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At least 1,009 records · Page 56Linked to original sources
PubMed2005

[Theoretical-mathematical models of the forces effected by allograft sling systems in incontinence therapy].

The various allograft sling systems are differentiated by their devices, the different pore sizes of the prolene bands as well as, importantly, the various anatomical sling positions. Retropubic slings are positioned through the Retzius space, transobturator slings are placed through the obturator foramen. One of the major risks of complications when inserting these slings is that of over-tightening. The forces exerted during the positioning and fine tuning of the mesh slings are explained by a mathematical model. The flatter the suburethral angle after the tape placement, the stronger a force is to be applied for a further tightening of the tape. Due to the effective strength vectors, there seems to be less chance of overcorrection with the transobturator approach.

Biomechanical Phenomena↗
PubMed2005

Higher disease prevalence can induce greater sociality: a game theoretic coevolutionary model.

There is growing evidence that communicable diseases constitute a strong selective force on the evolution of social systems. It has been suggested that infectious diseases may determine upper limits of host sociality by, for example, inducing territoriality or early juvenile dispersal. Here we use game theory to model the evolution of host sociality in the context of communicable diseases. Our model is then augmented with the evolution of virulence to determine coevolutionarily stable strategies of host sociality and pathogen virulence. In contrast to a controversial hypothesis by Ewald (1994), our analysis indicates that pathogens may become more virulent when contact rates are low, and their prevalence can ultimately induce greater sociality.

Biological Evolution↗
PubMed1983

Spectral shifts of ultrasonic propagation: a study of theoretical and experimental models.

The theoretical relationship between center frequency downshift and the spectral bandwidth was investigated for pulses with a sinc(x) spectrum propagating through lossy media. Power law and exponential models for frequency dependence of attenuation were used. Six target materials encompassing a range of attenuation parameters were used to verify the theoretical model. The frequency downshift data from these materials was used to calculate their respective attenuation parameters. It was shown theoretically and verified experimentally that for small frequency downshifts, the sinc(x) model yields the same material parameters as the Gaussian model. The choice of the model for the attenuation of the material was found to be inconsequential.

Biophysical Phenomena↗
PubMed1987

The combining of multiple hemispheric resources in learning-disabled and skilled readers' recall of words: a test of three information-processing models.

Three theoretical models (additive, independence, maximum rule) that characterize and predict the influence of independent hemispheric resources on learning-disabled and skilled readers' simultaneous processing were tested. Predictions related to word recall performance during simultaneous encoding conditions (dichotic listening task) were made from unilateral (dichotic listening task) presentations. The maximum rule model best characterized both ability groups in that simultaneous encoding produced no better recall than unilateral presentations. While the results support the hypothesis that both ability groups use similar processes in the combining of hemispheric resources (i.e., weak/dominant processing), ability group differences do occur in the coordination of such resources.

Cerebral Cortex↗
PubMed1999

Ultrasonic propagation in cancellous bone: a new stratified model.

The theoretical modeling of ultrasonic propagation in cancellous bone is pertinent to improving the ultrasonic diagnosis of osteoporosis. First, this paper reviews applications of Biot's theory to this problem. Next, a new approach is presented, based on an idealization of cancellous bone as a periodic array of bone-marrow layers. Schoenberg's theory is applied to this model to predict wave properties. Bovine bone samples were tested in vitro using pulses centered at 1 MHz over various angles relative to the orientated cancellous structure. Two longitudinal modes (fast and slow waves) were observed for propagation parallel to the structure, but only one was observed for propagation normal to the structure. Angular-dependence of velocities was examined, and the fast wave was found to be strongly anisotropic. These results gave qualitative agreement with predictions of Schoenberg's theory. Although this new model is a simplification of the cancellous architecture, it has potential for future research.

Animals↗
PubMed1995

Patient decision-making in relation to extensive restorative dental treatment. Part II: Evaluation of a patient decision-making model.

A theoretical model was proposed and tested to evaluate some of the factors involved in patients' decisions to undergo extensive restorative dental treatment. This model incorporates aspects of the environment within which the decision occurred (the patient/provider relationship, social influence and the role of cues in initiating treatment) and internal values held by the individual (perceptions of value of and barriers to treatment). Value of treatment was measured using aesthetics, function, health motivation and self-esteem. Barriers to treatment included fears and anxieties about treatment, the costs of treatment, the time involved in obtaining treatment and access to care. Data were collected by mailed questionnaire from 188 patients at a North American state university dental school who had received over $1,500 of restorative dental treatment during 1990/91. Data were analysed using path analysis multiple regression. The most important determinant in the decision to undergo treatment was patient/provider relationship. As expected, barriers exerted an inverse effect upon the outcome and had twice the influence compared with the patients' perceived value of treatment. Cues and social influence were not shown to play a significant role in initiating restorative dental treatment.

Adult↗
PubMed2006

Manipulating lek size and composition using decoys: an experimental investigation of lek evolution models.

Four theoretical models have been proposed to account for the origin and maintenance of leks: hotspot, female preference, hotshot, and black hole models. Each has been validated in particular cases, and most are not mutually exclusive; therefore, it has been difficult to contrast and separate them, empirically and experimentally. By using decoys to mimic natural leks in the little bustard, artificial leks attracted wild birds. Then, by manipulating artificial lek size and structure (sex ratio, male phenotype), the study of responses of wild males and females allowed us to test specific predictions derived from the four classical models of lek evolution. The hotspot model was not supported because female decoys did not attract wild males. Conversely, hotshot males do exist in this species (attracting both wild females and males), as does a female preference for a particular lek size (four males). Finally, males aggressive toward decoys attracted fewer females, consistent with one of the mechanisms by which the black hole model may work. Therefore, three models of lek evolution were partly or fully supported by our experimental results: hotshot, female preference, and black hole models. We suggest that these models actually fit within each other, ensuring the evolution, functioning, and long-term maintenance of leks.

