Search

A fundamental problem in mobile ad hoc and unstructured sensor networks is maintaining connectivity. A network is connected if all nodes have a communication route (typically multi-hop) to each other. Maintaining connectivity is a challenge due to the unstructured nature of the network topology and the frequent occurrence of link and node failures due to interference, mobility, radio channel effects and battery limitations. In order to effectively deploy techniques to improve the resilience of sensor and mobile ad hoc networks against failures or attacks one must be able to identify all the weak points of a network topology. Here we define the weak or critical points of the topology as those links and nodes whose failure results in partitioning of the network. In this dissertation, we propose a set of algorithms to identify the critical points of a network topology. Utilizing these algorithms we study the behavior of critical points and the effect of using only local information in identifying global critical points. Then, we propose both local and global based resilient techniques that can improve the wireless network connectivity around critical points to lessen their importance and improve the network resilience. Next we extend the work to examine the network connectivity for heterogeneous wireless networks that can be result due to factors such as variations in transmission power and signal propagation environments and propose an algorithm to identify the connectivity of the network. We also propose two schemes for constructing additional links to enhance the connectivity of the network and evaluate the network performance of when a random interference factor occurs. Lastly, we implement our resilience techniques to improve the performance.

Analyzing coordinative patterns among limb segments can be a cornerstone in studying human movement and the underlying structure of motor coordination. However, there is much unknown about multi-limb movements, such as how the upper and lower parts of the body move together. Sports which involve hitting a ball with some manipulandum (e.g., a bat, golf club, or tennis racket) offer ecologically valid tasks for exploring multi-limb coordination. Observing golf swings can provide important information about coordination patterns for hitting tasks, and is useful because golf is a popular sport regardless of age.This study addresses the three following issues: (1) the timing invariance of the clubhead force pattern and the weight shift, and adaptive capability for different task demands depending on age and skill level; (2) the predominance of an independent timing structure for upper and lower body coordination and change of this predominance with age; (3) the generalizability of previous research findings for chip shots to more forceful shots. In this study, two groups of older and younger golfers of two different skill levels were compared, using a golf swing as the primary task. Participants attempted two different shots with the same club, requiring the ball to travel different distances of 80-yards and 40-yards.Across golfers, the timing of the force pattern applied to the clubhead changed with the required distances but the weight shift timing was approximately invariant. This dissociation was the complement of the temporal adjustment found for chip shots, in which the clubhead timing was relatively invariant and the weight shift timing was adjusted. Analysis of the temporal variations across repeated attempts at the same shot for each golfer showed that temporal variations in the clubhead force pattern were independent or only weakly correlated with temporal variations of the weight shift for most golfers, similar to previous findings for chip shots. These two findings provide evidence for the presence of two separable, relatively independent rhythmic units in this hitting task.The predominance of this independent temporal structure decreased with age. The older adults also used an additional front foot weight shift to begin most of their shots, and this additional movement may simplify the overall rhythmic structure of their golf swings. The poorer balance capability in older adults was accompanied by more limited trunk rotation during their golf shots. This latter limitation may constrain the efficient transfer of force from the lower body to the trunk and in turn to the clubhead.Meta analysis of a previous chip shot study and the present study demonstrated that the applied backswing force magnitude as a function of trunk rotation was approximated by a non-linear spring characteristic. The effects of skill level were limited to decreased variability in some of the timing and force magnitudes.Overall, these findings may guide more detailed quantitative modeling of golf skill, and the methodology may be applicable to other hitting tasks for the analysis of swing components and whole body coordination.