Narrare la malattia. Un modello gnoseologico a partire dalle «Confessioni di un italiano»

Gli argomenti riferiti al mondo della medicina nel capolavoro di Nievo sono parti di un modello gnoseologico sviluppato nel romanzo. Negli aspetti narratologici che coinvolgono i personaggi e le sequenze si individuano riflessioni di argomento etico sulle dinamiche che reggono la società. Negli aspetti descrittivi ed in quelli riferiti alle componenti retoriche, semantiche e morfosintattiche, si rivelano interazioni di tipo costruttivista a cui corrisponde la descrizione di alcune patologie in cui si tratteggiano interazioni che anticipano le dinamiche dei neurotrasmettitori.The medical elements in Nievo’s masterpiece are the bricks of a gnoseological model. On the narrative level the character are mdium of some sequence to build the ethical reflection about society. On the level of semantic argouments – that through characters – there are some descriptions of sickness where it form a metaphore as the same as the dynamics of cells, neurons and glial cells, some times before the medical discveries of expert

Application of homogeneously precipitated nanosized Fe-doped alumina powders to carbon nanotube growth.

Homogeneous precipitation of hydroxides was investigated as an alternative method to synthesize Fe-doped aluminum oxide (α-Al2−2xFe2xO3) particles over which carbon nanotubes (CNTs) were grown via a catalytic chemical vapor deposition (CCVD) method. Performance of the homogeneously precipitated particles for CNT growth was quantitatively compared with that of the combustion-synthesized particles. The main advantage of the homogeneous precipitation of hydroxides and subsequent calcination process against to the combustion synthesis and other commonly practiced chemical routes is the ability to tailor the Fe-doped Al2O3 precursor powder characteristics such as size and specific surface area (SSA) without requiring any milling step and also to control the phase composition of the oxide powder with high Fe content, and subsequently the quality and quantity of CNTs during CCVD process. The particle size of the precipitated and calcined α-Al2−2xFe2xO3 powders varies between ∼50 and 400 nm for 5–10 cat.% Fe-containing systems. The monodispersed particle size distribution and optimum phase composition of the homogeneously precipitated powders, particularly for a 10 cat.% Fe content in the starting oxide, and their much higher SSA than similar materials prepared by other chemical routes lead to production of high amounts of good quality CNTs

Fermionic current densities induced by magnetic flux in a conical space with a circular boundary

We investigate the vacuum expectation value of the fermionic current induced by a magnetic flux in a (2+1)-dimensional conical spacetime in the presence of a circular boundary. On the boundary the fermionic field obeys MIT bag boundary condition. For irregular modes, a special case of boundary conditions at the cone apex is considered, when the MIT bag boundary condition is imposed at a finite radius, which is then taken to zero. We observe that the vacuum expectation values for both charge density and azimuthal current are periodic functions of the magnetic flux with the period equal to the flux quantum whereas the expectation value of the radial component vanishes. For both exterior and interior regions, the expectation values of the current are decomposed into boundary-free and boundary-induced parts. For a massless field the boundary-free part in the vacuum expectation value of the charge density vanishes, whereas the presence of the boundary induces nonzero charge density. Two integral representations are given for the boundary-free part in the case of a massive fermionic field for arbitrary values of the opening angle of the cone and magnetic flux. The behavior of the induced fermionic current is investigated in various asymptotic regions of the parameters. At distances from the boundary larger than the Compton wavelength of the fermion particle, the vacuum expectation values decay exponentially with the decay rate depending on the opening angle of the cone. We make a comparison with the results already known from the literature for some particular cases.Comment: 34 pages, 6 figure

Fundamental optical processes in armchair carbon nanotubes

Single-wall carbon nanotubes provide ideal model one-dimensional (1-D) condensed matter systems in which to address fundamental questions in many-body physics, while, at the same time, they are leading candidates for building blocks in nanoscale optoelectronic circuits. Much attention has been recently paid to their optical properties, arising from 1-D excitons and phonons, which have been revealed via photoluminescence, Raman scattering, and ultrafast optical spectroscopy of semiconducting carbon nanotubes. On the other hand, dynamical properties of metallic nanotubes have been poorly explored, although they are expected to provide a novel setting for the study of electronﾖhole pairs in the presence of degenerate 1-D electrons. In particular, (n,n)-chirality, or armchair, metallic nanotubes are truly gapless with massless carriers, ideally suited for dynamical studies of TomonagaﾖLuttinger liquids. Unfortunately, progress towards such studies has been slowed by the inherent problem of nanotube synthesis whereby both semiconducting and metallic nanotubes are produced. Here, we use post-synthesis separation methods based on density gradient ultracentrifugation and DNA-based ion-exchange chromatography to produce aqueous suspensions strongly enriched in armchair nanotubes. Through resonant Raman spectroscopy of the radial breathing mode phonons, we provide macroscopic and unambiguous evidence that density gradient ultracentrifugation can enrich ensemble samples in armchair nanotubes. Furthermore, using conventional, optical absorption spectroscopy in the nearinfrared and visible range, we show that interband absorption in armchair nanotubes is strongly excitonic. Lastly, by examining the G-band mode in Raman spectra, we determine that observation of the broad, lower frequency (G!) feature is a result of resonance with non-armchair “metallic” nanotubes. These !ndings regarding the fundamental optical absorption and scattering processes in metallic carbon nanotubes lay the foundation for further spectroscopic studies to probe many-body physical phenomena in one dimension

Vibrational properties of single-wall nanotubes and monolayers of hexagonal BN

We report a detailed study of the vibrational properties of BN single-walled nanotubes and of the BN monolayer. Our results have been obtained from a well-established Tight-Binding model complemented with an electrostatic model to account for the long-range interactions arising from the polar nature of the material, and which are not included in the Tight-Binding model. Our study provides a wealth of data for the BN monolayer and nanotubes, such as phonon band structure, vibrational density of states, elastic constants, etc. For the nanotubes we obtain the behavior of the optically active modes as a function of the structural parameters, and we compare their frequencies with those derived from a zone-folding treatment applied to the phonon frequencies of the BN monolayer, finding general good agreement between the two.Comment: 14 pages with 10 postscript figures, to appear in PRB, January 15th 200