102,135 research outputs found
Polymers and Food Packaging: A Short Overview
No full textA discussion on the state-of-the-art performance of biopolymers and functional biopolymers, focusing on food packaging applications, is presented in this chapter. An overview is given of the most important materials used for producing biobased films, their limitations, recycling pattern, and solutions thereof. Furthermore, transport phenomena and regulation concerns are extensively treated
Functional Polymers for Food Processing
No full textPolymeric materials can be used as functional elements for reaching an efficient food production and processing, with considerable advantages for the whole food industry. Among others, the applicability of polymers involves their use in agriculture, animal feed, modification of food rheology, and the development of functional food and nutraceutics
Optimization of metasurfaces for the design of noise trapping metadevices
No full textThe article deals with the design of a metadevice able to trap acoustic waves in a duct. The acoustic perturbation is produced by a source placed inside the duct. The aim is to limit the outgoing acoustic power and confine the perturbation inside the duct exploiting the unconventional reflection of the optimized metasurface. The metabehaviour is modeled by means of the generalized Snell's law for reflection from acoustically rigid surfaces. The realization of the device relies on a modular concept, which building set is made of eight elementary cells, able to induce a reflected field suitably phase-delayed with respect to the incident wave. The set spans the whole 0-2π phase delay range, and the anomalous reflection is obtained by the tailored design of the phase delay gradient profile on the metasurface. The cells are designed in order to extend the effective frequency range of the device, keeping the overall thickness of the metadevice smaller than a quarter of the design wavelength. The duct and the source are considered co-moving within the fluid at rest. The numerical analysis is performed in the frequency domain in a frame of reference rigidly connected to the duct, and considering several values for the Mach numbe
Design of metacontinua in the aeroacoustic spacetime
No full textThe effect of background flows on the response of acoustic metamaterials is a key aspect that prevented the full disclosure of their potential in those applications where an aerodynamic velocity field strongly influences the propagation of acoustic disturbances. Indeed, the classic approaches for metamaterial design do not consider the aeroacoustic interaction, and the resulting metamaterials cannot preserve their response when operating in flows. So far, only few authors have addressed the problem, mostly focusing on understanding the phenomenon or identifying corrective techniques with limited usability in practical applications. The present study proposes a general method for the modification of the mechanical properties of acoustic metacontinua to preserve their response in presence of a background flow. The method is based on the application of spacetime coordinate transformations exploiting the spacetime formal invariance of the generalised d’Alembertian. This methodology applies to the equation governing the propagation of acoustic disturbances in a metamaterial having arbitrary constitutive equations independently on the method used for its original design. The approach is validated through numerical simulations, using as a benchmark the problem of the acoustic cloaking of a cylinder impinged by a perturbation generated by an isotropic point source within a flowing medium. Numerical results are obtained for an asymptotic Mach number M∞≤ 0.35
G. Cordini, P. Fois, S. Marchisio, Diritto ambientale - Profili internazionali europei e comparati, Giappichelli, Quarta edizione, 2024
No full textSpaceTime-bending transformations in aeroacoustics
No full textThe paper deals with the spacetime reinterpretation of the phenomenon of aeroacoustic convection within the framework of the Lorentzian differential geometry. Specifically, the effect of the background aerodynamic velocity field on the propagation of the acoustic disturbances is revisited in terms of spacetime curvature. The analysis explores the local properties of the curved aeroacoustic spacetime to correlate the background aerodynamics with the local value of the Riemann's scalar, and the latter with the convective effect. The metric associated to the aeroacoustic spacetime is compare with that induced by the inverse Taylor transformation, which is based on the O(M) approximation of the convective wave equation. Although limited by the low-speed assumption, the inverse Taylor transformation bends the Minkowskian (i.e., flat) acoustic spacetime taking into account the spatial variation of the background velocity potential. Numerical simulations are conducted to verify and visualise the spacetime propertie
Il sistema elettorale come strumento di stabilità di governo: rischi e benefici nell’attuale esperienza francese e italiana
No full textThe contribution focuses on the relationship between the form of govern-
ment, the electoral system and the powers of the Head of State. The issues
involved are examined in a comparative perspective between France and Ita-
ly. The presidential and legislative elections held in France in 2022 led to an
unprecedented fragmentation: the contribution aims to analyse the causes and
consequences of this new state, comparing the French situation with that of
Italy. The latter is characterised by instability, also linked to the electoral sys-
tem, which the Government proposes to address by moving to a semi-
presidential system on the French model
NUMERICAL MODELLING OF A PHASE-GRADIENT LINING USING A METAFLUID MODEL
No full textThis contribution presents the modelling of a phase-gradient metamaterial for the surface treatment of the internal walls of a turbofan nacelle intake. The metamaterial is modelled through a metafluid, whose bulk modulus and inertia tensor are determined by a simulation-based numerical optimization, minimizing the acoustic emission from the duct inlet. The flow and its interaction with both the nacelle and lining are modelled in a simplified way using a potential flow over smooth surfaces. The parameters of the metafluid are tailored to tackle the incident field expressed in terms of duct modes propagating from the fan section for the blade passage frequency. Numerical results show the encouraging capabilities of a phase-gradient device to change the directivity of the noise radiated by an aeronautic turbofan nacelle, abating the propagation of a duct mode linked to a relevant noise generation mechanism
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