a very efficient one-pot three-component synthesis of pyran derivatives has been improved by condensation of aldehydes and malononitrile with dimedone under 80 °c using sucrose as natural and biodegradable catalyst in water. this method offers some advantages including inexpensive, high to quantitative yields, short reaction time, and easy work-up. therefore, this methodology is entirely green ...

an efficient and simple procedure for the synthesis of 1,8-dioxo-octahydroxanthenes from the aromatic aldehydes and 5,5-dimethylcyclohexane-1,3-dione (dimedone) in the presence of boric acid [bo3h3 or b(oh)3] as an inexpensive and reusable catalyst is described. the salient features of this methodology are: the elimination of corrosive liquid acids, high yields, simple methodology, short reacti...

Extended-spectrum -lactamases (ESBLs), such as the plasmid-mediated class A TEMand SHV-type enzymes, have developed by stepwise mutations in their structural genes, resulting in either single or multiple amino acid changes in the encoded enzymes, and these changes sufficiently remodel the active site to allow attack on aminothiazolyl compounds. Since they were first identified at the beginning ...

With the growing importance of XML in data exchange, much research has been done in proving flexible query mechanisms to extract data from structured XML documents. The semi-structured nature of XML data and the requirements on query flexibility pose unique challenges to database indexing methods. Recently, ViST that uses suffix tree and BTree was proposed to reduce the search time of the docum...

Agglomeration and addition are the two main algorithmic schemes for constructing a tree distance from a dissimilarity matrix. The former scheme iteratively agglomerates pairs of leaves to form larger and larger clusters, while the latter proceeds by stepwise addition of objects to a growing tree. A third approach involves improving the global fitness of an initial tree by exchanging subtrees. T...

The B method is a well known approach to the formal specification and development of sequential computer programs. Inspired by action systems, the B method has evolved to incorporate system modelling and distributed system development. This extension is called Event-B. Even though several of the structuring mechanisms of the original B method are absent from Event-B, the desire to define and ma...

We propose an approach to perform efficient model-checking of μ-calculus formulae on modular Petri nets. Given a formula φ, each module can be analysed separately, possibly yielding a conclusion about the truth value of φ on the global system. When no conclusion can be drawn locally, a minimal state space preserving φ is computed for the module and can be incrementally composed with others, thu...

Existing encoding schemes and index structures proposed for XML query processing primarily target the containment relationship, specifically the parent–child and ancestor–descendant relationship. The presence of preceding-sibling and following-sibling location steps in the XPath specification, which is the de facto query language for XML, makes the horizontal navigation, besides the vertical na...