Generic Misalignment Aberration Patterns in Wide-Field Telescopes

Axially symmetric telescopes produce well known "Seidel" off-axis third-order aberration patterns: coma, astigmatism, curvature of field and distortion. When axial symmetry is broken by the small misalignments of optical elements, additional third-order aberration patterns arise: one each for coma, astigmatism and curvature of field and two for distortion. Each of these misalignment patterns is characterized by an associated two-dimensional vector, each of which in turn is a linear combination of the tilt and decenter vectors of the individual optical elements. For an N-mirror telescope, 2(N-1) patterns must be measured to keep the telescope aligned. Alignment of the focal plane may require two additional patterns. For N = 3, as in a three mirror anastigmat, there is a two-dimensional "subspace of benign misalignment" over which the misalignment patterns for third-order coma, astigmatism and curvature of field are identically zero. One would need to measure at least one of the two distortion patterns to keep the telescope aligned. Alternatively, one might measure one of the fifth-order misalignment patterns, which are derived herein. But the fifth-order patterns are rather insensitive to misalignments, even with moderately wide fields, rendering them of relatively little use in telescope alignment. Another alternative would be to use telescope pointing as part of the alignment solution.Comment: 50 pages, 13 figures, Accepted for Publication in PAS

Value of Trail Access on Home Purchases

We use hedonic analysis of home sales data from the Twin Cities Metropolitan Area to estimate the effects of access of different types of trails on home value. Our model includes proximity to three distinct types bicycle facilities, controlling for local fixed effects and open space characteristics. Using interaction terms detect different preferences between city and suburban homebuyers. Regression results show that off-street bicycle trails situated alongside busy streets are negatively associated with home sale prices in both the city and suburbs. Proximity to off-street bicycle trails away from trafficked streets in the city are positively associated with home sale prices, with no significant result in the suburbs. On-street bicycle lanes have no effect in the city and are a disamenity in the suburbs. The following policy issues are relevant from this research. First, type of trail matters. On-street trails and road-side trails may not be as appreciated as many city planners or policy officials think. Second, city residents have different preferences than suburban residents. Third and as suspected, larger and more pressing factors likely influencing residential location decisions. The finding also suggest that urban planners and advocates need to be aware of the consequences of providing for bicycle facilities, as the change in welfare is not necessarily positive for all homeowners.

Accessibility Futures.

This study uses accessibility as a performance measure to evaluate a matrix of future land use and network scenarios for planning purposes. Previous research has established the coevolution of transportation and land use, demonstrated the dependence of accessibility on both, and made the case for the use of accessibility measures as a planning tool. This study builds off of these findings by demonstrating the use of accessibility-based performance measures on the Twin Cities Metropolitan Area. This choice of performance measure also allows for transit and highway networks to be compared side-by-side. A zone to zone travel time matrix was computed using SUE assignment with travel time feedback to trip distribution. A database of schedules was used on the transit networks to assign transit routes. This travel time data was joined with the land use data from each scenario to obtain the employment, population, and labor accessibility from each TAZ within specified time ranges. Tables of person- weighed accessibility were computed for 20 minutes with zone population as the weight for employment accessibility and zone employment as the weight for population and labor accessibility. The person-weighted accessibility results were then used to evaluate the planning scenarios. The results show that centralized population and employment produce the highest accessibility across all networks.Accessibility, Forecasting, Travel Demand, Scenarios, Trends, Transportation, Land Use.

