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PubMed2002

Misalignment tolerance analysis of free-space optical interconnects via statistical methods.

System-level packaging is one of the critical issues that need to be addressed for free space optical interconnections (FSOI) to become useful in desktop systems. The performance of FSOI, e.g., in terms of system bit-error rate, is greatly affected by misalignments in the optical system. Therefore tolerancing, i.e., the ability to analyze and predict the effects of misalignments in the system, is of prime importance to system designers. We introduce an approach in which we study the effects of optical misalignments and other tolerance factors using statistical methods. We use Monte Carlo simulations, design of the experiments, and regression techniques to fit a polynomial equation that expresses the relationship between the system performance and the tolerance factors. This prediction model can be used for design, cost optimization, and quality control purposes. In addition, we perform a sensitivity analysis to determine those tolerance variables that have the greatest effect on system performance.

Journal Article↗

PubMed1993

Bias in learning disabilities placement.

A nationally representative sample of 20,614 eighth grade students was examined for bias in placement decisions for children said to have learning disabilities. Factors investigated for bias were race, sex, and socioeconomic status. Path analysis showed significant and direct paths from sex and race to placement, controlling for socioeconomic status, academic ability, and behavioral competency. Boys were overrepresented in such classes beyond what their somewhat lower academic and behavioral competencies would predict. Caucasians were similarly overrepresented controlling for other variables in the model. It appears that boys and Caucasians are overrepresented in learning disabilities placements on a national scale even when other contributing factors are controlled.

Bias↗

PubMed2003

Variables related to graduate students' willingness to forgive a job-related transgression.

43 graduate students' willingness, within a hypothetical situation, to forgive a friend whose negligent actions negatively affected their chances of getting a job was examined. Self-actualization, age, and general interpersonal closeness were proposed as possible variables related to these students' ratings of willingness to forgive while controlling for sex. A hierarchical multiple regression analysis showed this model predicted 23% of the variability in Forgiveness scores using self-actualization and age as significantly related to forgiveness in a positive direction, but with sex and general interpersonal closeness showing no significant relation.

Adult↗

PubMed1999

Beta 2-adrenoceptor agonist-induced down-regulation after short-term exposure.

We examined the effect of duration of beta 2-adrenergic receptor (beta 2AR) occupancy by isoproterenol on specific binding of 125I-lodocyanopindolol (125I-ICYP) in membranes from rat L6 myoblasts. Ten minute exposure caused a time-and concentration-dependent maximal decrease in 125I-ICYP binding 24 hours after exposure equal to that following continuous exposure (p < 0.05). Low temperature, concanavalin A, H89 and ICl 118,551 blocked the decline in 125I-ICYP binding during the first hour following exposure probably representing receptor sequestration to a compartment or change to a form incapable of ligand binding. Compared to controls, receptor binding 4 and 24 hours following exposure was reduced 56 +/- 8.7% and 72 +/- 8.8%, respectively (p < 0.05), and was blocked by ICl 118,551 but not CGP12177. Isoproterenol-induced, but not forskolin-stimulated, cAMP accumulation was reduced 35% 24 hours following exposure (p < 0.05). 125I-ICYP binding in intact L6 cells 4 and 24 hours after exposure were respectively 56 +/- 8.9 and 61 +/- 13% of controls (p < 0.05). Following agonist exposure, CHO cell membranes expressing human beta 2ARs exhibited 125I-ICYP binding 85 +/- 2.0% and 6 +/- 2.8% of control values 4 and 24 hours, respectively (p < 0.05). A model predicting that full occupation of the beta 2AR activates receptor degradation explains our results that agonist-induced down-regulation of beta 2AR does not require continuous presence of the agonist.

Adrenergic beta-Agonists↗

PubMed1998

A general framework illustrating an approach to quantitative microbial food safety risk assessment.

Hazard analysis critical control point (HACCP), risk assessment, predictive microbiology, and dose-response modeling have been recognized as important tools for the assessment and management of health risks posed by food-borne pathogens. Unfortunately, the biology of both the food chain and food poisoning is complex and dynamic. Therefore, mathematical modeling of microbial risk from food production through to consumption and illness is difficult. Nevertheless, previous authors have made impressive progress in modeling specific pathogen-food-consumer combinations. In this study a framework for a Monte Carlo model of a generic food system was developed. It links together food ingredients, batch processing, cross contamination, microbial growth, cooking, recontamination, consumption, human exposure to pathogens, the dose-response relationship, and the biologic and economic impact components of such risks. This framework is presented to illustrate one potential approach to quantitative risk assessment for microbial food safety. It requires refinement with appropriate distributions and mathematical relationships before it can be applied to a specific pathogen-food-consumer situation.

