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 235 records · Page 13Linked to original sources
PubMedDate not supplied

[Institutionalization of community programs: review of theoretical models and proposal of a model-].

Community-based health promotion programs to change lifestyle habits must remain in their host organizations for extended periods of time in order to have impact. Their effectiveness can be closely linked to their long term viability or institutionalization. To remain viable, these programs must survive beyond initial investment and support by external organizations. However, some programs disappear when external investment is withdrawn. This can be costly and in addition can generate resistance to the implementation of other health promotion programs in the future. Recently, interest in the processes involved in the institutionalization of these programs has increased. Based on 28 publications, this article reviews selected conceptual models that highlight environmental, organizational, community and marketing-related, variables possibly related to the institutionalization process. A new model is proposed to link these diverse models according to: characteristics of the program, characteristics of the host organization, characteristics related to the adoption, implementation and incorporation of the program, and finally characteristics related to the fit (mutual adjustment) between the host and the program.

Community Health Planning↗
PubMed1978

Theoretical modeling of fine-particle deposition in 3-dimensional bronchial bifurcations.

A theoretical model is developed for the prediction of the peak to average particle deposition flux in the human bronchial airways. The model involves the determination of the peak flux by a round-nose 2-dimensional bifurcation channel and the average deposition flux by a curved-tube model. The "hot-spot" effect for all generations in the human respiratory system is estimated. It is found that the peak deposition flux is higher than the average deposition flux by a factor ranging between 5 and 30, depending on the generation number. The importance of this peak to average deposition flux ratio on consideration of environmental safety studies is discussed.

Air Pollutants↗
PubMed2004

Theoretical modeling and experimental evaluation of a microscale molecular mass sensor.

A theoretical model for a recently developed microscale molecular mass sensor (micro-MMS) is presented. The micro-MMS employs a widely applicable technique of measuring the refractive index gradient (RIG) in a microchannel created after two adjacent streams merge: a "sample stream" containing analyte(s) of interest in a host solvent and a "mobile-phase" stream containing only the host solvent. Because the flow in the microchannel is laminar, the analytes in the sample stream mix with the mobile-phase stream primarily by diffusion. The diffusion-induced RIG in the microchannel is measured by monitoring the deflection angle of a diode laser probe beam, which is orthogonal to both the direction of flow and the direction of analyte diffusion. The micro-MMS samples the RIG with probe beams at two positions along the direction of flow, and the ratio of the downstream to the upstream signal monitors the diffusion coefficient. Following calibration for a given class of compounds, the molecular mass of an analyte of interest can be determined. Along with the analyte diffusion coefficient, the theoretical model indicated three other specific parameters are important to interpret the micro-MMS output: the radius of the interrogating light probe beams, the time intervals between each of the detection positions, and the merge point relative to the detection positions. A series of experiments were conducted at different beam radii and flow rates to investigate these parameters, and the results are consistent with the model. The model shows that by using smaller beam radii and altering flow rates the molecular mass range of the micro-MMS can be, in principle, tuned from less than 10(2) g/mol to greater than 10(8) g/mol. The ratio data from the micro-MMS is also demonstrated to readily provide a "universal calibration", from which the determination of unknown diffusion coefficients can be readily obtained.

Journal Article↗
PubMed1981

Life satisfaction and chronic disease: exploration of theoretical model.

This research was undertaken to demonstrate the usefulness of a theoretical model for explaining differences in the life satisfaction of persons with different chronic diseases. Through stepwise multiple regression, an assessment was made of the effects of social activity, perceived health, health locus-of control and degree of disability on the life satisfaction of 51 persons with coronary artery disease (CAD) and 32 persons with chronic obstructive pulmonary disease (COPD). Findings were as follows: (1) COPD patients were significantly less satisfied, less socially active and more disabled, and they perceived their health as poorer than did the CAD patients; (2) social activity emerged as the single best predictor of life satisfaction for both groups; (3) the second best predictor was perceived health for the CAD patients and degree of disability for the COPD patients; (4) the four variables accounted for 48 per cent of the variance in life satisfaction for the COPD patients, 12.4 per cent of the CAD patients. It was concluded that predictors of life satisfaction vary with the particular disease, as does the manner in which these factors interact to mitigate or compound the impact of the particular disease. Suggestions are made regarding modification of the theoretical model.

Attitude to Health↗
PubMed1987

Blood oxygen equilibria and theoretical models. II. A critical estimation.

