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Search Results: 1 - 10 of 2125 matches for " Alessio;Ricci "
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Giant electroresistance and tunable magnetoelectricity in a multiferroic junction
Francesco Ricci,Alessio Filippetti,Vincenzo Fiorentini
Physics , 2013, DOI: 10.1103/PhysRevB.88.235416
Abstract: First-principles density functional calculations show that the $\textrm{SrRuO}_{3}/\textrm{PbTiO}_{3}/\textrm{SrRuO}_{3}$ multiferroic junction with asymmetric (RuO$_{2}$/PbO and TiO$_{2}$/SrO) interfaces has a large ferroelectric depolarizing field, whose switching changes the interface transmission probabilities for tunneling electrons, leading to electroresistance modulation over several orders of magnitude. The switching further affects the interface spin density, naturally driving magnetoresistance as well as modulated spin-dependent in-plane resistivity, which may be exploited in field-effect devices.
Rappresentazioni sociali dell'invecchiamento tra psicologia sociale e letteratura
Contarello, Alberta;Marini, Ilaria;Nencini, Alessio;Ricci, Gaia;
Psicologia & Sociedade , 2011, DOI: 10.1590/S0102-71822011000100019
Abstract: aim of the present paper is to propose the analysis of literary texts in order to study social representations of ageing. after introducing the theme, with reference to recent developments in terms of positive ageing and to the usefulness of a stronger interchange between social psychology and literature, the results of quali-quantitative and qualitative analyses of two italian recent books are presented. both correspondence analysis and a qualitative reading of the texts provide precious cues towards the purpose of co-constructing a good way of ageing. assonances and divergences with contemporary social psychological literature on ageing contribute to a critical and generative interpretation of the last 'gift of time'.
Multi-gap absorption in CaCu$_{3}$Ti$_{4}$O$_{12}$ and the predictivity of ab initio methods
Francesco Ricci,Paola Alippi,Alessio Filippetti,Vincenzo Fiorentini
Physics , 2014, DOI: 10.1103/PhysRevB.90.045132
Abstract: We report the electronic properties of the quadruple perovskite CaCu$_{3}$Ti$_{4}$O$_{12}$ as obtained via several density-functional based methods, and propose a new interpretation of optical experiments to the effect that four distinct transitions (centered around 0.7, 1.5, 2.5, and 3.5 eV) contribute to the spectrum. The comparison with experiment is satisfactory, especially after we account for the effects of spin disorder, which does not close the fundamental gap but suppresses the transition intensity. We find that some of the methods we employ tend to overestimate considerably the gaps for standard values of the respective adjustable parameters.
Prediction of a native ferroelectric metal
Alessio Filippetti,Vincenzo Fiorentini,Francesco Ricci,Pietro Delugas,Jorge í?iguez
Physics , 2015,
Abstract: The possibility that metals may support ferroelectricity is an open issue. Anderson and Blount showed that certain martensitic transitions involve inversion symmetry breaking and the formal existence of a polar axis, so 'metallic ferroelectric' behavior has been claimed for metals undergoing a centrosymmetric (CS) to non-CS structural transformation (Cd2ReO7, LiOsO3) or natively non-CS (SrCaRu2O), or for ferroelectric insulators whose polar distortion survives moderate metallicity induced by doping or proximity. However, none of these systems, nor any other to our knowledge, embodies a truly ferroelectric metal with native switchable polarization and native metallicity coexisting in a single phase. Here we report the first-ever theoretical prediction of such a material. By first-principles calculations, we show that the layered perovskite Bi5Ti5O17 has a non-zero density of states at the Fermi level and metal-like conductivity, as well as a spontaneous polarization in zero field. Further, we predict that the polarization of Bi5Ti5O17 is switchable both in principle, as the material complies with the sufficient symmetry requirements, and in practice, as Bi5Ti5O17 can sustain a sizable potential drop along the polar direction, as needed to revert its polarization by application of an electric bias.
Theoretical and experimental investigation of optical absorption anisotropy in $β$-Ga2O3
Francesco Ricci,Francesco Boschi,Andrea Baraldi,Alessio Filippetti,M. Higashiwaki,A. Kuramata,Vincenzo Fiorentini,Roberto Fornari
Physics , 2015,
Abstract: The question of optical bandgap anisotropy in the monoclinic semiconductor $\beta$-Ga2O3 was revisited by combining accurate optical absorption measurements with theoretical analysis, performed using different advanced computation methods. As expected, the bandgap edge of bulk $\beta$-Ga2O3 was found to be a function of light polarization and crystal orientation, with the lowest onset occurring at polarization in the ac crystal plane around 4.5-4.6 eV; polarization along b unambiguously shifts the onset up by 0.2 eV. The theoretical analysis clearly indicates that the shift of the b onset is due to a suppression of the transition matrix elements of the three top valence bands at $\Gamma$ point.
