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PubMed2004

A novel model of motor learning capable of developing an optimal movement control law online from scratch.

A computational model of a learning system (LS) is described that acquires knowledge and skill necessary for optimal control of a multisegmental limb dynamics (controlled object or CO), starting from "knowing" only the dimensionality of the object's state space. It is based on an optimal control problem setup different from that of reinforcement learning. The LS solves the optimal control problem online while practicing the manipulation of CO. The system's functional architecture comprises several adaptive components, each of which incorporates a number of mapping functions approximated based on artificial neural nets. Besides the internal model of the CO's dynamics and adaptive controller that computes the control law, the LS includes a new type of internal model, the minimal cost (IM(mc)) of moving the controlled object between a pair of states. That internal model appears critical for the LS's capacity to develop an optimal movement trajectory. The IM(mc) interacts with the adaptive controller in a cooperative manner. The controller provides an initial approximation of an optimal control action, which is further optimized in real time based on the IM(mc). The IM(mc) in turn provides information for updating the controller. The LS's performance was tested on the task of center-out reaching to eight randomly selected targets with a 2DOF limb model. The LS reached an optimal level of performance in a few tens of trials. It also quickly adapted to movement perturbations produced by two different types of external force field. The results suggest that the proposed design of a self-optimized control system can serve as a basis for the modeling of motor learning that includes the formation and adaptive modification of the plan of a goal-directed movement.

Adaptation, Physiological↗
PubMed2006

A neuromusculoskeletal tracking method for estimating individual muscle forces in human movement.

A neuromusculoskeletal tracking (NMT) method was developed to estimate muscle forces from observed motion data. The NMT method combines skeletal motion tracking and optimal neuromuscular tracking to produce forward simulations of human movement quickly and accurately. The skeletal motion tracker calculates the joint torques needed to actuate a skeletal model and track observed segment angles and ground forces in a forward simulation of the motor task. The optimal neuromuscular tracker resolves the muscle redundancy problem dynamically and finds the muscle excitations (and muscle forces) needed to produce the joint torques calculated by the skeletal motion tracker. To evaluate the accuracy of the NMT method, kinematics and ground forces obtained from an optimal control (parameter optimization) solution for maximum-height jumping were contaminated with both random and systematic noise. These data served as input observations to the NMT method as well as an inverse dynamics analysis. The NMT solution was compared to the input observations, the original optimal solution, and a simulation driven by the inverse dynamics torques. The results show that, in contrast to inverse dynamics, the NMT method is able to produce an accurate forward simulation consistent with the optimal control solution. The NMT method also requires 3 orders-of-magnitude less CPU time than parameter optimization. The speed and accuracy of the NMT method make it a promising new tool for estimating muscle forces using experimentally obtained kinematics and ground force data.

Algorithms↗
PubMed2004

Efficient algorithms for the laboratory discovery of optimal quantum controls.

The laboratory closed-loop optimal control of quantum phenomena, expressed as minimizing a suitable cost functional, is currently implemented through an optimization algorithm coupled to the experimental apparatus. In practice, the most commonly used search algorithms are variants of genetic algorithms. As an alternative choice, a direct search deterministic algorithm is proposed in this paper. For the simple simulations studied here, it outperforms the existing approaches. An additional algorithm is introduced in order to reveal some properties of the cost functional landscape.

Journal Article↗
PubMed2006

Changing the patterns of failure for high-risk prostate cancer patients by optimizing local control.

PURPOSE: Standard therapies for high-risk prostate cancer have resulted in suboptimal outcomes with both local and distant failures. Prostate-specific antigen (PSA) and distant metastases rates as well as biopsy outcomes are reported after a regimen of trimodality therapy with hormonal, radioactive seed, and external beam radiation therapy to demonstrate how patterns of failure are changed when local control is optimized. METHODS AND MATERIALS: From 1994 to 2003, a total of 360 patients with high-risk prostate cancer were treated with trimodality therapy. Patients were defined as being at high risk if they possessed at least one of the following high-risk features: Gleason score 8 to 10, PSA>20, clinical stage t2c to t3, or two or more intermediate risk features: Gleason score 7, PSA>10 to 20, or stage t2b. Patients were followed for a median of 4.25 years (range, 2 to 10 years). RESULTS: The actuarial 7-year freedom from PSA failure and freedom from distant metastases (FFDM) rates were 83% and 89% respectively. Patients (n=51) developing PSA failure exhibited aggressive disease behavior with short PSA doubling times (median, 5 months) and a 7-year freedom from distant metastases rate of 48%. Local control was high. The last posttreatment biopsy results were negative in 97% of cases (68 of 70 patients). In multivariate analysis, only PSA>20 predicted biochemical failure (p=0.04), and only seminal vesicle status predicted developing distant failure (p=0.01). CONCLUSIONS: Trimodality therapy results in excellent local control that alters patterns of failure, resulting in similar actuarial biochemical and distant failure rates. Most failures appear to be distant and exhibit biologically aggressive behavior.

