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Results for “model predictive control”

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At least 199 records · Page 11Linked to original sources

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↗

PubMed1993

Construction and characterization of a novel cross-regulation system for regulating cloned gene expression in Escherichia coli.

A novel cross-regulation system employing two pairs of interacting promoter-repressor systems was constructed using the tac-lacI and lambda pL-cI promoter-operator-repressor systems. In particular, transcription of the cat gene and the fused cI gene is regulated by the tac promoter, while transcription of the lacI gene is controlled by the lambda pL promoter. In order to compare CAT production from this new system with a currently employed transcription control configuration, a control expression vector utilizing the constitutive repressor synthesis configuration was also constructed. In this construct, cat is under the control of the tac promoter, and lac repressor is provided from a single copy of the lacIq allele included in the plasmid. Induction results using different copy number vectors indicate that induced cat expression levels are at least twofold higher using the cross-regulation system which has very low basal expression. These results match well with previous mathematical modeling predictions indicating excellent control of basal expression and also higher cloned-gene expression post-induction over a broad range of copy numbers for a cross-regulation control configuration. Induction of the cross-regulation system both up-regulated the activation pathway and down-regulated the inhibition pathway, shifting the system steady-state from lac repressor expression to cat and cI expression. The control strategy presented here should be equally applicable to regulate transcription in diverse hosts.

Bacteriophage lambda↗

PubMedDate not supplied

Design of metabolic engineering strategies for maximizing L-(-)-carnitine production by Escherichia coli. Integration of the metabolic and bioreactor levels.

In this work metabolic engineering strategies for maximizing L-(-)-carnitine production by Escherichia coli based on the Biochemical System Theory and the Indirect Optimization Method are presented. The model integrates the metabolic and the bioreactor levels using power-law formalism. Based on the S-system model, the Indirect Optimization Method was applied, leading to profiles of parameter values that are compatible with both the physiology of the cells and the bioreactor system operating conditions. This guarantees their viability and fitness and yields higher rates of L-(-)-carnitine production. Experimental results using a high cell density reactor were compared with optimized predictions from the Indirect Optimization Method. When two parameters (the dilution rate and the initial crotonobetaine concentration) were directly changed in the real experimental system to the prescribed optimum values, the system showed better performance in L-(-)-carnitine production (74% increase in production rate), in close agreement with the model's predictions. The model shows control points at macroscopic (reactor operation) and microscopic (molecular) levels where conversion and productivity can be increased. In accordance with the optimized solution, the next logical step to improve the L-(-)-carnitine production rate will involve metabolic engineering of the E. coli strain by overexpressing the carnitine transferase, CaiB, activity and the protein carrier, CaiT, responsible for substrate and product transport in and out of the cell. By this means it is predicted production may be enhanced by up to three times the original value.

Biomass↗

PubMed2005

Inferring the connectivity of a regulatory network from mRNA quantification in Synechocystis PCC6803.

A major task of contemporary biology is to understand and predict the functioning of regulatory networks. We use expression data to deduce the regulation network connecting the sigma factors of Synechocystis PCC6803, the most global regulators in bacteria. Synechocystis contains one group 1 (SigA) and four group 2 (SigB, SigC, SigD and SigE) sigma factors. From the relative abundance of the sig mRNA measured in the wild-type and the four group 2 sigma mutants, we derive a network of the influences of each sigma factor on the transcription of all other sigma factors. Internal or external stimuli acting on only one of the sigma factors will thus indirectly modify the expression of most of the others. From this model, we predict the control points through which the circadian time modulates the expression of the sigma factors. Our results show that the cross regulation between the group 1 and group 2 sigma factors is very important for the adaptation of the bacterium to different environmental and physiological conditions.

Bacterial Proteins↗

PubMed1999

Axis II comorbidity of substance use disorders among patients referred for treatment of personality disorders.

