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Results for “model predictive control”

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PubMed1980

Control of plasmid R1 replication: kinetics of replication in shifts between different copy number levels.

Plasmid R1 replication was studied in shifts between two steady states of copy number. The copy number was varied in two ways. First, we utilized the fact that it decreases with increasing growth rate. To minimize the metabolic effects of changes in the growth rate, the downshifts were obtained by adding alpha-methylglucoside to cultures growing in glucose-minimal medium, and the upshifts were obtained by adding glucose to cultures growing in the presence of glucose plus alpha-methylglucoside. Second, we used a temperature-dependent copy mutant of plasmid R1 (pKN301). Plasmid pPK301 shows a threefold higher copy number at 40 than at 30 degrees C. In both types of shift, plasmid replication immediately adjusted to the postshift differential rate. The copy number asymptotically adjusted to the new steady state. Hence, the system that controls plasmid R1 replication sets the frequency of replication without measuring the actual copy number. It has been suggested that plasmid R1 replication is under negative control by an R1-mediated repressor protein. Among the replication control models that involve negative control, the Pritchard inhibitor dilution model, the Sompayrac-Maaløe autorepressor model, and the plasmid lambdadv system all predict gene dose-independent copy number control.

DNA Replication↗

PubMed2001

Control of the threonine-synthesis pathway in Escherichia coli: a theoretical and experimental approach.

A computer simulation of the threonine-synthesis pathway in Escherichia coli Tir-8 has been developed based on our previous measurements of the kinetics of the pathway enzymes under near-physiological conditions. The model successfully simulates the main features of the time courses of threonine synthesis previously observed in a cell-free extract without alteration of the experimentally determined parameters, although improved quantitative fits can be obtained with small parameter adjustments. At the concentrations of enzymes, precursors and products present in cells, the model predicts a threonine-synthesis flux close to that required to support cell growth. Furthermore, the first two enzymes operate close to equilibrium, providing an example of a near-equilibrium feedback-inhibited enzyme. The predicted flux control coefficients of the pathway enzymes under physiological conditions show that the control of flux is shared between the first three enzymes: aspartate kinase, aspartate semialdehyde dehydrogenase and homoserine dehydrogenase, with no single activity dominating the control. The response of the model to the external metabolites shows that the sharing of control between the three enzymes holds across a wide range of conditions, but that the pathway flux is sensitive to the aspartate concentration. When the model was embedded in a larger model to simulate the variable demands for threonine at different growth rates, it showed the accumulation of free threonine that is typical of the Tir-8 strain at low growth rates. At low growth rates, the control of threonine flux remains largely with the pathway enzymes. As an example of the predictive power of the model, we studied the consequences of over-expressing different enzymes in the pathway.

Aspartate Kinase↗

PubMedDate not supplied

A temporal mechanism for generating the phase precession of hippocampal place cells.

The phase relationship between the activity of hippocampal place cells and the hippocampal theta rhythm systematically processes as the animal runs through the region in an environment called the place field of the cell. We present a minimal biophysical model of the phase precession of place cells in region CA3 of the hippocampus. The model describes the dynamics of two coupled point neurons--namely, a pyramidal cell and an interneuron, the latter of which is driven by a pacemaker input. Outside of the place field, the network displays a stable, background firing pattern that is locked to the theta rhythm. The pacemaker input drives the interneuron, which in turn activates the pyramidal cell. A single stimulus to the pyramidal cell from the dentate gyrus, simulating entrance into the place field, reorganizes the functional roles of the cells in the network for a number of cycles of the theta rhythm. In the reorganized network, the pyramidal cell drives the interneuron at a higher frequency than the theta frequency, thus causing a systematic precession relative to the theta input. The frequency of the pyramidal cell can vary to account for changes in the animal's running speed. The transient dynamics end after up to 360 degrees of phase precession when the pacemaker input to the interneuron occurs at a phase to return the network to the stable background firing pattern, thus signaling the end of the place field. Our model, in contrast to others, reports that phase precession is a temporally, and not spatially, controlled process. We also predict that like pyramidal cells, interneurons phase precess. Our model provides a mechanism for shutting off place cell firing after the animal has crossed the place field, and it explains the observed nearly 360 degrees of phase precession. We also describe how this model is consistent with a proposed autoassociative memory role of the CA3 region.

