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Results for “Models, Theoretical”

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PubMed2000

A method for measuring team skills.

A method for identifying and measuring team skills, specifying team training objectives and the objective assessment of team performance is described. First, a theoretical model of team performance is outlined and then a version of Hierarchical Task Analysis specially adapted to analysing team tasks is described. The two are then combined into an event-related measurement scheme, which provides a set of objective criteria by which key team skills can be assessed. The method is illustrated by an example from a basic Anti-Submarine Warfare training exercise which forms part of the Principal Warfare Officer's course at the Royal Naval School of Maritime Operations. The potential of the method is discussed, including the opportunities it may provide for the standardization of team performance assessment and in the use of new technology in the partial automation of shore-based and ship-board team training.

Group Processes↗

PubMed1991

Simulation as a tool in the measurement of human performance.

The paper outlines and discusses issues in the present-day development and application of simulations of complex tasks. It is noted that this development is observed in basic as well as in applied research, resulting in a trend away from the investigation of elementary properties of human functioning in favour of the analysis of complete tasks. One of the problems in simulation concerns appropriate output measures (section 2). Some recent sophisticated measures of performance are derivatives of more elementary measures of time and accuracy, but they still facilitate new insights into the measurement of performance. In addition, recent views are discussed of verbal reports as potential measures of cognitive skills. It is noted that the issue of performance measurement has been severely neglected and ignored in many applications of simulators. The paper also focuses on theoretical models (section 3). It is concluded that models for complete tasks face the problem of excessive complexity, thus inhibiting detailed parametric analysis. In this respect the analysis of elementary properties has a clear advantage. A strategy of back-to-back experimentation, originally proposed by Gopher and Sanders (1984), is reiterated and an example of a back-to-back study is described. Section 4 of the paper is devoted to the issue of validation with major emphasis on the possibilities and limitations of the transfer paradigm and the measurement of direct correspondence. The final section (5) is devoted to some selective remarks about the three main areas where simulators are applied, namely training, equipment design, and personnel assessment. The paper ends by summarizing some emerging trends and issues for future research.

Computer Simulation↗

PubMed1999

A comprehensive analysis of low-back disorder risk and spinal loading during the transferring and repositioning of patients using different techniques.

Although patient handlers suffer from low-back injuries at an alarming rate worldwide, there has been limited research quantifying the risk for the specific tasks performed by the patient handlers. The current study used both a comprehensive evaluation system (low-back disorder risk model) and theoretical model (biomechanical spinal loading model) to evaluate risk of LBD of 17 participants (12 experienced and five inexperienced) performing several patient handling tasks. Eight of the participants were female and nine were male. Several patient transfers were evaluated as well as repositioning of the patient in bed; these were performed with one and two people. The patient transfers were between bed and wheelchair (fixed and removable arms) and between commode chair and hospital chair. A 'standard' patient (a 50 kg co-operative female; non-weight bearing but had use of upper body) was used in all patient handling tasks. Overall, patient handling was found to be an extremely hazardous job that had substantial risk of causing a low-back injury whether with one or two patient handlers. The greatest risk was associated with the one-person transferring techniques with the actual task being performed having a limited effect. The repositioning techniques were found to have significant risk of LBD associated with them with the single hook method having the highest LBD risk and spinal loads that exceeded the tolerance limits (worst patient handling job). The two-person draw sheet repositioning technique had the lowest LBD risk and spinal loads but still had relatively high spinal loads and LBD risk. Thus, even the safest of tasks (of the tasks evaluated in this study) had significant risk. Additionally, the current study represented a 'best' case scenario since the patient was relatively light and co-operative. Thus, patient handling in real situations such as in a nursing home, would be expected to be worse. Therefore, to have an impact on LBD, it is necessary to provide mechanical lift assist devices.

Adult↗

PubMed2002

Benefit of population-based screening for phenotypic hemochromatosis in young men.

BACKGROUND: Hereditary hemochromatosis (HH) is a common genetic disease leading to accumulation of iron in the body, most notably in the liver. More men than women become clinically ill. The prognosis is excellent if phlebotomy treatment is started before liver cirrhosis develops. Screening has been recommended, but the benefit of population-based screening has never been shown in a randomized clinical trial. In this article, we estimate the benefit of screening young men, using a theoretical model. METHODS: A phenotypic screening scenario was modelled using a decision tree. Gain of quality-adjusted life-years was used as a measure of benefit, and estimated using Markov processes. Data on the accuracy of the screening tests, the prevalence of HH and the risk of liver cirrhosis were mainly derived from a cross-sectional study on the prevalence and morbidity of HH in 30509 men. Data on the excess mortality of cirrhosis were taken from relevant literature. Sensitivity analysis was done for important variables. RESULTS: Assuming basal case values for variables, screening a cohort of 1000 men aged 30 years for phenotypic HH would gain about 8 quality-adjusted life-years, compared to awaiting symptomatic disease. Based on actual costs of our cross-sectional study, the screening cost was US$250 per quality-adjusted life-year gained. The prevalence of phenotypic HH, the excess mortality of liver cirrhosis, the quality of life in non-cirrhotic HH patients, and the fractions of patients compliant with treatment were the most important variables in the sensitivity analysis. CONCLUSION: Incorporating screening for phenotypic HH in health survey programmes for young men may be worthwhile.

