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Modelling zero bids in contingent valuation surveys
Get PDFWhen modelling data generated from a discrete choice contingent valuation question, the treatment of zero bids affects the welfare estimates. Zero bids may come from respondents who are not interested in the provision of the public good; alternatively, some zero-bidders may be protesting about the valuation exercise, but hold positive values for the good. In this paper we investigate the effect of different levels of information on zero-bidders on welfare estimates for the population. We find that different strategies of identification may have non-trivial effects. We recommend use of full debriefing questions for zero-bidders, and use of sample selection models to correct for bias caused by protest behaviou
L'erbario del Prof. Manlio Chiappini (1924-1998) in Herbarium CAG
Get PDFThe herbarium of Chiappini, held in Herbarium CAG of Cagliari University, is presented. Prof. Manlio Chiappini, who dead the 4th of january 1998, teached Botany at the Athenaeum of Cagliari from 1965 to 1987 and from 1965 to 1986 he was director of Botanical Institute and Botanical gardens of Cagliari University. From a research carried out in Herbarium CAG is shown that Chiappini’s herbarium is compound of 1262 exsiccata, referred to 630 specific and subspecific entities (about the 30% of Sardinian flora), of which 45 referred to endemic species (about the 20% of Sardinian flora) and that the Museum Herbarium CAG itself is depositary of a number of 4 species pointed out, by the Author himself, for the first time to Sardinia
Modificazioni e strategie competitive osservate nella flora dell’isola Rossa di Teulada (Sardegna sud occidentale)
Get PDFThe authors report on the results of their survey on the Isola Rossa near Teulada (South-western Sardinia). The flora found on the island, which consisted of 206
entities, grouped in 59 families and distributed in 157 genera, differs notably from the flora surveyed 50 years ago. In particular, 81 new species have been found, while 44
species listed in the earlier survey have not been confirmed. Comparison of typically mediterranean biological spectra showed an increase in terophytes and a sharp
decrease in hemicriptophytes. The application of Grime’s triangular system to this survey and the earlier one showed that floral changes are characterised by a decrease
in stress-resistant species and an increase in ruderal species. The vegetation cover has also undergone major changes. The colonising capacity of Brassica insularis is
particularly interesting in this regard: this plant, which was previously found only on the northern side of the island, is now scattered throughout the island. All these changes have also been confirmed by the turnover ratio, which is in excess of 60%, and highlights the occurrence of deep environmental changes
Titolazioni chelometriche con EDTA: considerazioni sul grafico di Reilley
Get PDFTheory and procedure on which Reilley curve is based are discussed; it defines the minimum pH for an effective metal titration with EDTA. This curve, widely reported in Analytical Chemistry textbooks, was originally presented in an implicit way by Reilley, who assumed a 106 conditional constant for 0.01 M metal concentration. We report here the conditional constants necessary for 99, 99.9 and 99.99 complex formation percentage at various analytical concentration. An updated Reilley plot is furthermore presented, which takes into consideration all formation constants at 20°C reported till 1998 for EDTA complexes
L' esplorazione floristica nel Sulcis (Sardegna sud-occidentale)
Get PDFHere is show the account of floristic exploration in the Sulcis area. This study is based on existing bibliography and has been done through herbarium researches in the main national and international centres. The investigations allowed to take a census of all the works carried out in the Sulcis area, to verify the authors and the explored
environment as well as the exsiccata stored in the various herbarium. From the analysis emerges that the coastal and the lagoon areas have been deeply studied since the second
half of the XVIth century, the hill and the foot of the mountain areas since after the second world war, while the mountain areas and the rivers are nowadays still less
known and sometimes totally unexplored. Is finally put in evidence which areas have a greater need to be researched both from floristic and vegetational point of view
La performance di modelli non lineari per i tassi di cambio: un'applicazione con dati a diversa frequenza
Get PDFIn recent years there has been a considerable development in modelling nonlinearities and asymmetries in economic and financial variables. The aim of this work is to compare the forecasting performance of different models for the returns of some of the most traded exchange rates in terms of the US dollar, namely the French Franc (FF/) and the Japanese Yen (Y/$). We compare the relative performance of some nonlinear models and contrast them with their linear counterparts. Although we find evidence of some forecasting gains from nonlinear models, the results are sensitive to the forecast horizon and to the metric adopted to measure the forecasting accuracy. The use of data at different frequencies allows us to evaluate the possible effects of temporal aggregation
