Literatura académica sobre el tema "Bottom-up forcings"
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Artículos de revistas sobre el tema "Bottom-up forcings"
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Pielke, Roger A., Jimmy Adegoke, Faisal Hossain y Dev Niyogi. "Environmental and Social Risks to Biodiversity and Ecosystem Health—A Bottom-Up, Resource-Focused Assessment Framework". Earth 2, n.º 3 (12 de julio de 2021): 440–56. http://dx.doi.org/10.3390/earth2030026.
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Risks from human intervention in the climate system are raising concerns with respect to individual species and ecosystem health and resiliency. A dominant approach uses global climate models to predict changes in climate in the coming decades and then to downscale this information to assess impacts to plant communities, animal habitats, agricultural and urban ecosystems, and other parts of the Earth’s life system. To achieve robust assessments of the threats to these systems in this top-down, outcome vulnerability approach, however, requires skillful prediction, and representation of changes in regional and local climate processes, which has not yet been satisfactorily achieved. Moreover, threats to biodiversity and ecosystem function, such as from invasive species, are in general, not adequately included in the assessments. We discuss a complementary assessment framework that builds on a bottom-up vulnerability concept that requires the determination of the major human and natural forcings on the environment including extreme events, and the interactions between these forcings. After these forcings and interactions are identified, then the relative risks of each issue can be compared with other risks or forcings in order to adopt optimal mitigation/adaptation strategies. This framework is a more inclusive way of assessing risks, including climate variability and longer-term natural and anthropogenic-driven change, than the outcome vulnerability approach which is mainly based on multi-decadal global and regional climate model predictions. We therefore conclude that the top-down approach alone is outmoded as it is inadequate for robustly assessing risks to biodiversity and ecosystem function. In contrast the bottom-up, integrative approach is feasible and much more in line with the needs of the assessment and conservation community. A key message of our paper is to emphasize the need to consider coupled feedbacks since the Earth is a dynamically interactive system. This should be done not just in the model structure, but also in its application and subsequent analyses. We recognize that the community is moving toward that goal and we urge an accelerated pace.
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Molero, Francisco, Alfonso Javier Fernández, María Aránzazu Revuelta, Isabel Martínez-Marco, Manuel Pujadas y Begoña Artíñano. "Effect of Vertical Profile of Aerosols on the Local Shortwave Radiative Forcing Estimation". Atmosphere 12, n.º 2 (30 de enero de 2021): 187. http://dx.doi.org/10.3390/atmos12020187.
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In this work, the effect of the aerosol vertical distribution on the local shortwave aerosol radiative forcing is studied. We computed the radiative forcing at the top and bottom of the atmosphere between 0.2 and 4 microns using the libRadTran package and compared the results with those provided by AERONET (AErosol RObotic NETwork). Lidar measurements were employed to characterize the aerosol vertical profile, and collocated AERONET measurements provided aerosol optical parameters required to calculate its radiative forcing. A good correlation between the calculated radiative forcings and those provide by AERONET, with differences smaller than 1 W m−2 (15% of estimated radiative forcing), is obtained when a gaussian vertical aerosol profile is assumed. Notwithstanding, when a measured aerosol profile is inserted into the model, differences between radiative forcings can vary up to 6.54 W m−2 (15%), with a mean of differences = −0.74 ± 3.06 W m−2 at BOA and −3.69 W m−2 (13%), with a mean of differences = −0.27 ± 1.32 W m−2 at TOA due to multiple aerosol layers and aerosol types. These results indicate that accurate information about aerosol vertical distribution must be incorporated in the radiative forcing calculation in order to reduce its uncertainties.
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Pradeep Ram, A. S., S. Chaibi-Slouma, J. Keshri, J. Colombet y T. Sime-Ngando. "Functional Responses of Bacterioplankton Diversity and Metabolism to Experimental Bottom-Up and Top-Down Forcings". Microbial Ecology 72, n.º 2 (14 de mayo de 2016): 347–58. http://dx.doi.org/10.1007/s00248-016-0782-0.
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Dinápoli, Matías G., Claudia G. Simionato y Diego Moreira. "Model Sensitivity during Extreme Positive and Negative Surges in the Río de la Plata Estuary: Highlighting the Need for an Appropriate Hindcast/Forecast System". Weather and Forecasting 35, n.º 3 (15 de mayo de 2020): 1097–112. http://dx.doi.org/10.1175/waf-d-19-0171.1.
