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With power-related concerns becoming dominant aspects of hardware and software design, significant research effort has been devoted towards system power minimization. Among run-time power-management techniques, dynamic voltage scaling (DVS) has emerged as an important approach, with the ability to provide significant power savings. DVS exploits the ability to control the power consumption by varying a processor's supply voltage (V) and clock frequency (f). DVS controls energy by scheduling different parts of the computation to different (V, f) pairs; the goal is to minimize energy while meeting performance needs. Although processors like the Intel XScale and Transmeta Crusoe allow software DVS control, such control has thus far largely been used at the process/task level under operating system control. This is mainly because the energy and time overhead for switching DVS modes is considered too large and difficult to manage within a single program.In this paper we explore the opportunities and limits of compile-time DVS scheduling. We derive an analytical model for the maximum energy savings that can be obtained using DVS given a few known program and processor parameters. We use this model to determine scenarios where energy consumption benefits from compile-time DVS and those where there is no benefit. The model helps us extrapolate the benefits of compile-time DVS into the future as processor parameters change. We then examine how much of these predicted benefits can actually be achieved through optimal settings of DVS modes. This is done by extending the existing Mixed-integer Linear Program (MILP) formulation for this problem by accurately accounting for DVS energy switching overhead, by providing finer-grained control on settings and by considering multiple data categories in the optimization. Overall, this research provides a comprehensive view of compile-time DVS management, providing both practical techniques for its immediate deployment as well theoretical bounds for use into the future.

In this study, a novel visible-light-driven Bi4O5Br2 photocatalyst was successfully synthesized via the structure reorganization of BiOBr at room temperature using NH3·H2O as a structure-controlling agent. The obtained Bi4O5Br2 exhibited outstanding visible light activity and stability compared to BiOBr and P25 for the degradation of resorcinol. The physicochemical properties of Bi4O5Br2 were analyzed and calculated by modern characterization techniques and density functional theory (DFT). The results revealed that the excellent performance could be mainly attributed to the effect of O-richness on the electronic properties of Bi and Br atoms, unique morphology, high visible-light absorption capacity, and prominent oxidation ability of photo-induced holes. Radical trapping experiments demonstrated that h(+) and ˙OH radicals were the dominant active species. Moreover, a structure reorganization mechanism was proposed, revealing that ammonia and the water-steeping process both played important roles in the fabrication of Bi4O5Br2. We believe that this facile method could be extended to fabricate other three component Bi-O-Br nanostructure systems and help elucidate the relationship between BiOBr and BixOyBrz.

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