Louisiana State University

About: Louisiana State University is a education organization based out in Baton Rouge, Louisiana, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 40206 authors who have published 76587 publications receiving 2566076 citations. The organization is also known as: LSU & Louisiana State University and Agricultural and Mechanical College.

An absence of ex-companion stars in the type Ia supernova remnant SNR 0509−67.5

Abstract: The central region of the supernova remnant SNR 0509−67.5 in the Large Magellanic Cloud is shown to contain no ex-companion star, which suggests it was formed by an explosion resulting from the merger of two white dwarf stars. Type Ia supernovae are thought to result from a thermonuclear explosion of a white dwarf star, arising from either the merger of two white dwarfs (the 'double-degenerate' path), or by mass transfer from a companion star ('single-degenerate' path). The precise identity of the progenitor is still controversial. Bradley Schaefer and Ashley Pagnotta have examined high-resolution Hubble Space Telescope images of the central region of the supernova remnant SNR 0509-67.5 in the Large Magellanic Cloud, and find no sign of a point source. This lack of any ex-companion star rules out all published single-degenerate models for this supernova and points to a double-degenerate merger as the most likely origin. A type Ia supernova is thought to begin with the explosion of a white dwarf star1. The explosion could be triggered by the merger of two white dwarfs2,3 (a ‘double-degenerate’ origin), or by mass transfer from a companion star4,5 (the ‘single-degenerate’ path). The identity of the progenitor is still controversial; for example, a recent argument against the single-degenerate origin6 has been widely rejected7,8,9,10,11. One way to distinguish between the double- and single-degenerate progenitors is to look at the centre of a known type Ia supernova remnant to see whether any former companion star is present12,13. A likely ex-companion star for the progenitor of the supernova observed by Tycho Brahe has been identified14, but that claim is still controversial15,16,17,18. Here we report that the central region of the supernova remnant SNR 0509−67.5 (the site of a type Ia supernova 400 ± 50 years ago, based on its light echo19,20) in the Large Magellanic Cloud contains no ex-companion star to a visual magnitude limit of 26.9 (an absolute magnitude of MV = +8.4) within a region of radius 1.43 arcseconds. (This corresponds to the 3σ maximum distance to which a companion could have been ‘kicked’ by the explosion.) This lack of any ex-companion star to deep limits rules out all published single-degenerate models for this supernova. The only remaining possibility is that the progenitor of this particular type Ia supernova was a double-degenerate system.

Cross Comparison of Empirical Equations for Calculating Potential Evapotranspiration with Data from Switzerland

Abstract: Earlier studies (Singh and Xu, 1997; Xu and Singh, 2000, 2001) have evaluated and compared various popular empirical evapotranspiration equations that belonged to three categories:(1) mass-transfer based methods, (2) radiation based methods, and(3) temperature-based methods; and the best and worst equations of each category were determined for the study regions In this study a cross comparison of the best or representative equation forms selected from each category was made Five representativeempirical potential evapotranspiration equations selected from the three categories, namely: Hargreaves and Blaney-Criddle (temperature-based), Makkink and Priestley-Taylor (radiation-based) and Rohwer (mass-transfer-based) were evaluatedand compared with the Penman-Monteith equation using daily meteorological data from the Changins station in SwitzerlandThe calculations of the Penman-Monteith equation followed theprocedure recommended by FAO (Allen et al, 1998) Thecomparison was first made using the original constant valuesinvolved in each empirical equation and then made using therecalibrated constant values The study showed that: (1) theoriginal constant values involved in each empirical equationworked quite well for the study region, except that the valueof α = 126 in Priestley-Taylor was found to be too high and therecalibration gave a value of α = 090 for the region(2) Improvement was achieved for the Blaney-Criddle method by addinga transition period in determining the parameter k (3) The differences of performance between the best equation forms selected from each category are smaller than the differences between different equations within each category as reportedin earlier studies (Xu and Singh, 2000, 2001) Further examinationof the performance resulted in the following rank of accuracy ascompared with the Penman-Monteith estimates: Priestley-Taylor andMakkink (Radiation-based), Hargreaves and Blaney-Criddle (temperature-based) and Rohwer (Mass-transfer)

Compression properties of syntactic foams: effect of cenosphere radius ratio and specimen aspect ratio

Abstract: The present work is aimed at characterizing syntactic foams for flatwise (specimen aspect ratio of 0.5) properties and investigating the effect of change in the internal radius of cenospheres. The density and mechanical properties of the syntactic foam can be changed while keeping cenosphere volume fraction and particle–matrix interfacial area the same by using cenospheres of same outer radius but different inner radius. Five types of cenospheres, with the same mean outer radius but a different internal radius, have been selected for the fabrication of syntactic foams. ASTM C 365-94, a standard for the flatwise compressive properties of sandwich cores, is followed in the present work. The results obtained in the study are compared with the results of edgewise (specimen aspect ratio of 2) compressive properties evaluated in earlier work. Results show an increase in compressive strength and modulus with decrease in internal radius of cenospheres. The peak compressive strength and modulus were measured to be higher for the specimens tested in flatwise orientation compared to that in edgewise orientation. Varying only one parameter, the internal radius of cenospheres, helped in understanding the role of cenospheres and matrix resin in deformation and fracture process of syntactic foams.