Showing papers by "United States Coast Guard Academy published in 2000"

Relative importance of benthic microalgae, phytoplankton and the detritus of smooth cordgrass Spartina alterniflora and the common reed Phragmites australis to brackish-marsh food webs

Abstract: We conducted a study to determine the trophic pathways leading to juvenile fish in 2 mesohaline tidal marshes bordering Delaware Bay. The relative roles of the major primary producers in supplying energy, ultimately, to the mummichog Fundulus heteroclitus were assessed by measur- ing the stable isotopic compositions of juveniles (21 to 56 mm total length, TL; most of which were young-of-the-year) and those of macrophyte vegetation, phytoplankton, and benthlc microalgae at each site. We collected samples of primary producers and F. heteroclitus, the dominant fish species in this and other marshes along the east coast of the USA, in June and August 1997, at 2 study sites (upstream and downstream) within Mad Horse Creek (a Spartina alterniflora-dominated site) and Alloway Creek (a Phragmites australis-dominated site), for a total of 4 study sites. Our results indicate that F. heteroclitus production is based on a mixture of primary producers, but the mixture depends on the relative abundance of macrophytes. In S. alterniflora-dominated marshes, C and S isotope ratios indicate that F. heteroclitus production is supported by S. alterniflora production (ca 39%, pre- sumably via detritus), whde in P. australis-dominated marshes, secondary production is based upon P. australis (73%). To our knowledge, this finding provides the first evidence that P. australis may contribute to aquatic food webs in tidal marshes. Benthic microalgae also contribute to the food chain that leads to E heteroclitus in both marsh types, while phytoplankton may be of lesser importance. Benthic microalgal biomass was lower in the P. australis-dominated system, consistent with a greater effect of shading in P. australis- versus S. alterniflora-based creek systems. Based on the difference in nitrogen isotope values between F. heteroclitus and the primary producers, the trophic level of E heteroclitus appears to be similar in the 2 marsh types, despite the differing vegetation types. In summary, the relative roles of the primary producers in supplying energy to F. heteroclitus varies locally and, in particular, with respect to the type of marsh macrophyte vegetation.

Determination of Oxygenates in Gasoline by GC×GC

Abstract: Comprehensive two-dimensional gas chromatography (GC × GC) has been applied to the quantitation of oxygenates in reformulated gasoline. Target oxygenates were C 1 -C 4 alcohols, tert-pentanol, methyl tert-butyl ether (MTBE), diisopropyl ether (DIPE), ethyl tert-butyl ether (ETBE), and tert-amyl methyl ether (TAME). These were separated from the gasoline matrix using a volatility-based selectivity in the first chromatographic dimension, followed by a mixed-phase polarity/shape selectivity in the second dimension. The high resolving power of this stationary phase combination completely separated all oxygenates except DIPE, ETBE, and TAME, which exhibited coelution with other nonpolar gasoline components. Oxygenates quantitation was achieved with the use of an internal standard, an FID detector, and calibration curves. Quantitation results are in good agreement with ASTM and EPA standard methods. When coupled with our previous method for BTEX and aromatics, a single GC × GC method can now quantitate MTBE, alcohols, BTEX, and aromatics in a one-hour analysis.

Drug Trafficking, the International System, and Decision-Making Constraints: A Policy-Making Simulation

Abstract: The classroom simulation laid out in this article can help international relations educators to identify compelling linkages between the abstract global theories and concepts typically analyzed in an introductory international relations or international political economy course and what most students have experienced as a “local,” even deeply personal issue—illicit drugs. By role-playing an international drug cartel intent upon advancing the global production, trafficking, and consumption of illicit drugs, students will see the world as it increasingly appears to non-state actors—as effectively borderless. By assuming the role of consultants to the U.S. drug czar, students experience for themselves the often vexing decisional constraints that hamper the ability of governments to respond effectively to transsovereign challenges. By offering a primer on constructing and running this simulation, the article contributes to a growing literature within the discipline that advocates and supports moving away from traditional lecture methods of teaching toward approaches that advance discussion-based, interactive, and participatory learning.

Stock Market Volatility in an Emerging Market: Further Evidence from the Athens Stock Exchange

Abstract: We investigate the time series properties of the daily and weekly returns from the Athens Stock Exchange (ASE) index for the years 1987 to 1997. We investigate whether important time-series characteristics have changed significantly over time. The Greek market has recently undergone major changes including complete capital flow liberalization, the implementation of computerized trading, as well as significant increases in market volume and capitalization; we thus contrast the 1987–90 and 1991–97 periods. Our findings suggest the dynamics of the ASE composite index returns have changed as the market has developed.

CS1: perspectives on programming languages and the breadth-first approach

Abstract: With development of Curriculum 2001 now begun, it is important not to overlook the experiences of the past. Curriculum '91 allowed a number of approaches to the CS1 course, and they met with varying degrees of success in different environments. The authors of this paper applied a number of pedagogical ideas to this first course in computer science. Their experiences – successes and failures alike – are described and compared in this paper with the intent of triggering discussions for the Curriculum 2001 debate.

Indoor Geolocation System Operational Test Results

Abstract: Over the past 2 years, the United States Coast Guard Academy has been developing an indoor, spread spectrum geolocation system to track personnel inside buildings under a project funded by the Defense Advanced Research Projects Agency (DARPA) Small Unit Operations Geolocation program The system has evolved from a single time difference (TD) engineering testbed to a fully functional, six-receiver geolocation system A hand-held transmitter is carried by the soldier Six wideband receiver antennas are placed outside the structure with GPS one-pulse-per-second and a reference transmitter supplying sampling time synchronization to all the receivers In tests, a solution converged every 1 s over the 3,000 samples taken at 28 different points throughout the test area, while 90 percent of the fixes fell within an error circle radius of 286 m The live demonstration of the system reflected its ability to track the individual during a hostage recovery scenario

Design and performance of an integrated DGPS/LORAN receiver

Abstract: Design and implementation of a real-time integrated DGPS/LORAN receiver is described. Previous work by the authors articulated the advantages of integrating these two systems and proposed a tightly coupled Kalman filter architecture; this work examines the essential system interfaces in more detail. Features of these interfaces include a highly stable common frequency reference, hardware measurement of the time offset between GPS and LORAN sampling strobes, data structures incorporating range residuals, and algorithms to align data relative to different assumed positions. Finally, the expected performance of this receiver is briefly described in a variety of operational scenarios. One such operational scenario for integrated DGPS/LORAN is the harbor entrance and approach (HEA) phase of maritime navigation. A critical issue in this scenario is the spatial decorrelation of the LORAN additional secondary factors (ASFs). Most data thus far has focused on the temporal stability of LORAN data and indicates that in evolutions of less than two hours, LORAN may be sufficient to meet the harbor entrance accuracy requirement of 8 to 20 meters. Some preliminary data collected in Connecticut's Thames River are presented and indicates that spatial ASF variations may cause errors much larger than the accuracy requirement. This in turn indicates that precise mapping of these variations using some combination of theoretical calculations and measurements will be necessary in order for integrated DGPS/LORAN to be used in HEA operations.