The Long Story about the Short Medium -Twitter as a Communication Medium in Historical, Present, and Future Context

Twitt er, the hottest new medium in the social media landscape, has historical roots in such successful short forms as graffiti, telegrams, and book blurbs. The transformation of all consumers of social media into consumer‐producers has leveled the political playing field on Twitter, and the entertainment field as well, giving all Tweeters equal ability to converse with famous politicians and celebrities. As a written and multi‐medium, Twitter has evolved much like the evolution of all media, starting with writing and pictures, and moving on to sounds and moving images, in the same way that phylogeny recapitulates ontogeny in living organisms. Also like the biological world, Twitter is increasingly interconnected with other online organisms, e.g., Facebook and YouTube, moving our world ever closer to a noosphere of the Earth as an interconnected consciousness. Further, Twitter and its descendant Foursquare are merging the real and virtual worlds, as GPS components of smart phones can tell anyone online where the user is located. Twitter also has a growing impact on the arts, leading to television sitcoms based on Tweets, novels created on Twitter, and new forms of documentaries made of short interviews. Media survive based on how well they satisfy a natural human need－which means the future of Twitter as a medium looks very promising

Gasoline Prices and Their Relationship to Drunk-Driving Crashes

his study investigates the relationship between changing gasoline prices and drunk-driving crashes. Specifically, we examine the effects of gasoline prices on drunk-driving crashes in Mississippi by age, gender, and race from 2004Ð2008, a period experiencing great fluctuation in gasoline prices. An exploratory visualization by graphs shows that higher gasoline prices are generally associated with fewer drunk-driving crashes. Higher gasoline prices depress drunk- driving crashes among younger and older drivers, among male and female drivers, and among white, black, and Hispanic drivers. The statistical results suggest that higher gasoline prices lead to lower drunk-driving crashes for female and black drivers. However, alcohol consumption is a better predictor of drunk-driving crashes, especially for male, white, and older drivers.Drunk-driving crashes, gasoline prices, alcohol consumption, Mississippi

The Impact of NAFTA on Labor Legislation in Mexico

This PDF contains a central article and response articles, these are then followed by a short discussion piece

Figures of speech : figurative expressions and the management of topic transition in conversation

In conversation, speakers occasionally use figurative expressions such as “had a good innings,” “take with a pinch of salt,” or “come to the end of her tether.” This article investigates WHERE in conversation such expressions are used, in terms of their sequential distribution. One clear distributional pattern is found: Figurative expressions occur regularly in topic transition sequences, and specifically in the turn where a topic is summarized, thereby initiating the closing of a topic. The paper discusses some of the distinctive features of the topic termination/transition sequences with which figurative closings are associated, particularly participants' orientation to their moving to new topics. Finally, the interactional use of figurative expressions is considered in the context of instances where their use fails to secure topical closure, manifesting some conflict (disaffiliation, etc.) between the participants

Risk Stratification and Early Oncologic Outcomes Following Robotic Prostatectomy

Results of this study suggest that robotic prostatectomy provides good cancer outcomes for clinically localized disease

Measuring solar reflectance—Part I: Defining a metric that accurately predicts solar heat gain

Solar reflectance can vary with the spectral and angular distributions of incident sunlight, which in turn depend on surface orientation, solar position and atmospheric conditions. A widely used solar reflectance metric based on the ASTM Standard E891 beam-normal solar spectral irradiance underestimates the solar heat gain of a spectrally selective 'cool colored' surface because this irradiance contains a greater fraction of near-infrared light than typically found in ordinary (unconcentrated) global sunlight. At mainland U.S. latitudes, this metric RE891BN can underestimate the annual peak solar heat gain of a typical roof or pavement (slope {le} 5:12 [23{sup o}]) by as much as 89 W m{sup -2}, and underestimate its peak surface temperature by up to 5 K. Using R{sub E891BN} to characterize roofs in a building energy simulation can exaggerate the economic value N of annual cool-roof net energy savings by as much as 23%. We define clear-sky air mass one global horizontal ('AM1GH') solar reflectance R{sub g,0}, a simple and easily measured property that more accurately predicts solar heat gain. R{sub g,0} predicts the annual peak solar heat gain of a roof or pavement to within 2 W m{sup -2}, and overestimates N by no more than 3%. R{sub g,0} is well suited to rating the solar reflectances of roofs, pavements and walls. We show in Part II that R{sub g,0} can be easily and accurately measured with a pyranometer, a solar spectrophotometer or version 6 of the Solar Spectrum Reflectometer