1. Theoretical models can fit the oxygen equilibria of trout and human red cell suspensions, and describe the apparent oxygenation process in the red cell. 2. The assumption that full oxygenation is attained at atmospheric O2 pressures can result in biphasic Hill plots and high Hill coefficients for high O2 saturations. This phenomenon must not be confused with aggregation of hemoglobin. 3. Problems specific to measurements of red cell suspensions, regarding the ionic cellular composition and its stability with time, are approached. Changes of buffer osmolarity, and--for trout--addition of adrenaline, within physiological proportions, have no impact on the results. 4. This tends to validate the general significance of equilibrium data obtained on this material, regarding the effects of protons and organic phosphates, although complex ionic movements across the red cell membrane are known to occur in the animal under certain circumstances.

Animals↗
PubMed2004

The influence of contests on optimal clutch size: a game-theoretic model.

We develop a game-theoretic model to predict the effect of size-dependent contest outcomes on optimal-clutch-size decisions. We consider the case where larger individuals develop from smaller clutches and, as adults, are advantaged in competition for limiting resources. The relationship between fitness and size thus depends on the sizes of other members of the population. We show that clutch-size optima are decreased by body-size-dependent contest outcomes, with larger effects when body size is most affected by clutch size, when prior resource ownership has less influence on contest outcome and when contests occur more frequently. We also show the existence of polymorphisms in clutch-size optima and that clutch-size driven changes in population density can, via an effect on the probability of host finding, further influence optimal clutch size. Our model is formulated to match the life history of a parasitoid wasp, in which clutch size affects offspring size and females engage in direct contests for host ownership, which larger females tend to win; we confirm that female-female competition is likely to influence clutch size in this species. However, the model is also relevant to clutch size in other taxa and supports recent suggestions concerning reproductive decisions in great tits.

Animals↗
PubMed2000

Wave scattering through classically chaotic cavities in the presence of absorption: An information-theoretic model

We propose an information-theoretic model for the transport of waves through a chaotic cavity in the presence of absorption. The entropy of the S-matrix statistical distribution is maximized, with the constraint =alphan: n is the dimensionality of S, and 0</=alpha</=1, alpha=0(1) meaning complete (no) absorption. For strong absorption our result agrees with a number of analytical calculations already given in the literature. In that limit, the distribution of the individual (angular) transmission and reflection coefficients becomes exponential (Rayleigh statistics), even for n=1. For n>>1 Rayleigh statistics is attained even with no absorption; here, we extend the study to alpha<1. The model is compared with random-matrix-theory numerical simulations: it describes the problem very well for strong absorption, but fails for moderate and weak absorptions. Thus, in the latter regime, some important physical constraint is missing in the construction of the model.

Journal Article↗
PubMed2005

Mass transport in micellar surfactant solutions: 2. Theoretical modeling of adsorption at a quiescent interface.

Here, we apply the detailed theoretical model of micellar kinetics from part 1 of this study to the case of surfactant adsorption at a quiescent interface, i.e., to the relaxation of surface tension and adsorption after a small initial perturbation. Our goal is to understand why for some surfactant solutions the surface tension relaxes as inverse-square-root of time, 1/t(1/2), but two different expressions for the characteristic relaxation time are applicable to different cases. In addition, our aim is to clarify why for other surfactant solutions the surface tension relaxes exponentially. For this goal, we carried out a computer modeling of the adsorption process, based on the general system of equations derived in part 1. This analysis reveals the existence of four different consecutive relaxation regimes (stages) for a given micellar solution: two exponential regimes and two inverse-square-root regimes, following one after another in alternating order. Experimentally, depending on the specific surfactant and method, one usually registers only one of these regimes. Therefore, to interpret properly the data, one has to identify which of these four kinetic regimes is observed in the given experiment. Our numerical results for the relaxation of the surface tension, micelle concentration and aggregation number are presented in the form of kinetic diagrams, which reveal the stages of the relaxation process. At low micelle concentrations, "rudimentary" kinetic diagrams could be observed, which are characterized by merging of some stages. Thus, the theoretical modeling reveals a general and physically rich picture of the adsorption process. To facilitate the interpretation of experimental data, we have derived convenient theoretical expressions for the time dependence of surface tension and adsorption in each of the four regimes.

Adsorption↗
PubMed2003

Some theoretical models and constructs generic to substance abuse prevention programs for adolescents: possible relevance and limitations for problem gambling.

