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PubMed2005

The utility of the Trans-theoretical Model of Behavior Change in the treatment of sex offenders.

This paper discusses the use of the Trans-theoretical Model of Behavior Change in the treatment of sex offenders. Constructs within this theory are the Stages of Change, Processes of Change and Decisional Balance. The first section of this paper provides a brief description of these constructs. The second section provides a brief review of research related to these constructs and discusses the implications of this research in relation to the treatment of sex offenders. The third section of this paper provides a practical description of the use of the constructs of the Trans-theoretical Model of Behaviour Change in the treatment of sex offenders. Although the validity of this model among sex offenders requires further investigation, the Trans-theoretical Model of Behavior Change appears to have considerable utility as an overarching theoretical model to conceptualize and facilitate behavior change among sex offenders.

Behavior Control↗
PubMed2004

The effect of physical height on workplace success and income: preliminary test of a theoretical model.

In this article, the authors propose a theoretical model of the relationship between physical height and career success. We then test several linkages in the model based on a meta-analysis of the literature, with results indicating that physical height is significantly related to measures of social esteem (rho =.41), leader emergence (rho =.24), and performance (rho =.18). Height was somewhat more strongly related to success for men (rho =.29) than for women (rho =.21), although this difference was not significant. Finally, given that almost no research has examined the relationship between individuals' physical height and their incomes, we present four large-sample studies (total N = 8,590) showing that height is positively related to income (beta =.26) after controlling for sex, age, and weight. Overall, this article presents the most comprehensive analysis of the relationship of height to workplace success to date, and the results suggest that tall individuals have advantages in several important aspects of their careers and organizational lives.

Adult↗
PubMed2000

Theoretical model for an MRI radio frequency resonator.

A theoretical model is described for a magnetic resonance imaging (MRI) radio-frequency resonator (an MRI "coil") that is useful at ultrahigh frequencies. The device is a "TEM resonator," which is based on a concept originally proposed by Röschmann (1988). The coil comprises a circular cavity-like structure containing several coaxial transmission lines operating in a transverse electromagnetic (TEM) mode. The model developed herein treats the empty coil and is based on multiconductor transmission line theory. This work generalizes and extends similar analyses of the device by Röschmann (1995) and Chingas and Zhang (1996). The model employs explicit calculation of per-unit-length parameters for TEM lines having arbitrary geometries. Calculations of the resonator's frequency response are found to compare well with measurements. Fields produced by linear (single-point) and quadrature drive are also computed and compared to images of low-permittivity phantoms.

Electromagnetic Fields↗
PubMed1984

Theoretical models for application in school health education research.

Theoretical models that may be useful to research studies in school health education are reviewed. Selected, well-defined theories include social learning theory, problem-behavior theory, theory of reasoned action, communications theory, coping theory, social competence, and social and family theories. Also reviewed are multiple theory models including models of health related-behavior, the PRECEDE Framework, social-psychological approaches and the Activated Health Education Model. Two major reviews of teaching models are also discussed. The paper concludes with a brief outline of the general applications of theory to the field of school health education including applications to basic research, development and design of interventions, program evaluation, and program utilization.

Adolescent↗
PubMed2006

Theoretical model and experimental study of red blood cell (RBC) deformation in microchannels.

The motion and deformation of red blood cells (RBCs) flowing in a microchannel were studied using a theoretical model and a novel automated rheoscope. The theoretical model was developed to predict the cells deformation under shear as a function of the cells geometry and mechanical properties. Fluid dynamics and membrane mechanics are incorporated, calculating the traction and deformation in an iterative manner. The model was utilized to evaluate the effect of different biophysical parameters, such as: inner cell viscosity, membrane shear modulus and surface to volume ratio on deformation measurements. The experimental system enables the measurement of individual RBCs velocity and their deformation at defined planes within the microchannel. Good agreement was observed between the simulation results, the rheoscope measurements and published ektacytometry results. The theoretical model results imply that such deformability measuring techniques are weakly influenced by changes in the inner viscosity of the cell or the ambient fluid viscosity. However, these measurements are highly sensitive to RBC shear modulus. The shear modulus, estimated by the model and the rheoscope measurements, falls between the values obtained by micropipette aspiration and laser trapping. The study demonstrates the integration of a theoretical model with a microfabricated device in order to achieve a better understanding of RBC mechanics and their measurement using microfluidic shear assays. The system and the model have the potential of serving as quantitative clinical tools for diagnosing deformability disorders in RBCs.

