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At least 937 records · Page 52Linked to original sources
PubMed2002

Interorganizational networks: using a theoretical model to predict effectiveness of rural health care delivery networks.

Interorganizational health care delivery networks have potential for sustaining health services delivery in rural areas faced with economic and demographic challenges. Four Nebraska rural health care delivery networks (Albion-Ord, Blue River Valley, Rural Partners, Inc., and Western Nebraska) were compared to an interorganizational model based on theories of interorganizational relations, exchange, population ecology, and synthesized collaboration. It assumes that outcomes, including effectiveness, are influenced by external and internal factors that are operationalized through external control, technology, structure, and operational process variables. Data were collected by a non-random, two-level cluster mail survey of network members (45/59 = 76.3% response rate). All networks received technical assistance from the Nebraska Office of Rural Health. Networks have formal organization, strategic plans, and official coordinators. Hospital administrators hold most leadership positions; few doctors or citizens are involved. Correlation and multiple regression analysis show partial fit between the research model and study networks. Effectiveness, measure by the gap between best possible and actual practice, increased with network connectivity (r=.36, p<.05), group methods of administrative decision-making (r=.52, p<.001) and sequential pattern of service delivery (r=.39, p<.05). Greater dependence on vertical funding corresponds to greater external control (r=.43, p<.01). The prediction that, as scope narrows, task intensity (r=.56, p<.001), duration (r=.41, p<.01), and task volume (r=.50, p<.01) increase is upheld. Centrality and network size decrease together (r=.43, p<.01) where there is little reliance on vertical sources of funds (r=.36, p<.05). The integrated interorganizational model demonstrates some efficacy for testing potential effectiveness of networks.

Community Networks↗
PubMed2004

[Optical properties of human normal small intestine tissue with theoretical model of optics about biological tissues at Ar+ laser and 532 nm laser and their linearly polarized laser irradiation in vitro].

A double-integrating-spheres system, basic principle of measuring technology of ray radiation, and optical model of biological tissues were used for the study. Optical properties of human normal small intestine tissue at 476.5, 488, 496.5, 514.5 and 532 nm laser and their linearly polarized laser irradiation were studied. The results of measurement showed that the total attenuation coefficient and scattering coefficient of the tissue at these wavelengths of laser and their linearly polarized laser irradiation increased with decreasing wavelengths. And obviously there was a distinction at 514.5 to 532 nm wavelength between lasers and their linearly polarized laser irradiation. Absorption coefficient of tissue at these wavelengths of laser and their linearly polarized laser irradiation increased with decreasing wavelengths. Absorption coefficient of tissue at 514.5 to 532 nm wavelength of laser was obviously decreasing, which was independent of these wavelengths of laser or their linearly polarized laser irradiation. Mean cosine of scattering of tissue at these wavelengths of laser and their linearly polarized laser irradiation also increased with decreasing wavelengths. But penetration depth of tissue at these wavelengths of laser and their linearly polarized laser irradiation also increased with increasing of wavelengths. Refractive index of tissue between these wavelengths of laser was within 1.38 to 1.48. Absorption coefficient, scattering coefficient, total attenuation coefficient, effective attenuation coefficients of tissue in Kubelka-Munk two-flux model at the same wavelength of laser and their linearly polarized laser irradiation showed no prominent distinction (P>0.01). Absorption coefficient, scattering coefficient, total attenuation coefficient, effective attenuation coefficients of tissue in Kubelka-Munk two-flux model at different wavelength of laser and their linearly polarized laser irradiation showed obvious distinction. Optical properties of tissue at 514.5 to 532 nm wavelength of laser exhibited obvious distinction.

Absorption↗
PubMed2006

Potential increased tumor-dose delivery with combined 131I-MIBG and 90Y-DOTATOC treatment in neuroendocrine tumors: a theoretic model.

UNLABELLED: (131)I-Metaiodobenzylguanidine (MIBG) and (90)Y-DOTA-D-Phe1-Tyr3-octreotide (DOTATOC) have been used as radiotherapeutic agents for treating neuroendocrine tumors. The tumor dose delivered by these agents is often insufficient to control or cure the disease. However, these 2 agents used together could potentially increase tumor dose without exceeding the critical organ dose because the dose-limiting tissues are different. In this paper, we investigate the conditions in which combined-agent therapy is advantageous and we quantify the expected tumor-dose gain. METHODS: A series of equations was derived that predicted the optimal combination of agents and the fractional increase in tumor dose available from combined-agent therapy with respect to either (131)I-MIBG or (90)Y-DOTATOC. The results obtained from these derivations were compared with direct dose calculations using published dosimetric organ values for (131)I-MIBG and (90)Y-DOTATOC along with critical organ-dose limits. Tumor dose was calculated as a function of the tumor-dose ratio, defined as the (90)Y-DOTATOC tumor dose per megabecquerel divided by the (131)I-MIBG tumor dose per megabecquerel. Comparisons were made between the dose delivered to tumor with single-agent therapy and the dose delivered to tumor with combined-agent therapy as a function of the tumor-dose ratio and the fraction of activity contributed by each agent. RESULTS: The dose model accurately predicted the optimal combination of agents, the range at which combined-agent therapy was advantageous, and the magnitude of the increase. For the published organ dosimetry and critical organ-dose limits, combined-agent therapy increased tumor dose when the tumor-dose ratio was greater than 0.67 and less than 5.93. The maximum combined-agent tumor-dose increase of 68% occurred for a tumor-dose ratio of 2.57, using 92% of the maximum tolerated (90)Y-DOTATOC activity supplemented with 76% of the maximum tolerated activity of (131)I-MIBG. Variations in organ dose per megabecquerel and dose-limiting values altered both the magnitude of the increase and the range at which combined-agent therapy was advantageous. CONCLUSION: Combining (131)I-MIBG and (90)Y-DOTATOC for radiotherapy of neuroendocrine tumors can significantly increase the delivered tumor dose over the dose obtained from using either agent alone. Prior knowledge of the normal-organ and tumor dosimetry of both agents is required to determine the magnitude of the increase.

