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Results for “model predictive control”

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PubMed2006

Dopamine and cognitive control: the influence of spontaneous eyeblink rate, DRD4 exon III polymorphism and gender on flexibility in set-shifting.

Converging evidence suggests a modulatory role of dopamine in cognitive control. We investigated the influence of two correlates of dopaminergic activity, the spontaneous eyeblink rate and the DRD4 exon III polymorphism, and the potential impact of gender on flexibility in an attentional set-shifting paradigm. The objective of the study was to confirm previous findings of an association between high eyeblink rates and increased cognitive flexibility. These findings were replicated in 87 healthy volunteers this time using a continuous variable for eyeblink rates instead of a dichotomized variable. The interaction between eyeblink rate and DRD4 found in the previous study was lower and failed significance. Analysis of the collapsed sample of n=150 revealed a main effect of gender and an interaction of gender and eyeblink rate on cognitive control. The complete prediction model explained 26% of the total variance. These data suggest that (1) the eyeblink rate is a reliable predictor of dopamine-mediated flexibility of cognitive control and (2) it is useful to include gender as predictor in future studies of dopaminergic modulation of cognitive control.

Adolescent↗

PubMed2006

Nonlinear predictive control of a drying process using genetic algorithms.

A nonlinear predictive control technique is developed to determine the optimal drying profile for a drying process. A complete nonlinear model of the baker's yeast drying process is used for predicting the future control actions. To minimize the difference between the model predictions and the desired trajectory throughout finite horizon, an objective function is described. The optimization problem is solved using a genetic algorithm due to the successful overconventional optimization techniques in the applications of the complex optimization problems. The control scheme comprises a drying process, a nonlinear prediction model, an optimizer, and a genetic search block. The nonlinear predictive control method proposed in this paper is applied to the baker's yeast drying process. The results show significant enhancement of the manufacturing quality, considerable decrease of the energy consumption and drying time, obtained by the proposed nonlinear predictive control.

Journal Article↗

PubMed2006

Hypertensive disorders of pregnancy are an evolutionary adaptation to mitigate the reproductive consequences of the human physique.

The aetiology of hypertensive disorders of pregnancy remains unknown, despite over 30 years of research. The prevalence and natural history of these disorders and the lack of progress in identifying a cause calls for a radical new approach. It is hypothesised that these disorders arise as a consequence of abnormal maternal regulatory mechanisms. The evolution of the physical characteristics unique to humans (bi-pedal gait and a large brain) resulted in a narrow pelvis and a large head. Such a physique is not conducive to viviparity and caused difficult, prolonged and obstructed labour with post-partum haemorrhage--the commonest causes of maternal mortality in the absence of modern medical care. In such circumstances, up to 6.5% of pregnant women will die as a direct consequence of pregnancy, mainly as a result of obstructed labour and haemorrhage. The death toll would have been much higher over millions of years of evolution. These conditions exerted significant adaptive and evolutionary pressure on our species. The adaptations necessary to mitigate the reproductive consequences of the human physique include activation of the coagulation system to reduce post-partum haemorrhage, increased blood pressure to peak after delivery and maintain cerebral perfusion in the face of post-partum blood loss and restriction of fetal growth to prevent obstructed labour. These adaptations must be regulated to guarantee their occurrence but limit their extent to prevent disease. Evidence for blood pressure regulation during pregnancy and a proposed mechanism to achieve this are presented. Regulation requires a redundant feto-placental signal and a single tightly controlled regulator. To guarantee that blood pressure rises, the feto-placental signal is predicted to be conveyed by several different molecules and to be produced in excess in all pregnancies. Normality is then maintained by a single tightly controlled regulator. This model predicts that the feto-placental factors that cause a rise in maternal blood pressure are multiple and produced in disease-causing concentrations in all pregnancies. Disease arises as a consequence of abnormalities in the maternal regulatory mechanism as occurs in say gestational diabetes mellitus. The search for a placental cause for pre-eclampsia is therefore futile. Research should focus on normal pregnancy and the identification of the factor that regulates maternal blood pressure in the second half of pregnancy. This factor will cause hypotension and prevent endothelial activation and have a role analogous to insulin in the regulation of glycaemia and the development of gestational diabetes mellitus.

