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Results for “optimal control”

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PubMed1990

Lung function analysis and optimization during artificial ventilation. A personal computer-based system.

In an intensive care unit a personal computer (PC) application for lung function analysis has been in use for 5 years. The PC system is applied to measure conventional and new parameters for diagnosis and therapy. The primary goal was to find parameters which could be used as optimization indices in optimal control systems for mechanical ventilation. Another clinical application of the PC system was as an automatic controller that stabilizes end-tidal CO2 concentration. The controller and the next application, the optimizer, could be integrated into an optimal control system. Such a system is described and a simulation trial of the integrated structure has demonstrated the potential.

Humans↗

PubMed2004

Vibrational molecular quantum computing: basis set independence and theoretical realization of the Deutsch-Jozsa algorithm.

The phase of quantum gates is one key issue for the implementation of quantum algorithms. In this paper we first investigate the phase evolution of global molecular quantum gates, which are realized by optimally shaped femtosecond laser pulses. The specific laser fields are calculated using the multitarget optimal control algorithm, our modification of the optimal control theory relevant for application in quantum computing. As qubit system we use vibrational modes of polyatomic molecules, here the two IR-active modes of acetylene. Exemplarily, we present our results for a Pi gate, which shows a strong dependence on the phase, leading to a significant decrease in quantum yield. To correct for this unwanted behavior we include pressure on the quantum phase in our multitarget approach. In addition the accuracy of these phase corrected global quantum gates is enhanced. Furthermore we could show that in our molecular approach phase corrected quantum gates and basis set independence are directly linked. Basis set independence is also another property highly required for the performance of quantum algorithms. By realizing the Deutsch-Jozsa algorithm in our two qubit molecular model system, we demonstrate the good performance of our phase corrected and basis set independent quantum gates.

Journal Article↗

PubMed2003

Micronized fenofibrate normalizes the enhanced lipidemic response to a fat load in patients with type 2 diabetes and optimal glucose control.

This study evaluated the postprandial (PP) response to an oral fat load in 28 male patients with type 2 diabetes (mean HbA1c of 5.1%), all receiving metformin and performing physical exercise, compared with healthy subjects. The effects of micronized fenofibrate (200 mg once daily) on triglycerides (TG) and retinyl palmitate (RP) responses, lipoprotein mass concentrations, post-heparin lipase activities and coagulation factors were investigated after a 16-week double-blind, placebo-controlled period. Higher and delayed TG response after the oral fat load (P<0.001) corresponding to increases in both intestinally and endogenous TG-rich lipoproteins and lower lipoprotein lipase (LPL) activity 30 and 60 min post-heparin injection (P<0.05) were observed in the patients as compared with controls. Fasting PAI-1 activity, 6 h PP Factor VII and PAI-1 activities were higher in patients (P=0.036, P=0.032 and P=0.017, respectively). After fenofibrate treatment, TG and RP responses and peak LPL activity were no more significantly different from controls at baseline. Compared with placebo, fasting TG-rich lipoproteins and HDL(3) mass concentrations were significantly lower and higher, respectively; PP chylomicrons and very low density lipoprotein (VLDL) mass concentrations were lower; fasting and PP fibrinogen levels were significantly reduced after fenofibrate treatment. Diabetes control was unchanged throughout the study. Fenofibrate normalized the abnormal PP response and improved the fasting lipoprotein abnormalities in patients with type 2 diabetes and optimal glucose control.

Adult↗

PubMed2003

Computational approaches to motor control and their potential role for interpreting motor dysfunction.

PURPOSE OF REVIEW: Computational frameworks, notably internal models and optimal control theory, have led to rapid advances in our understanding of how the brain plans and controls movement. The purpose of this review is to provide an overview of these theoretical ideas, how they have been used to interpret motor control, as well as their potential role for interpreting motor dysfunction. RECENT FINDINGS: There are two general types of internal models, neural processes that mimic the mechanical properties of the limb (and environment). Forward internal models parallel the normal causal flow of the motor periphery and estimate limb motion from motor commands. Inverse internal models perform the reverse process by estimating motor commands from signals related to intended limb motion and/or spatial targets. This framework has led to several important behavioural observations on motor planning, control and learning, and has also been influential for interpreting neural activity in awake, behaving non-human primates. A more recent framework for interpreting motor function is optimal control theory, which recognizes that noise or errors are an inherent feature of the motor system and may influence strategies to plan and control movement. SUMMARY: Internal models and optimal feedback control both provide frameworks for interpreting motor performance, and may be of value for interpreting many motor dysfunctions associated with neurological injuries. Advanced technologies such as robots that have played a key role in these frameworks may be also of considerable value for motor assessment and rehabilitation.

