479 research outputs found
Deforestation in the long-run: the case of Brazil
No full textln this article we study the long-run average rate of forest conversion in Brazil. Deforestation results from the following trade-off: on the one hand, the uncertain value of benefits associated with forest conservation (biodiversity, carbon sequestration and other ecosystem services), on the other hand, the economic profits associated with land development (agriculture, ranching, etc.). We adopt the model by Bulte et al. (2002) as theoretical frame for studying land conversion and then derive, following Di Corato et al. (2013), the associated long-run average rate of forest conversion. We then identify the parameters to be used in our model. The object
of our simulation is Brazil and 27 states. Our aim is to compute under several scenarios the time required to develop the remaining forested land in these states. We provide potential future scenarios, in terms of forest coverage, for the next 20, 100 and 200 years. Our results suggest that the uncertainty characterizing forest benefits plays a relevant role in deterring deforestation. We find that these benefits, if growing at a sufficiently high rate, may
significantly slow down the conversion process. ln contrast, a higher volatility accelerates the process of deforestation. We indicate the Brazilian states where forests are expected to be saturated earlier. ln this respect, we find that forestland currently available may be expected to be fully converted within a 200-year horizon
Reply to "comment on 'Locomotion of a microorganism in weakly viscoelastic liquids' "
No full textIn the present reply we show that the comments casting doubts on the results of our recent paper [M. De Corato et al., Phys. Rev. E 92, 053008 (2015)] are based on a misinterpretation of the second-order fluid constitutive equation. Nevertheless, we show that, by considering alternative constitutive equations for the viscoelastic stress, we recover, to first-order in the Deborah number, the same results already obtained by De Corato et al. [Phys. Rev. E 92, 053008 (2015)], thus dissipating any possible doubt about their validity
Proprietà ottiche e vibrazionali di nanostrutture grafeniche
No full textGli effetti dovuti al confinamento quantico sono usati sistematicamente nell’ambito della scienza dei materiali per rendere modificabili e dipendenti dalla dimensione le proprietà dei materiali bulk. Questa strategia può essere utilizzata anche nel caso del grafene: riducendone la dimensionalità si possono produrre sistemi 1D -nanoribbon (GNR)- e 0D -nanoflakes (GNF)-. A partire dalla loro sintesi, queste nanostrutture sono state oggetto di un ampio numero di studi, in quanto consentono di combinare le eccellenti proprietà meccaniche ed di trasporto elettronico del grafene con il comportamento semiconduttore indotto dal confinamento quantico; inoltre il gap di questi sistemi è facilmente modificabile [1]. Tra i diversi metodi di sintesi, gli approcci di tipo bottom-up hanno il vantaggio di produrre sistemi in cui si ha il controllo della crescita su scala atomica, un risultato fondamentale dato che le proprietà dei GNR sono fortemente dipendenti dai singoli dettagli della struttura atomica. Il metodo di crescita bottom-up può essere applicato sia su substrato [2] che in soluzione [3]: in quest’ultimo caso si ha il vantaggio di produrre sistemi che possono essere facilmente processati.
Il primo contributo originale di questo lavoro consiste in un insieme di conti ab-initio per il calcolo dello spettro Raman e di assorbimento IR per i GNR cresciuti in soluzione [4]. I risultati di questi conti sono stai confrontati con i dati sperimentali ottenuti nell’ambito di collaborazioni con diversi gruppi di ricerca. Dal confronto è emerso che il metodo dello zone-folding, che lega la frequenza del radial-like breathing mode con l’ampiezza di un GNR con bordi zig-zag o armchair, non può essere usato per queste strutture. In questo lavoro è stato proposto un nuovo modello in cui si tiene conto sia della morfologia del bordo che della funzionalizzazione.
La recente sintesi dei GNR in soluzione ha sollevato interessanti interrogativi in merito agli effetti dell’accoppiamento pi-pi sullo spettro di assorbimento UV-VIS. Per comprendere meglio quest’effetto, ho effettuato delle simulazioni dello spettro UV-VIS per sistemi macromolecolari composti da GNF allungati, basandomi su metodi semiempirici HF [5]. I sistemi accoppiati analizzati sono i seguenti: due GNF identici ma con diverso impilamento, due GNF di diversa ampiezza e due GNF con diversa funzionalizzazione. Dalle simulazioni si è visto come sia lo spettro di assorbimento UV-VIS che il carattere indiretto degli stati eccitonici possano essere modificati tramite un’opportuna scelta delle componenti del sistema macromolecolare.
Considerando il rinnovato interesse per le eterostrutture 2D [6], si sono analizzate le proprietà vibrazionali di superreticoli bidimensionali costituiti da porzioni periodiche di grafene e nitruro di boro esagonale. Questo tipo di superreticolo può essere ottenuto tramite un’interfaccia zig-zag o armchair: in questo lavoro sono stati analizzati entrambi i casi. Inoltre per il caso dell’armchair si e’ potuto simulare anche lo spettro Raman. Ad oggi i nostri risultati indicano cche gli stati d’interfaccia sono possibili solo per il sistema zig-zag.
