Influence of ultrasonic vibration on the microstructure and texture evolution of AZ91 magnesium alloy during ultrasonic-assisted friction stir welding

The aim of this work is to investigate the influence of ultrasonic vibration on the microstructure and texture evolution in ultrasonic-assisted friction stir welding (UaFSW) of AZ91 Mg alloy. Ultrasonic vibration with an amplitude of 15 µm induced to the weld line perpendicularly to the welding direction. A scanning electron microscopy equipped with electron backscattered diffraction (EBSD) was used to investigate the microstructure and texture changes of the joints. A high fraction of low-angle grain boundaries (LAGBs) was observed during the occurrence of dynamic recovery (DRV) in thermomechanically affected zones (TMAZs) of welded specimens. Statistical analysis from the grain boundaries of the stir zone (SZ) revealed that the fraction of high-angle grain boundaries (HAGBs) in the SZ of UaFSW joint is higher than that of the FSW joint. The results along with the formation of simple shear texture components in the SZ of welds imply that continuous dynamic recrystallization (CDRX) is responsible for grain refinement in the SZs. Moreover, vibration associated with UaFSW assisted the DRV and CDRX mechanisms and increases the intensity of the developed texture in the SZ of the UaFSW joint

Addressing the illumination challenge in two‐dimensional face recognition: a survey

Uncontrolled illumination is one of the most widely researched and most encountered face recognition challenges in recent years. In this study, the authors propose the division of algorithms into two categories: (i) relighting and (ii) unlighting. Relighting methods try to match the probe's illumination conditions using a subset of representative gallery images, while unlighting methods seek to suppress the variations. A total of 64 state‐of‐the‐art methods are summarised and categorised in each of the groups. To make this work concise and easy to follow, they restricted themselves to selected conferences/journals and they limited the number of approaches reviewed. Also, eight past state‐of‐the‐art approaches are used in both identification and verification experiments. However, only significant reported results from all methods were compared and organised in tables. The author's main objective is not to provide an exhaustive analysis of each category, but to present a collection of papers that can be useful in identifying research directions. Results indicate that unlighting methods are a better and a practical solution to address illumination challenges