Animals↗

PubMed2000

Optimal glycemic control in type 2 diabetic patients. Does including insulin treatment mean a better outcome?

Type 2 diabetes is a progressive disease with a significant risk for developing late complications. This article presents evidence related to the effect of glycemic control on the outcome of daily symptoms, microvascular complications, and macrovascular complications. Literature limited to Medline and the Cochrane Library was searched primarily for randomized clinical trials. In terms of education, present intervention studies indicate a positive effect on surrogate end points such as glycemic control, knowledge, practical skills, and psychological performance. Studies show improved glycemic control and plasma lipid profiles after moderate weight reduction. However, this positive effect is limited in time because weight is regained. With regard to oral blood glucose-lowering drugs, clinical trials show a significant blood glucose-lowering effect of different available drugs. Both sulfonylurea and metformin have been shown to significantly reduce the risk of microvascular complications. In the U.K. Prospective Diabetes Study, intensive treatment with metformin in obese subjects reduced the risk for any diabetes-related event and stroke. A major problem is that many patients gradually experience increasing hyperglycemia, creating the need for combined treatment with several drugs including insulin. Insulin treatment has been shown to be effective in achieving satisfactory glycemic control over several years. There is also a positive effect on hard end points such as microvascular disease in the eye, kidney, and nerves. In conclusion, present evidence shows that optimal glycemic control can be attained in people with type 2 diabetes, resulting in fewer disease-related symptoms and a reduced risk of late complications.

Blood Glucose↗

PubMed1998

Optimal metabolic control design.

In a previous work [Acerenza, L. (1993). Metabolic Control Design. J. theor. Biol. 165, 63-85] we devised a procedure to design metabolic systems that respond according to pre-established patterns. This procedure includes the mandatory structural and kinetic constraints that narrow the spectrum of responses. In an evolutionary context, the structural and functional features shown during the history of the system would also be conditioned by other factors. Here we incorporate to the Metabolic Control Design procedure two additional requirements that could have influenced metabolic evolution. These are constraints that result from the adaptation to the environment (represented by independent control coefficients that take fixed values) and optimization of metabolic variables at constant total enzyme concentration. To illustrate the general strategy we consider metabolic systems consisting of r reaction steps where the variables are the fluxes, internal metabolite concentrations, enzyme concentrations and control coefficients. In our conditions the number of degrees of freedom, calculated as number of variables minus number of number of relationships, is r - 1. A detailed analysis of three particular schemes, unbranched chain of two and three steps and branch point, with simple linear rate laws is given. Novel results are obtained for the optimization of the input flux of the simple branch point. In the well studied case where there are no evolutionary constraints one of the limbs of the branch point disappears. However, for particular independent control coefficients, when we impose to the control coefficient a fixed value, the branched structure may or may not persist depending on the range to which the fixed value belongs.

Mathematics↗

PubMed1981

[Hemodynamic control by optimization of the cardiac pump].

Transport of energy appears as the ultimate finality of the force convection cardiovascular system. Blood pressure cardiac output and vascular resistances are the three major components of the circulatory system. Among them, blood pressure is regarded as the regulated parameter whose control value is the best adapted parameter, to each kind of activity, neurogenic mechanisms. The authors, considering the physiological variations of blood pressure during increasing energetic loads imposed on the organism, propose a new control function: optimization of cardiac mechanical power necessary to assure convection of the energy needed by the organism. Blood pressure is no more regarded as a constant. Simultaneous changes in cardiac output and blood pressure are both significant, adjusted to realize energetic minimisation of the cardiac pump. This cardiovascular regulation is described by a system of equations whose resolution leads to results in good accordance with physiological data.

Adaptation, Physiological↗

PubMed2003

Effect of unrealistic optimism, perceived control over disease, and experience with female cancer on behavioral intentions of Israeli women to undergo screening tests.

