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PubMed2006

A stochastic model simulating paratuberculosis in a dairy herd.

Paratuberculosis (PTB) causes severe economic losses to farmers and the infection has very complex effects (many indirect) on the production of a dairy herd. These indirect effects have not or only briefly been described by earlier PTB-simulation models, and therefore they were included in a new model called PTB-Simherd. Our aim was to develop the basis for a decision-support tool which can predict herd-specific production-related effects from introduction of different control strategies against PTB. The PTB-Simherd is a dynamic, stochastic, and mechanistic Monte-Carlo model simulating a dairy herd including young stock. Paratuberculosis and relevant control strategies against this infection were built into an existing herd simulation model. The model simulates epidemiological and production related consequences of PTB and control strategies against it in the herd. It also reflects indirect effects of PTB and control strategies through effects on replacements and herd demographics. Every animal in the herd is specified with biological parameters (including PTB state and test results) and it is updated in weekly time-steps. Management is specified at herd level with 353 parameters of which 78 are related to PTB. To demonstrate the basic characteristics of the model, scenarios with varying infection risks (sensitivity analyses) plus scenarios with seven different control strategies in two herds with good and poor reproduction were simulated for 10 years. Breaking of infection routes turned out to be the only strategy predicted to reduce the true prevalence of PTB in a herd. Supplementing this strategy with test-&-cull strategies had limited effect on prevalence and using test-&-cull alone just delayed the increase in prevalence. The effects of different PTB-control strategies on the production (especially sale/purchase of heifers, feed consumption and prevalences of other diseases) were predicted to be affected by other conditions like heat-detection success, replacement% and herd demographics--which were again affected by PTB infection of the herd. These links and indirect effects of control strategies thus seem important to include when modeling and predicting effects of PTB control in dairy herds.

Animals↗

PubMed1997

Uptake of desflurane and isoflurane during closed-circuit anesthesia with spontaneous and controlled mechanical ventilation.

Although theoretical models predict uptake of inhaled anesthetics during closed-circuit anesthesia (CCA), clinical data for most anesthetics are conflicting or non-existent. In addition, the effects of patient characteristics and mode of ventilation on anesthetic uptake are unclear. Forty-one ASA physical status I or II adult patients undergoing a variety of 1-1.5 h surgical procedures were randomly allocated to receive CCA with desflurane or isoflurane with ventilation being either spontaneous or controlled. An end-expired anesthetic concentration of 1.3 minimum alveolar anesthetic concentration (MAC) was maintained by continuous injection of the liquid anesthetic into the circuit using a syringe pump. After an initial 4-min wash-in period, uptake during the first hour of CCA was nearly constant. Uptake was the same whether ventilation was spontaneous or controlled. Patient characteristics (age, height, weight, weight3/4, and body surface area) were comparable between groups and did not correlate with uptake. The virtually constant uptake after wash-in of desflurane and isoflurane contrasts with the square root of time model of Lowe and Ernst. These findings may greatly simplify CCA.

Adult↗

PubMed2003

Influence of surfactant-facilitated interfacial tension reduction on chlorinated solvent migration in porous media: observations and numerical simulation.

The ability of a multiphase flow model to capture the migration behavior of chlorinated solvents under conditions of surfactant-facilitated interfacial tension (IFT) reduction is assessed through comparison of model predictions with observations from controlled laboratory experiments. Tetrachloroethene (PCE) was released in two-dimensional saturated systems, packed with sandy media that incorporated rectangular lenses of capillary contrast. Spatially uniform interfacial tension conditions were created in the tanks by pre-flushing the porous medium with either Milli Q water or an aqueous surfactant solution. Experimental observations showed that surfactant-facilitated IFT reductions substantially lowered capillary resistance to the vertical downward migration of PCE and enabled PCE to enter finer grained, less permeable lenses that were not penetrated in the absence of surfactant. An immiscible flow model was used to simulate the conditions of the laboratory experiments. Under higher IFT conditions (47.5 and 5 dyn/cm), the model could successfully predict the general migration behavior of the organic liquid. Model predictions, however, exhibited poorer agreement with observed migration pathways under low IFT conditions (0.5 dyn/cm). In all cases, the predicted PCE distributions were influenced by selection of the parametric model for capillary retention and relative permeability. Simulated migration rates were more consistent with observed behavior when the Brooks-Corey/Burdine model was employed. For low interfacial tensions, improved predictions of migration pathways were obtained through grid refinement and incorporation of small-scale packing variability. Simulations highlight the substantial sensitivity of model predictions to the capillary pressure-scaling factor, grid resolution, and small-scale porosity variations at interfaces of permeability contrast under reduced IFT conditions.

