Origin of Local Structures of U-Co Melts: A First-Principles Study

The local structures of U-Co melts have been studied by first-principle calculations. Two sub-peaks are observed in the first peaks of U-U pair distribution functions. The Voronoi polyhedral analyses also show two separate core-shell U-U distances. Therefore, the calculated results propose that U atoms will play dual roles, “chemical” and “topological”, in the local structures of U-Co melts. In addition, the chemical effect of U atoms will be strengthened when containing more U atoms. The interaction of Co and U atoms is slightly affected by the compositions. The Co-centered clusters are mostly prism-like or antiprism-like polyhedral, which can be predicted by the solute-solvent model. The distribution of the coordinated numbers of Co atoms is much narrower than that of U atoms, showing relatively stable Co-centered clusters. The chemical and topological roles of U atoms are intuitively observed in the electron density of U-Co melts, which presents both metallic and covalent bonding characteristics for U-U bonds. In the end, we conclude that the partial localization of U 5f-electron is responsible for the dual roles of U atoms. The present results provide a theoretical understanding of the origin of the local structures of U-Co melts.

Towards emotional responsive mentoring of at-risk students in last-resort programs

Background Mentors guide students in their challenges at school and in life. At-risk students in last-resort programs who are at a high risk of leaving school unqualified are especially in need of highly competent and adaptive mentors. This study therefore aimed to identify mentor qualities as perceived by at-risk students and their mentors that meet students’ needs and mentors’ capabilities. Methods Face-to-face individual semi-structured interviews were conducted with students and mentors of two specialized programs in the Netherlands. Sensitizing concepts, derived from literature, were used to identify themes. Data analysis was conducted using thematic analyses and was validated by performing an audit. Results The mentor qualities that at-risk students and their mentors reported were classified in three different themes. Mentor tasks consisted of guiding and motivating students and providing them with tangible methods of support. Relationships between mentor and student were based on levels of respect, equality, and bonding. Characteristics of mentors related to empathy, care, and trust. Research implications Emotional responsiveness deserves further exploration as it appears to be an underlying concept of being a good mentor. Future research might explore mentor qualities in the context of other last-resort programs for at-risk students. Practical implications Findings implicate that mentors have to walk a tightrope between keeping professional distance and being sensitive, suggesting constant attention to their professional development is needed. Originality In the context of last-resort programs, an alternative perspective on mentoring at-risk students is outlined, based on perceptions of both students and mentors.

Hierarchical Morphology and Formation Mechanism of Collision Surface of Al/Steel Dissimilar Lap Joints via Electromagnetic Pulse Welding

The aim of this study was to characterize detailed microstructural changes and bonding characteristics and identify the formation mechanism of collision surface of Al6061–Q355 steel dissimilar welded joints via electromagnetic pulse welding (EMPW). The collision surface was observed to consist of five zones from the center to the outside. The central non-weld zone exhibited a concave and convex morphology. The welding-affected zone mainly included melting features and porous structures, representing a porous joining. The secondary weld zone presented an obvious mechanical joining characterized by shear plateaus with stripes. The primary weld zone characterized by dimples with cavity features suggested the formation of diffusion or metallurgical bonding. The impact-affected zone denoted an invalid interfacial bonding due to discontinuous spot impact. During EMPW, the impact energy and pressure affected the changes of normal velocity and tangential velocity, and in turn, influenced the interfacial deformation behavior and bonding characteristics, including the formation of micropores which continued to grow into homogeneous or uneven porous structures via cavitation, surface tension, and depressurization, along with the effect of trapped air.

Assessment on Bonding Potentials of Trackless Tack under a Thin Overlay

Trackless tacks are used to minimize the loss of tack materials caused by adherence to moving tires. During the last two decades, the paving industry and highway agencies have had an increasing interest in the use of trackless tacks to ensure an adequate bond between the overlay and the existing pavement. Therefore, the need for more studies on the bonding characteristics of various trackless tacks is growing. The purpose of this study is to measure the bonding potential of trackless tacks and identify several variables that affect the shear resistance in terms of bonding strength and energy using statistical analysis. The improvement of interlayer shear resistance by tack treatment is different depending on the tack and surface types. Higher tack reactivation temperatures increase the interlayer shear resistance. Compaction effort is considered to have only a marginal effect on bond performance. Tack and surface types play a more critical role in determining the shear bond strength than residual tack rate in the field experiment.

Preparation and properties of a novel polystyrene solid-phase fluorescence pH sensor based on a naphthalimide derivative

A novel naphthalimide-based solid-phase fluorescence pH sensor (PS-Acyl-II) is prepared by immobilization of a small molecule probe (II) on polystyrene microspheres through an ester bond and is characterized by Fourier-transform infrared spectroscopy, optical microscope, scanning electron microscope, and conductiometric titrations. The sensor can determine the pH of a solution within the pH 4.0–7.0, free from interference of common metal ions, and can be reused several times. The geometries of II, PS-Acyl-II, and its product with H+ are optimized at the B3LYP/6-31G** level by density functional theory. The charge distribution, orbital interactions, and bonding characteristics are analyzed and compared in detail to discuss the recognition mechanism and structure–fluorescence property relationships.