Wave energy is one of the most attractive forms of renewable energy. The reasons include its promising availability, predictability, persistence, and power density. This study focuses on all linear generator designs and technologies which have been used so far in direct-drive wave energy converters (DD-WECs). Currently, linear permanent magnet generators (LPMG) have been proposed as the most advantageous generator system developed for DD-WECs. After a brief description of linear generator based wave energy converters, all proposed state-of-the-art of LPMG topologies available in the literature are discussed and compared in terms of flux path, core type, location of PMs, and etc. In addition, other linear generator technologies such as linear switched reluctance and linear superconducting generators, as an alternative to LPMGs, are reviewed. Finally, based on the surveyed quantitative comparisons performed in previous works, eight major concepts are evaluated in terms of economic and operational aspects.

Recent advances show that it is possible to reuse the legacy binary code to bridge the semantic gap in virtual machine introspection (VMI). However, existing such VMI solutions often have high performance overhead (up to hundreds of times slowdown), which significantly hinders their practicality especially for cloud providers who wish to perform real-time monitoring of the virtual machine states. As such, this paper presents HYBRID-BRIDGE, a new system that uses an efficient decoupled execution and training memoization approach to automatically bridge the semantic gap. The key idea is to combine the strengths of both offline training based approach and online kernel data redirection based approach, with a novel training data memoization and fall back mechanism at hypervisor layer that decouples the expensive Taint Analysis Engine (TAE) from the execution of hardware-based virtualization and moves the TAE to softwarebased virtualization. The experimental results show that HYBRID-BRIDGE substantially improves the performance overhead of existing binary code reuse based VMI solutions with at least one order of magnitude for many of the tested benchmark tools including ps, netstat, and lsmod. Permission to freely reproduce all or part of this paper for noncommercial purposes is granted provided that copies bear this notice and the full citation on the first page. Reproduction for commercial purposes is strictly prohibited without the prior written consent of the Internet Society, the first-named author (for reproduction of an entire paper only), and the author's employer if the paper was prepared within the scope of employment.

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