[1] Dutta et al., J. Mater. Chem., 2010,20, 8207 and refs. therein
[2] Cai et al., Nature 466, 470 (2010)
[3] Narita et al., Nature Chemistry 6, 126; ACS Nano 8, 11622 (2014)
[4] I.Verzhbitskiy; M. De Corato; A. Ruini; E. Molinari; A.Narita; H.Yunbin; M.Schwab; M.Bruna; D.Yoon; S.Milana; X.Feng; K.Müllen; A.C Ferrari; C.Casiraghi; D.Prezzi; “Raman fingerprints of atomically precise graphene nanoribbon “ submitted to Nano Letters
[5] M.De Corato, C.Cocchi, D.Prezzi, M.J. Caldas, E.Molinari, and A.Ruini “Optical Properties of Bilayer Graphene Nanoflakes” JPCC 118, 23219 (2014)
[6] Liu et al., Nat. Nano 8, 119 (2013); Zaho et al. Sci. Rep, 5, 022015 (2015) and refs. thereinQuantization effects are widely used in materials science to properly modify the properties of a bulk material, making them also size-dependent and tuneable. This approach has received much attention also in the graphene-related research field, where graphene nanoribbons (GNR) or quantum dots are produced by cutting this 2D material into 1D nanostripes or 0D nanoflakes (GNF). Since their experimental realizations, these nanostructures have triggered a wealth of studies for their remarkable properties, which combine the unique electronic and mechanical features of graphene with the semiconducting behaviour induced by quantum confinement, and also in view of their easily tuneable band gap [1]. Among the different GNR synthesis techniques, the bottom-up approaches have the advantage to provide atomically precise systems, which is a crucial achievement due to the high sensitivity of their properties to the details of the atomic structure. The bottom-up growing methods can be performed either on substrate [2] or in solution [3]; the latter has the advantage to produce GNRs that can be easily processed.
The first original contribution of this thesis consists in a set of ab-initio calculations aimed to predict the Raman and infrared (IR) spectra of GNRs, as obtained through solution-mediated approaches [4]. The results allowed the interpretation of experimental data provided by different research groups. Our combined analysis showed that the well-known zone-folding method - that links the width of a purely zig-zag or armchair GNR with the frequency of the radial-like breathing mode - does not hold anymore for these nanostructures; therefore, we proposed here a more refined model to correctly take into account the specific edge morphology as well as the presence of edge-functionalizing alkyl chains. Furthermore, our investigation of the IR spectra allowed to fingerprint the position of the alkyl chains at the edges for the target systems.
The solution-mediated synthesis of GNRs raises also an interesting question about the impact of π-π coupling on the UV-VIS absorption spectrum. In order to get an insight on this point [5], I adopted Hartree-Fock-based semiempirical methods to predict the UV-VIS absorption spectrum of different macromolecular systems composed by different combinations of elongated GNFs; these include two identical GNFs stacked in different configurations, two GNFs with different widths and two identical GNFs with different edge functionalization. From these simulations, the UV-VIS absorption spectrum as well as the charge transfer character of excitonic states were demonstrated to be possibly engineered by properly choosing the nanostructures that compose the macromolecular system.
Finally, in view of the renewed interest for 2D heterostructures [6], the vibrational properties of two 2D superlattices composed by a periodic repetition of stripes of graphene and hexagonal boron nitride were investigated. Such superlattices can be obtained through either a zig-zag junction or an armchair one. Here, a lattice dynamics analysis was performed for both cases, and the Raman spectrum was calculated for the armchair case. Our results show that the interface modes are allowed only for the zig-zag junction.
[1] Dutta et al., J. Mater. Chem., 2010,20, 8207 and refs. therein
[2] Cai et al., Nature 466, 470 (2010)
[3] Narita et al., Nature Chemistry 6, 126; ACS Nano 8, 11622 (2014)
[4] I.Verzhbitskiy; M. De Corato; A. Ruini; E. Molinari; A.Narita; H.Yunbin; M.Schwab; M.Bruna; D.Yoon; S.Milana; X.Feng; K.Müllen; A.C Ferrari; C.Casiraghi; D.Prezzi; “Raman fingerprints of atomically precise graphene nanoribbon” submitted to Nano Letters
[5] M.De Corato, C.Cocchi, D.Prezzi, M.J. Caldas, E.Molinari, and A.Ruini “Optical Properties of Bilayer Graphene Nanoflakes” JPCC 118 (40), 23219-23225 (2014)
[6] Liu et al., Nat. Nano 8, 119 (2013); Zaho et al. Sci. Rep, 5, 022015 (2015) and refs. therei
An equilibrium model of habitat conservation under uncertainty and irreversibility
No full textIn this paper stochastic dynamic programming is used to investigate habitat conservation by a multitude of landholders under uncertainty about the value of environmental services and irreversible development. We study land conversion under competition on the market for agricultural products when voluntary and mandatory measures are combined by the Government to induce adequate participation in a conservation plan. We analytically determine the impact of uncertainty and optimal policy conversion dynamics and discuss different policy scenarios on the basis of the relative long-run expected rate of deforestation. Finally, some numerical simulations are provided to illustrate our findings
Land conversion pace under uncertainty and irreversibility: Too fast or too slow?
