Characterization of count data distributions involving additivity and binomial subsampling

In this paper we characterize all the $r$-parameter families of count distributions (satisfying mild conditions) that are closed under addition and under binomial subsampling. Surprisingly, few families satisfy both properties and the resulting models consist of the $r$th-order univariate Hermite distributions. Among these, we find the Poisson ($r=1$) and the ordinary Hermite distributions ($r=2$).Comment: Published at http://dx.doi.org/10.3150/07-BEJ6021 in the Bernoulli (http://isi.cbs.nl/bernoulli/) by the International Statistical Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm

A modal-spectral model for flanking transmissions

A model for the prediction of direct and indirect (flanking) sound transmissions is presented. It can be applied to geometries with extrusion symmetry. The structures are modelled with spectral finite elements. The acoustic domains are described by means of a modal expansion of the pressure field and must be cuboid-shaped. These reasonable simplifications in the geometry allow the use of more efficient numerical methods. Consequently the coupled vibroacoustic problem in structures such as junctions is efficiently solved. The vibration reduction index of T-junctions with acoustic excitation and with point force excitation is compared. The differences due to the excitation type obey quite general trends that could be taken into account by prediction formulas. However, they are smaller than other uncertainties not considered in practice. The model is also used to check if the sound transmissions of a fully vibroacoustic problem involving several flanking paths can be reproduced by superposition of independent paths. There exist some differences caused by the interaction between paths, which are more important at low frequencies.Peer ReviewedPostprint (author's final draft

Transmission Loss formulas for junctions taking into accountin-plane waves

In the transmission of vibrations through structural junctions at high frequencies,the distribution of energy between wave types con suffer important variations. It means, for example, that incoming energy concentrated in a bending wave(out-of-plane vibration) can be split in transmitted energy of other wave types:bending, quasi-longitudinal or transverse shear waves. The goal of the research is to provide simple formulas to include this phenomenon in a Statistical Energy Analysis (SEA) model through the Coupling Loss Factor (CLF) coefficients. A large number of simulations of a population of junctions is generated by means of a numerical model. Afterwards, this data is post-processed in order to obtain the Transmission Loss (TL) between the different wave types by means of a procedure that mimics the Experimental SEA (it is ESEA with some modifications because in the numerical simulations, the internal loss factor is imposed a priori). Each junction is characterised by means of a parameter that minimises the scattering of the TL data with respect to the approximation formula. Some application examples to building structures are shown.Postprint (published version

Dichroism in a plasmonic lattice based on triskelion nanoelements

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2022, Tutor: Amílcar Labarta RodríguezDichroism is the different optical response obtained for left or right circular polarised light and characteristically occurs in chiral systems. This work is focused on enhancing the dichroism observed in the plasmonic response of Au planar nanoelements (triskelion) showing helicity. Numerical simulations have been performed to study the electromagnetic response of these systems. First, a free-standing triskelion has been studied to obtain its natural response. Then, a triskelion on a silica substrate and two stacked free-standing triskelia have been considered so as to observe the response of 3-dimensional true chiral structures. Finally, a hexagonal array of the triskelion stack has been tested to analyse the hybridisation of localised and collective modes