Differential Imaging with a Multicolor Detector Assembly: A New ExoPlanet Finder Concept

Simultaneous spectral differential imaging is a high contrast technique by which subtraction of simultaneous images reduces noise from atmospheric speckles and optical aberrations. Small non-common wave front errors between channels can seriously degrade its performance. We present a new concept, a multicolor detector assembly (MCDA), which can eliminate this problem. The device consists of an infrared detector and a microlens array onto the flat side of which a checkerboard pattern of narrow-band micro-filters is deposited, each micro-filter coinciding with a microlens. Practical considerations for successful implementation of the technique are mentioned. Numerical simulations predict a noise attenuation of 10^-3 at 0.5" for a 10^5 seconds integration on a mH=5 star of Strehl ratio 0.9 taken with an 8-m telescope. This reaches a contrast of 10^-7 at an angular distance of 0.5" from the center of the star image.Comment: 13 pages, 5 figures, accepted APJ

Ribbon Turbulence

We investigate the non-linear equilibration of a two-layer quasi-geostrophic flow in a channel forced by an imposed unstable zonal mean flow, paying particular attention to the role of bottom friction. In the limit of low bottom friction, classical theory of geostrophic turbulence predicts an inverse cascade of kinetic energy in the horizontal with condensation at the domain scale and barotropization on the vertical. By contrast, in the limit of large bottom friction, the flow is dominated by ribbons of high kinetic energy in the upper layer. These ribbons correspond to meandering jets separating regions of homogenized potential vorticity. We interpret these result by taking advantage of the peculiar conservation laws satisfied by this system: the dynamics can be recast in such a way that the imposed mean flow appears as an initial source of potential vorticity levels in the upper layer. The initial baroclinic instability leads to a turbulent flow that stirs this potential vorticity field while conserving the global distribution of potential vorticity levels. Statistical mechanical theory of the 1-1/2 layer quasi-geostrophic model predict the formation of two regions of homogenized potential vorticity separated by a minimal interface. We show that the dynamics of the ribbons results from a competition between a tendency to reach this equilibrium state, and baroclinic instability that induces meanders of the interface. These meanders intermittently break and induce potential vorticity mixing, but the interface remains sharp throughout the flow evolution. We show that for some parameter regimes, the ribbons act as a mixing barrier which prevent relaxation toward equilibrium, favouring the emergence of multiple zonal jets

Effects of Quasi-Static Aberrations in Faint Companion Searches

We present the first results obtained at CFHT with the TRIDENT infrared camera, dedicated to the detection of faint companions close to bright nearby stars. The camera's main feature is the acquisition of three simultaneous images in three wavelengths (simultaneous differential imaging) across the methane absorption bandhead at 1.6 micron, that enables a precise subtraction of the primary star PSF while keeping the companion signal. The main limitation is non-common path aberrations between the three optical paths that slightly decorrelate the PSFs. Two types of PSF calibrations are combined with the differential simultaneous imaging technique to further attenuate the PSF: reference star subtraction and instrument rotation to smooth aberrations. It is shown that a faint companion with a DeltaH of 10 magnitudes would be detected at 0.5 arcsec from the primary.Comment: 12 pages, 10 figures, to appear in Astronomy with High Contrast Imaging, EAS Publications Serie

Angular Differential Imaging: a Powerful High-Contrast Imaging Technique

Angular differential imaging is a high-contrast imaging technique that reduces quasi-static speckle noise and facilitates the detection of nearby companions. A sequence of images is acquired with an altitude/azimuth telescope while the instrument field derotator is switched off. This keeps the instrument and telescope optics aligned and allows the field of view to rotate with respect to the instrument. For each image, a reference PSF is constructed from other appropriately-selected images of the same sequence and subtracted to remove quasi-static PSF structure. All residual images are then rotated to align the field and are combined. Observed performances are reported for Gemini North data. It is shown that quasi-static PSF noise can be reduced by a factor \~5 for each image subtraction. The combination of all residuals then provides an additional gain of the order of the square root of the total number of acquired images. A total speckle noise attenuation of 20-50 is obtained for one-hour long observing sequences compared to a single 30s exposure. A PSF noise attenuation of 100 was achieved for two-hour long sequences of images of Vega, reaching a 5-sigma contrast of 20 magnitudes for separations greater than 8". For a 30-minute long sequence, ADI achieves 30 times better signal-to-noise than a classical observation technique. The ADI technique can be used with currently available instruments to search for ~1MJup exoplanets with orbits of radii between 50 and 300 AU around nearby young stars. The possibility of combining the technique with other high-contrast imaging methods is briefly discussed.Comment: 27 pages, 7 figures, accepted for publication in Ap

Novel Buildings: Architectural and Narrative Form in Victorian Fiction

This dissertation, “Novel Buildings: Architectural and Narrative Form in Victorian Fiction,” offers an interdisciplinary study of the relationship between the economic and social histories of built space and the Victorian literary imagination. At its most fundamental level, it claims that the spaces we inhabit shape the stories we tell. Reading Victorian literature through the architectural archive of the period, it argues that the nineteenth century’s rapidly evolving built environment resulted in a new set of narrative possibilities and laid the foundations for authorial innovations in genre, style, and form. Organized taxonomically around four architectural types reinvented in the nineteenth century—courthouses, hotels, theaters, and hospitals—my work examines novels that co-opt realism’s thick descriptions of these spaces for political and aesthetic ends. Drawing upon contemporary approaches to literary studies, including affect studies and environmental studies, these readings are connected by a consideration of the performative and intersubjective nature of public space. Parallel to my project’s critical engagement with material culture, human geography, and spatial embodiment is its attentiveness to the imbrication of literary and physical forms, thus taking up Victorian studies’ recent turn to new formalisms and its efforts at grounding the aesthetic within the everyday. My dissertation’s historical arc extends from the end of the eighteenth century through the end of the nineteenth, and its geographic trajectory traces a course from England’s agricultural and manufacturing provinces, through its urban metropole, to its continental and colonial outposts. Building upon previous literary studies of domestic, carceral, and commercial architecture, my project expands the critical archive to include a set of relatively understudied public spaces whose cultural significance remains profound even today. Moreover, it contributes to Victorian studies’—and literary studies’ in general—recent reinvestment in formalism(s) as it demonstrates the relationship between the various, intersecting, forms that govern and compose built environments, social relations, and literature. Beyond the portability of my methodology to additional architectural forms and/or other literary fields, my project also provides new humanistic avenues of inquiry in the study of urban development and it shifts the ways in which we read and understand representations of space

