A key challenge of photoregulated living radical polymerization is developing efficient and robust photocatalysts. Now carbon dots (CDs) have been exploited for the first time as metal-free photocatalysts for visible-light-regulated reversible addition-fragmentation chain-transfer (RAFT) polymerization. Screening of diverse heteroatom-doped CDs suggested that the P- and S-doped CDs were effective photocatalysts for RAFT polymerization under mild visible light following a photoinduced electron transfer (PET) involved oxidative quenching mechanism. PET-RAFT polymerization of various monomers with temporal control, narrow dispersity (Đ≈1.04), and chain-end fidelity was achieved. Besides, it was demonstrated that the CD-catalyzed PET-RAFT polymerization was effectively performed under natural solar irradiation.
In next-generation LTE-advanced cellular networks, Device-to-Device (D2D) communication has emerged as an effective way to offload cellular traffic and improve system performance. Conventionally, a device exclusively relies on cellular communication to retrieve the content it desires. With D2D communication, however, if the same piece of content is available in the vicinity of the device, the content can be directly retrieved from one of its neighbouring devices. Naturally, the key problem becomes how to maximize content sharing via D2D communication. Existing works on content sharing are mainly concerned with a multi-hop communication setting, while works on D2D communication have primarily focused on the communication aspects, including interference avoidance and energy efficiency. In this paper, we study the problem of maximizing cellular traffic offloading with D2D communication, by selectively caching popular content locally, and by exploring maximal matching for sender-receiver pairs. Specifically, we consider an interferenceaware communication model and formulate selective caching as a Knapsack problem, and sender-receiver matching as a maximum weighted matching problem in a bipartite graph. We propose decentralized algorithms to solve both problems, and our simulation results demonstrate that our algorithms are effective in maximizing cellular traffic offloading.
Content Delivery Network (CDN) and Hypertext Transfer Protocol Secure (HTTPS) are two popular but independent web technologies, each of which has been well studied individually and independently. This paper provides a systematic study on how these two work together. We examined 20 popular CDN providers and 10,721 of their customer web sites using HTTPS. Our study reveals various problems with the current HTTPS practice adopted by CDN providers, such as widespread use of invalid certificates, private key sharing, neglected revocation of stale certificates, and insecure back-end communication. While some of those problems are operational issues only, others are rooted in the fundamental semantic conflict between the end-to-end nature of HTTPS and the man-in-the-middle nature of CDN involving multiple parties in a delegated service. To address the delegation problem when HTTPS meets CDN, we proposed and implemented a lightweight solution based on DANE (DNSbased Authentication of Named Entities), an emerging IETF protocol complementing the current Web PKI model. Our implementation demonstrates that it is feasible for HTTPS to work with CDN securely and efficiently. This paper intends to provide a context for future discussion within security and CDN community on more preferable solutions.
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