Action Potentials↗

PubMed1981

Sex ratio evolution in a variable environment.

We develop a natural selection model for sex ratio control in a spatially variable environment. Predictions of sex ratio alteration as a function of environmental change are tested in laboratory experiments with two parasitic wasps. Field data from a variety of other organisms also support the model. Finally, we discuss possibilities and difficulties for testing this type of evolutionary model.

Animals↗

PubMed2005

Neural mechanisms of autonomic, affective, and cognitive integration.

Influential theoretical models propose a central role for afferent information from the body in the expression of emotional feeling states. Feedback representations of changing states of bodily arousal influence learning and facilitate concurrent and prospective decision-making. Functional neuroimaging studies have increased understanding of brain mechanisms that generate changes in autonomic arousal during behavior and those which respond to internal feedback signals to influence subjective feeling states. In particular, anterior cingulate cortex is implicated in generating autonomic changes, while insula and orbitofrontal cortices may be specialized in mapping visceral responses. Independently, ventromedial prefrontal cortex is recognized to support processes of internal (self-) reference that predominate in states of rest and disengagement and which putatively serve as a benchmark for dynamic interactions with the environment. Lesion data further highlight the integrated role of these cortical regions in autonomic and motivational control. In computational models of control, forward (efference copies) and inverse models are proposed to enable prediction and correction of action and, by extension, the interpretation of the behavior of others. It is hypothesized that the neural substrate for these processes during motivational and affective behavior lies within the interactions of anterior cingulate, insula, and orbitofrontal cortices. Generation of visceral autonomic correlates of control reinforce experiential engagement in simulatory models and underpin concepts such as somatic markers to bridge the dualistic divide.

Afferent Pathways↗

PubMed1980

Prediction of velopharyngeal orifice area: a re-examination of model experimentation.

Warren has advanced a modification of the hydrokinetic equation for predicting velopharyngeal orifice area (Warren and DuBois, 1964). In the present work, this equation was subjected to extensive controlled model experimentation. The results of this experimentation show that, given the pressure differential across the orifice and the rate of airflow through the orifice, accurate predictions can be made of the area of the velopharyngeal port. These results were interpreted to provide strong support for both clinical and research use of the hydrokinetic equation for predicting velopharyngeal orifice area.

Airway Resistance↗

PubMed1981

Prediction of food intakes, weight gains, organ weights, and tumor size in tumor-bearing rats by the four-parameter mathematical model for physiological responses.

Groups of male weanling rats bearing the transplantable Novikoff ascites hepatoma were fed diets containing graded levels of protein. The food intakes and weight gains were recorded daily. Seven days after inoculation of the rats with the tumor (6 days in Experiment 2), the rats were sacrificed, their organs were weighed, and the tumor and ascites fluid volumes were determined. These results were analyzed by the four-parameter mathematical model for physiological responses. It was found that tumor-bearing rats eat and gain weight at the same rates as control rats fed identical diets, implying that this rapidly growing tumor does not interfere with the normal food intake and growth control mechanisms and that food intakes and weight gains are predictable by the four-parameter model. Organ growth was regulated in both normal and tumor-bearing rats but some actual organ weights in tumor-bearing rats were smaller than in control rats due to the presence of the tumor. However, other organs (spleen, lung, kidneys, and small intestine) of the tumor-bearing rats showed significant differences (p less than 0.01, Student's t test) from control rats. It was also possible to predict the growth of the tumor on the basis of the casein content of the diet.

Animals↗

PubMedDate not supplied

Determinants of physical activity in middle school children.

OBJECTIVE: To evaluate the theory of reasoned action (TRA) and planned behavior (TPB) in predicting moderate-to-vigorous physical activity (MVPA) in sixth-grade youth. METHODS: One hundred ninety-eight students completed a questionnaire measuring attitudes, subjective norms, perceived behavioral control, and intentions to be active. MVPA was measured using the CSA 7,164 accelerometer. RESULTS: Although demonstrating an acceptable fit, the TRA and TPB accounted for only a small percentage of the variance in MVPA. In support of the TPB, the addition of control perceptions to the reasoned action model added to the prediction of intentions and MVPA. CONCLUSION: Within our sample of sixth graders, the utility of the TRA or TPB as a framework for activity interventions appears to be limited.