For the past several years the author and his colleagues have explored the area of how social psychological constructs and theoretical models can be applied to the prevention of health threatening behaviors in adolescents. In examining the need for the development of gambling prevention programs for adolescents, it might be of value to consider the application of such constructs and theoretical models as a foundation to the development of prevention programs in this emerging problem behavior among adolescents. In order to provide perspective to the reader, the present paper reviews the history of various psychosocial models and constructs generic to programs directed at prevention of substance abuse in adolescents. A brief history of some of these models, possibly most applicable to gambling prevention programs, are presented. Social inoculation, reasoned action, planned behavior, and problem behavior theory, are among those discussed. Some deficits of these models, are also articulated. How such models may have relevance to developing programs for prevention of problem gambling in adolescents is also discussed. However, the inherent differences between gambling and more directly health threatening behaviors such as substance abuse must, of course, be seriously considered in utilizing such models. Most current gambling prevention programs have seldom been guided by theoretical models. Developers of gambling prevention programs should consider theoretical foundations, particularly since such foundations not only provide a guide for programs, but may become critical tools in evaluating their effectiveness.

Adolescent↗
PubMed2002

Donnan equilibrium of ionic drugs in pH-dependent fixed charge membranes: theoretical modeling.

We have studied theoretically the partition equilibrium of a cationic drug between an electrolyte solution and a membrane with pH-dependent fixed charges using an extended Donnan formalism. The aqueous solution within the fixed charge membrane is assumed to be in equilibrium with an external aqueous solution containing six ionic species: the cationic drug (DH(+)), the salt cations (Na(+) and Ca(2+)), the salt anion (Cl(-)), and the hydrogen and hydroxide ions. In addition to these mobile species, the membrane solution may also contain four fixed species attached to the membrane chains: strongly acid sulfonic groups (SO(3)(-)), weakly acid carboxylic groups in dissociated (COO(-)) and neutral (COOH) forms, and positively charged groups (COO...Ca(+)) resulting from Ca(2+) binding to dissociated weakly acid groups. The ionization state of the weak electrolyte groups attached to the membrane chains is analyzed as a function of the local pH, salt concentration, and drug concentration in the membrane solution, and particular attention is paid to the effects of the Ca(2+) binding to the negatively charged membrane fixed groups. The lipophilicity of the drug is simulated by the chemical partition coefficient between the membrane and external solutions giving the tendency of the drug to enter the membrane solution due to hydrophobic interactions. Comparison of the theoretical results with available experimental data allows us to explain qualitatively the effects that the pH, salt concentration, drug concentration, membrane fixed charge concentration, and Ca(2+) binding exert on the ionic drug equilibrium. The role of the interfacial (Donnan) electric potential difference between the membrane and the external solutions on this ionic drug equilibrium is emphasized throughout the paper.

Calcium↗
PubMed1993

[A theoretical model for the study of Lyme borreliosis].

This article is a short review of: a) development of theory on natural foci of communicable diseases in man, b) methodological approach to the investigation of natural foci, e.g. theoretical model in their investigation, and c) the use of theoretical model in the investigation of Lyme borreliosis. A great number of multidisciplinary studies on natural foci zooanthroponoses conducted through many years, in which ecological approach and numerous methods were applied, commencing from studies of the processes at the level of molecules, genes, cells, tissues, organismus, populations and species, contributed to the knowledge that epizootical process of natural foci of zooanthroponoses is almost an ideal natural model. Its investigation allows the establishment of the rules of epidemiological process which, for many reasons (ethical above all), is not accessible for experimental studies. On these principles a general block model has been worked out, which serves for the estimation of epidemiological manifestations of natural foci zooanthroponoses, and which, applied to Lyme borreliosis, enables the determination of active and potential foci and the estimation of the degree of risk of man infection in determined foci. Data obtained in such a way allow planning and application of adequate preventive measures.

Disease Reservoirs↗
PubMed2006

Theoretical model and Rasch analysis to develop a revised Foot Function Index.

BACKGROUND: The Foot Function Index (FFI) is a widely used self-reported measure of health-related foot function. Several areas have been identified for potential improvement, and this study responds to such criticisms. The objectives of this study were to: (1) develop a theoretical model of foot functioning, (2) develop a revised FFI (FFI-R), and (3) field-test the FFI-R. METHODS: A literature review was conducted to develop the theoretical model. The FFI-R items were developed from the original 23 FFI items, and more items were added as a result of the literature review. A focus group discussion with clinicians and pilot interviews with patients resulted in a final draft of the FFI-R. This draft consisted of four subscales and comprised 68 items with a six-point response scale. The FFI-R was field tested on 92 patients in the podiatry clinic of a Veterans Administration Hospital in the Midwest. Psychometric analyses were conducted with modern item response theory (IRT) methods. RESULTS: A theoretical model of foot functioning was developed. The FFI-R response scale was revised from six to five categories since confusion was found between categories 4 and 5. Rasch analyses indicated a person reliability of 0.96 and item reliability of 0.93. The subscale reliability of pain and stiffness, psychosocial, and disability were all >0.80; the exception was assistive devices (>0.50). Construct validity of FFI-R was supported based on the correlation of 50-ft walk time with an FFI-R total of 0.306, p = 0.018, N = 59. Rasch analyses indicated several items with poor fit statistics and a short form with 34 items was developed. CONCLUSION: The FFI was revised, and new items were added to compose the FFI-R. The chief theoretical change was adding a psychosocial scale. Both long and short forms had very good psychometric properties.

