On the low frequency acoustic properties of novel multifunctional honeycomb sandwich panels with micro-perforated faceplates

This paper explores further possibilities of structurally-efficient honeycomb sandwich panels by replacing one of the faceplates with the perforated faceplate from the viewpoint of sound absorption coefficient (SAC) as well as sound transmission loss (STL). An analytical model is presented to calculate both the STL and SAC, with the displacements of the two faceplates assumed identical at frequencies below the faceplate resonance frequency. Influences of core configuration are investigated by comparing different honeycomb core designs. Finite element (FE) models are subsequently developed to validate the proposed analytical model, with agreement achieved. Subsequently, parametric surveys, including the influences of perforation ratio, pore size and core configuration on STL and SAC, are conducted based on the analytical model. Unlike classical honeycomb sandwich panels which are poor sound absorbers, honeycomb sandwiches with perforated faceplates lead to high SAC at low frequencies, which in turn brings about increment in the low frequency STL. Moreover, sandwich panels with triangular cores are found to have the lowest peak frequency in the STL and SAC curves compared with the other kinds of sandwich panels having the same effective mass and perforations

Anisotropic acoustical properties of sintered fibrous metals

A combined theoretical and experimental study is carried out to investigate the anisotropic acoustic properties of sintered fibrous metals. In the theoretical model, based on the transversal and longitudinal dynamic mass densities and effective bulk modulus of randomly placed parallel fibers, the dynamic mass densities and effective dynamic bulk modulus of a sintered fibrous metal in the direction normal and parallel to its surface are obtained. Sound absorption coefficient, sound speed and attenuation coefficient in each of the two directions are calculated once the dynamic mass densities and effective dynamic bulk modulus are determined. For validation, experimental measurements are performed, with good agreement between theoretical prediction and measurement data achieved. Subsequent numerical investigations focus on the influence of fiber diameter and porosity on the anisotropic acoustical properties of the sintered fibrous metal. The sintered fibrous metal exhibits better sound absorption/attenuation performance in the parallel direction than in the normal direction. The anisotropy in acoustical properties increases with decreasing fiber diameter and porosity due mainly to increasing interactions between adjacent fibers

Small perforations in corrugated sandwich panel significantly enhance low frequency sound absorption and transmission loss

Numerical and experimental investigations are performed to evaluate the low frequency sound absorption coefficient (SAC) and sound transmission loss (STL) of corrugated sandwich panels with different perforation configurations, including perforations in one of the face plates, in the corrugated core, and in both the face plate and the corrugated core. Finite element (FE) models are constructed with considerations of acoustic-structure interactions and viscous and thermal energy dissipations inside the perforations. The validity of FE calculations is checked against experimental measurements with the tested samples provided by additive manufacturing. Compared with the classical corrugated sandwich without perforation, the corrugated sandwich with perforated pores in one of its face plate not only exhibits a higher SAC at low frequencies but also a better STL as a consequence of the enlarged SAC. The influences of perforation diameter and perforation ratio on the vibroacoustic performance of the sandwich are also explored. For a corrugated sandwich with uniform perforations, the acoustical resonance frequencies and bandwidth in its SAC and STL curves decrease with increasing pore diameter and decreasing perforation ratio. Non-uniform perforation diameters and perforation ratios result in larger bandwidth and lower acoustical resonance frequencies relative to the case of uniform perforations. The proposed perforated sandwich panels with corrugated cores are attractive ultralightweight structures for multifunctional applications such as simultaneous load-bearing, energy absorption, sound proofing and sound absorption

Perturbative and nonperturbative contributions to the strange quark asymmetry in the nucleon

There are two mechanisms for the generation of an asymmetry between the strange and anti-strange quark distributions in the nucleon: nonperturbative contributions originating from nucleons fluctuating into virtual baryon-meson pairs such as $\Lambda K$ and $\Sigma K$, and perturbative contributions arising from gluons splitting into strange and anti-strange quark pairs. While the nonperturbative contributions are dominant in the large-$x$ region, the perturbative contributions are more significant in the small-$x$ region. We calculate this asymmetry taking into account both nonperturbative and perturbative contributions, thus giving a more accurate evaluation of this asymmetry over the whole domain of $x$. We find that the perturbative contributions are generally a few times larger in magnitude than the nonperturbative contributions, which suggests that the best region to detect this asymmetry experimentally is in the region $0.02 < x < 0.03$. We find that the asymmetry may have more than one node, which is an effect that should be taken into account, e.g. for parameterizations of the strange and anti-strange quark distributions used in global analysis of parton distributions.Comment: 14 pages, 4 figures, figures comparing theoretical calculations with NNPDF global analysis added, accepted for publication in EPJ

Fitting the integrated Spectral Energy Distributions of Galaxies

Fitting the spectral energy distributions (SEDs) of galaxies is an almost universally used technique that has matured significantly in the last decade. Model predictions and fitting procedures have improved significantly over this time, attempting to keep up with the vastly increased volume and quality of available data. We review here the field of SED fitting, describing the modelling of ultraviolet to infrared galaxy SEDs, the creation of multiwavelength data sets, and the methods used to fit model SEDs to observed galaxy data sets. We touch upon the achievements and challenges in the major ingredients of SED fitting, with a special emphasis on describing the interplay between the quality of the available data, the quality of the available models, and the best fitting technique to use in order to obtain a realistic measurement as well as realistic uncertainties. We conclude that SED fitting can be used effectively to derive a range of physical properties of galaxies, such as redshift, stellar masses, star formation rates, dust masses, and metallicities, with care taken not to over-interpret the available data. Yet there still exist many issues such as estimating the age of the oldest stars in a galaxy, finer details ofdust properties and dust-star geometry, and the influences of poorly understood, luminous stellar types and phases. The challenge for the coming years will be to improve both the models and the observational data sets to resolve these uncertainties. The present review will be made available on an interactive, moderated web page (sedfitting.org), where the community can access and change the text. The intention is to expand the text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics & Space Scienc

Female chromosome X mosaicism is age-related and preferentially affects the inactivated X chromosome

To investigate large structural clonal mosaicism of chromosome X, we analysed the SNP microarray intensity data of 38,303 women from cancer genome-wide association studies (20,878 cases and 17,425 controls) and detected 124 mosaic X events42Mb in 97 (0.25%) women. Here we show rates for X-chromosome mosaicism are four times higher than mean autosomal rates; X mosaic events more often include the entire chromosome and participants with X events more likely harbour autosomal mosaic events. X mosaicism frequency increases with age (0.11% in 50-year olds; 0.45% in 75-year olds), as reported for Y and autosomes. Methylation array analyses of 33 women with X mosaicism indicate events preferentially involve the inactive X chromosome. Our results provide further evidence that the sex chromosomes undergo mosaic events more frequently than autosomes, which could have implications for understanding the underlying mechanisms of mosaic events and their possible contribution to risk for chronic diseases