OBJECTIVE: The purpose of this study was to determine the extent of comorbid substance use disorders in patients referred for treatment of personality disorders. METHOD: Two hundred inpatients and outpatients were assessed by semistructured interviews for substance use and personality disorders. Univariate odds ratios were calculated for groups of substance use disorders and each DSM-III-R axis II disorder; comorbidity among axis II disorders was controlled in multivariate models predicting current or lifetime substance use disorder groups. The impact of personality disorder on chronicity and overall impairment associated with substance use disorders was evaluated. RESULTS: Close to 60% of subjects with substance use disorders had personality disorders. Borderline personality disorder was significantly associated with current substance use disorders, excluding alcohol and cannabis, and with lifetime alcohol, stimulant, and other substance use disorders, excluding cannabis. Antisocial personality disorder was associated with lifetime substance use disorders other than alcohol, cannabis, and stimulants. These relationships remained significant after controlling for the presence of all other personality disorders. There was no evidence that personality disorders increased the chronicity of substance use disorders, but comorbid personality disorders were associated with greater global impairment. CONCLUSIONS: Borderline personality disorder may be associated with a wide variety of substance use disorders, especially among patients seeking treatment for personality problems.

Adult↗

PubMed2000

Predictors of glycemic control in insulin-using adults with type 2 diabetes.

OBJECTIVE: To determine the characteristics that influence glycemic control among insulin-using adults with type 2 diabetes. RESEARCH DESIGN AND METHODS: We studied all 1,333 eligible members of a large not-for-profit health maintenance organization who responded to a 1997 survey. We tested associations among demographic, treatment, and psychometric variables with mean 1997 HbA1c values. The Problem Areas in Diabetes (PAID) instrument was used to assess the emotional effect of living with diabetes, and the Short Form 12 Physical Function Scale was used to assess the effect of physical limitations on daily activities. Based on differences between and within treatment groups, we built models to predict glycemic control for subgroups of subjects who were using insulin alone and those who were using insulin in combination with an oral hypoglycemic agent. RESULTS: Younger age, lower BMI, and increased emotional distress about diabetes (according to the PAID scale) were all significant predictors (P < 0.05) of worse glycemic control. However, except among individuals with an HbA1c level of >8.0 who were receiving combination therapy, only approximately 10% of the variance in glycemic control could be predicted by demographic, treatment, or psychometric characteristics. CONCLUSIONS: Personal characteristics explain little of the variation in glycemic control in insulin-using adults with type 2 diabetes. Possible explanations are that the reduced complexity of control in type 2 diabetes makes the disease less sensitive to personal factors than control in type 1 diabetes, that health-related behavior is less driven by personal and environmental characteristics among older individuals, or that, in populations exposed to aggressive glycemic control with oral hypoglycemic agents and nurse care managers, personal differences become largely irrelevant.

Activities of Daily Living↗

PubMed2005

Model applications and mechanism study on the degradation of atrazine by Fenton's system.

Atrazine (ATZ), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine, was effectively degraded by hydroxyl radicals that were generated by FeII/H2O2 in the Fenton's process. Up to 98% ATZ removal can be achieved in the process if the doses of FeII and H2O2 are selected appropriately. Oxidation capacity of the process was successfully predicted through a kinetic approach with three simple and measurable parameters (i.e., two rate constants and a break point time), which makes the model useful in predicting, controlling and optimizing the degradation of ATZ. In addition, the transformation pathways of ATZ decay was successfully investigated by using a novel technology, liquid chromatography electrospray tandem mass spectrometry (LC/ESI-MS/MS). Ten intermediates were identified in the process. The alkylic-oxidation followed by dealkylation and/or dechlorination-hydroxylation were found to be the major pathways of the decay of ATZ in Fenton's process. All the detected intermediates were found to be dealkylated in different levels or positions. The dealkylated species may be further dechlorinated but generally at a lower fraction (<10%) due to the depletion of oxidants.

Atrazine↗

PubMed2004

Dosimetry and radiobiologic model comparison of IMRT and 3D conformal radiotherapy in treatment of carcinoma of the prostate.

