3 research outputs found
Economic Design of XÌ… Control Chart under Double EWMA
Designing of parameters plays an important role in economic design of control charts for lowering the cost and time. Manipulating sample size (n) and sampling interval (h), the effect of double exponentially weighted moving average (DEWMA) model was studied for the Economic Design (ED) of XÌ… control chart. Optimum sizes and level were obtained when the characteristics of an item possesses DEWMA model. When shifts are uncertain the optimal design for DEWMA chart should be more conservative and should be implemented for benefiting the consumers as well as producers
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Enhanced structure determination from powder diffraction data via algorithm optimisation and the use of conformational information
The performance of DASH has been evaluated against powder X-ray diffraction data collected
from 101 molecular crystal structures, representing the most comprehensive testing of a
"structure determination from powder diffraction data" (SDPD) program carried out to date.
These 101 structures cover a broad range of molecular complexities, from very simple (6
degrees of freedom) to very challenging (49 degrees of freedom). 95 of the crystal structures
could be solved with the current version of DASH, going some way to explaining why the
parameterisation of its simulated annealing (SA) algorithm has not been altered since the
launch of the program in 1999.
This thesis explores optimisation of key DASH SA parameters using the program irace. The
irace runs, comprising 255,000 individual DASH runs and requiring approximately 1300 CPU
days of compute time, produced six sets of SA parameters which differed greatly from the
DASH default parameters and which markedly improved the performance of DASH. Further
evaluation of these six sets against all 101 compounds (a further 2874 of days of CPU time),
allowed selection of one best-performing set, which delivered an order of magnitude
improvement in the success rate with which crystal structures were solved. The adoption of
these parameter values as the defaults in future releases of DASH is strongly recommended
and is expected to broaden the range of molecular complexities to which the program can be
applied.
Three distinct approaches to further improving DASH performance, based on introducing prior
conformational knowledge derived from the Cambridge Structural Database (CSD), have also
been assesed. The findings show that inclusion of conformational knowledge brings significant
additional gains in SDPD performance, and that existing implementations of these approaches
in the DASH / CSD System are close to being ready for routine use