Small, low power analog-to-digital converter

A small, low-power, high-speed, 8-bit analog-to-digital converter using silicon chip integrated circuits is suitable for use in airborne test data systems. The successive approximation method of analog-to-digital conversion is used to generate the digital output

The effects of clumping on wind line variability

We review the effects of clumping on the profiles of resonance doublets. By allowing the ratio of the doublet oscillator strenghts to be a free parameter, we demonstrate that doublet profiles contain more information than is normally utilized. In clumped (or porous) winds, this ratio can lies between unity and the ratio of the f-values, and can change as a function of velocity and time, depending on the fraction of the stellar disk that is covered by material moving at a particular velocity at a given moment. Using these insights, we present the results of SEI modeling of a sample of B supergiants, zeta Pup and a time series for a star whose terminal velocity is low enough to make the components of its Si IV 1400 doublet independent. These results are interpreted within the framework of the Oskinova et al. (2007) model, and demonstrate how the doublet profiles can be used to extract infromation about wind structure.Comment: 3 pages, to appear in Clumping in Hot Star Winds, W.-R. Hamann, A. Feldmeier & L. Oskinova, eds., Potsdam: Univ.-Verl., 2007, URN: http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-1398

Mass loss rates from mid-IR excesses in LMC and SMC O stars

We use a combination of BVJHK and Spitzer [3.6], [5.8] and [8.0] photometry to determine IR excesses for a sample of 58 LMC and 46 SMC O stars. This sample is ideal for determining IR excesses because the very small line of sight reddening minimizes uncertainties due to extinction corrections. We use the core-halo model developed by Lamers & Waters (1984a) to translate the excesses into mass loss rates and demonstrate that the results of this simple model agree with the more sophisticated CMFGEN models to within a factor of 2. Taken at face value, the derived mass loss rates are larger than those predicted by Vink et al. (2001), and the magnitude of the disagreement increases with decreasing luminosity. However, the IR excesses need not imply large mass loss rates. Instead, we argue that they probably indicate that the outer atmospheres of O stars contain complex structures and that their winds are launched with much smaller velocity gradients than normally assumed. If this is the case, it could affect the theoretical and observational interpretations of the "weak wind" problem, where classical mass loss indicators suggest that the mass loss rates of lower luminosity O stars are far less than expected.Comment: 15 pages, 10 figures. Accepted for publication in MNRA

Cavity Tree Selection and Effects of Inter-Annual Weather Variation on Nesting Phenology and Success of Red-Cockaded Woodpeckers in the Ouachita Mountains of Oklahoma and Arkansas

The Ouachita Mountains ecoregion in southeast Oklahoma and west-central Arkansas contains two populations of the red-cockaded woodpecker (Dryobates borealis, RCW), a federally endangered, cooperatively breeding species. Since the region is at the northwestern RCW range periphery, ecological thresholds are limiting for the species. To assess potential constraining factors for RCWs, we conducted a cavity tree selection analysis using data collected from 63 active cavity trees and 121 unused trees during 2017 - 2018. We also summarized attributes from active cavity trees and performed a chi-square analysis for directional cavity orientation. For cavity tree selection, we created single-variable generalized linear mixed models and used an AIC model comparison approach. Only one variable, canopy openness as measured from 0.5 m aboveground, was strongly supported. The χ2 analysis indicated that cavity trees generally had a northwest orientation. We found cavity tree selection to be based on high levels of canopy openness, and to a lesser extent, large tree crown areas. However, tree age was unimportant, likely due to the abundance of mature trees in our study area.Inter-annual weather variation is predicted to increase with climate change, causing potential range shifts for many species. RCWs may be susceptible to the effects of climate change, especially at the northwestern range periphery in the Ouachita Mountains ecoregion. We used 26 years of nesting data (1991 – 2016) from two RCW populations in the region to determine how inter-annual weather variation affects nesting date, clutch size, and number of nestlings fledged. For each population, we used daily temperature and precipitation data from Oregon State University’s PRISM® network for 3 periods (30 and 60 days before nesting and 40 days overlapping nesting) to determine effects at the population level. For a separate analysis, we created smaller windows for individual RCW nests to determine how extreme weather events (i.e. “heat waves” and high precipitation events) affected overall nest success and partial brood loss. Single-variable generalized mixed models were used for the longer windows, and mixed models were created for nest-specific windows. AIC model comparisons were conducted separately for population- and nest-level analyses. RCWs for both populations experienced shifts in nesting dates and clutch sizes in response to weather conditions leading up to nesting. RCWs also experienced reduced nestling survival to fledging with higher precipitation levels during the nesting period. For individual nests, high temperatures during the brooding period reduced the probability of nesting success for the Arkansas population, while high precipitation events reduced partial brood loss in Oklahoma. Our results indicate that RCWs are responding to inter-annual weather variation, though particular responses are complex and variable

is Social Security Part of the Social Safety Net?

