Characteristics and problems of unplugged computer science curriculum for young children: comparative and practical research based on the curriculum in four countries

With the progress of computer science education in recent years, more and more educators have brought attention to computer science education among young children. Among all these strategies, the unplugged form has been shown to be more effective in teaching. However, recent studies have focused more on the impact of unplugged computer science courses on young children and less on whether these courses are appropriate for the developmental stage of young children. Therefore, this research summarized the curriculum characteristics by comparing different series of unplugged courses for young children from four nations. Then, in a 7-day workshop conducted in China\u27s urban areas, we explored the issues that arise in the implementation of these courses. This research reveals that, although the existing courses cater to a young age range, four issues can still be found, including difficulty, ability difference, too much cooperation, and emphasis on abstraction. Some of these issues may be handled by instructors, while others need consideration of the connection between curriculum design and the physical and cognitive development levels of young children. Furthermore, this research explored the acceptance of unplugged computer science among Chinese young children as well as its impact on their computational thinking level, achieving positive results

Ultrafast laser microwelding of glass-to-glass and glass-to-opaque materials

Techniques for joining materials, especially glass to dissimilar materials, while maintaining their surface and optical properties are essential for a wide range of industrial applications. Current techniques rely on adhesives or interlayers which can exhibit issues with creep, out-gassing or aging. Ultrafast laser welding based on nonlinear absorption in transparent material offers an attractive solution to this problem. Bringing two material surfaces into close (optical) contact and focusing the ultrafast laser onto the interface allows for localised melting and rapid resolidification, forming strong bond and welding the two surfaces together. The highly localised nature of this absorption means that welds can be created whilst avoiding significant heating of the surrounding material―important for joining materials with significantly different thermal expansion coefficients. Using a picosecond laser system (Trumpf TruMicro), a range of welds between similar material (borosilicate glass to borosilicate glass, fused silica to fused silica, borosilicate glass to fused silica) and highly dissimilar materials (sapphire to stainless steel, fused silica/borosilicate glass to silicon/aluminium/copper/stainless steel) have been demonstrated. Theoretical simulations were carried out to investigate the aberrations that occur to a laser beam focused inside material and to describe the behaviour of the generated plasma. With the guidance of theoretical work and developed experiment setup, a large range of parameters related to welding were investigated both in bulk material and welding for different materials and surface conditions. Shear strength tests on welds shows a maximum value could be obtained between parameters resulting in barely welded seams, for low power, and obvious cracking, for higher power. Optimised welding for borosilicate to borosilicate glass creates stronger bonds (108.8 N/mm2) than traditional joining methods (adhesive, typically 15~25 N/mm2). Parameter maps were made for different surface separation and surface conditions to determine a successful weld. In order to weld highly dissimilar materials, different welding patterns were designed to relax residual stress and eliminate cracks. Welding with galvo-scanner was also introduced as an alternative method for industrial applications which provides a high scan speed and flexible patterns. To increase welding strength and expand the parameter tolerance for a successful welding, focus vibration methods were proposed to reduce the residual stress. Finally, welding of example industrial parts was demonstrated for different application requirements

A Chiral Nonracemic Enolate with Dynamic Axial Chirality: Direct Asymmetric Alkylation of α-Amino Acid Derivatives (SYNTHETIC ORGANIC CHEMISTRY-Fine Organic Synthesis)

The structure of enolate was long believed to be achiral. However, a chiral nonracemic enolate with a racemization barrier of 16 kcal/mol at -78 oC was found to be the crucial intermediate for the asymmetric -methylation of 1 to give 2 in 81% ee and 96% yield. The asymmetric -methylation occurs in other amino acid derivatives (Val, Leu, Trp, His, Tyr, Dopa) in 78-93% ee

Unveiling the Roles of Binder in the Mechanical Integrity of Electrodes for Lithium-Ion Batteries

In lithium-ion secondary batteries research, binders have received the least attention, although the electrochemical performance of Li-ion batteries such as specific capacity and cycle life cannot be achieved if the adhesion strengths between electrode particles and between electrode films and current collectors are insufficient to endure charge-discharge cycling. In this paper, the roles of binders in the mechanical integrity of electrodes for lithium-ion batteries were studied by coupled microscratch and digital image correlation (DIC) techniques. A microscratch based composite model was developed to decouple the carbon particle/particle cohesion strength from the electrode-film/copper-current-collector adhesion strength. The dependences of microscratch coefficient of friction and the critical delamination load on the PVDF binder content suggest that the strength of different interfaces is ranked as follows: Cu/PVDF \u3c carbon-particle/PVDF \u3c PVDF/PVDF. The particle/particle cohesion strength increases while electrode-film/current-collector adhesion strength decreases with increasing PVDF binder content (up to 20% of binder). The electrolyte soaking-and-drying process leads to an increase in particle/particle cohesion but a decrease in electrode-film/copper-current-collector adhesion. Finally, the methodology developed here can provide new guidelines for binder selection and electrode design and lay a constitutive foundation for modeling the mechanical properties and performance of the porous electrodes in lithium-ion batteries