1,720,963 research outputs found
a Thermoeconomic analysis and off-design performance of an organic Rankine cycle powered by medium-temperature heat sources
No full textThe model is based on zero-dimensional energy and mass balances for all the components of the system. It is also strictly related to the geometrical and design parameters of its components, especially in case of heat exchangers. The model evaluates the energetic and economic performance of the system, for different operating conditions and design criteria. In particular, the model allows one to set the geometrical parameters of heat exchanger and evaluate the off-design performance of the system. Hence, it could be an useful tool in the preliminary design of the plant. The n-butane has been used as working fluid according to results of the previous authors' work. Two types of simulations have been performed. The first simulation aims at selecting a design optimization criterion of some geometrical parameters of the shell and tube heat exchangers. The total cost of ORC plant has been selected as objective function. The parametrical analysis has been performed in steady-state regime. The second simulation evaluates the off-design performance of the ORC power plant. The thermal input of the cycle, i.e. diathermic oil coming from the heat source, has been varied in terms of mass flow rate and temperature to analyze the plant response to variations of boundary conditions starting from the design point. With respect to the total cost minimization, as objective function, the simulation results show that for all heat exchangers the higher the heat transfer area, the higher the net power generated and income. Instead, the evaporator shows different trends, hence it represents a key element in ORC design. The geometric optimization of heat exchangers allows the ORC to increase the economic benefit, the net power generated and the global efficiency of about 21.06%, 20.01% and 33.60% respectively. The results of the off-design analysis show that the heat source mass flow rate is a key parameter in net power generation. Fixed the heat source temperature on the upper bound of its variation range (185. °C), the net power generation shows both the maximum and minimum value, 335.4. kW and 269.3. kW, in correspondence of the lowest and the highest value of heat source mass flow rate respectively. Moreover, the results show that the plant efficiency decreases as both heat source mass flow rate and temperature increase. Its maximum value, 14.7%, is achieved for heat source temperature and mass flow rate equal to 155. °C and 18. kg/s, while its minimum value, 9.54%, is reached for heat source temperature and mass flow rate equal to 185. °C and 24. kg/
Design and parametric optimization of an organic rankine cycle powered by solar energy
No full textThis study presents the simulation and performance analysis of a regenerative and superheated Organic Rankine Cycle (ORC). To this scope, anew simulation model has been developed. The model is based on zero-dimensional energy and mass balances for all the components of the system. Shell and tube heat expanders with single shell and double tube pass have been chosen. Pump and expander have been considered only form a thermodynamic point of view, with constant compressor and expansion efficiency. The simulations havebeen carried out in order to find different optimization criteria to use as preliminary design tools,especially for the organic fluid choice and the heat exchanger design. Firstly, the ORC performances have been evaluated for different organic medium, varying the temperature of the heat source. The global efficiency of the plant, the net electric power generation and the volumetric expansion ratio has been considered as evaluation parameters. The simulation results show that two hydrocarbons demonstrate good performance for low, medium and high heat source, namely Isobutene, n-Butene; R245fa can add to them for the exploitation of heat source up to 170°C. Additional simulations have been carried out to discover an optimization criterion for the heat exchanger design. The plant performances have been first evaluated varying one by one the following parameters: tube length, tube number and shell diameter. Then a global optimization was also performed using the Golden Search technique. The total cost of the plant has been considered as objective functions. With respect to the objective function, higher the boiling heat transfer area higher the electric power generation and the economical benefit. The optimal configuration, compared to the initial one, shows an increase of incomes and mechanical power equal to 60.1 and 48.2% respectively, against a decrease of global efficiency equal to 10.9%
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Preliminare analisi strutturale ai loci ACACA e FASN nella bufala Mediterranea italiana.
No full textImportanti funzioni nella biosintesi degli acidi grassi a catena lunga nei mammiferi sono svolte dagli enzimi ACACA e FASN. Il gene ACACA codifica per l’enzima citosolico Acetil-Coenzima-A Carbossilasi che catalizza la carbossilazione ATP-dipendente dell'acetil-CoA in malonil-CoA. Il gene FASN codifica per l’enzima multifunzionale acido grasso sintasi che catalizza la reazione di sintesi NADPH-dipendente di acido palmitico da acetil-CoA e malonil-CoA. Tali geni sono stati già investigati in altre specie di interesse zootecnico, ma nessuna informazione è attualmente disponibile per la specie bufalina. Pertanto obiettivo del lavoro è stato una preliminare analisi strutturale dei geni ACACA e FASN ed una caratterizzazione della naturale variabilità genetica a tali loci.
Il DNA genomico è stato estratto da 17 campioni individuali di sangue di bufale proveniente da diversi allevamenti campani. Mediante PCR sono state amplificate e sequenziate l’esone 1, 7 e 8 per il gene ACACA e le regioni esone 6-esone 9 del gene FASN, usando primers disegnati sull’omologa sequenze bovina. Metodiche PCR-RFLP sono state sviluppate per gli SNP g.34T>C (esone 1) e g.557T>G (introne 8) rispettivamente per i geni ACACA e FASN.
Per il gene ACACA è stato sequenziato un frammento di 257bp del 1°esone e 923bp appartenenti alla regione esonica 7-8. L’analisi delle sequenze di 7 individui ha messo in evidenza 1 SNP al 34°nt del 1°esone. Si tratta di una transversione T>C, che non è responsabile di alcun cambiamento aminoacidico. Per il gene FASN è stato sequenziato un frammento di ~1400bp, includente gli esoni 6-9. Dal confronto delle sequenze sono emersi 7 SNP (5 intronici e 2 esonici). Entrambe le mutazioni esoniche sono responsabili di cambiamento aminoacidico. In particolare lo SNP al 14nt dell’esone 6 (AAC>CAC) cambia Asn>His, mentre lo SNP al 16nt nell’esone 7 ACT>TCT è responsabile del cambio Thr>Ser.
Sia per lo SNP trovato sul gene ACACA che per uno degli SNP messi in evidenza al locus FASN è stato possibile sviluppare un protocollo PCR-RFLP per una rapida ed economica genotipizzazione degli animali. In particolare per g.34T>C la digestione con MnlI (CCTCNNNNNNN!) ha prodotto nei campioni analizzati il seguente pattern elettroforetico: 106, 67, 43 e 41bp (omozigote T/T), il secondo contraddistinto da tre frammenti di restrizione di 147, 67 e 43bp (omozigote C/C) ed il terzo rappresentato da cinque bande: 147, 106, 67, 43 e 41bp (eterozigote T/C); mentre per lo SNP g.557T>G, il pattern di restrizione generato dall’endonucleasi TspEI (!AATT) è 1246bp (omozigote G/G), 1014 e 232bp (omozigote T/T); e 1246,1014 e 232bp (eterozigote T/G). Una genotipizzione condotta su un elevato numero di individui sottoposti a controlli funzionali sarebbe auspicabile al fine di poter utilizzare tali SNP in studi di associazione per il miglioramento delle caratteristiche quali-quantitative del grasso nel latte di bufala
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