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Results for “model predictive control”

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PubMed1980

Variable open-loop gain in the control of thermogenesis in cold-exposed rabbits.

We have previously demonstrated a multiplicative interaction between mean skin temperature (Tsk) and hypothalamic temperature (Thy) in the control of thermogenesis in cold exposed rabbits. Such a model predicts that open-loop gain will not be constant, but will vary according to the direction and degree of Thy displacements and to the prevailing level of Tsk when Thy is altered. Open-loop gain was calculated from steady-state displacements in body temperature induced by sustained step displacements in Thy. Hypothalamic temperature of rabbits was clamped at various levels ranging from 2 degrees C above to 3 degrees C below normal Thy and the resulting changes in rectal temperature attained at steady state were recorded. Experiments were conducted at ambient temperatures (Ta) of 2 degrees and 15 degrees C. Open-loop gain in response to hypothalamic heating was always greater than that obtained in response to equivalent levels of hypothalamic cooling. Furthermore, at lower levels of Tsk (Ta = 2 degrees C) open-loop gain was greater for all levels of Thy displacement when compared to that measured at higher levels of Tsk (Ta = 15 degrees C).

Animals↗

PubMed1995

Costs of care and outcomes for high-dose therapy and autologous transplantation for lymphoid malignancies: results from the University of Nebraska 1987 through 1991.

PURPOSE AND METHODS: High-dose therapy with autologous stem-cell support has become common treatment for relapsed or refractory lymphomas. We conducted a study of 178 patients with Hodgkin's disease and 149 patients with non-Hodgkin's lymphoma who received high-dose therapy with stem-cell support. We evaluated the following: (1) whether improvements in outcomes over time found for surgical procedures were also true for a new nonsurgical procedure, autologous bone marrow and peripheral stem-cell transplantation; and (2) whether such a relationship, if it existed, applied to both clinical and economic outcomes. RESULTS: Mortality rates for patients with Hodgkin's disease decreased from 20% in 1987 to 0% in 1991. For non-Hodgkin's lymphoma, the mortality rate decreased from 29% in 1987 to 4% in 1991. Multivariate analyses indicated that the number of previous transplants was the most important factor associated with survival and low-cost care. After controlling for differences in clinical factors, a logistic regression model predicted that patients with Hodgkin's disease had a 20% chance of dying after 30 cases and a 5% chance after 178 cases; patients with non-Hodgkin's disease had a 33% chance of dying after 14 cases and a 5% chance after 149 cases. For patients with Hodgkin's disease, the cost decreased at a rate of 10% per year from 1987 to 1991 (P = .001), while for patients with non-Hodgkin's lymphoma, the cost of transplants decreased at a rate of 8% per year. CONCLUSION: Survival rates improved and costs of care decreased over time for patients who received high-dose therapy with stem-cell support. These changes are most likely related to improvements in supportive care technologies, better patient selection, and experience of the transplant team.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed1999

Cost-effectiveness of donepezil in the treatment of mild or moderate Alzheimer's disease.

OBJECTIVE: To demonstrate the use of cost-effectiveness analysis to assess the economic impact of donepezil in the treatment of mild or moderate AD. BACKGROUND: Cost-effectiveness analyses show the relationship between resources used (costs) and health benefits achieved (effects) for an intervention compared with an alternative strategy. METHODS: We developed a model to estimate the incremental cost-effectiveness of donepezil compared with no treatment. We determined costs per quality-adjusted life-years gained, a measurement that enhances the comparability of diverse studies. The model projects the progression of AD patients into more severe disease stages and into nursing homes. Data from a randomized clinical trial of donepezil were used to assess the drug's impact on the 6-week probabilities of progression. Data on the costs and health-related quality of life associated with different disease stages and settings were taken from published estimates and our companion cross-sectional study, respectively. RESULTS: Donepezil costs are partially offset by a reduction in the costs of care due to enhancement in cognitive functioning and the delay to more costly disease stages and settings. The magnitude of this cost offset and of the effect of donepezil on health-related quality of life depends on the model's assumptions about the duration of the drug effect, where controlled data are lacking. If the drug effect exceeds 2 years, the model predicts that for mild AD the drug would pay for itself in terms of cost offsets. CONCLUSIONS: The results of the cost-effectiveness model presented here suggest that donepezil may be cost-effective but additional controlled data on long-term drug efficacy are needed.

Alzheimer Disease↗

PubMed2004

Hysteresis and cell cycle transitions: how crucial is it?

