Disturbance observer based sliding mode control for a continuous stirred tank reactor (CSTR)

A continuous stirred tank reactor (CSTR) is typical of equipment found in the process control industry. The dynamics represent a wide class of second order nonlinear systems and thus as well as having specific industrial application, control of the CSTR is frequently used as a benchmark problem for application and testing of new control algorithms. Due to the high complexity of the CSTR system, the robust control design problem is challenging. This paper first establishes a mathematical model of the system. A disturbance observer is then designed to estimate the disturbance and a corresponding asymptotically stable sliding mode control is developed. Stability analysis is presented in terms of the Lyapunov method. Finally, based on experimental data, the proposed method is validated using simulation experiments

Host-free Survival of Boll Weevils (Coleoptera: Curculionidae) from Two Regions of Texas

New information regarding boll weevil, Anthonomus grandis Boheman, overwintering is important to efforts to improve efficiency of eradication efforts. The boll weevil diapause remains a contentious issue despite intense study and some evidence suggests the diapause response differs among weevil populations

Distributed model predictive control for the atmospheric and vacuum distillation towers in a petroleum refining process

This paper develops a distributed model predictive control strategy for the atmospheric and vacuum distillation tower, which constitutes a key process involved in refining petroleum. When considering an MPC implementation, it is known that computational complexity can be reduced if the system is first decomposed into multiple smaller dimensional subsystems. Optimally exploiting the modern computer networks available in industry, a distributed model predictive control implementation is developed for the atmospheric and vacuum tower system, which is assumed to be part of a wider petroleum refining process comprised of a number of sub-systems connected in series. For each subsystem, given the availability of mutual communication channels between subsystems and by using an iterative calculation approach, it will be seen that Nash optimality can be achieved. A low-cost solution that is readily implementable online is seen to achieve the control objective. The effectiveness of the approach presented in the paper is validated by the results of nonlinear simulation experiments

Boll Weevil (Coleoptera: Curculionidae) Feeding and Reproduction as Functions of Cotton Square Availability

The influence of food item availability on boll weevil, Anthonomus grandis grandis Boheman, feeding and reproduction was determined by providing different numbers of cotton squares (flower buds) to individual weevils. Squares were replaced daily after a 5-d feeding and mating conditioning period. The number of lifetime punctures produced by boll weevil females and males increased with square availability. The total number of punctures caused by boll weevil females was 2.7-fold higher than that caused by males. Fecundity was significantly higher in the 10:1, 15:1, and 20:1 (squares:female) treatments than in the 1:1 treatment. The relationship between eggs laid per day and the square to female ratio significantly changed over the life of the female, with the largest differences among treatments occurring in the first 3 wk of adulthood. Survival of weevil progeny to adulthood was about two-fold higher in the 10:1, 15:1, and 20:1 treatments than in the 1:1 and 5:1 treatments. When each boll weevil female was provided 10, 15, or 20 cotton squares per day, estimates of a population growth index (percent of immatures surviving to adulthood divided by immature development time) and the exponential rate of increase (rm) were significantly higher than for those provided only one or five squares per day. Boll weevil populations maintained at a square:weevil ratio of 10:1 or above will increase \u3e60-fold each generation (Ro), a rate significantly higher than that exhibited under 5:1 or 1:1 square:female regimens. These data show that daily provision of 10 squares per female provides sufficient resources to elicit a maximal oviposition response in the laboratory. Our results also will be useful in predicting changes in boll weevil populations relative to crop phenology and starting population density