Acclimatization↗

PubMed2006

Adaptive predictive functional control of a class of nonlinear systems.

This paper describes the use of pseudo-partial derivative (PPD) to dynamically linearize a nonlinear system, and aggregation is applied to the predicted PPD, resulting in a model-free adaptive predictive control algorithm for a nonlinear system. The algorithm design is only based on the PPD derived online from the input/output data of the controlled process, however it does provide bounded input/output sequence and setpoint tracking without steady-state error. A detailed discussion on parameter selection is also provided. To show the capability of the algorithm, simulations of a time-delay plant and a pH neutralization process show that the proposed method is effective for system parameter perturbation and external disturbance rejection.

Journal Article↗

PubMed2003

Control strategies correcting inaccurately programmed fingertip forces: model predictions derived from human behavior.

When picking up a familiar object between the index finger and the thumb, the motor commands are predetermined by the CNS to correspond to the frictional demand of the finger-object contact area. If the friction is less than expected, the object will start to slip out of the hand, giving rise to unexpected sensory information. Here we study the correction strategies of the motor system in response to an unexpected frictional demand. The motor commands to the mononeuron pool are estimated by a novel technique combining behavioral recordings and neuromuscular modelling. We first propose a mathematical model incorporating muscles, hand mechanics, and the action of lifting an object. A simple control system sends motor commands to and receives sensory signals from the model. We identify three factors influencing the efficiency of the correction: the time development of the motor command, the delay between the onset of the grip and load forces (GF-LF-delay), and how fast the lift is performed. A sensitivity analysis describes how these factors affect the ability to prevent or stop slipping and suggests an efficient control strategy that prepares and corrects for an altered frictional condition. We then analyzed fingertip grip and load forces (GF and LF) and position data from 200 lifts made by five healthy subjects. The friction was occasionally reduced, forcing an increase of the GF to prevent the object being dropped. The data were then analyzed by feeding it through the inverted model. This provided an estimate of the motor commands to the motoneuron pool. As suggested by the sensitivity analysis the GF-LF-delay was indeed used by the subjects to prevent slip. In agreement with recordings from neurons in the primary motor cortex of the monkey, a sharp burst in the estimated GF motor command (NGF) efficiently arrested any slip. The estimated motor commands indicate a control system that uses a small set of corrective commands, which together with the GF-LF-delay form efficient correction strategies. The selection of a strategy depends on the amount of tactile information reporting unexpected friction and how long it takes to arrive. We believe that this technique of estimating the motor commands behind the fingertip forces during a precision grip lift can provide a powerful tool for the investigation of the central control of the motor system.

Adult↗

PubMed1995

Temperature prediction of space flight experiments by computer thermal analysis.

Life sciences experiments are especially sensitive to temperature. A small temperature difference between otherwise identical samples can cause various differences in biological reaction rates. Knowledge of experimental temperatures and temperature histories help to distinguish the effects of microgravity and temperature on spaceflight experiments compared to ground based studies, and allow appropriate controls and sensitivity tests. Up to the present time, the Orbiter (Space Shuttle) has not generally provided temperature measurement instrumentation inside ambient lockers located in the Mid-deck of the Orbiter, or inside similar facilities such as Spacehab and Spacelab, but many pieces of hardware do have temperature recording capability. Most of these temperatures, however, have only been roughly measured or estimated. Such reported experimental temperatures, while accurate within a range of several degrees Celsius, are of limited utility to biological researchers. The temperature controlled lockers used in spaceflight, such as Commercial-Refrigeration Incubation Modules (C-R/IMs), severely reduce the mass and volume available for test samples and do not necessarily provide uniform thermal environments. While these test carriers avoid some of the experimental temperature variations of the ambient lockers, the number of samples which can be accommodated in these temperature controlled units is limited. In the present work, improved models of thermal prediction and control were sought. Temperatures are predicted by thermal analysis software using empirical temperatures recorded during STS-57. These temperatures are compared to data recorded throughout the mission using Ambient Temperature Recorders (ATRs) located within several payload lockers. Additional test cases are undertaken using controlled ground experiments to more precisely determine the reliability of the thermal model. The approach presented should increase the utility of various spaceflight carriers in the support of biological and material science research and ground control studies done in preparation for flight.