Food Handling↗

PubMed2002

Cigarette smoking in an adolescent psychiatric population.

OBJECTIVE: To examine the relationship between cigarette smoking and psychiatric symptomatology in an outpatient psychiatric population of adolescents. METHOD: A retrospective analysis was done of 934 patient charts at an outpatient psychiatric centre. RESULTS: 48.4% of the psychiatric sample reported regular smoking behaviour, which is substantially more than the 18.1% prevalence found in a local epidemiological study. In comparing smokers and non-smokers within the psychiatric sample, it was noted that smokers were significantly younger and scored somewhat higher on depression rating scales than non-smokers. A logistical regression, using quasi-Newton estimation, was chosen as the most suitable statistical method for building a classificatory model of smoking. Two continuous variables, age and the Hamilton depression score, along with 39 discrete variables, were chosen for modelling purposes. Model building was conducted in a hierarchical fashion, starting with demographic variables, the variable selection being controlled by using chi-square tests of model differences. A predictive model of smoking with nine variables was finally selected. CONCLUSIONS: As a whole the results support the strong association between smoking and psychiatric problems, but in this adolescent sample smoking is more likely to be part of a general risk-taking behaviour pattern than an attempt to medicate depression. Anti-tobacco campaigns that highlight the risks of smoking are therefore open invitations for adolescents to take up the habit.

Adolescent↗

PubMedDate not supplied

[A complex approach to modeling the functional status of a human operator based on the theory of fuzzy sets].

At present the man-operator acting as part of an automatic system experiences ever increasing physical and emotional stresses which makes it highly important to know how to measure reliably his functional state (FS). It is generally recognized that the FS is of systemic nature but the system concept has not been adequately investigated by experiment. The FS evaluation is usually reduced to one of the FS levels. The FS concept is replaced with the concept of the state of bodily functions. It is claimed that the FS can be better explored and estimated with the aid of mathematical models which represent it as a complex psychological event produced by interactions of all psychophysiological systems, operator's activities and his attitudes to them. This paper discusses an FS model which describes the FS from the systemic point of view and helps an investigator to test his hypotheses and heuristics. The model is hierarchic. Its first level is determined by models of such elements of the man-machine system as activities, psycho-physiological transformations, psychological transformations, object of monitoring and control, information system. Such models can be used to evaluate and predict the quality of the function of the above elements in relation to their inherent tasks. The second level of the FS model is associated with its complex evaluation as a systemic formation based on potential interactions (links) between elements.

Humans↗

PubMed1989

Limb segment information transmission capacity.

Movement time for finger, wrist, and whole arm motions were investigated in relation to Fitts' Index of Difficulty (ID = log2 2A/W) over movement distances of 0.25 to 30.5 cm. Results supported Fitts' original theory that various limb segments may show different maximum information processing rates. Short-distance finger and wrist motions showed much higher rates than longer distance arm motions. Examination of motion trajectories qualitatively supported a descriptive model whereby a visually mediated discrete correction control process is used. However, evidence of severe nonlinearities in the measured humam movement responses did not support the use of linear control models in explaining the empirical validity of Fitts' law in predicting human motor performance.

Adult↗

PubMed2005

Oscillations in plant membrane transport: model predictions, experimental validation, and physiological implications.

