Optimal dynamic inversion-based semi-active control of benchmark bridge using MR dampers

A new two-stage state feedback control design approach has been developed to monitor the voltage supplied to magnetorheological (MR) dampers for semi-active vibration control of the benchmark highway bridge. The first stage contains a primary controller, which provides the force required to obtain a desired closed-loop response of the system. In the second stage, an optimal dynamic inversion (ODI) approach has been developed to obtain the amount of voltage to be supplied to each of the MR dampers such that it provides the required force prescribed by the primary controller. ODI is formulated by optimization with dynamic inversion, such that an optimal voltage is supplied to each damper in a set. The proposed control design has been simulated for both phase-I and phase-II study of the recently developed benchmark highway bridge problem. The efficiency of the proposed controller is analyzed in terms of the performance indices defined in the benchmark problem definition. Simulation results demonstrate that the proposed approach generally reduces peak response quantities over those obtained from the sample semi-active controller, although some response quantities have been seen to be increasing. Overall, the proposed control approach is quite competitive as compared with the sample semi-active control approach.

Genetic control of nodal root angle in sorghum and its implications on water extraction

Genotypic variability in root system architecture has been associated with root angle of seedlings and water extraction patterns of mature plants in a range of crops. The potential inclusion of root angle as a selection criterion in a sorghum breeding program requires (1) availability of an efficient screening method, (2) presence of genotypic variation with high heritability, and (3) an association with water extraction pattern. The aim of this study was to determine the feasibility for inclusion of nodal root angle as a selection criterion in sorghum breeding programs. A high-throughput phenotypic screen for nodal root angle in young sorghum plants has recently been developed and has been used successfully to identify significant variation in nodal root angle across a diverse range of inbred lines and a mapping population. In both cases, heritabilities for nodal root angle were high. No association between nodal root angle and plant size was detected. This implies that parental inbred lines could potentially be used to asses nodal root angle of their hybrids, although such predictability is compromised by significant interactions. To study effects of nodal root angle on water extraction patterns of mature plants, four inbred lines with contrasting nodal root angle at seedling stage were grown until at least anthesis in large rhizotrons. A consistent trend was observed that nodal root angle may affect the spatial distribution of root mass of mature plants and hence their ability to extract soil water, although genotypic differences were not significant. The potential implications of this for specific adaptation to drought stress are discussed. Results suggest that nodal root angle of young plants can be a useful selection criterion for specific drought adaptation, and could potentially be used in molecular breeding programs if QTLs for root angle can be identified. (C) 2012 Elsevier B.V. All rights reserved.

Weed age affects chemical control of Conyza bonariensis in fallows

In the last decade, Conyza bonariensis has become a widespread and difficult-to-control weed in Australian broad-acre cropping, particularly in glyphosate-based zero-tilled fallows of the subtropical grain region. The first Australian populations of C. bonariensis, where it is known as flaxleaf fleabane, were confirmed resistant to glyphosate in 2010. Control with alternative herbicides in fallows has been inconsistent, with earlier research indicating that weed age could be a potential contributing factor. In two field experiments, the impact of weed age (one, two and three months) was measured on the efficacy of six non-selective herbicide mixtures and sequential applications for control in fallows. In another two experiments we evaluated 11 non-selective herbicides, mixtures and sequential applications applied to one and three month old weeds using higher rates on older weeds. When herbicide rates were consistent for different weed ages, efficacy was reduced only by an average of 1% when two month old weeds were treated compared to one month old weeds. However when applied to three month old weeds, efficacy of treatments was significantly (P < 0.001) reduced by 3-30%. When herbicide rates were increased, weed age had no adverse effect on efficacy, which ranged from 90 to 100%, for amitrole, glyphosate mixed with 2,4-D amine plus picloram, and three sequential application treatments of glyphosate mixtures followed with bipyridyl products. Thus, this problem weed can be controlled effectively and consistently at the rosette stage of one to two months old, or three month old weeds with several different treatments at robust rates. These effective glyphosate alternatives and sequential-application tactics will minimise replenishment of the soil seed-bank and further reduce the risk for further evolution of glyphosate resistance. (C) 2012 Elsevier Ltd. All rights reserved.

The potential for monitoring and control of insect pests in Southern Hemisphere forestry plantations using semiochemicals

Southern Hemisphere plantation forestry has grown substantially over the past few decades and will play an increasing role in fibre production and carbon sequestration in future. The sustainability of these plantations is, however, increasingly under pressure from introduced pests. This pressure requires an urgent and matching increase in the speed and efficiency at which tools are developed to monitor and control these pests. To consider the potential role of semiochemicals to address the need for more efficient pest control in Southern Hemisphere plantations, particularly by drawing from research in other parts of the world. Semiochemical research in forestry has grown exponentially over the last 40 years but has been almost exclusively focussed on Northern Hemisphere forests. In these forests, semiochemicals have played an important role to enhance the efficiency of integrated pest management programmes. An analysis of semiochemical research from 1970 to 2010 showed a rapid increase over time. It also indicated that pheromones have been the most extensively studied type of semiochemical in forestry, contributing to 92% of the semiochemical literature over this period, compared with research on plant kairomones. This research has led to numerous applications in detection of new invasions, monitoring population levels and spread, in addition to controlling pests by mass trapping or disrupting of aggregation and mating signals. The value of semiochemicals as an environmentally benign and efficient approach to managing forest plantation pests in the Southern Hemisphere seems obvious. There is, however, a lack of research capacity and focus to optimally capture this opportunity. Given the pressure from increasing numbers of pests and reduced opportunities to use pesticides, there is some urgency to develop semiochemical research capacity.