Early detection of cancer can lower mortality rates. Detection tests are available for some cancers such as breast and cervical cancer. Unrealistic optimism can affect compliance with health recommendations. Factors such as past experience (personal or at workplace) and perceived control over the disease influence unrealistic optimism. The purpose of this study was to examine the influence of past experience and perceived control over disease on unrealistic optimism towards breast and cervical cancer, and to examine the effect of unrealistic optimism, perceived control over the disease, and past experience on intentions to undergo screening tests. The study design was quasi-experimental correlative. Past experience was measured among 3 groups of women living in Tel-Aviv ranging in age from 21 to 60 years: oncology nurses (n = 50), obstetric nurses (n = 50), and laywomen (n = 50). These groups were presumed to differ from each other in the extent to which they were aware of cancer. In addition, the 2 types of malignancy represented different levels of awareness. Questionnaires were used to measure the study variables. Experience had a strong impact on unrealistic optimism with both cancers. However, the cancers differed in the impact of unrealistic optimism on behavioral intentions. With breast cancer (the more frequent), there was only a main effect of unrealistic optimism. A 3-way interaction was found with cervical cancer. The results indicate that unrealistic optimism plays a role in predicting participation in early detection testing and should be considered as an influencing factor in health-promoting plans.

Adult↗

PubMed2003

Optimal HIV treatment by maximising immune response.

We present an optimal control model of drug treatment of the human immunodeficiency virus (HIV). Our model is based upon ordinary differential equations that describe the interaction between HIV and the specific immune response as measured by levels of natural killer cells. We establish stability results for the model. We approach the treatment problem by posing it as an optimal control problem in which we maximise the benefit based on levels of healthy CD4+ T cells and immune response cells, less the systemic cost of chemotherapy. We completely characterise the optimal control and compute a numerical solution of the optimality system via analytic continuation.

Algorithms↗

PubMedDate not supplied

Combination therapy with insulin and oral agents: optimizing glycemic control in patients with type 2 diabetes mellitus.

The United Kingdom Prospective Diabetes Study (UKPDS) showed that tight glycemic control with any of several therapeutic regimens has the potential to significantly reduce the risk for long-term microvascular complications of type 2 diabetes. An important question that remains to be answered is what is the best approach to optimizing glycemic control in patients with this disease. This article reviews results of studies in which insulin was used alone or in combination with oral antidiabetic agents for treatment of patients with type 2 diabetes. Analysis of comparative studies (13 in insulin-naive and 26 in previously insulin-treated patients) showed that combination therapy involving one to two insulin injections per day plus oral therapy is usually more effective than insulin monotherapy for achieving and maintaining glycemic control. Combination treatment for type 2 diabetes can be significantly improved by newly developed preparations that lack the major limitations of older products. Once-daily administration of isophane insulin (NPH insulin) is limited by a 15-18-h duration of action and a peak effect that occurs about 6 h after injection. Insulin glargine, a new insulin analogue developed using recombinant DNA technology, has a flat pharmacodynamic profile and a 24-h duration of action. Results from a recent comparative study indicate that insulin glargine plus oral therapy may provide better post-dinner glucose control as well as less symptomatic and nocturnal hypoglycemia than oral therapy combined with NPH insulin. The studies reviewed in the present article support the conclusion that combination therapy with insulin glargine combined with one or more oral antidiabetic agents may be the treatment of choice for achieving glycemic control in patients with type 2 diabetes.

Administration, Oral↗

PubMed2003

Manipulation of self-aggregation patterns and waves in a reaction-diffusion system by optimal boundary control strategies.

Reaction-diffusion systems are of considerable importance in many areas of physical sciences. For many reasons, an external manipulation of the dynamics of these processes is desirable. Here we show numerically how spatiotemporal behavior like pattern formation and wave propagation in a two component nonlinear reaction-diffusion model of bacterial chemotaxis can be externally controlled. We formulate the control goal as an objective functional and apply numerical optimization for the solution of the resulting control problem.

Journal Article↗

PubMed2006

Improving the mixing performance of side channel type micromixers using an optimal voltage control model.

Electroosmotic flow in microchannels is restricted to low Reynolds number regimes. Since the inertia forces are extremely weak in such regimes, turbulent conditions do not readily develop, and hence species mixing occurs primarily as a result of diffusion. Consequently, achieving a thorough species mixing generally relies upon the use of extended mixing channels. This paper aims to improve the mixing performance of conventional side channel type micromixers by specifying the optimal driving voltages to be applied to each channel. In the proposed approach, the driving voltages are identified by constructing a simple theoretical scheme based on a 'flow-rate-ratio' model and Kirchhoff's law. The numerical and experimental results confirm that the optimal voltage control approach provides a better mixing performance than the use of a single driving voltage gradient.

