59 research outputs found
CAutoCSD-evolutionary search and optimisation enabled computer automated control system design
This paper attempts to set a unified scene for various linear time-invariant (LTI) control system design schemes, by transforming the existing concept of 'Computer-Aided Control System Design' (CACSD) to the novel 'Computer-Automated Control System Design' (CAutoCSD). The first step towards this goal is to accommodate, under practical constraints, various design objectives that are desirable in both time and frequency-domains. Such performance-prioritised unification is aimed to relieve practising engineers from having to select a particular control scheme and from sacrificing certain performance goals resulting from pre-committing to the adopted scheme. With the recent progress in evolutionary computing based extra-numeric, multi-criterion search and optimisation techniques, such unification of LTI control schemes becomes feasible, analytically and practically, and the resultant designs can be creative. The techniques developed are applied to, and illustrated by, three design problems. The unified approach automatically provides an integrator for zero-steady state error in velocity control of a DC motor, meets multiple objectives in designing an LTI controller for a non-minimum phase plant and offers a high-performing LTI controller network for a nonlinear chemical process
Numerical study of carrier velocity for p-type strained silicon MOSFET
Strained induced in the silicon channel layer provides lower effective mass and suppresses intervalley scattering. In this paper, a numerical study of carrier concentration for P-type strained Silicon MOS is presented. Density of state proportion of Fermi-Dirac integral that covers the carrier statistics to all degenerate level is studied and its limits are obtained. In the nondegenerate regime the results replicate Boltzmann statistic and its result is vary in degenerate regime. The Fermi energy with respect to the transformed band edge is a function of carrier concentration for quasi two dimensional strained Silicon PMOS. Based on the Fermi - Dirac statistic, density of state the carrier concentration is obtained. Fermi energy is a function of temperature that independent of the carrier concentration in the nondegenrate regime. In the other strongly degenerate, the Fermi energy is a function of carrier concentration appropriate for given dimensionality, but is independent of temperature. The limitations on carrier drift due to high-field streamlining of otherwise randomly velocity vector in equilibrium is reported. The results are based on asymmetrical distribution function that converts randomness in zero-field to streamlined one in a very high electric field. The ultimate drift velocity is found to be appropriate thermal velocity for a given dimensionality for non- degenerately doped nanostructure. However, the ultimate drift velocity is the Fermi velocity for degenerately doped nanostructures
Do diverse landscapes provide for effective natural pest control in subtropical rice?
While the biocontrol potential of natural enemies is well established, it is largely unknown how landscapeāmediated effects on pest and natural enemy communities impact the cascade of biocontrol potential, crop injury, yield and profit, taking into account crop management and surrounding landscape composition.We compared natural biocontrol with chemical control according to local farmersā practice, across the āfull cascadeā from natural enemy and pest abundance to crop injury, yield loss, yield and economic performance. This twoāyear study was conducted in 20 rice fields embedded in a gradient of landscapes from cropādominated to semiānatural habitatādominated, in subtropical China, the world's largest rice producing region.Natural enemies suppressed brown planthopper population growth in unsprayed plots, irrespective of landscape composition. However, crop injury was lower in pesticide treated plots than in unsprayed plots, and yields in sprayed plots were 20% higher than in unsprayed plots. Nevertheless, pesticide applications were only profitable in less than half of the cases when only costs for pesticides were considered, and in less than one third of the cases when costs for pesticides and labour were considered.Synthesis and applications. Our findings question the costāeffectiveness of current chemicalābased pest management in farming, and highlight opportunities for more ecologically based pest management strategies based on the widespread activity of natural enemies. Pest damage and biocontrol, however, are largely independent from the landscape context, which might be due to the smallāscale character of Chinese rice landscapes. To maintain high levels of biocontrol, conserving this smallāscale character appears more important than increasing the proportion of semiānatural habita
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