Erythrocyte Deformability↗
PubMed2005

Chiral separation in capillary electrophoresis using dual neutral cyclodextrins: theoretical models of electrophoretic mobility difference and separation selectivity.

Simple equations and theoretical models, related to enantioselectivity (kappa) and C, have been developed for prediction of electrophoretic mobility difference (Deltamu) and separation selectivity (alpha) for enantiomers in CE using dual CDs, where alpha and kappa are defined as the ratio of mu and the ratio of binding constant (K) for enantiomers to each CD, respectively, C the CD concentration, and the average K for enantiomers and each CD. Experiments were carried out using dual CDs as beta-CD and dimethyl-beta-cyclodextrin (DM-beta-CD) and test analytes as five pairs of amphetamine drug enantiomers. A change in observed Deltamu and alpha of enantiomers in dual CDs was found to be in excellent agreement with the theoretical models. For example, in comparison with single CD1, dual CDs can enhance Deltamu and alpha up to the maximum value when enantiomers migrate with the same order in CD1 and CD2, and have the value of rho > 1.0, where rho is the enantioselectivity ratio for CD2 to CD1, while worse Deltamu and alpha are obtained for enantiomers with rho < 1.0.

Amphetamines↗
PubMed1996

Clusters of DNA induced by ionizing radiation: formation of short DNA fragments. I. Theoretical modeling.

We have developed a general theoretical model for the interaction of ionizing radiation with chromatin. Chromatin is modeled as a 30-nm-diameter solenoidal fiber comprised of 20 turns of nucleosomes, 6 nucleosomes per turn. Charged-particle tracks are modeled by partitioning the energy deposition between primary track core, resulting from glancing collisions with 100 eV or less per event, and delta rays due to knock-on collisions involving energy transfers >100 eV. A Monte Carlo simulation incorporates damages due to the following molecular mechanisms: (1) ionization of water molecules leading to the formation of OH, H, eaq, etc.; (2) OH attack on sugar molecules leading to strand breaks: (3) OH attack on bases; (4) direct ionization of the sugar molecules leading to strand breaks; (5) direct ionization of the bases. Our calculations predict significant clustering of damage both locally, over regions up to 40 bp and over regions extending to several kilobase pairs. A characteristic feature of the regional damage predicted by our model is the production of short fragments of DNA associated with multiple nearby strand breaks. The shapes of the spectra of DNA fragment lengths depend on the symmetries or approximate symmetries of the chromatin structure. Such fragments have subsequently been detected experimentally and are reported in an accompanying paper (B. Rydberg, Radiat, Res. 145, 200-209, 1996) after exposure to both high- and low-LET radiation. The overall measured yields agree well quantitatively with the theoretical predictions. Our theoretical results predict the existence of a strong peak at about 85 bp, which represents the revolution period about the nucleosome. Other peaks at multiples of about 1,000 bp correspond to the periodicity of the particular solenoid model of chromatin used in these calculations. Theoretical results in combination with experimental data on fragmentation spectra may help determine the consensus or average structure of the chromatin fibers in mammalian DNA.

Chromatin↗
PubMed2006

Morphological transitions during the formation of templated mesoporous materials: theoretical modeling.

