PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Models, Theoretical”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 883 records · Page 49Linked to original sources
PubMed1995

Theoretical modelling of plasma protein adsorption/desorption processes onto solid surfaces.

Experimental data from particle electrophoretic measurements of polymer particles have been used for modelling competitive protein adsorption. It could be demonstrated that protein adsorption onto a solid surface is a two-step process: firstly fast reversible adsorption and, secondly, irreversible coupling at the adsorption centres dependent on contact time. The extent of protein competition is influenced by a characteristic time-dependence of the adsorption process. Analysis of the experimental findings results in two models whose corresponding systems of kinetic equations were solved. Both suggested models are based upon relatively simple mechanisms: (a) the parallel reaction; and (b) the exchange reaction. It has been shown that in our experiments a classical exchange process for describing competitive protein adsorption can be very probably supposed.

Adsorption↗
PubMed2000

Social support in a worksite smoking intervention. A test of theoretical models.

To better understand how social support operates in smoking cessation, three models of support were tested: main effect, stress-buffering, and indirect. Employees from 61 worksites received (a) self-help manuals (SH); (b) self-help manuals and incentives (I); or (c) self-help manuals, incentives, and social support groups (G). At 24 months, results suggest that the main effect model of social support was operating in this study. That is, social support had a direct influence on smoking cessation. The group intervention significantly enhanced positive partner support across all time points, and partner support facilitated quitting smoking. Higher levels of appraisal support also significantly predicted successful quitting. The beneficial effects of social support were sustained throughout the process of quitting and long-term maintenance.

Adult↗
PubMed2006

Dating violence among college men and women: evaluation of a theoretical model.

This study empirically evaluates the Riggs and O'Leary (1989) model of dating violence. A sample of 200 college students completes assessments concerning the occurrence of violence in their dating relationships. The incidence of self-reported partner violence is 25% for women and 10% for men. Multivariate logistic regression analyses are performed to determine the most salient predictors of dating violence for each gender. Findings reveal that the model is more accurate in predicting female, as compared with male perpetration of dating violence. The model accurately classifies 83% of violent women and only 30% of violent men. This study has several implications for the field of dating violence. Results indicate that although there is some degree of overlap, variant constructs predict violence for each gender. Identifying these constructs will guide prevention efforts in more effectively decreasing the occurrence of dating violence.

Adult↗
PubMed1999

Predicting breast-feeding intention among low-income pregnant women: a comparison of two theoretical models.

This study examined the applicability of the transtheoretical model and a model derived from the theory of reasoned action for predicting breast-feeding intention among low-income pregnant women. Participants completed a 70-item self-report questionnaire assessing their breast-feeding attitudes, intentions, and support. A positive correlation existed between Stages of Change for breast-feeding and the number of Processes of Change used by respondents. A negative correlation existed between Stages of Change for breast-feeding and the number of negative breast-feeding beliefs held by respondents. Furthermore, women's normative beliefs and outcome beliefs were significantly correlated with breast-feeding intention in manners consistent with the model developed from the theory of reasoned action. After accounting for significant sociodemographic and lifestyle factors, the Processes of Change and outcome beliefs remained independently correlated with breast-feeding intention. These models are capable of predicting the intention to breast-feed and might offer an innovative approach for further breast-feeding research and intervention development.

Adolescent↗
PubMed2003

A simple theoretical model to study the voltage dependence of the electronic structure of phenyl ethylene oligomers.

Although very few measurements have appeared in the open literature and there seems to be a controversy about the existence of the NDR phenomenon in molecules, the prospects of building such systems have attracted significant attention. In the work reported in this paper we used a model based on DFT calculations of the electronic structure of the 2'-amino-4,4'-di(ethynylphenyl)-5'-nitro-1-benzenethiolate molecule (previously reported to exhibit NDR behavior) in a capacitor-like electric field that mimics the potential spatial profile of the junction. Our results suggest that in these systems, there seems to be a correlation between a substantial charge density rearrangement of the neutral bridge at a threshold voltage and the NDR behavior observed in previous experiments. Our results highlight the importance of inclusion of the field in the study of electrified interfaces. We applied this model to a fluorine-substituted conjugated diethynylphenyl molecule and found that these calculations predict similar behavior. Results based on extended system calculations, including electrode-molecule interactions, confirm the validity of the model based on the isolated molecule and suggest the use of these simple models to rationally design molecular devices with similar switching characteristics.

Algorithms↗
PubMed1987

Biomechanics of hydrocephalus: a new theoretical model.

The finite element method (FEM), an advanced method of computer simulation, is used to examine biomechanical studies of hydrocephalus. Biot's theory of consolidation, which describes the mechanical behavior of a porous medium containing viscous fluid, is applied to represent the coupled behavior of tissue and fluid in the hydrocephalic brain. A computer simulation of the hydrocephalic process is carried out by FEM to evaluate the mathematical model. A two-dimensional finite element model is constructed using a horizontal computed tomographic (CT) slice of the brain. Specifying the material properties of the brain parenchyma, the loading characteristics, and the boundary conditions, the change of interstitial pressure, intracerebral stress distribution, and ventricular configuration are computed and graphically represented. The results of the computer simulation are compared with the findings of CT and magnetic resonance imaging of hydrocephalic patients. The progress of periventricular cerebrospinal fluid edema and ventricular enlargement is well represented by the mathematical model. The model demonstrated that stress concentration in the brain tissue and increased parenchymal hydraulic conductivity play an important role in the generation of periventricular cerebrospinal fluid edema.

Brain↗
PubMed2000

Influence of age (body size) on the Fontan circulation--analysis by a theoretical model.

