DETERMINATION OF THE PARAMETERS OF THE LIMITING EXPANSION OF THE FLOW IN THE PROBLEM OF FREE SPREADING OF A TURBULENT FLOW

The authors consider the problem of free spreading of two-dimensional, in terms of turbulent, potential uniform flows and obtain an analytical solution. In this case, the flow movement occurs in a smooth horizontal channel along short watercourses, when the flow resistance forces can be neglected. The article approximates the limits of the applicability of the obtained solution. For this purpose, the basic principles of the formation of a flow spreading lobe are considered, taking into account the friction forces. The main task is to determine the extreme line of the current before it hits the side walls and the maximum expansion of the flow, taking into account the resistance forces.

Lyman-alpha spectroscopy of extreme [O iii] emitting galaxies at z ≃ 2-3: implications for Lyα visibility and LyC leakage at z > 6

ABSTRACT Spectroscopic observations of massive z > 7 galaxies selected to have extremely large [O iii] + H β equivalent width (EW ∼1500 Å) have recently revealed large Ly α detection rates, in contrast to the weak emission seen in the general population. Why these systems are uniquely visible in Ly α at redshifts where the intergalactic medium (IGM) is likely significantly neutral is not clear. With the goal of better understanding these results, we have begun a campaign with MMT and Magellan to measure Ly α in galaxies with similar [O iii] + H β EWs at z ≃ 2–3. At these redshifts, the IGM is highly ionized, allowing us to clearly disentangle how the Ly α properties depend on the [O iii] + H β EW. Here, we present Ly α EWs of 49 galaxies at z = 2.2–3.7 with intense [O iii] + H β line emission (EW = 300–3000 Å). Our results demonstrate that strong Ly α emission (EW >20 Å) becomes more common in galaxies with larger [O iii] + H β EW, reflecting a combination of increasingly efficient ionizing photon production and enhanced transmission of Ly α. Among the galaxies with the most extreme [O iii] + H β emission (EW ∼1500 Å), we find that strong Ly α emission is not ubiquitous, with only 50 per cent of our population showing Ly α EW >20 Å. Our data suggest that the range of Ly α strengths is related to the observed ellipticity, with those systems that appear edge-on or elongated having weaker Ly α emission. We use these results to interpret the anomalous Ly α properties seen in z > 7 galaxies with extreme [O iii] + H β emission and discuss implications for the escape of ionizing radiation from these extreme line emitting galaxies.

The Effects of Line Length on Reading Performance of Online News Articles

Previous research has shown that typographical factors of online text may influence its readability. This study examines the effects of line length on reading speed, comprehension, and user satisfaction of online news articles. Twenty college-age students read news articles displayed in 35, 55, 75, or 95 characters per line (cpl) from a computer monitor. Comprehension was assessed using six question types — title, main idea, main factual, structure, incidental, and recognition (Dyson & Haselgrove, 2001). Results showed that passages formatted with 95 cpl resulted in faster reading speed. Structure questions were found to be more challenging overall when compared to factual and other lower-level questions. Overall satisfaction was not affected by line length; however, users indicated a strong preference for the extreme line lengths.