824 research outputs found

    Systematic Floral Anatomy of Pontederiaceae

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    Twenty species of Pontederiaceae and six species of the outgroup families Haemodoraceae and Philydraceae were investigated with regard to floral anatomy, using standard histological methods and graphic reconstructions. Variation is described in several features, including functional carpel number, the distribution of floral aerenchyma, the presence of unusual floral epithelial cells, the presence, type, and distribution of tannin cells, crystal type and distribution, aspects of placentation, ovule number, number of ovule rows per carpel, and septal nectary presence. In order to better assess character homology, one of these features, placentation, was divided into three discrete characters: septal fusion, placenta position, and placenta evagination. Several of the floral characters were optimized onto a most parsimonious cladogram from a relatively recent study using combined chloroplast DNA data. Associations of character states with specific clades were observed in functional carpel number, aerenchyma distribution, epithelial cell presence, tannin cell distribution, septal nectary presence, and the three redefined aspects of placentation: septal fusion, placenta position, and placenta evagination. These floral data will be valuable in further elucidating relationships in Pontederiaceae in future studies of the group

    Multiple Time Scales in Diffraction Measurements of Diffusive Surface Relaxation

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    We grew SrTiO3 on SrTiO3 (001) by pulsed laser deposition, using x-ray scattering to monitor the growth in real time. The time-resolved small angle scattering exhibits a well-defined length scale associated with the spacing between unit cell high surface features. This length scale imposes a discrete spectrum of Fourier components and rate constants upon the diffusion equation solution, evident in multiple exponential relaxation of the "anti-Bragg" diffracted intensity. An Arrhenius analysis of measured rate constants confirms that they originate from a single activation energy.Comment: 4 pages, 3 figure

    Monofilament Vaporization Propulsion (MVP) - CubeSat Propulsion System with Inert Polymer Propellant

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    CUA has developed an electrothermal thruster which consumes an inert polymer propellant fiber. This technology retains performance characteristics competitive with other warm gas systems, but enables more accessibility to micropropulsion via dramatically reduced cost and the elimination of range safety concerns. CUA’s Monofilament Vaporization Propulsion (MVP) draws from extrusion 3D printer technology to feed and melt polymer propellant in preparation for evaporation and heating up to 1100K using CUA’s micro-resistojet technology. Despite undergoing depolymerization and two separate phase changes, the system power requirements are manageable, demonstrating typical specific thrusts of 0.16 mN/W, and a maximum specific impulse in excess of 100 s. 1U system performance exceeds 500 N-s total impulse

    Conversion and Extraction of Insoluble Organic Materials in Meteorites

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    We endeavor to develop and implement methods in our laboratory to convert and extract insoluble organic materials (IOM) from low car-bon bearing meteorites (such as ordinary chondrites) and Precambrian terrestrial rocks for the purpose of determining IOM structure and prebiotic chemistries preserved in these types of samples. The general scheme of converting and extracting IOM in samples is summarized in Figure 1. First, powdered samples are solvent extracted in a micro-Soxhlet apparatus multiple times using solvents ranging from non-polar to polar (hexane - non-polar, dichloromethane - non-polar to polar, methanol - polar protic, and acetonitrile - polar aprotic). Second, solid residue from solvent extractions is processed using strong acids, hydrochloric and hydrofluoric, to dissolve minerals and isolate IOM. Third, the isolated IOM is subjected to both thermal (pyrolysis) and chemical (oxidation) degradation to release compounds from the macromolecular material. Finally, products from oxidation and pyrolysis are analyzed by gas chromatography - mass spectrometry (GCMS). We are working toward an integrated method and analysis scheme that will allow us to determine prebiotic chemistries in ordinary chondrites and Precambrian terrestrial rocks. Powerful techniques that we are including are stepwise, flash, and gradual pyrolysis and ruthenium tetroxide oxidation. More details of the integrated scheme will be presented

    Observed Effects of a Changing Step-Edge Density on Thin-Film Growth Dynamics

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    We grew SrTiO3 on SrTiO3 [001] by pulsed laser deposition, while observing x-ray diffraction at the (0 0 .5) position. The drop dI in the x-ray intensity following a laser pulse contains information about plume-surface interactions. Kinematic theory predicts dI/I = -4sigma(1-sigma), so that dI/I depends only on the amount of deposited material sigma. In contrast, we observed experimentally that |dI/I| < 4sigma(1-sigma), and that dI/I depends on the phase of x-ray growth oscillations. The combined results suggest a fast smoothing mechanism that depends on surface step-edge density.Comment: 4 figure

    Effects of E-Cigarette Health Warnings and Modified Risk Ad Claims on Adolescent E-Cigarette Craving and Susceptibility

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    Introduction A between-subjects experiment examines the effects of different warning types and modified risk e-cigarette ad claims on adolescent e-cigarette craving and future e-cigarette susceptibility for two different themes. One theme focuses on nicotine and addiction, and the other on the effects of potentially harmful constituents (eg, flavored chemicals and lung disease). Methods The effects of warning type (control, text-only, graphic health warning [GHW] and text) and modified risk e-cigarette ad claims (control, exposure reduction, risk reduction) are tested experimentally with two different arms (themes) for a sample of 1011 adolescents who had tried either e-cigarettes or cigarettes. Results For addiction, the text-only warning led to significantly less e-cigarette susceptibility than the no warning control condition. As expected, there were no differences between the GHW + text condition and text-only or control conditions for e-cigarette craving. An interaction between warning type and modified risk claims revealed significantly fewer e-cigarette cravings and less susceptibility for the text-only warning and no claim (control) condition than for any other condition. For fatal lung disease, the GHW + text condition led to fewer e-cigarette cravings and less susceptibility than the text-only warning and no warning (control) conditions. Conclusions Warning type effects can be very different under different themes (eg, addiction, fatal lung disease). In general, our results point to the effectiveness of the text-only warning for addiction and GHW + text for fatal lung disease. Relative exposure and risk modification claims (eg, less nicotine; less addicting) tend to undercut addiction warnings. Implications More than one type of e-cigarette warning may be necessary as e-cigarette research evolves. Our results show different warning type effects (eg, text-only; GHW + text) on e-cigarette craving and future susceptibility for adolescent experimenters depending on the risk theme (eg, addiction; lung disease) and presence of ad claims (eg, exposure and risk reduction). As research emerges on risks associated with e-cigarette use, it is important to first know what at-risk populations (eg, adolescents) believe about such risks. Such research will aid our understanding of what types of warnings might be most effective, especially in the presence of ad claims

    Development of a Fiber-Fed Pulsed Plasma Thruster for Small Satellites

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    CU Aerospace has developed a fiber-fed pulsed plasma thruster (FPPT) which consumes PTFE (Teflon) propellant in spooled form, fed with extrusion 3D printer technology. The thruster uses a parallel energy storage unit (ESU) design, assembling \u3e300 COTS capacitors into discrete 10 J modules while maintaining low per-cap current levels. The discharge is initiated by a pulsed regenerative carbon igniter located in the thruster cathode. Thruster performance varies with pulse energy and fuel feed rate, with measured impulse bits ranging from 0.057 – 0.241 mN-s and 960 – 2400 s specific impulse. The highest specific impulse measured is 2423 s for 40 J pulse energy. A 1U 20 J ESU flight design with 331 g PTFE fuel provides 5500 N-s total impulse. Accelerated subsystem life testing has demonstrated \u3e 600 million capacitor charge / discharge cycles with nearly identical per-cap current waveforms
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