Si microwire-array solar cells

Si microwire-array solar cells with Air Mass 1.5 Global conversion efficiencies of up to 7.9% have been fabricated using an active volume of Si equivalent to a 4 μm thick Si wafer. These solar cells exhibited open-circuit voltages of 500 mV, short-circuit current densities (J_(sc)) of up to 24 mA cm^(-2), and fill factors >65% and employed Al_2O_3 dielectric particles that scattered light incident in the space between the wires, a Ag back reflector that prevented the escape of incident illumination from the back surface of the solar cell, and an a-SiN_x:H passivation/anti-reflection layer. Wire-array solar cells without some or all of these design features were also fabricated to demonstrate the importance of the light-trapping elements in achieving a high J_(sc). Scanning photocurrent microscopy images of the microwire-array solar cells revealed that the higher J_(sc) of the most advanced cell design resulted from an increased absorption of light incident in the space between the wires. Spectral response measurements further revealed that solar cells with light-trapping elements exhibited improved red and infrared response, as compared to solar cells without light-trapping elements

Ionic Tuning of Cobaltites at the Nanoscale

Control of materials through custom design of ionic distributions represents a powerful new approach to develop future technologies ranging from spintronic logic and memory devices to energy storage. Perovskites have shown particular promise for ionic devices due to their high ion mobility and sensitivity to chemical stoichiometry. In this work, we demonstrate a solid-state approach to control of ionic distributions in (La,Sr)CoO$_{3}$ thin films. Depositing a Gd capping layer on the perovskite film, oxygen is controllably extracted from the structure, up-to 0.5 O/u.c. throughout the entire 36 nm thickness. Commensurate with the oxygen extraction, the Co valence state and saturation magnetization show a smooth continuous variation. In contrast, magnetoresistance measurements show no-change in the magnetic anisotropy and a rapid increase in the resistivity over the same range of oxygen stoichiometry. These results suggest significant phase separation, with metallic ferromagnetic regions and oxygen-deficient, insulating, non-ferromagnetic regions, forming percolated networks. Indeed, X-ray diffraction identifies oxygen-vacancy ordering, including transformation to a brownmillerite crystal structure. The unexpected transformation to the brownmillerite phase at ambient temperature is further confirmed by high-resolution scanning transmission electron microscopy which shows significant structural - and correspondingly chemical - phase separation. This work demonstrates room-temperature ionic control of magnetism, electrical resistivity, and crystalline structure in a 36 nm thick film, presenting new opportunities for ionic devices that leverage multiple material functionalities

Workplace violence in Queensland, Australia: the results of a comparative study

[Abstract]: This paper presents the results on workplace violence from a larger study undertaken in 2004. Comparison is made with the results of a similar study undertaken in 2001. The study involved the random sampling of 3000 nurses from the Queensland Nurses’ Union’s membership in the public (acute hospital and community nursing), private (acute hospital and domiciliary nursing) and aged care sectors (both public and private aged care facilities). The self-reported results suggest an increase in workplace violence in all three sectors. Whilst there are differences in the sources of workplace violence across the sectors, the major causes of workplace violence are: clients/patients, visitors/relatives, other nurses, nursing management and medical practitioners. Associations were also found between workplace violence and gender, the designation of the nurse, hours of employment, the age of the nurse, morale and perceptions of workplace safety. Whilst the majority of nurses reported that policies were in place for the management of workplace violence, these policies were not always adequate

Is tagging with visual implant elastomer a reliable technique for marking earthworms?

Visual implant elastomer (VIE) has recently been employed to investigate different aspects of earthworm ecology. However, a number of fundamental questions relating to the detection and positioning of the tag, its persistence and potential effects on earthworms remain unknown. Seven earthworm species belonging to three ecological groupings, with different pigmentation and burrowing behaviour, were tagged using different coloured VIE. External inspection after two days, one week and 1, 10 and 27 months were followed by preservation, dissection and internal inspection. Tags could be seen in living specimens to 27 months, and dissection revealed that in most cases they were lodged in the coelomic cavity, held in place by septa. However, over longer time periods (more than two years), the chlorogogenous tissue tended to bind to the tags and made external observation increasingly difficult. Migration of the VIE material towards the posterior of the earthworm and potential loss of the tag were only observed on rare occasions, and a recovery rate in excess of 98% was recorded. By introducing a reasonable amount of VIE into segments, just after the clitellum, this technique can become a valuable tool in earthworm ecology and life history studies, particularly in short-medium term laboratory and field experiments