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Abstract The large and fast-flowing Río de la Plata (RdP) estuary is affected by extreme storm surges (above ±2 m with respect to tidal datum), which have large impacts on the millions of inhabitants and for navigation. In this work the Coastal and Regional Ocean Community Model (CROCO) numerical model was modified and implemented as a set of regional one-way nested 2D applications for the hindcast/forecast of water level in the RdP. A sensitivity analysis (SA) was carried out to determine the impact on the numerical solutions of the uncertainties in the different modeling parameter forcings and to highlight the need for the construction of a modeling system that provides meaningful information to the potential users. The SA included the friction coefficients, the wind speed and direction, the atmospheric surface pressure, and the continental discharge. Water level is most sensitive to uncertainties in the wind forcing; even small changes in this input can create large errors in the water level forecast/hindcast. Forcing with different analyses’ wind products yielded differences of up to 50% in the peak water levels. Results also showed that the modeling system requires a reasonable adjustment of the bottom friction parameters; that it is important to include the atmospheric surface pressure forcing; and that, from the point of view of water level forecast, it is not necessary to couple a hydrological model in spite of the enormous runoff of this estuary. Given the strong sensitivity to errors in the wind forcing, we believe it is important to provide estimates of uncertainty together with hindcast/forecast water level for these predictions to be of greatest quality and practical applicability.
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Habib, Md Ahsan y Gary A. Zarillo. "Construction of a Real-Time Forecast Model for Coastal Engineering and Processes Nested in a Basin Scale Model". Journal of Marine Science and Engineering 11, n.º 7 (21 de junio de 2023): 1263. http://dx.doi.org/10.3390/jmse11071263.
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A numerical model was developed using Delft3D to simulate the circulation dynamics in Port Everglades, FL, and the adjacent coastal area. The model was nested within the HYCOM (Hybrid Coordinate Ocean Model), while meteorological data were obtained from the NARR (North American Regional Reanalysis) model. To evaluate the model, model outputs were compared with observed data from the NOAA. Calibration experiments were conducted on the model parameters, including the bottom friction, wind forcings, and vertical layer specification. These experiments revealed that implementing a 10-layer model slightly improved the vertical stratification, while the utilization of 2-D wind data resulted in more pronounced surface layer characteristics in temperature and velocity profiles and employing moderate values of the Chezy coefficient produced optimal outcomes for the bottom roughness parameter. The model demonstrated satisfactory performance across major parameters, including water level, salinity, temperature, and currents. A real-time forecast system has been constructed with this nested model, providing up to 3-day forecasts that are updated daily. To facilitate automated forecasting without manual intervention, an automation system has been developed using a combination of bash, MATLAB, and Python scripts. This study provides a comprehensive documentation of the concepts and detailed methods involved in developing a real-time forecast model for estuarine and coastal regions.
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Anet, J. G., S. Muthers, E. V. Rozanov, C. C. Raible, A. Stenke, A. I. Shapiro, S. Brönnimann et al. "Impact of solar versus volcanic activity variations on tropospheric temperatures and precipitation during the Dalton Minimum". Climate of the Past 10, n.º 3 (9 de mayo de 2014): 921–38. http://dx.doi.org/10.5194/cp-10-921-2014.
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Abstract. The aim of this work is to elucidate the impact of changes in solar irradiance and energetic particles versus volcanic eruptions on tropospheric global climate during the Dalton Minimum (DM, AD 1780–1840). Separate variations in the (i) solar irradiance in the UV-C with wavelengths λ < 250 nm, (ii) irradiance at wavelengths λ > 250 nm, (iii) in energetic particle spectrum, and (iv) volcanic aerosol forcing were analyzed separately, and (v) in combination, by means of small ensemble calculations using a coupled atmosphere–ocean chemistry–climate model. Global and hemispheric mean surface temperatures show a significant dependence on solar irradiance at λ > 250 nm. Also, powerful volcanic eruptions in 1809, 1815, 1831 and 1835 significantly decreased global mean temperature by up to 0.5 K for 2–3 years after the eruption. However, while the volcanic effect is clearly discernible in the Southern Hemispheric mean temperature, it is less significant in the Northern Hemisphere, partly because the two largest volcanic eruptions occurred in the SH tropics and during seasons when the aerosols were mainly transported southward, partly because of the higher northern internal variability. In the simulation including all forcings, temperatures are in reasonable agreement with the tree ring-based temperature anomalies of the Northern Hemisphere. Interestingly, the model suggests that solar irradiance changes at λ < 250 nm and in energetic particle spectra have only an insignificant impact on the climate during the Dalton Minimum. This downscales the importance of top–down processes (stemming from changes at λ < 250 nm) relative to bottom–up processes (from λ > 250 nm). Reduction of irradiance at λ > 250 nm leads to a significant (up to 2%) decrease in the ocean heat content (OHC) between 0 and 300 m in depth, whereas the changes in irradiance at λ < 250 nm or in energetic particles have virtually no effect. Also, volcanic aerosol yields a very strong response, reducing the OHC of the upper ocean by up to 1.5%. In the simulation with all forcings, the OHC of the uppermost levels recovers after 8–15 years after volcanic eruption, while the solar signal and the different volcanic eruptions dominate the OHC changes in the deeper ocean and prevent its recovery during the DM. Finally, the simulations suggest that the volcanic eruptions during the DM had a significant impact on the precipitation patterns caused by a widening of the Hadley cell and a shift in the intertropical convergence zone.