Recently, experiments have shown that cyclin-dependent kinase (CDK) activity exhibits hysteresis in its response to total cyclin when cyclin is made nondegradable and controlled externally. This observation was taken to support mathematical modeling predictions regarding the underlying dynamics of the cell cycle. However, cell cycle dynamics can also be generated by other nonhysteretic mechanisms. To examine the robustness of the hysteretic response of CDK activity to total cyclin, we simulated various cell cycle signal transduction networks, and correlated the dynamics to the response function of CDK activity versus total cyclin. By randomly searching the parameter space, we assessed robustness by estimating the frequency of hysteretic versus nonhysteretic dynamical mechanisms. When the dynamical instabilities were caused by feedback loops in CDK phosphorylation and dephosphorylation or by feedback between cyclin and the CDK inhibitor, the response function of CDK activity versus total cyclin correlated well with the dynamical instabilities. However, when the dynamical instabilities originated from feedback between cyclin and APC-CDH1 or RB-E2F, the response function did not correlate with dynamical instabilities. Thus, although a hysteretic response is neither necessary nor sufficient, it is in general a much more robust mechanism for generating cell cycle dynamics than nonhysteretic mechanisms.

Biological Clocks↗

PubMed2004

Adherence to conventional and atypical antipsychotics after hospital discharge.

BACKGROUND: This prospective study measured adherence to conventional and atypical antipsychotics after hospital discharge in patients with a diagnosis of schizophrenia and schizoaffective disorder. We examined the interaction of several predictors such as gender, severity of illness, attitudes toward medications, side effects, and dose frequency. METHOD: The sample consisted of consecutive randomized and nonrandomized patients who were discharged from an inpatient unit with a DSM-IV diagnosis of schizophrenia or schizoaffective disorder between December 1995 and July 1999. All patients were taking oral antipsychotics and consented to the use of an electronic adherence monitor at discharge. Medications were prescribed by usual care providers, and medication adherence was followed weekly for 3 months. The outcome measure was the medication adherence rate registered in the electronic monitors. RESULTS: We found no significant difference in adherence between the combined groups of atypical and conventional antipsychotics. Individual medication analysis found better medication adherence with olanzapine in comparison with risperidone and conventional antipsychotics, but the difference disappeared in the final model controlling for dose frequency. Dose frequency, gender, and akathisia predicted adherence. CONCLUSIONS: Olanzapine initially appeared to be associated with an adherence advantage over risperidone and conventional antipsychotics, but the apparent advantage may have been due to a usual care dose frequency practice that associated olanzapine more often with once-daily dosing. This study suggests that dose frequency is an important predictor of medication adherence. An important caveat is that these results apply only to short-term adherence.

Adult↗

PubMed1984

A cardiovascular model for studying impairment of cerebral function during +Gz stress.

A digital computer model of the human cardiovascular system has been developed which can be used for studying impairment of cerebral function during +Gz stress. The model includes simulation of the arterial and venous systems, the heart, baroreceptor control of heart rate, control of venous tone, and the effect of gravity. Model predictions suggest that, for unprotected subjects, carotid pressure at eye level decreases to 50 mm Hg (beginning of peripheral light loss) at approximately 2.7 Gz. The pressure decreases to 20 mm Hg (beginning of central light loss) at approximately 3.6 Gz. An anti-G suit provides an extra 1.1 to 1.5 Gz protection. Even though blood pressure supplying retinal vessels drops significantly at the above G levels, cerebral blood flow is maintained due to protective and compensatory mechanisms. These observations compare favorably with results reported in the literature. The results suggest that this model can be used to improve our understanding of the cardiovascular system's response to +Gz stress.

Aerospace Medicine↗

PubMed2005

Chemical reaction dynamics within anisotropic solvents in time-dependent fields.

The dynamics of low-dimensional Brownian particles coupled to time-dependent driven anisotropic heavy particles (mesogens) in a uniform bath (solvent) have been described through the use of a variant of the stochastic Langevin equation. The rotational motion of the mesogens is assumed to follow the motion of an external driving field in the linear response limit. Reaction dynamics have also been probed using a two-state model for the Brownian particles. Analytical expressions for diffusion and reaction rates have been developed and are found to be in good agreement with numerical calculations. When the external field driving the mesogens is held at constant rotational frequency, the model for reaction dynamics predicts that the applied field frequency can be used to control the product composition.