Child↗

PubMed2000

The planning and control of reaching movements.

The notion of internal models has become central to the study of visually guided reaching. Armed with this theoretical framework, researchers are gleaning insights into long-standing problems in the field, such as the ability to respond rapidly to changes in the location of a reach target and the fine control of the multi-joint dynamics of the arm. A key factor in these advances is our increased understanding of how the brain integrates feedforward control signals, sensory feedback, and predictions based on internal models of the arm.

Animals↗

PubMed1999

Preoperative risk factors associated with symptomatic pulmonary embolism after total knee arthroplasty.

This retrospective case-control study reviewed 124 consecutive patients undergoing cemented total knee arthroplasty under regional anesthesia for osteoarthritis. Seven (5.6%) patients developed symptomatic pulmonary embolism despite warfarin prophylaxis. Bilateral procedures and preoperative hemoglobin were identified as significant risk factors for the development of symptomatic pulmonary embolism after total knee arthroplasty (hemoglobin > or =14 g/L, odds ratio 2.4, confidence interval [CI] 1.2-4.6, and bilateral cases odds ratio 7.2, CI 1.3-39.6). Additionally, preoperative hemoglobin <14 gm/L was associated with a 98% negative predictive value of developing symptomatic pulmonary embolism with a 14% false-negative rate (sensitivity 85.7%, 95% CI 80-92; specificity 67.9%, 95% CI 60-77; positive predictive value 14%, 95% CI .08-2). These findings indicate preoperative hemoglobin levels should be considered in addition to the usual patient demographics in future thromboembolism studies as a potential risk factor for symptomatic pulmonary embolism.

Anticoagulants↗

PubMedDate not supplied

Optimization of biofiltration for odor control: model calibration, validation, and applications.

A dynamic model that describes the biofiltration process for hydrogen sulfide removal from wastewater treatment plant air emissions was calibrated and validated using pilot- and full-scale biofilter data obtained from the Cedar Rapids (Iowa) Water Pollution Control Facilities. After calibration, the model was found to predict the dynamic effluent concentrations of the pilot- and full-scale biofilters well, with the measured data falling within 58 to 80% of the model output values. In addition, the model predicted the trend of the field data, even under field conditions of changing input concentration and at effluent concentrations below 1 ppm by volume. The model demonstrated that increasing gas residence time and temperature and decreasing influent concentration decreases effluent concentration. In addition, model simulations showed that a longer residence time is required to treat dynamic loading increases, indicating that biofilter design should account for the maximum influent concentration. These results can be used to help design and operate biofilters for controlling odorous and hazardous air emissions.

Air Pollutants↗

PubMed1998

A developmental transition in prehension modeled as a cusp catastrophe.

The purpose of the study was to show that the change from reaching without grasping to reaching with grasping during the first 6 months of life carried the characteristics of a discontinuous phase transition (catastrophe). A cross-sectional study was carried out with 58 infants between 60 and 408 days old. The infants were seated in a specially designed seat, and presented with nine detachable balls on a black curved board within reaching distance at shoulder height. The number of reaches without and with grasping were scored from video. A cusp catastrophe model was fitted to the data. A Likelihood-Ratio test indicated that the likelihood of the cusp model was significantly higher, p < .001, than a linear regression model. The cusp model was also compared with a logistic model. Akaike's Information criterion for the cusp catastrophe exceeded the logistic model, thus indicating a general better fit. Based on prior research, the following potential control parameters were chosen: crown-heel length, total body weight, arm length, arm circumference, ponderal index, arm volume, arm weight, and body position relative to the horizontal. The cusp model predicted that arm weight and arm circumference significantly contributed to the control parameters. It was found that these two variables had their largest contribution to the asymmetry control parameters.

Anthropometry↗

PubMed2001

An adaptive model of sensory integration in a dynamic environment applied to human stance control.