Comparisons of heart rate and duration of submergence during voluntary diving in three species of turtles

Thesis (M.A.)--University of Kansas, Department of Systematics and Ecology, 1979

In-Suit Doppler Technology Assessment

The objective of this program was to perform a technology assessment survey of non-invasive air embolism detection utilizing Doppler ultrasound methodologies. The primary application of this technology will be a continuous monitor for astronauts while performing extravehicular activities (EVA's). The technology assessment was to include: (1) development of a full understanding of all relevant background research; and (2) a survey of the medical ultrasound marketplace for expertise, information, and technical capability relevant to this development. Upon completion of the assessment, LSR was to provide an overview of technological approaches and R&D/manufacturing organizations

Acute intermittent hypoxia - a novel non-invasive therapy that promotes regeneration akin to brief electrical stimulation in peripheral nerve repair

Peripheral nerve regeneration often results in poor functional outcomes, a reality we aim to change. Injured peripheral neurons mount an intrinsic repair response as they undergo regenerative neuronal reprogramming, which can be enhanced by brief electrical stimulation (ES) of the injured nerve at the time of surgical repair, resulting in improved regeneration in rodents and humans. However, this approach is invasive. Acute intermittent hypoxia (AIH) - breathing alternate cycles of regular air and air with ~50% normal oxygen levels (11% O2) is emerging as a promising non-invasive intervention that promotes respiratory and non-respiratory motor function in spinal cord injured rats and humans. However, this therapy has the potential to globally impact the nervous system beyond the motor system. Of note, hypoxic conditions can increase neural activity in injured sensory neurons and peripheral axons and promote repair. Thus, I hypothesized that an AIH paradigm similar to that used for spinal cord repair, will improve peripheral nerve repair in a manner akin to ES, including its impact on regeneration-associated gene (RAG) expression – a predictor of growth states. To this end, alterations in early RAG expression (growth-associated protein 43, brain-derived neurotrophic factor, hypoxia-inducible factor alpha and a neural specific growth- associated protein, superior cervical ganglion 10) were examined for rats that had undergone tibial nerve transection and repair with either 2 days of normoxia treatment or AIH treatment begun two days post-repair, or 1 hour continuous ES treatment (20 Hz) at the time of repair. Three days post-repair, AIH or ES treatments effected significant and parallel elevated RAG expression relative to normoxia control treatment, most evident at the growing axon front. Behavioural, thermal and mechanical sensitivity assessments revealed that neither ES nor AIH elevated regeneration-associated pain states. Finally, ES showed significant impacts on functional recovery relative to normoxia controls in mid (25 day)- and late (70 day)-regeneration stages and AIH in mid (25 day)-regeneration stages. These indicators of an enhanced regenerative state for AIH and ES were supported by significantly increased numbers of newly myelinated fibers detected 20 mm distal to the tibial nerve repair site at 25 days post nerve repair. Collectively, these results support a role for brief AIH treatment, as a promising noninvasive adjunct therapy for improved peripheral nerve repair in a manner consistent with that observed with the more invasive direct nerve stimulation

Addressing Critical Shortages: An Examination of Supports For Early Career Special Educators in Maine

Alarming percentages of early career special educators, as many as 50%, leave education within five years (Edgar & Pair, 2005; Menlove, Games, & Salzberg, 2004; Plash & Piotrowski, 2006). These statistics are cause for grave concern. The purpose of this survey research study was to discover early career special educators\u27 perceptions of the induction support they received

First Application of Articulated Concrete Block Armoring with a Stabilized Stone Drainage Layer

Results from recent hydraulic testing of Articulated Concrete Block (ACB) systems have shown variations in the level of the ACB surface is attributed to the movement of an unconfined stone drainage layer. This movement appears to be exacerbated by thicker drainage layers, higher overtopping depths, and longer test flumes. While the apparent movement did not constitute “threshold of performance” as currently defined by ASTM D7276 and D7277, there was a desire to mitigate movement of the stone drainage layer and maintain conservatism in ACB design and construction. This paper will review the findings of Nadeau and Wedin’s paper from Protections 2018, which proposed an ACB system with a stone drainage layer stabilized with geocell to increase ACB performance under steady state and hydraulic jump conditions. A similar ACB system was recently designed and constructed to provide overtopping protection at Hollymead Lake Dam located near Charlottesville, VA. The system was selected for added conservatism to address overtopping depths approaching 1.6m (5.4-ft), hydraulic jump conditions occurring on the downstream slope, and other complex flow conditions due to site geometry. The authors believe this to be the first application of its kind. Design and analysis of the Hollymead Lake Dam ACB will be summarized and include a comparison of the factor of safety with and without the geocell stabilized stone drainage layer. The project was completed in November 2019. Details from construction will also be presented