Building on the existing literature that examines the extent of redistribution in the Social Security system as a whole, this paper focuses more specifically on how Social Security affects the poor. This question is important because a Social Security program that reduces overall inequality by redistributing from high income individuals to middle income individuals may do nothing to help the poor; conversely, a program that redistributes to the poor may nonetheless be regressive according to broader measures if it also redistributes from middle to upper income households. We have four major findings. First, as we expand the definition of income to use more comprehensive measures of well-being, we find that Social Security becomes less progressive. Indeed, when we use an "endowment" defined by potential labor earnings at the household level, rather than actual earnings at the individual level, we find that Social Security has virtually no effect on overall inequality. Second, we find that this result is driven largely by the lack of redistribution across the middle and upper part of the income distribution, so it masks some small positive net transfers to those at the bottom of the lifetime income distribution. Third, in cases where redistribution does occur, we find it is not efficiently targeted: many high income households receive positive net transfers, while many low income households pay net taxes. Finally, the redistributive effects of Social Security change over time, and these changes depend on the income concept used to classify someone as "poor".

A COMPARISON OF THE ECONOMIC RENT AND CONSUMER SURPLUS METHODS OF VALUING RECREATION BOATING SITES

Resource /Energy Economics and Policy,

Modeling Ultraviolet Wind Line Variability in Massive Hot Stars

We model the detailed time-evolution of Discrete Absorption Components (DACs) observed in P Cygni profiles of the Si IV lam1400 resonance doublet lines of the fast-rotating supergiant HD 64760 (B0.5 Ib). We adopt the common assumption that the DACs are caused by Co-rotating Interaction Regions (CIRs) in the stellar wind. We perform 3D radiative transfer calculations with hydrodynamic models of the stellar wind that incorporate these large-scale density- and velocity-structures. We develop the 3D transfer code Wind3D to investigate the physical properties of CIRs with detailed fits to the DAC shape and morphology. The CIRs are caused by irregularities on the stellar surface that change the radiative force in the stellar wind. In our hydrodynamic model we approximate these irregularities by circular symmetric spots on the stellar surface. We use the Zeus3D code to model the stellar wind and the CIRs, limited to the equatorial plane. We constrain the properties of large-scale wind structures with detailed fits to DACs observed in HD 64760. A model with two spots of unequal brightness and size on opposite sides of the equator, with opening angles of 20 +/- 5 degr and 30 +/- 5 degr diameter, and that are 20 +/- 5 % and 8 +/- 5 % brighter than the stellar surface, respectively, provides the best fit to the observed DACs. The recurrence time of the DACs compared to the estimated rotational period corresponds to spot velocities that are 5 times slower than the rotational velocity. The mass-loss rate of the structured wind model for HD 64760 does not exceed the rate of the spherically symmetric smooth wind model by more than 1 %. The fact that DACs are observed in a large number of hot stars constrains the clumping that can be present in their winds, as substantial amounts of clumping would tend to destroy the CIRs.Comment: 58 pages, 16 figures, 1 animation. Accepted for publication in The Astrophysical Journal, Main Journal. More information and animations are available at http://alobel.freeshell.org/hotstars.htm

Does Practice-Based Teacher Preparation Increase Student Achievement? Early Evidence from the Boston Teacher Residency

The Boston Teacher Residency is an innovative practice-based preparation program in which candidates work alongside a mentor teacher for a year before becoming a teacher of record in Boston Public Schools. We find that BTR graduates are more racially diverse than other BPS novices, more likely to teach math and science, and more likely to remain teaching in the district through year five. Initially, BTR graduates for whom value-added performance data are available are no more effective at raising student test scores than other novice teachers in English language arts and less effective in math. The effectiveness of BTR graduates in math improves rapidly over time, however, such that by their fourth and fifth years they out-perform veteran teachers. Simulations of the program’s overall impact through retention and effectiveness suggest that it is likely to improve student achievement in the district only modestly over the long run.