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- 저자 : Qixin Gao (검색결과 2 건)
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Quantifying AS Path Inflation by Routing Policies
Qixin Gao,Feng Wang,Lixin Gao 보안공학연구지원센터 2016 International Journal of Future Generation Communi Vol.9 No.1
A route in the Internet may take a longer AS path than the shortest AS path due to routing policies. In this paper, we systematically analyze AS paths and quantify the extent to which routing policies inflate AS paths. The results show that AS path inflation in the Internet is more prevalent than expected. We first present the extent of AS path inflation observed from the RouteView and RIPE routing tables. We then employ three common routing policies to show the extent of AS path inflation. We find that No-Valley routing policy causes the least AS path inflation among the three routing policies. Prefer-Customer-and-Peer-over-Provider policy causes the most AS path inflation. In addition, we find that single-homed stub ASes experience more path inflations than transit ASes and multi-homed ASes. The AS pairs with shortest AS path of 3 AS hops experience more path inflations than other AS pairs. Finally, we investigate the AS path inflation on the end-to-end path from end users to two popular content providers, Google and Comcast. Although the majority of the shortest AS paths from end users to the two providers consists of no more than three AS hops, the actual end-to-end paths that the traffic will take are longer than the shortest AS paths in many cases. Quantifying AS path inflation in the Internet has important implications on the extent of routing policies, traffic engineering performed on the Internet, and BGP convergence speed.
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Experimental study on ZnO-TiO2 sorbents for the removal of elemental mercury
Kunzan Qiu,Jinsong Zhou,Pan Qi,Qixin Zhou,Xiang Gao,Zhongyang Luo 한국화학공학회 2017 Korean Journal of Chemical Engineering Vol.34 No.9
ZnO-TiO2 sorbents synthesized by an impregnation method were characterized through XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy) and EDS (Energy dispersive spectrometer) analyses. An experiment concerning the adsorption of Hg0 by ZnO-TiO2 under a simulated fuel gas atmosphere was then conducted in a benchscale fixed-bed reactor. The effects of ZnO loading amounts and reaction temperatures on Hg0 removal performance were analyzed. The results showed that ZnO-TiO2 sorbents exhibited excellent Hg0 removal capacity in the presence of H2S at 150 oC and 200 oC; 95.2% and 91.2% of Hg0 was removed, respectively, under the experimental conditions. There are two possible causes for the H2S reacting on the surface of ZnO-TiO2: (1) H2S directly reacted with ZnO to form ZnS, (2) H2S was oxidized to elemental sulfur (Sad) by means of active oxygen on the sorbent surface, and then Sad provided active absorption sites for Hg0 to form HgS. This study identifies three reasons why higher temperatures limit mercury removal. First, the reaction between Hg0 and H2S is inhibited at high temperatures. Second, HgS, as the resulting product in the reaction of mercury removal, becomes unstable at high temperatures. Third, the desulfurization reaction strengthens at higher temperatures, and it is likely that H2S directly reacts with ZnO, thus decreasing the Sad on the sorbent surfaces.
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