Search results for "efficiency."
showing 10 items of 1362 documents
Impact de l'intervalle d'échantillonnage sur les tests d'efficience : application au marché français des actions
1994
Efficiency of financial markets is one of the most studied subject in theoretical finance. Formalization of this idea is realised by the random walk model. Numerous tests have been developped to validate the hypothesis of identically and independantly distributed innovations. But the results of empirical works are not unanimous ; the acceptation of the random walk is not systematic and depend too much on sample features. This constatation leads us to study the impact of the sample frequency on empirical results by distinguishing two different methodologies of tests : the first one is based on unit root (DICKEY et FULLER 1979, 1981) and the other one on variance ratio (LO et MACKINLAY 1988).…
Inverse Malthusianism and Recycling Economics: The Case of the Textile Industry
2020
The current use of natural resources in the textile industry leads us to introduce a new economic concept called inverse Malthusianism describing a context in which population grows linearly and resource consumption grows exponentially. Inverse Malthusianism implies an exponential increase in environmental impact that recycling may contribute to reduce. Our main goal is to extend the analysis of materials selection under the principle of equimarginality proposed by Jevons. As a first result, we show the particular circumstances under which policies excluding recycled supplies are never optimal. We also aim to overcome the difficulties of reducing environmental aspects to monetary units. To …
Theoretical analysis of the optimum energy band gap of semiconductors for fabrication of solar cells for applications in higher latitudes locations
2005
In this work some results of theoretical analysis on the selection of optimum band gap semiconductor absorbers for application in either single or multijunction (up to five junctions) solar cells are presented. For calculations days have been taken characterized by various insolation and ambient temperature conditions defined in the draft of the IEC 61836 standard (Performance testing and energy rating of terrestrial photovoltaic modules) as a proposal of representative set of typical outdoor conditions that may influence performance of photovoltaic devices. Besides various irradiance and ambient temperature ranges, these days additionally differ significantly regarding spectral distributio…
Participation Costs and Inefficiency in Takeover Contests
2010
We consider a takeover in which risk neutral bidders incur private costs to participate to the auction. Supposing that valuations for target firm are common knowledge, we study the optimal strategy of bidders and analyze the takeover result when they get or not toeholds in the target firm. We found that bidder's decision of participation is endogenous. By analyzing bidder's condition of participation, we found that the probability that the potential bidder with the highest valuation will not participate to the control, exists. We show that this probability increases with the size of toeholds possessed by the bidder with low valuation. Nevertheless, the size of toeholds possessed by the bidd…
Sustainable Social Housing in Temperate Areas. Italy and Brazil: the use of vegetation as a retrofit strategy
2014
La tesi si pone come obiettivo l’individuazione di strategie sostenibili per il retrofit del Social Housing in aree a clima temperato, con particolare riferimento all'utilizzo della vegetazione per la riqualificazione degli spazi esterni e per l'incremento delle prestazioni dell'involucro edilizio. La ricerca parte dall’assunto che le regioni del sud Italia e le aree subtropicali del Brasile, accomunati da caratteristiche climatiche affini, si trovano attualmente impegnati nell'identificazione di politiche e soluzioni per la riqualificazione di interi quartieri destinati all'housing sociale, responsabili di elevati consumi energetici e di inadeguate condizioni di comfort abitativo. In quest…
Comparative study of modelling the thermal efficiency of a novel straight through evacuated tube collector with MLR, SVR, BP and RBF methods
2021
Abstract Data-based methods are useful for accurate modelling of solar thermal systems. In this work, several artificial neural network (ANN) techniques are proposed to predict the thermal performance of an all-glass straight through evacuated tube solar collector. These are compared to support vector regression analysis. Extensive experimental data sets were collected for training the ANN models. Solar radiation intensity, ambient temperature, wind speed, mass flow rate and collector inlet temperature were selected as the input layer to predict the thermal efficiency of the solar collector. The prediction precision of the ANN models was compared to the multiple linear regression and suppor…
Investigation of flashing phenomena in MSF chambers
2007
The MSF process has covered in the last years more than 50% of world production of desalinated water from the sea. Although this process has been used for several decades, the large energy requirements force to search for new and feasible ways to improve the overall thermal efficiency. Few studies have bee carried out in lab-scale, pilot and industrial MSF units, underlining the complexity of flashing phenomena and the importance of operating parameters settings for optimal performance. In the present work a study on fundamental phenomena occurring inside MSF chambers has been carried out, focusing on the dependence of flashing efficiency on operating parameters and the effects of flashing …
ANALYSIS OF A RECIPROCATE ENGINE–BASED COGENERATION PLANT WITH HIGH TEMPERATURE HEAT RECOVERY FOR INDUSTRIAL USES
2012
In consequence of the increasing awareness on the future scarcity of fossil energy sources and the global warming impact of energy conversion processes, the European Union has been planning several actions to enhance the efficiency of energy use and reduce the environmental impact. The declared goals of EU actions are synthetized in the 20-20-20 formula, consisting of an expected 20% increase of energy efficiency, a 20% contribution to the total energy supply by renewable sources and a 20% abatement of pollutant emissions. Applications of cogeneration in process industry can significantly contribute to achieve these targets. In this paper a reciprocate engine-based Combined Heat and Power (…
An ultrathin suspended hydrophobic porous membrane for high-efficiency water desalination
2017
Abstract An ultrathin highly fluorinated porous membrane was designed for a large production of desalted water at very low energy consumption. Imprinting water droplets were used through a low thermally conductive tetra-fluoroethylene (TFE)/2,2,4-trifluoro-5-tri-fluorometoxy-1,3-dioxol (TIT) (HYFLON AD 60) solution and the generated porous nanofilm was suspended onto a polyethersulfone (PES) honeycomb texture. The very tiny fluorinated thickness together with a large number of small-shaped pores provided the membrane for enhanced anti-wetting surface properties, extremely reduced resistance to water vapor transfer and outstanding thermal efficiency. Fine materials structure-transport relati…
CFD simulation of a membrane distillation module channel
2009
The interest towards the use of membrane distillation (MD) processes for seawater desalination has been rising recently due to the ease of coupling MD with waste and/or solar thermal energy. Notwithstanding the flexibility of the process and its potential for further developments in membrane performances, one of the main drawbacks is the thermal efficiency reduction caused by temperature polarization. Because of such phenomenon, only a small amount of the driving force potentially available for the separation process, i.e. the temperature difference between evaporating and condensing fluids, is actually used for the separation. In order to reduce temperature polarization a study on the effe…