1,721,018 research outputs found
Modeling for Effective Crop Disease Control: A Case Study for Banana Xanthomonas Wilt in Africa
No full textA fungal disease, (banana) Xanthomonas wilt (XW) is spreading from Eastern Africa to the rest of the continent, endangering the principal source of food and income for a hundred million people. The only measures that are currently known to be effective are cultural practices on the farm-level, and timely and sustained interventions on the policy-level. Potential consequences of alternative scenarios of using these measures on the continental scale have not yet been quantified. This study applies a novel integrated modeling framework that links application of the cultural practices and policy measures to the dynamics of XW spread, and the subsequent consequences for the agricultural sector and food security. The modeling framework links a mathematical model of XW spread at field level, with a global assessment of food-system consequences using a partial equilibrium model. The results show that over the 10-year frame, with no intervention, African XW prevalence could increase by 89%
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Integrating risk and uncertainty in PMP models
Get PDFPositive Mathematical Programming (PMP) is one of the most commonly used methods
of calibrating activity linear programming (LP) models in agriculture. PMP applications
published thus far focus on the estimation of a farm’s nonlinear cost or profit function
and rely on the recovery of unobserved or implicit information that can explain the initial
model’s inability to calibrate. In this paper we use the PMP procedure to calibrate
an expected utility model under the assumption that this implicit information can reveal a
farmer’s profit expectations and risk attitude. The perfect calibration shows that PMP can
be applied not only to LP models, but also to models that incorporate risk and this provides
an interesting alternative to the traditional PMP methodology
Calibration of agricultural risk programming models
No full textPositive Mathematical Programming (PMP) is one of the most commonly used methods for calibrating activity programming models. In this article we consider PMP as a calibration method for risk programming models with a mean-variance (E-V) specification. We argue that the restrictive theoretical assumptions employed by typical linear E-V models limit their applicability in analyzing the effects of decoupled payments on agricultural production decisions. Furthermore, the requirement for eliciting a risk aversion coefficient renders such models incompatible with the PMP method. For this reason we propose a nonlinear E-V specification and develop a PMP-based procedure for its calibration which does not aim at introducing (further) nonlinearities in the objective function, but at recovering the "true" distribution of wealth that will allow the final model to reproduce base year observations. We also examine how our approach relates to the recent PMP developments on calibration against elasticity priors and we show how such priors can be used for the calibration of the nonlinear E-V model
Integrating agrobiodiversity into foresight models
No full textPresentation in the CGIAR Webinar: “Advancing Agrobiodiversity: Metrics, Innovations, and Perspectives for Sustainable Agri-Food Systems
Models and muddles: comment on ‘Calibration of agricultural risk programming models using positive mathematical programming’
Get PDFThere is an emerging strand in the agricultural economics literature which examines the calibration of risk programming models using the principles of Positive Mathematical Programming (PMP). In a recent contribution to this journal, Liu et al. (2020) compare three different PMP approaches and attempt to find the ‘most practical’ method for calibrating risk programming models to be used in policy analysis. In this article, we argue that the comparison design by Liu et al. (2020) is problematic, as it is based on inappropriate metrics and it ignores recent advancements in PMP. This word of caution intends to provide constructive criticism and aims at contributing to the use of risk programming models in policy analysis
A bio-economic approach to building farm activity programming models: an application of policy analysis in the sector of arable crops
