Formality theorems for Hochschild complexes and their applications

We give a popular introduction to formality theorems for Hochschild complexes and their applications. We review some of the recent results and prove that the truncated Hochschild cochain complex of a polynomial algebra is non-formal.Comment: Submitted to proceedings of Poisson 200

Advances in Real-Time Database Systems Research Special Section on RTDBS of ACM SIGMOD Record 25(1), March 1996.

A Real-Time DataBase System (RTDBS) can be viewed as an amalgamation of a conventional DataBase Management System (DBMS) and a real-time system. Like a DBMS, it has to process transactions and guarantee ACID database properties. Furthermore, it has to operate in real-time, satisfying time constraints imposed on transaction commitments. A RTDBS may exist as a stand-alone system or as an embedded component in a larger multidatabase system. The publication in 1988 of a special issue of ACM SIGMOD Record on Real-Time DataBases signaled the birth of the RTDBS research area -- an area that brings together researchers from both the database and real-time systems communities. Today, almost eight years later, I am pleased to present in this special section of ACM SIGMOD Record a review of recent advances in RTDBS research. There were 18 submissions to this special section, of which eight papers were selected for inclusion to provide the readers of ACM SIGMOD Record with an overview of current and future research directions within the RTDBS community. In this paper [below], I summarize these directions and provide the reader with pointers to other publications for further information. -Azer Bestavros, Guest Edito

Gene probing reveals the widespread distribution, diversity and abundance of isoprene-degrading bacteria in the environment

Background: Approximately 500 Tg of isoprene are emitted to the atmosphere annually, an amount similar to that of methane, and despite its significant effects on the climate, very little is known about the biological degradation of isoprene in the environment. Isolation and characterisation of isoprene degraders at the molecular level has allowed the development of probes targeting isoA encoding the α-subunit of the isoprene monooxygenase. This enzyme belongs to the soluble diiron centre monooxygenase family and catalyses the first step in the isoprene degradation pathway. The use of probes targeting key metabolic genes is a successful approach in molecular ecology to study specific groups of bacteria in complex environments. Here, we developed and tested a novel isoA PCR primer set to study the distribution, abundance, and diversity of isoprene degraders in a wide range of environments. Results: The new isoA probes specifically amplified isoA genes from taxonomically diverse isoprene-degrading bacteria including members of the genera Rhodococcus, Variovorax, and Sphingopyxis. There was no cross-reactivity with genes encoding related oxygenases from non-isoprene degraders. Sequencing of isoA amplicons from DNA extracted from environmental samples enriched with isoprene revealed that most environments tested harboured a considerable variety of isoA sequences, with poplar leaf enrichments containing more phylogenetically diverse isoA genes. Quantification by qPCR using these isoA probes revealed that isoprene degraders are widespread in the phyllosphere, terrestrial, freshwater and marine environments. Specifically, soils in the vicinity of high isoprene-emitting trees contained the highest number of isoprene-degrading bacteria. Conclusion: This study provides the molecular ecology tools to broaden our knowledge of the distribution, abundance and diversity of isoprene degraders in the environment, which is a fundamental step necessary to assess the impact that microbes have in mitigating the effects of this important climate-active gas

DeeDS Towards a Distributed and Active Real-Time Database System

Introduction There is a great need for building research prototypes of real-time database systems, because existing techniques are often ad hoc or concealed in internal solutions, and few, if any, commercial offerings exist. As real-time applications inherently use reactive mechanisms, and a wealth of results now exists on active database management systems [5], we decided to build DeeDS, a [D]istributed Activ[e], Real-Tim[e] [D]atabase [S]ystem prototype. This research effort is challenging due to the unique combination of reactive mechanisms, distributed technology, dynamic scheduling, and integrated monitoring, under a mixture of soft and hard real-time constraints. To make all this feasible with a limited amount of man-power, we have taken a deliberate approach of building with existing components where possible, and including only those features absolutely necessary to obtain the benefit of each of the architectural dimensions. At the same time, features

DeeDS: A Distributed Active Real-Time Database System

DeeDS combines active database functionality with critical timing constraints and integrated system monitoring. Since the reactive database mechanisms, or rule management system, must meet critical deadlines, we must employ methods that make triggering of rules and execution of actions predictable. We will focus on the scheduling issues associated with dynamic scheduling of workloads where the triggered transactions have hard, firm or soft deadlines, and how transient overloads may be resolved by substituting transactions by computationally cheaper ones. The rationale for a loosely coupled general purpose event monitoring facility, that works in tight connection with the scheduler, is presented. For performance and predictability, the scheduler and event monitor are executing on a separate CPU from the rest of the system. Real-time database accesses in DeeDS are made predictable and efficient by employing methods such as main memory resident data, full replication, eventual consistency, and prevention of global deadlocks