The Capacity of Smartphone Peer-To-Peer Networks

We study three capacity problems in the mobile telephone model, a network abstraction that models the peer-to-peer communication capabilities implemented in most commodity smartphone operating systems. The capacity of a network expresses how much sustained throughput can be maintained for a set of communication demands, and is therefore a fundamental bound on the usefulness of a network. Because of this importance, wireless network capacity has been active area of research for the last two decades. The three capacity problems that we study differ in the structure of the communication demands. The first problem is pairwise capacity, where the demands are (source, destination) pairs. Pairwise capacity is one of the most classical definitions, as it was analyzed in the seminal paper of Gupta and Kumar on wireless network capacity. The second problem we study is broadcast capacity, in which a single source must deliver packets to all other nodes in the network. Finally, we turn our attention to all-to-all capacity, in which all nodes must deliver packets to all other nodes. In all three of these problems we characterize the optimal achievable throughput for any given network, and design algorithms which asymptotically match this performance. We also study these problems in networks generated randomly by a process introduced by Gupta and Kumar, and fully characterize their achievable throughput. Interestingly, the techniques that we develop for all-to-all capacity also allow us to design a one-shot gossip algorithm that runs within a polylogarithmic factor of optimal in every graph. This largely resolves an open question from previous work on the one-shot gossip problem in this model

Effects of Long-Term Stowage on the Deployment of Bistable Tape Springs

In the context of strain-energy-deployed space structures, material relaxation effects play a significant role in structures that are stowed for long durations, for example, in a space vehicle prior to launch. Here, the deployment of an ultrathin carbon fiber reinforced plastic (CFRP) tape spring is studied, with the aim of understanding how long-duration stowage affects its deployment behavior. Analytical modeling and experiments show that the deployment time increases predictably with stowage time and temperature, and analytical predictions are found to compare well with experiments. For cases where stress relaxation is excessive, the structure is shown to lose its ability to deploy autonomously

P2_14 Shotgun patterns

This article provides a model of particle collisions for producing shot patterns from shotgun ammunition of a constant mass, for different numbers of pellets. The scatter pattern is found to be Gaussian, and the mean deviation for pellets from the centre increases linearly with range. Interestingly, this deviation is slightly greater for fewer large pellets, than the same mass of smaller pellets

P2_7 Power Curves and Gear Ratios in Bicycles

This article investigates how the power exerted by a cyclist varies with cyclist speed, and gear ratio. From Hill’s relation, both relations are determined and plotted. Suggestions are made on how these results might be useful to recreational and competitive cyclists

P2_10 Shotgun!

This paper looks at the stopping power of shotguns as a function of distance from the target and number of shot in the shell.  This relationship is determined, and it is found that the stopping power falls off quickly for larger numbers of pellets. Avenues for a more thorough investigation are also suggested

P2_13 Dominoes and Self-Organised Criticality

This article presents a very simple model of self-organised criticality using a 1 dimensional system of dominoes. It is found that when the likelihood of a domino falling is small, a power law exists between number of dominoes which fall in each event, and the frequency with which it occurs. This is determined to be of the form y=x-1.88