Androgen Antagonists↗
PubMed2004

Can guideline-defined asthma control be achieved? The Gaining Optimal Asthma ControL study.

For most patients, asthma is not controlled as defined by guidelines; whether this is achievable has not been prospectively studied. A 1-year, randomized, stratified, double-blind, parallel-group study of 3,421 patients with uncontrolled asthma compared fluticasone propionate and salmeterol/fluticasone in achieving two rigorous, composite, guideline-based measures of control: totally and well-controlled asthma. Treatment was stepped-up until total control was achieved (or maximum 500 microg corticosteroid twice a day). Significantly more patients in each stratum (previously corticosteroid-free, low- and moderate-dose corticosteroid users) achieved control with salmeterol/fluticasone than fluticasone. Total control was achieved across all strata: 520 (31%) versus 326 (19%) patients after dose escalation (p < 0.001) and 690 (41%) versus 468 (28%) at 1 year for salmeterol/fluticasone and fluticasone, respectively. Asthma became well controlled in 1,071 (63%) versus 846 (50%) after dose escalation (p < 0.001) and 1,204 (71%) versus 988 (59%) at 1 year. Control was achieved more rapidly and at a lower corticosteroid dose with salmeterol/fluticasone versus fluticasone. Across all strata, 68% and 76% of the patients receiving salmeterol/fluticasone and fluticasone, respectively, were on the highest dose at the end of treatment. Exacerbation rates (0.07-0.27 per patient per year) and improvement in health status were significantly better with salmeterol/fluticasone. This study confirms that the goal of guideline-derived asthma control was achieved in a majority of the patients.

Adrenal Cortex Hormones↗
PubMed2006

Modeling the influence of a laser pulse on the potential energy surface in optimal molecular control theory.

Understanding and modeling the interaction between light and matter is essential to the theory of optical molecular control. While the effect of the electric field on a molecule's electronic structure is often not included in control theory, it can be modeled in an optimal control algorithm by a set or toolkit of potential energy surfaces indexed by discrete values of the electric field strength where the surfaces are generated by Born-Oppenheimer electronic structure calculations that directly include the electric field. Using a new optimal control algorithm with a trigonometric mapping to limit the maximum field strength explicitly, we apply the surface-toolkit method to control the hydrogen fluoride molecule. Potential energy surfaces in the presence and absence of the electric field are created with two-electron reduced-density-matrix techniques. The population dynamics show that adjusting for changes in the electronic structure of the molecule beyond the static dipole approximation can be significant for designing a field that drives a realistic quantum system to its target observable.

Journal Article↗
PubMed1989

Optimal birth control of population dynamics.

The authors studied optimal birth control policies for an age-structured population of McKendrick type which is a distributed parameter system involving 1st order partial differential equations with nonlocal bilinear boundary control. The functional analytic approach of Dubovitskii and Milyutin is adopted in the investigation. Maximum principles for problems with a free end condition and fixed final horizon are developed, and the time optimal control problems, the problem with target sets, and infinite planning horizon case are investigated.

Demography↗
PubMed1995

Artificial intelligence programming with LabVIEW: genetic algorithms for instrumentation control and optimization.

A genetic algorithm for instrumentation control and optimization was developed using the LabVIEW graphical programming environment. The usefulness of this methodology for the optimization of a closed loop control instrument is demonstrated with minimal complexity and the programming is presented in detail to facilitate its adaptation to other LabVIEW applications. Closed loop control instruments have variety of applications in the biomedical sciences including the regulation of physiological processes such as blood pressure. The program presented here should provide a useful starting point for those wishing to incorporate genetic algorithm approaches to LabVIEW mediated optimization of closed loop control instruments.

