Nowadays, app developers tend to integrate advertisement libraries (or ad libraries) into their apps to get revenue from ad networks. However, researches have shown that both ad libraries and ad contents could raise serious security and privacy concerns. In this paper, we propose AdCapsule, a user-level solution to practically confine advertisements, including ad libraries and ad contents. Our solution does not need to change the Android framework, nor requires the root privilege, thus can be readily deployed. Specifically, we propose the permission sandbox, which isolates the permissions used by ad libraries from the host app, and the file sandbox, which separates the file operations of advertisements. The ad library and ad content cannot read or write any file outside this sandbox. We have implemented a prototype of AdCapsule. Our evaluation results indicate that AdCapsule can successfully enforce security policies to block attempts of accessing private information or manipulating files of the host app, and the performance overhead introduced by AdCapsule is low.

LLC resonant converter has been widely used in DC-DC converters because of its high efficiency characteristic. However, the output voltage will be accompanied by 120 Hz ripple when the DC input is supplied by an uncontrolled diode rectifier in the 60 Hz grid. In order to remove the double frequency voltage ripple, the quasi-resonant controller is used in this paper, which inherits the advantages of the resonant controller. And the quasi-PI-resonant (quasi-PIR) controller is designed to eliminate AC ripple and keep the output voltage constant. The converter system with the quasi-PIR controller is investigated and compared with traditional PI controller. Experimental results on a 300 W LLC converter are provided. The experimental results show that with 10 V RMS 120 Hz AC voltage at the input of 400 V, the 120 Hz ripple at the output is reduced from 380 mV to 22.5 mV using the quasi-PIR controller instead of the PI controller.