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Anet, J. G., S. Muthers, E. V. Rozanov, C. C. Raible, A. Stenke, A. I. Shapiro, S. Brönnimann et al. "Impact of solar vs. volcanic activity variations on tropospheric temperatures and precipitation during the Dalton Minimum". Climate of the Past Discussions 9, n.º 6 (4 de noviembre de 2013): 6179–220. http://dx.doi.org/10.5194/cpd-9-6179-2013.
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Abstract. The aim of this work is to elucidate the impact of changes in solar irradiance and energetic particles vs. volcanic eruptions on tropospheric global climate during the Dalton Minimum (DM, 1780–1840 AD). Separate variations in the (i) solar irradiance in the UV-C with wavelengths λ < 250 nm, (ii) irradiance at wavelengths λ > 250 nm, (iii) in energetic particle spectrum, and (iv) volcanic aerosol forcing were analyzed separately, and (v) in combination, by means of small ensemble calculations using a coupled atmosphere-ocean chemistry-climate-model. Global and hemispheric mean surface temperatures show a significant dependence on solar irradiance at λ > 250 nm. Also, powerful volcanic eruptions in 1809, 1815, 1831 and 1835 significantly decrease global mean temperature by up to 0.5 K for 2–3 yr after the eruption. However, while the volcanic effect is clearly discernible in the southern hemispheric mean temperature, it is less significant in the Northern Hemisphere, partly because the two largest volcanic eruptions occurred in the SH tropics and during seasons when the aerosols were mainly transported southward, partly because of the higher northern internal variability. In the simulation including all forcings, temperatures are in reasonable agreement with the tree-ring-based temperature anomalies of the Northern Hemisphere. Interestingly, the model suggests that solar irradiance changes at λ < 250 nm and in energetic particle spectra have only insignificant impact on the climate during the Dalton Minimum. This downscales the importance of top-down processes (stemming from changes at λ < 250 nm) relative to bottom-up processes (from λ > 250 nm). Reduction of irradiance at λ > 250 nm leads to a significant (up to 2%) decrease of the ocean heat content (OHC) between the 0 and 300 m of depth, whereas the changes in irradiance at λ < 250 nm or in energetic particle have virtually no effect. Also, volcanic aerosol yields a very strong response, reducing the OHC of the upper ocean by up to 1.5%. In the simulation with all forcings, the OHC of the uppermost levels recovers after 8–15 yr after volcanic eruption, while the solar signal and the different volcanic eruptions dominate the OHC changes in the deeper ocean and prevent its recovery during the DM. Finally, the simulations suggest that the volcanic eruptions during the DM had a significant impact on the precipitation patterns caused by a widening of the Hadley cell and a shift of the intertropical convergence zone.
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Rumín-Caparrós, A., A. Sanchez-Vidal, A. Calafat, M. Canals, J. Martín, P. Puig y R. Pedrosa-Pàmies. "External forcings, oceanographic processes and particle flux dynamics in Cap de Creus submarine canyon, NW Mediterranean Sea". Biogeosciences Discussions 9, n.º 12 (18 de diciembre de 2012): 18571–600. http://dx.doi.org/10.5194/bgd-9-18571-2012.
