Debugging and Run-time Monitoring of Active Rules

Especially during the design and tuning of active rules, it is possible that rule execution enters an endless loop, where rules cascade by triggering each other indefinitely, so that their processing does not terminate. Commercial systems detect this situation in a simple way, by keeping counters on the number or depth of cascading rules, and suspending an execution when the counters exceed given thresholds. However, the setting of these counters is quite critical: too low thresholds may cause the halting of rule processing in absence of loops, too high thresholds may reveal a loop only after an expensive processing. In this paper, we propose a technique for revealing loops, which is based on recognizing that a given situation has already occurred in the past and therefore will occur an infinite number of times in the future. We exploit this property to develop cycle monitors, which check at run time that critical rule sequences, detected at compile time, do not repeat forever. We describe the run-time monitoring environment of Chimera, an active DBMS prototype currently under development at the Politecnico di Milano, and we illustrate with a concrete applicative example the results obtained with the cycle monitoring technique.     

Mechanistic Insights into the Cytochrome P450‐Mediated Oxidation and Rearrangement of Littorine in Tropane Alkaloid Biosynthesis

During the biosynthesis of certain tropane alkaloids, littorine ( 1 ) is rearranged to hyoscyamine ( 3 ). Recent evidence indicates that this isomerisation is a two‐step process in which the first step is an oxidation/rearrangement to give hyoscyamine aldehyde ( 2 ). This step is catalysed by CYP80F1, a cytochrome P450 enzyme, which was recently identified from the plant Hyoscyamus niger; CYP80F1 also catalyses the hydroxylation of littorine at the 3′‐position. The mechanisms of the reactions catalysed by CYP80F1 were probed with synthetic deutero and arylfluoro analogues of 1 . Measurement of the primary kinetic isotope effects indicates that C3′ hydrogen abstraction is the rate‐limiting step for the oxidation/rearrangement of natural littorine, and for the 3′‐hydroxylation reaction of the unnatural S enantiomer of littorine. The character of the intermediates in the oxidation/rearrangement and hydroxylation reaction was probed with the use of arylfluorinated analogues of (R)‐littorine (natural stereoisomer) and (S)‐littorine (unnatural stereoisomer) as substrates for CYP80F1. The relative conversions of ortho‐, meta‐ and para‐fluorolittorine analogues were used to obtain information on the likely intermediacy of either a benzylic radical or benzylic carbocation intermediate. The data suggest that hydroxylation takes place via a benzylic carbocation intermediate, whereas the product profile arising from rearrangement is more consistent with a benzylic radical intermediate.     

CMIS/P++: extensions to CMIS/P for increased expressiveness andefficiency in the manipulation of management information

CMIS/P is the OSI systems management service and protocol used as the base technology for the telecommunications management network. It is a generic object oriented protocol that provides multiple object access capabilities to managed object clusters administered by agent applications. Its navigation and object selection capabilities rely on traversing containment relationships. This is restrictive because information models for emerging broadband technologies (SDH/SONET, ATM) exhibit various other relationships. We present extensions to the CMIS service that provide a richer access language and show how these extensions can be supported by corresponding extensions to the CMIP protocol. These extensions allow traversal of any object relationship and filtering out objects at any stage of the selection process. CMIS++ provides much greater expressive power than CMIS, while CMIP++ supports the remote evaluation of the corresponding expressions, minimizing the management traffic required for complex management information retrieval. These extensions follow an incremental approach, starting from a version compatible with the current standard and gradually adding sophisticated features. The applicability and importance of the proposed concepts is demonstrated through an example from SDH management, while we also discuss implementation considerations     

Model-driven Engineering of Active Context-awareness

More and more Web users ask for contents and services highly tailored to their particular contexts of use. Especially due to the increasing affordability of new and powerful mobile communication devices, they also appreciate the availability of ubiquitous access, independent from the device actually in use. Due to such premises, traditional software design methods need to be extended, and new issues and requirements need to be addressed for supporting context-aware access to services and applications. In this paper we propose a model-driven approach towards adaptive, context-aware Web applications, accompanied by a general-purpose execution framework enabling active context-awareness. Whereas conventional adaptive hypermedia systems address the problem of adapting HTML pages in response to user-generated requests, in this work we especially stress the importance of user-independent, context-triggered adaptivity actions. This finally leads us to interpret the context as an active actor, operating independently from users during their navigations.     

On the existence of surface acoustic waves on piezoelectric substrates

The existence of surface waves on anisotropic materials was proven under fairly general conditions by Lothe and Barnett in 1976. But, until now, the status of surface waves on piezoelectric materials has remained unresolved. This paper presents general existence theorems for surface waves on piezoelectric substrates. It is demonstrated that for short circuit boundary conditions a surface wave solution must exist under virtually any circumstances. However, for a free surface, comparatively stringent existence conditions are required. Numerical examples are given for both free and shorted surfaces, and it is demonstrated that, in some situations, a surface wave solution may not exist for free surface propagation. The existence proofs were developed as a result of theoretical work on Green function modeling, which is now the preferred technique for rigorous SAW and pseudo-SAW device analysis. The mechanisms of the existence proofs and the associated mathematical results give great insight into the structure and properties of the Green functions and include many results that are directly relevant to device analysis     

Systematic Study of the Oxidation of Methane Using Supported Gold Palladium Nanoparticles Under Mild Aqueous Conditions

The oxidation of methane using hydrogen peroxide has been studied using supported gold palladium catalysts prepared using the incipient wetness technique. The effect of reaction conditions and catalyst parameters has been investigated. The supported gold palladium nanoparticles produce methyl hydroperoxide as the primary reaction product which is subsequently converted to methanol with high selectivity, ca. 40–70 %. The selectivity to methanol is influenced by the oxidation state the palladium component of the catalyst. In contrast to homogeneous gold and palladium catalysts the heterogeneous gold palladium nanoalloys are reusable and affords high oxygenate selectivity (ca. 90 %).