Complex Mixtures↗

PubMed2002

Optimal enhancement of immune response.

MOTIVATION: Therapeutic enhancement of innate immune response to microbial attack is addressed as the optimal control of a dynamic system. Interactions between an invading pathogen and the innate immune system are characterized by four non-linear, ordinary differential equations that describe rates of change of pathogen, plasma cell, and antibody concentrations, and of an indicator of organic health. Without therapy, the dynamic model evidences sub-clinical or clinical decay, chronic stabilization, or unrestrained lethal growth of the pathogen; the response pattern depends on the initial concentration of pathogens in the simulated attack. In the model, immune response can be augmented by therapeutic agents that kill the pathogen directly, that stimulate the production of plasma cells or antibodies, or that enhance organ health. A previous paper demonstrated open-loop optimal control solutions that defeat the pathogen and preserve organ health, given initial conditions that otherwise would be lethal (Stengel et al. (2002)). Therapies based on separate and combined application of the agents were derived by minimizing a quadratic cost function that weighted both system response and control usage, providing implicit control over harmful side effects. RESULTS: We demonstrate the ability of neighboring-optimal feedback control to account for a range of unknown initial conditions and persistent input of pathogens by adjusting the therapy to account for perturbations from the nominal-optimal response history. We examine therapies that combine open-loop control of one agent with closed-loop control of another. We show that optimal control theory points the way toward new protocols for treatment and cure of human diseases. CONTACT: stengel@princeton.edu; rghiglia@princeton.edu; nkulkarn@princeton.edu

Antibodies↗

PubMed1997

Hyperinsulinemia and hypofibrinolysis: effects of short-term optimized glycemic control with continuous insulin infusion in type II diabetic patients.

A defect in the fibrinolytic system results from an increase in type 1 plasminogen activator inhibitor (PAI-1) in diabetes. It can be considered an independent risk factor for the development of cardiovascular disease. In obese and type II diabetic patients, plasma PAI-1 level correlates with fasting insulinemia. However, during the euglycemic clamp, acute hyperinsulinemia does not increase PAI-1 production. The present study was undertaken to investigate the effect of optimized glycemic control by continuous subcutaneous insulin infusion (CSII) on the hypofibrinolytic state for 14 days in 16 type II diabetic patients with poor metabolic control despite maximal oral antidiabetic treatment. Plasma PAI-1 activity levels decreased from 13.38 +/- 2.85 IU/mL to 6.77 +/- 1.81 IU/mL (P = .002) during CSII, along with a concurrent improvement in insulin sensitivity (index obtained by basal glycemia-nadir glycemia/basal glycemia) during the insulin sensitivity test (0.121 +/- 0.03 v 0.057 +/- 0.02, P = .02). These results suggest that insulin resistance rather than hyperinsulinism may be involved in the hypofibrinolytic state in type II diabetic patients. The positive correlation between the changes in triglycerides and in PAI-1 activity (r = .589, P = .026) strongly suggests a role for triglycerides in the impairment of fibrinolysis, which could be a link between insulin resistance and hypofibrinolysis.

Blood Glucose↗

PubMed2002

Breaking the barriers to optimal glycaemic control--what physicians need to know from patients' perspectives.

Diabetes is a largely self-managed disease with a major psychosocial impact on the lives of patients and their families. Coping effectively with the stresses related to living with and having to manage diabetes on a daily basis is not a simple function of education, i.e., knowing "what is right for you." Clearly, knowledge is a prerequisite, but in no way a guarantee, of making the recommended changes in self-care necessary to achieve optimal glycaemic control. To understand patients' self-care behaviour, we need to take into account various psychological and social factors. Behavioural research findings underscore the role of attitudes and illness beliefs as determinants of patients' health behaviours. For example, misperceptions regarding the seriousness and controllability of diabetes can inhibit active participation of the patient in the treatment. A reluctance to start insulin therapy can be observed in patients with type 2 diabetes who have poor glycaemic control on maximum dosage of oral hypoglycaemic agents. This phenomenon of "psychological insulin resistance" clearly demonstrates how even irrational beliefs can impact health outcomes. Misconceptions about having to start insulin treatment ("now I am seriously ill") are often linked to negative emotions, e.g. anger and fear. Negativistic attitudes and low self-efficacy expectations are not uncommon among people with diabetes, precipitated and maintained by repeated experiences of failure to "master" the diabetes and achieve satisfactory diabetes control. Ultimately, cumulative negative experiences can result in a state of "learned helplessness" or "diabetes burnout." Relational conflicts and lack of social support can also seriously hamper patients' self-care behaviours. In addition, contextual factors such as financial barriers and difficulty with access to health care influence peoples' self-care behaviours. In diabetes care, a bio-psychosocial approach to the patient and his or her coping problems is warranted. Learning to understand the patient's perspective will help health care professionals communicate more effectively and tailor the treatment to the needs of the individual.

