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Three theoretical models have been proposed to represent self-concept: (a) unidimensional; (b) multidimensional; (c) multidimensional hierarchical. Inventories have been developed under each of the three competing theoretical models; which model best represents self-concept is unclear. Typically, self-concept construct validation has utilized various approaches including correlational, multitrait-multimethod, and factor analytic methods. Another method, however, for assessing validity would be to determine the consequences of score interpretations using different measures specific to each of the theoretical models. This paper examined Messick's notion (1989) of the validity of test-score interpretations as applied to three of the most widely used measures derived under each of the three different theoretical models of self-concept. Results suggest that overall multidimensional measures are more consistent in classifying individual's self-concept than unidimensional measures.
Various theoretical models have been proposed to explain the periodicity in the pattern of limb chondrogenesis, but experimental comparison of these models have seldom been performed properly. In the present study, micromass culture of limb bud mesenchyme cells was undertaken to test the validity of three theoretical models: the reaction-diffusion model, the cell sorting model, and the mechanochemical model. Computer simulations were undertaken to predict the factors that can affect the coarseness of the chondrogenic pattern. According to the predictions, we performed micromass culture of limb mesenchyme in collagen and agarose gel. Then we carried out time-lapse observation to analyze the cell movement during pattern formation. From computer simulations it was theoretically predicted that changes in the surrounding extracellular matrix should alter the periodicity of the chondrogenic pattern in vitro, and we found that pattern changes actually occurred under different culture conditions. When compared with the culture in a liquid medium, the chondrogenic pattern became less coarse when the cells were cultured in collagen or agarose gel, and the pattern change appeared to be independent of the cell differentiation. Time-lapse observation revealed a decrease in cell motility when the cells were cultured in gel. It was found that both the reaction-diffusion and cell sorting models fit the pattern change produced and that the mechanochemical model is not primarily important in the chondrogenic pattern formation in vitro.
The theoretical models put forth separately by Bremer, Lang, and Schwartz to account for the data on biofeedback and cardiovascular responses are summarized and evaluated in light of recent empirical studies. Although each model makes some use of the idea that learning to control heart rate, particularly heart rate acceleration, is like motor skills learning, each model also emphasizes different sets of factors or variable. An attempted integration of these three models is presented.
A theoretical model is developed for an electrochemical sensor for toxic substances which works by measuring the inhibition of the enzyme activity. The enzyme is assumed to follow Michaelis-Menten kinetics and the diffusion kinetic equation describing the concentration profile of the enzyme's substrate in the electrolyte layer between the electrode and the membrane covering the electrode is solved. A complete set of analytical solutions is found which corresponds to a number of different rate limiting processes. The set of solutions is described in a case diagram. The use of cytochrome oxidase in particular is discussed.
A theoretical model of the heart, which suggests a direct relationship between segmental abnormalities of left ventricular (LV) wall motion (WM) and LV ejection fraction (EF), was tested using two-dimensional echocardiography (2DE) and multiple-gated equilibrium blood pool scintigraphy (MGES) in a population of 25 coronary artery disease patients. MGES was used to determine EF, and 2DE was used to develop a method of analysis of LV segmental WM abnormalities. Two orthogonal apical 2DE views were analyzed. The length of the end-diastolic segments in which normal contraction occurred during systole were measured in each view, summed and divided by the sum of the end-diastolic silhouette lengths. The fraction thus created was multiplied by 100 and defined as the percentage of normally contracting myocardium (%NCM). %NCM correlated well with EF determined by MGES (r = 0.94). Determination of %NCM was highly reproducible for the same observer (r = 0.98), as well as for two observers (r = 0.98), and the standard error of estimate was low in both cases (4%). These findings, in addition to confirming the theoretical model, provide a new technique to assess LV segmental WM abnormalities by 2DE.
