177,712 research outputs found
Tidal courses: classification, origin and functionality
No full textAn Integrated and Ecosystem Approach provides an understanding of the functioning of coastal ecosystems and the ecological services that they provide. As coastal wetlands are under a great deal of pressure from the dual forces of rising sea levels and the intervention of human populations, both along the estuary and in the river catchment, this book covers important issues, such as the destruction or degradation of wetlands from land reclamation and infrastructures, impacts from the discharge of pollutants, changes in river flows and sediment supplies, land clearing, and dam operations.Fil: Perillo, Gerardo Miguel E.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentin
Coastal wetlands: A Synthesis
No full textThis book and this synthesis address the pressing need for better management of coastal wetlands worldwide because these wetlands are disappearing at an alarming rate; in some countries the loss is 70%–80% in the last 50 years. Managing requires understanding. Although our understanding of the functioning of coastal wetland ecosystems has grown rapidly over the past decade, still much remains to be learned and understood. We have gained insight into the roles of geomorphic processes, hydrologic dynamics, biotic feedback, and disturbance agents in creating and molding a variety of coastal wetland ecosystems across climatic gradients. The variety is expressed not so much in the more obvious differences in vegetation cover, but rather how physical processes both facilitate and constrain a diversity of plant and animal communities. At one level, coastal wetlands are the product of tidal forces and freshwater inputs at the margin of continents. At another level, the plants control the water currents in the tidal creeks draining the wetlands by generating a tidal current asymmetry that controls sediment transport and results in a deep tidal creek surrounded by shallow vegetated wetlands. The vegetation also influences the physics of water and sediment through several other processes including biofilms, bioturbation of sediments, the buffeting of currents and waves, organic enrichment of sediments, and the closing of nutrient cycles. Few ecosystems provide us with so many clear examples of such feedback controls. What we do understand about the structure and functioning of coastal wetlands should provide the theoretical underpinnings for effective management in protecting them for their many contributions to ecosystem goods and services. What we do not understand should compel us to focus our attention and energies toward seeking optimal solutions to some of the most perplexing and urgent problems facing natural resource management.Fil: Hopkinson, Charles S.. University of Georgia; Estados UnidosFil: Wolanski, Eric. James Cook University; Australia. Australian Institute of Marine Science; AustraliaFil: Cahoon, Donald R.. Patuxent Wildlife Research Center; Estados UnidosFil: Perillo, Gerardo Miguel E.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; ArgentinaFil: Brinson, Mark M.. No especifíca;Fil: Hopkinson, Charles S.. University of Georgia; Estados Unido
Coastal Wetlands: A Synthesis
No full textWhat are coastal wetland ecosystems, what are their limits of distribution, and where dothey exist in the overall coastal landscape? There are several general definitions for wetlands,but the Ramsar definition is likely the most broadly encompassing (http://www.ramsar.org/), whereas others are more focused definitions tailored to country-specific protectionand management policies (Mitsch and Gosselink, 2006). We offer a very general approachrather than a precise definition: coastal wetlands are ecosystems that are found within anelevation gradient that ranges between subtidal depths where light penetrates to supportphotosynthesis of benthic plants to the landward edge where the sea passes its hydrologicinfluence to groundwater and atmospheric processes. At the seaward margin, biofilms,benthic algae, and seagrasses are representative biotic components. At the landward margin,vegetation boundaries range from those located on groundwater seeps or fens in humidclimates to relatively barren salt flats in arid climates.Fil: Hopkinson, Charles S.. University of Georgia; Estados UnidosFil: Wolanski, Eric. James Cook University; Australia. Australian Institute of Marine Science; AustraliaFil: Brinson, Mark M.. Brinson East Carolina University; Estados UnidosFil: Cahoon, Donald R.. United States Geological Survey; Estados UnidosFil: Perillo, Gerardo Miguel E.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur. Departamento de Geología; Argentin
Geomorphology of Tidal Courses and Depressions
No full textWetlands are unique environments along the coasts of the world since their origin, andtheir preservation is required for the conjunction of a series of factors. First of all, the geomorphologyof the initial coast must have enough accommodation space to allow the retention,minimizing the bypass, of the sediment being provided by the various possible sources. Sedimentsupply must also be important; therefore, the sources must provide a continuous inputto build the wetland both vertically and horizontally, and keep it in equilibrium with the energyconditions proper of the coast, and potential modifications due to mean sea level variations.The location of the coastal setting should be such as to minimize the energy of the sea;for instance, protected coasts have a better chance to retain sediment than those found in theopen shores. Furthermore, progradation and/or aggradation of the wetland, as it happens indeltaic coasts, requires a positive balance between the sediment input from the different sourcesand the material removed by waves, tides, and their corresponding currents (Perillo andPiccolo, 2011). This balance must also be positive for longer periods because the wetlandneeds to aggrade at least to the same rate to counterbalance the potential compaction/subsidence of the sediments and the increase in mean sea level.Tidal courses and depressions are incisions or negative elevations in an otherwise level orslightly seaward-inclined surface represented by a typical coastal wetland. From the initialstage of wetland formation, courses and depressions are common features of the environmentmorphology. Even the smoothest topography has depressions where tidal water is retainedduring low tide. In fact, the irregularities of the surface when connected develop coursesthat, for a part of the tidal cycle, conduct the water and the substances and organism thatit mobilizes. Therefore, courses are necessary features for the circulation of water and sedimentduring the preliminary stages of the formation of the wetland.Fil: Perillo, Gerardo Miguel E.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur. Departamento de Geología; Argentin
Effects of discontinuous transmission on the performance of a WCDMA cellular system
No full textIn this article we investigate the side effects of DTX (Discontinuous Transmission) on the performance of a WCDMA radio interface with SIR-based closed-loop power control. The aim of DTX is to reduce the energy consumption of the mobile terminal and the total interfering power in a cellular system; here, it is shown that this technique can also lead to a temporary performance degradation when the interfering terminals turn on their data channel after some frames of inactivity. The main parameters that characterize the dynamics of the DTX mechanism are described and their effects are investigated. We also propose a suitable variation to the DTX mechanism which reduces the unwanted effects
Treatment effects of R-Appliance and Fränkel-2 in Class II division 1 malocclusions
No full textAim The purpose of this study was to compare the effects of a differently designed functional appliance (the R-appliance) with Fränkel-2. Study Design Twenty-seven patients (16 girls and 11 boys) with a mean age of 9.8 (SD 1.6) years were treated with the R-appliance for 15.4 (SD 0.4) months and twentyseven (15 girls and 12 boys) patients with a mean age of 9.1 (SD 1.1) years were treated with a Fränkel-2 appliance for 19 (SD 5.6) months. All patients had Class II division 1 malocclusions due to mandibular deficiency and all of them had prepubertal stages of skeletal development. Lateral cephalograms obtained at the beginning (T1) and at the end (T2) of the study were analysed. Results Paired t-tests showed that SNB significantly increased in both groups. The incisor mandibular plane angle (IMPA) was reduced in the R-appliance group by 2.2 (SD 4.9) degrees (P < 0.03) but increased by 2.2 (SD 2.6) degrees (P < 0.001) in the Fränkel-2 group. The SNA in the R-appliance group showed an increase of 0.2 (SD 2) degrees (P < 0.6), while it was decreased by 0.4 (SD 0.5) degrees (P < 0.6) in the Fränkel-2 group. Conclusions Both treatment modalities were successful in moving the mandible forward. However, with the R-appliance, this was achieved without proclination of the lower incisors
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