Algorithms↗
PubMed2005

[Is guideline-defined asthma control achievable?--secondary publication. The Gaining Optimal Asthma ControL (GOAL) Study].

In this study, the percentage of patients with uncontrolled asthma who can achieve guideline-defined asthma control was assessed in 3,421 patients. Significantly more patients (71%) treated with salmeterol-fluticasone achieved asthma control than did patients receiving fluticasone alone (59%). The patients treated with salmeterol-fluticasone achieved asthma control more rapidly and at a lower dose of inhaled corticosteroid than did patients treated with fluticasone alone. Achievement of asthma control was associated with marked improvements in exacerbation rates and quality of life. Thus guideline-defined asthma control can be achieved in the majority of patients and should be the goal of asthma treatment.

Adrenal Cortex Hormones↗
PubMed2004

Optimal laser control of ultrafast photodissociation of I2- in water: mixed quantum/classical molecular dynamics simulation.

A linearized optimal control method in combination with mixed quantum/classical molecular dynamics simulation is used for numerically investigating the possibility of controlling photodissociation wave packets of I(2)(-) in water. Optimal pulses are designed using an ensemble of photodissociation samples, aiming at the creation of localized dissociation wave packets. Numerical results clearly show the effectiveness of the control although the control achievement is reduced with an increase in the internuclear distance associated with a target region. We introduce effective optimal pulses that are designed using a statistically averaged effective dissociation potential, and show that they semiquantitatively reproduce the control achievements calculated by using optimal pulses. The control mechanisms are interpreted from the time- and frequency-resolved spectra of the effective optimal pulses.

Journal Article↗
PubMed2004

A cardiovascular-respiratory control system model including state delay with application to congestive heart failure in humans.

This paper considers a model of the human cardiovascular-respiratory control system with one and two transport delays in the state equations describing the respiratory system. The effectiveness of the control of the ventilation rate is influenced by such transport delays because blood gases must be transported a physical distance from the lungs to the sensory sites where these gases are measured. The short term cardiovascular control system does not involve such transport delays although delays do arise in other contexts such as the baroreflex loop (see [46]) for example. This baroreflex delay is not considered here. The interaction between heart rate, blood pressure, cardiac output, and blood vessel resistance is quite complex and given the limited knowledge available of this interaction, we will model the cardiovascular control mechanism via an optimal control derived from control theory. This control will be stabilizing and is a reasonable approach based on mathematical considerations as well as being further motivated by the observation that many physiologists cite optimization as a potential influence in the evolution of biological systems (see, e.g., Kenner [29] or Swan [62]). In this paper we adapt a model, previously considered (Timischl [63] and Timischl et al. [64]), to include the effects of one and two transport delays. We will first implement an optimal control for the combined cardiovascular-respiratory model with one state space delay. We will then consider the effects of a second delay in the state space by modeling the respiratory control via an empirical formula with delay while the the complex relationships in the cardiovascular control will still be modeled by optimal control. This second transport delay associated with the sensory system of the respiratory control plays an important role in respiratory stability. As an application of this model we will consider congestive heart failure where this transport delay is larger than normal and the transition from the quiet awake state to stage 4 (NREM) sleep. The model can be used to study the interaction between cardiovascular and respiratory function in various situations as well as to consider the influence of optimal function in physiological control system performance.

Adult↗
PubMed2000

A Missed Opportunity: Our Failure to Control Hypertension Optimally.

At a time when we know from randomized trials that control of hypertension will reduce morbidity and mortality from all of its complications, only 27% of the 50 million hypertensives in the U.S. have their blood pressures controlled to less than 140/90 mm Hg. Reasons for this failure to control blood pressure are many and include reluctance to use multidrug regimens, particularly in combination tablets, and failure to set and pursue blood pressure goals which should be discussed in advance with the patient by explaining the risks of elevated blood pressure and the proven benefits of optimal control. (c)2000 by Le Jacq Communications, Inc.

Journal Article↗
PubMed2005

An improved robust fuzzy-PID controller with optimal fuzzy reasoning.