Although oscillations in membrane-transport activity are ubiquitous in plants, the ionic mechanisms of ultradian oscillations in plant cells remain largely unknown, despite much phenomenological data. The physiological role of such oscillations is also the subject of much speculation. Over the last decade, much experimental evidence showing oscillations in net ion fluxes across the plasma membrane of plant cells has been accumulated using the non-invasive MIFE technique. In this study, a recently proposed feedback-controlled oscillatory model was used. The model adequately describes the observed ion flux oscillations within the minute range of periods and predicts: (i) strong dependence of the period of oscillations on the rate constants for the H+ pump; (ii) a substantial phase shift between oscillations in net H+ and K+ fluxes; (iii) cessation of oscillations when H+ pump activity is suppressed; (iv) the existence of some 'window' of external temperatures and ionic concentrations, where non-damped oscillations are observed: outside this range, even small changes in external parameters lead to progressive damping and aperiodic behaviour; (v) frequency encoding of environmental information by oscillatory patterns; and (vi) strong dependence of oscillatory characteristics on cell size. All these predictions were successfully confirmed by direct experimental observations, when net ion fluxes were measured from root and leaf tissues of various plant species, or from single cells. Because oscillatory behaviour is inherent in feedback control systems having phase shifts, it is argued from this model that suitable conditions will allow oscillations in any cell or tissue. The possible physiological role of such oscillations is discussed in the context of plant adaptive responses to salinity, temperature, osmotic, hypoxia, and pH stresses.

Adaptation, Physiological↗

PubMed1999

Development of a kinetic model for L-lysine biosynthesis in Corynebacterium glutamicum and its application to metabolic control analysis.

A mathematical model describing intracellular lysine synthesis by Corynebacterium glutamicum in batch fermentation was developed. The model is based on material balance equations of the key metabolites, and includes mechanistically based, experimentally matched rate equations for individual enzymes. From the measurements of the levels of intra- and extracellular metabolites during cultivation, the kinetic parameters in the model were identified through the decomposition of the network of reactions. The model predictions and experimental observations were in reasonable agreement. Using the model developed, metabolic control analysis was carried out to identify the rate-limiting steps, by evaluating the control on the overall lysine synthesis flux exerted by individual enzymatic reactions, which suggested how the control on lysine synthesis changes from aspartokinase to lysine permease as fermentation proceeded and indicated that lysine production could be enhanced by improving aspartokinase activity of this strain through genetic manipulation.

Journal Article↗

PubMed1993

Effect of obesity on vancomycin pharmacokinetic parameters as determined by using a Bayesian forecasting technique.

Few data exist concerning the effect of obesity on the pharmacokinetic parameters of vancomycin. The purpose of this investigation was to assess the effect of obesity on vancomycin pharmacokinetic parameters in 95 nonobese and 135 obese adult patients (age range, 18 to 92 years) receiving vancomycin. All subjects had normal renal function as defined by a creatinine concentration in serum of < or = 1.5 mg/dl (mean estimated creatinine clearance +/- 1 standard deviation, 76 +/- 34; range, 23 to 215 ml/min). Vancomycin concentrations in serum were determined by the fluorescence polarization immunoassay. All data for vancomycin concentration in serum versus time for each course of therapy were fitted by using a two-compartment Bayesian forecasting program. Subjects were stratified into nine groups on the basis of the percent difference between actual body weight (ABW) and lean body weight (LBW) (> -10%, -10 to 0%, > 0 to 10%, > 10 to 20%, > 20 to 30%, > 30 to 40%, > 40 to 50%, > 50 to 60%, > 60%). Analysis of variance with post hoc Scheffe's testing revealed that statistically significant differences occurred in terminal disposition half-life (t1/2 beta) between the extremes of modestly obese (group 4) and morbidly obese (group 9, P < 0.05) patients. Similar analysis with distribution volume (V) identified significant differences in patients at or near their LBW (groups 2 to 4) and patients who were morbidly obese (groups 8 and 9, P < 0.05). Multiple regression models for the pharmacokinetic parameters V, t1/2beta, and vancomycin total body clearance were developed to assess the joint predictive power of LBW, ABW, and percent over LBW, controlling for the effects of age, initial creatinine concentration in serum, initial creatinine clearance, and gender. In the final model for V, both ABW and percent over LBW were independent and significant predictors. For total body clearance, only ABW was significant and predictive. Percent over LBW was a significant and independent predictor of t1/2beta. LBW is not predictive of these pharmacokinetic parameters and should not be used for initial dosing. On the basis of these data, ABW appears to be superior to LBW for calculating initial dose requirements for vancomycin.

Adolescent↗

PubMed1996

Pharmacodynamic modeling of prolonged administration of etoposide.