Adult↗
PubMed2001

Evaluation of Selected Behavior Change Theoretical Models Used in Weight Management Interventions.

Purpose: This paper evaluates selected behavior change theoretical models used in weight reduction interventions and presents recommendations for the use of theory in weight reduction research. Overweight and obesity are complex problems, requiring long-term behavioral change. Behavioral treatments for overweight and obesity are as varied as the elements of behavior, and the long-term efficacy of most approaches is poor. Because of the complexity of both the problem and its treatment, investigations must target the development of cause-effect explanations. CONCLUSIONS: Many of the behavioral change intervention studies reviewed lacked external validity, primarily due to the failure to consider salient moderators. The theoretical models reviewed in this paper were primarily tested on white, employed populations. These and other data suggest that extant theoretical approaches may not be salient in certain groups. IMPLICATIONS: Practice implications include: 1) assess indicators for readiness to engage in weight reduction efforts; 2) base interventions on multiple theories; and 3) develop context-based interventions. Future research should include a focus on innovative methods in theory development, development of theory acknowledging mediator/moderator interactions, development of theory in context, and development of theory reflecting cultural meaning and diversity.

Journal Article↗
PubMed2001

Examining theoretical models through research synthesis. The benefits of model-driven meta-analysis.

Quantitative research synthesis methods can be used to examine theoretical models for substantive research questions. Model-driven syntheses can address more complex questions than have typically been addressed in quantitative reviews in a more systematic and organized manner than in a traditional narrative review. A rationale and set of objectives for syntheses involving models are reviewed. The author describes how to incorporate models into each stage of a review, outlining problems and limitations that may arise at each stage. Examples from several model-driven syntheses illustrate the points made in the article.

Data Collection↗
PubMed2003

A theoretical model for the optimal allocation of health resources in Greece.

This paper presents a theoretical model that enables us to rate the efficiency of health resources in different regions. The model is based on the theory of production and refers to two specific regions. The hypotheses that determine the relationship between health care resources and their indicators are examined as well as the necessary conditions for the optimal regional allocation of these resources.

Efficiency, Organizational↗
PubMed2005

Indentation and adhesive probing of a cell membrane with AFM: theoretical model and experiments.

In probing adhesion and cell mechanics by atomic force microscopy (AFM), the mechanical properties of the membrane have an important if neglected role. Here we theoretically model the contact of an AFM tip with a cell membrane, where direct motivation and data are derived from a prototypical ligand-receptor adhesion experiment. An AFM tip is functionalized with a prototypical ligand, SIRPalpha, and then used to probe its native receptor on red cells, CD47. The interactions prove specific and typical in force, and also show in detachment, a sawtooth-shaped disruption process that can extend over hundreds of nm. The theoretical model here that accounts for both membrane indentation as well as membrane extension in tip retraction incorporates membrane tension and elasticity as well as AFM tip geometry and stochastic disruption. Importantly, indentation depth proves initially proportional to membrane tension and does not follow the standard Hertz model. Computations of detachment confirm nonperiodic disruption with membrane extensions of hundreds of nm set by membrane tension. Membrane mechanical properties thus clearly influence AFM probing of cells, including single molecule adhesion experiments.

Animals↗
PubMed2005

A theoretical model describing the transfer characteristics of a membrane hydrophone and validation.

This paper presents a theoretical model describing the transfer characteristics of a bilaminar polyvinylidene fluoride membrane hydrophone. The model applied uses a matrix formulation for one-dimensional propagation in multi-layered media. Arbitrary interconnections of piezoelectric layers are possible. The electrical transfer characteristics of the hydrophone leg and cable are modelled as transmission lines using a two-port network approach. The model is validated against measured open-circuit sensitivities for a 25 microm film thickness 0.5 mm active element diameter bilaminar hydrophone (50 microm total film thickness). Good agreement between theory and experiment is demonstrated. A 9 microm film thickness 0.5 mm active element diameter bilaminar hydrophone (18 microm total film thickness) together with amplifier is also modelled. The voltage at the output stage of the amplifier is measured and, by knowledge of the transfer characteristics of the complete system, the pressure waveform at the hydrophone position is estimated and compared with the acoustic pressure waveform derived using a laser interferometer. Good agreement is obtained.

Acoustics↗