Saperi locali, innovazione tecnologica e sviluppo economico: indagine su un campione di imprese sarde
Get PDFL'analisi empirica dello sviluppo locale ha fornito un notevole contributo alla comprensione dei meccanismi sottostanti alle dinamiche dei sistemi economici locali. L'oggetto di tale analisi sono stati prevalentemente sistemi locali di successo come i distretti industriali. Minore attenzione hanno invece ricevuto le aree in cui, nonostante la presenza diffusa di un know how ricco e sofisticato, non si è ancora innescato alcun meccanismo di sviluppo endogeno. Il lavoro analizza il caso di un campione di imprese sarde appartenenti a settori fortemente radicati nei saperi tradizionali, esaminando in particolare il comportamento innovativo e le sue determinanti. La limitata crescita delle imprese è attribuita ad alcune caratteristiche peculiari di queste produzioni che agiscono come fattori inibenti dell'innovazione e dell'ampliamento dei mercati. In particolare la scelta di perseguire una strategia di nicchia sul mercato locale è incentivata dal vantaggio competitivo di cui queste imprese godono sul mercato locale, grazie alla capacità di soddisfare specifiche esigenze dei consumatori locali. Inoltre la scarsa propensione a innovare è influenzata dal fatto che in questi settori non sempre l'innovazione accresce la competitività dell'impresa
Contributo alla conoscenza della brioflora del Sulcis (Sardegna sud-occidentale)
Get PDFA first contribution to the knowledge of the bryological flora of Sulcis is presented. The total number of species amounts to 216 entities belonging to classes of Musci(186), Hepaticae (29) and Anthocerotae (1); finding of 30 new species to Sulcis is reported. A chorological analysis is also done
Modificazioni dei livelli di acido arachidonico e vitamina A in relazione alla attività anticancerogena attribuita all'apporto alimentare di burro naturalmente arricchito in acido linoleico a dieni coniugati (CLA)
Get PDFConsiderable attention has recently been directed to the naturally occurring trace fatty acid conjugated linoleic acid (CLA), based on its dual ability to act both as a preventive and therapeutic agent in a number of rodent and human tumor model systems. CLA, which is synthesized by rumen bacteria, is found in meat and dairy products, and is of particular interest since it is effective at low levels in the diet. Our research interest is to explore whether the mechanism of the anticarcinogenic activity of CLA may be reconductible to its metabolism and influence on tissue lipid metabolism. CLA is a polyunsaturated fatty acid (PUFA) with two singular properties: 1) Its metabolism is alike that of linoleic acid and thus competes with the latter for the elongation and desaturation enzyme systems, leading on one hand to a decreased generation of eicosatrienoic and arachidonic acids for eicosanoid synthesis, and on the other to a replacement of the natural substrates with CLA metabolites known to inhibit the cyclooxigenase (COX) and lipooxygenase (LPOX) pathways; and 2) It increases the retinol content of different tissues, an effect that may be due to β-oxidation of CLA by peroxisomes with consequent activation of peroxisome proliferator activated receptor a (PPARα). The effects of CLA on eicosanoid synthesis may be the key factor of a
common mechanism underlying its pleiotropic activities, and our current working hypothesis is that this factor along with tissue retinol increase, mediate the anticarcinogenic
action of CLA
Nuova teoria della crescita e sviluppo locale: alcune possibili connessioni
Get PDFA differenza del modello di crescita neoclassico, piuttosto avaro di indicazioni utili sui problemi dello sviluppo locale, la nuova teoria della crescita appare più ricca di suggerimenti di policy. I più interessanti riguardano la composizione dell’output, e il mix ottimale fra la ricerca per l’introduzione di nuove tecnologie e l’apprendimento sulle tecnologie esistenti. Per quanto riguarda la composizione dell’output i modelli di crescita endogena pongono in evidenza il rischio che l’economia locale possa rimanere intrappolata in un equilibrio a bassa crescita nel caso accetti una specializzazione su beni low-tec e l’opportunità di forzare la logica dei vantaggi comparati con politiche di sostegno all’innovazione. Peraltro un’eccessiva enfasi sull’introduzione di nuove tecnologie a scapito dell’apprendimento nei settori produttivi locali priva la ricerca dell’apporto dell’esperienza e tende a inaridirla accrescendo i costi di introduzione e di adozione di nuove tecnologie. Allo stesso modo l’apprendimento in assenza di ricerca è soggetto a rendimenti decrescenti e può dare luogo a una trappola delle competenze in cui l’abbandono delle tecnologie tradizionali e l’innovazione divengono troppo costose