We put forward a theoretical model for the morphological transitions of templated mesoporous materials. These materials consist of a mixture of surfactant molecules and inorganic compounds which evolve dynamically upon mixing to form different morphologies depending on the composition and conditions at which mixing occurs. Our theoretical analysis is based on the assumption that adsorption of the inorganic compounds onto mesoscopic assemblies of surfactant molecules changes the effective interactions between the surfactant molecules, consequently lowering the spontaneous curvature of the surfactant layer and inducing morphological changes in the system. On the basis of a mean field phase diagram, we are able to follow the trajectories of the system starting with different initial conditions, and predict the final morphology of the product. In a typical scenario, the reduction in the spontaneous curvature leads first to a smooth transition from compact spherical micelles to elongated worm-like micelles. In the second stage, the layer of inorganic material coating the micelles gives rise to attractive inter-micellar interactions that eventually induce a collapse of the system into a closely packed hexagonal array of coated cylinders. Other pathways may lead to different structures including disordered bicontinuous and ordered cubic phases. The model is in good qualitative agreement with experimental observations.

Journal Article↗
PubMed1989

Mechanisms of atypical atrioventricular Wenckebach periodicity. A theoretical model derived from the concepts of inhomogeneous excitability and electrotonically mediated conduction.

To explain the mechanisms of atypical atrioventricular (AV) Wenckebach periodicity, a model of the AV node was theoretically derived from the concepts of "inhomogeneous excitability" and "electrotonically mediated conduction." The theoretical model of the AV node has the following characteristics: (1) increased vagal tone depresses excitability in the AV node, (2) depressed excitability in the AV node is inhomogeneous in both transverse and longitudinal directions, and (3) electrotonically mediated conduction occurs across inexcitable gaps in the AV node. Many features in atypical AV Wenckebach periodicity are explained by the use of this model. Delayed AV conduction is caused mostly by electrotonically mediated conduction across a much-depressed region in the AV node, and thereafter AV conduction is blocked at the same region, resulting in the occurrence of an AV Wenckebach period with gradual lengthening of PR intervals. Occasionally, longitudinal dissociaton and concealed reentry in the AV node occur in the part below (distal to) the above depressed region, resulting in the occurrence of an AV Wenckebach period with sudden marked lengthening of a PR interval. The sinus impulse following such suddenly delayed AV conduction is usually blocked in the AV node as the result of concealed reentry of the preceding impulse.

Arrhythmias, Cardiac↗
PubMed2004

A three-dimensional theoretical model incorporating spatial detection uncertainty in continuous detector PET.

In this paper, we will describe a theoretical model of the spatial uncertainty for a line of response, due to the imperfect localization of events on the detector heads of a positron emission tomography (PET) camera. The forward acquisition problem is modelled by a Gaussian distribution of the position of interaction on a detector head, centred at the measured position. The a posteriori probability that an event originates from a certain point in the field of view (FOV) is calculated by integrating all the possible lines of response (LORs) through this point, weighted with the Gaussian detection likelihood at the LOR's end points. We have calculated these a posteriori probabilities both for perpendicular and oblique coincidences. For the oblique coincidence case it was necessary to incorporate the effect of the crystal thickness in the calculations. We found in the perpendicular incidence case as well as in the oblique incidence case that the probability density function cannot be analytically expressed in a closed form, and it was thus calculated by means of numerical integration. A Gaussian was fit to the transversal profiles of this function for a given distance to the detectors. From these fits, we can conclude that the profiles can be accurately approximated by a Gaussian, both for perpendicular and oblique coincidences. The FWHM reaches a maximum at the detector heads, and decreases towards the centre of the FOV, as was expected. Afterwards we extended this two-dimensional model to three dimensions, thus incorporating the spatial uncertainty in both transversal directions. This theoretical model was then evaluated and a very good agreement was found with theoretical calculations and with geometric Monte Carlo simulations. Possible improvements for the above-described incorporation of crystal thickness are discussed. Therefore a detailed Monte Carlo study has been performed in order to investigate the interaction probability of photons of different energies along their path in several detector materials dedicated to PET. Finally two approaches for the incorporation of this theoretical model in reconstruction algorithms are outlined.

