Screening of Starch Quality Traits in Cassava (Manihot esculenta Crantz)

Cassava (Manihot esculenta Crantz) is one of the most important sources of starch in the tropics. There is limited and contradictory information regarding cassava starch characteristics. The International Center for Tropical Agriculture (CIAT) holds in trust FAO's cassava germplasm collection. Starches from 3272 landraces (including 12 wild relatives) and 772 improved clones were extracted and analyzed over a period of several years. In most cases only one starch sample per genotype was analyzed. Average cyanogenic potential was 327 ppm but considerably higher in the landraces (340 ppm) than in improved clones (267 ppm). Average total and reducing sugars were slightly higher in improved clones (4.06 and 1.56%, respectively) than in landraces (3.68 and 1.25%, respectively). Amylose content was similar in both types of germplasm with an average of 20.7%. Average pasting temperature was 65.3°C. Maximum viscosity was 777.5 mPa s, breakdown was 298.1 mPa s, consistency was 155.8 mPa s and setback was ‐144.5 mPa s. The large sample of starches analyzed provides very robust information regarding the actual characteristics of cassava starch.     

Push: An experimental facility for implementing distributed database services in operating systems

Distributed database systems need speciaal operating system support. Support routines can be implemented inside the kernel or at the user level. Kernel-level functions, while efficient, are hard to implement. User-level implementations are easier but suffer from poor performance and lack of security. This article proposes a new approach to supplement or modify kernel facilities for database transaction processing. Our experimental facility, called Push, is based on an extension language interpreted within the kernel. Our implementation provides the efficiency of kernel-resident code as well as the simplicity and safety of user-level programming. This facility enables experimentation that would be difficult and time-consuming in current environments. The overhead of the Push implementation can be factored out to give a good estimate of the performance of a native kernel implementation. We have used Push to implement several kernel-resident services. In the case of multi-RPC and commit protocols, Push implementations significantly improve performance and scalability over user-level implementations. The experiments show the benefits of Push both as an operational tool for improving transaction processing performance and as an experimental tool for investigating the benefits of operating systems extension without costly implementation.This research is supported by NASA and AIRMICS under grant number NAG-1-676, NSF grant IRI-8821398, and AT&T.     

Communication facilities for distributed transaction-processingsystems

The study of communication designs in the context of the Raid system, a robust and adaptable distributed database system for transaction processing, is discussed. Related research work on local interprocess communication, remote interprocess communication, and communication protocols for both local area and wide area networks is briefly summarized. A series of experiments on the performance of the facilities available for building the Raid communication software is described. Raid's communication software, called Raidcomm, has evolved as a result of the knowledge gained both from other systems and from the authors' experiments. Several communication services and mechanisms that can be used to make Raid efficient are identified