No abstract

We propose a distributed, scalable, energy-efficient MAC protocol that works despite long, unknown propagation delays of the underwater acoustic medium. This protocol can be used for delay-tolerant applications such as underwater ecological sensor networks between energy-limited nodes. Our protocol differs significantly from ALOHA, MACA, and MACAW protocols in that energy is the main performance metric in our case rather than bandwidth utilization. It is shown that under a realistic underwater sensor network scenario, our proposed MAC protocol wastes only 3 percent of the transmit energy due to collisions, when an average number of 1-hop neighbors is 5, and the duty cycle is 0.004. This distributed, scalable MAC protocol has the potential to serve as a primer for the development of energy-efficient MAC protocols for future underwater sensor networks.

The aim of this study was to estimate time of biomineralization in developmental stages of rat lower incisors. Eruption length was measured. Four stages of incisor development were identified on histologic and microscopic computerized tomography (micro-CT) sections: (1) preodontoblast, (2) dentin matrix secretion, (3) enamel matrix secretion, and (4) enamel calcification. The overall eruption rate of the rat lower incisor was 600 ± 70 µm/day (mean ± SD; n = 12). The length of the enamel secretion was 4.59 ± 0.75 mm in histologic section, was 3.64 ± 0.63 mm in radiographic section, which converts to 180.4 ± 30.0 hours, 145 ± 25 hours respectively (n = 24). These findings suggested that the four biomineralizing developmental stages of the rat incisor took only several days. The significance of this animal study was to provide understanding for the rapid biomineralization process of developing rat tooth germ by analysis of tooth forming period.

We analyze the problem of minimizing the energy required to send a fixed amount of data subject to delay constraints on portable networks. We develop a traffic allocation algorithm based on dynamic programming using a finite time horizon, and assuming that the network topology is uncertain. We demonstrate that portability reduces the energy consumption of wireless networks compared with stationary configurations. The proposed traffic allocation algorithm adaptively finds the optimal allocation strategy for the delay-constrained traffic by exploiting the statistics ofportability in wireless networks. The quantitative results show that the proposed algorithm saves a total energy of up to 55% over a strategy which allocates a constant amount of traffic per stage.