Repair of Sandwich Structure in Support of the Payload Adapter Fitting (PAF) Part II: Severe Damage Repair

As part of a program examining a Payload Adaptor Fitting (PAF) for NASAs Space Launch System (SLS), a repair study of impact damage and misdrilled holes in composite sandwich structure was undertaken.1 In that study, it was shown that small holes and barely visible impact damage (BVID) could be repaired and all the measured undamaged in-plane compression strength recovered without removing the damaged material using a simple patch repair. It was noted that for more severe damage, either larger patches or removal of damage (or both) may be necessary to regain all of the measured undamaged compression strength. This Technical Memorandum (TM) presents the results of an experimental investigation into repair of more severely damaged sandwich structure than what was studied in reference 1

The complex process of scaling the integration of technology enhanced learning in mainstream classrooms

The early optimism for how technology might transform teaching and learning practices in mainstream school classrooms has long faded in many countries around the world. Whilst early research findings suggested that this was due to obvious barriers such as access to the technology itself, more recent attempts to scale student-access have illuminated other factors and provided a more sound theoretical foundation for us to understanding the processes and products of scaling educational technology innovations. This keynote will use findings from key projects and initiatives to highlight what is being learned – and how this might inform future endeavours to realise a more 21st century curriculum

Baselines for Assessment of Choice Programs

Critics of choice argue that it will allow alert and aggressive parents to get the best of everything for their children, leaving poor and minority children concentrated in the worst schools. (Note 1) But choice is not the only mechanism whereby this occurs. Alert and aggressive parents work the bureaucracy to get the best for their children. Thus, choice programs should be compared against the real performance of the current public education system, not its idealized aspirations

Giant Topological Hall Effect in the Noncollinear Phase of Two-Dimensional Antiferromagnetic Topological Insulator MnBi₄Te₇

Magnetic topological insulators provide an important platform for realizing several exotic quantum phenomena, such as the axion insulating state and the quantum anomalous Hall effect, owing to the interplay between topology and magnetism. MnBi4Te7 is a two-dimensional Z(2) antiferromagnetic (AFM) topological insulator with a Ne ' el temperature of similar to 13 K. In AFM materials, the topological Hall effect (THE) is observed owing to the existence of nontrivial spin structures. A material with noncollinearity that develops in the AFM phase rather than at the onset of the AFM order is particularly important. In this study, we observed that such an unanticipated THE starts to develop in a MnBi4Te7 single crystal when the magnetic field is rotated away from the easy axis (c-axis) of the system. Furthermore, the THE resistivity reaches a giant value of similar to 7 mu Omega-cm at 2 K when the angle between the magnetic field and the c-axis is 75 degrees. This value is significantly higher than the values for previously reported systems with noncoplanar structures. The THE can be ascribed to the noncoplanar spin structure resulting from the canted state during the spinflip transition in the ground AFM state of MnBi4Te7. The large THE at a relatively low applied field makes the MnBi4Te7 system a potential candidate for spintronic applications

Berry curvature induced anomalous Hall conductivity in the magnetic topological oxide double perovskite Sr₂FeMoO₆

Oxide materials exhibit several structural, magnetic, and electronic properties. Their stability under ambient conditions, easy synthesis, and high transition temperatures provide such systems with an ideal ground for realizing topological properties and real-life technological applications. However, experimental evidence of topological states in oxide materials is rare. In this paper, we have synthesized single crystals of oxide double perovskite Sr2FeMoO6 and revealed its topological nature by investigating its structural, magnetic, and electronic properties. We observed that the system crystallized in the cubic space group Fm3¯m, which is a half-metallic ferromagnet. Transport measurements show an anomalous Hall effect (AHE), and it is evident that the Hall contribution originates from the Berry curvature. Assuming a shift of the Fermi energy toward the conduction band, the contribution of the AHE is enhanced owing to the presence of a gapped nodal line. This paper can be used to explore and realize the topological properties of bulk oxide systems. © 2022 authors. Published by the American Physical Society

Stereoselective Alder-ene reactions of bicyclo[1.1.0]butanes: facile synthesis of cyclopropyl- and aryl-substituted cyclobutenes

Bicyclo[1.1.0]butanes (BCBs), strained carbocycles comprising two fused cyclopropane rings, have become well-established building blocks in organic synthesis, medicinal chemistry, and chemical biology due to their diverse reactivity profile with radicals, nucleophiles, cations, and carbenes. The constraints of the bicyclic ring system confer high p-character on the interbridgehead C–C bond, leading to this broad reaction profile; however, the use of BCBs in pericyclic processes has to date been largely overlooked in favor of such stepwise, non-concerted additions. Here, we describe the use of BCBs as substrates for ene-like reactions with strained alkenes and alkynes, which give rise to cyclobutenes decorated with highly substituted cyclopropanes and arenes. The former products are obtained from highly stereoselective reactions with cyclopropenes, generated in situ from vinyl diazoacetates under blue light irradiation (440 nm). Cyclobutenes featuring a quaternary aryl-bearing carbon atom are prepared from equivalent reactions with arynes, which proceed in high yields under mild conditions. Mechanistic studies highlight the importance of electronic effects in this chemistry, while computational investigations support a concerted pathway and rationalize the excellent stereoselectivity of reactions with cyclopropenes