INTRODUCTION: Intensity-modulated radiotherapy (IMRT) has introduced novel dosimetry that often features increased dose heterogeneity to target and normal structures. This raises questions of the biologic effects of IMRT compared to conventional treatment. We compared dosimetry and radiobiologic model predictions of tumor control probability (TCP) and normal tissue complication probability (NTCP) for prostate cancer patients planned for IMRT as opposed to standardized three-dimensional conformal radiotherapy (3DCRT). METHODS AND MATERIALS: Segmented multileaf collimator IMRT treatment plans for 32 prostate cancer patients were compared to 3DCRT plans for the same patients. Twenty-two received local-field irradiation (LFI), and 10 received extended-field irradiation (EFI) that included pelvic lymph nodes. For LFI, IMRT was planned for delivery of 2 Gy minimum dose to the prostate (> or =99% volume coverage) for 35 fractions. The 3DCRT plans, characterized by more homogenous dose to the target, were designed according to a different protocol to deliver 2 Gy to the center of the prostate for 37 fractions. Mean total dose from 35 fractions of IMRT was equal to mean total dose from 37 fractions of 3DCRT. For EFI, both IMRT and 3DCRT were planned for 2 Gy per fraction to a total dose of 50 Gy to prostate and pelvic lymph nodes, followed by 2 Gy per fraction to 20 Gy to the prostate alone. Treatment dose for EFI-IMRT was defined as minimum dose to the target, whereas for EFI-3DCRT, it was defined as dose to the center of the prostate. TCP was calculated for the prostate in the linear-quadratic model for two choices of alpha/beta. NTCP was calculated with the Lyman model for organs at risk, using Kutcher-Burman dose-volume histogram reduction with Emami parameters. RESULTS AND CONCLUSIONS: Dose to the prostate, expressed as mean +/- standard deviation, was 74.7 +/- 1.1 Gy for IMRT vs. 74.6 +/- 0.3 Gy for 3D for the LFI plans, and 74.8 +/- 0.6 Gy for IMRT vs. 71.5 +/- 0.6 Gy for 3D for the EFI plans. For the studied protocols, TCP was greater for IMRT than for 3D across the full range of target sensitivity, for both localized- and extended-field irradiation. For LFI, this was due to the smaller number of fractions (35 vs. 37) used for IMRT, and for EFI, this was due to the greater mean dose for IMRT, compared to 3D. For all organs, mean NTCP tended to be lower for IMRT than for 3D, although NTCP values were very small for both 3D and IMRT. Differences were statistically significant for rectum (LFI and EFI), bladder (EFI), and bowel (EFI). For both LFI and EFI, the calculated NTCPs qualitatively agreed with early published clinical data comparing genitourinary and gastrointestinal complications of IMRT and 3D. Present calculations support the hypothesis that accurately delivered IMRT for prostate cancer can limit dose to normal tissue by reducing treatment margins relative to conventional 3D planning, to allow a reduction in complication rate spanning several sensitive structures while maintaining or increasing tumor control probability.

Algorithms↗

PubMed1989

Application of the Mayo primary biliary cirrhosis survival model to Mayo liver transplant patients.

Liver transplantation is considered lifesaving for selected patients with end-stage primary biliary cirrhosis (PBC). A mathematical model to predict survival in the patient with PBC who has not undergone transplantation would be valuable for improving selection of patients for and timing of transplantation and for providing control information for assessment of the efficacy of transplantation. The Cox regression method and data from 312 Mayo Clinic patients with PBC were used to develop a model based on age, total serum bilirubin, serum albumin, prothrombin time, and severity of edema. When cross-validated on an independent set of 106 Mayo patients, the model accurately predicted their survival. It was similar to two other published survival models in terms of risk measurement but had the advantage of not necessitating liver biopsy. The model was used to assess the efficacy of liver transplantation by comparing the Kaplan-Meier survival of 32 Mayo patients after transplantation with the average model prediction of survival without transplantation. Beyond 3 months after transplantation, Kaplan-Meier survival probabilities were significantly greater than control survival predicted by the model (P less than 0.001). Examples of using the model for aiding in selection of patients for and timing of transplantation are provided.