Algorithms↗
PubMed1984

Application of gas adsorption kinetics--II. A theoretical model for respirator cartridge service life and its practical applications.

A previously introduced theoretical model addressing respirator cartridge contaminant breakthrough was further developed in this study. This development involved the introduction of a new theoretical parameter, a, to complement the parameters k' and tau employed in the initial theoretical approach. The extension of the theory permits the theoretical investigation of the following: (1) the effect of contaminant concentration on breakthrough time; (2) the effect of flow rate on breakthrough time; (3) the influence of contaminant concentration on percentage of breakthrough; and (4) the effect of contaminant concentration on the weight of adsorbed contaminant at a given time. We also compared new theoretical expressions with previously published empirical equations. Utilizing the parameter a, we derived a set of equations of significant practical value. These equations relate the ratio of two contaminant concentrations (one experimental reference concentration and any other concentration of interest) to either the ratio of the corresponding breakthrough times or the corresponding weights of adsorbed contaminant. Three practical examples are provided demonstrating that the new theoretical model reduces experimental work required to predict respirator cartridge service life.

Adsorption↗
PubMed2006

Theoretical model of coping among relatives of patients in intensive care units: a simultaneous concept analysis.

UNLABELLED: This paper reports the development of a theoretical model of relatives' coping approaches during the patient's intensive care unit stay and subsequent recovery at home by performing an analysis of concepts generated from two empirically grounded, theoretical studies in this area. BACKGROUND: When supporting relatives of intensive care unit patients, it is important that nurses have access to evidence-based knowledge of relatives' coping approaches during the period of illness and recovery. METHOD: Simultaneous concept analysis was used to refine and combine multiple coping concepts into a theoretical model of coping. The concepts were generated in two previous empirical studies of relatives' coping approaches during mechanically ventilated patients' intensive care unit stays and recovery at home. FINDINGS: The theoretical model was developed in 2004-2005 and illustrates the effectiveness of different coping approaches in relation to each other and to social support. Definitions summarizing each coping approach and containing the knowledge gained through the simultaneous concept analysis method were also formulated. CONCLUSION: This middle-range theory of relatives' coping approaches may make a valuable contribution to international intensive care unit nursing practice, especially as it is based on empirical studies and may therefore serve as a basis for the development of future clinical guidelines. However, the theoretical model needs to be empirically validated before it can be used.

Adaptation, Psychological↗
PubMed1994

A theoretical model for input impedance of interstitial microwave antennas with choke.

PURPOSE: Two important characteristics for interstitial microwave antennas used in clinical hyperthermia are: (1) a good impedance match to minimize reflected power; and (2) a good power deposition pattern which is independent of insertion depth. A major problem of the miniature coaxial dipole antennas used for interstitial hyperthermia is the fact that the impedance and power deposition patterns of these antennas change with insertion depth. One possible solution is the addition of a coaxial choke. A theoretical model for calculating the input impedance of interstitial microwave antennas having a coaxial choke is presented, which may serve as the first step in the design of such antennas. METHODS AND MATERIALS: A theoretical model for calculating the input impedance of coaxial microwave antennas with and without a choke is presented using insulated antenna theory. The theoretical model was used to calculate the input impedance of several prototype antennas having various choke and feedline dimensions, and comparison was made with experimentally measured impedance measurements in tissue-equivalent phantom. RESULTS: The choke section of the antenna is not ideal if conventional plastic insulation is used as the choke dielectric, because the desired radiating length of the antenna is significantly shorter than the quarter-wavelength in the choke dielectric. Impedance calculations based on the theoretical model correlate reasonably well with experimentally measured impedance. Based on these calculations, the effect of parameters such as choke layer thickness and choke dielectric constant are discussed for a 915 MHz antenna with choke. CONCLUSION: The theoretical model can serve as a design aid for optimizing choked microwave antenna designs, as well as predicting the impedance match of a given antenna design at a given insertion depth. The model allows the effect of some variables not accessible experimentally such as termination impedance to be studied, which may also be useful in the understanding of these antennas. Calculations are easily performed on a desktop computer.