No full textThe specificities of the agricultural sector and the relational complexity between economic,bio-physical and environmental factors that define agricultural production havelead to the development of a type of economic models, called bio-economic models. Thegoal of this dissertation is to present an integrated framework of bio-economic analysisat the farm level which can be used for the assessment of different policy options in theagricultural sector. The methodology developed in this dissertation is based on thecoupling of a Positive Mathematical Programming (PMP) model with empirical yieldwaterresponse functions which are estimated from an ad hoc bio-physical model thatruns for different soil and climatic conditions and irrigation water availability. Morespecifically, an alternative specification of PMP models is presented so that the riskwhich farmers face, because of the variability of crop yields and prices, is explicitlyconsidered. The proposed bio-economic approach is implemented in a case study basedon a sample of ex-tobacco producing farms from the region of Karditsa, in order to testthe validity and analytical capacity of the model, as well as to examine the degree ofsynergy or contradiction between the Water Framework Directive (WFD) and the latestreforms of the Common Agricultural Policy (CAP), with respect to water saving underdifferent water pricing scenarios. Results indicate that the CAP may contradict the goalsof the WFD concerning sustainable water use when water prices are below 0.04€/m3.Furthermore, coupled payments for cotton produce a distorted price signal that favorsthe expansion of the land allocated to the crop. Finally, flatter (lower) decoupledpayments have no significant effect on water saving, yet they result in lower economicefficiency because the reduction of the non stochastic part of farmer’s income willeventually lead them to production choices that reduce downside risk.Οι ιδιαιτερότητες του γεωργικού τομέα και η πολυπλοκότητα των σχέσεων μεταξύ τωνοικονομικών, βιο-φυσικών και περιβαλλοντικών συνιστωσών της γεωργικής δραστηρι-ότητας, έχουν οδηγήσει στην ανάπτυξη μιας κατηγορίας οικονομικών υποδειγμάτωνπου ονομάζονται βιο-οικονομικά. Στόχος της παρούσας διατριβής είναι η παρουσίασημιας ολοκληρωμένης προσέγγισης βιο-οικονομικής ανάλυσης σε επίπεδο εκμετάλλευ-σης για αναλύσεις πολιτικής στο γεωργικό τομέα. Η προτεινόμενη προσέγγιση στηρίζε-ται στη χρήση ενός υποδείγματος Θετικού Μαθηματικού Προγραμματισμού (ΘΜΠ), σεσυνδυασμό με συναρτήσεις απόδοσης-νερού που προκύπτουν από τα αποτελέσματαενός ad hoc βιο-φυσικού υποδείγματος για διαφορετικές εδαφοκλιματικές συνθήκεςκαι ποσότητες νερού άρδευσης. Ειδικότερα, παρουσιάζεται μια νέα μορφή ΘΜΠ πουστηρίζεται στη θεωρία της προσδοκώμενης χρησιμότητας και συνεπώς λαμβάνεταιρητά υπόψη ο οικονομικός κίνδυνος που αντιμετωπίζει ο παραγωγός εξαιτίας των δια-κυμάνσεων των αποδόσεων και των τιμών των προϊόντων. Η προτεινόμενη βιο-οικο-νομική μέθοδος εφαρμόστηκε στην περιοχή της Καρδίτσας σε δείγμα καπνοπαραγωγι-κών εκμεταλλεύσεων, προκειμένου, αφενός να διαπιστωθεί η αξιοπιστία και ηπροβλεπτική ικανότητα του υποδείγματος και αφετέρου να αναλυθεί ο βαθμός της συ-νέργειας/συμπληρωματικότητας, ή αντίθεσης μεταξύ των συνεχών μεταρρυθμίσεωντης Κοινής Αγροτικής Πολιτικής (ΚΑΠ) και της Οδηγίας Πλαίσιο για το Νερό (ΟΠΝ) σεσχέση με την εξοικονόμηση νερού άρδευσης σε διάφορα πιθανά σενάρια τιμολόγησηςνερού. Τα αποτελέσματα της ανάλυσης δείχνουν πως η ΚΑΠ πιθανώς να αποτελέσειτροχοπέδη στους στόχους της ΟΠΝ για ορθολογικότερη διαχείριση των υδάτων, αν ητιμή του νερού άρδευσης περιοριστεί σε επίπεδα μικρότερα των 0.04€/m3. Επίσης, οισυνδεδεμένες ενισχύσεις του βαμβακιού προκαλούν σημαντική στρέβλωση του «σήμα-τος των τιμών» που λαμβάνουν οι παραγωγοί, με αποτέλεσμα να ευνοείται η εξάπλωσητης καλλιέργειας εις βάρος των υπολοίπων αρδευομένων καλλιεργειών. Τέλος, η περι-φερειοποίηση δεν οδηγεί σε εξοικονόμηση νερού άρδευσης, ενώ εμφανίζει μειωμένηοικονομική αποδοτικότητα λόγω της απώλειας ενός σταθερού και βέβαιου εισοδήμα-τος, γεγονός που πιθανώς να οδηγήσει τους παραγωγούς σε καλλιεργητικές επιλογέςπου μειώνουν την έκθεση τους στον οικονομικό κίνδυνο
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