Adult↗

PubMed2001

Experimental determination of baseball spin and lift.

The aim of this study was to develop a new method for the determination of lift on spinning baseballs. Inertial trajectories of (a) ball surface markers during the first metre of flight and (b) the centre of mass trajectory near home-plate were measured in a pitch using high-speed video. A theoretical model was developed, incorporating aerodynamic Magnus-Robins lift, drag and cross forces, which predicts the centre of mass and marker trajectories. Parameters including initial conditions and aerodynamic coefficients were estimated iteratively by minimizing the error between predicted and measured trajectories. We compare the resulting lift coefficients and spin parameter values with those of previous studies. Lift on four-seam pitches can be as much as three times that of two-seam pitches, although this disparity is reduced for spin parameters greater than 0.4.

Baseball↗

PubMed2005

Why do high jumpers use a curved approach?

Currently, all elite high jumpers use the Fosbury Flop technique with a curved approach. This suggests that the curved approach presents some clear advantage, although there is no general agreement upon the mechanism or the mechanics. This study aimed to determine the characteristics of the approach curve and to investigate how it contributes to the generation of somersault rotation. A simple theoretical model was used to demonstrate that a tightening approach curve would change the inward lean towards the centre of the curve into outwards lean. Three-dimensional video analysis was used to record the performances of two elite male high jumpers in competition. It was found that in each case the radius of the approach curve and the inward lean angle both decreased towards the end of the approach. The amount of outward lean angular velocity generated was shown to be a major proportion of the required somersault angular velocity for a jump. It was concluded that the main advantage of a curved approach was that it resulted in the generation of somersault velocity providing the curve tightened towards the end of the approach.

Biomechanical Phenomena↗

PubMed2003

A collaborative student affairs and faculty health assessment and intervention initiative.

The authors describe a collaborative partnership forged between faculty and student affairs staff to improve student health at a large urban university. They examine skills and reward structures of each constituency and the stages of the collaboration in the context of 2 theoretical models. A comprehensive data collection and dissemination process in the campus community provided goals for the initial stage of the partnership, leading to implementation of campus initiatives that use the reciprocal skills of each stakeholder. Outcomes of the collaboration included (1) a working relationship between faculty and student affairs staff, (2) increased dialogue with high-level administrators, (3) more coordinated campus efforts to decrease high-risk drinking, (4) use of outcome measures for implementing and evaluating health programs, and (5) an opportunity for interdisciplinary research. The authors offer suggestions for implementing the process on other campuses.

Data Collection↗

PubMed1997

Radon daughter deposition on surfaces carrying alternating electric fields.

A theoretical model is proposed to explain the radon daughter deposition enhancements on surfaces subject to power frequency AC fields, recently reported by Henshaw et al. (1996). The effect of oscillatory contacts with the surface combined with turbulent diffusion is investigated within the framework of the convective-diffusion equation, through an approximation of the dividing surface. The fine and the course activity fractions are treated separately for flat-plate and wire-plane configurations. The results indicate maximum enhancement factors for 218Po in the range 1.7-3.3 for flat-plate and 5.2-15.5 for wire-plane configurations under typical indoor environmental conditions. While these compare favourably with the corresponding observed values, further analysis appears necessary to explain the greater enhancements observed in the case of 214Po.

Air Pollution, Indoor↗

PubMed2004

Factors influencing food choices, dietary intake, and nutrition-related attitudes among African Americans: application of a culturally sensitive model.

OBJECTIVES: The goals of the project were: (1) to explore how culture and community impact on the nutrition attitudes, food choices, and dietary intake of a selected group of African Americans in north central Florida; and (2) to identify segments of the population and community that should be targeted for education programs, desirable components of nutrition education programs, topics of interest, and health promotion channels to reach the target group. DESIGN: Six focus groups were conducted with African American males and females. The data were analyzed using the PEN-3 model, a theoretical model that centralizes culture as the primary reason for health behavior and the primary consideration for health promotion and diseases prevention programs. RESULTS: There was a general perception that 'eating healthfully' meant giving up part of their cultural heritage and trying to conform to the dominant culture. Friends and relatives usually are not supportive of dietary changes. Barriers to eating a healthful diet also included no sense of urgency, the social and cultural symbolism of certain foods, the poor taste of 'healthy' foods, the expense of 'healthy' foods, and lack of information. Segments of the population that potentially could be motivated to make dietary changes included women, men with health problems, young adults, the elderly, and those diagnosed with a severe, life-threatening disease. CONCLUSION: The findings suggest that the PEN-3 model is an appropriate framework for assessing how community and culture impact dietary habits of African Americans. African Americans will need information on basic nutrition topics such as serving sizes and reading food labels. The findings also suggest that programs and materials should be specifically developed for churches, neighborhood grocery stores, and local restaurants.