Anisotropy↗

PubMedDate not supplied

Factors controlling sorption of prosulfuron by variable-charge soils and model sorbents.

Prosulfuron [1-(4-methoxy-6-methyltriazin-2-yl)-3-[2-(3,3,3-trifluoropropyl) phenylsulfonyl]-urea), a relatively new sulfonylurea herbicide, is a weak acid (pK(a) 3.76), and therefore, will undergo pH-dependent speciation and sorption. Understanding prosulfuron sorption in soils is important for predicting its environmental fate. Soil and solution factors controlling sorption were investigated by measuring prosulfuron sorption on five model sorbents (amorphous silica, alpha-alumina, CaSWy1 montmorillonite, commercial humic acid, and anion exchange resin) and 10 variable-charge soils from CaCl(2) and Ca(H(2)PO(4))(2) solutions as a function of pH and ionic strength. Anion exchange of prosulfuron accounted for up to 82% of overall sorption in the pH range from 3 to 7. The relative importance of anion exchange to prosulfuron sorption was positively correlated to the ratio of anion and cation exchange capacities. Comparison between organic carbon (OC)-normalized sorption (K(oc)) versus pH for humic acid and variable-charge soils show similar trends with sorption decreasing with increasing pH. However, K(oc) values estimated from variable-charge soils in the lower pH range where anion exchange has the greatest contribution to sorption was almost one log unit greater than that estimated from humic acid clearly exemplifying the impact of anion exchange. Similarity in K(oc)-pH curves for humic acid and variable-charge soils may result from the fact that (i) cation exchange capacity increases with increasing OC content, thus effective anion exchange capacity is reduced; and (ii) the relative contribution of hydrophobic and hydrophilic sorption mechanisms was fairly constant. Given that both hydrophilic and hydrophobic sorption of prosulfuron decrease with increasing pH, addition of fertilizer and lime amendments may enhance the potential for off-site leaching of recently applied acidic pesticides.

Adsorption↗

PubMed1999

How well do elderly people cope with uncertainty in a learning task?

The relation between age, task complexity and learning performance in a Multiple Cue Probability Learning task was studied by systematically varying the level of uncertainty present in the task, keeping constant the direction of relationships. Four age groups were constituted: young adults (mean age = 21), middle-aged adults (45), elderly people (69) and very elderly people (81). Five uncertainty levels were considered: predictability = 0.96, 0.80, 0.64, 0.48, and 0.32. All relationships involved were direct ones. A strong effect of uncertainty on 'control', a measure of the subject's consistency with respect to a linear model, was found. This effect was essentially a linear one. To each decrement in predictability of the task corresponded an equal decrement in participants' level of control. This level of decrement was the same, regardless of the age of the participant. It can be concluded that elderly people cope with uncertainty in probability learning tasks as well as young adults.

Adaptation, Psychological↗

PubMedDate not supplied

Predicting the ultraviolet radiation distribution in a room with multilouvered germicidal fixtures.

Irradiating the upper part of a room with 254-nm ultraviolet (UV) radiation from a low-pressure mercury discharge lamp has the potential to be a relatively inexpensive method to reduce transmission of airborne infectious diseases such as tuberculosis. To protect occupants in the lower part of a room from radiation, multilouvered UV germicidal fixtures producing a horizontal, collimated beam are often used, particularly in rooms having a normal ceiling height. Knowledge of the fixture's emission characteristics and the airflow field are needed to estimate the UV dose to airborne microorganisms and assess the fixture's overall effectiveness in controlling disease transmission. In this article, a model is developed to predict the UV fluence rate at any location in the upper room for ceiling-mounted, multilouvered, pendant-type fixtures, which provide 360-degree emission in the horizontal plane. The model also predicts total UV power emitted by the fixture, which is the best single-number effectiveness index for comparing multilouvered UV germicidal fixtures. Model predictions compared favorably with laboratory and field measurements.

Disinfection↗

PubMed2002

Stochastic modelling of phosphorus transfers from agricultural land to aquatic ecosystems.

