Model predictive control using dynamic integrated system optimisation and parameter estimation (DISOPE)

DISOPE is a technique for solving optimal control problems where there are differences in structure and parameter values between reality and the model employed in the computations. The model reality differences can also allow for deliberate simplification of model characteristics and performance indices in order to facilitate the solution of the optimal control problem. The technique was developed originally in continuous time and later extended to discrete time. The main property of the procedure is that by iterating on appropriately modified model based problems the correct optimal solution is achieved in spite of the model-reality differences. Algorithms have been developed in both continuous and discrete time for a general nonlinear optimal control problem with terminal weighting, bounded controls and terminal constraints. The aim of this paper is to show how the DISOPE technique can aid receding horizon optimal control computation in nonlinear model predictive control.

A new approach for the solution of the optimal set-point tracking problem for nonlinear systems

In this paper, a discrete time dynamic integrated system optimisation and parameter estimation algorithm is applied to the solution of the nonlinear tracking optimal control problem. A version of the algorithm with a linear-quadratic model-based problem is developed and implemented in software. The algorithm implemented is tested with simulation examples.

Development and application of a novel algorithm for steady-state optimising control using dynamic information

A novel optimising controller is designed that leads a slow process from a sub-optimal operational condition to the steady-state optimum in a continuous way based on dynamic information. Using standard results from optimisation theory and discrete optimal control, the solution of a steady-state optimisation problem is achieved by solving a receding-horizon optimal control problem which uses derivative and state information from the plant via a shadow model and a state-space identifier. The paper analyzes the steady-state optimality of the procedure, develops algorithms with and without control rate constraints and applies the procedure to a high fidelity simulation study of a distillation column optimisation.

Composite control of non-linear singularly perturbed systems: a geometric approach

Using a geometric approach, a composite control—the sum of a slow control and a fast control—is derived for a general class of non-linear singularly perturbed systems. A new and simpler method of composite control design is proposed whereby the fast control is completely designed at the outset. The slow control is then free to be chosen such that the slow integral manifold of the original system approximates a desired design manifold to within any specified order of ε accuracy.

Composite control of non-linear singularly perturbed systems: a geometric approach

Using a geometric approach, a composite control—the sum of a slow control and a fast control—is derived for a general class of non-linear singularly perturbed systems. A new and simpler method of composite control design is proposed whereby the fast control is completely designed at the outset. The slow control is then free to be chosen such that the slow integral manifold of the original system approximates a desired design manifold to within any specified order of ε accuracy.

Optimal growth strategies when mortality and production rates are size-dependent

Pontryagin's maximum principle from optimal control theory is used to find the optimal allocation of energy between growth and reproduction when lifespan may be finite and the trade-off between growth and reproduction is linear. Analyses of the optimal allocation problem to date have generally yielded bang-bang solutions, i.e. determinate growth: life-histories in which growth is followed by reproduction, with no intermediate phase of simultaneous reproduction and growth. Here we show that an intermediate strategy (indeterminate growth) can be selected for if the rates of production and mortality either both increase or both decrease with increasing body size, this arises as a singular solution to the problem. Our conclusion is that indeterminate growth is optimal in more cases than was previously realized. The relevance of our results to natural situations is discussed.

Bifurcation Analysis of Eigenstructure Assignment Control in a Simple Nonlinear Aircraft Model

Aircraft systems are highly nonlinear and time varying. High-performance aircraft at high angles of incidence experience undesired coupling of the lateral and longitudinal variables, resulting in departure from normal controlled � ight. The construction of a robust closed-loop control that extends the stable and decoupled � ight envelope as far as possible is pursued. For the study of these systems, nonlinear analysis methods are needed. Previously, bifurcation techniques have been used mainly to analyze open-loop nonlinear aircraft models and to investigate control effects on dynamic behavior. Linear feedback control designs constructed by eigenstructure assignment methods at a � xed � ight condition are investigated for a simple nonlinear aircraft model. Bifurcation analysis, in conjunction with linear control design methods, is shown to aid control law design for the nonlinear system.

Latching control of a point absorber

In this paper the authors investigate the use of optimal control techniques for improving the efficiency of the power conversion system in a point absorber wave power device. A simple mathematical model of the system is developed and an optimal control strategy for power generation is determined. They describe an algorithm for solving the problem numerically, provided the incident wave force is given. The results show that the performance of the device is significantly improved with the handwidth of the response being widened by the control strategy.

Closed loop design for a simple nonlinear aircraft model using eigenstructure assignment

Aircraft systems are highly nonlinear and time varying. High-performance aircraft at high angles of incidence experience undesired coupling of the lateral and longitudinal variables, resulting in departure from normal controlled flight. The aim of this work is to construct a robust closed-loop control that optimally extends the stable and decoupled flight envelope. For the study of these systems nonlinear analysis methods are needed. Previously, bifurcation techniques have been used mainly to analyze open-loop nonlinear aircraft models and investigate control effects on dynamic behavior. In this work linear feedback control designs calculated by eigenstructure assignment methods are investigated for a simple aircraft model at a fixed flight condition. Bifurcation analysis in conjunction with linear control design methods is shown to aid control law design for the nonlinear system.