PURPOSE: A refined pharmacodynamic model for toxicity is necessary for successful adaptive control of the administration of an anticancer drug to avoid toxicity. We sought to establish a pharmacodynamic model of leukopenia in a 14-day administration of etoposide. METHODS: Pharmacokinetic data of 32 patients treated with etoposide infused over 14 days in a phase I study (20 patients) or in an adaptive control study (12 patients) were used to develop a model for the prediction of a leukocyte nadir count. The concentrations of both estimated unbound and total etoposide at steady state, as well as patient demographic factors, were included in linear and nonlinear models. The unbound fraction of etoposide was estimated using an equation based on serum albumin and total bilirubin. The efficacy of the models was evaluated in terms of correlation coefficient (r), mean predictive error (MPE) and root mean square error (RMSE). RESULTS: For both total and unbound drug concentration, a nonlinear model predicted leukopenia more precisely and with less bias than a linear model, and unbound drug explained more variability of leukopenia than total drug concentration in both linear and nonlinear models. The best model was a nonlinear model with three variables of unbound concentration, pretreatment leukocyte count and prior treatment (r = 0.76, MPE +/- SEM = 0.07 +/- 0.17 x 10(3)/microl, RMSE = 0.95 x 10(3) microl), which was better than the best linear model. CONCLUSIONS: The nonlinear model using unbound etoposide concentration explained the interpatient variability of leukocyte nadir count to a fairly large extent. Although the model provided useful information on the pharmacodynamics of etoposide, it was still imprecise and a more refined model is necessary for application to an adaptive control study.

Antineoplastic Agents, Phytogenic↗

PubMed1982

Quantitative model for gene regulation by lambda phage repressor.

A statistical thermodynamic model has been developed to account for the cooperative interactions of the bacteriophage lambda repressor with the lambda right operator. The model incorporates a general theory for quantitatively interpreting cooperative site-specific equilibrium binding data. Values for all interaction parameters of the model have been evaluated at 37 degrees C, 0.2 M KCl, from results of DNase protection experiments in vitro [A. D. Johnson, B. J. Meyer, & M. Ptashne, Proc. Natl. Acad. Sci. USA (1979) 76, 5061-5065]. With these values, the model predicts repression curves at the divergent promoters PR and PRM that control transcription of genes coding for the regulatory proteins cro and repressor, respectively. At physiological repressor concentrations, repression at PR is predicted to be nearly complete whereas PRM is predicted to remain highly active. The results demonstrate the importance of cooperative interactions between repressor dimers bound to the adjacent operator sites OR1 and OR2 in maintaining a stable lysogenic state and in allowing efficient switchover to the lytic state during induction.

Bacteriophage lambda↗

PubMed1975

Altered control of skin blood flow at high skin and core temperatures.

Five subjects were studied during periods of controlled increases and decreases in skin temperature (Ts) over the Ts range of 34-40 degrees C. One protocol was designed to observe changes in forearm blood flow (FBF) and heart rate (HR) with changes in core temperature (Tc; right atrial blood temperature and esophageal temperature were measured) with Ts held constant at two levels. FBF and HR changed linearly with Tc in the Tc range of 37-38 degrees C with Ts constant at 38 degrees C. A second protocol imposed Ts changes at two levels of Ts and Tc; this protocol also included a prolonged cooling period. The influence of Ts on FBF and HR was reduced when Ts changes occurred at an elevated Ts and Tc, and FBF showed considerable hysteresis during cooling. We conclude that a linear model for the control of FBF or HR is inadequate as a tool for predicting the control of these variables.

Adult↗

PubMed1999

Between intention and behavior: an application of community pharmacists' assessment of pharmaceutical care.