Many fuzzy control schemes used in industrial practice today are based on some simplified fuzzy reasoning methods, which are simple but at the expense of losing robustness, missing fuzzy characteristics, and having inconsistent inference. The concept of optimal fuzzy reasoning is introduced in this paper to overcome these shortcomings. The main advantage is that an integration of the optimal fuzzy reasoning with a PID control structure will generate a new type of fuzzy-PID control schemes with inherent optimal-tuning features for both local optimal performance and global tracking robustness. This new fuzzy-PID controller is then analyzed quantitatively and compared with other existing fuzzy-PID control methods. Both analytical and numerical studies clearly show the improved robustness of the new fuzzy-PID controller.

Algorithms↗
PubMed1991

Rationale for insulin management in gestational diabetes mellitus.

A prospective study was undertaken to test the hypothesis that insulin treatment in patients with gestational diabetes mellitus (GDM) with fasting plasma glucose (FPG) greater than 5.3 mM significantly reduces adverse perinatal outcome. Assigned to insulin or diet treatment based on FPG were 471 GDM women. Four factors believed to be associated with infants large for gestational age (LGA) were evaluated: FPG, overall glycemic control, maternal weight, and treatment regimen. We found that when glycemic control was optimized, the key factors related to large infants were FPG and treatment modality. In the low-FPG group (less than 5.3 mM), diet therapy achieved an incidence of 5.3% LGA. When insulin therapy was used to optimize control, an incidence of 3.5% LGA was found. Patients in the mid-FPG group (5.3-5.8 mM) had a higher increased rate of LGA (28.6%) for diet-treated versus insulin-treated women (10.3%). In addition, a fourfold increased risk for LGA was found in the diet-treated obese subjects in the mid-FPG group compared with insulin-treated obese women. Finally, treatment with insulin resulted in similar incidence of LGA within all FPG groups. We concluded that FPG greater than 5.3 mM can be the basis for initiation of insulin treatment in GDM subjects with optimization of glycemic control as the goal. This approach may contribute significantly to reduced neonatal risk and may foster a standardized method for rapid and effective assignment to treatment.

Adult↗
PubMed1994

The illusion of control and optimism about health: on being less at risk but no more in control than others.

If unrealistic optimism is simply a manifestation of the illusion of control (McKenna, 1993), differences in estimates of the likelihood of events for the self and others (comparative optimism) should have concomitant differences in perceived capacity to control these events. This possibility was tested in the domain of health, along with Perloff & Fetzer's (1986) risk-factor version of this downward comparison hypothesis and the hitherto neglected possibility that unrealistic optimism is an artifact of the comparative procedures employed in studies to date. It was found that likelihood judgements for a range of illnesses tended to be significantly lower when made by subjects providing self-ratings than when made by those providing judgements for the 'typical' student and, to a lesser extent, those making judgements for a friend's friend, but not by those doing so for an acquaintance. This comparative optimism was associated with equivalent differences in perceptions of these targets on a selection of relevant risk factors, but not in ratings of their capacity to control these outcomes (for which there was consensus across targets). The data are thus consistent with the risk-factor version of the hypothesis rather than the control version or the artifact explanation. The theoretical implications of these findings are addressed along with their consequences for health promotion.

Adult↗
PubMed1993

An optimal time control problem for the administration of 2',3'-dideoxycytidine by using red blood cells as bioreactors.

The problem of optimal dosage is studied for the administration of ddCyd using erythrocytes as carriers and bioreactors. The volume of erythrocytes and the initial amount of drug to be loaded have to be determined in such a way that the duration of the therapeutic effect is maximized without exceeding the toxic threshold. It is found that the optimal control is unique and it is at the upper vertex of the set of the admissible controls. A more general case is also briefly discussed.

Drug Carriers↗
PubMed2001

Optimization of secondary metabolite production using singular approximation and minimum principle.

Optimal control profiles as calculated with two control algorithms, singular approximation and minimum principle, are compared in this article. Switching points were determined using the singular approximation by mathematical calculation. The optimal growth rate was calculated using minimum principle. With an increased number of switching points, the calculated optimal control profiles approached the theoretical optimal control profile as calculated using the minimum principle. With three switching times, the product concentration approached 96% of the theoretical optimal control profile. From these results, optimal control can be achieved with more than a three-switching-point approximation.

Bioreactors↗