Acoustic Transmission Loss in Hilbert Fractal Metamaterials

Acoustic metamaterials are increasingly being considered as a viable technology for sound insulation. Fractal patterns constitute a potentially groundbreaking architecture for acoustic metamaterials. We describe in this work the behaviour of the transmission loss of Hilbert fractal metamaterials used for sound control purposes. The transmission loss of 3D printed metamaterials with Hilbert fractal patterns related to configurations from the zeroth to the fourth order is investigated here using impedance tube tests and Finite Element models. We evaluate, in particular, the impact of the equivalent porosity and the relative size of the cavity of the fractal pattern versus the overall dimensions of the metamaterial unit. We also provide an analytical formulation that relates the acoustic cavity resonances in the fractal patterns and the frequencies associated with the maxima of the transmission losses, providing opportunities to tune the sound insulation properties through control of the fractal architecture.Comment: Submitted to Scientific Report

Sound absorption in Hilbert Fractal and Coiled Acoustic Metamaterials

We describe here a class of acoustic metamaterials with fractal Hilbert space-filling and coiled geometry with equal tortuosity for noise mitigation. Experiments are performed using a four-microphone impedance tube and benchmarked against non-viscous and viscothermal Finite Element models related to configurations spanning up to five fractal/geometry orders. We show that the acoustic absorption can be predicted by the resonance of the cavities associated to the tortuous paths. For a given fractal/geometry order, the acoustic absorption at specific frequencies is also enhanced by maximising the difference between the minimum and maximum fluid particle velocity of the air inside the patterns. These principles can be used to design high-performance acoustic metamaterials for sound absorption over broad frequency ranges.Comment: 4 pages, 3 figures, Submitted to Applied Physics Letter

Analytical model for uniaxial compressive behavior of timber columns with longitudinal cracking, with and without retrofitting solutions.

Two simple analytical models are developed with Matlab to predict the mid-lateral displacement of cracked, un-cracked or retrofitted timber columns. In the models are considered the presence of retrofitting elements with high modulus of elasticity, like: carbon, glass, pbo fibres with different spacing, and how those elements influencing the mid-lateral displacement. The first model is based on the "displacement method analysis for frame" and the second one is based on a "frame stability analysis by finite element method". The results obtained with these models is useful to determine the maximum length that a vertical crack can have before is necessary a retrofitting action in a timber column

Comprehensive Geriatric Assessment in older women with breast cancer

none9Comprehensive Geriatric Assessment in older women with breast cancerCOMANDINI D; PARODI S; IVALDI C; GIANNI W; FRATINO L; VENTURINO A; ZAGONEL V; REPETTO L; M. VERCELLIComandini, D; Parodi, S; Ivaldi, C; Gianni, W; Fratino, L; Venturino, A; Zagonel, V; Repetto, L; Vercelli, Marin

Rigid polyurethane foams from commercial castor oil resins

Rigid polyurethane foams (RPUFs) are among the most used polymeric materials due to their tailorable properties. Greener and biobased polyol sources for synthesising RPUFs have been recently prototyped because of the ever-growing demand for more sustainable materials solutions. Castor Oil has also rapidly become one of the most successful alternatives to replace polyurethane fossil-based components. This study extensively investigates three types of RPUFs developed from commercially available Castor Oil-based resins, correlating their properties across different length scales. In particular, X-ray diffraction identified a characteristic peak whose intensity correlated with the apparent foam density, morphology (obtained from computed tomography scans) and mechanical properties. Furthermore, quasi-static compression and vibration transmissibility tests revealed distinctive anisotropic mechanical responses among the foams, with one type of RPUF consistently outperforming the others due to its lower porosity, reaching 13.3 MPa of compressive modulus. These findings demonstrate the possibility of tuning the mechanical properties of foams via compositional control