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841.
It is difficult to deny that comparison between recommender systems requires a common way for evaluating them. Nevertheless, at present, they have been evaluated in many, often incompatible, ways. We affirm this problem is mainly due to the lack of a common framework for recommender systems, a framework general enough so that we may include the whole range of recommender systems to date, but specific enough so that we can obtain solid results. In this paper, we propose such a framework, attempting to extract the essential features of recommender systems. In this framework, the most essential feature is the objective of the recommender system. What is more, in this paper, recommender systems are viewed as applications with the following essential objective. Recommender systems must: (i) choose which (of the items) should be shown to the user, (ii) decide when and how the recommendations must be shown. Next, we will show that a new metric emerges naturally from this framework. Finally, we will conclude by comparing the properties of this new metric with the traditional ones. Among other things, we will show that we may evaluate the whole range of recommender systems with this single metric. 相似文献
842.
Using the principle of geochemistry of fluoride, green and cost effective anion adsorbents were developed for the removal of F? from water systems. The scheme was further applied for the removal of NO3? also. Carboxymethylated starch functionalized through network formation with acrylamide was used as adsorbent, and the resultant hydrogels were loaded with Fe2+ ions to generate anchorage for the anions. Sorption of Fe2+ was studied as a function of different factors such as time, temperature, pH, and ion strength. The network having the highest Fe2+ uptake was loaded with the Fe2+ ions under optimum conditions and used for the sorption of F? and NO3?. High efficiency has been observed for F?, as even up to 100% uptake has been observed within just 10 minutes. The support shows high selectivity for NO3?, which was used as anion reference. Thermodynamics of sorption confirms low order and low energy processes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献
843.
844.
845.
Helmus Stärker ÖVE Richard Eltschka ÖVE Gerhard Bartak Günther Brauner ÖVE 《e & i Elektrotechnik und Informationstechnik》2000,117(4):298-301
Ohne Zusammenfassung 相似文献
846.
Tungsten trioxide and two types of tin dioxide were compacted at different pressures and then sintered at different temperatures
in order to study how the microstructure formed is dependent on these parameters. The structures were studied using dilatometric
and porosimetric techniques and also using electron microscopy. X-ray diffraction was used to ascertain the completeness of
the decomposition reaction of SnSO4 being converted to SnO2. Tin dioxide, which was prepared from tin sulphate by calcining, was characterised by a large specific surface area. For
all three materials studied the mean pore size was found to increase and the specific surface area was found to decrease with
increasing sintering temperature. In the case of WO3 the total pore volume decreased markedly as the sintering temperature was increased from 900 to 1000° C. However, in the
case of SnO2, the total pore volume remained almost constant in the sintering temperature range of 600 to 1500° C. In the case of SnO2 derived from SnSO4 the sintered density was about 45% of the theoretical value while for the conventionally made SnO2 the sintered density was about 55% of the theoretical value. The sintered density of WO3 was found to show a marked increase, from 55% to 70% of the theoretical value, as the sintering temperature was raised from
1000 to 1100° C. 相似文献
847.
848.
María del Carmen García‐Martínez Luis M. Rodríguez‐Alcalá Susana Marmesat Leocadio Alonso Javier Fontecha Gloria Márquez‐Ruiz 《International Journal of Food Science & Technology》2010,45(11):2337-2344
Lipid stability of standard infant formula was evaluated at ambient temperatures, namely 25, 30 and 37 °C, during 3 months. Lipids were thoroughly analysed to evaluate changes in fatty acid composition and trans fatty acid isomers, non‐volatile oxidation compounds including oxidised, dimeric and polymeric triacylglycerols, and tocopherol. No significant changes in either of the parameters examined were found in total lipids extracted from infant formula along the storage period. However, the minor free oil fractions (about 7.5% of total lipids) showed a significant increase in oxidation compounds and marked decrease in tocopherol levels during storage at all temperatures. Samples stored at 37 °C for 3 months were rancid and, accordingly, contained the highest oxidation level in the free oil fraction, whereas total lipids extracted were apparently not oxidised. Results showed the necessity of analysing separately the free oil fraction in infant formulae to obtain a clear picture of the oxidation status. 相似文献
849.
850.
We give a careful, fixed-size parameter analysis of a standard (Blum and Micali in SIAM J. Comput. 13(4):850–864, 1984; Goldreich and Levin in Proceedings of 21st ACM Symposium on Theory of Computing, pp. 25–32, 1989) way to form a pseudo-random generator from a one-way function and then pseudo-random functions from said generator (Goldreich
et al. in J. Assoc. Comput. Mach. 33(4):792–807, 1986) While the analysis is done in the model of exact security, we improve known bounds also asymptotically when many bits are
output each round and we find all auxiliary parameters efficiently, giving a uniform result. These optimizations makes the
analysis effective even for security parameters/key-sizes supported by typical block ciphers and hash functions. This enables
us to construct very practical pseudo-random generators with strong properties based on plausible assumptions. 相似文献