Age Factors↗

PubMed1999

Growth Kinetics of Nanosize Silica in a Nonionic Water-in-Oil Microemulsion: A Reverse Micellar Pseudophase Reaction Model.

The growth kinetics of silica nanoparticles synthesized by the microemulsion-mediated alkoxide hydrolysis method was investigated with tetraethoxysilane (TEOS) as the silica precursor and polyoxyethylene (5) nonylphenylether (NP-5)/cyclohexane/ammonium hydroxide as the water-in-oil microemulsion system. The time evolution of the mean diameter of the silica particles was determined for different values of the water-to-surfactant molar ratio (R). Particle growth was found to be a slow process, where under typical experimental conditions at room temperature ([TEOS] = 0.024 M, 29.6 wt% NH(3), water-to-TEOS molar ratio (h) = 7.8) the particles achieved their terminal size after several days. During the early stages of the reaction, particle growth followed first-order kinetics, and the observed first-order growth rate constants decreased with increase in R. A reverse micellar pseudophase model (which considered the partition of reactants between the reverse micellar pseudophase and the bulk oil phase) was developed to analyze the growth kinetics under the hypothesis that TEOS hydrolysis was rate controlling. The pseudophase model predicted an inverse relationship between the observed growth rate and R, in agreement with experiment. The roles of steric effects and the bound state of water molecules, in retarding the hydrolysis rate, were highlighted by examining the effect of R on the TEOS hydrolysis rate constant in the reverse micellar pseudophase. Copyright 1999 Academic Press.

Journal Article↗

PubMed2005

Statistical kinematics of axillary nodal metastases in breast carcinoma.

The number of involved lymph nodes in individuals with breast cancer is highly variable, and of both prognostic and therapeutic importance. A statistical description for the frequency distribution of the numbers of involved nodes in an affected population could potentially reveal mechanisms of axillary metastasis, and eventually facilitate predictive models for tumor control and axillary sampling. A meta-analysis of 15 studies involving 24,757 axillary dissections was performed, including conventional dissections, sentinel node dissections and studies of occult metastases. Frequency histograms for the numbers of involved axillary lymph nodes from the populations were tested for clustering and they were fitted, as a first approximation, to a negative binomial distribution. Although the number of involved nodes per individual was quite variable, some individuals sustained more involved nodes than could be expected from a random (Poisson) distribution. The negative binomial distribution, however, provided acceptable descriptions for the distributions of involved nodes in all populations studied. Two mechanisms could explain these observations: (1) an apparent contagion model, where involved nodes seeded further nodal metastases, and (2) a spurious contagion model where the number of involved nodes per individual was randomly (Poisson) distributed and population heterogeneity accounted for the more severe cases. Both models were consistent with the hypothesis that the nodal metastasis is a chance event, with the probability of involvement greatest for nodes contiguous to the primary tumor and proportioned by lymphatic flow.

Biomechanical Phenomena↗

PubMed2005

Modeling of under-detection of cases in disease surveillance.

PURPOSE: Accurate epidemiological surveillance of leprosy is a matter of international public health concern. It often suffers, however, from potential problems of under-registration of reported cases, particularly in poorer and more socially deprived areas. Such problems also apply in the surveillance of many other communicable or transmissible diseases. We develop a Bayesian model for small-area disease rates that allows for censoring of case detection in suspect districts and can therefore be used to estimate under-reporting of cases in a given study region. METHODS: Such methods are applied to leprosy incidence in a municipality of Pernambuco State in North Eastern Brazil, using a social deprivation indicator as the basis for considering data from certain districts to be censored. The time period we consider was immediately prior to an extension of the coverage and efficacy of the control program and model predictions concerning under reporting can therefore be compared with more reliable data subsequently collected from the same region. RESULTS: The proposed method produces informative estimates of under detection of leprosy cases in the defined study region and these estimates compare well, both in size and in geographical location, with the numbers of cases subsequently detected. CONCLUSIONS: As illustrated by the application discussed in this article, the proposed model provides a general tool that may be used in spatial epidemiological surveillance situations where the available data is suspected to contain significant under-registrations of cases in certain geographical areas.