Adult↗

PubMedDate not supplied

Exploring links between the concepts of Quality of Life and resilience.

This paper explores links between the concepts of Quality of Life (QoL) and resilience. First, the definitions of QoL and resilience are explored separately, emphasizing that both concepts have been criticized for a lack of theory with resulting problems in description, prediction and measurement. The similarities and differences are then considered between these two related psychological concepts-resilience and QoL. The need is identified for establishing a theoretical model of QoL, and how elements from resilience research can be beneficially integrated within such a model is discussed. Further empirical work is needed to explore explicitly the relationship between these two related psychological concepts, and establish how well resilience can help explain individual variation in QoL reports in young children.

Adaptation, Psychological↗

PubMed1979

Cotton dust sampling efficiency of the vertical elutriator.

A theoretical model of the vertical elutriator air sampler based upon the phenomenon of flow separation at the inlet was developed at SRRC. The model's equations were simulated by a computer program (VELUT). The model was calibrated by comparison of available experimental results to isokinetic sampling efficiencies calculated by the model. The calibrated model was used to predict integral efficiencies for a systematic assortment of size distributions of cotton dust. Rather than cutting off cleanly at 15 micrometers, the computer model exhibited a 50% differential efficiency at approximately 20 micrometers. Furthermore, the model predicted substantial non-zero collection efficiencies in the aerodynamic size range of individual cotton fibers. Program VELUT represents an objective method whereby the isokinetic sampling efficiency of the vertical elutriator can be explicitly calculated for any known or postulated ambient dust distribution presented to the sampler at its inlet plane.

Dust↗

PubMed1990

Electrostatic effects in asbestos sampling. II: Comparison of theory and experiment.

A series of calculations was conducted to estimate the degree and type of electrostatic interactions that might occur with electrically charged asbestos samplers collecting charged particles. Relatively simple theoretical models were constructed assuming only charge-charge electrostatic interactions between a charged particle and a charged sampler. The results of these calculations were compared with some experimental measurements and the agreement between the two allowed some confidence in predicting behavior trends. Under conditions where both the particles and the sampler are charged, the nonconductive sampler exhibits increased particle loss, especially near the filter edge, and increased variability of the particle deposit. The variability of the deposit also tends to be greatest near the filter edge. Under similar conditions, conductive cowled samplers also can be expected to exhibit losses in particle deposit, especially near the filter edge. The variability over the filter surface, however, is less than for the nonconductive cowl. Particle collection onto the sampler filter generally is expected to be greatest for isokinetic, isoaxial sampling conditions. Particle collection on the filter decreases with lower sampling flow rates, lower air velocities near the sampler inlet, and increased turbulence near the inlet.

Air Pollutants↗

PubMed2003

Adsorption of pesticides on resins.

The objective of this work was to assess the capability of organic hydrophobic polymeric resins Amberlite XAD-4 and XAD-7 to remove the pesticides alachlor and amitrole from water. The pesticides adsorption on the two different adsorbents was measured by batch equilibrium technique and isotherm types and parameters were estimated. Two theoretical models were applied based on a Freundlich and a Langmuir isotherms. The effect of pesticides chemical composition and structure as well as the nature of solid surface on the efficiency of adsorption was evaluated. The influence of pH also was studied. In low pH solutions adsorption of amitrole was higher upon the nonionic aliphatic acrylic ester copolymer XAD-7 in comparison to the nonionic, crosslinked macroreticular copolymer of styrene divinylbenzene XAD-4. In neutral and intermediate pH solutions the polar acrylic ester copolymer XAD-7 was more effective to the retention of alachlor. The acrylic ester copolymer showed at pH 3 the lower effectiveness in alachlor removal from water. The data of the adsorption isotherms of pesticides upon the examined polymeric resins seemed to conform to both the Freundlich and the Langmuir isotherm models.

Acetamides↗

PubMed1967

Evidence for carrier-mediated transport of monosaccharides in the Ehrlich ascites tumor cell.

