Surface differential rotation and prominences of the Lupus post T Tauri star RX J1508.6-4423

We present in this paper a spectroscopic monitoring of the Lupus post T Tauri star RX J1508.6-4423 carried out at two closely separated epochs (1998 May 06 and 10) with the UCL Echelle Spectrograph on the 3.9-m Anglo-Australian Telescope. Applying least-squares convolution and maximum entropy image reconstruction techniques to our sets of spectra, we demonstrate that this star features on its surface a large cool polar cap with several appendages extending to lower latitudes, as well as one spot close to the equator. The images reconstructed at both epochs are in good overall agreement, except for a photospheric shear that we interpret in terms of latitudinal differential rotation. Given the spot distribution at the epoch of our observations, differential rotation could only be investigated between latitudes 15° and 60°. We find in particular that the observed differential rotation is compatible with a solar-like law (i.e., with rotation rate decreasing towards high latitudes proportionally to sin 2l, where l denotes the latitude) in this particular latitude range. Assuming that such a law can be extrapolated to all latitudes, we find that the equator of RX J1508.6-4423 does one more rotational cycle than the pole every 50 ±10 d, implying a photospheric shear 2 to 3 times stronger than that of the Sun. We also discover that the Hα emission profile of RX J1508.6-4423 is most of the time double-peaked and strongly modulated with the rotation period of the star. We interpret this rotationally modulated emission as being caused by a dense and complex prominence system, the circumstellar distribution of which is obtained through maximum entropy Doppler tomography. These maps show in particular that prominences form a complete and inhomogeneous ring around the star, precisely at the corotation radius. We use the total Hα and Hβ emission flux to estimate that the mass of the whole prominence system is about 10 20g. From our observation that the whole cloud system surrounding the star is regenerated in less than 4 d, we conclude that the braking time-scale of RX J1508.6-4423 is shorter than 1 Gyr, and that prominence expulsion is thus likely to contribute significantly to the rotational spindown of young low-mass stars

Winds of Planet Hosting Stars

The field of exoplanetary science is one of the most rapidly growing areas of astrophysical research. As more planets are discovered around other stars, new techniques have been developed that have allowed astronomers to begin to characterise them. Two of the most important factors in understanding the evolution of these planets, and potentially determining whether they are habitable, are the behaviour of the winds of the host star and the way in which they interact with the planet. The purpose of this project is to reconstruct the magnetic fields of planet hosting stars from spectropolarimetric observations, and to use these magnetic field maps to inform simulations of the stellar winds in those systems using the Block Adaptive Tree Solar-wind Roe Upwind Scheme (BATS-R-US) code. The BATS-R-US code was originally written to investigate the behaviour of the Solar wind, and so has been altered to be used in the context of other stellar systems. These simulations will give information about the velocity, pressure and density of the wind outward from the host star. They will also allow us to determine what influence the winds will have on the space weather environment of the planet. This paper presents the preliminary results of these simulations for the star $\tau$ Bo\"otis, using a newly reconstructed magnetic field map based on previously published observations. These simulations show interesting structures in the wind velocity around the star, consistent with the complex topology of its magnetic field.Comment: 8 pages, 2 figures, accepted for publication in the peer-reviewed proceedings of the 14th Australian Space Research Conference, held at the University of South Australia, 29th September - 1st October 201

Placement and source effects of phosphate fertilizers on phosphorus availability and reaction products in two reduced-till soils: A greenhouse study

Citation: Khatiwada, Raju, et al. “Placement and Source Effects of Phosphate Fertilizers on Phosphorus Availability and Reaction Products in Two Reduced-Till Soils: A Greenhouse Study.” Soil Science, vol. 179, no. 3, Mar. 2014, pp. 141–152. journals.lww.com, doi:10.1097/SS.0000000000000055.Crop yields are limited primarily by unavailability of nutrients in agricultural soil. Adoption of reduced tillage and no-tillage systems leads to stratification of nutrients in surface soil, so management of phosphorus (P) in these systems is a major issue. The objective of this research was to understand the influence of placement (broadcast vs. deep-placed P) and fertilizer source (granular versus liquid P) on the reaction products of P under greenhouse conditions using soil columns. Phosphorus was added at a rate of 75 kg/ha to two soils: an acid soil from Manhattan, KS, and a slightly acid to neutral soil from Ottawa, KS. At 5 weeks after P application soil pH, resin-extractable P, and speciation of P in soils were determined at different distances from the point of fertilizer application. Scanning electron microscope with energy dispersive X-ray analysis(SEM-EDXA) and synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy were used to understand P speciation. Results for P fertilizer sources and placement with respect to resin-extractable P showed no clear differences between the treatments except for granular broadcast and granular deep-placed treatments in the Ottawa soil.Reaction products formed after application of P in two soils showed some clear differences. The XANES speciation revealed that Fe-P-like forms dominated in the acidic soil, whereas adsorbed and Fe and Ca-P-like forms dominated in the neutral to slightly acid soil. No clear trends in reaction products were detected with respect to P source or the P placement method. Furthermore, SEM-EDXA analysis of incubated fertilizer granules extracted from soils at 5 weeks showed enrichment of Al, Fe, and Ca in the zones of remaining P in incubated granules, indirectly indicating that these cations enter and or remaining in the granules and begin to react with P before the granules dissolve completely