Humans↗
PubMed2003

Hostility, unemployment and health status: testing three theoretical models.

This study examined three theoretical models of hostility, health and life context. According to the psychosocial vulnerability hypothesis, there is an interaction between hostility and adverse conditions. The increased health risk in hostile individuals is assumed to stem from their lower ability to benefit from existing psychosocial resources. The second hypothesis, called here the social context model, considers adverse conditions as an antecedent of both hostility and health problems. The third model states that hostility is a predictor of being selected to adverse conditions involving risk to health (the selection hypothesis). The results from a survey of a population-based random sample (2153 non-institutionalized citizens aged 18-64 years) in Finland, showed that hostile men had a high prevalence of non-optimal health, irrespective of employment status. In non-hostile men, employment was associated with better health than unemployment. This association between hostility and unemployment was not found in women. Corresponding findings were obtained from a 1959-born cohort of 311 individuals followed up for 27 years. The combination of high hostility at school age and unemployment in adulthood had an additive effect on poor health in adult men but not in adult women. Hostility in childhood was not significantly associated with unemployment in adulthood. Thus, this study supported the psychosocial vulnerability model in men.

Adolescent↗
PubMed1993

An application of mechanostat theory to research design: a theoretical model.

In this paper a theoretical model for research into the area of bone health is proposed. The model is based on the mechanostat theory of bone biology, originally proposed by Harold M. Frost, and is directed toward research in the area of osteoporosis. The mechanostat theory is briefly reviewed, including the concept of changes in minimum effective strain thresholds. Each of the model's five levels is then detailed, followed by discussion of their application to research design and interpretation. The proposed research model may provide a systematic approach to research design, and thereby a method to increase the current understanding of bone biology.

Biomechanical Phenomena↗
PubMed2000

College student drinking: an examination of theoretical models of drinking tendencies in freshmen and upperclassmen.

OBJECTIVE: The present research contrasted theoretical models of college student drinking tendencies (normative, social control, maturing out). METHOD: Three groups of students (N = 364; 62. 1% female) from a moderately sized northwestern university were examined: traditional freshmen, nontraditional freshmen and upperclassmen. Participants completed measures assessing drinking tendencies, drinking consequences and drinking beliefs. RESULTS: Support for a given theoretical model was dependent upon which outcome variables were being examined (e.g., drinking tendencies vs drinking consequences). Nontraditional freshmen were similar to their traditional freshmen counterparts in the amount of alcohol they consumed but were more like upperclassmen in the experience of consequences of drinking alcohol. Examination of drinking beliefs yielded inconsistent model support. CONCLUSIONS: It appears that different types of college students drink for different reasons, suggesting a "one size fits all" intervention is less likely to be effective. The findings are discussed with respect to different interventions for changing drinking tendencies, drinking consequences and drinking beliefs, and the timing of those interventions.

Adolescent↗
PubMed2006

[Validation of a theoretical model applied on the care of families with a child with cardiopathy].

This article is based on a survey aimed at validating the theoretical model "Trying to preserve the integrity of the family unit" by applying it to the situation of families living through the experience of having a child undergoing heart surgery. Data was collected through interviews with six family members who had gone through that experience. The questions were laid out according to the model, focusing on the family experience during the time of heart surgery. The data was analyzed according to the Grounded Theory. Results showed that it is possible to validate the theoretical model for the experience of families who had a child undergoing heart surgery through the comparative analysis of the results of both studies. Because of the specific nature of the experience, two new themes emerged: living a lonely experience and overcoming a phase, thus widening the original theoretical model.

Adult↗