Polytechnic University of Milan

About: Polytechnic University of Milan is a education organization based out in Milan, Italy. It is known for research contribution in the topics: Computer science & Finite element method. The organization has 18231 authors who have published 58416 publications receiving 1229711 citations. The organization is also known as: PoliMi & L-NESS.

Broadband, electrically tunable third-harmonic generation in graphene

Abstract: Optical harmonic generation occurs when high intensity light (>1010 W m–2) interacts with a nonlinear material. Electrical control of the nonlinear optical response enables applications such as gate-tunable switches and frequency converters. Graphene displays exceptionally strong light–matter interaction and electrically and broadband tunable third-order nonlinear susceptibility. Here, we show that the third-harmonic generation efficiency in graphene can be increased by almost two orders of magnitude by controlling the Fermi energy and the incident photon energy. This enhancement is due to logarithmic resonances in the imaginary part of the nonlinear conductivity arising from resonant multiphoton transitions. Thanks to the linear dispersion of the massless Dirac fermions, gate controllable third-harmonic enhancement can be achieved over an ultrabroad bandwidth, paving the way for electrically tunable broadband frequency converters for applications in optical communications and signal processing. Gate tunable and ultrabroadband third-harmonic generation can be achieved in graphene, paving the way for electrically tunable broadband frequency converters for applications in optical communications and signal processing.

Gravitational tests of the generalized uncertainty principle

Abstract: We compute the corrections to the Schwarzschild metric necessary to reproduce the Hawking temperature derived from a generalized uncertainty principle (GUP), so that the GUP deformation parameter is directly linked to the deformation of the metric. Using this modified Schwarzschild metric, we compute corrections to the standard general relativistic predictions for the light deflection and perihelion precession, both for planets in the solar system and for binary pulsars. This analysis allows us to set bounds for the GUP deformation parameter from well-known astronomical measurements.

Foundational issues in risk assessment and risk management.

Abstract: In spite of the maturity reached by many of the methods used in risk assessment and risk management, broad consensus has not been established on fundamental concepts and principles. The risk fields still suffer from a lack of clarity on many key scientific pillars. The purpose of this article is to point to this situation and through some illustrating examples discuss the challenges that the fields here face. Moreover, the purpose of the article is to reflect on how to improve the present situation and enhance the risk fields. We argue that the establishment of some common scientific pillars as well as a strong and continuous research focus on foundational issues are critical success factors. The article specifically addresses the role of the peer-reviewed journals and the international standards in the fields. We hope that the article can contribute to a revitalization of the discussion of foundational issues in risk assessment and risk management.

Finite element simulation of ring expansion and fragmentation: The capturing of length and time scales through cohesive models of fracture

Abstract: The expanding ring test of Grady and Benson (1983) is taken as a convenient yet challenging validation problem for assessing the fidelity of cohesive models in situations involving ductile dynamical fracture. Attention has been restricted to 1100-0 aluminum samples. Fracture has been modelled by recourse to an irreversible cohesive law embedded into cohesive elements. The finite element model is three-dimensional and fully Lagrangian. In order to limit the extent of deformation-induced distortion, we resort to continuous adaptive remeshing. The cohesive behavior of the material is assumed to be rate independent and, consequently, all rate effects predicted by the calculations are due to inertia and the rate dependency in plastic deformation. The numerical simulations are revealed to be highly predictive of a number of observed features, including: the number of dominant and arrested necks; the fragmentation patterns; the dependence of the number of fragments and the fracture strain on the expansion speed; and the distribution of fragment sizes at fixed expansion speed.

Three-dimensional Mach-Zehnder interferometer in a microfluidic chip for spatially-resolved label-free detection

Abstract: Ultrafast laser writing of waveguides in glasses is a very flexible and simple method for direct on-chip integration of photonic devices. In this work we present a monolithic optofluidic device in fused silica providing label-free and spatially-resolved sensing in a microfluidic channel. A Mach-Zehnder interferometer is inscribed with the sensing arm orthogonally crossing the microfluidic channel and the reference arm passing over it. The interferometer is integrated either with a microchannel fabricated by femtosecond laser technology or into a commercial lab-on-chip for capillary electrophoresis. The device layout, made possible by the unique three-dimensional capabilities of the technique, enables label-free sensing of samples flowing in the microchannel with spatial resolution of about 10 μm and limit of detection down to 10−4 RIU.