Bayes Theorem↗

PubMed2002

A method for analytically generating three-dimensional isocomfort workspace based on perceived discomfort.

The purpose of this study was to develop a new method for analytically generating three-dimensional isocomfort workspace for the upper extremities using the robot kinematics. Subjective perceived discomfort scores in varying postures for manipulating four types of controls were used. Fifteen healthy male subjects participated in the experiment. The subjects were asked to hold the given postures manipulating controls for 60 s in the seated position, and to rate their perceived discomfort during the following rest of 60 s using the magnitude estimation. Postures of the upper extremities set by shoulder and elbow motions, types of controls, and left right hand were selected as experimental variables, in which the L32 orthogonal array was adopted. The results showed that shoulder flexion and adduction-abduction, elbow flexion, and types of controls significantly affected perceived discomfort for postures operating controls, but hand used for operating controls did not. Depending upon the types of controls, four regression models predicting perceived discomfort were presented. Using the models, a sweeping algorithm to generate three-dimensional isocomfort workspace was developed, in which the robot kinematics was employed to describe the translational relationships between the upper arm and the lower arm/hand. It is expected that the isocomfort workspace can be used as a valuable design guideline when ergonomically designing three-dimensional workplaces.

Adult↗

PubMed1999

Cortical potentials during imagined movements in individuals with chronic spinal cord injuries.

A closed-loop model of motor control predicts that central deafferentation should disrupt cortical motor processes when imagining movements of paralyzed limbs. To test this prediction, event-related potentials (ERP) were recorded from the supplementary motor area and the primary sensorimotor area in individuals with paraplegia or quadriplegia as well as able-bodied controls during executed/attempted and imagined movements of the hand and foot. The cross-correlation of ERPs generated during hand movement and imagery was slightly negative for controls, moderate and positive for paraplegics, and high and positive for quadriplegics. The cross-correlation between foot movement and imagery was moderate for controls, moderate to high for paraplegic and high for quadriplegic groups. For hand tasks, ERPs were uncorrelated between controls and quadriplegics; for the foot tasks, the correlations were low between controls and both paraplegics and quadriplegics. Amplitudes and latencies of the ERP were also compared between movement and imagery and between the three injury groups. A biphasic waveform appears prior to and during movements in controls that is absent during imagery and when attempting/imagining movements of paralyzed limbs. Two hypotheses are proposed to explain the differences in cortical processing between movement and imagery and between injury groups. First, cortical motor processes are altered by the absence of kinesthetic feedback during attempted movement of a deafferented limb as well as during imagery. Second, inhibitory processes, present during imagined movements of an intact limb, may be weakened by a spinal cord injury (SCI) so that movement and imagery processes appear isomorphic. While the absence of kinesthetic feedback from deafferented limbs likely contributes to some variability in motor processing, the influence of an SCI on movement inhibition requires further testing.

Adult↗

PubMed2003

Fuzzy cluster analysis of high-field functional MRI data.

Functional magnetic resonance imaging (fMRI) based on blood-oxygen level dependent (BOLD) contrast today is an established brain research method and quickly gains acceptance for complementary clinical diagnosis. However, neither the basic mechanisms like coupling between neuronal activation and haemodynamic response are known exactly, nor can the various artifacts be predicted or controlled. Thus, modeling functional signal changes is non-trivial and exploratory data analysis (EDA) may be rather useful. In particular, identification and separation of artifacts as well as quantification of expected, i.e. stimulus correlated, and novel information on brain activity is important for both, new insights in neuroscience and future developments in functional MRI of the human brain. After an introduction on fuzzy clustering and very high-field fMRI we present several examples where fuzzy cluster analysis (FCA) of fMRI time series helps to identify and locally separate various artifacts. We also present and discuss applications and limitations of fuzzy cluster analysis in very high-field functional MRI: differentiate temporal patterns in MRI using (a) a test object with static and dynamic parts, (b) artifacts due to gross head motion artifacts. Using a synthetic fMRI data set we quantitatively examine the influences of relevant FCA parameters on clustering results in terms of receiver-operator characteristics (ROC) and compare them with a commonly used model-based correlation analysis (CA) approach. The application of FCA in analyzing in vivo fMRI data is shown for (a) a motor paradigm, (b) data from multi-echo imaging, and (c) a fMRI study using mental rotation of three-dimensional cubes. We found that differentiation of true "neural" from false "vascular" activation is possible based on echo time dependence and specific activation levels, as well as based on their signal time-course. Exploratory data analysis methods in general and fuzzy cluster analysis in particular may help to identify artifacts and add novel and unexpected information valuable for interpretation, classification and characterization of functional MRI data which can be used to design new data acquisition schemes, stimulus presentations, neuro(physio)logical paradigms, as well as to improve quantitative biophysical models.

