Infiltration and soil water distribution in irrigation furrows treated with polyacrylamide

Few if any studies have measured water-soluble anionic polyacrylamide’s (WSPAM) effects on infiltration and soil water distribution in different segments of irrigation furrows. We conducted a three year study on a silt loam soil with 1.5% slopes, planted to corn. Control furrows received no WSPAM and inflows were 15.1 L/min, whereas WSPAM was applied using 8 mg/L a.i. to 45 L/min inflows during furrow advance. After advance, treatments were identical, with inflows of 15.1 L/min. Soil profile water content and net infiltration in upper (inflow-end) and lower (outflow-end) furrow sectors were measured during the growing season. The results indicate mean whole-furrow, net infiltration was the same between treatments in each irrigation. The WSPAM increased lateral wetting from furrow to planted row by as much as 1.3-fold in the lower furrow sector. Mean field-wide soil water content was an average 1.2-fold greater in WSPAM furrows than for the control, but the effect was more significant in lower furrow sectors. This was consistent with infiltration data, which showed that WSPAM decreased the upper-to-lower-sector, net infiltration ratio 33% to 40% relative to control furrows, indicating improved irrigation uniformity. A 62% reduction in furrow advance time afforded by WSPAM accounts for some of the increased uniformity, but opposing changes in infiltration rate between upper and lower furrow sectors suggests that other factors are involved. The WSPAM management approach, while protecting against furrow erosion, provides a means of improving irrigation uniformity, and could potentially reduce associated percolation water and nutrient losses

Atomic X-ray Spectroscopy of Accreting Black Holes

Current astrophysical research suggests that the most persistently luminous objects in the Universe are powered by the flow of matter through accretion disks onto black holes. Accretion disk systems are observed to emit copious radiation across the electromagnetic spectrum, each energy band providing access to rather distinct regimes of physical conditions and geometric scale. X-ray emission probes the innermost regions of the accretion disk, where relativistic effects prevail. While this has been known for decades, it also has been acknowledged that inferring physical conditions in the relativistic regime from the behavior of the X-ray continuum is problematic and not satisfactorily constraining. With the discovery in the 1990s of iron X-ray lines bearing signatures of relativistic distortion came the hope that such emission would more firmly constrain models of disk accretion near black holes, as well as provide observational criteria by which to test general relativity in the strong field limit. Here we provide an introduction to this phenomenon. While the presentation is intended to be primarily tutorial in nature, we aim also to acquaint the reader with trends in current research. To achieve these ends, we present the basic applications of general relativity that pertain to X-ray spectroscopic observations of black hole accretion disk systems, focusing on the Schwarzschild and Kerr solutions to the Einstein field equations. To this we add treatments of the fundamental concepts associated with the theoretical and modeling aspects of accretion disks, as well as relevant topics from observational and theoretical X-ray spectroscopy.Comment: 63 pages, 21 figures, Einstein Centennial Review Article, Canadian Journal of Physics, in pres