwright and Spangler syn. nov.), A. wenzelii Horn (= A. rudellus Fall, syn. nov.). New state records are presented for A. spretulus (Haldeman) (Washington) and A. cognatus (LeConte) (Indiana, Missouri, and Mississippi). The taxa are diagnosed, keyed and illustrated; available biological information and distribution data are given
An Improved molecular tool for distinguishing monoecious and dioedious Hydrilla
Two biotypes of hydrilla [Hydrilla verticillata(L.f.) Royle]
occur in the United States, a dioecious type centered
in the southeast and a monoecious type in the central Atlantic and northeastern states. Ecosystem managers need tools to distinguish the types as the ranges of each type expand and begin to overlap. A molecular tool using the randomly amplified polymorphic DNA (RAPD) procedure is available but its use is limited by a need for reference samples. We describe an alternative molecular tool which uses “universal primers” to sequence the trnL intron and trnL-F intergenic spacer of the chloroplast genome. This sequence yields three differences between the biotypes (two gaps and one single nucleotide polymorphism). A primer has been designed which ends in a gap that shows up only in the dioecious plant. A polymerase chain reaction (PCR) using this primer produces a product for the monoecious but not the dioecious plant
Calibration of quasi-static aberrations in exoplanet direct-imaging instruments with a Zernike phase-mask sensor
Context. Several exoplanet direct imaging instruments will soon be in
operation. They use an extreme adaptive optics (XAO) system to correct the
atmospheric turbulence and provide a highly-corrected beam to a near-infrared
(NIR) coronagraph for starlight suppression. The performance of the coronagraph
is however limited by the non-common path aberrations (NCPA) due to the
differential wavefront errors existing between the visible XAO sensing path and
the NIR science path, leading to residual speckles in the coronagraphic image.
Aims. Several approaches have been developed in the past few years to
accurately calibrate the NCPA, correct the quasi-static speckles and allow the
observation of exoplanets at least 1e6 fainter than their host star. We propose
an approach based on the Zernike phase-contrast method for the measurements of
the NCPA between the optical path seen by the visible XAO wavefront sensor and
that seen by the near-IR coronagraph. Methods. This approach uses a focal plane
phase mask of size {\lambda}/D, where {\lambda} and D denote the wavelength and
the telescope aperture diameter, respectively, to measure the quasi-static
aberrations in the upstream pupil plane by encoding them into intensity
variations in the downstream pupil image. We develop a rigorous formalism,
leading to highly accurate measurement of the NCPA, in a quasi-linear way
during the observation. Results. For a static phase map of standard deviation
44 nm rms at {\lambda} = 1.625 {\mu}m (0.026 {\lambda}), we estimate a possible
reduction of the chromatic NCPA by a factor ranging from 3 to 10 in the
presence of AO residuals compared with the expected performance of a typical
current-generation system. This would allow a reduction of the level of
quasi-static speckles in the detected images by a factor 10 to 100 hence,
correspondingly improving the capacity to observe exoplanets.Comment: 11 pages, 14 figures, A&A accepted, 2nd version after language-editor
correction
Benzene formation in the inner regions of protostellar disks
Benzene (c-C6H6) formation in the inner 3 AU of a protostellar disk can be
efficient, resulting in high abundances of benzene in the midplane region. The
formation mechanism is different to that found in interstellar clouds and in
protoplanetary nebulae, and proceeds mainly through the reaction between allene
(C3H4) and its ion. This has implications for PAH formation, in that some
fraction of PAHs seen in the solar system could be native rather than inherited
from the interstellar medium.Comment: 9 pages, 2 colour figures, to be published in the Astrophysical
Journal Letter
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