Toward High-Precision Astrometry with WFPC2. I. Deriving an Accurate PSF

The first step toward doing high-precision astrometry is the measurement of individual stars in individual images, a step that is fraught with dangers when the images are undersampled. The key to avoiding systematic positional error in undersampled images is to determine an extremely accurate point-spread function (PSF). We apply the concept of the {\it effective} PSF, and show that in images that consist of pixels it is the ePSF, rather than the often-used instrumental PSF, that embodies the information from which accurate star positions and magnitudes can be derived. We show how, in a rich star field, one can use the information from dithered exposures to derive an extremely accurate effective PSF by iterating between the PSF itself and the star positions that we measure with it. We also give a simple but effective procedure for representing spatial variations of the HST PSF. With such attention to the PSF, we find that we are able to measure the position of a single reasonably bright star in a single image with a precision of 0.02 pixel (2 mas in WF frames, 1 mas in PC), but with a systematic accuracy better than 0.002 pixel (0.2 mas in WF, 0.1 mas in PC), so that multiple observations can reliably be combined to improve the accuracy by $\surd N$.Comment: 33 pp. text + 15 figs.; accepted by PAS

Large-scale Advanced Prop-fan (LAP) static rotor test report

Discussed is Static Rotor Testing of the SR-7L Large Scale Advanced Prop-Fan (LAP). The LAP is an advanced 9 foot diameter, 8 bladed propeller designed and built by Hamilton Standard under contract to the NASA Lewis Research Center. The Prop-Fan employs thin swept blades to provide efficient propulsion at flight speeds up to Mach .85. Static Testing was conducted on a 10,000 HP whirl rig at Wright Patterson Air Force Base. The test objectives were to investigate the Prop-Fan static aerodynamic and structural dynamic performance, determine the blade steady state stressers and deflections and to measure steady and unsteady pressures on the SR-7L blade surface. The measured performance of the LAP correlated well with analytical predictions at blade pitch angles below 30 deg. A stall buffet phenomenon was observed at blade pitch angles above 30 deg. This phenomenon manifested itself by elevated blade vibratory stress levels and lower than expected thrust produced and power absorbed by the Prop-Fan for a given speed and blade angle

TRADABLE PERMITS FOR CONTROLLING NITRATES IN GROUNDWATER AT THE FARM LEVEL: A CONCEPTUAL MODEL

Nitrate contamination of municipal and domestic well water supplies is becoming an increasing problem in many rural and urban areas, raising the cost of providing safe drinking water. The objective of this paper is to describe a marketable permit scheme that can effectively manage nitrate pollution of groundwater supplies for communities in rural areas without hindering agricultural production in watersheds. They key to implementing this scheme is being able to link nitrate leaching from nitrogen fertilizer applied to crops at a farm to nitrate levels measured at a drinking water well.agriculture, groundwater pollution, leaching, nitrates, pollution trading, Environmental Economics and Policy,

PERTS: A Prototyping Environment for Real-Time Systems

PERTS is a prototyping environment for real-time systems. It is being built incrementally and will contain basic building blocks of operating systems for time-critical applications, tools, and performance models for the analysis, evaluation and measurement of real-time systems and a simulation/emulation environment. It is designed to support the use and evaluation of new design approaches, experimentations with alternative system building blocks, and the analysis and performance profiling of prototype real-time systems

Red blood cell transfusion in palliative care: what are we doing and why are we doing it?

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141052/1/trf14437.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141052/2/trf14437_am.pd

Teaching Undergraduate Business Students About the Ethicality, Utility, and Risk of Using Personal Social Media Accounts to Vet Candidates in the Employee Recruitment Process

The present study explores the ethicality, utility, and risk of using personal social media accounts to vet candidates in the employee recruitment process. This article details a class lecture and corresponding group activity. The student groups were required to perform a social media deep dive on two individuals viewed as job candidates. Special attention was paid to selection of the correct candidates and information that cannot legally be asked in a job interview. Of the seven student groups, five groups selected incorrect profiles for at least one candidate, while identifying reasons for concern or competitive advantage for each candidate

Issues Related to Text Comprehensibility: The Future of Readability

Cet article situe la lisibilité dans une perspective historique. Il présente un tour d’horizon des différentes mesures de la lisibilité qui existent ainsi que de leur impact, s’intéresse aux différentes composantes qui influencent la construction du sens et présente des préoccupations pédagogiques relatives à l’intelligibilité.This paper places readability in an historical context, reviews the development of present day formulas and their liabilities, explores other factors that influence meaning making, and considers comprehensibility from the point of view of the educator. The authors conclude that determining how easy or how difficult a particular book may be for a particular reader is a complex task. There may be a time when it is possible to develop a formula that includes all elements that impact upon readability, but at present, estimating text comprehensibility requires personal judment

Superoperator Analysis of Entanglement in a Four-Qubit Cluster State

In this paper we utilize superoperator formalism to explore the entanglement evolution of four-qubit cluster states in a number of decohering environments. A four-qubit cluster state is a resource for the performance of an arbitrary single logical qubit rotation via measurement based cluster state quantum computation. We are specifically interested in the relationship between entanglement evolution and the fidelity with which the arbitrary single logical qubit rotation can be implemented in the presence of decoherence as this will have important experimental ramifications. We also note the exhibition of entanglement sudden death (ESD) and ask how severely its onset affects the utilization of the cluster state as a means of implementing an arbitrary single logical qubit rotation.Comment: 9 pages, 9 composite figures, presentation of results completely rewritte