Dielectric constant boost in amorphous sesquioxides

High-kappa dielectrics for insulating layers are a current key ingredient of microelectronics. X2O3 sesquioxide compounds are among the candidates. Here we show for a typical material of this class, ScO3, that the relatively modest dielectric constant of its crystalline phase is enhanced in the amorphous phase by over 40% (from ~15 to ~22). This is due to the disorder-induced activation of low frequency cation-related modes which are inactive or inefficient in the crystal, and by the conservation of effective dynamical charges (a measure of atomic polarizability). The analysis employs density-functional energy-force and perturbation-theory calculations of the dielectric response of amorphous samples generated by pair-potential molecular dynamics.Comment: 3 pages, 3 figures, submitted to AP

Method and apparatus for analyzing material properties using reflected ultrasound

A method and apparatus which assesses the mechanical properties of a material by launching an ultrasound signal at the material while varying the angle of incidence and analyzing the amplitude of the ultrasound wave reflected by the material. The method and apparatus correlates extrema (maxima or minima inflection points) in the reflected angle with the angle of incidence of the transmitted signal to identify critical angles of incidence. The velocity of the pressure wave in the material has been found to be a function of a first critical angle corresponding to a first maxima as the angle of incidence is increased in the range 0.degree.-90.degree.. The velocity of the shear wave in the material has been found to be a function of a second critical angle corresponding to a second maxima following the first maxima. Young's modulus of elasticity, Poisson's modulus, and density can be approximated using the velocity of the pressure wave and shear wave for isotropic materials. A third critical angle corresponding to a minima after the first critical angle (reflected amplitude approaching o) has been found particularly useful in conjunction with the first and second critical angles in assessing bone density and in determining whether the second critical point is at a maximum or an inflection point. The extension of the method in which the plane of scattering is rotated around the normal to bone while keeping the point of observation fixed has been found particularly useful in assessing the mechanical properties of anisotropic materials such as cortical bone.Board of Regents, University of Texas Syste

Complex delay dynamics on railway networks: from universal laws to realistic modelling

Railways are a key infrastructure for any modern country. The reliability and resilience of this peculiar transportation system may be challenged by different shocks such as disruptions, strikes and adverse weather conditions. These events compromise the correct functioning of the system and trigger the spreading of delays into the railway network on a daily basis. Despite their importance, a general theoretical understanding of the underlying causes of these disruptions is still lacking. In this work, we analyse the Italian and German railway networks by leveraging on the train schedules and actual delay data retrieved during the year 2015. We use {these} data to infer simple statistical laws ruling the emergence of localized delays in different areas of the network and we model the spreading of these delays throughout the network by exploiting a framework inspired by epidemic spreading models. Our model offers a fast and easy tool for the preliminary assessment of the {effectiveness of} traffic handling policies, and of the railway {network} criticalities.Comment: 32 pages (with appendix), 28 Figures (with appendix), 2 Table

Spectral weight redistribution in (LaNiO3)n/(LaMnO3)2 superlattices from optical spectroscopy

We have studied the optical properties of four (LaNiO$_3$)$_n$/(LaMnO$_3$)$_2$ superlattices (SL) ($n$=2, 3, 4, 5) on SrTiO$_3$ substrates. We have measured the reflectivity at temperatures from 20 K to 400 K, and extracted the optical conductivity through a fitting procedure based on a Kramers-Kronig consistent Lorentz-Drude model. With increasing LaNiO$_3$ thickness, the SLs undergo an insulator-to-metal transition (IMT) that is accompanied by the transfer of spectral weight from high to low frequency. The presence of a broad mid-infrared band, however, shows that the optical conductivity of the (LaNiO$_3$)$_n$/(LaMnO$_3$)$_2$ SLs is not a linear combination of the LaMnO$_3$ and LaNiO$_3$ conductivities. Our observations suggest that interfacial charge transfer leads to an IMT due to a change in valence at the Mn and Ni sites.Comment: Accepted for publication in Phys. Rev. Lett. 5 pages, 5 figure

El 'Céfalo y Pocris' de Calderón entre reescritura y juego meta burlesco

A partir de la premisa fundamental de la insuficiencia de un acercamiento puramente descriptivo a las comedias burlescas del Siglo de Oro, y de la necesidad de analizar cada texto de este género no sólo en sus caracteres convencionales de dramaturgia cómico-disparatada, el presente estudio intenta un análisis del carácter paródico y de las funciones literarias subyacentes en 'Céfalo y Pocris', la única comedia burlesca que nos queda de Calderón de la Barca. Subrayando la necesidad de detectar un más exacto nexo entre el hipertexto burlesco y su complejo hipotexto (donde priman las dos obras del propio Calderón, 'Celos, aun del aire, matan' y 'Auristela y Lisidante'), el estudio destaca el fuerte componente metateatral de la comedia. En fin, a partir de este elemento esencial de la obra, el estudio —haciendo hincapié en las ideas sobre la pintura que Calderón nos deja en su Tratado defendiendo la nobleza de la pintura— intenta demostrar cómo en 'Céfalo y Pocris' el dramaturgo, en las continuas alusiones a la imaginación figurativa que el teatro comparte con la pintura, y a pesar del régimen cómico-burlesco, confirma los fundamentos estéticos y poéticos de su dramaturgia y de su cosmovisión. Starting from the fundamental premise of the insufficiency of a purely descriptive approximation to the Golden Age burlesque comedies, and the need to analyze each text of this genre not only through the conventional characters of comic-absurd playwriting, the present study aims for an analysis of the parody character and of the underlying literary functions in 'Céfalo y Pocris', the only burlesque comedy that we have from Calderón de la Barca. Underlying the necessity to detect a more exact link between the burlesque hypertext and its complex hipotext (where the two works of Calderón take precedence, 'Celos, aun del aire, matan' and 'Auristela y Lisidante'), the study highlights the strong meta-theatrical component of the comedy. Ultimately, through this essential element of the work, the study-stressing the ideas about painting that Calderón leaves us with in his Treaty defending the nobleness of painting-attempts to demonstrate how in 'Céfalo y Pocris' the playwright, in continual allusions to the figurative imagination that theater shares with painting, and in spite of the comic-burlesque regime, confirms the aesthetic and poetic foundations of his playwriting and his worldview

Influence of the halo upon angular distributions for elastic scattering and breakup

The angular distributions for elastic scattering and breakup of halo nuclei are analysed using a near-side/far-side decomposition within the framework of the dynamical eikonal approximation. This analysis is performed for 11Be impinging on Pb at 69 MeV/nucleon. These distributions exhibit very similar features. In particular they are both near-side dominated, as expected from Coulomb-dominated reactions. The general shape of these distributions is sensitive mostly to the projectile-target interactions, but is also affected by the extension of the halo. This suggests the elastic scattering not to be affected by a loss of flux towards the breakup channel.Comment: 11 pages, 3 figures, accepted for publication in Phys. Lett.