A trade-off between maxima in efficiency and specific work output of super- and trans-critical CO2 Brayton cycles

Several operational aspects for thermal power plants in general are non-intuitive and involve simultaneous optimization of a number of operational parameters. In the case of solar operated power plants, it is even more difficult due to varying heat source temperatures induced by variability in insolation levels. This paper introduces a quantitative methodology for load regulation of a CO2 based Brayton cycle power plant using the `thermal efficiency and specific work output' coordinate system. The analysis shows that a transcritical CO2 cycle offers more flexibility under part load performance than the supercritical cycle in case of non-solar power plants. However, for concentrated solar power, where efficiency is important, supercritical CO2 cycle fares better than transcritical CO2 cycle. A number of empirical equations relating heat source temperature, high side pressure with efficiency and specific work output are proposed which could assist in generating control algorithms. (C) 2015 Elsevier B.V. All rights reserved.

Energy Harvesting WSNs for Accurately Estimating the Maximum Sensor Reading: Trade-Offs and Optimal Design

Computing the maximum of sensor readings arises in several environmental, health, and industrial monitoring applications of wireless sensor networks (WSNs). We characterize the several novel design trade-offs that arise when green energy harvesting (EH) WSNs, which promise perpetual lifetimes, are deployed for this purpose. The nodes harvest renewable energy from the environment for communicating their readings to a fusion node, which then periodically estimates the maximum. For a randomized transmission schedule in which a pre-specified number of randomly selected nodes transmit in a sensor data collection round, we analyze the mean absolute error (MAE), which is defined as the mean of the absolute difference between the maximum and that estimated by the fusion node in each round. We optimize the transmit power and the number of scheduled nodes to minimize the MAE, both when the nodes have channel state information (CSI) and when they do not. Our results highlight how the optimal system operation depends on the EH rate, availability and cost of acquiring CSI, quantization, and size of the scheduled subset. Our analysis applies to a general class of sensor reading and EH random processes.

The Trade-offs with Space Time Cube Representation of Spatiotemporal Patterns

Space time cube representation is an information visualization technique where spatiotemporal data points are mapped into a cube. Fast and correct analysis of such information is important in for instance geospatial and social visualization applications. Information visualization researchers have previously argued that space time cube representation is beneficial in revealing complex spatiotemporal patterns in a dataset to users. The argument is based on the fact that both time and spatial information are displayed simultaneously to users, an effect difficult to achieve in other representations. However, to our knowledge the actual usefulness of space time cube representation in conveying complex spatiotemporal patterns to users has not been empirically validated. To fill this gap we report on a between-subjects experiment comparing novice users error rates and response times when answering a set of questions using either space time cube or a baseline 2D representation. For some simple questions the error rates were lower when using the baseline representation. For complex questions where the participants needed an overall understanding of the spatiotemporal structure of the dataset, the space time cube representation resulted in on average twice as fast response times with no difference in error rates compared to the baseline. These results provide an empirical foundation for the hypothesis that space time cube representation benefits users when analyzing complex spatiotemporal patterns.

The role of the terms of trade in the trade channel of transmission of oil price shocks

This paper highlights the role of the terms of trade in the trade channel of propagation of oil price shocks both empirically and theoretically. Empirically, I show that oil price shocks have a large, persistent and statistically significant impact on the US terms of trade. Theoretically, I add oil in the model by Corsetti and Pesenti (2005) and analyse under what conditions the terms of trade plays a relevant role in the international transmission of oil price shocks. With nominal price rigidities and full exchange rate pass-through positive oil price shocks depreciate the currency of the oil importing country. The subsequent negative wealth effect adds to the recessive effect of the supply channel and may trongly reduce the consumption in the oil importing country economy. Without exchange rate pass-through oil shocks transmit to the economy only through the supply channel. The model suggests that a change in the exchange rate pass-through might contribute to explain the evidence of a weaker impact of oil price shocks on the macroeconomic activity in recent times.

Background paper on the international seafood trade and poverty

(121 p.)

FFA Fisheries Trade Briefing, Vol. 1, Issue 8 & 9, pp. 1-12, July-August 2008

Contents: Fisheries Subsidies. Status of fisheries subsidies talks at the WTO. Preferential Free Trade Agreements. Collapse of Doha Round results in rise of FTAs Update on EU Generalised System of Preferences regime Fisheries Trade-related Regulation. Soltai encounters quality problems. Update on Fiji seafood export ban to the EU. EU sanitary inspections in other developing countries Tuna Markets. Developments in the US debate on the mercury content of tuna. Other developments in the US market. Japanese tuna fisheries and seafood markets. Greenpeace tuna campaign moves to the UK. Thai Union predicts growth for 2008. (PDF contains 12 pages)

The African slave trade and its remedy

Esta edição é revista e aumentada, com mais do dobro de páginas da edição primitiva, de 1839, que continha 240 páginas. Buxton, presidente da Sociedade para a Extinção do Tráfico de Escravos, apresenta um detalhadíssimo estudo do comércio de negros, desde a África Central e ambas as costas do Continente, até o Brasil, os Estados Unidos, Cuba, etc. Há estimativas de mortalidade em todos os estágios do cativeiro. A maior parte das referências são sobre Cuba e o Brasil. É um clássico pioneiro dos estudos sobre escravidão.

Rights of Portugal, in reference to Great Britain and the question of the slave trade, or, the manifesto and protest of the weak, against the ingratitude, oppression, and violence of the strong ...

Enquanto os políticos e diplomatas polemizavam e agiam, Thomas Buxton publicava, depois de viajar ao Brasil e ao Caribe, o mais completo levantamento sobre o tráfico negreiro jamais feito até então.

International trade in live, ornamental "fish" in the US & Florida

The importance of international markets as a source of live, ornamental “fish” supply is growing due to more stringent wild-harvest regulations in Florida. In addition, foreign markets are increasing in importance as a source of demand for Florida purveyors of live, ornamental “fish”. Florida plays an important role in this growing international market. Trends in imports and exports of live, ornamental “fish” are described for two primary data sets: U.S. Customs and U.S. Fish and Wildlife Service. These trends are described primarily for the 1994-98 period for Florida and the United States. Florida imports and exports are described for the two major ports: Miami and Tampa. The most important trading countries are also described. This information will help Florida purveyors of live, ornamental “fish” better understand the international markets upon which they have become more dependent. (PDF has 18 pages)

Dealing with Energy-QoE Trade-Offs in Mobile Video

Scalable video coding allows an efficient provision of video services at different quality levels with different energy demands. According to the specific type of service and network scenario, end users and/or operators may decide to choose among different energy versus quality combinations. In order to deal with the resulting trade-off, in this paper we analyze the number of video layers that are worth to be received taking into account the energy constraints. A single-objective optimization is proposed based on dynamically selecting the number of layers, which is able to minimize the energy consumption with the constraint of a minimal quality threshold to be reached. However, this approach cannot reflect the fact that the same increment of energy consumption may result in different increments of visual quality. Thus, a multiobjective optimization is proposed and a utility function is defined in order to weight the energy consumption and the visual quality criteria. Finally, since the optimization solving mechanism is computationally expensive to be implemented in mobile devices, a heuristic algorithm is proposed. This way, significant energy consumption reduction will be achieved while keeping reasonable quality levels.