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Abstract. Atmospheric forcing during 2009–2010 and 2010–2011 winter months showed differences in both intensity and persistence that led to distinct oceanographic responses. Persistent dry northern winds caused strong heat losses (14 211 W m−2) in winter 2009–2010 that triggered a pronounced sea surface cooling compared to winter 2010–2011 (1597 W m−2 lower). As a consequence, a large volume of dense shelf water formed in winter 2009–2010, which cascaded at high speed (up to ∼ 1 m s−1) down Cap de Creus canyon, as measured by current-meters in mooring lines deployed inside the canyon at 300 m and 1000 m water depth. The lower heat losses recorded in winter 2010–2011, together with an increased river discharge, resulted in lowered density waters over the shelf, thus preventing the formation of dense shelf water. Particle fluxes were concurrently measured by using sediment traps at the same mooring stations. High total mass fluxes (up to 84.9 g m−2 d−1) recorded in winter 2009–2010 indicate that dense shelf water cascading resuspended and transported sediments at least down to 1000 m deep within the canyon. Sediment fluxes were lower (28.9 g m−2 d−1) under the quieter conditions of winter 2010–2011. The dominance of the lithogenic fraction in mass fluxes during the two winters points to a resuspension origin for most of the particles transported down canyon. The variability in organic matter and opal contents relates to seasonally controlled inputs associated to the plankton spring bloom during March and April of both years. Our measurements of particle fluxes (including major components and grain size distribution), together with meteorological and oceanographic parameters such as wind speed, turbulent heat flux, near-bottom water temperature, current speed and suspended sediment concentration, during winters 2009–2010 and 2010–2011 along the Cap de Creus submarine canyon, show the important role of atmospheric forcings in transporting particulate matter through the submarine canyon and towards the deep sea.
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Rumín-Caparrós, A., A. Sanchez-Vidal, A. Calafat, M. Canals, J. Martín, P. Puig y R. Pedrosa-Pàmies. "External forcings, oceanographic processes and particle flux dynamics in Cap de Creus submarine canyon, NW Mediterranean Sea". Biogeosciences 10, n.º 6 (3 de junio de 2013): 3493–505. http://dx.doi.org/10.5194/bg-10-3493-2013.
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Abstract. Particle fluxes (including major components and grain size), and oceanographic parameters (near-bottom water temperature, current speed and suspended sediment concentration) were measured along the Cap de Creus submarine canyon in the Gulf of Lions (GoL; NW Mediterranean Sea) during two consecutive winter-spring periods (2009–2010 and 2010–2011). The comparison of data obtained with the measurements of meteorological and hydrological parameters (wind speed, turbulent heat flux, river discharge) have shown the important role of atmospheric forcings in transporting particulate matter through the submarine canyon and towards the deep sea. Indeed, atmospheric forcing during 2009–2010 and 2010–2011 winter months showed differences in both intensity and persistence that led to distinct oceanographic responses. Persistent dry northern winds caused strong heat losses (14.2 × 103 W m−2) in winter 2009–2010 that triggered a pronounced sea surface cooling compared to winter 2010–2011 (1.6 × 103 W m−2 lower). As a consequence, a large volume of dense shelf water formed in winter 2009–2010, which cascaded at high speed (up to ∼1 m s−1) down Cap de Creus Canyon as measured by a current-meter in the head of the canyon. The lower heat losses recorded in winter 2010–2011, together with an increased river discharge, resulted in lowered density waters over the shelf, thus preventing the formation and downslope transport of dense shelf water. High total mass fluxes (up to 84.9 g m−2 d−1) recorded in winter-spring 2009–2010 indicate that dense shelf water cascading resuspended and transported sediments at least down to the middle canyon. Sediment fluxes were lower (28.9 g m−2 d−1) under the quieter conditions of winter 2010–2011. The dominance of the lithogenic fraction in mass fluxes during the two winter-spring periods points to a resuspension origin for most of the particles transported down canyon. The variability in organic matter and opal contents relates to seasonally controlled inputs associated with the plankton spring bloom during March and April of both years.
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Cerralbo, Pablo, Manuel Espino, Manel Grifoll y Arnoldo Valle-Levinson. "Subtidal circulation in a microtidal Mediterranean bay". Scientia Marina 82, n.º 4 (16 de enero de 2019): 231. http://dx.doi.org/10.3989/scimar.04801.16a.
