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PubMed1999

A behavior-based inverse kinematics algorithm to predict arm prehension postures for computer-aided ergonomic evaluation.

In this paper, the computational problem of inverse kinematics of arm prehension movements was investigated. How motions of each joint involved in arm movements can be used to control the end-effector (hand) position and orientation was first examined. It is shown that the inverse kinematics problem due to the kinematic redundancy in joint space is ill-posed only at the control of hand orientation but not at the control of hand position. Based upon this analysis, a previously proposed inverse kinematics algorithm (Wang et Verriest, 1998a) to predict arm reach postures was extended to a seven-DOF arm model to predict arm prehension postures using a separate control of hand position and orientation. The algorithm can be either in rule-based form or by optimization through appropriate choice of weight coefficients. Compared to the algebraic inverse kinematics algorithm, the proposed algorithm can handle the non-linearity of joint limits in a straightforward way. In addition, no matrix inverse calculation is needed, thus avoiding the stability and convergence problems often occurring near a singularity of the Jacobian. Since an end-effector motion-oriented method is used to describe joint movements, observed behaviors of arm movements can be easily implemented in the algorithm. The proposed algorithm provides a general frame for arm postural control and can be used as an efficient postural manipulation tool for computer-aided ergonomic evaluation.

Adult↗

PubMed1981

Alleviation of performance deficits of depression through thermal biofeedback training.

Explored thermal biofeedback as a method of reducing performance deficits associated with depression. A depressed and nondepressed control group and a depressed group given pretreatment with biofeedback were (N = 30) compared on their performance on an escape/avoidance task. As predicted by the learned helplessness model of depression, depressed controls showed significantly poorer performance than both other groups. The depressed biofeedback and nondepressed control groups did not differ from one another. Implications for alleviation of depression are discussed.

Achievement↗

PubMed1996

The applicability of the theory of planned behavior to abusive men's cessation of violent behavior.

This study examined the ability of Ajzen's (1988; 1991) Theory of Planned Behavior (TPB) to explain men's cessation of violent behavior. TPB suggests that a man's intention to abuse his female partner, and therefore his subsequent abusive behavior will be determined by: (1) his evaluation of possible outcomes of abusive behavior (attitudes toward behavior); (2) his perception of the expectations of others around him concerning violence and (3) the degree to which he believes he can control his abusive behavior. Pretest self-report measures from men and follow-up recidivism data based on partner report were available for 176 cases drawn from a previous study conducted by Harrell (1991). Reliable proxy measures for TPB variables (intentions/expectations to use violence, attitudes toward behavior, social norms, perceived behavioral control) were created. Regression analyses testing the TPB model provided modest support for prediction of intention to reabuse and subsequent abusive behavior. Of the TPB variables, perceived control appeared to be most important in understanding batterers' intentions to abuse and their subsequent abusive behavior. Refinement in measurements and the need for additional modifications to the model are discussed.

Adult↗

PubMed1988

A dynamic analysis of the ventilatory response to carbon dioxide inhalation in man.

1. The dynamics of the ventilatory response to carbon dioxide inhalation were studied in ten healthy young men using four different inspired fractions of carbon dioxide (FI, CO2) in air (0.015, 0.030, 0.045 and 0.060) successively increasing and decreasing stepwise. 2. Seven such different progressions were performed for each subject and each of seven different durations of the steps (t) ranging between 0.1 (i.e. one ventilatory cycle) and 10 min ('steady-state' conditions). The overall duration of one test (T) was taken as the sum of the seven successive FI, CO2 steps (t) plus one step, t, of air breathing. Thus, the values of T ranged between 0.8 (i.e. eight ventilatory cycles) and 80 min. Three subjects were tested twice. 3. We measured, as a function of T, the magnitude of the loops formed by the curves PA, CO2-VE and the value of the highest ventilatory response (VE max) to each progression. For all ten subjects, both functions had two maxima, one for T values of 2.6 or 8.0 min and one for T values of 24 or 40 min, and one minimum at T equal to 12 min. 4. The same measurements were made on tidal volume-response curves (PA, CO2-VT) and ventilatory frequency-response curves (PA, CO2-f) and yielded the same results except for the ventilatory frequency-response curves, for which we only found a statistically insignificant single maximum for T values of 24 or 40 min. 5. The locations of the maxima in loop magnitude and VE max were similar in duplicate tests in three subjects, whereas the quantitative values of these variables showed wide differences. 6. We compared our results with what is expected from the current linear dynamic model of ventilatory control submitted to the same forcing function: the first maximum in the loop magnitude is predicted by the model, but the second is not. The model shows no peak in the evolution of VE max. 7. We conclude that controlled system dynamics, which are the only ones included in dynamic models of ventilatory control, cannot by themselves account for our observations, and that one should take into consideration the dynamics of the controlling neuronal network.