This paper describes a simple model of phosphorus (P) transfer from agricultural land to surface waters which incorporates the effects of spatial variability in catchment properties and uncertainty in model parameter values. TOPMODEL concepts are used to estimate water, solute and sediment fluxes to water bodies. The model predicts the spatial distribution of water table depth and saturation-excess overland flow based on topography. Dissolved P (DP) transfer is assumed to occur vertically in the unsaturated zone and laterally in the saturated zone. Readily soluble P is assumed to decrease exponentially with soil depth. Particulate P (PP) transfers are modelled by estimating overland flow discharge and associated sediment transport capacity. Uncertainty in the distribution of soil surface P concentrations and model parameters controlling the mobility of soil P are incorporated using Monte Carlo simulation. Predicted losses of DP are well correlated with discharge and those of PP are episodic. Highest losses of P tended to be predicted near to the stream where the water table is close to the surface. The combination of a deterministic model core with a stochastic generation of model parameters or state variables provides an attractive way of embracing variability and uncertainty in models of this kind.

Agriculture↗

PubMed2000

Economic assessment of troglitazone as an adjunct to sulfonylurea therapy in the treatment of type 2 diabetes.

OBJECTIVE: To assess the economic efficiency of adding troglitazone to sulfonylurea therapy to improve glycemic control. BACKGROUND: Despite the high prevalence of type 2 diabetes, existing treatment strategies often fail. New oral agents give a wider segment of the population with type 2 diabetes hope of achieving near-normal blood-glucose levels. Troglitazone, a novel chemical entity, is one promising new agent. METHODS: We conducted an economic analysis based on glycemic-control data from a randomized clinical trial comparing troglitazone with placebo, each added to glyburide. A patient simulation model was used to translate these data to long-term outcomes associated with diabetes. Patients had poorly controlled type 2 diabetes mellitus despite glyburide therapy. Risk functions of developing and progressing through nephropathy, retinopathy, neuropathy, hypoglycemia, and macrovascular disease were developed from the Diabetes Control and Complications Trial and large epidemiologic studies. Cost estimates were based on data from 5 states, all payor databases, surveys, and literature. The main outcomes of the model were cost-consequences, number of patients developing each type of complication, mean time to development of the complication, cost per life-year gained (LYG), and cost per quality-adjusted life-year. RESULTS: The model predicts that for every 1000 patients treated with troglitazone, the improved glycemic control could mean that 95 to 140 fewer patients would experience one of the most severe diabetic complications (eg, blindness, end-stage renal disease, amputation), which may increase life expectancy by 2.0 years. These benefits are obtained at an additional $2100 per LYG (undiscounted). The ratio remains <$50,000 per LYG for most variations in input. CONCLUSIONS: The clinical trial demonstrated that troglitazone + glyburide improves glycemic control compared with glyburide alone. Based on these results, the model estimates fewer diabetic complications at a cost well below accepted cost-effective thresholds.

Adult↗

PubMed2002

The cerebellum and the timing of coordinated eye and hand tracking.

The cerebellum is known to have important functions in motor control, coordination, motor learning, and timing. It may have other "higher" functions as well, up to and including cognitive processing independent of motor behavior. In this article, we will review some of the evidence from functional imaging, lesion studies, electrophysiological recordings, and anatomy which support the theory that the cerebellum provides a "forward model" of the motor system. This forward model would be used for control of movement; it could also underlie a cerebellar role in coordination. In this role, the forward model would generate time-specific signals predicting the motion of each motor effector, essential for predictive control of, for example, eye and hand movements. Data are presented from human eye and hand tracking that support this. Tracking performance is better if eye and hand follow the same spatial trajectory, but better still if the eye leads the hand by about 75 to 100 ms. This suggests that information from the ocular control system feeds into the manual control system to assist its tracking.

Adult↗

PubMed1999

Associations between drug abuse treatment and cigarette use: evidence of substance replacement.

The influence of risk-behavior bias, drug use, prior cigarette use, and prior and current participation in drug treatment on cigarette use was analyzed using a 3-wave survey of 346 drug abusers. Participation in drug treatment and a risk-behavior bias were hypothesized to predict greater cigarette use. After controlling for prior levels of cigarette use with a longitudinal path model, it was found that participation in drug treatment at Wave 2 significantly predicted increased cigarette use at Wave 2. There were similar results at Wave 3. Additional analyses indicated that reduced heroin use was especially associated with more smoking. Risk-behavior bias predicted more drug and cigarette use and predicted less participation in drug treatment at Wave 3. These results suggest that drug treatment, reduced heroin use, and a tendency toward risky behavior may lead to increased cigarette use, which may represent a form of substance replacement.

Adult↗

PubMed2002

Soft sensors for control of nitrogen and phosphorus removal from wastewaters by neural networks.