An adaptive estimator model of human spatial orientation is presented. The adaptive model dynamically weights sensory error signals. More specific, the model weights the difference between expected and actual sensory signals as a function of environmental conditions. The model does not require any changes in model parameters. Differences with existing models of spatial orientation are that: (1) environmental conditions are not specified but estimated, (2) the sensor noise characteristics are the only parameters supplied by the model designer, (3) history-dependent effects and mental resources can be modelled, and (4) vestibular thresholds are not included in the model; instead vestibular-related threshold effects are predicted by the model. The model was applied to human stance control and evaluated with results of a visually induced sway experiment. From these experiments it is known that the amplitude of visually induced sway reaches a saturation level as the stimulus level increases. This saturation level is higher when the support base is sway referenced. For subjects experiencing vestibular loss, these saturation effects do not occur. Unknown sensory noise characteristics were found by matching model predictions with these experimental results. Using only five model parameters, far more than five data points were successfully predicted. Model predictions showed that both the saturation levels are vestibular related since removal of the vestibular organs in the model removed the saturation effects, as was also shown in the e xperiments. It seems that the nature of these vestibular-related threshold effects is not physical, since in the model no threshold is included. The model results suggest that vestibular-related thresholds are the result of the processing of noisy sensory and motor output signals. Model analysis suggests that, especially for slow and small movements, the environment postural orientation can not be estimated optimally, which causes sensory illusions. The model also confirms the experimental finding that postural orientation is history dependent and can be shaped by instruction or mental knowledge. In addition the model predicts that: (1) vestibular-loss patients cannot handle sensory conflicting situations and will fall down, (2) during sinusoidal support-base translations vestibular function is needed to prevent falling, (3) loss of somatosensory information from the feet results in larger postural sway for sinusoidal support-base translations, and (4) loss of vestibular function results in falling for large support-base rotations with the eyes closed. These predictions are in agreement with experimental results.

Adaptation, Physiological↗

PubMed2004

Magnetic resonance imaging-based volumetry differentiates progressive supranuclear palsy from corticobasal degeneration.

Because there are no biological markers for the clinical diagnosis of progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD), we established a mathematical model based on three-dimensional magnetic resonance (MR) imaging to differentiate between these parkinsonian disorders. Using MR imaging-based volumetry we studied the pattern of atrophic changes in patients with probable, possible or definite PSP (n = 33) or CBD (n = 18). Patients were compared with 22 controls with similar age. To establish a mathematical model that would allow for differentiation of PSP, CBD and controls we performed a discriminant analysis. We found a significant reduction in average brain, brainstem, midbrain and frontal gray matter volumes in patients with PSP, whereas patients with CBD showed atrophy of parietal cortex and corpus callosum. With the exception of reduced midbrain volumes in PSP, the measured volumes of anatomical structures showed an extensive overlap with the normal range on an individual basis. Using only post mortem confirmed cases of PSP (n = 8) and CBD (n = 7) as well as all controls, the volumes of midbrain, parietal white matter, temporal gray matter, brainstem, frontal white matter and pons were identified to separate best between groups and were used to construct a model with two canonical variables. This model allowed to correctly predict the diagnosis in 95% of controls as well as in 76% of all PSP and 83% of all CBD patients. Similar results were obtained only when patients with a possible and probable diagnosis of PSP and CBD, who were not involved in the development of the discriminant analysis, were classified. 3D-MR imaging-based volumetry may help to differentiate PSP from CBD ante mortem.

Aged↗

PubMed1999

Effects of sustained control of brushtail possums on levels of Mycobacterium bovis infection in cattle and brushtail possum populations from Hohotaka, New Zealand.