Adult↗

PubMedDate not supplied

Design of a novel apparatus to study nitric oxide (NO) inhibition of platelet adhesion.

Nitric oxide (NO) is a simple biological molecule which inhibits adhesion and aggregation of platelets. A novel NO delivery device has been developed to quantitatively study the effects of NO concentration and flux on the adhesion of platelets to a surface. The slit-flow device is lined with a protein-coated membrane through which NO gas permeates into a perfusing platelet suspension. A model predicting spatial NO concentrations and fluxes within the flow slit was validated. At a wall shear rate of 250 s(-1), platelet adhesion was inhibited 87% relative to controls for exposures as low as 0.1 ppm NO. Corresponding model predictions of the aqueous NO concentration and fluxes at the surface were 0.15 nM, and between 0.5 and 1.1 nanomoles cm(-2) s(-1), respectively. Endothelial cells, which release NO to inhibit platelet adhesion in vivo, generate NO at an estimated flux similar to the above values. At a NO exposure of 0.02 ppm, platelet inhibition was only 10%. The delivery device is useful for other studies in which a knowledge of the spatial NO fluxes or concentrations is desired. Knowledge of these fluxes or concentrations is beneficial towards the design of biomaterials incorporating NO to inhibit platelet adhesion.

Biomedical Engineering↗

PubMed1990

A simple deterministic model for bancroftian filariasis transmission dynamics.

A differential equation model for bancroftian filariasis transmission dynamics is developed. Fluctuations of the mosquito vector population are related to environmental variables such as climate and vector control operations. Prevalence in the mosquito population and mean worm burden in the human population are considered. The behaviour of the model is compared with epidemiologic and entomological data from Pondicherry (South India). The model enables one to make predictions on the effect of future control operations.

Animals↗

PubMed2004

Pharmaceutical pricing, price controls, and their effects on pharmaceutical sales and research and development expenditures in the European Union.

BACKGROUND: Each country in the European Union (EU) currently employs direct price controls or permutations of direct price controls, such as reference pricing or limitations on returns to capital. Some countries also use volume controls. A new proposal that is being discussed would have all of the countries in the EU adopt uniform pricing for each pharmaceutical. OBJECTIVE: This paper analyzes the economic effects of free-market pricing individual-country price controls, and uniform EU price controls. METHODS: Microeconomic and mathematical models were used to simulate and predict probable economic outcomes in a comparative static setting. RESULTS: Price controls may be in the form of price ceilings or price floors. Both forms of price control generate deadweight economic losses in the short run and long run. A uniform EU price for each pharmaceutical sold there would have elements of a price ceiling in some of the countries and of a price floor in other countries. The deadweight loss incurred would be a function of the level at which the uniform price was set by the EU and the price elasticity of demand for each pharmaceutical in each country. CONCLUSIONS: Economic efficiency is maximized in both the short run and long run when prices are set in freely competitive markets. An additional important dimension of Ramsey pricing within a competitive context is that it generates funds for investment in pharmaceutical research and development, which enhances economic efficiency in the long run.

Cost Control↗

PubMed2004

Finite concentration effects on diffusion-controlled reactions.

The algorithm by Northrup, Allison, and McCammon [J. Chem. Phys. 80, 1517 (1984)] has been used for two decades for calculating the diffusion-influenced rate-constants of enzymatic reactions. Although many interesting results have been obtained, the algorithm is based on the assumption that substrate-substrate interactions can be neglected. This approximation may not be valid when the concentration of the ligand is high. In this work, we constructed a simulation model that can take substrate-substrate interactions into account. We first validated the model by carrying out simulations in ways that could be compared to analytical theories. We then carried out simulations to examine the possible effects of substrate-substrate interactions on diffusion-controlled reaction rates. For a substrate concentration of 0.1 mM, we found that the diffusion-controlled reaction rates were not sensitive to whether substrate-substrate interactions were included. On the other hand, we observed significant influence of substrate-substrate interactions on calculated reaction rates at a substrate concentration of 0.1M. Therefore, a simulation model that takes substrate-substrate interactions into account is essential for reliably predicting diffusion-controlled reaction rates at high substrate concentrations, and one such simulation model is presented here.