Air Conditioning↗

PubMed2003

Patterns of reproductive skew in the polygynandrous acorn woodpecker.

We compared observed levels of reproductive skew in the cooperatively breeding acorn woodpecker (Melanerpes formicivorus) with those predicted by two alternative transactional models. "Concession" models predict the degree to which parentage is shared assuming that a single dominant is in complete control of reproduction. Alternatively, "restraint" models predict reproductive sharing assuming that the dominant controls only whether subordinates remain in the group but does not control its share of reproduction. Reproductive skew is high among males: on average, the most successful male sires more than three times as many offspring as the next most successful male. Females share parentage equally and have lower constraints on dispersal and lower survival rates compared with males, which is consistent with predictions from the concessions model. Also as predicted by the concessions model, yearly variation in opportunities for dispersal before the breeding season correlates positively with skew. However, in contrast to concessions but consistent with the restraint model, skew decreases with relatedness. Thus, neither model consistently predicts patterns of reproductive skew in this species. We suggest that models of reproductive skew will need to include competitive interactions among potential breeders and mate choice before they will adequately predict patterns of reproductive partitioning in most vertebrate societies.

Animals↗

PubMed2003

Treatment of trichlorophenol by catalytic oxidation process.

The oxidation of 2,4,6-trichlorophenol (TCP) by ferrous-catalyzed hydrogen peroxide was quantified and modeled in the study. TCP was effectively degraded by hydroxyl radicals that were generated by Fe(II)/H(2)O(2) in the oxidation process. The oxidation capacity (OC) of the process depends on the concentrations of oxidant (hydrogen peroxide) and oxidative catalyst (ferrous ion). Up to 99.6% of TCP removal can be achieved in the process, provided the doses of Fe(II) and H(2)O(2) are selected correctly. The OC of the process was successfully predicted through a kinetic approach in a two-stage model with some simple and measurable parameters, which makes the model useful for predicting, controlling and optimizing the catalyzed oxidation process in the degradation of TCP.

Catalysis↗

PubMedDate not supplied

Identifying the determinants of viable microorganisms in the air and bulk metalworking fluids.

Exposure assessment was conducted for an epidemiologic study of the respiratory effects of exposure to metalworking fluids (MWF). As part of the study, airborne microorganisms were collected with a two-stage microbial impactor, and a sample of the bulk soluble MWF was collected from each machine sump, as well as information about the work environment. These data were then used to develop multivariate statistical models of the determinants bulk MWF and airborne microbial levels. Microbial concentrations in the bulk MWF ranged from 5 x 10(4) to 5 x 10(10) colony-forming units (CFU)/mL, with a geometric mean of 3.4 x 10(7) CFU/mL. The geometric mean airborne microbial level was 182 CFU/m3 (for particles size <8 microm) with a range of 1 to 8,308 CFU/m3. In modeling the determinants of bulk microorganisms, fluid-related factors were the most important characteristics associated with microbial levels, followed by process-related and environmental factors. The final full multivariate model predicted a significant reduction in bulk microbial levels by increasing pH of the fluid and reducing the amount of tramp oil leaking into the fluid. For the airborne microbial models, process-related factors were the major characteristics associated with microbial levels, followed by factors related to worker activities and environmental factors. The final full multivariate model predicted a significant control of airborne microorganisms by increasing worker distance from the machine, reducing the number of machines within 10 feet of the worker, decreasing the bulk microbial levels, and adding machine enclosures. These models can be used to prioritize nonbiocidal interventions to control microbial contamination of the bulk MWF and the air.

Air Microbiology↗

PubMed1994

Object-oriented model-driven control.