Among the original selection criteria for the Fontan operation, the recommended age at the time of surgery has been 4 years or older, but recent clinical data have indicated the feasibility of this procedure in younger patients. Because age may influence the properties of the systemic vascular bed, changes in systemic vascular resistance (Rs) and systemic vascular compliance (Cs) associated with physical development were quantified in 86 pediatric patients without known abnormalities of the systemic circulation, and the effects of age (body size) on Fontan circulation were then analyzed using an analytical model of the cardiovascular system. As the body surface area (BSA) of the patient decreased, Cs also decreased significantly (r=0.81, p<0.001). Based upon this relationship between BSA and Cs, the analytical model showed that the impedance (ventricular afterload) of the Fontan circulation significantly increased as Cs decreased with the decrease in BSA. Moreover, the increase in impedance in response to changes in heart rate or Rs was inversely proportional to the BSA. However, these findings were significant only when the BSA was below 0.3 m2. Small BSA, or a lower age, has minimal effects on the Fontan circulation until it comes close to the infant value, and thus the Fontan procedure may be feasible much earlier than formerly recommended when the hemodynamics are otherwise acceptable.

Age Factors↗
PubMed1998

A theoretical model for simultaneous mixed irradiation with multiple types of radiation.

Several models for the action of mixed irradiation with two types of radiation have been proposed in the last two decades, although the superiority or inferiority of these models is not completely elucidated. However, mixed irradiation is sometimes composed of more than two types of radiation, and for this type of mixed irradiation, no model has yet been proposed. Therefore, I have tried to make a model for this type of mixed irradiation. This paper presents a survival model for simultaneous mixed irradiation with multiple (n) types of radiation, and this model would be helpful for assessing the effects of simultaneous mixed irradiation with multiple types of radiation in nature, accidents, etc.

Animals↗
PubMed1979

Homosexual identity formation: a theoretical model.

A six-stage model of homosexual identity formation is outlined within the framework of interpersonal congruency theory. Stages are differentiated on the basis of the person's perceptions of his/her own behavior and the actions that arise as a consequence of this perception. The person is seen to have an active role in the acquisition of a homosexual identity. Alternative paths of development are proposed within each stage. The notion that people can accept homosexuality as a positively valued status is assumed. Several factors believed to be influential in determining whether a person takes one line of development or another are discussed. The model is intended to be applied to both female and male homosexuals.

Adaptation, Psychological↗
PubMed1986

Adaptive supervision: a theoretical model for social workers.

Two models of leadership styles are prominent in the management field: Blake and Mouton's managerial Grid and Hersey and Blanchard's Situational Leadership Model. Much of the research on supervisory styles in social work has been based on the former. A recent public debate between the two sets of theorists suggests that both have strengths and limitations. Accordingly, an adaptive model of social work supervision that combines elements of both theories is proposed.

Humans↗
PubMed2003

Direct fit of a theoretical model of phase transition in oscillatory finger motions.

This paper presents a general method to fit the Schöner-Haken-Kelso (SHK) model of human movement phase transitions directly to time series data. A robust variant of the extended Kalman filter technique is applied to the data of a single subject. The options of covariance resetting and iteration within recursion were used to obtain time-dependent estimates of both the alpha and beta parameters in the SHK model. Comparison between transition onset time and the time at which /beta(t/T)/alpha(t/T)/ becomes critical indicates that the transitions are advanced by noise. The method can be extended to handle non-normal data and generalization across subjects and/or experimental conditions.

Adult↗
PubMed2001

Magneto-optical visualization of metal-loss defects in a ferromagnetic plate: experimental verification of theoretical modeling.

Rare-earth iron garnet films with in-plane magnetic anisotropy grown on [111]-oriented substrates are promising for the visualization of magnetic leakage fields in nondestructive evaluation. Such magneto-optical films have to be specifically engineered, and we give an example of this technology. To assess the validity and accuracy of finite-element calculations of a magnetization assembly combined with the physical modeling of the image formation, comparisons between calculated and experimentally obtained magneto-optical images of metal-loss defects have been made. A convincing quantitative agreement is demonstrated. It is shown that both physical and computer modeling techniques allow for a predictive engineering design of the prospective applications and provide greater insight into the method.

Journal Article↗
PubMed2003

Mechanotransduction determines the structure and function of lung and bone: a theoretical model for the pathophysiology of chronic disease.

Multicellular organisms have evolved in adaptation to the Earth's gravitational and oxygen environment. This epigenetic process is dependent on the capacity of mesodermal cells to act as mechanosensors that can conform, deform, and reform in adaptation to the organism's physical environment. Mechanical forces, such as hydrostatic pressure and gravity, play important roles in the embryonic development, homeostasis, and repair of lung and bone. We discuss the role of parathyroid hormone-related protein (PTHrP) as a mechanotransducer for stretch in these organs during normal development, particularly as it lends itself to homeostasis; we further demonstrate that "uncoupling" of such mechanisms may play a central role in injury repair, particularly as it relates to chronic diseases of lung and bone. Endothermal PTHrP signaling through its G-protein coupled receptor promotes normal cell-cell signaling that maintains the homeostatic phenotypes of lung and bone. Molecular disruption of the PTHrP/PTHrP receptor pathway from endoderm to mesoderm, because of such factors as volutrauma, hyperoxia, inflammation, and microgravity, alters intracellular signaling, causing maladaptive cellular changes, resulting in myofibroblast proliferation and granulation. Examples of such pathologic changes specifically related to this cellular/molecular mechanism of maladaptation are chronic lung disease and osteoporosis. We suggest a new paradigm that may help in the future creation of diagnostic and therapeutic modalities for a wide range of developmental and chronic diseases ranging from bronchopulmonary dysplasia in newborns to idiopathic pulmonary fibrosis and osteoporosis as a result of aging or microgravity.

Animals↗