Focal Plane Wavefront Sensing using Residual Adaptive Optics Speckles

Optical imperfections, misalignments, aberrations, and even dust can significantly limit sensitivity in high-contrast imaging systems such as coronagraphs. An upstream deformable mirror (DM) in the pupil can be used to correct or compensate for these flaws, either to enhance Strehl ratio or suppress residual coronagraphic halo. Measurement of the phase and amplitude of the starlight halo at the science camera is essential for determining the DM shape that compensates for any non-common-path (NCP) wavefront errors. Using DM displacement ripples to create a series of probe and anti-halo speckles in the focal plane has been proposed for space-based coronagraphs and successfully demonstrated in the lab. We present the theory and first on-sky demonstration of a technique to measure the complex halo using the rapidly-changing residual atmospheric speckles at the 6.5m MMT telescope using the Clio mid-IR camera. The AO system's wavefront sensor (WFS) measurements are used to estimate the residual wavefront, allowing us to approximately compute the rapidly-evolving phase and amplitude of speckle halo. When combined with relatively-short, synchronized science camera images, the complex speckle estimates can be used to interferometrically analyze the images, leading to an estimate of the static diffraction halo with NCP effects included. In an operational system, this information could be collected continuously and used to iteratively correct quasi-static NCP errors or suppress imperfect coronagraphic halos.Comment: Astrophysical Journal (accepted). 26 pages, 21 figure

Do Affluent Countries Face an Incomes-Jobs Tradeoff?

A commonly-held view suggests that affluent nations face a tradeoff between incomes and jobs. According to this view, in the United States pay for workers at the bottom of the earnings distribution (relative to those in the middle) is very low and government unemployment-related benefits (the "replacement rate") are stingy, but this facilitates the creation of lots of new jobs and encourages such individuals to take those jobs. The result is a high rate of employment and low unemployment. In much of Western Europe relative pay levels are higher for those at the bottom and benefits are more generous, but this is said to discourage job creation and to reduce the willingness of the unemployed to accept low-wage jobs. The consequence is low employment and high unemployment. I undertake a comparative assessment of this tradeoff view, based on pooled cross-section time-series analyses of 14 OECD countries in the 1980s and 1990s. The findings suggest that greater pay equality and a higher replacement rate do reduce employment growth in low-productivity private-sector service industries and in the economy as a whole. However, these effects are relatively weak. The results point to a variety of viable options for countries wishing to maintain or move toward a desirable combination of jobs and equality.Eine weit verbreitete Ansicht ist, dass in Industrienationen ein Zielkonflikt zwischen Einkommen und Beschäftigung besteht. Demzufolge sind die Löhne in den USA am unteren Ende der Einkommensverteilung im Vergleich zu den mittleren Einkommen sehr niedrig und gesetzliche Arbeitslosenbezüge ausgesprochen gering bemessen. Dies aber stimuliert sowohl die Schaffung neuer Arbeitsplätze als auch die Bereitschaft der Erwerbstätigen, sich mit niedrigen Einkommen zufrieden zu geben. Das Resultat ist eine hohe Beschäftigungs- und eine niedrige Arbeitslosenquote. In vielen westeuropäischen Ländern ist das Niveau der Niedrigeinkommen höher und sind Arbeitslosenbezüge großzügiger. Dies aber hemmt, nach Ansicht vieler, die Entstehung neuer Arbeitsplätze und die Bereitschaft von Arbeitslosen, niedrig bezahlte Arbeit anzunehmen. Das vorliegende Discussion Paper ist eine vergleichende Untersuchung dieser Zielkonflikt-Ansicht auf der Basis von kombinierten Querschnitts-/Zeitreihenanalysen in 14 OECD-Ländern in den 1980er- und 1990er-Jahren. Die Ergebnisse lassen den Schluss zu, dass eine gerechtere Einkommensverteilung und eine höhere Arbeitslosenvergütung ein geringes Beschäftigungswachstum zur Folge haben, sowohl in Bereichen der Wirtschaft mit geringem Produktivitätsausstoß (Dienstleistungssektor) als auch gesamtwirtschaftlich. Gleichwohl sind die Auswirkungen relativ geringfügig. Die Ergebnisse deuten überdies darauf hin, dass es eine Vielzahl von Lösungsmöglichkeiten zur Herstellung beziehungsweise Erhaltung eines ausgewogenen Verhältnisses von Beschäftigung und gerechter Einkommensverteilung gibt.1 Introduction 2 Existing Evidence 3 Method and Data 4 Findings 5 A High-Equality, High-Employment Society? Reference

Aerothermal modeling, phase 1. Volume 2: Experimental data

The experimental test effort is discussed. The test data are presented. The compilation is divided into sets representing each of the 18 experimental configurations tested. A detailed description of each configuration, and plots of the temperature difference ratio parameter or pattern factor parameter calculated from the test data are also provided

Aerothermal modeling. Executive summary

One of the significant ways in which the performance level of aircraft turbine engines has been improved is by the use of advanced materials and cooling concepts that allow a significant increase in turbine inlet temperature level, with attendant thermodynamic cycle benefits. Further cycle improvements have been achieved with higher pressure ratio compressors. The higher turbine inlet temperatures and compressor pressure ratios with corresponding higher temperature cooling air has created a very hostile environment for the hot section components. To provide the technology needed to reduce the hot section maintenance costs, NASA has initiated the Hot Section Technology (HOST) program. One key element of this overall program is the Aerothermal Modeling Program. The overall objective of his program is to evolve and validate improved analysis methods for use in the design of aircraft turbine engine combustors. The use of such combustor analysis capabilities can be expected to provide significant improvement in the life and durability characteristics of both combustor and turbine components

First On-Sky High Contrast Imaging with an Apodizing Phase Plate

We present the first astronomical observations obtained with an Apodizing Phase Plate (APP). The plate is designed to suppress the stellar diffraction pattern by 5 magnitudes from 2-9 lambda/D over a 180 degree region. Stellar images were obtained in the M' band (4.85 microns) at the MMTO 6.5m telescope, with adaptive wavefront correction made with a deformable secondary mirror designed for low thermal background observations. The measured PSF shows a halo intensity of 0.1% of the stellar peak at 2 lambda/D (0.36 arcsec), tapering off as r^{-5/3} out to radius 9 lambda/D. Such a profile is consistent with residual errors predicted for servo lag in the AO system. We project a 5 sigma contrast limit, set by residual atmospheric fluctuations, of 10.2 magnitudes at 0.36 arcsec separation for a one hour exposure. This can be realised if static and quasi-static aberrations are removed by differential imaging, and is close to the sensitivity level set by thermal background photon noise for target stars with M'>3. The advantage of using the phase plate is the removal of speckle noise caused by the residuals in the diffraction pattern that remain after PSF subtraction. The APP gives higher sensitivity over the range 2-5 lambda/D compared to direct imaging techniques.Comment: 22 pages, 5 figures, 1 table, ApJ accepte