102,152 research outputs found
Benedetto Cacciatori (1794-1870)
No full textPersonalità d’artista ingiustamente trascurata dagli studi, lo scultore carrarese Benedetto Cacciatori (professore di Scultura dal 1842 al 1861 all’Accademia di Brera, a Milano) segna uno spartiacque tra l’Accademia classicista del primo Ottocento e il rinnovamento romantico e realista di tanti suoi contemporanei e allievi. Nelle sue opere più significative Cacciatori registra sensibilmente – o almeno segue con innegabile abilità e perizia esecutiva – quest’evoluzione. Il suo stile segue una linea che, senza prescindere dal formulario neoclassico, si sviluppa verso un compassato purismo, memore di un “decoro” che non si concede abbandoni né all’espressione, né alla sensualità del vero.
Questo primo studio monografico sull’artista fa luce sulla vita e sull’opera dello scultore nel suo complesso, attraverso un’accurata ricostruzione storica basata su una copiosa documentazione, in massima parte inedita, e sulla diretta indagine delle numerose, per lungo tempo neglette, realizzazioni scultoree identificate; soffermandosi sulla formazione del Cacciatori, sulla sua prima attività in Lombardia e su alcune delle sue imprese più cospicue, quali le realizzazioni per i Savoia e quelle per l’arco della Pace o per il duomo milanese.
Il lavoro di reperimento e di analisi delle opere del Cacciatori – reso possibile o favorito, in molti casi, dalla cortesia delle sovrintendenze, dei direttori e conservatori dei musei, dei parroci o dei privati proprietari – ha consentito di identificare e restituire all’artista alcune sculture inedite o generalmente attribuite ad altri (in particolare a Camillo Pacetti, suocero e maestro di Cacciatori), costituendo un primo contributo organico al catalogo dello scultore. Particolare cura è stata riservata all’apparato iconografico, che in molti casi illustra per la prima volta e mette a confronto tra loro realizzazioni, anche importanti, per le quali non esisteva alcuna adeguata documentazione a stampa. È il caso, in particolare, dell’ampia campagna fotografica relativa alla decorazione scultorea della chiesa abbaziale di Hautecombe, appositamente realizzata per questa edizione
Experimental quantum cosmology in time-dependent optical media
No full textIt is possible to construct artificial spacetime geometries for light by using intense laser pulses that modify the spatiotemporal properties of an optical medium. Here we theoretically investigate experimental possibilities for studying spacetime metrics of the form . By tailoring the laser pulse shape and medium properties, it is possible to create a refractive index variation that can be identified with . Starting from a perturbative solution to a generalized Hopfield model for the medium described by an , we provide estimates for the number of photons generated by the time-dependent spacetime. The simplest example is that of a uniformly varying that therefore describes the Robertson–Walker metric, i.e. a cosmological expansion. The number of photon pairs generated in experimentally feasible conditions appears to be extremely small. However, large photon production can be obtained by periodically modulating the medium and thus resorting to a resonant enhancement similar to that observed in the dynamical Casimir effect. Curiously, the spacetime metric in this case closely resembles that of a gravitational wave. Motivated by this analogy, we show that a periodic gravitational wave can indeed act as an amplifier for photons. The emission for an actual gravitational wave will be very weak but should be readily observable in the laboratory analogue
Hyperbolic geometry and amplituhedra in 1+2 dimensions
No full textRecently, the existence of an Amplituhedron for tree level amplitudes in the bi-adjoint scalar field theory has been proved by Arkani-Hamed et al. We argue that hyperbolic geometry constitutes a natural framework to address the study of positive geometries in moduli spaces of Riemann surfaces, and thus to try to extend this achievement beyond tree level. In this paper we begin an exploration of these ideas starting from the simplest example of hyperbolic geometry, the hyperbolic plane. The hyperboloid model naturally guides us to re-discover the moduli space Associahedron, and a new version of its kinematical avatar. As a by-product we obtain a solution to the scattering equations which can be interpreted as a special case of the two well known solutions in terms of spinor-helicity formalism. The construction is done in 1 + 2 dimensions and this makes harder to understand how to extract the amplitude from the dlog of the space time Associahedron. Nevertheless, we continue the investigation accommodating a loop momentum in the picture. By doing this we are led to another polytope called Halohedron, which was already known to mathematicians. We argue that the Halohedron fulfils many criteria that make it plausible to be understood as a 1-loop Amplituhedron for the cubic theory. Furthermore, the hyperboloid model again allows to understand that a kinematical version of the Halohedron exists and is related to the one living in moduli space by a simple generalisation of the tree level map
Odd characteristic classes in entire cyclic homology and equivariant loop space homology
No full textGiven a compact manifoldM and a smooth map g:M → U.(l×l:C) from M to the Lie group of unitary l×l matrices with entries in C, we construct a Chern character Ch-(g) which lives in the odd part of the equivariant (entire) cyclic Chen-normalized cyclic complex Nε(ωT(M × T)) of M, and which is mapped to the odd Bismut-Chern character under the equivariant Chen integral map. It is also shown that the assignment g → Ch-(g) induces a well-defined group homomorphism from the K-1 theory of M to the odd homology group of Nε(ωT(M × T))
Central sensitization and sensory symptoms spread in carpal tunnel syndrome: A response to Ginanneschi and Rossi's letter on the relationship between central plastic changes and sensory symptoms in peripheral entrapment neuropathies.