Computer Simulation↗

PubMed2005

Internal models in sensorimotor integration: perspectives from adaptive control theory.

Internal models and adaptive controls are empirical and mathematical paradigms that have evolved separately to describe learning control processes in brain systems and engineering systems, respectively. This paper presents a comprehensive appraisal of the correlation between these paradigms with a view to forging a unified theoretical framework that may benefit both disciplines. It is suggested that the classic equilibrium-point theory of impedance control of arm movement is analogous to continuous gain-scheduling or high-gain adaptive control within or across movement trials, respectively, and that the recently proposed inverse internal model is akin to adaptive sliding control originally for robotic manipulator applications. Modular internal models' architecture for multiple motor tasks is a form of multi-model adaptive control. Stochastic methods, such as generalized predictive control, reinforcement learning, Bayesian learning and Hebbian feedback covariance learning, are reviewed and their possible relevance to motor control is discussed. Possible applicability of a Luenberger observer and an extended Kalman filter to state estimation problems-such as sensorimotor prediction or the resolution of vestibular sensory ambiguity-is also discussed. The important role played by vestibular system identification in postural control suggests an indirect adaptive control scheme whereby system states or parameters are explicitly estimated prior to the implementation of control. This interdisciplinary framework should facilitate the experimental elucidation of the mechanisms of internal models in sensorimotor systems and the reverse engineering of such neural mechanisms into novel brain-inspired adaptive control paradigms in future.

Adaptation, Physiological↗

PubMed2000

A novel octahydropyridobenzothiazepine metabolite in human urine: biomimetic formation from the melanogen 5-S-cysteinyldopa and formaldehyde via a peculiar sulfur-controlled double Pictet-Spengler condensation.

HPLC evidence is reported demonstrating the occurrence in some human urine samples of a novel catecholic metabolite, (3R,7S)-3, 7-dicarboxy-10,11-dihydroxy-2,3,4,5,6,7,8,9-octahydropyrido[ 4,3-g][1, 4]benzothiazepine (2). The compound was shown to arise by a double Pictet-Spengler condensation of the urinary melanogen 5-S-cysteinyldopa (1) with formaldehyde, in which regioselective formation of the six-membered ring ortho to the activating hydroxyl group lends assistance to the subsequent closure of the seven-membered 1,4-thiazepine moiety. Under physiologically relevant conditions, i.e., in 0.1 M phosphate buffer pH 7.4 and at 37 degrees C, the 7,8-tetrahydroisoquinoline 5 was the sole detectable intermediate in the formation of 2. N-Acetylcysteinyldopa (4) reacted likewise with formaldehyde to give the 7, 8-dihydroxytetrahydroisoquinoline 6. The anomalous regiochemistry underlying formation of 5 and 6 was rationalized with the aid of AM1/PM3 calculations on the model alkylthiocatechol 10, predicting a higher HOMO-controlled reactivity on the position ortho rather than para to the activating hydroxyl group. The potential of the reported chemistry as a convenient synthetic access to the 2,3,4, 5-tetrahydro[1,4]benzothiazepine ring system is suggested by the efficient conversion of the cysteinylcatechol 3 to 8 in the presence of formaldehyde.

Cysteinyldopa↗

PubMedDate not supplied

The impact of three-monthly age-targetted chemotherapy on Ascaris lumbricoides infection.

The impact of 3 chemotherapeutic regimens at 3-monthly intervals against Ascaris lumbricoides infection, targetted at under 15 years old children with and without initial mass chemotherapy, and at 2-12 years old children, was studied in three Myanmar [Burmese] rural communities over a period of 2 years. Computation was made of prevalence and intensity (worm burden) of Ascaris infection, and other parameters for estimation of basic reproductive rate (R0) of the parasite and of the proportion of target age group to be treated 3-monthly (g) by employing the mathematical model for targetted chemotherapy. The 3 treatment regimens were almost equally effective in reducing prevalence and intensity in both the targetted and non-targetted age groups. Ascaris transmission in each of the 3 communities was interrupted, as indicated by the values of mean worm burden per person. The findings are compared with those of other similar studies and the reasons for the impact are discussed. The possible impact in similar endemic areas of applying the mathematical model predictions for age-targetted chemotherapy in controlling ascariasis is also discussed.