Aggression↗
PubMed2002

Psychological well-being of Black and White grandmothers raising grandchildren: examination of a two-factor model.

A theoretical model predicting the positive and negative affect of caregiving grandmothers was tested with a sample of 867 grandmothers caring for a grandchild in households that did not include either of the grandchild's parents. Results confirm that the principles guiding a two-factor model of psychological well-being operate at the level of subjective role appraisals. Unique predictors of positive and negative affect as well as unique predictors of caregiving satisfaction and burden were identified. The stability of the model for Black and White grandmothers highlights the similarity of the experience across race.

Adaptation, Psychological↗
PubMedDate not supplied

The health practices of homeless women: a causal model.

A theoretical model was developed and tested to explain the effects of learned helplessness, self-esteem, and depression on the health practices of homeless women. Data were collected from a sample of 122 homeless women recruited from six shelters. Structural equation analysis was used to evaluate the model. Analysis revealed a goodness-of-fit index of 98, indicating a good fit of the model with the data. Overall, the variables in the model accounted for 14% to 21% of the variance in the health practices of homeless women.

Adolescent↗
PubMed2002

Surface effects in thin films of antiferroelectric smectic liquid crystals in terms of the short-pitch long-pitch competition model.

A theoretical model based on the competition between short-pitch and long-pitch types of helical order is developed for thin films of antiferroelectric smectic liquid crystals. In the case of the "bookshelf" structure of the film and non-polar surfaces, subsurface perturbations of the ordering are found out analytically. Corresponding contributions to the free energies of the different phases are analysed. The possibility of sufficient influence of the boundaries on phase sequences is predicted even in the case of weak surface anchoring. A consistent explanation of the controversial experimental information is given; further ways of experimental justification of the model assumptions are discussed.

Journal Article↗
PubMed2005

Characterization of polyvinyl alcohol/acrylamide holographic memories with a first-harmonic diffusion model.

Several theoretical models have been proposed to predict the behavior of photopolymers as holographic recording materials. Basically these models have been applied to study thin layers (around 100 microm thick). The increasing importance of holographic memories recorded in photopolymers (thickness of > 500 microm) makes it necessary to extend the ideas proposed by these models to study thick photopolymer layers. We calculate the temporal evolution of the diffraction efficiencies for thick layers using a first-harmonic diffusion model, and the results obtained are compared with the corresponding values for thin layers. Furthermore, the values of the average diffusivity of the polymer chains after the grating is formed are also obtained. In general, we find that the monomer and polymer diffusivity increases when higher values of thickness are used.

Journal Article↗
PubMed1984

Up- and down-regulation of insulin receptors. Kinetic models.

A theoretical model for insulin receptor synthesis and degradation in differentiating 3T3-L1 adipocytes is described. This three-step irreversible ordered sequence model explains the up- and down-regulation of receptors in terms of the level of insulin concentration. Kinetic expressions were derived for the model. Numerical solutions for these equations, based on data reported by Reed and Lane (Reed, B.C., and Lane, M. D. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 285-289) were used for computer-generated curves illustrating insulin-dependent receptor synthesis and degradation. Results show that this model provides the best fit to the reported data and lend support to the suggestion that the free recycled receptor may differ from the newly synthesized receptor. A possible role for the recycled receptor in signal modulation is suggested.

Adipose Tissue↗
PubMed1998

Nursing case management for psychogeriatric patients and their families: description of a clinical model.

A theoretical model of clinical case management for psychogeriatric patients and their families is described. Psychogeriatric patients often have complex health care needs, requiring specific nursing interventions. The increasing frailty of these patients over time, together with the risk for institutionalization, make professional nursing contribution to their care even more desirable. Nursing case management is described by means of a conceptual-operational continuum. On the conceptual site, the continuum includes a geriatric definition and core principles of case management. On the operational site, case management is described as a clinical system, a process, a technology, and a role. The process of case management is a deliberate, intellectual activity whereby the practice of nursing is approached in an orderly, systematic manner. It includes components of assessment, diagnosis, planning, implementation, and evaluation. The case management approach requires nurses to assume an active role in designing care maps and to work collaboratively with members of a multidisciplinary team.

Aged↗
PubMed1984

Theoretical temperature distributions produced by an annular phased array-type system in CT-based patient models.

Theoretical calculations for the specific absorption rate (SAR) and the resulting temperature distributions produced by an annular phased array (APA)-type system are made. The finite element numerical method is used in the formulation of both the electromagnetic (EM) and thermal boundary value problems. A number of detailed two-dimensional patient models based on CT-scan data from the pelvic, visceral, and thoracic regions are generated to simulate a variety of tumor locations and surrounding normal tissues. The SAR values from the EM solution are put into the bioheat transfer equation, and steady-state temperature distributions are calculated for a wide range of blood flow rates. Based on our theoretical modeling, the APA shows no preferential heating of superficial over deep-seated tumors. However, in most cases for all three regions of the human trunk only fair thermal profiles (therapeutic area near 60%) are obtained in tumors with little or no blood flow and poor temperature patterns (therapeutic area less than 50%) are found in tumors with moderate to high perfusion rates. These theoretical calculations should aid the clinician in the evaluation of the effectiveness of APA-type devices in heating tumors located in the trunk region.

Humans↗