27 research outputs found
An evaluation of four crop : weed competition models using a common data set
To date, several crop : weed competition models have been developed. Developers of the various models were invited to compare model performance using a common data set. The data set consisted of wheat and Lolium rigidum grown in monoculture and mixtures under dryland and irrigated conditions. Results from four crop : weed competition models are presented: ALMANAC, APSIM, CROPSIM and INTERCOM. For all models, deviations between observed and predicted values for monoculture wheat were only slightly lower than for wheat grown in competition with L. rigidum, even though the workshop participants had access to monoculture data while parameterizing models. Much of the error in simulating competition outcome was associated with difficulties in accurately simulating growth of individual species. Relatively simple competition algorithms were capable of accounting for the majority of the competition response. Increasing model complexity did not appear to dramatically improve model accuracy. Comparison of specific competition processes, such as radiation interception, was very difficult since the effects of these processes within each model could not be isolated. Algorithms for competition processes need to be modularized in such a way that exchange, evaluation and comparison across models is facilitated
An evaluation of four crop : weed competition models using a common data set
To date, several crop : weed competition models have been developed. Developers of the various models were invited to compare model performance using a common data set. The data set consisted of wheat and Lolium rigidum grown in monoculture and mixtures under dryland and irrigated conditions. Results from four crop : weed competition models are presented: ALMANAC, APSIM, CROPSIM and INTERCOM. For all models, deviations between observed and predicted values for monoculture wheat were only slightly lower than for wheat grown in competition with L. rigidum, even though the workshop participants had access to monoculture data while parameterizing models. Much of the error in simulating competition outcome was associated with difficulties in accurately simulating growth of individual species. Relatively simple competition algorithms were capable of accounting for the majority of the competition response. Increasing model complexity did not appear to dramatically improve model accuracy. Comparison of specific competition processes, such as radiation interception, was very difficult since the effects of these processes within each model could not be isolated. Algorithms for competition processes need to be modularized in such a way that exchange, evaluation and comparison across models is facilitated
An enhanced model for digital reference services
Digital Reference Service (DRS) play a vital role in the Digital Library (DL) research.
DRS is a very valuable service provided by DL. Unfortunately, the reference service
movement towards digital environment begins late, and this shift was not model
based. So, a journey towards a digital environment without following a proper model
raises some issues. A few researchers presented a general process model (GPM) in
the late 1990s, but this process model could not overcome the problems of DRS. This
paper proposes an enhanced model for DRS that use the storage and re-use
mechanism with other vital components like DRS search engine and ready reference
for solving the issues in DRS. Initially, storage and re-use mechanism are designed
and finally, DRS search engine is designed to search appropriate answers in the
knowledge base. We improved the GPM by incorporating the new components. The
simulation results clearly states that the proposed model increased the service
efficiency by reducing the response time from days to seconds for repeated questions
and decreased the workload of librarian
Civil-Military Relations: A Comparative Study of Pakistan: From Barracks to Corporate Culture (Paths Toward Re-Democratization: Theoretical and Comparative Considerations
An evaluation of four crop:weed competition models using a common data set
To date, several crop : weed competition models have been developed. Developers of the various models were invited to compare model performance using a common data set. The data set consisted of wheat and Lolium rigidum grown in monoculture and mixtures under dryland and irrigated conditions. Results from four crop : weed competition models are presented: almanac, apsim, cropsim and intercom. For all models, deviations between observed and predicted values for monoculture wheat were only slightly lower than for wheat grown in competition with L. rigidum , even though the workshop participants had access to monoculture data while parameterizing models. Much of the error in simulating competition outcome was associated with difficulties in accurately simulating growth of individual species. Relatively simple competition algorithms were capable of accounting for the majority of the competition response. Increasing model complexity did not appear to dramatically improve model accuracy. Comparison of specific competition processes, such as radiation interception, was very difficult since the effects of these processes within each model could not be isolated. Algorithms for competition processes need to be modularised in such a way that exchange, evaluation and comparison across models is facilitated