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RETHINKING THE ECONOMICS OF WAR: THE INTERSECTION OF NEED, CREED, AND GREED edited by Cynthia J. Arnson and I. William Zartman Washington, DC: Woodrow Wilson Center Press Baltimore, MD: The [...]

Thomas Battle and Donna Wells, eds., Moorland-Spingarn Research Center, Legacy: Treasures of Black History. Introduction by John Hope Franklin. Washington, DC: National Geographic Publishers, 2006. Pp. 224. Cloth $35.00. If [...]

THE GLOBAL COLD WAR Odd Arne Westad Cambridge: Cambridge University Press, 2007 484 Pages, cloth, $20.00 Most histories of the Cold War assume the origins of the conflict can be [...]

The latest series of Canadian Coast Guard ice-breakers feature a diesel electric propulsion system using synchronous motors and synchronous generators. The synchronous generators supply power to a constant-voltage 60 Hz bus that feeds the ship's hotel load and the propulsion system's cycloconverters. The cycloconverters convert 60 Hz ac power to variable frequency 0-18 Hz ac power for the synchronous propulsion motors. The propulsion motors are directly connected to the ship's propellers by means of shafting. The combination of cycloconverters, synchronous motors, and generators constitute a 'smart' transmission of the diesel power to drive the ship's propellers. This ac-ac propulsion system realizes the 'power plant' concept, which optimizes the number of generators that are on line in order to match the generated electrical power to the total electrical demand of the ship. The propulsion control system has two control loops that limit the power delivered by the propulsion motors to prevent the diesel engines, which drive the generators, from stalling during instantaneous or sustained overloads.

Connecting tropical rainforests to larger rivers, tropical headwaters export large quantities of carbon and nutrients as dissolved organic matter (DOM), and are thus a key component of the global carbon cycle. This DOM transport is not passive, however; sunlight and microbial activity alter DOM concentrations and compositions, affecting riverine greenhouse gas emissions and downstream ecosystems. The effects of sunlight and microbial turnover/activity on DOM concentrations and compositions in tropical headwaters are currently poorly understood, but novel Size Exclusion Chromatography (SEC) techniques coupled to suitable detectors can for the first time quantify their influences. Here, we present in-situ incubation experiments from from headwaters of the Essequibo River, in the Iwokrama Rainforest, Guyana, where sunlight oxidised up to 9% of dissolved organic carbon (DOC) over 12 hours, at higher rates than in larger tropical rivers. DOM transformations occurred in both photo-sensitive and supposedly photo-resistant pools. Microbial activity had varying, less clear influences on DOC concentrations over the same time span; compositionally, this appeared to extend beyond known bio-labile components. Biopolymers were particularly reactive to both processes. We show sunlight has the greater potential to mineralise headwater DOM and thus potentially influence degassing. Our approach provides a future template to constrain DOM transformations along river networks, identify biogeochemical activity hotspots, and improve greenhouse gas emissions estimations under changing environmental conditions. [ABSTRACT FROM AUTHOR]