Adolescent↗

PubMedDate not supplied

Parental influences on adolescent problem behavior: revisiting Stattin and Kerr.

High school students (approximately 14-18 years old; N=2,568) completed questionnaires in which they reported on their involvement in substance use and delinquency, and their perceptions of parental warmth, control, monitoring, and knowledge. Three alternative models were compared describing the nature of relations among these variables. Problem behavior was best predicted by a model that included indirect effects of warmth, control, and monitoring (all by way of parental knowledge), as well as direct effects of control and monitoring. Analyses are framed and findings are discussed with reference to recent work by Stattin and Kerr (2000; Kerr & Stattin, 2000) on the measurement and meaning of parental monitoring.

Adolescent↗

PubMed2006

Cross-validation of a model for predicting functional status and length of stay in patients with stroke.

OBJECTIVE: In a study published in 2002, it was observed that a variable composed by the Functional Independence Measure (FIM) and the trunk control test at admission predicted 66.5% of the FIM at discharge in stroke patients. The objective was to confirm the reproducibility of this predictive model. METHODS: Retrospective study of 245 hemiparetic stroke inpatients of the rehabilitation department. The main variables studied were: trunk control test FIM at admission and compound variable (FIM+trunk control test) as independent variables and FIM at discharge and inpatient rehabilitation length of stay as dependent variables. RESULTS: Correlation between the compound variable and the length of stay was statistically significant (r=0.59), as was its correlation with the total FIM at discharge (r=0.82). The regression analysis predicted 34.3% of the length of stay variability and 66.4% of the total FIM at discharge variability. CONCLUSION: The compound variable is a reliable tool because of its reproducibility in predicting the functional level at hospital discharge in hemiparetic patients.

Activities of Daily Living↗

PubMed1984

Cognitive predictors of compliance in chronic disease patients.

Variables derived from the health locus of control construct and the Health Belief Model were used to predict compliance with medical regimen in chronically ill patients (adult-onset diabetics, hypertensives, and pulmonary disease patients). Stepwise multiple regression analyses were conducted with predictor variables: age, socioeconomic status, Internal Health Locus of Control (HLC), powerful others HLC, chance HLC, perceived severity of illness, outlook on illness, experienced symptoms, satisfaction with treatment, family support, and support of others. Dependent variables included three measures of compliance with medication regimen and two measures of compliance with self-management regimen. Patient satisfaction was a significant predictor of medication compliance, and lack of symptoms was most strongly associated with self-management compliance. Limitations of cognitive variables in predicting compliance in many chronic disease patients are discussed.

Attitude to Health↗

PubMed1997

Personal-model beliefs and social-environmental barriers related to diabetes self-management.

OBJECTIVE: The specific aims of the present study were to report on the level of personal beliefs and social and environmental barriers across different regimen areas and patient subgroups and on the relationship of personal models and perceived barriers to the level of self-management. RESEARCH DESIGN AND METHODS: This study focused on several issues related to personal models (representations of illness) and perceived barriers to diabetes self-management among a large heterogeneous survey sample of 2,056 adults throughout the U.S. RESULTS: Respondents felt that diabetes was a serious disease and that their self-management activities will control their diabetes and reduce the likelihood of long-term complications. Most frequently reported barriers were related to dietary adherence, followed by exercise and glucose testing barriers. Both personal models and barriers significantly predicted level of self-management in all three regimen areas studied (diet, exercise, and glucose testing) after controlling for the influence of demographic and medical history factors. Regimen-specific models and barriers proved to be stronger predictors than more global measures. Differences on personal models and barriers were observed among different patient groups (e.g., age, health insurance, and insulin-taking status). Possible reasons for these differences and implications for intervention and future research are discussed. CONCLUSIONS: Both the personal-model and barriers scales had good internal consistency and predicted variance in each of the self-management variables after controlling for demographic and medical history factors. These brief self-report personal-model scales demonstrated good internal reliability and were as predictive of self-management as the lengthier interview-based measures in previous studies. The assessment of the treatment effectiveness component of personal models may be sufficient for most clinical purposes.