No full textno abstract availabl
The dynamic limits of specialization: Vertical integration reconsidered
No full textExisting studies, largely based in transaction cost economics, approach the issue of vertical scope as the decision of the individual firm about whether to make or buy, given the set of existing markets and well defined vertical segments. However, recent research has shown that the ability to make or buy should not be taken for granted. We argue that this applies not only to dis-integration, but also to re-integration, which often demands new 'all-in-one' markets. Drawing on the British building industry, we develop an inductive framework to explain why, after long periods of vertical specialization, industries shift to vertical reintegration. We observe that various groups, including professionals, play an active role in shaping the nature and the boundaries of the industry, facilitating the onset of vertical specialization, which, in turn, shapes a number of increasingly distinct knowledge bases in the industry, defining the trajectories along which capabilities evolve over time. As specialization in scope begets specialization in knowledge, difficulties in managing technical and organizational interdependencies arise, especially in the face of changing environmental conditions. The gap between what the vertically specialized system can produce, and what a changing environment demands, sets in motion a process of experimentation with integrated service provision, which is strengthened by broader social forces such as the deinstitutionalization of professions, or changes in demand structure. Reintegration is advanced by firms seeking to protect their position; enter new, related markets; or find new ways of leveraging their capabilities: Firms strategize to change their institutional environment, helping to create new all-in-one, integrated markets
Central sensitization in carpal tunnel syndrome with extraterritorial spread of sensory symptoms.
No full textExtraterritorial spread of sensory symptoms is frequent in carpal tunnel syndrome (CTS). Animal models suggest that this phenomenon may depend on central sensitization. We sought to obtain psychophysical evidence of sensitization in CTS with extraterritorial symptoms spread. We recruited 100 unilateral CTS patients. After selection to rule out concomitant upper-limb causes of pain, 48 patients were included. The hand symptoms distribution was graded with a diagram into median and extramedian pattern. Patients were asked on proximal pain. Quantitative sensory testing (QST) was performed in the territory of injured median nerve and in extramedian territories to document signs of sensitization (hyperalgesia, allodynia, wind-up). Extramedian pattern and proximal pain were found in 33.3% and 37.5% of patients, respectively. The QST profile associated with extramedian pattern includes: (1) thermal and mechanic hyperalgesia in the territory of the injured median nerve and in those of the uninjured ulnar and radial nerves and (2) enhanced wind-up. No signs of sensitization were found in patients with the median distribution and those with proximal symptoms. Different mechanisms may underlie hand extramedian and proximal spread of symptoms, respectively. Extramedian spread of symptoms in the hand may be secondary to spinal sensitization but peripheral and supraspinal mechanisms may contribute. Proximal spread may represent referred pain. Central sensitization may be secondary to abnormal activity in the median nerve afferents or the consequence of a predisposing trait. Our data may explain the persistence of sensory symptoms after median nerve surgical release and the presence of non-anatomical sensory patterns in neuropathic pain
Plane waves from double extended spacetimes
No full textWe study exact string backgrounds (WZW models) generated by nonsemisimple algebras which are obtained as double extensions of generic D-dimensional semisimple algebras. Even if a suitable change of coordinates always exists which reduces these backgrounds to be the product of the non-trivial background associated to the original algebra and two-dimensional Minkowski, under Inönü-Wigner contraction the algebra reduces to a Nappi-Witten algebra and the corresponding plane wave spacetime, no more factorized, is the Penrose limit of the original background. We construct the spectrum of D-branes for the double-extended background and study their behavior under the Penrose limit. While in general D-branes become singular in this limit, we prove that a class of solutions with a well-defined limit exists and it gives rise to the spectrum of configurations of the contracted model. Therefore, all D-branes of the plane wave background can be obtained as suitable contractions of original ones. We also discuss the Penrose limit at the quantum level and argue that the procedures of contraction and quantization commute
Noncommutative electrodynamics
No full textIn this paper we define a causal Lorentz covariant noncommutative (NC) classical Electrodynamics. We obtain an explicit realization of the NC theory by solving perturbatively the Seiberg-Witten map. The action is polynomial in the field strenght , allowing to preserve both causality and Lorentz covariance. The general structure of the Lagrangian is studied, to all orders in the perturbative expansion in the NC parameter . We show that monochromatic plane waves are solutions of the equations of motion to all orders. An iterative method has been developed to solve the equations of motion and has been applied to the study of the corrections to the superposition law and to the Coulomb law
Networked resource access and networked growth: a double network hypothesis on the innovative entrepreneurial firm
No full textEmpirical study on the relations betweek networked resource supply and networked growth of new technology based firm
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