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 & Nonlinear system. The organization has 11553 authors who have published 41395 publications receiving 789320 citations. The organization is also known as: POLITO & Politecnico di Torino.

Ferroelectric Response and Induced Biaxiality in the Nematic Phase of a Bent-Core Mesogen

Abstract: The still undiscoveredfluid ferroelectric nematic phase isexpected to exhibit a much faster and easier response to an external electric field compared to conventional ferroelectric smectic liquid crystals; therefore, the discovery of such a phase could open new avenues in electro-optic device technology. Here, experimental evidence of a ferroelectric response to a switching electric field inalowmolarmassnematicliquid crystalisreported andconnected with field-induced biaxiality. The fluid is made of bent-core polar molecules and is nematic over a range of 120-C. Combining repolarization current measurements, electro-optical characterizations, X-ray diffraction and computer simulations, ferroelectric switching is demonstrated and it is concluded that the response is due to field-induced reorganization of polar cybotactic groups within the nematic phase. This work represents significant progress toward the realization of ferroelectric fluids that can be aligned at command with a simple electric field.

On the eigenfunctions of the Dirac operator on spheres and real hyperbolic spaces

Abstract: The eigenfunctions of the Dirac operator on spheres and real hyperbolic spaces of arbitrary dimension are computed by separating variables in geodesic polar coordinates. These eigenfunctions are used to derive the heat kernel of the iterated Dirac operator on these spaces. They are then studied as cross sections of homogeneous vector bundles, and a group-theoretic derivation of the spinor spherical functions and heat kernel is given based on Harish-Chandra's formula for the radial part of the Casimir operator.

π bands and gap states from optical absorption and electron-spin-resonance studies on amorphous carbon and amorphous hydrogenated carbon films

Abstract: Amorphous carbon a-C and amorphous hydrogenated carbon a-C:H films were prepared by rf sputtering of a graphite target in argon and argon-plus-hydrogen atmospheres, respectively. The optical-absorption coefficients of these films were measured by a spectrophotometer in the high-absorption range and by photothermal deflection spectroscopy in the low-absorption range. They were also studied by electron-spin-resonance (ESR) measurements. The optical-absorption spectrum is found to have a rather broad peak, in contrast to the sharp rise in absorption near the band gap observed for normal semiconductors. To explain this broad peak, a model density of states (DOS) for these materials is proposed, in accordance with their well-known microstructure. This consists of a pair of broad Gaussian-like distributions lying above and below the Fermi level and separated by about 4 eV, arising out of the \ensuremath{\pi} states of the aromatic sixfold rings that comprise the bulk of the graphitic ${\mathit{sp}}^{2}$ regions, as well as pairs of discrete levels that are about 0.6 eV apart and are produced by fivefold and sevenfold rings present in these regions. The proposed DOS explains the essential features of the optical-absorption spectra and ESR data. The validity of the concept of the optical gap for these materials is also discussed.