York University

About: York University is a education organization based out in Toronto, Ontario, Canada. It is known for research contribution in the topics: Population & Politics. The organization has 18899 authors who have published 43357 publications receiving 1568560 citations.

A catalog of broad absorption line quasars in Sloan digital sky survey data release 5

Abstract: We present a catalog of 5039 broad absorption line (BAL) quasars (QSOs) in the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) QSO catalog that have absorption troughs covering a continuous velocity range ≥2000 km s–1. We have fitted ultraviolet (UV) continua and line emission in each case, enabling us to report common diagnostics of BAL strengths and velocities in the range –25, 000 to 0 km s–1 for Si IV λ1400, C IV λ1549, Al III λ1857, and Mg II λ2799. We calculate these diagnostics using the spectrum listed in the DR5 QSO catalog, and also for spectra from additional SDSS observing epochs when available. In cases where BAL QSOs have been observed with Chandra or XMM-Newton, we report the X-ray monochromatic luminosities of these sources. We confirm and extend previous findings that BAL QSOs are more strongly reddened in the rest-frame UV than non-BAL QSOs, and that BAL QSOs are relatively X-ray weak compared to non-BAL QSOs. The observed BAL fraction is dependent on the spectral signal-to-noise ratio (S/N); for higher S/N sources, we find an observed BAL fraction of ≈ 15%. BAL QSOs show a similar Baldwin effect as for non-BAL QSOs, in that their C IV emission equivalent widths decrease with increasing continuum luminosity. However, BAL QSOs have weaker C IV emission in general than do non-BAL QSOs. Sources with higher UV luminosities are more likely to have higher-velocity outflows, and the BAL outflow velocity and UV absorption strength are correlated with relative X-ray weakness. These results are in qualitative agreement with models that depend on strong X-ray absorption to shield the outflow from overionization and enable radiative acceleration. In a scenario in which BAL trough shapes are primarily determined by outflow geometry, observed differences in Si IV and C IV trough shapes would suggest that some outflows have ion-dependent structure.

Global lake responses to climate change

Abstract: Climate change is one of the most severe threats to global lake ecosystems. Lake surface conditions, such as ice cover, surface temperature, evaporation and water level, respond dramatically to this threat, as observed in recent decades. In this Review, we discuss physical lake variables and their responses to climate change. Decreases in winter ice cover and increases in lake surface temperature modify lake mixing regimes and accelerate lake evaporation. Where not balanced by increased mean precipitation or inflow, higher evaporation rates will favour a decrease in lake level and surface water extent. Together with increases in extreme-precipitation events, these lake responses will impact lake ecosystems, changing water quantity and quality, food provisioning, recreational opportunities and transportation. Future research opportunities, including enhanced observation of lake variables from space (particularly for small water bodies), improved in situ lake monitoring and the development of advanced modelling techniques to predict lake processes, will improve our global understanding of lake responses to a changing climate. Climate change affects lakes worldwide and is predicted to continue to alter lake ice cover, surface temperature, evaporation rates, water levels and mixing regimes. This Review discusses recent and expected lake responses to climate change and looks towards future research opportunities in lake monitoring and modelling.

Gaze-Centered Remapping of Remembered Visual Space in an Open-Loop Pointing Task

Abstract: Establishing a coherent internal reference frame for visuospatial representation and maintaining the integrity of this frame during eye movements are thought to be crucial for both perception and motor control. A stable headcentric representation could be constructed by internally comparing retinal signals with eye position. Alternatively, visual memory traces could be actively remapped within an oculocentric frame to compensate for each eye movement. We tested these models by measuring errors in manual pointing (in complete darkness) toward briefly flashed central targets during three oculomotor paradigms; subjects pointed accurately when gaze was maintained on the target location (control paradigm). However, when steadily fixating peripheral locations (static paradigm), subjects exaggerated the retinal eccentricity of the central target by 13.4 +/- 5.1%. In the key "dynamic" paradigm, subjects briefly foveated the central target and then saccaded peripherally before pointing toward the remembered location of the target. Our headcentric model predicted accurate pointing (as seen in the control paradigm) independent of the saccade, whereas our oculocentric model predicted misestimation (as seen in the static paradigm) of an internally shifted retinotopic trace. In fact, pointing errors were significantly larger than were control errors (p /= 0.25) from the static paradigm errors. Scatter plots of pointing errors (dynamic vs static paradigm) for various final fixation directions showed an overall slope of 0.97, contradicting the headcentric prediction (0. 0) and supporting the oculocentric prediction (1.0). Varying both fixation and pointing-target direction confirmed that these errors were a function of retinotopically shifted memory traces rather than eye position per se. To reconcile these results with previous pointing experiments, we propose a "conversion-on-demand" model of visuomotor control in which multiple visual targets are stored and rotated (noncommutatively) within the oculocentric frame, whereas only select targets are transformed further into head- or bodycentric frames for motor execution.

Presumed incompetent? Stigmatization and affirmative action efforts.

Abstract: Two studies investigated whether a stigma of incompetence marks those associated with affirmative action programs. In an experiment, 129 male and female undergraduates reviewed the application materials of someone said to be recently hired for one of two jobs. The hiree was either a man or a woman, and the woman either was or was not associated with an affirmative action program. The affirmative action label was found to negatively affect the perceived competence of women hirees regardless of the degree to which the job was male sex-typed. A field investigation in which 184 White men provided information about their co-workers supported these results. It additionally demonstrated that the relationship between perceived competence and presumed affirmative action status held not only when co-workers were White women but when they were Black men and Black women as well