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We examine the role of different forcings on the subtidal circulation in a microtidal bay with freshwater inputs in the NW Mediterranean Sea: Alfacs Bay. Observations of subtidal flow in summer 2013 and winter 2014 reveal a two-layered, vertically sheared circulation. During the summer, there is a significant positive correlation between surface currents and winds along the main axis of the bay, while a negative correlation is observed between wind and the bottom layers. During the winter, the cross-shore response is correlated with the most energetic winds, showing a two-layered vertical structure inside the bay and a nearly depth-independent water motion caused by high wind speeds at the bay mouth. The vertical structure of the velocities, as determined through empirical orthogonal function analysis, confirms that surface layers are affected by winds and bottom currents correlated negatively with winds as a response of the wind set-up. Seasonal mean circulation reveals gravitational exchange at the bay mouth during the summer. However, mean circulation is unclear in the inner bay and close to the drainage channels. Observed flow patterns are supported by modelling results that confirm the persistence of averaged current in the low-frequency dynamics. Re-circulation areas in the inner bay indicate the rich spatial variability in flow at low-frequency time scales.
Tesis sobre el tema "Bottom-up forcings"
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Sergi, Sara. "Nutrient input from seamounts and hydrothermal vents in the Southern Ocean : impacts on the pelagic ecosystems and implications for conservation". Electronic Thesis or Diss., Sorbonne université, 2021. http://www.theses.fr/2021SORUS508.
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Les processus bottom-up contôlent une portion importante de la variabilité des écosystèmes marins. Dans l'océan Austral, des contrastes intenses dans la distribution des écosystèmes pélagiques sont génerés par la limitation de la production primaire par le fer et la Courant Circumpolaire Antarctique. Les efflorescences massives en phytoplancton en aval des îles entretiennent des vastes réseaux trophiques. En comparaison, l'impact des sources profondes de nutriments sur la production pélagique semble négligeable. Les programmes de conservation dans la Courant Circumpolaire Antarctique vont de pair avec cette description, avec des Aires Marines Protégées uniquement autour des îles. En combinant des données multi-satellites, des observations in-situ, des données de télémétrie animale et des sorties de modèles, cette thèse réévalue le rôle écologique des sources profondes de nutriments sur les écosystèmes pélagiques. L’analyse Lagrangienne des courants géostrophiques relie des vastes blooms phytoplanctoniques à des sources hydrothermaux ou des monts sous-marins. Les études contenues dans cette thèse démontrent que les forçages bottom-up induits par les sources profondes en nutriments façonnent le paysage marin pélagique à l'échelle du bassin, des producteurs primaires aux mégafaunes. Les résultats issus de cette thèse sont ainsi considérés dans le contexte des programmes de conservation. Il s’agit notamment des travaux de la CCAMLR visant à développer un système représentatif d’Aires Marines Protégées et dans le projet actuel d'extension de l’Aire Marine Protégée des îles françaises Saint-Paul et d'AmsterdamBottom-up forces control a large fraction of marine ecosystem variability. In the Southern Ocean, intense contrasts in the distribution of pelagic ecosystems are driven by the iron limitation of biological productivity and the vigorous Antarctic Circumpolar Current. Massive phytoplankton blooms stemming from islands support large trophic chains. By comparison, the impact of deep nutrient sources on the pelagic production appears negligible. Conservation efforts in the Antarctic Circumpolar Current are in line with this description, with Marine Protected Areas only occurring around islands. By combining multi-satellite data, in-situ observations, animal telemetry data and model outputs, this thesis revaluates the ecological role of deep nutrient sources. Lagrangian analyses of altimetry-derived velocity fields link vast phytoplankton blooms to hydrothermal vents or seamounts. The studies contained in this thesis demonstrate that bottom-up forcings driven by deep nutrient sources shape the pelagic seascape at basin scale (O(103 km)) from primary producers up to megafauna species. These findings underline the ecological importance of the open Southern Ocean waters and advocate for a connected vision of future conservation actions along the Antarctic Circumpolar Current. The analyses of bottom-up forcings are consequentially considered within the CCAMLR’s effort for developing a representative system of Marine Protected Areas and within the ongoing extension project of the French Saint Paul and Amsterdam islands’ Marine Protected Areas
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Saba, Vincent Sellitto. "Bottom-up and climatic forcing on the nesting and foraging ecology of leatherback turtles (Dermochelys coriacea)". W&M ScholarWorks, 2007. http://www.vims.edu/library/Theses/Saba07.pdf.
Texto completoLibros sobre el tema "Bottom-up forcings"
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Faust, Avraham. The Neo-Assyrian Empire in the Southwest. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198841630.001.0001.