Antioxidants and basal cell carcinoma of the skin : a nested case-control study

Objective To investigate the relationship between basal cell carcinoma (BCC) and antioxidant nutrients, specifically carotenoids, vitamin E and selenium.

Methods The Nambour Skin Cancer Study is an ongoing, community-based study of randomly selected adult residents of a township in sub-tropical Queensland, Australia. Using a nested case–control design, incident cases of BCC (n=90) were compared with age and sex matched controls (n=90). Dietary exposure was measured using food frequency questionnaire estimates of intake as well as serum biomarkers. Other determinants of skin cancer including sun exposure were also considered. Dietary intakes were adjusted for energy intake, and serum carotenoids and vitamin E were adjusted for serum cholesterol. Odds ratios were calculated across quartiles of dietary intake and serum biomarkers and linear trends were assessed using logistic regression, adjusting for age, sex and supplement use.

Results and conclusions In this prospective study no significant associations were found between BCC and carotenoids, vitamin E or selenium, as measured by serum biomarkers or dietary intake, although there was a suggestion of a positive association with lutein intake.

Emergency nurse practitioner care and emergency department patient flow: case-control study

Objective: The present study aimed to compare ED waiting times (for medical assessment and treatment), treatment times and length of stay (LOS) for patients managed by an emergency nurse practitioner candidate (ENPC) with patients managed via traditional ED care. Methods: A case–control design was used. Patients were selected using the three most common ED discharge diagnoses for ENPC managed patients: hand/wrist wounds, hand/wrist fractures and removal of plaster of Paris. The ENPC group (n = 102) consisted of patients managed by the ENPC who had ED discharge diagnoses as mentioned above. The control group (n = 623) consisted of patients with the same ED discharge diagnoses who were managed via traditional ED care. Results: There were no significant differences in median waiting times, treatment times and ED LOS between ENPC managed patients and patients managed via traditional ED processes. There appeared to be some variability between diagnostic subgroups in terms of treatment times and ED LOS. Conclusion: Patient flow outcomes for ENPC managed patients are comparable with those of patients managed via usual ED processes.

Predictors of critical care admission in emergency department patients triaged as low to moderate urgency

Aim. This paper is a report of a study to identify predictors of critical care admission in emergency department patients triaged as low to moderate urgency that may be apparent early in the emergency department episode of care.

Background. Observations of clinical practice show that a number of emergency department patients triaged as low to moderate urgency require critical care admission, raising questions about the relationship between illness severity and physiological status early in the emergency department episode of care.

Methods. A retrospective case control design was used. All participants were aged over 18 years, triaged to Australasian Triage Scale categories 3, 4 or 5, and attended emergency department between 1 July 2004 and 30 June 2005. Cases were admitted to intensive care unit or coronary care unit and controls were admitted to general medical or surgical units. Cases (n = 193) and controls (n = 193) were matched by age, gender, emergency department discharge diagnosis and triage category.

Results. Critical care admission associated with: (i) a presenting complaint of nausea, vomiting and diarrhoea (OR = 3·40, 95%CI:1·22–9·47, P = 0·019), (ii) heart rate abnormalities at triage (OR = 2·10, 95%CI:1·19–3·71, P = 0·011), (iii) temperature abnormalities at triage (OR = 2·87 95%CI:1·05–7·89, P = 0·041), (iv) respiratory rate at first nursing assessment (OR = 1·66, 95%CI:1·05–2·06, P = 0·31) or (v) heart rate abnormalities at first nursing assessment (OR = 1·57, 95%CI = 1·04−2·39, P = 0·033).

Conclusion. Derangements in temperature, respiratory rate and heart appear to increase risk of critical care admission. Further work using a prospective approach is needed to establish which physiological parameters have the highest predictive validity, the level(s) of physiological abnormality with highest clinical utility, and the optimal timing for collection of physiological data.

Effect of emergency department fast track on emergency department length of stay : a case-control study

Objective: To examine the effect of fast track on emergency department (ED) length of stay (LOS).

Design and setting: Pair-matched case–control design in a public teaching hospital in metropolitan Melbourne, Australia.

Participants: Patients treated by the ED fast track (cases) between 1 January and 31 March 2007 were compared with patients treated by the usual ED processes (controls) from 1 July to 15 November 2006 (n = 822 matched pairs).

Intervention: ED fast track was established in November 2006 and focused on the management of patients with non-urgent complaints.

Main outcome measures: The primary outcome measure was ED LOS for fast-track patients. Secondary outcomes were waiting times and ED LOS for other ED patients.

Results: Median ED LOS for non-admitted patients was 132 minutes (interquartile range (IQR) 83–205.25) for controls and 116 minutes (IQR 75.5–159.0) for cases (p<0.01). Fast-track patients had a significantly higher incidence of discharge within 2 h (53% vs 44%, p<0.01) and 4 h (92% vs 84%, p<0.01).

Conclusions: ED fast track decreased ED LOS for non-admitted patients without compromising waiting times and ED LOS for other ED patients

Power control in CDMA systems based on channel identification

Power control design is a critical aspect of CDMA cellular systems design. This paper develops an adaptive power controller design method for CDMA systems. The key to the power control design is on the recursive identification of the underlying wireless stochastic channel model parameters. The identification process guarantees the power controller to work well for systems in unknown or time varying network environment.