Adaptation, Psychological↗

PubMedDate not supplied

Proper orthogonal decomposition based optimal neurocontrol synthesis of a chemical reactor process using approximate dynamic programming.

The concept of approximate dynamic programming and adaptive critic neural network based optimal controller is extended in this study to include systems governed by partial differential equations. An optimal controller is synthesized for a dispersion type tubular chemical reactor, which is governed by two coupled nonlinear partial differential equations. It consists of three steps: First, empirical basis functions are designed using the 'Proper Orthogonal Decomposition' technique and a low-order lumped parameter system to represent the infinite-dimensional system is obtained by carrying out a Galerkin projection. Second, approximate dynamic programming technique is applied in a discrete time framework, followed by the use of a dual neural network structure called adaptive critics, to obtain optimal neurocontrollers for this system. In this structure, one set of neural networks captures the relationship between the state variables and the control, whereas the other set captures the relationship between the state and the costate variables. Third, the lumped parameter control is then mapped back to the spatial dimension using the same basis functions to result in a feedback control. Numerical results are presented that illustrate the potential of this approach. It should be noted that the procedure presented in this study can be used in synthesizing optimal controllers for a fairly general class of nonlinear distributed parameter systems.

Models, Chemical↗

PubMed2006

Properties of synergies arising from a theory of optimal motor behavior.

We consider the properties of motor components, also known as synergies, arising from a computational theory (in the sense of Marr, 1982) of optimal motor behavior. An actor's goals were formalized as cost functions, and the optimal control signals minimizing the cost functions were calculated. Optimal synergies were derived from these optimal control signals using a variant of nonnegative matrix factorization. This was done using two different simulated two--joint arms--an arm controlled directly by torques applied at the joints and an arm in which forces were applied by muscles--and two types of motor tasks-reaching tasks and via-point tasks. Studies of the motor synergies reveal several interesting findings. First, optimal motor actions can be generated by summing a small number of scaled and time-shifted motor synergies, indicating that optimal movements can be planned in a low-dimensional space by using optimal motor synergies as motor primitives or building blocks. Second, some optimal synergies are task independent--they arise regardless of the task context-whereas other synergies are task dependent--they arise in the context of one task but not in the contexts of other tasks. Biological organisms use a combination of task--independent and task--dependent synergies. Our work suggests that this may be an efficient combination for generating optimal motor actions from motor primitives. Third, optimal motor actions can be rapidly acquired by learning new linear combinations of optimal motor synergies. This result provides further evidence that optimal motor synergies are useful motor primitives. Fourth, synergies with similar properties arise regardless if one uses an arm controlled by torques applied at the joints or an arm controlled by muscles, suggesting that synergies, when considered in "movement space," are more a reflection of task goals and constraints than of fine details of the underlying hardware.

Animals↗

PubMed1995

Application of high-performance computing to numerical simulation of human movement.

We have examined the feasibility of using massively-parallel and vector-processing supercomputers to solve large-scale optimization problems for human movement. Specifically, we compared the computational expense of determining the optimal controls for the single support phase of gait using a conventional serial machine (SGI Iris 4D25), a MIMD parallel machine (Intel iPSC/860), and a parallel-vector-processing machine (Cray Y-MP 8/864). With the human body modeled as a 14 degree-of-freedom linkage actuated by 46 musculotendinous units, computation of the optimal controls for gait could take up to 3 months of CPU time on the Iris. Both the Cray and the Intel are able to reduce this time to practical levels. The optimal solution for gait can be found with about 77 hours of CPU on the Cray and with about 88 hours of CPU on the Intel. Although the overall speeds of the Cray and the Intel were found to be similar, the unique capabilities of each machine are better suited to different portions of the computational algorithm used. The Intel was best suited to computing the derivatives of the performance criterion and the constraints whereas the Cray was best suited to parameter optimization of the controls. These results suggest that the ideal computer architecture for solving very large-scale optimal control problems is a hybrid system in which a vector-processing machine is integrated into the communication network of a MIMD parallel machine.

Computer Systems↗