Artifacts↗

PubMed2006

Predicting the global spread of H5N1 avian influenza.

The spread of highly pathogenic H5N1 avian influenza into Asia, Europe, and Africa has resulted in enormous impacts on the poultry industry and presents an important threat to human health. The pathways by which the virus has and will spread between countries have been debated extensively, but have yet to be analyzed comprehensively and quantitatively. We integrated data on phylogenetic relationships of virus isolates, migratory bird movements, and trade in poultry and wild birds to determine the pathway for 52 individual introduction events into countries and predict future spread. We show that 9 of 21 of H5N1 introductions to countries in Asia were most likely through poultry, and 3 of 21 were most likely through migrating birds. In contrast, spread to most (20/23) countries in Europe was most likely through migratory birds. Spread in Africa was likely partly by poultry (2/8 introductions) and partly by migrating birds (3/8). Our analyses predict that H5N1 is more likely to be introduced into the Western Hemisphere through infected poultry and into the mainland United States by subsequent movement of migrating birds from neighboring countries, rather than from eastern Siberia. These results highlight the potential synergism between trade and wild animal movement in the emergence and pandemic spread of pathogens and demonstrate the value of predictive models for disease control.

Animals↗

PubMed1980

Local contrast and maintained generalization.

Pigeons received variable-interval reinforcement for key pecking during presentations of horizontal and vertical line-orientation stimuli, while pecks during five intermediate orientations were extinguished. Lowest peck rates were observed during presentations of negative stimuli adjacent to the positive orientations while peck rate during 45 degrees (the intermediate negative orientation) was relatively high, i.e., there were negative contrast shoulders. When peck rates were manipulated in the positive orientations, peck rate in neithboring orientations changed in the opposite direction. Contrast shoulders faded after prolonged training. A second type of contrast, local contrast, was correlated with similarity of preceding stimulus and different average peck rates during different stages of the discrimination process. The data suggest that sequential local contrast accompanying the formation of a discrimination contributes to the form of generalization gradients. Blough's model of stimulus control predicts the changes in gradient form described here, but may not accurately depict the underlying process responsible for gradient form.

Animals↗

PubMed1997

Phasic temperature control appraised with the Ceres-Wheat model.

Phasic control refers to the specification of a series of different environmental conditions during a crop's life cycle, with the goal of optimizing some aspect of productivity. Because of the enormous number of possible scenarios, phasic control is an ideal situation for modeling to provide guidance prior to experiments. Here we use the Ceres-Wheat model, modified for hydroponic growth chambers, to examine temperature effects. We first establish a baseline by running the model at constant temperatures from 10 degrees C to 30 degrees C. Grain yield per day peaks at 15 degrees C at a value that is 25% higher than the yield at the commonly used 23 degrees C. We then show results for phasic control limited to a single shift in temperature and, finally, we examine scenarios that allow each of the five phases of the life cycle to have a different temperature. Results indicate that grain yield might be increased by 15-20% over the best yield at constant temperature, primarily from a boosted harvest index, which has the additional advantage of less waste biomass. Such gains, if achievable, would help optimize food production for life support systems. Experimental work should first verify the relationship between yield and temperature, and then move to selected scenarios of phasic control, based on model predictions.

Biomass↗