Chlorine Compounds↗

PubMed1997

A longitudinal study of the growth of matched pairs of vegetarian and omnivorous children, aged 7-11 years, in the north-west of England.

OBJECTIVE: To assess the ability of a meat free diet to support normal growth of children. DESIGN: A one year longitudinal observational case--comparison study of growth. SETTING: Children were recruited mainly through schools from Merseyside and all measurements were taken in their homes. SUBJECTS: Fifty 'free-living' children following meat free diets, aged 7-11 y (expected to be pre-pubertal), were compared with a control group of 50 omnivores matched for age, sex and ethnic group. INTERVENTION: None. MAIN OUTCOME MEASURES: Height, weight, upper arm skinfold thicknesses and mid-upper arm circumference measurements were taken at baseline and one year later. The increments over one year were each analysed using a multiple stepwise regression model which derived predicted increments controlled for a variety of factors other than the diet factor. RESULTS: Of all the anthropometric measurements examined only the predicted height increment of the vegetarians was slightly greater than that of the omnivores (difference in predicted height increment = 0.47 cm, P = 0.05). This difference was only apparent after allowing for father's height, maternal smoking habit and number of siblings. A tendency for the vegetarians to be leaner than the omnivores was not significant at the 5% level and both the vegetarian and omnivorous groups lay close to the 50th percentiles for both height and weight (Child Growth Foundation, 1994). CONCLUSIONS: The results suggest that these children who followed a meat free diet and conventional lifestyles grew at least as well as children who ate meat.

Anthropometry↗

PubMed2004

A longitudinal study comparing the effort-reward imbalance and demand-control models using objective measures of physician utilization.

BACKGROUND: The objectives of this study were to compare the predictive validity of the demand-control and effort-reward imbalance models using objective measures of physician utilization. METHODS: Self-reports for psychosocial work conditions were obtained in interviews with 1,028 workers using the demand-control and effort-reward imbalance models. Physician utilization outcomes were obtained through linkage to the British Columbia Linked Health Database. Outcomes were any visit to a physician for mental health reasons and 30 or more physician visits for any reason. The predictive validity of both models was compared in a longitudinal study using logistic regression. RESULTS: Neither job strain nor effort-reward imbalance predicted either outcome. However, low esteem reward and low status control increased the risk for 30 or more physician visits by, respectively, approximately 60% and 30%. CONCLUSIONS: In a sample of middle-aged blue-collar current and ex-sawmill workers in Western Canada, followed prospectively, after controlling for sociodemographic and workplace confounders, and reducing the potential for adverse health selection into high-stress jobs, low esteem reward and low status control were associated with a significantly greater risk for 30 or more physician visits for any reason.

Adult↗

PubMedDate not supplied

Predicting the impact of school-based treatment for urinary schistosomiasis given by the Ghana Partnership for Child Development.

Mathematical models can be used to predict the impact of interventions to control infectious diseases. In this paper, an epidemiological model is used to predict the impact of chemotherapy of school-age children infected with Schistosoma haematobium, in a programme conducted by the Ghana Partnership for Child Development in the Volta Region, Ghana. Existing data were used to validate the predictions of the model, demonstrating convincingly the ability of the model to make correct predictions. Predictions of trends in mean egg count, infection prevalence and prevalence of heavy infection (> 50 eggs/10 mL urine) were then made for the period 1997-1999, and will be compared to the data collected in the programme in the future.

Adolescent↗

PubMedDate not supplied

Applying the theory of planned behavior to predict dairy product consumption by older adults.