In this paper, we describe the results of research aimed to evaluate the possibility of using a neural network (NN) model for predicting biological nitrogen and phosphorus removal processes in activated sludge, utilising oxidation reduction potential (ORP) and pH as NN inputs. Based on N and P concentrations predictions obtained via the NN, a strategy for controlling sequencing batch reactors (SBRs) phases duration, optimising pollutants removal and saving energy, is proposed. The NN model allowed us to reproduce the concentration trends (change in slope, or process end), with satisfactory accuracy. The NN results were generally in good agreement with the experimental data. These results demonstrated that NN models can be used as "soft on-line sensors" for controlling biological processes in SBRs. By monitoring ORP and pH, it is possible to recognise the N and P concentrations during different SBRs phases and, consequently, to identify the end of the biological nutrient removal processes. This information can then be used to design control systems.

Hydrogen-Ion Concentration↗

PubMed2001

Neuromodulatory control of interacting medial temporal lobe and neocortex in memory consolidation and working memory.

A model of the interacting medial temporal lobe and neocortical association areas is formulated and applied to memory consolidation and working memory. A simplified connectivity in terms of superassemblies and assemblies of neurons representing types and values, respectively, of object features is underlying the model. Realistic low-dimensional model neurons, developed in particular to take neuronal adaptation into account, are employed. Observed short- and long-term potentiation and depression of plastic synaptic couplings are incorporated. It is shown that memory consolidation by long-term potentiation, based on repeated activations of neocortical patterns, may be guided by neuromodulated dynamics of the medial temporal lobe via short-term couplings acting as pointers. Bifurcations, i.e. transitions between different modes of network dynamics, with respect to developing synaptic couplings are shown to depend on the adaptivity of excitatory neurons in the medial temporal lobe and thus to be under neuromodulatory control. At weak adaptivity, after an initial temporal segmentation of several objects accounting for the capacity of working memory to resolve several items, attention is selectively focused on a single object according to the model. At intermediate adaptivity, reactivations may persist and long-term synaptic couplings gradually develop. At strong adaptivity, the model predicts attention and memory consolidation to be subsequently terminated. The neuromodulatory control of the interacting medial temporal lobe and neocortical system via the adaptivity of excitatory neurons may account for several observations on the influence of neuromodulators on various cognitive processes and brain disorders.

Animals↗

PubMed2005

Automatic intraaortic balloon pump timing using an intrabeat dicrotic notch prediction algorithm.

PURPOSE: The efficacy of intraaortic balloon counterpulsation (IABP) during arrhythmic episodes is questionable. A novel algorithm for intrabeat prediction of the dicrotic notch was used for real time IABP inflation timing control. DESCRIPTION: A windkessel model algorithm was used to calculate real-time aortic flow from aortic pressure. The dicrotic notch was predicted using a percentage of calculated peak flow. Automatic inflation timing was set at intrabeat predicted dicrotic notch and was combined with automatic IAB deflation. EVALUATION: Prophylactic IABP was applied in 27 patients with low ejection fraction (< 35%) undergoing cardiac surgery. Analysis of IABP at a 1:4 ratio revealed that IAB inflation occurred at a mean of 0.6 +/- 5 ms from the dicrotic notch. In all patients accurate automatic timing at a 1:1 assist ratio was performed. Seventeen patients had episodes of severe arrhythmia, the novel IABP inflation algorithm accurately assisted 318 of 320 arrhythmic beats at a 1:1 ratio. CONCLUSIONS: The novel real-time intrabeat IABP inflation timing algorithm performed accurately in all patients during both regular rhythms and severe arrhythmia, allowing fully automatic intrabeat IABP timing.

Aged↗

PubMed1989

Limitation of experimental infarct size by drugs.

Testing drugs on their efficacy in limiting infarct size is difficult in the experimental setting because of the considerable variation in the sizes of infarcts produced in control animals, mainly in dogs. This variation in infarct size in the canine model is theoretically related to variations in the size of the ischemic bed or area at risk, in pre-existing collateral blood flow, and in myocardial metabolic demand. In this study, we identified the determinants of infarct size after different periods of coronary artery occlusion in unconscious dogs and constructed a mathematical model based on these determinants using stepwise logistic regression analysis. Eighty-nine percent of the variability in infarct size is accounted for by variations in the size of the ischemic bed and coronary collateral blood flow. Using this model, we were able to predict infarct size and to make valid comparisons between treated and control groups.

Animals↗