5,635 research outputs found
Simultaneous exoplanet detection and instrument aberration retrieval in multispectral coronagraphic imaging
High-contrast imaging for the detection and characterization of exoplanets
relies on the instrument's capability to block out the light of the host star.
Some current post-processing methods for calibrating out the residual speckles
use information redundancy offered by multispectral imaging but do not use any
prior information on the origin of these speckles. We investigate whether
additional information on the system and image formation process can be used to
more finely exploit the multispectral information. We developed an inversion
method in a Bayesian framework that is based on an analytical imaging model to
estimate both the speckles and the object map. The model links the instrumental
aberrations to the speckle pattern in the image focal plane, distinguishing
between aberrations upstream and downstream of the coronagraph. We propose and
validate several numerical techniques to handle the difficult minimization
problems of phase retrieval and achieve a contrast of 10^6 at 0.2 arcsec from
simulated images, in the presence of photon noise. This opens up the the
possibility of tests on real data where the ultimate performance may override
the current techniques if the instrument has good and stable coronagraphic
imaging quality. This paves the way for new astrophysical exploitations or even
new designs for future instruments
Influence of smectite suspension structure on sheet orientation in dry sediments: XRD and AFM applications
The structure-building phenomena within clay aggregates are governed by forces acting between clay particles. Measurements of such forces are important to understand in order to manipulate the aggregate structure for applications such as dewatering of mineral processing tailings. A parallel particle orientation is required when conducting XRD investigation on the oriented samples and conduct force measurements acting between basal planes of clay mineral platelets using at. force microscopy (AFM). To investigate how smectite clay platelets were oriented on silicon wafer substrate when dried from suspension range of methods like SEM, XRD and AFM were employed. From these investigations, we conclude that high clay concns. and larger particle diams. (up to 5 ÎĽm) in suspension result in random orientation of platelets in the substrate. The best possible laminar orientation in the clay dry film, represented in the XRD 0 0 1/0 2 0 intensity ratio of 47 was obtained by drying thin layers from 0.02 wt.% clay suspensions of the natural pH. Conducted AFM investigations show that smectite studied in water based electrolytes show very long-range repulsive forces lower in strength than electrostatic forces from double-layer repulsion. It was suggested that these forces may have structural nature. Smectite surface layers rehydrate in water environment forms surface gel with spongy and cellular texture which cushion approaching AFM probe. This structural effect can be measured in distances larger than 1000 nm from substrate surface and when probe penetrate this gel layer, structural linkages are forming between substrate and clay covered probe. These linkages prevent subsequently smooth detachments of AFM probe on way back when retrieval. This effect of tearing new formed structure apart involves larger adhesion-like forces measured in retrieval. It is also suggested that these effect may be enhanced by the nano-clay particles interaction
Integration of overseas-trained doctors into the Australian medical workforce
The document attached has been archived with permission from the editor of the Medical Journal of Australia. An external link to the publisher’s copy is included. See page 7 of PDF for this item.Linsey S Hart, Jane Vernon-Robert
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