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PubMed1995

Intracellular transport mechanisms: a critique of diffusion theory.

It is argued that Brownian motion makes a less significant contribution to the movements of molecules and particles inside cells than is commonly believed, and that the numbers of similar molecules and particles within any near-homogeneous subcompartment of the cell internum are insufficient to justify the statistical assumptions implicit in the derivation of the diffusion equation. For these reasons, it is contended that, contrary to accepted opinion, diffusion theory cannot provide an explanation for intracellular transport at the molecular level. Although attempts have been made to adapt diffusion theory to complex media, the conclusion is that none satisfactorily overcomes the problem of applying the theory to cell biology. However, the heuristic influence of the theory on cellular biophysics and physiology is noted, and possible alternative frameworks for interpreting the valuable experimental data obtained from such studies are outlined.

Animals↗
PubMedDate not supplied

The informatics nurse specialist as change agent. Application of innovation-diffusion theory.

The informatics nurse specialist (INS) is often the primary change agent in facilitating the implementation of clinical information systems (CIS) in healthcare settings. The INS has a unique understanding of the nursing issues that can affect the change process, and thus is in a key position to facilitate positive implementation outcomes. Innovation-diffusion theory is particularly useful in its application to the change agent role of the INS. With this theoretical knowledge, the INS can design CIS training interventions according to the psychological phenomena of Rogers' Innovation-Decision Process. An understanding of the decision-making process and the distribution of different rates of innovation adoption within a given population enable the INS to anticipate and address influential factors that affect the implementation process. Thus, Innovation-Diffusion Theory may be used as a powerful cognitive tool for the INS in facilitating the diffusion process and nurses' adoption of the technology in practice.

Attitude of Health Personnel↗
PubMed1995

Theory of osteogenesis behavior based on calcium diffusion theory.

Osteogenesis is completed by the nucleation mechanism on crystal nuclei formation and growth after amorphous calcium phosphate accretion to collagen fibers. For nuclei formation, it is necessary to have preliminary ionic diffusion such as that of Ca2+ and PO4(3-) ions to this part. Therefore, promotion of ionic diffusion to this part is the first essential condition for osteogenesis. We have considered this phenomenon as the nucleation mechanism accompanied by preliminary diffusion behavior and shown the optimum mechanical condition on promoting this ionic diffusion. Furthermore, we noticed callus by callotasis as the typical example which fits this mechanical condition and investigated its histology. However, necking occurs at the site of callus sandwiched by cortical bones due to tensile stress, three axial tensile stress in radial and tangential directions, in addition to the tensile stress occurs at the netsection of the callus due to the constraint of cortical bones. Therefore, the size of pore along the collagen lamination and hole zone becomes large under this mechanical condition and ionic diffusion such as Ca2+, PO4(3-) is liable to occur at this part. By solving the partial differential equation of the stress-induced diffusion, diffusive particles are shown to concentrate at the high three axial tensile stress region. Therefore, a high concentrated region of Ca, PO4 is achieved and selective osteogenesis due to hydroxyapatite nucleation is considered to progress in this region. Histological investigation of the callus of rabbit showed that mineralization occurs at this site and supports the theory of stress-induced diffusion on osteogenesis behavior.

Animals↗
PubMed1988

Analysis of the diffusion theory of negative capacitance: the role of K+ and the unstirred layer thickness.

The diffusion theory of negative capacitance is extended to take into account potassium transport as well as proton or hydroxyl transport. It is shown that both the capacitance spectrum and the frequency at which the capacitance is zero can be used to experimentally test the theory. The effects of the fraction of potassium current, membrane conductance, NaCl concentration, and unstirred layer thickness on these two characteristics is investigated. Maximum negative capacitance can be obtained when the current flowing through the membrane is mainly carried by protons, the membrane conductance is high, the solution conductivity is low, and the unstirred layer thickness is large. The effect of a dominant hydroxyl transport in place of a proton transport is also discussed. We suggest simple experiments to test the theory on Characeaen plant cells.

Cell Membrane↗
PubMed1983

A reaction-diffusion theory of morphogenesis with inherent pattern invariance under scale variations.

In the framework of reaction-diffusion theory we deal with the problem of pattern regulation in morphogenesis. A generic model is proposed where the kinetic terms follow constraints imposed by scale invariance considerations. These constraints allow a class of kinetic schemes to be formulated so that, starting with an initially homogeneous morphogen distribution in the field, a stable gradient is established of the form: S(chi,L) = Lpf(chi/L). Here L is the length of the morphogenetic field, chi is the position variable and f(chi/L) is some monotonic function of the relative distance. With this distribution a scale invariant gradient can be constructed which leads to pattern regulation. A linear stability analysis of the model permits the definition of the parameter values enabling the system to abandon the homogeneous state spontaneously. Simulations of the evolution of the system towards its final stable state result in approximate pattern invariance for different field lengths. The accuracy of this invariance is in agreement with some recent quantitative experimental findings in both developing and regenerating systems.

Animals↗
PubMedDate not supplied

Innovation-diffusion theory and the evolution of the nurse practitioner role: how a good thing has caught on.

Nurse practitioners are one of the most unique innovations in health care delivery in recent decades. In this article, Roger's innovation-diffusion theory is applied to an analysis of the evolution of the nurse practitioner role. The four elements of the diffusion process, the innovation, communication, time, and social system, are addressed. Consequences of the innovation-diffusion process, as well as research implications, are presented.

Communication↗
PubMed2002

Determination of optical parameters of human breast tissue from spatially resolved fluorescence: a diffusion theory model.

