Owing to numerous potential applications, wireless sensor networks have been attracting significant research effort recently. The critical challenge that wireless sensor networks often face is to sustain long-term operation on limited battery energy. Coverage maintenance schemes can effectively prolong network lifetime by selecting and employing a subset of sensors in the network to provide sufficient sensing coverage over a target region. We envision future wireless sensor networks composed of a vast number of miniaturized sensors in exceedingly high density. Therefore, the key issue of coverage maintenance for future sensor networks is the scalability to sensor deployment density. In this paper, we propose a novel coverage maintenance scheme, scalable coverage maintenance (SCOM), which is scalable to sensor deployment density in terms of communication overhead (i.e., number of transmitted and received beacons) and computational complexity (i.e., time and space complexity). In addition, SCOM achieves high energy efficiency and load balancing over different sensors. We have validated our claims through both analysis and simulations.
Brain regulation of bodily functions requires interoceptive feedback signals carrying information about the periphery. As mice with low serum IGF-I levels (LID mice) show reduced spontaneous physical activity, we speculated that body vigor information might be conveyed by circulating IGF-I, a regulator of skeletal muscle and bone mass that enters the brain during physical activity. Since hypothalamic orexin neurons, that are involved in regulating physical activity, express IGF-I receptors (IGF-IR), we hypothesized that these neurons might gauge circulating IGF-I levels. Inactivation of IGF-IR in mouse orexin neurons (Firoc mice) reduced spontaneous activity. Firoc mice maintain normal physical fitness but show anxiety- and depressive-like behaviors that seems to interfere with the rewarding effects of exercise, as they were less sensitive to the rewarding actions of exercise. Further, in response to exercise, Firoc mice showed reduced activation of hypothalamic orexin neurons and ventro-tegmental area (VTA) monoaminergic neurons, as indicated by c-fos staining. Collectively, these results suggest that circulating IGF-I is gauged by orexin neurons to modulate physical activity in part by stimulation of the VTA to motivate motor output. Hence, serum IGF-I may constitute a feedback signal, informing orexin neurons to adapt physical activity to physical vigor.
This research investigates transient behaviors of a rotor passing through resonance in a highsuperconducting bearing system. Such a low-damping multi-degree-of-freedom system, subjected to nonlinear force, can show complex dynamical behaviors, in which energy transfer occurs between modes through nonlinear coupling. Our numerical and experimental results show that, in a system of a high-Tc superconducting bearing, internal resonance can occur even in transient cases where the rotor passes through resonance. Effects of the internal resonance and also effects of the spin-up rate on the transient dynamics of the rotor have been examined and clarified by changing the period of increasing voltage applied to a D.C. motor for rotating the rotor.
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