Michael J. O'SHea

We analyse a lead climber pendulum fall, a fall that can occur after the climber traverses horizontally away from their highest anchor. The model is based on a spring pendulum with a nonlinear component and incorporates air resistance. The resulting set of equations can be solved numerically using an Excel spreadsheet that is easily implemented by a student. The maximum tension and speed during the fall were calculated for a real dynamic climbing rope. The inclusion of rope elasticity can, under the right conditions, lead to a speed at the bottom of the swing that is less than that found for a stiff rope. The path of the climber is not closed as they swing back and forth, and we analyse radial oscillations to gain further insight. For multiple swings, the air resistance is important for removing energy from the system.

The backpack weight a hiker is capable of carrying depends on several factors. These include the hiker’s weight, body mass index (BMI), fitness, and training. It can also depend on the terrain on which the hiker travels, e.g., off-trail or on-trail. However, online advice has tended to focus on the hiker’s weight and suggests that pack weight should be a certain percentage of the hiker’s weight. We developed a model of how the ability of a hiker to carry a backpack depends on the weight of the hiker. Modeling such real-life situations helps grab the attention of students in introductory physics. We have expanded on our earlier idea and present a more sophisticated model of an adult backpacker. In particular, we generalize our model for scaling of the human frame, and investigate how the ability to carry a backpack (within our model) varies with the form of scaling used.

We have prepared (Sm-Co)/Co multilayers with two different Co thicknes to study the hard magnetic properties (coercivity H_ci and energy product BH_max ) of nanostructured SmCo magnets consisting of hard SmCo and softer higher moment Co phases. Samples are annealed at a temperature in the range 450 – 700°C, for 20 minutes in vacuum (standard anneal) or rapidly annealed for 30 seconds under flowing nitrogen (rapid anneal) to form the hard Sm-Co phase. We find that samples subjected to a standard anneal at 500°C or a rapid anneal at 650°C show the largest energy products in these thin films, about 21 MG.Oe. This is closely related to the fact that the high field magnetization is highest for these anneal temperatures and decreases at higher anneal temperatures.

We have prepared Nb/Dy/Nb trilayers to study size effects on the magnetic and superconductor properties and to look at the influence of the magnetic layer on a superconductor layer in a nanoscale system. We find size effects on the magnetic properties of the Dy layer for thickness less than 10 nm and size effects associated with the superconductor layer for Nb layers of thickness less than 50 nm. In addition increasing the thickness the Dy layer reduces the superconductor transition temperature of the Nb layer.