Evidence for carrier-mediated transport of monosaccharides in the Ehrlich ascites tumor cells was provided through kinetic analysis of data obtained by: (a) studying sugar uptake by dilute cell suspensions with an optical densimetric apparatus, (b) studying sugar uptake by thicker cell suspensions by means of direct chemical analytical methods using packed cell plugs, (c) observing the effects of a competitive inhibitor upon sugar uptake with the chemical analytical method, and (d) measurement of tracer uptake of a high affinity sugar in thick cell suspensions in the absence of net movement. Quantitative application of the data obtained with the above experimental procedures to theoretical model systems derived for both carrier-mediated transport and simple passive diffusion indicated that the results were consonant with predictions for the carrier-mediated transport model, but could not be explained on the basis of uncomplicated diffusion.

Animals↗

PubMed1993

Cross section parameterizations for cosmic-ray nuclei. I. Single nucleon removal.

Parameterizations of single nucleon removal from the electromagnetic and strong interactions of cosmic rays with nuclei are presented. These parameterizations are based upon the theoretical models developed by Baur, Bertulani, Benesh, Cook, Vary, Norbury, and Townsend. They should be very suitable for use in cosmic-ray propagation through interstellar space, Earth's atmosphere, lunar samples, meteorites, spacecraft walls, and lunar and martian habitats.

Cosmic Radiation↗

PubMed2003

A theoretical investigation of the evolution and maintenance of mirror-image flowers.

Enantiostyly is the deflection of the female sex organ either to the left or to the right side of the floral axis, resulting in mirror-image flowers. Two types of enantiostyly occur: in monomorphic enantiostyly, individuals exhibit both flower forms, whereas in dimorphic enantiostyly, the forms occur on separate plants. Monomorphic enantiostyly is known from at least 10 families, whereas dimorphic enantiostyly is reported in only three. Phylogenetic evidence suggests that monomorphic enantiostyly has evolved from a straight-styled ancestor and that dimorphic enantiostyly is derived from monomorphic enantiostyly. Here, we use theoretical models to investigate the role of pollen transfer in influencing these evolutionary transitions. We used numerical calculations to examine the evolution of monomorphic and dimorphic enantiostyly under different conditions of pollen transfer, inbreeding depression, and pollinator visitation. Our results demonstrate that in comparison to a putative straight-styled ancestor, both monomorphic and dimorphic enantiostyly function to reduce geitonogamous pollen transfer with a concomitant increase in pollen export. Our calculations suggest that the first stage in the evolution of monomorphic enantiostyly involves the deflection of the style only, followed by selection for reciprocity in anther position to promote more precise cross-pollination. Constraints associated with the developmental genetics of left-right asymmetries may account for the low number of evolutionary transitions from monomorphic to dimorphic enantiostyly, despite the evolutionary stability of this condition once it arises.

Biological Evolution↗

PubMed2006

Scale-dependent inhibition drives regular tussock spacing in a freshwater marsh.

Regular spatial patterning is common in nature, and various mechanisms of self-organization have been proposed to explain regular patterning. We report on regular spatial patterning in Carex stricta in a freshwater wetland and investigate the applicability of theoretical models that explain regular patterning based on inhibition, facilitation, or interaction between the two. Spectral analysis of aerial photographs revealed that tussocks were regularly spaced at an average distance of 60 cm. Photosynthetically active radiation varied significantly with distance from the tussock and was lowest at intermediate distance from the tussock center (15-40 cm). Using transplants to assay growth conditions, we found that C. stricta grew well in all distance classes with and without natural C. stricta biomass, except at intermediate distances when buried in C. stricta wrack. Our experimental results reveal that C. stricta inhibits its growth in a scale-dependent manner: inhibition was found to peak at intermediate distance from the tussock. We compared three alternative models to examine potential mechanisms driving regularity and found that, similar to our experimental results, scale-dependent inhibition provides the best explanation for the observed regular tussock spacing. Our study underlines the importance of scale-dependent feedback in the formation of regular spatial patterning in ecosystems.

Carex Plant↗

PubMed2006

Relating environmental variation to selection on reaction norms: an experimental test.

Theoretical models predict that selection on reaction norms should depend on the relative frequency of environmental states experienced by a population. We report a laboratory experimental test of this prediction for thermal performance curves of larval growth rate in Pieris rapae in relation to their thermal environment. We measured short-term relative growth rate (RGR) for each individual at a series of five temperatures, and then we assigned individuals randomly to warm or cool selection treatments, which differ in the frequency distributions of environmental temperatures. Selection gradient analyses of two independent experiments demonstrated significant positive selection for increasing RGR, primarily through its effects on survival to adulthood and on development rate. In both the warm and cool selection treatments, the magnitude of directional selection on RGR was consistently greater at lower (suboptimal) temperatures than at higher temperatures; differences in selection between the treatments did not match model predictions. The temporal order and duration of environmental conditions may affect patterns of selection on thermal performance curves and other continuous reaction norms, complicating the connections between variation in environment, phenotype, and fitness.

Animals↗