Infrared Transmission in Porous Silicon Multilayers  [PDF]
Alessio Palavicini, Chumin Wang
Optics and Photonics Journal (OPJ) , 2013, DOI: 10.4236/opj.2013.32A003
Abstract:

Porous silicon is a nanostructured material and exhibits efficient photo- and electro-luminescence in the visible range at room temperature, as well as a tunable refractive index determined by its porosity. Porous silicon samples can be obtained by etching a crystalline silicon wafer in a solution of hydrofluoric acid. In this work, we report the fabrication of porous silicon multilayers alternating layers with high and low porosities, which correspondingly produce low and high refractive indices. The free-standing multilayers were formed following three different sequences: periodic, Fibonacci and ThueMorse. These structures were verified by scanning electron microscopy and their infrared transmission spectra were measured by means of Fourier-transform infrared spectroscopy. On the other hand, we calculate the light transmittance of porous silicon multilayers by using the transfer matrix method for all directions of incidence and a wide range of wavelengths. The experimental measurements are compared with theoretical results and a good agreement is observed. In addition, an analysis of infrared absorption peaks due to the molecular vibrations at pore surfaces reveals the presence of hydrogen and oxygen atoms.

On a conjecture of Wilf about the Frobenius number
Alessio Moscariello,Alessio Sammartano
Mathematics , 2014, DOI: 10.1007/s00209-015-1412-0
Abstract: Given coprime positive integers $a_1 < ...< a_d$, the Frobenius number $F$ is the largest integer which is not representable as a non-negative integer combination of the $a_i$. Let $g$ denote the number of all non-representable positive integers: Wilf conjectured that $d \geq \frac{F+1}{F+1-g}$. We prove that for every fixed value of $\lceil \frac{a_1}{d} \rceil$ the conjecture holds for all values of $a_1$ which are sufficiently large and are not divisible by a finite set of primes. We also propose a generalization in the context of one-dimensional local rings and a question on the equality $d = \frac{F+1}{F+1-g}$.
Internet Districts in Italy: Is Proximity an Antidote against Weak Broadband Competition?  [PDF]
Alessio D’Ignazio, Emanuele Giovannetti
Modern Economy (ME) , 2011, DOI: 10.4236/me.2011.23044
Abstract: We study the effects of proximity in the interconnections between Internet providers participating at the three main Italian Internet Exchange Points. We find that geographical proximity plays a role in driving Internet Providers’ interconnection, positively affecting the likelihood of an agreement. This suggests the existence of localized positive externalities in the form of mutual knowledge and reputation, one of the cited drivers underlying the formation of districts in non high-tech industries. We interpret these results as resulting from the necessity for cooperation in interconnection between smaller providers facing the weak competitiveness of the highly concentrated Italian broadband access market.
Is it possible to block the cancer cells in circulating blood by extracorporeal circulation? Implications of the immune system and other factors (review)  [PDF]
Sante Basso Ricci, Francesco Garbagnati
Open Journal of Immunology (OJI) , 2013, DOI: 10.4236/oji.2013.34029
Abstract: The presence of cancer cells in circulating blood and the possibility of colonization in the tissues of the body worsen in a determinant way the prognosis of the disease. Nevertheless, there are factors in the body that can lead to a prognostic improvement, even in such conditions. In addition to the immune system, other favorable factors can act at the level of the microenvironment of the tumor so much that cases of spontaneous total regression, not only of primary tumors but also metastases, have been reported in the literature. Since it was recently reported that patients with renal tumors and in permanent hemodialysis present at post mortem examination, a metastatic spread much less extensive than observed in patients deceased for renal tumors but not on hemodialysis. The authors maintain it likely that the dialytic membrane concurs to block at least in part the cancer cells circulating in the blood. The possibility to block cancer cells can be extended in addition to the dialytic membrane also to other types of filters inserted in the extracorporeal circulation. The block of the cancer cells thus is obtained and that occurs in regional lymph nodes and in the microenvironment of the tumor causing a relative increase in the elements of the immune system compared to the number of cancer cells, which could determine clearly positive therapeutic results also in cases with advanced metastatic spread.
A “Hard to Die” Series Expansion and Lucas Polynomials of the Second Kind  [PDF]
Pierpaolo Natalini, Paolo E. Ricci
Applied Mathematics (AM) , 2015, DOI: 10.4236/am.2015.68116
Abstract: We show how to use the Lucas polynomials of the second kind in the solution of a homogeneous linear differential system with constant coefficients, avoiding the Jordan canonical form for the relevant matrix.
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