A monitoring and control subsystem architecture has been developed that capitalizes on the use of model-driven monitoring and predictive control, knowledge-based data representation, and artificial reasoning in an operator support mode. We have developed an object-oriented model of a Controlled Ecological Life Support System (CELSS). The model, based on the NASA Kennedy Space Center CELSS breadboard data, tracks carbon, hydrogen, and oxygen, carbon dioxide, and water. It estimates and tracks resource-related parameters such as mass, energy, and manpower measurements such as growing area required for balance. We are developing an interface with the breadboard systems that is compatible with artificial reasoning. Initial work is being done on use of expert systems and user interface development. This paper presents our approach to defining universally applicable CELSS monitor and control issues, and implementing appropriate monitor and control capability for a particular instance: the KSC CELSS Breadboard Facility.

Animals↗

PubMed1978

Model for human controller performance in vibration environments.

A model has been developed to predict biomechanical response and human controller performance as a function of vibration environment and tracking-task parameters. The model consists of three major elements: 1) a biodynamic model to predict limb and body motion resulting from platform vibration, 2) a pilot/vehicle model to predict tracking performance, and 3) an interface model to relate changes in certain pilot-related model parameters to biodynamic response. Linearity of biodynamic response mechanisms is demonstrated, and the model is shown to predict accurately the effects of tracking performance of vibration amplitude and spectrum, control gain, R.M.S. tracking input, and direction of vibration input.

Aviation↗

PubMed2000

Hydrophilic matrices for controlled drug delivery: an improved mathematical model to predict the resulting drug release kinetics (the "sequential layer" model).

PURPOSE: The aims of this study were (i) to elucidate the transport mechanisms involved in drug release from hydrophilic matrices; and (ii) to develop an improved mathematical model allowing quantitative predictions of the resulting release kinetics. METHODS: Our previously presented model has been substantially modified, by adding: (i) inhomogeneous swelling; (ii) poorly water-soluble drugs; and (iii) high initial drug loadings. The validity of the improved model has been tested experimentally using hydroxypropyl methylcellulose (HPMC)-matrices, containing either a poorly or a freely water-soluble drug (theophylline or chlorpheniramine maleate) at various initial loadings in phosphate buffer pH 7.4 and 0.1 N HCl, respectively. RESULTS: By overcoming the assumption of homogeneous swelling we show that the agreement between theory and experiment could be significantly improved. Among others, the model could describe quantitatively even the very complex effect on the resulting relative release rates (first slowing down, then accelerating drug release) observed when increasing the initial loading of poorly water-soluble drugs. CONCLUSIONS: The practical benefit of this work is an improved design model that can be used to predict accurately the required composition and dimensions of drug-loaded hydrophilic matrices in order to achieve desired release profiles, thus facilitating the development of new pharmaceutical products.

Chemistry, Pharmaceutical↗

PubMed2004

The role of endogenous opioids in the control of gastrointestinal motility: predictions from in vitro modelling.

Gastrointestinal motility can be assessed in vitro by investigating the effects of drugs or gene knockouts on intestinal propulsion, and on neurone-mediated responses evoked by electrical field stimulation (EFS). The latter predominantly measure enteric motor activity and can detect prokinetic activity of exogenous agents. Some evidence suggests that naloxone has prokinetic activity when evaluated for an ability to modulate responses to EFS, but the effects are inconsistent across different species or intestinal regions. Models of intestinal peristalsis measure an integrated sensory-motor nerve function and possess more intact neuro-neuronal connections. In such preparations, the effects of naloxone also suggest a prokinetic property but again, this is inconsistent. By contrast, consistent prokinetic activity of naloxone is apparent in models where peristalsis is compromised by drug-induced suppression of motor nerve activity or by modulation of endogenous processes using receptor antagonists or inappropriate intraluminal distension. These data suggest that endogenous opioids play little or no role in normal intestinal physiology, but suppress intestinal motility when motor function is compromised. Consequently, drugs that antagonize opioid receptors may exert prokinetic activity in conditions where intestinal motility is reduced, such as constipation. Further work is required to elucidate the opiate receptor(s) involved.

Animals↗

PubMed2001

Cooperation, control, and concession in meerkat groups.