No full textIn this paper stochastic dynamic programming is used to investigate land conversion decisions taken by a multitude of landholders under uncertainty about the value of environmental services and irreversible development. We study land conversion under competition on the market for agricultural products when voluntary and mandatory measures are combined by the Government to induce adequate participation in a conservation plan. We study the impact of uncertainty on the optimal conversion policy and discuss conversion dynamics under different policy scenarios on the basis of the relative long-run expected rate of deforestation. Interestingly, we show that uncertainty, even if it induces conversion postponement in the short-run, increases the average rate of deforestation and reduces expected time for total conversion in the long run. Finally, we illustrate our findings through some numerical simulations
Long-run Investment under Uncertain Demand
No full textIn the literature investigating the impact of uncertainty on short-run and long-run investment, most authors have used a log linear profit function. This functional form has been generally considered a reasonable approximation for more general ones and has the advantage of providing closed form solutions for both short-run investment rule and long-run rate of capital accumulation. In this paper, we consider a firm facing a linear demand function with additive shocks and present a technique for the analytical approximation of the long-run average rate of capital accumulation for the case of an inverted U-shape profit function. We then compare the long-run rates of capital accumulation calculated under both assumptions within a plausible range of parameter values. We notice significant differences and conclude that the choice of a log linear functional form has a non-trivial impact on the magnitude of the long run rate of capital accumulation
Selling real assets: The impact of idiosyncratic project risk in an auction environment
No full textConsider a seller auctioning a real asset among n agents. Each agent contemplates a specific investment project and the asset is crucial for its activation. Project cash flows and their volatility are private information. A first-price auction is considered and the asset is granted in exchange for a payment to be paid at the investment time. Here we determine the optimal bid function and show that the auction is efficient. The asset is assigned to the project characterized by the highest volatility in the associated cash flows. Interestingly, the bid does not depend on the time at which the project is actually executed or on the changes in post-auction cash flows. We also address concerns about the distribution of the project value among the parties and show that i) the winner always holds the largest share of the ex-post project value when projects are characterized by sufficiently high cash flow volatility and ii) negative systematic risk reduces, ceteris paribus, the share accruing to the seller. Finally, we show that cash flow volatility has an ambiguous effect on losses due to the presence of information asymmetry
Passive farming and land development: a real option approach�
No full textWe examine the impact that subsidies paid to passive farmers have on the lease of land and on the speed of land development. First, we find that, even if delaying land development, paying passive farmers increases the value of the land. Second, when bargaining for the lease of land, we show that the agreement between the parties is conditional on an underlying development project passing a threshold level in terms of profitability. Third, we identify the conditions leading to a Pareto improvement. Last, we illustrate our findings by considering the establishment of an energy crop on leased land
Long-run Investment under Uncertain Demand. NOTE DI LAVORO DELLA FONDAZIONE ENI ENRICO MATTEI, vol. 2013.065, ISSN: 2037-1209
No full textIn the literature investigating the impact of uncertainty on short-run and long-run investment, most authors have used a log linear profit function. This functional form has been generally considered a reasonable approximation for more general ones and has the advantage of providing closed form solutions for both short-run investment rule and long-run rate of capital accumulation. In this paper, we consider a firm facing a linear demand function with additive shocks and present a technique for the analytical approximation of the long-run average rate of capital accumulation for the case of an inverted U-shape profit function. We then compare the long-run rates of capital accumulation calculated under both assumptions within a plausible range of parameter values. We notice significant differences and conclude that the choice of a log linear functional form has a non-trivial impact on the magnitude of the long run rate of capital accumulation
Deforestation and Government Conservation Policies
No full textIn this paper we investigate land conversion in the presence of voluntary and mandatory habitat conservation policies. Conversion decisions are taken under uncertainty about the value of environmental services by a multitude of landholders competing on the market for agricultural products. We show that land conversion can be delayed by compensating landholders providing environmental services and by limiting the individual extent of developable land. In contrast, we find that setting a ceiling on aggregate land conversion may lead to runs which rapidly exhaust the targeted amount of land. Finally, studying conversion dynamics under different policy scenarios, we show that uncertainty, even if inducing conversion postponement in the short-run, increases the average rate of deforestation and reduces the expected time for total conversion in the long run
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