Synthesis of dihydropyridine and piperidine derivatives via an unexpected reaction of pyridine with acetyl chloride

Acetyl chloride reacts with pyridine to give a mixture of N-acetyl-1,4- and 1,2-dihydropyridyl acetic acid (1a,b) after water quenching. The reactioninvolves the formation of a zwitterionic ketene enolate intermediate which results from deprotonation of the acetyl moiety of the in situ formed N-acetyl pyridinium ion. The effect on the reaction outcome of different parameters as temperature, pyridine/acetyl chloride molar ratio, and as Lewis acids and triflate counterion presence has been studied in detail, and a reaction mechanism has been proposed

La scrittura politico-culturale: Callisto Cosulich tra televisione, critica e lotta alla censura

1L'opera di Callisto Cosulich, come risultato di una pratica costante: la scrittura come strumento privilegiato di divulgazione professionale e cinefiliaca dei contenuti, come luogo prediletto d’appassionata enunciazione politico-culturale, mezzo e fine di lotta intellettuale atti alla trasformazione, verso un miglioramento complessivo e istituzionale, attraverso la difesa e la divulgazione del bello e dell’etico nel proprio specifico estetico, quello critico e cinematografico. La sua scrittura come impegno radical, anche quando mestierante: mai organica, sempre militante, pur libera da specifiche militanze.nonemixedSpanu M.Spanu, Massimilian

The nature and strength of inter-layer binding in graphite

We computed the inter-layer bonding properties of graphite using an ab-initio many body theory. We carried out variational and diffusion quantum Monte Carlo calculations and found an equilibrium inter-layer binding energy in good agreement with most recent experiments. We also analyzed the behavior of the total energy as a function of interlayer separation at large distances comparing the results with the predictions of the random phase approximation.Comment: 5 pages; to appear in Phys. Rev. Let

Finite compressibility in the low-doping region of the two-dimensional t−Jt{-}J model

We revisit the important issue of charge fluctuations in the two-dimensional $t{-}J$ model by using an improved variational method based on a wave function that contains both the antiferromagnetic and the d-wave superconducting order parameters. In particular, we generalize the wave function introduced some time ago by J.P. Bouchaud, A. Georges, and C. Lhuillier [J. de Physique {\bf 49}, 553 (1988)] by considering also a {\it long-range} spin-spin Jastrow factor, in order to correctly reproduce the small-$q$ behavior of the spin fluctuations. We mainly focus our attention on the physically relevant region $J/t \sim 0.4$ and find that, contrary to previous variational ansatz, this state is stable against phase separation for small hole doping. Moreover, by performing projection Monte Carlo methods based on the so-called fixed-node approach, we obtain a clear evidence that the $t{-}J$ model does not phase separate for $J/t \lesssim 0.7$ and that the compressibility remains finite close to the antiferromagnetic insulating state.Comment: 10 page

Urban military geographies: New directions in the (re)production of space, militarism, and the urban

Armed forces in urban areas are a very visible source of socio-spatial and urban change. Even in contemporary cities ‘at peace’, this presence and ensuing changes can be wide-ranging, evident across infrastructure, organisations, narratives of place, events, and everyday activities. Although over the past 2 decades critical military studies and urban geopolitics have explored some of these themes, an urban studies perspective on such military geographies in peacetime has elicited far less attention. The aim of this article is to open up opportunities for deeper conceptualisation and research on urban military geographies. This article establishes a dialogue between critical military studies and urban geopolitics, to review the different dimensions of the influence of a military presence in urban space, and to provide a synthesis of these two bodies of literature. Using Lefebvre's dialectical theory of spatial production, this review shows how cities can be privileged spaces for the reproduction of militarism and preparation for war. Moreover, it examines how the presence of military forces in peacetime can influence the material and immaterial production of urban space

Theoretical constraints for the magnetic-dimer transition in two-dimensional spin models

