Joining the laser welding club: Laser welding is an integral part of modern manufacturing, but it fractures ceramic materials. Penilla et al. developed two methods for welding ceramics using ultrafast lasers. One method tunes the ceramic properties, allowing the laser to transit through the ceramic and weld at the interface between pieces. The other method optimizes a gap between pieces to efficiently deposit energy. Both methods leverage short but energetic pulses to create a melt pool that allows ceramics to be joined, without the high temperature used for traditional ceramic welds. Science , this issue p. 803

Avocado (Persea americana) and papaya (Carica papaya) are tropical fruits with high international demand. However, these commercially important crops are affected by the fungusColletotrichum gloeosporioides, which causes anthracnose and results in significant economic losses. The antifungal activity of metal oxide nanomaterials (zinc oxide (ZnO), magnesium oxide (MgO), and ZnO:MgO and ZnO:Mg(OH)₂composites) prepared under different conditions of synthesis was evaluated against strains ofC. gloeosporioidesobtained from papaya and avocado. All nanoparticles (NPs) at the tested concentrations significantly inhibited the germination of conidia and caused structural damage to the fungal cells. According to the radial growth test, the fungal strain obtained from avocado was more susceptible to the NPs than the strain obtained from papaya. The effect of the tested NPs on the fungal strains confirmed that these NPs could be used as strong antifungal agents againstC.gloeosporioidesto control anthracnose in tropical fruits.

We report a technology for supporting gold nanoparticles (GNPS) with preserved SERS activity in substrates capable of sustaining temperatures as high as the melting point of gold. The material processing involved dispersion of citrate-capped GNPS in colloidal pseudoboehmite. The suspension was dried at 100 °C followed by annealing in air at temperatures of up to 1000 °C. Thus prepared substrates crystallized in γ-Al₂O₃ or θ-Al₂O₃ phases depending on the annealing temperature. XRD, TEM, and Raman spectroscopy characterizations show that GNPS remain nano-crystalline with preserved SERS activity and no apparent changes in size or shape after being treated at high temperatures. These results were also corroborated by the substrate UV-Vis absorption spectra. The SERS enhancement factor for Rhodamine 6G remained stable across the samples and showed no dependence on exposure to harsh environments.

Color-induced changes in stones due to heating can be useful in determining the degree of degradation generated in their components and structure. We evaluate the effect of heating in three types of limestones, useful in building and restoration, corresponding to biomicrite (BC), biosparite (BS), and intramicrite (IM), in the range of temperature from 100°C to 600°C. Our analyses indicate that the strongest changes in reflectance occur in the samples of intramicrite, followed by biomicrite, being biosparite showing the smallest ones. Additionally, IM samples suffer the largest modifications in effective porosity due to the thermal treatment; in contrast, BS and BC samples show smaller temperature-induced alterations associated with smaller changes in reflectance. Moreover, we reveal that most of the thermally induced variations are associated, in this range of temperature, to the dehydroxylation of goethite that transforms into hematite, as well as by the burning and partial release of the organic matter present in the rock. Colorimetry analyses show that the sequence of thermally induced changes can be followed by the evolution of the three coordinates, L (lightness), a (red-green), and b (yellow-blue), of the CIE 1976 Lab space.

In materials science, the knowledge of the thermal properties of thin films on thick substrates is crucial in determining the role of the film in the physical properties of the entire system. Even though the role of the film can be very important, the determination of its thermal properties is a challenging task due to the fact that its contribution to heat transfer is generally hard to single out from the influence of the substrate. Herein, a simple analytical methodology, based on the photoacoustic technique, useful in the thermal characterization of thin films on thick substrates, is presented. The approach is based on illuminating one side of the substrate with a modulated laser beam and monitoring the thermal contrast when a thin film is formed on the opposite side. This methodology allows to unambiguously determine the volumetric heat capacity of micrometric polymeric thin films. The limits of applicability of the method as well as the possibility of performing a full characterization of the thermal properties of the film are discussed.