35,786 research outputs found
Content-Aware DataGuides for Indexing Large Collections of XML Documents
XML is well-suited for modelling structured data with
textual content. However, most indexing approaches perform
structure and content matching independently, combining
the retrieved path and keyword occurrences in a third
step. This paper shows that retrieval in XML documents can
be accelerated significantly by processing text and structure
simultaneously during all retrieval phases. To this end,
the Content-Aware DataGuide (CADG) enhances the wellknown
DataGuide with (1) simultaneous keyword and path
matching and (2) a precomputed content/structure join. Extensive
experiments prove the CADG to be 50-90% faster
than the DataGuide for various sorts of query and document,
including difficult cases such as poorly structured
queries and recursive document paths. A new query classification
scheme identifies precise query characteristics with
a predominant influence on the performance of the individual
indices. The experiments show that the CADG is applicable
to many real-world applications, in particular large
collections of heterogeneously structured XML documents
Towards Economic Models for MOOC Pricing Strategy Design
MOOCs have brought unprecedented opportunities of making high-quality courses
accessible to everybody. However, from the business point of view, MOOCs are
often challenged for lacking of sustainable business models, and academic
research for marketing strategies of MOOCs is also a blind spot currently. In
this work, we try to formulate the business models and pricing strategies in a
structured and scientific way. Based on both theoretical research and real
marketing data analysis from a MOOC platform, we present the insights of the
pricing strategies for existing MOOC markets. We focus on the pricing
strategies for verified certificates in the B2C markets, and also give ideas of
modeling the course sub-licensing services in B2B markets
On the 7-azaindole in acetonitrile anhydrous solutions as an inappropriate photophysical model for DNA base pairs
Multiple Hydrogen-bonding is a fundamental issue to explain base-pairing in DNA structures, which was firstly described by Watson and Crick^1^ using stable keto tautomer forms. In their analysis, they considered the possibility of mutations via proton transfer reactions within a base pair. Such reactions can be induced by electronic excitation, for example, adenine-cytosine mispairing may be caused by double-proton phototautomerism.^2^ The 7-azaindole (7AI) doubly-hydrogen bonded dimer was firstly proposed as a suitable model for explaining the DNA base mispairing owing to excited state two-proton phototautomerization in 1969 by Taylor _et al_.^3^ The concerted nature of this excited state biprotonic transfer has been strongly supported by available evidence (see references 4-6 and references therein). Recently, Kwon and Zewail^7^ (K&Z) have reported femtosec time-resolved evidence on the stepwise mechanism in polar solvents, using very concentrated solutions of 7AI (0.1 M) in anhydrous acetonitrile, diethylether and dichloromethane on excitation at 320 nm. However, based on a careful spectroscopic analysis of the absorption and emission spectra of anhydrous 0.1 M 7-azaindole solutions in acetonitrile and butyronitrile, we demonstrate in this letter that the 7AI molecule does not form the doubly hydrogen bonded dimer at room temperature (rt) in acetonitrile, but it does generate another aggregate which emits fluorescence at ca. 500 nm. Consequently, the assertion of Kwon and Zewail^7,8^ that the rate of proton transfer in 7-azaindole dimers is significantly dependent on the solvent polarity and its stepwise mechanism for the process is not rightly stated as no C~2h~ dimer is formed in the medium used to record their femtosecond time resolved and fluorescence spectroscopic evidence (viz. 7-azaindole 0.1 M solution in acetonitrile at rt)
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