An Evaluation of the Social Dance Program at the Box Elder Junior Division

Social dancing has for many years occupied a position of prominence in the physical education curriculum at the Box Elder Junior Division. It has maintained this position because of the recognized necessity to help students of the junior high age overcome asocial barrier which is quite pronounced

Low cost, SPF aluminum cryogenic tank structure for ALS

Past production work has shown that cryogenic tank structure for the Shuttle Booster Rockets and the Titan system have very high life cycle costs for the fuel tank structure. The tanks are machined stiffener-skin combination that are subsequently formed into the required contour after machining. The material scrap rate for these configurations are usually high, and the loss of a tank panel due to forming or heat treatment problems is very costly. The idea of reducing the amount of scrap material and scrapped structural members has prompted the introduction of built-up structure for cryogenic tanks to be explored on the ALS program. A build-up structure approach that has shown improvements in life cycle cost over the conventional built-up approach is the use of superplastically formed (SPF) stiffened panels (reducing the overall part count and weight for the tank) resistance spot welded (RSW) to outer tank skin material. The stiffeners provide for general stability of the tank, while the skin material provides hoop direction continuity for the loads

Students’ In-class and Out of Class Mathematical Activities

In this chapter, the authors zoom in on students’ in-class and out-of-class practices, use of resources out-of-class, role in assessment practices, responses to active learning initiatives, and in-class mathematical practices. They do so with a sharp theoretical focus on situating students’ mathematical practices in relation to interactions with other students, the teacher, the mathematics, and resources. They conclude by considering how future research might engage in cross-pollination of the above themes and they highlight potential benefits from theoretical networking as well as from deploying theories that are appropriate for, but hitherto under-used in, examining students’ in-class and out-of-class practices in complementary ways.Peer reviewe

Corridors of barchan dunes: stability and size selection

Barchans are crescentic dunes propagating on a solid ground. They form dune fields in the shape of elongated corridors in which the size and spacing between dunes are rather well selected. We show that even very realistic models for solitary dunes do not reproduce these corridors. Instead, two instabilities take place. First, barchans receive a sand flux at their back proportional to their width while the sand escapes only from their horns. Large dunes proportionally capture more than they loose sand, while the situation is reversed for small ones: therefore, solitary dunes cannot remain in a steady state. Second, the propagation speed of dunes decreases with the size of the dune: this leads -- through the collision process -- to a coarsening of barchan fields. We show that these phenomena are not specific to the model, but result from general and robust mechanisms. The length scales needed for these instabilities to develop are derived and discussed. They turn out to be much smaller than the dune field length. As a conclusion, there should exist further - yet unknown - mechanisms regulating and selecting the size of dunes.Comment: 13 pages, 13 figures. New version resubmitted to Phys. Rev. E. Pictures of better quality available on reques