AIMS: To examine the effect of reducing the abundance of brushtail possums (Trichosurus vulpecula) on the distribution and prevalence of bovine tuberculosis (Mycobacterium bovis, Tb) in possums and the incidence of Tb in domestic cattle on a group of farms in the central North Island, New Zealand. METHODS: The cumulative yearly incidence of Tb infection from 12 cattle herds was estimated from annual tuberculin testing and abattoir inspection data over the period 1983-98. Intensive control of possum populations began for six of the herds in 1988, five herds in 1994 and the remaining herd in 1996. The prevalence and distribution of macroscopic M. bovis infection in possums and an index of possum abundance was estimated during yearly cross-sectional surveys from 1988 to 1998. This enabled formal testing of the link between the abundance of tuberculous possums and the incidence of Tb in cattle. RESULTS: Before possum control, infected possums were clustered in foci on or adjacent to the farms with the highest annual incidence of tuberculosis in cattle, and had an overall prevalence of macroscopic M. bovis infection of 2.3%. The prevalence of disease declined to zero with ongoing possum control, although infected possums continued to be found during the first 5 years of control. Maintaining the possum population at an average of 22.1% of its pre-control density significantly reduced the odds of the cumulative yearly incidence of Tb in cattle by 77% during the first 5 years of possum control and a further 65% in the second 5-year period. Nine of 11 tuberculous possums identified since the start of possum control were found within the areas where infected possums were clustered during the pre-control survey, suggesting that the persistence of infection within these clusters rather than infected immigrants was the source of ongoing disease. Annual estimates of the prevalence of tuberculous possums broadly followed the predictions of Barlow's possum-Tb model for a controlled possum population. CONCLUSION: The results support the hypothesis that tuberculous possums transmit bovine tuberculosis to domestic cattle, and therefore that reducing the abundance of tuberculous possums reduces the incidence of Tb in cattle. If the level of possum culling is sufficient, it appears that M. bovis infection may be eradicated from possum populations. Better information on population density, rate of increase and annual culling rates would have been needed for a truly independent examination of the Barlow possum-Tb model.

Journal Article↗

PubMed1995

A model for multiple subcutaneous insulin injections developed from individual diabetic patient data.

Many diabetic patients taking multiple subcutaneous insulin injections cannot adjust their dosage appropriately to maintain blood glucose within a normal range. It is hard to predict how dosage changes and physiological fluctuations affect insulin levels and subsequently glucose control. To examine these issues, we have developed a model representing the link between dosage and blood insulin levels. Our model adequately predicts insulin concentrations for individual patients and could be incorporated into an overall glucose-insulin representation. More importantly, parameter and sensitivity analysis results highlight insulin kinetic features that are difficult to isolate in a clinical setting and that may significantly influence glucose dynamics. For example, large interpatient variation, measured quantitatively by model parameters, emphasizes the need for individualized design of insulin regimens. Intrapatient variations are also large in some patients. Improved control for these patients may only be possible through more frequent sampling and control action. The sensitivity coefficient for absorption suggests a significant overlapping injection effect that is not considered in present patient management strategies.

Diabetes Mellitus↗

PubMedDate not supplied

Computational modeling of oligonucleotide positional densities for human promoter prediction.

OBJECTIVE: The gene promoter region controls transcriptional initiation of a gene, which is the most important step in gene regulation. In-silico detection of promoter region in genomic sequences has a number of applications in gene discovery and understanding gene expression regulation. However, computational prediction of eukaryotic poly-II promoters has remained a difficult task. This paper introduces a novel statistical technique for detecting promoter regions in long genomic sequences. METHOD: A number of existing techniques analyze the occurrence frequencies of oligonucleotides in promoter sequences as compared to other genomic regions. In contrast, the present work studies the positional densities of oligonucleotides in promoter sequences. The analysis does not require any non-promoter sequence dataset or any model of the background oligonucleotide content of the genome. The statistical model learnt from a dataset of promoter sequences automatically recognizes a number of transcription factor binding sites simultaneously with their occurrence positions relative to the transcription start site. Based on this model, a continuous naïve Bayes classifier is developed for the detection of human promoters and transcription start sites in genomic sequences. RESULTS: The present study extends the scope of statistical models in general promoter modeling and prediction. Promoter sequence features learnt by the model correlate well with known biological facts. Results of human transcription start site prediction compare favorably with existing 2nd generation promoter prediction tools.

Base Sequence↗

PubMed1993

Microcomputer-assisted kinetic modeling of mammalian gene expression.

New software for microcomputers enables predictive, quantitative models of genetic systems to be produced that can account for the elements of time, scale, and feedback control of hierarchical systems. The flow of genetic information during protein synthesis can be addressed by treating each intermediate as a kinetic element in a linked series of reactions. When the rate of transcription changes, the time required to achieve a new level of the encoded protein is expected to be a function of the conversion rates or half-lives of all intermediates. Kinetic modeling may be used to make predictions and integrate primary data concerning rates of transcription, nuclear mRNA dynamics, nucleocytoplasmic transport, translational control, and other processes that govern the rate of synthesis for specific proteins.

Animals↗