1,721,006 research outputs found
Soil degradation, landscape and climate variations in a Mediterranean agro-forest system (Thriasio, Greece): proposal for a desertification indicator using time series analysis
No full textAs a contribution to soil degradation and desertification monitoring in the northern Mediterranean basin, the present study investigates long-term climate variations in the traditional agro-forest system of Thriasio Plain (Greece) by examining month average temperature, precipitation, relative humidity, Standardised Precipitation Index (SPI) and de Martonne index time series between 1958 and 2011. In the last twenty years, the area experienced an increased anthropogenic pressure due to urbanisation and industrialisation processes. Results indicate a moderate trend towards a warmer and drier climate with a slight increase in the range of the observed values for precipitation and temperature. Relative humidity decrease by 0.1% per year at both year and month base. Results point out the complexity of climate variations at the local scale and the importance of air humidity trends depending on rainfall and temperature regimes in the Mediterranean basin
Cities as selective land predators? A lesson on urban growth, deregulated planning and sprawl containment
No full textThe present study investigates changes in the use of land caused by the expansion of an informal city in the Mediterranean region (Athens, Greece) and it proposes a simplified methodology to assess selective land take at the scale of municipalities. The amount of land take over twenty years (1987-2007) for cropland, sparsely vegetated areas and natural land was compared with the surface area of the respective class at the beginning of the study period (1987). Indicators of selective land take by class were correlated with socioeconomic indicators at the scale of municipalities to verify the influence of the local context and the impact of urban planning on land take processes. Evidence indicates that urban expansion into fringe land consumes primarily cropland and sparse vegetation in the case of the Athens' metropolitan region. Cropland and sparse vegetation were consumed proportionally more than the respective availability in 16 municipalities out of 60. Agricultural land take was positively correlated with population density and growth rate, rate of participation to the job market and road density. Sparse vegetation land take was observed in municipalities with predominance of high density settlements. As a result of second-home expansion in coastal municipalities, natural land was converted to urban use in proportion to the availability in the landscape. Urban planning seems to have a limited impact on selective land tak
Feasibility Analysis of MCFC (Molten Carbonate Fuel Cell) – Anaerobic Digester Power Plant
No full textBesides traditional approaches for the valorization of biogas, the possibility of
using biogas to run Molten Carbonate Fuel Cells (MCFC) for the production of
combined heat and power (co-generation) is showing interesting results. The aim
of this study is to assess the benefits and draw-backs of this energy system and to
compare it with traditional biogas applications. Both technical and economical
analysis of a real case-study are carried out. The selected case-study is a pig
manure treatment plant located in Marsciano, near Perugia, Italy. The
performance of MCFC operating on biogas is assessed through experimental
activities carried out at the Fuel Cell Group laboratory of the University of
Perugia (Italy). Every test in which the MCFC has been run with biogas from an
anaerobic digester, showed a highly satisfactory operation of the fuel cell. The
economical analysis is based on the net present value (NPV) of an MCFC system and compared to an internal combustion engine system. Costs for the MCFC
system are assumed to be equal to 1500 €/kW, 2000€/kW and 3000€/kW and it
has been analyzed the difference between them. Different cases with or without
economic incentives and with or without co-generation have been studied. Green
certificates (i.e. governmental incentives due to the low emissions) are also taken
into account for NPV calculation
Thermal energy assessment of a small scale photovoltaic, hydrogen and geothermal stand-alone system for greenhouse heating
No full textThis experimental study shows the results of an analysis of the performance of a stand-alone renewable energy system for greenhouse heating on a winter day. The systems consist of photovoltaic panels connected to an electrolyzer which during daylight hours produce hydrogen by electrolysis and then store it in a pressure tank. During the night, thanks to a fuel cell, the hydrogen is converted into electricity in order to feed a ground source geothermal heat pump to heat a tunnel greenhouse. The procedure for estimating hourly solar radiation, hydrogen production and consumption for short-term energy storage on a partly cloudy day is also given. The solar energy usability concept, the capacity of energy storage systems and the thermal energy load govern the effective energy management of the system. This performance analysis is necessary to determine the actual total efficiency of integrated photovoltaic, geothermal and hydrogen renewable energy systems and their contribution to the load. The overall system efficiency obtained, starting from the amount of solar energy available during daylight hours until it is used as thermal energy at night, was 11%
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Photovoltaic and hydrogen plant integrated with a gas heat pump for greenhouse heating: A mathematical study
Full text linkNowadays, the traditional energy sources used for greenhouse heating are fossil fuels such as LPG, diesel and natural gas. The global energy demand will continue to grow and alternative technologies need to be developed in order to improve the sustainability of crop production in protected environments. Innovative solutions are represented by renewable energy plants such as photovoltaic, wind and geothermal integrated systems, however, these technologies need to be connected to the power grid in order to store the energy produced. On agricultural land, power grids are not widespread and stand-alone renewable energy systems should be investigated especially for greenhouse applications. The aim of this research is to analyze, by means of a mathematical model, the energy efficiency of a photovoltaic (8.2 kW), hydrogen (2.5 kW) and ground source gas heat pump (2.2 kW) integrated in a stand-alone system used for heating an experimental greenhouse tunnel (48 m2) during the winter season. A yearlong energy performance analysis was conducted for three different types of greenhouse cover materials, a single layer polyethylene film, an air inflated-double layer polyethylene film, and a double acrylic or polycarbonate. The results of one year showed that the integrated system had a total energy efficiency of 14.6%. Starting from the electric energy supplied by the photovoltaic array, the total efficiency of the hydrogen and ground source gas heat pump system was 112% if the coefficient of the performance of the heat pump is equal to 5. The heating system increased the greenhouse air temperatures by 3â 9â ¦C with respect to the external air temperatures, depending on the greenhouse cover material used
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Impact of the expander lubricant oil on the performance of the plate heat exchangers and the scroll expander in a micro-scale organic Rankine cycle system
No full textOrganic Rankine Cycles (ORCs) are recognized as suitable systems to convert the thermal energy from low-grade heat sources to electricity. However, their performance and reliability are subjected to several deficiencies especially at micro-to-small scales. In this work, the impact of the expander lubricant oil on the performance of the heat exchangers and the scroll expander of a non-regenerative, micro-scale ORC unit is investigated. In particular, the oil circulation rate (OCR) is theoretically assessed for each experimental data set based on the thermal balance between the hot and cold streams of the condenser. Then, the performance of the other components is assessed using the lubricant-R134a mixture properties, assuming the same OCR.
Results have shown that the presence of the lubricant oil leads to 5–15% capacity loss of the evaporator and the condenser of the studied ORC system. The calculated mass charge of the evaporator can also be underestimated up to 6.5% approximately if the oil is neglected. In addition, neglecting the lubricant oil may lead to over-estimation of the expander mechanical efficiency and under-estimation of its volumetric efficiency up to about 50% in very low shaft speeds. Hence, despite it is usually neglected in the literature, the results of the present analysis show that the impact of expander oil is relevant in micro-scale ORC systems
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