Individual-based modelling of the efficacy of fumigation tactics to control lesser grain borer (Rhyzopertha dominica) in stored grain

Increasing resistance to phosphine (PH 3) in insect pests, including lesser grain borer (Rhyzopertha dominica) has become a critical issue, and development of effective and sustainable strategies to manage resistance is crucial. In practice, the same grain store may be fumigated multiple times, but usually for the same exposure period and concentration. Simulating a single fumigation allows us to look more closely at the effects of this standard treatment.We used an individual-based, two-locus model to investigate three key questions about the use of phosphine fumigant in relation to the development of PH 3 resistance. First, which is more effective for insect control; long exposure time with a low concentration or short exposure period with a high concentration? Our results showed that extending exposure duration is a much more efficient control tactic than increasing the phosphine concentration. Second, how long should the fumigation period be extended to deal with higher frequencies of resistant insects in the grain? Our results indicated that if the original frequency of resistant insects is increased n times, then the fumigation needs to be extended, at most, n days to achieve the same level of insect control. The third question is how does the presence of varying numbers of insects inside grain storages impact the effectiveness of phosphine fumigation? We found that, for a given fumigation, as the initial population number was increased, the final survival of resistant insects increased proportionally. To control initial populations of insects that were n times larger, it was necessary to increase the fumigation time by about n days. Our results indicate that, in a 2-gene mediated resistance where dilution of resistance gene frequencies through immigration of susceptibles has greater effect, extending fumigation times to reduce survival of homozygous resistant insects will have a significant impact on delaying the development of resistance. © 2012 Elsevier Ltd.

Biological Control of Oilseed Rape Pests with Entomopathogenic Nematodes

Biological control techniques attract increasing attention as one of the sustainable alternatives to pesticide use in integrated pest management programs. In order to develop sustainable pest management methods for arable crops based on entomopathogenic nematodes (EPN), their efficacy and persistence needed to be investigated, and an economically feasible delivery system had to be developed. In this study, first a survey of entomopathogens was conducted, and a system approach was tested, using the oilseed Brassica (OSB) growing system (OSB, spring wheat, and red clover) as a model. The system approach aimed at determining the potential of Steinernema feltiae (Filipjev) for the control of OSB pests, developing OSB rotation schemes that support EPN persistence, and investigating the impact of the selected biotic and abiotic factors on efficacy and persistence of EPN. This study employed abductive logic (which employs constant interplay between the theory and empirical observation), quantitative methods, and a case study on OSB. Laboratory and field experiments were carried out, and two types of pathogen surveys. A horizontal survey included OSB fields across Estonia, Germany, Poland, Sweden and the UK, while a vertical survey included sampling from two sets of differently managed experimental fields during three years. A new approach was introduced for measuring occurrence, where the prevalence and relative intensity of entomopathogens, biotic agents, and unidentified insect antagonists were determined. The effect of dose, timing, and the application method on S. feltiae in the control of pests in OSB, and the potential of a controlled release delivery system (CRS) were evaluated in the field. Studies on the impact of selected biotic and abiotc factors (Brassica plant, bait insects, developmental stages of Meligethes aeneus Fab., Isaria fumosorosea Wize (Ifr), and organic and synthetic fertilizers) on the efficacy of S. feltiae were conducted in the laboratory. Persistence of S. feltiae in the OSB growing system, and the effect of dose, timing, and the application method, was assessed in the field as part of the efficacy experiments. The impact of selected biotic and abiotic factors on S. feltiae persistence was assessed in laboratory experiments. The pathogen survey showed that the occurrence of entomopathogens is low in the OSB growing system, and that a management system causing less disturbance (ICM) to the soil increases the relative intensity of insect parasitic nematodes and other insect antagonists. A longer study period is required to show any possible impact of ICM on the relative intensity of entomopathogenic fungi, or on the prevalence of entomopathogens. Two different measures of the occurrence yielded different results: the relative intensity revealed the difference between the two different crop management methods, while prevalence did not. The highest efficacy of S. feltiae was achieved by using a low dose and targeting all stages of M. aeneus. When only the larval stage was targeted, the application method and dose had no significant effect. The CRS decreased the pest abundance significantly more than the surface application method. S. feltiae persisted in the OSB fields in Finland for several months, but did not survive the winter. The strain survived for 7 months when it was applied in autumn in Germany, but its populations declined rapidly after winter. The examined biotic and abiotic factors had variable impacts on S. feltiae efficacy and persistence. The two measures, prevalence and relative intensity of entomopathogens, gave valuable information for their use in biocontrol programs. The recommended biocontrol strategy for OSB growing in Finland is inundation and seasonal inoculation of EPN. The impact of some biotic and abiotic factors on S. feltiae efficacy and persistence is significant, and can be used to improve the efficacy of EPN. The CRS is a novel alternative for EPN application, and should also be considered for use on other crops. Keywords: Biological control, inundation, inoculation, conservation, formulation, slow release method, crop rotation, Entomopathogenic nematodes, Steinernema feltiae, oilseed rape pests, Meligethes aeneus, Phyllotreta spp., occurrence, prevalence, intensity, efficacy, persistence, field, Isaria fumosorosea, biotic factors, abiotic factors, interaction, impact, insect stages, integrated crop management, standard (conventional) crop management

Microprocessor-Based Field-Oriented Control of A CSI-Fed Induction Motor Drive

This paper describes the method of field orientation of the stator current vector with respect to the stator, mutual, and rotor flux vectors, for the control of an induction motor fed from a current source inverter (CSI). A control scheme using this principle is described for orienting the stator current with respect to the rotor flux, as this gives natural decoupling between the current coordinates. A dedicated microcomputer system developed for implementing this scheme has been described. The experimental results are also presented.