OBJECTIVE: The purpose of this study was to explain intention to consume dairy products and consumption of dairy products by older adults using the Theory of Planned Behavior (TPB). The factors examined were attitudes, subjective norms, and perceived behavioral control. DESIGN: A cross-sectional questionnaire was administered. SETTING: Community centers with congregate dining programs, group classes, and recreational events for older adults. SUBJECTS: One hundred and sixty-two older adults (mean age 75 years) completed the questionnaire. Subjects were mostly women (76%) and white (65%), with about half having less than a high school education or completing high school. VARIABLES MEASURED: Variables based on the TPB were assessed through questionnaire items that were constructed to form scales measuring attitudes, subjective norms, perceived behavioral control, and intention to consume dairy products. Dairy product consumption was measured using a food frequency questionnaire. ANALYSIS: Regression analyses were used to determine the association between the scales for the 3 variables proposed in the TPB and intention to consume and consumption of dairy products; the alpha level was set at.05 to determine the statistical significance of results. RESULTS: Attitudes toward eating dairy products and perceived behavioral control contributed to the model for predicting intention, whereas subjective norms did not. Attitudes toward eating dairy products were slightly more important than perceived behavioral control in predicting intention. In turn, intention was strongly related to dairy product consumption, and perceived behavioral control was independently associated with dairy product consumption. CONCLUSIONS AND IMPLICATIONS: These results suggest the utility of the TPB in explaining dairy product consumption for older adults. Nutrition education should focus on improving attitudes and removing barriers to consumption of dairy products for older adults.

Aged↗

PubMed2003

Modeling of host genetics and resistance to infectious diseases: understanding and controlling nematode infections.

This paper considers approaches to modeling the dynamics of infectious disease and the application of such models to nematode parasite infections in ruminants. Particularly, these models are developed to account for host genetics and may be used to assess the effects of using genetics to control nematode infections. Three main issues are critically examined: the infection transmission cycle from pasture to host to pasture, the expected genetic relationships between resistance and performance, and the risks of parasite evolution in response to genetic changes in the host. To obtain answers that are realistic and of practical use, the modeling approaches require a solid grounding in biology. This biology is formalized and described using mathematical techniques, with the models parameterized using experimental or field data. Transmission dynamics have been quantified by modeling and are backed by strong experimental data. Selection for resistance will be successful in reducing egg output, pasture larval contamination and hence subsequent larval challenge. Modeling frameworks have been developed to predict genetic relationships between resistance to infectious disease and performance in general, and genetic correlations predicted for nematode resistance are close to mean published values. These predicted correlations strengthen as the larval challenge increases and the dietary (protein) adequacy decreases, however modeling challenges remain. Lastly, although convincing experimental data is not yet available, arguments based on modeling suggest that the risks of parasite evolution in response to genetic changes in the host should be less than the risks arising from other control strategies, such as anthelmintics. Thus, modeling techniques predict that selective breeding for resistance should be an effective and sustainable complementary control measure.

Animals↗

PubMed2002

The potential for establishment of axial temperature profiles during solid-state fermentation in rotating drum bioreactors.

The mixing and heat transfer phenomena within rotating drum bioreactors (RDBs) used for solid-state fermentation processes are poorly studied. The potential for the establishment of axial temperature gradients within the substrate bed was explored using a heat transfer model. For growth of Aspergillus oryzae on wheat bran within a 24 L RDB with air at a superficial velocity of 0.0023 m s(-1) and 15% relative humidity, the model predicts an axial gradient between the air inlet and outlet of 2 degrees C during rapid growth, compared to experimental axial temperature gradients of between 1 and 4 degrees C. Undesirably high temperatures occur throughout the bed under these operating conditions, but the model predicts that good temperature control can be achieved using humid air (90% relative humidity) at superficial velocities of 1 m s(-1) for a 204 L RDB. For a 2200 L RDB, good temperature control is predicted with superficial velocities as low as 0.4 m s(-1) with the airflow being switched from 90% to 15% relative humidity whenever the temperature at the outlet end of the drum exceeds the optimal temperature for growth. This work suggests that significant axial temperature gradients can arise in those RDBs that lack provision for axial mixing. It is therefore advisable to use angled lifters within RDBs to promote axial mixing.

