1,720,973 research outputs found
Analisi delle relazioni tra indici di stato idrico e firme spettrali in piante adulte di olivo (Olea europea L.)
No full textLa conoscenza dello stato idrico della vegetazione riveste un ruolo rilevante in svariate
applicazioni biofisiche riguardanti gli ecosistemi, naturali ed agrari, dove lo stress
idrico costituisce una delle più importanti limitazioni per la produzione primaria ed
agricola.
L’obiettivo della ricerca ha riguardato la valutazione dello stato idrico di piante di
olivo, a partire da misure di riflettanza nelle bande del visibile (VIS) e del vicino
infrarosso (NIR), eseguite sia a scala fogliare che di canopy. Si sono, pertanto,
analizzate le firme spettrali in riflettanza fogliare e di canopy di piante di olivo il cui
stato idrico è stato monitorato attraverso l’ausilio di indicatori ecofisiologici quali il
potenziale idrico xilematico. Le misure spettrali sono state condotte utilizzando uno
spettroradiometro da campo operante nell’intervallo spettrale 350-1050 nm. Per
l’analisi spettrale si è fatto riferimento sia a indici legati direttamente lo stato idrico
della foglia/canopy, quali il “Water Index” (WI) e l’Absorption Index (AI), che ad
indici indiretti come il “Normalized Difference Vegetation Index” (NDVI) e il “Red
Edge Position” (REP), che tengono conto della variazione di altri parametri
biochimici, quali la quantità e l’attività della clorofilla, nonché la variazione delle
caratteristiche morfo-anatomici della vegetazione
Uso di modelli agroidrologici per la gestione dell’irrigazione di colture arboree mediterranee
Full text linkNel presente lavoro viene presentato un confronto tra due modelli di bilancio idrologico: il modello proposto dalla
FAO e il modello SWAP, basato sulla soluzione dell’equazione di Richards. Il confronto ha riguardato i valori delle
componenti del bilancio idrologico ed i contenuti idrici del suolo relativamente alle due stagioni irrigue 2005 e 2006
su colture di Vite ed Olivo. È stata inoltre valutata la performance dei due modelli sulla programmazione
dell’irrigazione impostando i parametri di scheduling ordinari della zona
Agro-hydrological models to schedule irrigation of Mediterranean tree crops
No full textIn this paper a comparison between two agro-hydrological models, used to schedule irrigation of typical Mediterranean tree crops, is assessed. In particular the comparison between the model proposed by FAO, using a black box processes schematization, and the SWAP model based on the numerical analysis of Richards’ equation is initially presented for two irrigation seasons, 2005 and 2006, and two Mediterranean tree crops, i.e. grapevine (Vitis vinifera, L.) and olive oil (Olea europea, L.). The comparison mainly focuses on hydrological balance components and on soil
water contents.
After investigating and setting the scheduling parameters ordinarily practiced by the framers in the area (i.e ordinary management), the performance of the two models aimed to evaluate seasonal water requirement and irrigation time, is assessed.
In the validation phase both the models satisfactorily simulated the soil water content, allowing to obtain quite comparable values of evapotraspiration fluxes. On the other hand, when the models are used for scheduling irrigation, the FAO 56 model usually overestimates the irrigation amount, as a result of an overestimation of the transpiration fluxes. On the contrary the SWAP model simulates values of crops water requirements and a number of irrigation corresponding to those evaluated in the ordinary scheduling at the investigated area. Finally, in order to improve the FAO 56 model performance, a modification of the stress function is presented and discussed
Gestione dell'irrigazione del vigneto attraverso l'uso di modelli di simulazione e misure di campo
No full textViene valutata l’applicabilità di un modello numerico, SWAP (Soil Water Atmosphere Plant, van Dam et al., 1997) e di uno funzionale, FAO 56 (Allen et al., 1998), nella programmazione degli interventi irrigui a scala aziendale. Dopo la validazione, i due modelli sono stati utilizzati al fine di verificare la possibilità di simulare la gestione dell’irrigazione tipica dell’area di indagine, attraverso la determinazione del numero e della distribuzione degli adacquamenti, nonché stima dei consumi idrici totali nel corso del ciclo vegeto-produttivo della coltura. Entrambi i modelli simulano in modo soddisfacente l’andamento dei contenuti idrici medi del suolo, evidenziando errori di stima non superiori al 2,0%. Il modello SWAP ha consentito di simulare con buona approssimazione la gestione irrigua tipica della zona, permettendo di valutare sia l’inizio della stagione irrigua che i consumi idrici totali da parte della coltura. Nella sua formulazione originale, il modello FAO 56, invece, non si è dimostrato altrettanto affidabile. In vista di un successivo uso ai fini della gestione irrigua vengono suggerite delle modifiche utili a migliorare la performance del modello FAO. L’analisi delle performance ha evidenziato che, in annate caratterizzate da carenza di piogge, il numero di adacquamenti suggeriti da entrambi i modelli risulta comparabile
Assessing agro-hydrological models to schedule irrigation for crops of Mediterranean enviroment
Full text linkDespite in Mediterranean environment water resources for irrigation are limited, water management
for agriculture is often practiced ignoring principles of environmental sustainability.
Objective of the paper is to asses the possibility of using agro-hydrological models for irrigation scheduling, in
order to optimize the water use efficiency.
The results of a comparison between the numerical SWAP model and the functional model proposed by
FAO to estimate water requirements in two typical arboreal Mediterranean Crops (grapevine and olive) are
showed.
In the initial phase of the research, involving both irrigation seasons 2005 and 2006, after a preliminary
analysis of soil hydraulic and biophysical plant parameters, two intensive field measurements campaigns
were carried out to measure the soil water content at different depths, to proceed to the validation of both the
models.
Validation of the model was carried out by means of the comparison between measured and predicted soil
water content.
Finally different irrigation scheduling options were examined, in order to compare the scheduled irrigation
times with those planned by the farmers.
The results of investigations evidenced that FAO model simulates reliably the values of average water content
of the soil profile, even if a certain overestimation of evapotranspiration fluxes can be observed with the FAO
56 model compared with SWAP. Consequently, the FAO model anticipates the starting date for irrigation
obtained with SWAP, but, in terms of seasonal water requirements, the estimates determined by the two
modes did not result significantly different
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
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