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The Neo-Assyrian empire—the first large empire of the ancient world—had attracted a great deal of public attention ever since the spectacular discoveries of the nineteenth century. The southwestern part of this empire, located in the lands of the Bible, is archaeologically speaking the best-known region in the world, and its history is also described in a plethora of texts, including the Hebrew Bible. Using a bottom-up approach, this book utilizes this unparalleled information to reconstruct the outcomes of the Assyrian conquest of the region, and how it impacted the diverse political units and ecological zones that comprised it, forcing the reader to appreciate the transformations the imperial takeover brought in its wake. The analysis reveals the marginality of the annexed territories in the southwest, and that the empire focused its activities in small border areas, facing the prospering clients. A comparison of this surprising picture to the information available from other parts of the empire suggests that the distance of these provinces from the imperial core is responsible for their fate, leading to a better appreciation of factors influencing imperial expansion, the considerations leading to annexation, and the imperial methods of control, challenging some old conventions about the development of the Assyrian empire and its rule. The detailed information also enables an examination of the Assyrian empire within the context of other ancient Near Eastern empires, and of imperialism at large, shedding a new light on the nature of Assyrian domination, and the reasons for the harsh treatment of the distant provinces. The book also examines what set the limits on the Assyrian empire, and highlights the historical development of imperial control in antiquity, and how later empires were able to overcome these limitations, paving the way to much larger and longer-lasting polities.
Capítulos de libros sobre el tema "Bottom-up forcings"
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Bletsas, Michail y Adolfo Plasencia. "The Emergence of a Nonbiological Intelligence". En Is the Universe a Hologram? The MIT Press, 2017. http://dx.doi.org/10.7551/mitpress/9780262036016.003.0016.
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Michail Bletsas, Director of Computing at the MIT Media Lab and Director of the Network Computing Systems Group at MIT, is convinced that the 21st century will see the emergence of biological intelligence. He starts the dialogue with an explanation of why the Internet and its huge computational system, - the most complex human-built system -, is forcing us to learn to engage with systems that are becoming even more complicated, with varying levels of complexity. He describes later the arrival of the finely granular Internet, which in consequence led to the concept of connectivity everywhere. Later he outlines the Internet of Things’ capabilities that he and his team have deployed inside the new MIT Media Lab building. Michael then goes on to argue why we have to separate issues of business from scientific arguments and prediction—the important thing in business is not only what’s going to happen, but when it will happen. Michael also relates why the best type of innovation is bottom up, before going on to explain how not only innovation, but also evolution, is gradually improving things.
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"Advancing an Ecosystem Approach in the Gulf of Maine". En Advancing an Ecosystem Approach in the Gulf of Maine, editado por Michael J. Fogarty, Kevin D. Friedland, Laurel Col, Robert Gamble, Jonathan Hare, Kimberly Hyde, Jason S. Link et al. American Fisheries Society, 2012. http://dx.doi.org/10.47886/9781934874301.ch12.
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<i>Abstract</i>.—The northeast U.S. Continental Shelf large marine ecosystem (NES LME) has supported important commercial fisheries for several centuries. The NES LME has experienced structural change due to both intensive exploitation and physical forcing in relation to broader climate impacts in the North Atlantic over the past several decades. Here, we examine the combined effects of anthropogenic and environmental factors on the state of the NES LME using a driverpressure- state-impact-response framework to structure our assessment of patterns of change in this system. We partitioned both drivers and pressures according to natural and anthropogenic sources. Ecological state variables encompassed a broad spectrum of trophic levels. Impact metrics are based on economic trends in the fisheries. To represent regulatory responses, we trace the history of management actions in this region over the past five decades. The critical importance of changes in temperature and water column stratification in ecosystem change, in relation to bottom-up forcing, is identified using canonical proredundancy analysis. Analysis of anthropogenic pressures indicate a clear effect of fishing pressure, and removals due to fishing, in the dynamics of fish communities in the region, highlighting an important top-down control mechanism. Analysis of zooplankton community dynamics confirms previous indications of a regime-like change in species composition during the 1990s. Observed changes in fish community dynamics appears to be most clearly related to large-scale switches from a demersal to a pelagic fish dominated system and to changes within the demersal fish community itself.
Actas de conferencias sobre el tema "Bottom-up forcings"
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Belibassakis, K. A., Th P. Gerostathis y G. A. Athanassoulis. "A Coupled-Mode Technique for the Prediction of Wave-Induced Set-Up and Mean Flow in Variable Bathymetry Domains". En ASME 2007 26th International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2007. http://dx.doi.org/10.1115/omae2007-29365.