Air Movements↗

PubMed1997

Consumer Versus Resource Control in Freshwater Pelagic Food Webs

Models predict that food-web structure is regulated by both consumers and resources, and the strength of this control is dependent on trophic position and food-web length. To test these hypotheses, a meta-analysis was conducted of 11 fish (consumer)-by-nutrient (resource) factorial plankton community experiments. As predicted, zooplankton biomass was under strong consumer control but was weakly stimulated by nutrient additions; phytoplankton biomass was under strong resource control with moderate control by fish. However, the phytoplankton and zooplankton responses to nutrient additions did not follow theoretical predictions based on the number of trophic levels in the food web.

Journal Article↗

PubMed2003

Regression methods for assessing familial aggregation of disease.

This paper reviews methods for assessing familial aggregation of disease based on simple logistic regression models. Studies are based on a case-control sampling design, where the disease status of the first degree relatives of both cases and controls are obtained. Both 'proband predictive' and 'family predictive' models are discussed, and an example is given using a case-control sample from a lung cancer study in non-smokers. The methods are extended to characterize co-aggregation of two disorders, that is, presence of one disorder in the proband increases the risk of a second disorder in the relative. An example involving eating disorders and depression is given.

Case-Control Studies↗

PubMed2004

Inter-joint coupling strategy during adaptation to novel viscous loads in human arm movement.

When arm movements are perturbed by a load, how does the nervous system adjust control signals to reduce error? While it has been shown that the nervous system is capable of compensating for the effects of limb dynamics and external forces, the strategies used to adapt to novel loads are not well understood. We used a robotic exoskeleton [kinesiological instrument for normal and altered reaching movements (KINARM)] to apply novel loads to the arm during single-joint elbow flexions in the horizontal plane (shoulder rotation was allowed). Loads varied in magnitude with the instantaneous velocity of elbow flexion, and were applied to the shoulder in experiment 1 (interaction loads) and the elbow in experiment 2 (direct loads). Initial exposure to both interaction and direct loads resulted in perturbations at both joints, even though the load was applied to only a single joint. Subjects tended to correct for the kinematics of the elbow joint while perturbations at the shoulder persisted. Electromyograms (EMGs) and computed muscle torque showed that subjects modified muscle activity at the elbow to reduce elbow positional deviations. Shoulder muscle activity was also modified; however, these changes were always in the same direction as those at the elbow. Current models of motor control based on inverse-dynamics calculations and force-control, as well as models based on positional control, predict an uncoupling of shoulder and elbow muscle torques for adaptation to these loads. In contrast, subjects in this study adopted a simple strategy of modulating the natural coupling that exists between elbow and shoulder muscle torque during single-joint elbow movements.

Adaptation, Physiological↗

PubMed2002

[The research on linear control of pneumatic artificial muscles used in medical robots].

This paper presents the properties of Pneumatic artificial muscles and its application in medical robots. The linear model construction and minimum predictive error control algorithm for artificial muscles are discussed here too. This paper provides the experimental results of linear adaptive control, which show the control algorithm has certain applicable value.

Algorithms↗

PubMed1994

Predictive control of nonlinear systems based on identification by backpropagation networks.

Using the property of universal approximation of multilayer perceptron neural network, a class of discrete nonlinear dynamical systems are modeled by a perceptron with two hidden layers. A backpropagation algorithm is then used to train the model to identify the nonlinear systems to a desired level of accuracy. Based on the identified model, a one-step-ahead predictive control scheme is proposed in which the future control inputs are obtained through some nonlinear optimization process. Making use of the online learning properties of neural networks, the predictive control scheme is further developed into an adaptive one which is robust to the incompleteness of identification. Simulation results show that this neural control scheme works well even for some very complicated nonlinear systems.

Mathematics↗

PubMed2004

Dynamical epidemic suppression using stochastic prediction and control.

We consider the effects of noise on a model of epidemic outbreaks, where the outbreaks appear randomly. Using a constructive transition approach that predicts large outbreaks prior to their occurrence, we derive an adaptive control scheme that prevents large outbreaks from occurring. The theory is applicable to a wide range of stochastic processes with underlying deterministic structure.

Journal Article↗

PubMedDate not supplied

Metabolic inhibition and di-2-ethylhexyl phthalate pharmacokinetics in fish.

