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We have built a database that provides term vector information for large numbers of pages (hundreds of millions). The basic operation of the database is to take URLs and return term vectors. Compared to computing vectors by downloading pages via HTTP, the Term Vector Database is several orders of magnitude faster, enabling a large class of applications that would be impractical without such a database. This paper describes the Term Vector Database in detail. It also reports on two applications built on top of the database. The first application is an optimization of connectivity-based topic distillation. The second application is a Web page classifier used to annotate results returned by a Web search engine. 相似文献
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Radioprotection of mice by dietary squalene 总被引:1,自引:0,他引:1
Male C3H mice were fed a diet containing 2% squalene for 14 d prior to and 30 d subsequent to exposure to 6, 7 or 8 Gy of
whole body γ-irradiation (Cesium-137). After 14 d on squalene-supplemented diet, plasma and jejunal tissue squalene levels
were 2X and 15X that of controls. Seven days after irradiation, total white cell counts and total lymphocyte counts were substantially
depressed in a radiation dose-dependent manner. Although counts in the squalene group were consistently (18–119%) higher than
those in the corresponding dietary control group, the differences between dietary groups at any single dose were not significant.
Nuclear area of villus cells in the jejunum of both dietary groups was significantly reduced (20%) by day 11 post-irradiation
but the nuclear area in squalene-fed mice was significantly greater (15%) than in controls, before and after irradiation.
There were no differences in body weight as a function of either diet or radiation dose prior to the first observations of
animal lethality. Animal survival was decreased from 100 to 0% at 30 d post-irradiation by radiation doses of 6–8 Gy, with
the greatest difference between dietary groups being observed at 7 Gy (median survival times of 12 and 16 d for control and
squalene groups, respectively). Overall, survival of squalene-fed mice was significantly prolonged compared with control-fed
mice (P=0.0054 by censored multiple regression analysis). It is concluded that squalene conferred some cellular and systemic radioprotection
to mice receiving these lethal whole-body radiation doses. 相似文献
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Graph structure in the Web 总被引:11,自引:0,他引:11
Andrei Broder Ravi Kumar Farzin Maghoul Prabhakar Raghavan Sridhar Rajagopalan Raymie Stata Andrew Tomkins Janet Wiener 《Computer Networks》2000,33(1-6)
The study of the Web as a graph is not only fascinating in its own right, but also yields valuable insight into Web algorithms for crawling, searching and community discovery, and the sociological phenomena which characterize its evolution. We report on experiments on local and global properties of the Web graph using two AltaVista crawls each with over 200 million pages and 1.5 billion links. Our study indicates that the macroscopic structure of the Web is considerably more intricate than suggested by earlier experiments on a smaller scale. 相似文献
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