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In the present work, a complete, phase-resolving wave model is coupled with an iterative solver of the mean-flow equations in intermediate and shallow water depth, permitting an accurate calculation of wave set-up and wave-induced current in intermediate and shallow water environment with possibly steep bathymetric variations. The wave model is based on the consistent coupled-mode system of equations, developed by Athanassoulis & Belibassakis (1999) for the propagation of water waves in variable bathymetry regions. This model improves the predictions of the mild-slope equation, permitting the treatment of wave propagation in regions with steep bottom slope and/or large curvature. In addition, it supports the consistent calculation of wave velocity up to and including the bottom boundary. The above wave model has been further extended to include the effects of bottom friction and wave breaking, which are important factors for the calculation of radiation stresses on decreasing depth. The latter have been used as forcing terms to the mean flow equations in order to predict wave-induced set up and mean flow in open and closed domains. Numerical results obtained by the present model are presented and compared with predictions obtained by the mild-slope approximation (Massel & Gourlay 2000), and experimental data (Gourlay 1996).
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Littleford, Wayne y Sanjeev Jolly. "An Innovative Approach to Emission Reductions and Heat Recovery: Comply Units". En ASME Turbo Expo 2010: Power for Land, Sea, and Air. ASMEDC, 2010. http://dx.doi.org/10.1115/gt2010-23814.
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Emissions from power plants are increasingly becoming a global concern that is forcing countries to set tougher and tougher standards for meeting regulations. Compliance with these requirements comes at a cost — resources required to install and maintain the necessary equipment that is often exacerbated by a reduction in efficiency. These harmful emissions that are products of combustion (POC) are typically classified as NOx, SO2, CO2, UHC (unburned hydrocarbons) and Particulate and sometimes heavy metals like mercury, arsenic, etc. Currently there are specific methods available for reducing each of these emissions individually but there is no single system in use that can remove all these unwanted emissions simultaneously — at least not until now. With the proposed system, all these emissions can almost be entirely eliminated from the flue gases concurrently. The process essentially consists of ozone injection for NOx conversion, fogging spray mixed with hydrogen peroxide solution for SO2 conversion and condensing these along with other pollutants over coils to remove all pollutants from exhaust gas stream. As a result, the NOx and SO2 end up as nitric and sulfuric acid in the wastewater stream collected at the bottom of the unit. In addition, UHC and particulate are also removed during the condensation process along with some carbonic acid resulting from dissolved CO2. This waste water can then be treated accordingly and recycled. Another major advantage of this process is the heat absorbed by circulating water in the condensing coils that can be effectively utilized to improve plant performance and overall thermal efficiencies.
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Vested, Malene H., Stefan Carstensen y Erik Damgaard Christensen. "Experimental Study of Wave Force Distribution on a Monopile Structure". En ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/omae2018-77509.
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As the demand for offshore wind energy continues to grow, the strive to understand the wave forces acting on the substructure of the wind turbines continues. In regard to wind turbine design, it is vital to consider not only the total wave force, but also the local wave forces. Local forces are particularly important for the design of secondary structures as e.g. mooring platforms. Typically, however, experimental studies mainly concern total forces or idealized local forces. We present here a rather simple way to measure local forces along a model monopile. The study is conducted in a wave flume of 28 m in length, in which waves are generated by a piston-type wave maker at a water depth of 0.515 m and shoal onto a bed of slope 1:25. A model monopile is installed and subjected to forcing from a series of both regular and irregular waves. In the experimental set-up, the model monopile is fixed at the bottom and the top and consists of seven independent cylindrical sections. The cylindrical sections are connected by force transducers which measure local shear, and so the associated local forces may be determined. The measured local forces are compared to the force distribution given by Morisons equation combined with linear theory and Wheeler stretching, which is a force estimate commonly used in the industry. This study shows that the total force is rather well captured by Morison’s equation. The force distribution estimated from Morison’s equation, however, shows larger discrepancies from the measured forces. This encourages for further measurements. In this study, we show that it is possible to measure force distribution on a model monopile in a simple and cost-effective manner. The aim is here to demonstrate the method and we will later present a larger body of work associated with the outcome of the measurements.
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Zhang, Hua, Jamal uddin Muhammad y Naif Mutlaq Alhajri. "Successful Managed Pressure Drilling Application in a Challenging Well With Crossflow in Unconventional Field". En Middle East Oil, Gas and Geosciences Show. SPE, 2023. http://dx.doi.org/10.2118/213441-ms.