Adult↗

PubMed2004

Time to include time to death? The future of health care expenditure predictions.

Government projections of future health care expenditures--a great concern given the aging baby-boom generation--are based on econometric regressions that control explicitly for age but do not control for end-of-life expenditures. Because expenditures increase dramatically on average at the end of life, predictions of future cost distributions based on regressions that omit time to death as an explanatory variable will be biased upward (or, more explicitly, the coefficients on age will be biased upward) if technology or other social factors continue to prolong life. Although health care expenditure predictions for a current sample will not be biased, predictions for future cohorts with greater longevity will be biased upwards, and the magnitude of the bias will increase as the expected longevity increases. We explore the empirical implications of incorporating time to death in longitudinal models of health expenditures for the purpose of predicting future expenditures. Predictions from a simple model that excludes time to death and uses current life tables are 9% higher than from an expanded model controlling for time to death. The bias increases to 15% when using projected life tables for 2020. The predicted differences between the models are sufficient to justify reassessment of the value of inclusion of time to death in models for predicting health care expenditures.

Aged↗

PubMed1980

Molecular mechanism of acetylcholine receptor-controlled ion translocation across cell membranes.

Two molecular processes, the binding of acetylcholine to the membrane-bound acetylcholine receptor protein and the receptor-controlled flux rates of specific inorganic ions, are essential in determining the electrical membrane potential of nerve and muscle cells. The measurements reported establish the relationship between the two processes: the acetylcholine receptor-controlled transmembrane ion flux of (86)Rb(+) and the concentration of carbamoylcholine, a stable analog of acetylcholine. A 200-fold concentration range of carbamoylcholine was used. The flux was measured in the millisecond-to-minute time region by using a quench flow technique with membrane vesicles prepared from the electric organ of Electrophorus electricus in eel Ringer's solution at pH 7.0 and 1 degrees C. The technique makes possible the study of the transmembrane transport of specific ions, with variable known internal and external ion concentrations, in a system in which a determinable number of receptors is exposed to a known concentration of ligand. The response curve of ion flux to ligand was sigmoidal with an average maximum rate of 84 sec(-1). Carbamoylcholine induced inactivation of the receptor with a maximum rate of 2.7 sec(-1) and a different ligand dependence so that it was fast relative to ion flux at low ligand concentration but slow relative to ion flux at high ligand concentration. The simplest model that fits the data consists of receptor in the active and inactive states in ligand-controlled equilibria. Receptor inactivation occurs with one or two ligand molecules bound. For channel opening, two ligand molecules bound to the active state are required, and cooperativity results from the channel opening process itself. With carbamoylcholine, apparently, the equilibrium position for the channel opening step is only one-fourth open. The integrated rate equation, based on the model, predicts the time dependence of receptor-controlled ion flux over the concentration range of carbamoylcholine investigated. The values of the constants in the rate equation form the basis for predicting receptor-controlled changes in the transmembrane potential of cells and the conditions leading to transmission of signals between cells.

Animals↗

PubMed1999

A prediction model for moderate or severe dehydration in children with diarrhoea.

A hospital-based unmatched case-control study (387 cases and 387 controls) was carried out at the Government Medical College Hospital, Nagpur, India, to devise and validate a risk-scoring system for predicting the development of moderate or severe dehydration in children, aged less than five years, with acute watery diarrhoea. On unconditional multiple logistic regression, 12 risk factors--infancy, minority religion, undernutrition, not washing hands by mother before preparation of food, frequency of stools > 8/day, frequency of vomiting > 2/day, measles in previous 6 months, withdrawal of breast-feeding/other feedings, withdrawal of fluids during diarrhoea, not giving oral rehydration solutions (ORS), home available fluids and both during diarrhoea--were significant. Based on regression coefficients, these factors were ascribed statistical weights of 5, 5, 4, 4, 22, 9, 11, 13, 5, 5, 5, and 7 respectively. The receiver-operating characteristic curve suggested a total score of 48 to be the best cut-off for predicting the development of moderate or severe dehydration. At this cut-off, the sensitivity, specificity, positive predictive value, Cohen's kappa, and overall predictive accuracy were 0.81, 0.81, 0.81, 0.61, and 0.86 respectively. If substantiated by further validation, this system can be used for predicting the development of dehydration at the earlier stage, thereby reducing the mortality associated with life-threatening dehydration.

Acute Disease↗