The Diels-Alder reaction rate constants of methyl vinyl ketone with cyclopentadiene and cyclohexadiene in the presence of a novel organotungsten catalyst, [P(2-py)(3)W(CO)(NO)(2)](2+), have been measured experimentally and modeled theoretically at several temperatures. The uncatalyzed systems were also studied for direct comparison. When 0.0022 M of catalyst is present at room temperature, the rate constants were found to be approximately 5.3 and 5300 times higher than the corresponding uncatalyzed reactions for cyclopentadiene and cyclohexadiene systems, respectively. Experimental data suggested that the catalyst reduced the activation energies by 5-10 kcal/mol. However, the preexponential factors showed reduction of more than 3 orders of magnitude upon catalysis due to the entropic effects. The energy barriers and the rate constants of the uncatalyzed systems were accurately modeled by correlated electronic structure and dual-level variational transition state theory calculation. The calculated endo selectivity is in good agreement with the observed product distribution. Theoretical calculation also suggested the catalyzed reactions proceeded in a highly asynchronous or even stepwise fashion.
The purpose of this cross-sectional, correlational study was to test a middle-range theory of adaptation to chronic pain that was deduced from the Roy adaptation model using structural equation modeling. The sample consisted of 200 community-dwelling older adults with a mean age of 76. The Roy adaptation model theoretical framework provided an adequate fit to the data and supported the majority of the hypothesized relationships and findings from prior research. Significant direct effects, however, were found between both focal and contextual stimuli, suggesting that contextual stimuli need to be considered when developing a plan of care for older adults experiencing chronic pain.
Ventilation-perfusion (VA/Q) inhomogeneity was modeled to measure its effect on gas exchange in the presence of inspired mixtures of two soluble gases using a two-compartment computer model. Theoretical studies involving a mixture of hypothetical gases with equal solubility in blood showed that the effect of increasing inhomogeneity of distributions of either ventilation or blood flow is to paradoxically increase uptake of the gas with the lowest overall uptake in relation to its inspired concentration. This phenomenon is explained by the concentrating effects that uptake of soluble gases exert on each other in low VA/Q compartments. Repeating this analysis for inspired mixtures of 30% O(2) and 70% nitrous oxide (N(2)O) confirmed that, during "steady-state" N(2)O anesthesia, uptake of N(2)O is predicted to paradoxically increase in the presence of worsening VA/Q inhomogeneity.
Six theoretical models of social support in relation to perceived job stress, burnout, and health were tested both cross-sectionally and longitudinally. Participants at Time 1 were state correctional officers (N = 262) who completed questionnaires in which multiple indicators of each construct were assessed. Time 2 participants (N = 177) were those officers from the Time 1 sample who completed the questionnaire again three months later. Structural equation analyses revealed that only one of the six models was supported by cross-sectional results. In this model a direct negative relationship between the WORKPLACE SOCIAL SUPPORT and BURNOUT latent variables was specified, along with direct, positive relationships between the JOB STRESS and BURNOUT latent variables and the BURNOUT and POOR HEALTH latent variables. However, none of the six models was supported by the longitudinal results. Thus, cross-sectional results were consistent with a model in which social support on the job influences positive health only through its direct and negative effect on burnout symptoms, but such causal connections were not validated longitudinally.
A theoretical model is developed to predict pressure changes and velocity profiles within the foetal lung during its sporadic bursts of activity. Because of the small volume flow rates and relatively high frequencies, the linearised, unidirectional Navier-Stokes equations are used to calculate these values. About 70% of the pressure drop occurs in the first four generations and is an order of magnitude higher than the equivalent Poiseuille pressure drop. Velocity profiles, pressure falls within each generation together with the total pressure drop at different times during the cycle are illustrated.
A theoretical model is presented based on the idea that the immune system of a patient with a tumour can cross-react against transplanted normal foreign cells as well as against the patient's own neoplastic cells, thereby rejecting both. This hypothesis is shown in a diagram, the potential use of which is discussed.
A theoretical model for the assessment of the interaction between the patient with Parkinson's disease and his caregiver during assisted feeding is suggested. It is based on literature about impairments in Parkinson's disease and about interaction. The main concepts of the model are clarity of cues, sensitivity, interpretation, responsiveness and synchrony. It is suggested that the patient should be allowed to focus on the socio-emotional content versus the task content of communication during different phases of interaction during the meal.