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Abstract Unconventional tight gas well encountered unexpected losses at target depth and simultaneously well control took place from water source in upper zone. Bleed off tests concluded it was kick rather than ballooning. Combining upper flow and lower loss zones resulted in downhole crossflow and near zero mud window providing high operational risks to drill next 5-7/8 inch horizontal section. Managed Pressure Drilling (MPD) was utilized to drill horizontal section, mitigate well control risk and reach reservoir target. Prior to MPD selection, several attempts could not heal losses. The contigent 7 inch drilling liner was installed however it could not isolate the flow zone. MPD maintains constant bottom-hole pressure and enables full circulation. Under near zero mud weight (MW) window condition using same method of maintaining flow out equal to flow in would create high risk of well control as there is high possibility of influx moving up and diluting drilling fluid. It was necessary to maintain constant bottom-hole pressure during drilling and tripping by forcing influx to move down to lower fracture zone with acceptable rate of losses. During well construction with a fully automated MPD system, as a starting point MPD static pore pressure test (PPT) precisely detected pore pressure of water flow zone, establishing the low limit of the drilling window. During successful drilling of 3,027 feet in horizontal section, the influx was forced to move down to the lower loss zone with 5 to 20 barrels per hour dynamic losses. Real-time instantaneous annular pressure adjustment with MPD system minimized losses and managed well without interrupting drilling process even under condition of losses change to gain varying by only 25 psi surface back pressure (SBP). Benefits of multi stage displacement, detection and mitigation the swab and surge by stripping in and out also proved that MPD system made the process safer. Furthermore, in such well having no mud window, early detection of gain or losses tendency was imperative, so that the remedy actions could be applied immediately before things worsened with time. MPD system had the capability to detect gain/loss relatively early than the rig pit-volume system. Moreover, the target bottomhole pressure was adjusted almost instantly by adjusting the SBP by MPD system. The well would be considered un-drillable without MPD. MPD added safety factor during releasing stuck pipe operations where the low weight spotting fluids utilized. A fully automated MPD system provided a solution for specific risk condition such as near zero MW window and crossflow while drilling unconventional tight gas horizontal well. The precise and instant control of bottom hole pressure was the key factor of overall success. This paper summarizes the implementation of the fully automated MPD system as a sophisticated tool to precisely control such situations instantly, saving time, associated mud costs and hence optimize the overall drilling process.
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Gore, Daniel J. "Maritime Administration’s Formulation of a Maritime Energy and Clean Emissions Program". En ASME 2002 Internal Combustion Engine Division Spring Technical Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/ices2002-462.
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The Environmental Protection Agency promulgation of “Control of Emissions of Air Pollution from New Marine Compression Ignition Engines at or above 37 kW,” on December 29, 1999, marked the first time federal air pollution regulations were directly applied to marine engines for commercial U.S. ships. Perhaps surprisingly, these regulations are not having as much impact as are individual State Implementation Plans (SIP) for Nitrogen Oxides (NOx) attainment, and local political pressures. These regional plans and pressures are forcing many domestic marine operators and ports to get a quick education on the cause and mitigation of air pollution. Cases in point, include: • The State of Alaska now fines passenger vessels that enter ports with greater than allowable stack gas opacities. One cruise operator has opted to plug into shore power when its vessels are tied up to pier. • In the Ports of Los Angeles and Long Beach vessel operators have been asked to slow vessel speeds below normal while entering and exiting in a voluntary attempt to reduce NOx emissions. • Environmentalists in the San Francisco Bay Area are applying significant political pressures to ensure proposed new ferry systems emit a minimum of air pollution. • The State of Texas briefly considered stopping all industrial equipment in the Port of Houston for twelve hours per day as a method of decreasing area ozone formation. • Potential NOx emissions generated during imminent channel dredging in the Port of New York and New Jersey is impeding the development of the latest State Implementation Plan. Local pressures are likely to continue to grow, federal regulations are set to become more stringent, and international conventions loom on the horizon. However, as expected in such a competitive industry, concerns are often focused on the bottom line in which cost of operations is a pre-eminent factor. It was in view of these dynamics that the federal Maritime Administration (MARAD) recently launched the Maritime Energy and Clean Emissions Program. This paper introduces the Program, including the background, evolution, and progress of each strategic goal. This paper is intended to be an overview. Attention is paid to the potential transferability and/or development of technologies not previously deployed in the U.S. marine environment. Any of the specific projects described could become the basis for a separate technical paper.