"Limited control" models of reproductive skew in cooperative societies suggest that the frequency of breeding by subordinates is determined by the outcome of power struggles with dominants. In contrast, "optimal skew" models suggest that dominants have full control of subordinate reproduction and allow subordinates to breed only when this serves to retain subordinates' assistance with rearing dominants' own litters. The results of our 7-year field study of cooperative meerkats, Suricata suricatta, support the predictions of limited control models and provide no indication that dominant females grant reproductive concessions to subordinates to retain their assistance with future breeding attempts.

Africa, Southern↗

PubMed2001

Curvature effects in rapid alloy solidification.

The growth of a cylindrical or spherical crystal into its undercooled melt is a process whose description is complicated by the lack of a stationary regime. A simple approach to the problem, justified for low growth rates and widely used in the past for both pure substances and alloy solidification, is based on a quasistatic approximation which assumes an instantaneous adaptation of the diffusional field to the interface configuration. For alloy solidification, assuming isothermal conditions and local interface equilibrium, this simplified model predicts a diffusion controlled growth, with the radius of the crystal increasing asymptotically as ~t(1/2). However, as pointed out by recent investigations, thermal diffusion and nonequilibrium effects enter as essential ingredients in rapid alloy solidification. In the present paper we use the phase-field model to simulate the cylindrical and spherical growth of a solid germ into a supersaturated alloy melt. The problem is treated in its full time-dependent characteristics, accounting for nonequilibrium effects as well as for the rejection of both heat and solute away from the advancing front. We observe a complex behavior and a rich variety of dynamic regimes: in different regions of parameter space the growth rate is limited by diffusion (either thermal or chemical) or is kinetic controlled. Traversing the boundaries which limit these regions, the process undergoes sharp transitions which leave a trace in the solidified alloy. For realistic values of the Lewis number, thermal effects drive the process into a a diffusive regime, in which the rate limiting mechanism is the rejection of solute.

Journal Article↗

PubMed1997

Diaphyseal bone growth and adaptation: models and data.

The cross-sectional growth and development of the long bone diaphysis is strongly influenced by in vivo mechanical loading. An analytical approach was developed to model these mechanobiologic influences. First, human growth under normal loading conditions was modeled. Our model predictions were validated by comparison to human data obtained during adolescence. Next, skeletal adaptation during growth under altered loading conditions was examined using an animal model. Rat hindlimb suspension experiments were performed and femoral adaptation to reduced loading during growth was measured and compared to normal controls. Then our model predictions of adaptation during growth were compared directly to our experimental data.

Adaptation, Physiological↗

PubMed2002

Effects of practice on executive control investigated with fMRI.

Various models of executive control predict that practice should modulate the recruitment of executive brain mechanisms. To investigate this issue, we asked 15 participants to perform a cued global/local attention task while brain activity was recorded with event-related functional magnetic resonance imaging (fMRI). Practice significantly reduced the recruitment of left inferior parietal regions that were engaged when participants oriented attention in response to global and local cue stimuli. In contrast, practice increased the recruitment of midline frontal regions that were engaged by interference between global and local forms during target processing. These findings support models of executive control in which practice increases the tendency for stimuli to automatically evoke task-relevant processes and responses.

Adult↗

PubMed2000

Dynamic programming to investigate financial impacts of mastitis control decisions in milk production systems.

An adaptive stochastic dynamic programming model was used to solve the optimum replacement decision problem for the dairy cow under a range of alternative mastitis control procedures. The model predicted that reducing milk yield losses and somatic cell count penalties by, using milking machine test, post-milking teat disinfection and dry cow therapy added approximately pounds sterling 4, pounds sterling 10 and pounds sterling 13 respectively to an original annuity equivalent net present value for the replacement heifer of pounds sterling 286. Assuming that these procedures also reduced involuntary culling due to mastitis by 50% added pounds sterling 8.90 to the annuity. This latter figure indicated that an important part of the benefit of mastitis control procedures might come from a reduction in the culling risk of persistent clinical cases. We concluded that the strength of the dynamic programming model in this context was that it provided an integrated evaluation of the various impacts of each alternative mastitis procedure in the long term, which is essential for correct economic evaluation of mastitis.

Animals↗