We report the measurement of optical transport parameters of pathologically characterized malignant tissues, normal tissues, and different types of benign tumors of the human breast in the visible wavelength region. A spatially resolved steady-state diffuse fluorescence reflectance technique was used to estimate the values for the reduced-scattering coefficient (mu(s)') and the absorption coefficient (mu(a)) of human breast tissues at three wavelengths (530, 550, and 590 nm). Different breast tissues could be well differentiated from one another, and different benign tumors could also be distinguished by their measured transport parameters. A diffusion theory model was developed to describe fluorescence light energy distribution, especially its spatial variation in a turbid and multiply scattering medium such as human tissue. The validity of the model was checked with a Monte Carlo simulation and also with different tissue phantoms prepared with polystyrene microspheres as scatterers, riboflavin as fluorophores, and methylene blue as absorbers.

Breast↗
PubMed2003

[Decomposition of EMG signals based on combination of information diffusion theory and fuzzy neural network].

OBJECTIVE: To solve the problem of large samples and contradictory samples in EMG during high level muscle contraction. METHOD: By means of recording EMG during muscle contraction with linearly increasing force instead of constant force, basic MUAP templates were obtained with the combination of information diffusion theory and fuzzy neural network. Samples were compressed and contradictory samples were eliminated. RESULT: The method was tested by simulated and real EMG data and the results were satisfactory. CONCLUSION: This method is meaningful for decomposing NEMG at high level muscle contraction.

Computer Simulation↗
PubMed1994

Frequency-domain optical absorption spectroscopy of finite tissue volumes using diffusion theory.

The goal of frequency-domain optical absorption spectroscopy is the non-invasive determination of the absorption coefficient of a specific tissue volume. Since this allows the concentration of endogenous and exogenous chromophores to be calculated, there is considerable potential for clinical application. The technique relies on the measurement of the phase and modulation of light, which is diffusely reflected or transmitted by the tissue when it is illuminated by an intensity-modulated source. A model of light propagation must then be used to deduce the absorption coefficient. For simplicity, it is usual to assume the tissue is either infinite in extent (for transmission measurements) or semi-infinite (for reflectance measurements). The goal of this paper is to examine the errors introduced by these assumptions when measurements are actually performed on finite volumes. Diffusion-theory calculations and experimental measurements were performed for slabs, cylinders and spheres with optical properties characteristic of soft tissues in the near infrared. The error in absorption coefficient is presented as a function of object size as a guideline to when the simple models may be used. For transmission measurements, the error is almost independent of the true absorption coefficient, which allows absolute changes in absorption to be measured accurately. The implications of these errors in absorption coefficient for two clinical problems--quantitation of an exogenous photosensitizer and measurement of haemoglobin oxygenation--are presented and discussed.

Algorithms↗
PubMed2004

Improving the state of health programming by using diffusion theory.

Year by year, the gaps between what is known about behavior change and what is actually practiced in social programs grow larger, especially for community-based programs intended to help minority populations, the poor, and those living in inner-city and rural areas. Internationally, such gaps between the state of knowledge and the state of practice lead to disparities in health, education, and development among societal groups, demographic sub-populations, communities, and countries. Data about disparities are used as evidence of inequality. Here, I discuss uses of certain diffusion of innovation theory-based concepts to systematically redress problems of inequality and disparity by reducing the differences between evidence and practice in social programs that are implemented by intermediaries (practitioners) and communicated by them to needy populations. The emphasis here is on the integrated application of knowledge about innovation attributes, opinion leadership, and clustering from diffusion theory to achieve the objective of more extensive and more rapid diffusion of especially effective programs. A set of implementation steps are offered for researchers, funders of international health programs, and the intermediaries who implement health programs.

Communication↗
PubMed1984

Application of diffusion theory to the relationship between partition coefficient and biological response.

A diffusion model for transport through multilaminates is studied as a possible way to predict the optimal biological response of a set of congeners with respect to the oil-water partition coefficient, P. The model predicts the bilinear form typical of biological response data and, unlike the earlier kinetic model, also relates the results to physical processes, predicts the structure with the optimal response in terms of diffusion constants, and shows such an optimum prior to steady state for an infinite dose. Diffusion through an oil-water multilaminate causes extraordinary separation of permeating species based on partition coefficient and diffusion constant for times shorter than the lag time.

Diffusion↗
PubMed2001

Diffusion theory and drug use.

This paper examines the applicability of the diffusion model to drug use. A variety of studies that employ the diffusion model to examine drug-related behaviour, including the use of alcohol, tobacco and illicit drugs, are discussed. Studies include those that focus on "natural" or spontaneous diffusion and those in which diffusion of a drug or a drug-related intervention is planned. Most studies examined support the application of the diffusion model in the study of drug use. The model is particularly valuable when new substances are introduced to a population or subgroup. The addition of economic and other forms of availability as a determinant of adoption would increase the power of the model. Recommended directions for research are outlined. The diffusion model has been used successfully in the study of drug use for several decades. More rigorous designs would strengthen this type of research and provide direction for policymakers and those involved in public health and education.

Diffusion of Innovation↗
PubMed2001

A diffusion theory model of spatially resolved fluorescence from depth-dependent fluorophore concentrations.

A photon diffusion model has been developed to calculate the steady-state spatially resolved fluorescence from pencil beam excitation in layered tissue. The model allows the calculation of both the excitation reflectance and the fluorescence escape for an arbitrary continuous depth distribution of tissue optical properties and fluorophore concentration. The validity of this model was verified by comparison with Monte Carlo simulations and experimental measurements using phantoms with tissue-like optical properties. The potential usefulness of the spatially resolved fluorescence was explored using the model and simulations of realistic drug distributions. It was shown that using this technique it may be possible to quantify the diffusion of a topically administered drug into the skin, or the photobleaching of a sensitizer during photodynamic therapy.

Algorithms↗