A new practice philosophy for pharmacists, pharmaceutical care, encourages pharmacists to ensure that medication-related health outcomes are optimized. However, its adoption by community pharmacists has been slow due to numerous barriers including the economic structure of retail pharmacy, interprofessional conflicts, information limitations, gaps in pharmacy training and uneven patient demand. The specific study objectives were to (1) describe self-efficacy, beliefs, evaluations and perceived behavioral control in the provision of pharmaceutical care, (2) quantify intention and behavior to provide pharmaceutical care in a period of two weeks and (3) examine the relationships between intention and behavior. A 20% sample of Alberta community pharmacists received an attitude survey followed in two weeks by a behavior survey. Both surveys were developed for this study. Of the 320 pharmacists receiving the attitude survey, 230 completed surveys were obtained (71.9%). The behavior survey was received from 182 of those completing the attitude survey (79.1%). A causal model was constructed predicting pharmaceutical care behavior/s from pharmacists' self-efficacy, beliefs, evaluations and behavioral control. Behavioral control exerted its effect upon behavior via three pathways and its direct effect on belief was strongest. The only direct predictor of behavior was self-efficacy. The chi2 measure indicated that the model was not a perfect fit (chi2 = 99.24, df = 67, p<0.006), but the goodness of fit index (0.931), adjusted goodness of fit index (0.876), and root mean squared error (0.067) fall within acceptable ranges. Thus, it appears that pharmaceutical care implementation programs which address individual factors singly in providing pharmaceutical care will not be successful. The control pharmacists' perceive over their patient care behaviors in their practice environment is critical. Programs which help pharmacists assess their work environment and determine strategies to impact or reconstruct their environments are required.

Adult↗

PubMed2001

Learning the dynamics of reaching movements results in the modification of arm impedance and long-latency perturbation responses.

Some characteristics of arm movements that humans exhibit during learning the dynamics of reaching are consistent with a theoretical framework where training results in motor commands that are gradually modified to predict and compensate for novel forces that may act on the hand. As a first approximation, the motor control system behaves as an adapting controller that learns an internal model of the dynamics of the task. It approximates inverse dynamics and predicts motor commands that are appropriate for a desired limb trajectory. However, we had previously noted that subtle motion characteristics observed during changes in task dynamics challenged this simple model and raised the possibility that adaptation also involved sensory-motor feedback pathways. These pathways reacted to sensory feedback during the course of the movement. Here we hypothesize that adaptation to dynamics might also involve a modification of how the CNS responds to sensory feedback. We tested this through experiments that quantified how the motor system's response to errors during voluntary movements changed as it adapted to dynamics of a force field. We describe a nonlinear approach that approximates the impedance of the arm, i.e., force response as a function of arm displacement trajectory. We observe that after adaptation, the impedance function changes in a way that closely matches and counters the effect of the force field. This is particularly prominent in the long-latency (> 100 ms) component of response to perturbations. Therefore, it appears that practice not only modifies the internal model with which the brain generates motor commands that initiate a movement, but also the internal model with which sensory feedback is integrated with the ongoing descending commands in order to respond to error during the movement.

Adult↗

PubMed2003

S100B and response to treatment in major depression: a pilot study.

S100B is a protein which exerts both detrimental and neurotrophic effects, depending on its concentration in brain tissue. An increase of S100B in micromolar concentrations is observed in traumatic brain conditions and is associated with poor outcome. Micromolar levels of extracellular S100B in vitro may have deleterious effects. However, in nanomolar concentrations S100B has multiple neurotrophic effects in vitro may in vivo be regarded as a hallmark of neuroprotective efforts. This pilot study addresses the hypothesis that S100B serum concentrations may be of predictive validity for the response to antidepressant treatment in patients with major depression. S100B plasma levels were determined in 25 patients with major depression and 25 matched healthy controls using an immunofluorimetric sandwich assay. S100B plasma levels were significantly higher in major depressive patients than in healthy controls and positively correlated with treatment response after 4 weeks of treatment. In a linear regression model, a significant predictive effect was found only for S100B and severity of depressive symptoms upon admission. These results suggest that neuroprotective functions of S100B counterbalance neurodegenerative mechanisms that are involved in the pathophysiology of major depression and in the response to antidepressant treatment.

Adult↗

PubMed2001

Toward a model for the evaluation of clinical coding systems.

OBJECTIVE: To demonstrate an empirical method to evaluate the utility of clinical coding systems. To use this method to assess the predictive power of two codes. METHOD: Controlled trial of two coding systems. SETTING: The Read Clinical Codes, version II and the International Classification of Primary Care (ICPC). OUTCOME MEASURES: The association between codes and pharmaceuticals prescribed. RESULTS: The power of both codes to predict pharmaceuticals increased with their precision. ICPC performed better than Read at the same level of precision. CONCLUSION: ICPC may be a more efficient coding system to use than Read. Assessment of the predictive power of a code is central to assessing its utility.

Diagnosis-Related Groups↗