18 research outputs found
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Insights from recent fires into juniper savanna dynamics at Wupatki National Monument, Arizona, USA
We tested the hypothesis that recurrent fires may limit juniper expansion into southwestern semiarid grasslands and savannas. Seven large fires at Wupatki National Monument, Arizona, burned 38% of the grasslands and dynamic savannas between 1995 and 2017. Mortality of one-seed junipers (Juniperus monosperma) was >50% among smaller trees (2 m tall), and 0% in trees >4 m tall. Herbaceous vegetation recovered within 2 to 3 years postfire. This suggests that fires may have limited juniper expansion historically and that fire may be an option for controlling juniper expansion and restoring grassland/savanna ecosystems today.The Rangelands archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information
In Situ Measurements of Carbon Dioxide, 0.37-4.0 µm Particles, and Water Vapor in the Stratospheric Plumes of Small Rockets
Carbon dioxide (CO2) and large particles (0.37-4.0 μm) were measured in the stratospheric plume wakes of three rockets, an Atlas IIAS, a Delta II, and an Athena II. The correlations between CO2 mass and particle number densities in each plume are consistent with the unique combination of solid and liquid engine emissions of each rocket. Measured size distributions indicate a 1.1 μm mode with density of 2 g cm-3, consistent with spherical alumina particles emitted by solid rocket motors. Disagreement between the measured size distributions and the mean sizes inferred from the known alumina and CO2 emission indices and an observed increase in the particle number emission index with altitude are evidence for large particle oversampling effects and the presence of condensed volatile compounds within the particle population. Direct evidence for the latter is a persistent ~0.5-1 part per million (ppm) shortfall of water vapor relative to CO2 measured in the plume of the Athena II rocket based on the expected H2O/CO2 emission ratio. Although pure ice particles would not persist at the conditions of the measurements, a more stable coating of HNO3 (as either nitric acid trihydrate or as a liquid layer) could have reduced the sublimation rate of the underlying ice, thereby increasing the lifetimes of volatile particles within the plume. If confirmed, such a process would have important implications for the radiative and chemical properties of rocket plumes, including global ozone depletion associated with rocket launch activities
Sozialstruktur und Politik
Sozialstruktur und Politik : Forschungsstand und Forschungsperspektiven / Frank Brettschneider ; Jan van Deth ; Edeltraud Roller. - In: Ende der politisierten Sozialstruktur? / Frank Brettschneider ... (Hrsg.). - Opladen : Leske + Budrich, 2002. - S. 7-22. - (Veröffentlichung des Arbeitskreises "Wahlen und Politische Einstellungen" der Deutschen Vereinigung für Politische Wissenschaft ; 8