A theoretical model is presented describing the reopening by an advancing air bubble of an initially liquid-filled collapsed airway lined with deformable epithelial cells. The model integrates descriptions of flow-structure interaction (accounting for nonlinear deformation of the airway wall and viscous resistance of the airway liquid flow), surfactant transport around the bubble tip (incorporating physicochemical parameters appropriate for Infasurf), and cell deformation (due to stretching of the airway wall and airway liquid flows). It is shown how the pressure required to drive a bubble into a flooded airway, peeling apart the wet airway walls, can be reduced substantially by surfactant, although the effectiveness of Infasurf is limited by slow adsorption at high concentrations. The model demonstrates how the addition of surfactant can lead to the spontaneous reopening of a collapsed airway, depending on the degree of initial airway collapse. The effective elastic modulus of the epithelial layer is shown to be a key determinant of the relative magnitude of strains generated by flow-induced shear stresses and by airway wall stretch. The model also shows how epithelial-layer compressibility can mediate strains arising from flow-induced normal stresses and stress gradients.
A theoretical model allowed the simultaneous determination of the reflexion coefficients of capillary membrane to small hydrophilic molecules and of the ratios of their permeability to filtration coefficient. This was applied to dilution curves obtained after injection of a hypertonic solution containing a vascular tracer. The calculated variables did not depend on the capillary exchange surface area.
A theoretical model for the assessment of the interaction between the patient with Parkinson's disease and his caregiver during assisted feeding is suggested. It is based on literature about impairments in Parkinson's disease and about interaction. The main concepts of the model are clarity of cues, sensitivity, interpretation, responsiveness and synchrony. It is suggested that the patient should be allowed to focus on the socioemotional content versus the task content of communication during different phases of interaction during the meal.
A theoretical model is suggested that allows calculating a yield of cells with a number of aberrations caused by fractionated gamma irradiation using the corresponding data for a separate irradiation. The value of a cytogenetic interaction of damages induced by two fractions of irradiation doses was used as a free parameter of the model. In terms of the model, approximation of experimental functions of the cell distribution in a number of exchange aberrations caused by gamma and/or neutron irradiation was made. At a stage G0, with the 1 h interval between the dose fractions, approximation was successful only for irradiation with equal or isoeffective dose fractions; with the interval of 5 h, it was successful for all types of irradiation except for two highest doses of fractionated neutron and gamma/neutron irradiation. At a stage G1, approximation was satisfactory almost for all types of fractionated gamma/neutron irradiation irrespective of the interval between the dose fractions and of a dose of fractionated gamma irradiation with the interval 1 h. For the fractionated neutron and neutron/gamma irradiation at a stage G1, approximation of experimental distributions was unsatisfactory in all the cases.
BACKGROUND: Innovative theoretical models are needed to explain the occurrence of high-risk sexual behaviors, alcohol and other-drug (AOD) use, and academic engagement among ethnically diverse, inner-city adolescents. OBJECTIVE: The aim of this study was to test the credibility of a theoretical model based on the Bowen family systems theory to explain adolescent risk behavior. Specifically tested was the relationship between the predictor variables of differentiation of self, chronic anxiety, and social problem solving and the dependent variables of high-risk sexual behaviors, AOD use, and academic engagement. METHODS: An ex post facto cross-sectional design was used to test the usefulness of the theoretical model. Data were collected from 161 racially/ethnically diverse, inner-city high school students, 14 to 19 years of age. Participants completed self-report written questionnaires, including the Differentiation of Self Inventory, State-Trait Anxiety Inventory, Social Problem Solving for Adolescents, Drug Involvement Scale for Adolescents, and the Sexual Behavior Questionnaire. RESULTS: Consistent with the model, higher levels of differentiation of self related to lower levels of chronic anxiety (p < .001) and higher levels of social problem solving (p < .01). Higher chronic anxiety was related to lower social problem solving (p < .001). A test of mediation showed that chronic anxiety mediates the relationship between differentiation of self and social problem solving (p < .001), indicating that differentiation influences social problem solving through chronic anxiety. Higher levels of social problem solving were related to less drug use (p < .05), less high-risk sexual behaviors (p < .01), and an increase in academic engagement (p < .01). CONCLUSIONS: Findings support the theoretical model's credibility and provide evidence that differentiation of self is an important cognitive factor that enables adolescents to manage chronic anxiety and motivates them to use effective problem solving, resulting in less involvement in health-comprising behaviors and increased academic engagement.