Tra virtuosismo e truffa: l’arte del falsario

The history of artistic forgery boasts rather old origins and numerous facets. On this occasion, some emblematic cases between the Cinquecento and the present day (from the Sleeping Cupid of Michelangelo to the ‘Modiglianis’ that hit the headlines only some decades ago) will be taken into account, along with the activity of some great forgers who lived between the nineteenth and twentieth centuries. Gifted with notable technical ability and virtuosic stylistic “mobility”, some of these realized true masterpieces in meeting the requests of a growing market of Italian and foreign collectors. Above all others, one should mention the names of Egisto Rossi (1824-1899), falsifier of Old Masters’ drawings, and that of Icilio Federico Joni (nicknamed Paicap; 1866-1946), who specialized in counterfeiting fondo oro paintings by the Sienese School and was the leader of the city’s forgers

An evolutionary model with best response and imitative rules

We formulate an evolutionary oligopoly model where quantity setting players produce following either the static expectation best response or a performance-proportional imitation rule. The choice on how to behave is driven by an evolutionary selection mechanism according to which the rule that brought the highest performance attracts more followers. The model has a stationary state that represents a heterogeneous population where rational and imitative rules coexist and where players produce at the Cournot–Nash level. We find that the intensity of choice, a parameter representing the evolutionary propensity to switch to the most profitable rule, the cost of the best response implementation as well as the number of players have ambiguous roles in determining the stability property of the Cournot–Nash equilibrium. This marks important differences with most of the results from evolutionary models and oligopoly competitions. Such differences should be referred to the particular imitative behavior we consider in the present modeling setup. Moreover, the global analysis of the model reveals that the above-mentioned parameters introduce further elements of complexity, conditioning the convergence toward an inner attractor. In particular, even when the Cournot–Nash equilibrium loses its stability, outputs of players little differ from the Cournot–Nash level and most of the dynamics is due to wide variations of imitators’ relative fraction. This describes dynamic scenarios where shares of players produce more or less at the same level alternating their decision mechanisms

Global dynamic scenarios in a discrete-time model of renewable resource exploitation: a mathematical study

We consider the two-dimensional map introduced in Bischi et al. (J Differ Equ Appl 21(10):954–973, 2015) formulated as a model for a renewable resource exploitation process in an evolutionary setting. The global dynamic scenarios displayed by the model are not so often encountered in smooth two-dimensional dynamical systems. We explain the occurrence of such scenarios at the light of the theory of noninvertible maps. Moreover, complex structures of basins of attraction of coexisting invariant sets are observed. We analyze such structures by examining stability properties of chaotic sets, in the case in which a non-topological Milnor attractor is present. Stability changes of a chaotic set occur through global bifurcations (such as riddling and blowout) and are detected by means of the study of the spectrum of Lyapunov exponents associated with the set

La mano di Apelle. Sassoferrato e l'incisione: dalla copia alla divulgazione

Il saggio di A. Cerboni Baiardi compare in un volume miscellaneo che ha segnato una nuova prospettiva negli studi su Giovan Battista Salvi, detto Sassoferrato (1609-1685), pittore noto soprattutto per le tele, eseguite nel rispetto di un’altissima qualità, raffiguranti Madonne con o senza Bambino che gli valsero l’appellativo di Pictor Virginum. In questo contributo si indaga il tema dei rapporti tra Sassoferrato e l’incisione, affrontato da vari punti di vista. Il confronto tra le opere del Salvi con un buon numero di stampe derivate da altri maestri ha dimostrato come per questo artefice l’esercizio della copia andasse ben oltre ciò che si poteva fino ad oggi ritenere. Il ricorso alle incisioni come medium figurativo rispetto alle invenzioni di altri maestri precedenti ed anche coevi costituì infatti per Sassoferrato molto più di un atteggiamento occasionale, tanto da poter essere interpretato come un vero e proprio metodo di lavoro dal quale ogni tanto poter derogare. Il saggio ha inoltre evidenziato come la tardiva traduzione incisoria delle opere del Salvi, iniziata non prima della fine del XVIII secolo e perlopiù a scopo devozionale, vada posta in relazione con un’altrettanto tardiva fortuna critica rintracciabile, se si escludono gli accenni di Luigi Lanzi, solo nell’Ottocento

Evolutionary competition between boundedly rational behavioral rules in oligopoly games

In this paper, we propose an evolutionary model of oligopoly competition where agents can select between different behavioral rules to make decisions on productions. We formalize the model as a general class of evolutionary oligopoly games and then we consider an example with two specific rules, namely Local Monopolistic Approximation and Gradient dynamics. We provide several results on the global dynamic properties of the model, showing that in some cases the attractor of the system may belong to an invariant plane where only one behavioral rule is adopted (monomorphic state). The attractors on the invariant planes can be either strong attractors or weak attractors. However, we also explain why the system can be in a state of Evolutionary Stable Heterogeneity, where it is more profitable for the agents to employ both heuristics in the long term (polymorphic state)

Side effects of nonlinear profit taxes in an evolutionary market entry model: Abrupt changes, coexisting attractors and hysteresis problems

In order to demonstrate that nonlinear tax systems may have surprising and potentially undesirable side effects, we develop an evolutionary market entry model in which firms decide on the basis of past profit opportunities whether or not to enter a competitive market. Our main focus is on the case of a proportional tax on positive profits. Such a piecewise-linear tax scheme induces a kink in the firms’ profit functions, and may lead to abrupt changes in a market's dynamics, coexisting attractors and hysteresis problems. Since these phenomena can also be observed in more general models, a proper understanding of their basic mechanism may be helpful to explain the intricate behavior of many economic systems

GW170104: Observation of a 50-Solar-Mass Binary Black Hole Coalescence at Redshift 0.2

We describe the observation of GW170104, a gravitational-wave signal produced by the coalescence of a pair of stellar-mass black holes. The signal was measured on January 4, 2017 at 10: 11: 58.6 UTC by the twin advanced detectors of the Laser Interferometer Gravitational-Wave Observatory during their second observing run, with a network signal-to-noise ratio of 13 and a false alarm rate less than 1 in 70 000 years. The inferred component black hole masses are 31.2(-6.0)(+8.4)M-circle dot and 19.4(-5.9)(+5.3)M(circle dot) (at the 90% credible level). The black hole spins are best constrained through measurement of the effective inspiral spin parameter, a mass-weighted combination of the spin components perpendicular to the orbital plane, chi(eff) = -0.12(-0.30)(+0.21) . This result implies that spin configurations with both component spins positively aligned with the orbital angular momentum are disfavored. The source luminosity distance is 880(-390)(+450) Mpc corresponding to a redshift of z = 0.18(-0.07)(+0.08) . We constrain the magnitude of modifications to the gravitational-wave dispersion relation and perform null tests of general relativity. Assuming that gravitons are dispersed in vacuum like massive particles, we bound the graviton mass to m(g) <= 7.7 x 10(-23) eV/c(2). In all cases, we find that GW170104 is consistent with general relativity