Polytechnic University of Turin

About: Polytechnic University of Turin is a education organization based out in Turin, Piemonte, Italy. It is known for research contribution in the topics: Finite element method & Computer science. The organization has 11553 authors who have published 41395 publications receiving 789320 citations. The organization is also known as: POLITO & Politecnico di Torino.

Early appearance of Delta isobars in neutron stars

Abstract: We discuss the formation of $\ensuremath{\Delta}$ isobars in neutron star matter. We show that their threshold density strictly correlates with the density derivative of the symmetry energy of nuclear matter: the $L$ parameter. By restricting $L$ to the range of values indicated by recent experimental and theoretical analysis, i.e., $40\phantom{\rule{4.pt}{0ex}}\text{MeV}\ensuremath{\lesssim}L\ensuremath{\lesssim}62\phantom{\rule{4.pt}{0ex}}\text{MeV}$, we find that $\ensuremath{\Delta}$ isobars appear at a density of the order of 2 to 3 times the nuclear matter saturation density, i.e., the same range as for the appearance of hyperons. The range of values of the couplings of the $\ensuremath{\Delta}\mathrm{s}$ with the mesons is restricted by the analysis of the data obtained from photoabsorption, electron and pion scattering on nuclei. If the potential of the $\ensuremath{\Delta}$ in nuclear matter is close to the one indicated by the experimental data then the equation of state becomes soft enough that a ``\ensuremath{\Delta} puzzle'' exists, similar to the ``hyperon puzzle'' widely discussed in the literature. Possible solutions to this puzzle are also discussed.

Guided modes of Ti:LiNbO/sub 3/ channel waveguides: a novel quasi-analytical technique in comparison with the scalar finite-element method

Abstract: Two different techniques for the calculation of optical modes of Ti:LiNbO/sub 3/ channel waveguides are presented. The first one is an almost analytical technique based on the effective-refractive-index method. The second one is based on the well-known finite-element method. Both approaches use a rather realistic waveguide model considering crystal anisotropy, wavelength dispersion of the refractive index distributions, and also the nonlinear dependence of the ordinary refractive index on the Ti/sup 4+/ concentration. Effective indices and field distributions obtained by both techniques are compared for wavelengths of 0.6 and 1.2 mu m, for both quasi-TE and -TM polarization, considering Y-cut and Z-cut crystal orientation and both isotropic and anisotropic Ti/sup 4+/ diffusion. >

U duality and central charges in various dimensions revisited

Abstract: A geometric formulation which describes extended supergravities in any dimension in the presence of electric and magnetic sources is presented. In this framework, the underlying duality symmetries of the theories are manifest. Particular emphasis is given to the construction of central and matter charges and to the symplectic structure of all D=4, N-extended theories. The latter may be traced back to the existence, for N>2, of a flat symplectic bundle which is the N>2 generalization of N=2 Special Geometry.

Randomized algorithms for probabilistic robustness with real and complex structured uncertainty

Abstract: There has been a growing interest in developing randomized algorithms for probabilistic robustness of uncertain control systems. Unlike classical worst case methods, these algorithms provide probabilistic estimates assessing, for instance, if a certain design specification is met with a given probability. One of the advantages of this approach is that the robustness margins can be often increased by a considerable amount, at the expense of a small risk. In this sense, randomized algorithms may be used by the control engineer together with standard worst case methods to obtain additional useful information. The applicability of these probabilistic methods to robust control is presently limited by the fact that the sample generation is feasible only in very special cases which include systems affected by real parametric uncertainty bounded in rectangles or spheres. Sampling in more general uncertainty sets is generally performed through overbounding, at the expense of an exponential rejection rate. In the paper, randomized algorithms for stability and performance of linear time invariant uncertain systems described by a general M-/spl Delta/ configuration are studied. In particular, efficient polynomial-time algorithms for uncertainty structures /spl Delta/ consisting of an arbitrary number of full complex blocks and uncertain parameters are developed.

Improving the Efficiency of Hematite Nanorods for Photoelectrochemical Water Splitting by Doping with Manganese

Abstract: Here, we report a significant improvement of the photoelectrochemical (PEC) properties of hematite (α-Fe2O3) to oxidize water by doping with manganese. Hematite nanorods were grown on a fluorine-treated tin oxide (FTO) substrate by a hydrothermal method in the presence on Mn. Systematic physical analyses were performed to investigate the presence of Mn in the samples. Fe2O3 nanorods with 5 mol % Mn treatment showed a photocurrent density of 1.6 mA cm–2 (75% higher than that of pristine Fe2O3) at 1.23 V versus RHE and a plateau photocurrent density of 3.2 mA cm–2 at 1.8 V versus RHE in a 1 M NaOH electrolyte solution (pH 13.6). We attribute the increase in the photocurrent density, and thus in the oxygen evolving capacity, to the increased donor density resulting from Mn doping of the Fe2O3 nanorods, as confirmed by Mott–Schottky measurement, as well as the suppression of electron–hole recombination and enhancement in hole transport, as detected by chronoamperometry measurements.