3-Iodobenzylguanidine↗
PubMed1991

A theoretical model for understanding dentists' behavior in treating patients with AIDS.

This paper attempts to expand on a model from the theory of reasoned action to help us identify and better understand the reasons dentists do or do not treat dental patients with, or at risk for, AIDS. We propose in the model that the dentist's actual behavior in treating dental patients with, or at risk for, AIDS, in his or her practice is a function of both his or her intention to treat such patients and his or her nonvolitional factors relevant to the behavior. The dentist's intention to treat patients with AIDS or HIV infection, or those belonging to high risk groups, is influenced by two belief components: (1) attitudinal variables, which are the dentist's beliefs about the consequences of treating such patients and the value that these consequences have for him or her; and (2) normative variables, which indicate the dentist's perceptions of how his or her reference groups view the treatment of such patients in his or her practice and his or her motivation to comply with those views. Finally, both the two belief components and the nonvolitional factors are affected by the personal characteristics and the environmental variables.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Theoretical model of blood flow through hollow fibres considering hematocrit-dependent, non-Newtonian blood properties.

Accounting for the non-Newtonian blood viscosity by the Quemada descriptive viscosity equation, we deduced velocity profiles and volumetric capillary flows from the Navier-Stokes-equation. An arbitrary axial and/or radial hematocrit profile can be chosen. The hematocrit dependence of the intrinsic viscosities k0 (H) (characterizing, at least in part, the RBC aggregation) and k infinity (H) (describing orientation/deformation of RBC) was taken into account. Velocity profiles for pressure gradients of 4-4000 Pa/cm show a distinct flattening, if a pronounced axial migration of RBC is assumed. The higher the axial concentration, the higher the flow at the same pressure gradient. Small deviations (less than or equal to 10%) of the capillary number per dialyzer or of the radius of capillaries lead to a strong change of the pressure gradient with the same dialyzer flow. Whereas small hydraulic conductivities do not significantly change this gradient, high conductivities decrease the pressure gradient by about 10%. Impaired blood flow properties (hemoconcentration) result in a slight deviation from the linear axial pressure drop.

Blood Flow Velocity↗
PubMed1989

[Electrocardiogram simulation. A theoretical model of ischemia].

Using an electric circuit model, made of two segments formed of sections that behave electrically as subendocardial and subepicardial cells, we simulated myocardial ischemia in one of the two segments. The changes in the ST segment and in the T wave were obtained respectively by diminishing the intercellular potential from -90 mV to -60 mV and by shortening or prolonging the duration of action potentials. In order to simulate acute subendocardial, subepicardial and transmural ischemia, the potentials of the internal section, the outer section, and of both sections were diminished respectively. The ST segment appeared depressed both in the segment involved and in the undamaged one in subendocardial ischemia. In subepicardial ischemia it appeared elevated in the segment involved and was normal in the undamaged one. In transmural ischemia it was elevated in the segment with reduced potential and it was depressed in the undamaged segment. The depression of the ST segment in the undamaged part, both in subendocardial ischemia and in transmural ischemia, depends on the imbalance of the central point and therefore the whole subendocardial layer behaves electrically as if it really were ischemic. The T-wave changes in acute ischemia are in keeping with those of the ST segment.

Action Potentials↗
PubMed1989

Problems of field testing theoretical models: a case study.

The problems of field-testing models are discussed with reference to a population simulation model for the tsetse fly glossina pallidipes Austen developed by us at Nguruman in southwestern Kenya. Model predictions showed a reasonable fit to the changes in the biconical trap index of population size, but tended to overestimate some changes and underestimate others. A more rigorous test for the model is to manipulate one of the population parameters and compare model predictions with the observed population trends. This revealed that some changes in population size resulted more from fly movement than from changes in mortality rates. Fly movement must therefore be incorporated in the model for it to be a useful tool in the development of appropriate control strategies.

Algorithms↗
PubMed1988

[A theoretical model of the transition phase in human locomotion].

In this study we examine the bifurcation of the transition between walking and running. Beuter and Lalonde (1986) have conjectured that the pertinent parameters separating walking and running can be described by a cusp singularity (Thom, 1972). In this model, the unidimensional state space is characterized by support duration and the bidimensional parameter space is characterized by the subject's weight and speed. To test this model eight males walked and ran on a motor driven treadmill at an increasing or decreasing speed with or without additional loads corresponding to 0%, 7% and 14% of their body weight. Velocities corresponding to transitions between the two modes of locomotion indicate that on the average the walk-run transition occurs at higher speed than the run-walk transition illustrating an hysteresis effect. In addition, the average difference between the transitions decreases as the load increases [mean 0 = 0.235 m/s, +/- 0.09 m/s, mean 7 = 0.104 m/s, +/- 0.07 m/s and mean 14 = 0.041 m/s, +/- 0.06 m/s] corresponding to an F ratio of F = 2.72, 0.05 less than p less than 0.1. A comparison of the differences in transition velocity at 0% and 14% is statistically different (t = 2.8, p less than 0.025). These results tend to support the existence of an elementary cusp singularity separating the two locomotion modes and suggest that the mechanisms controlling these transitions can be described by a hysterisis cycle and a small number of parameters.

Adipose Tissue↗