From general arguments, that are valid for spin models with sufficiently short-range interactions, we derive strong constraints on the excitation spectrum across a continuous phase transition at zero temperature between a magnetic and a dimerized phase, that breaks the translational symmetry. From the different symmetries of the two phases, it is possible to predict, at the quantum critical point, a branch of gapless excitations, not described by standard semi-classical approaches. By using these arguments, supported by intensive numerical calculations, we obtain a rather convincing evidence in favor of a first-order transition from the ferromagnetic to the dimerized phase in the two-dimensional spin-half model with four-spin ring-exchange interaction, recently introduced by A.W. Sandvik et al. [Phys. Rev. Lett. 89, 247201 (2002)].Comment: 7 pages and 5 figure

Development of nanostructured supported photocatalysts for hydrogen production and inorganic pollutants removal

Semiconductor photocatalysis has emerged as one of the most promising approach to exploit a renewable energy source (i.e. sunlight irradiation) for several environmental purposes such as the production of clean energy (e.g. photocatalytic H2 evolution), the removal of organic and inorganic pollutants in natural water, purification of air and antibacterial activity. In view of these recent trends, the focus of this thesis was directed towards the study of different supported photo(electro)catalytic materials for topical environmental applications: i) Photocatalytic hydrogen gas evolution from aqueous solutions under UV light irradiation (365 nm) over highly ordered TiO2 nanotubes decorated through a sputtering/dewetting approach with a well-defined stacked co-catalyst (a WO3 layer decorated with Pt NPs); ii) Photocatalytic hydrogen gas evolution from aqueous solutions under UV light irradiation (365 nm) over highly ordered TiO2 nanotubes decorated through a sputtering/dewetting approach with dewetted-alloyed NiCu nanoparticles; iii) Photocatalytic reduction/scavenging of inorganic mercury (Hg(II)) from water under solar light irradiation over templated-dewetted Au on TiO2 nanotubes; iv) Photoelectrocatalytic oxidation/abatement of inorganic arsenic (As(III)) over hematite-based photoanodes under solar light irradiation. After a general introduction about photocatalytic processes and materials, each chapter of this dissertation contains the outcomes of the above listed studies

Ab initio investigation of the melting line of nitrogen at high pressure

Understanding the behavior of molecular systems under pressure is a fundamental problem in condensed matter physics. In the case of nitrogen, the determination of the phase diagram and in particular of the melting line, are largely open problems. Two independent experiments have reported the presence of a maximum in the nitrogen melting curve, below 90 GPa, however the position and the interpretation of the origin of such maximum differ. By means of ab initio molecular dynamics simulations based on density functional theory and thermodynamic integration techniques, we have determined the phase diagram of nitrogen in the range between 20 and 100 GPa. We find a maximum in the melting line, related to a transformation in the liquid, from molecular N_2 to polymeric nitrogen accompanied by an insulator-to-metal transition

Ab-initio calculations for the beta-tin diamond transition in Silicon: comparing theories with experiments

We investigate the pressure-induced metal-insulator transition from diamond to beta-tin in bulk Silicon, using quantum Monte Carlo (QMC) and density functional theory (DFT) approaches. We show that it is possible to efficiently describe many-body effects, using a variational wave function with an optimized Jastrow factor and a Slater determinant. Variational results are obtained with a small computational cost and are further improved by performing diffusion Monte Carlo calculations and an explicit optimization of molecular orbitals in the determinant. Finite temperature corrections and zero point motion effects are included by calculating phonon dispersions in both phases at the DFT level. Our results indicate that the theoretical QMC (DFT) transition pressure is significantly larger (smaller) than the accepted experimental value. We discuss the limitation of DFT approaches due to the choice of the exchange and correlation functionals and the difficulty to determine consistent pseudopotentials within the QMC framework, a limitation that may significantly affect the accuracy of the technique.Comment: 13 pages, 9 figures, submitted to the Physical Review B on October 2