2,479 research outputs found

    When The War Is Over

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    https://digitalcommons.library.umaine.edu/mmb-vp/2962/thumbnail.jp

    If I Only Had A Sweetheart

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    https://digitalcommons.library.umaine.edu/mmb-vp/4618/thumbnail.jp

    Supersonic Aerodynamic Characteristics of a Space Shuttle Orbiter Model at Angles of Attack from 20 Deg to 90 Deg

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    Space Shuttle Orbiter aerodynamic characteristics have been determined in the angle-of-attack range from 20 to 90 degrees and Mach numbers from 4.60 to 1.80 at Reynolds numbers, based on body length, of 2.15 x 10 to the 6th and 4.30 x 10 to the 6th power. Emphasis is on vehicle stability, control, and trim characteristics above a 60 degree angle of attack. The model used was a 0.986 percent scale Orbiter, having a blade-mounted support system entering the model in the region of the vertical tail. Elevon deflections of 0, -10, -20, and -40 degrees and body-flap deflections of 0, +6 and -12 degrees were investigated individually and in combination. Schlieren photographs are also presented for selected configurations and Mach numbers. The Orbiter was found to be longitudinally stable and trimmable in the angle-of-attack range from approximately 60 to 80 degrees. Both the elevon and body flap provided positive pitch control-effectiveness at angles of attack from 60 to 80 degrees and the Mach numbers of this study. For the range of neutral to stable trim in the angle-of-attack range above about 55 degrees, the deflected elevon/body-flap combination provided positive trimmed lift and lift/drag ratios

    Unofficial answers to the Uniform certified public accountants examination, May 1948 to November 1950

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    https://egrove.olemiss.edu/aicpa_exam/1111/thumbnail.jp

    Common Garden Comparisons of Native and Introduced Plant Populations: Latitudinal Clines Can Obscure Evolutionary Inferences

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    Common garden studies are increasingly used to identify differences in phenotypic traits between native and introduced genotypes, often ignoring sources of among-population variation within each range. We re-analyzed data from 32 common garden studies of 28 plant species that tested for rapid evolution associated with biological invasion. Our goals were: (i) to identify patterns of phenotypic trait variation among populations within native and introduced ranges, and (ii) to explore the consequences of this variation for how differences between the ranges are interpreted. We combined life history and physiologic traits into a single principal component (PCALL) and also compared subsets of traits related to size, reproduction, and defense (PCSIZE, PCREP, and PCDEF, respectively). On average, introduced populations exhibited increased growth and reproduction compared to native conspecifics when latitude was not included in statistical models. However, significant correlations between PC-scores and latitude were detected in both the native and introduced ranges, indicating population differentiation along latitudinal gradients. When latitude was explicitly incorporated into statistical models as a covariate, it reduced the magnitude and reversed the direction of the effect for PCALL and PCSIZE. These results indicate that unrecognized geographic clines in phenotypic traits can confound inferences about the causes of evolutionary change in invasive plants

    Stability and Reversibility of Lithium Borohydrides Doped by Metal Halides and Hydrides

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    In an effort to develop reversible metal borohydrides with high hydrogen storage capacities and low dehydriding temperature, doping LiBH4 with various metal halides and hydrides has been conducted. Several metal halides such as TiCl3, TiF3, and ZnF2 effectively reduced the dehydriding temperature through a cation exchange interaction. Some of the halide doped LiBH4 are partially reversible. The LiBH4 + 0.1TiF3 desorbed 3.5 wt % and 8.5 wt % hydrogen at 150 and 450 °C, respectively, with subsequent reabsorption of 6 wt % hydrogen at 500 °C and 70 bar observed. XRD and NMR analysis of the rehydrided samples confirmed the reformation of LiBH4. The existence of the (B12H12)−2 species in dehydrided and rehydrided samples gives insight into the resultant partial reversibility. A number of other halides, MgF2, MgCl2, CaCl2, SrCl2, and FeCl3, did not reduce the dehydriding temperature of LiBH4 significantly. XRD and TGA-RGA analyses indicated that an increasing proportion of halides such as TiCl3, TiF3, and ZnCl2 from 0.1 to 0.5 mol makes lithium borohydrides less stable and volatile. Although the less stable borohydrides such as LiBH4 + 0.5TiCl3, LiBH4 + 0.5TiF3, and LiBH4 + 0.5ZnCl2 release hydrogen at room temperature, they are not reversible due to unrecoverable boron loss caused by diborane emission. In most cases, doping that produced less stable borohydrides also reduced the reversible hydrogen uptake. It was also observed that halide doping changed the melting points and reduced air sensitivity of lithium borohydrides
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