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Understanding the failure mechanisms in textile composites based on acoustic emission signals is a challenging task. In the present work, unsupervised cluster analysis is performed on the acoustic emission data registered during tensile tests on two-dimensional and three-dimensional woven carbon fiber/epoxy composites. The analysis is based on the k-meansþ þ algorithm and principal component analysis. Peak amplitude and frequency features -peak frequency for two-dimensional woven composites and frequency centroid for three-dimensional woven composites -were found to be dominant in cluster analysis. Cluster bounds were identified for both reinforcement types. These bounds do not differ for both reinforcement types and can be used as a starting point for acoustic emission analysis of other carbon fiber/ epoxy composites. The statistics of high-frequency acoustic emission events are compared with the estimates obtained from a fiber bundle model based on Weibull fiber strength statistics. The number of acoustic emission events agrees well with the number of groups of carbon fibers that fail simultaneously. This finding may provide a new way to explain why the Weibull distribution predicts much more fiber breaks than measured by acoustic emission.

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Context. Asteroseismic modelling of the internal structure of main-sequence stars born with a convective core has so far been based on homogeneous analyses of space photometric Kepler light curves of four years in duration, to which most often incomplete inhomogeneously-deduced spectroscopic information was added to break degeneracies. Aims. Our goal is twofold: (1) to compose an optimal sample of gravity-mode pulsators observed by the Kepler space telescope for joint asteroseismic and spectroscopic stellar modelling, and (2) to provide spectroscopic parameters for its members, deduced in a homogeneous way. Methods. We assembled HERMES high-resolution optical spectroscopy at the 1.2 m Mercator telescope for 111 dwarfs, whose Kepler light curves allowed for the determination of their near-core rotation rates. Our spectroscopic information offers additional observational input to also model the envelope layers of these non-radially pulsating dwarfs. Results. We determined stellar parameters and surface abundances from atmospheric analysis with spectrum normalisation based on a new machine-learning tool. Our results suggest a systematic overestimation of metallicity ([M/H]) in the literature for the studied F-type dwarfs, presumably due to normalisation limitations caused by the dense line spectrum of these rotating stars. CNO surface abundances were found to be uncorrelated with the rotation properties of the F-type stars. For the B-type stars, we find a hint of deep mixing from C and O abundance ratios; N abundance uncertainties are too great to reveal a correlation of N with the rotation of the stars. Conclusions. Our spectroscopic stellar parameters and abundance determinations allow for the future joint spectroscopic, astrometric (Gaia), and asteroseismic modelling of this legacy sample of gravity-mode pulsators, with the aim of improving our understanding of transport processes in the core-hydrogen burning phase of stellar evolution.

The eighteenth data release (DR18) of the Sloan Digital Sky Survey (SDSS) is the first one for SDSS-V, the fifth generation of the survey. SDSS-V comprises three primary scientific programs or “Mappers”: the Milky Way Mapper (MWM), the Black Hole Mapper (BHM), and the Local Volume Mapper. This data release contains extensive targeting information for the two multiobject spectroscopy programs (MWM and BHM), including input catalogs and selection functions for their numerous scientific objectives. We describe the production of the targeting databases and their calibration and scientifically focused components. DR18 also includes ∼25,000 new SDSS spectra and supplemental information for X-ray sources identified by eROSITA in its eFEDS field. We present updates to some of the SDSS software pipelines and preview changes anticipated for DR19. We also describe three value-added catalogs (VACs) based on SDSS-IV data that have been published since DR17, and one VAC based on the SDSS-V data in the eFEDS field.

We employ X-ray micro-computed tomography to generate an extensive dataset of voids' characteristics in carbon/epoxy laminates with different stacking sequences. The voids are deliberately induced by modifying the cure cycle. The three-dimensional images with voids are segmented and quantified using an in-house software package, VoxTex. The characteristics of voids, i.e. shape, size parameters, orientation, and spatial location distribution, are obtained. The majority of voids have slightly flattened cross-sections. The voids prefer to localize in the inner plies of the laminate, rather than in the outer ones. Near the laminate mid-thickness, they become more elongated. The stacking sequence affects the size and shape of voids. The planar location of voids is not random and tends to create a pattern, corresponding to the the ply orientations in the laminate. The data is reported in detail, ready to use, for example, as input for modeling studies of similar composites with voids. Response to Reviewers: The response to the reviewer's comments is provided in a separate MS Word file, which is uploaded along with the submission.

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