A pharmacokinetic model for the accumulation of di-2-ethylhexyl phthalate (DEHP) by sheepshead minnow predicted a significant increase in the bioconcentration factor (BCF) of DEHP if its metabolism were inhibited. To test this prediction, fish were treated with either piperonyl butoxide (PBO) or bis-(p-nitrophenyl)phosphate (BNPP) before and during their exposure to DEHP. Compared with the controls, the PBO-treated fish showed no significant differences in either the amount of total metabolites in the fish and exposure water or the amount of DEHP in the fish. Conversely, the total amount of metabolites formed by BNPP-treated fish was only 23% of that in the control. This indicated that hydrolysis was a major pathway for DEHP metabolism in sheepshead minnow. The amount of DEHP accumulated by the BNPP-treated fish was almost twice that of the controls, which also agreed with the model prediction. A pharmacokinetic analysis of the time course of DEHP accumulation and metabolism indicated that BNPP altered the dynamics of DEHP in the fish beyond simply reducing the metabolic clearance. BNPP reduced the value of the absorption clearance to half that of the control, and the phthalate appeared to distribute more rapidly to the poorly perfused tissues. These effects may have been caused by the anticholinesterase activity of BNPP. The model-predicted BCF of DEHP in BNPP-treated fish was more than 6 times the control value, apparently as a consequence of decreased metabolic clearance and increased volume of distribution.

Animals↗

PubMed2002

Neither homeostasis model assessment nor quantitative insulin sensitivity check index can predict insulin resistance in elderly patients with poorly controlled type 2 diabetes mellitus.

To clarify whether homeostasis model assessment (HOMA IR) and quantitative insulin sensitivity check index (QUICKI) may be indicators of insulin resistance in elderly patients with type 2 diabetes mellitus, their relationship with the glucose infusion rate during the euglycemic hyperinsulinemic clamp study (clamp IR) was assessed. This study comprised 56 Japanese patients with type 2 diabetes mellitus; of these, 28 were 70 yr of age or older (group 1) and 28 were less than 70 yr of age (group 2). Their blood sugars were in poor control (fasting plasma glucose levels: group 1, 9.0 +/- 2.6 mmol/liter; group 2, 8.9 +/- 2.3 mmol/liter; hemoglobin A1c: group 1, 9.5 +/- 2.0%; group 2, 9.2 +/- 1.7%). Log-transformed HOMA IR was significantly correlated with the clamp IR in group 2 patients (r = -0.51, P < 0.01), but not in group 1 patients (r = -0.28, P = 0.15). There was a significant positive correlation between QUICKI and clamp IR in group 2 patients (r = 0.50, P < 0.01). However, no significant correlation was observed between QUICKI and clamp IR in group 1 patients (r = 0.31, P = 0.12). There was a significant correlation between log-transformed HOMA IR (r = -0.37, P < 0.01) or QUICKI (r = 0.37, P < 0.01) and clamp IR when both groups were combined. In conclusion, neither HOMA IR nor QUICKI should be used as an index of insulin resistance in elderly patients with poorly controlled type 2 diabetes mellitus. The results of this study suggest the need for developing a new noninvasive method for evaluating insulin resistance in those patients.

Aged↗

PubMed1999

Predicting variability in biological control of a plant-pathogen system using stochastic models.

A stochastic model for the dynamics of a plant-pathogen interaction is developed and fitted to observations of the fungal pathogen Rhizoctonia solani (Kühn) in radish (Raphanus sativus L.), in both the presence and absence of the antagonistic fungus Trichoderma viride (Pers ex Gray). The model incorporates parameters for primary and secondary infection mechanisms and for characterizing the time-varying susceptibility of the host population. A parameter likelihood is developed and used to fit the model to data from microcosm experiments. It is shown that the stochastic model accounts well for observed variability both within and between treatments. Moreover, it enables us to describe the time evolution of the probability distribution for the variability among replicate epidemics in terms of the underlying epidemiological parameters for primary and secondary infection and decay in susceptibility. Consideration of profile likelihoods for each parameter provides strong evidence that T. viride mainly affects primary infection. By using the stochastic model to study the dependence of the probability distribution of disease levels on the primary infection rate we are therefore able to predict the effectiveness of a widely used biological control agent.

Models, Biological↗