The origin of very wide binary systems

The majority of stars in the Galactic field and halo are part of binary or multiple systems. A significant fraction of these systems have orbital separations in excess of thousands of astronomical units, and systems wider than a parsec have been identified in the Galactic halo. These binary systems cannot have formed through the 'normal' star-formation process, nor by capture processes in the Galactic field. We propose that these wide systems were formed during the dissolution phase of young star clusters. We test this hypothesis using N-body simulations of evolving star clusters and find wide binary fractions of 1-30%, depending on initial conditions. Moreover, given that most stars form as part of a binary system, our theory predicts that a large fraction of the known wide 'binaries' are, in fact, multiple systems.Comment: 4 pages, 1 figure, to appear in the proceedings of IAU Symposium 266, eds. R. de Grijs & J.R.D. Lepin

Life Satisfaction and Perceived Meaningfulness of Learning Experience among First-Year Traditional Graduate Social Work Students

Knowledge about life satisfaction and learning experience among first-year graduate students is sparse, despite its relevance to instructional decisions, academic support, and success of students. Adequate knowledge is crucial, as it may help graduate students manage personal and professional life changes associated with graduate education. Using a convenience sample of 118 first-year traditional social work graduate students in a northeastern U.S. university the study examined associations of life satisfaction and peer support with perception of meaningfulness of learning experience, as well as associations of gender, marital status, family support and perceived stress with life satisfaction. Results suggest that receiving higher peer support was associated with perceived meaningfulness of learning experience, whereas being female, being married, having lower perceived stress, and receiving higher family support were associated with life satisfaction. Reciprocal predictive relationship between life satisfaction and perceived meaningfulness of learning experience was found. In general, findings suggest that stress and support are important variables to consider in understanding life satisfaction and learning experience of first-year traditional social work graduate students and highlight the importance of peer and family support to navigating challenges of graduate education. Most importantly, findings have implications for social work education, highlighting how instructor’s utilization of instructional approaches that facilitate peer support may help ease transition into graduate education or help prevent drop out during the first year graduate students are most vulnerable to dropping out. Altogether, findings highlight why exploring perceived meaningfulness of learning experience and life satisfaction is crucial for identifying supportive needs of graduate students. Keywords: Life satisfaction; learning experience; perceived stress; family support; peer support

A review of Bayesian belief network models as decision-support tools for wetland conservation : are water birds potential umbrella taxa?

10 pagesCreative approaches to identifying umbrella species hold promise for devising effective surrogates of ecological communities or ecosystems. However, mechanistic niche models that predict range or habitat overlap among species may yet lack development. We reviewed literature on taxon-centered Bayesian belief network (BBN) models to explore a novel approach to identify umbrella taxa identifying taxonomic groups that share the largest proportion of habitat requirements (i.e., states of important habitat variables) with other wetland-dependent taxa. We reviewed and compiled published literature to provide a comprehensive and reproducible account of the current understanding of habitat requirements for freshwater, wetland-dependent taxa using BBNs. We found that wetland birds had the highest degree of shared habitat requirements with other taxa, and consequently may be suitable umbrella taxa in freshwater wetlands. Comparing habitat requirements using a BBN approach to build species distribution models, this review also identified taxa that may not benefit from conservation actions targeted at umbrella taxa by identifying taxa with unique habitat requirements not shared with umbrellas. Using a standard node set that accurately and comprehensively represents the ecosystem in question, BBNs could be designed to improve identification of umbrella taxa. In wetlands, expert knowledge about hydrology, geomorphology and soils could add important information regarding physical landscape characteristics relevant to species. Thus, a systems-oriented framework may improve overarching inferences from BBNs and subsequent utility to conservation planning and management.Postprin

Nitrogen Application Effects on Forage Sorghum Biomass Production and Nitrates

Forage sorghum (Sorghum bicolor (L.) Moench) is a highly productive annual summer forage that can be grazed, hayed or ensiled for winter feed, confined feeding, or grazed to supplement native pasture. Recently, there has been interest in growing forage sorghum for hay or grazing in place of fallow to increase residue cover as part of an integrated forage or cover crop system. The high water use efficiency and heat and drought tolerance of sorghum makes it an ideal forage crop choice for growers in the water-limited Great Plains environment. Furthermore, due to the declining saturated thickness of the Ogallala and High Plains aquifers, there is a need for more water efficient forages like sorghum compared to corn silage or alfalfa. Despite the great potential of forage sorghum as animal feed, high nitrate content is a major concern when fed to cattle. Forage containing 3,000 ppm nitrates are generally considered safe as livestock feed, nitrate concentrations between 3,000 and 6,000 ppm may be limit fed, and concentrations \u3e 9,000 ppm should not be fed to livestock. Ensiling reduces nitrate concentration but still requires caution when fed. Environmental stressors (including drought, frost, or cloudy weather conditions) and high manure or N fertilizer application rates can predispose forage crops to accumulate greater nitrate concentration in the aboveground biomass. Nitrogen application generally increased DM production, but excessive N application will also increase nitrate concentration in the harvested biomass. Limited research has been conducted on forage sorghum DM production and nitrate concentration responses to N fertilizer application in the semi-arid Great Plains region. Objectives of this study were to determine optimum N rates and quantify forage sorghum hay nitrate concentration as affected by N application under rain-fed no-till conditions in the semiarid central Great Plains