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PubMed1978

[Microbial metabolic activity and transmembrane transport phenomena by potentiometric analysis of lipoic acid oxidation-reduction, in a minimal culture medium].

A method of measuring and studying metabolic bacterial activity is proposed, by following the kinetic evolution of the ratio of the oxidized and reduced forms of an electron transporter as a consequence of decreasing oxidizing power--due to oxygen consumption in the culture,--and increasing. Reduction power of bacterial activity. Namely, with minimum composition using salts and glucose the oxido-reduction of lipoic acid is well indicated by a gold electrode without any major bio-or electrochemical interference. A kinetic diffusion reaction theory takes into account the passive or active transmembrane transport of lipoic acid in good agreement with the experimentally observed shapes of the electrical signal. The various types of antibiotic activities are well reflected by the modifications of the signal.

Bacteria↗
PubMed2004

Beyond the diffusing-wave spectroscopy model for the temporal fluctuations of scattered light.

We extend the theory of diffusing-wave spectroscopy using a random-walk approach and a numerical solution of the radiative transfer equation. The theory is not restricted to the diffusive regime and allows one to describe the crossover between the single-scattering and the diffusive regimes, which has been observed experimentally. It also predicts a lower bound of the scattered-field correlation time at long paths. This extended theory should have broad experimental applications in the field of imaging through biological tissues.

Journal Article↗
PubMed2001

Phase synchronization of chaotic systems with small phase diffusion.

The geometric theory of phase locking between periodic oscillators is extended to phase coherent chaotic systems. This approach explains the qualitative features of phase locked chaotic systems and provides an analytical tool for a quantitative description of the phase locked states. Moreover, this geometric viewpoint allows us to identify obstructions to phase locking even in systems with negligible phase diffusion, and to provide sufficient conditions for phase locking to occur. We apply these techniques to the Rössler system and a phase coherent electronic circuit and find that numerical results and experiments agree well with theoretical predictions.

Journal Article↗
PubMed1988

Phloem mobility of xenobiotics: I. Mathematical model unifying the weak Acid and intermediate permeability theories.

A passive diffusion model has been developed which simultaneously accounts for the dependence of phloem mobility on permeability and acid dissociation. The model is consistent with the observation that the addition of an acid moiety to an otherwise phloem immobile compound may enhance that compound's ability to move in the phloem. However, acid trapping in the basic phloem is not the only enhancement factor. Acid functionalization also lowers the effective permeability usually towards its optimum value. The unified theory predicts that for a given acid dissociation constant there is an optimum permeability and conversely for a given permeability there is an optimum dissociation constant.

Journal Article↗
PubMedDate not supplied

Diffusion of an innovation: adoption of CT scanners.

"Diffusion of Innovation" is a marketing theory that predicts the pattern of adoption of new products. The characteristics of an innovation and the "diffusion stages" of a new product as it moves toward widespread adoption are described. Then, the predictions of diffusion theory are compared to the pattern of adoption of CT.

Communication↗
PubMed1983

Microscopic diffusion-reaction coupling in steady-state enzyme kinetics.

The theory of diffusion-controlled processes is applied to describe the steady state of a reversible enzymatic reaction with special emphasis on the effects of enzyme saturation. A standard macroscopic steady-state treatment requires only that the average diffusional influx of substrate equals the net reaction flux as well as the average diffusional efflux of product. In contrast, the microscopic diffusion-reaction coupling used here takes properly into account the conditional concentration distributions of substrate and product: Only when the enzyme is unoccupied will there be a diffusional association flux; when the enzyme is occupied, the concentration distributions will relax towards their homogeneous bulk values. In this way the relaxation effects of the non-steady state will be constantly reoccurring as the enzyme shifts between unoccupied and occupied states. Thus, one is forced to describe the steady state as the weighted sum of properly time-averaged non-stationary conditional distributions. The consequences of the theory for an appropriate assessment of the parameters obtained in Lineweaver-Burk plots are discussed. In general, our results serve to justify the simpler macroscopic coupling scheme. However, considerable deviations between the standard treatment and our analysis can occur for fast enzymes with an essentially irreversible product release.

Diffusion↗
PubMed2002

Generalized theory of steady-state voltammetry without a supporting electrolyte. Effect of product and substrate diffusion coefficient diversity.

A generalized theory of the steady-state voltammetric response of a microelectrode in the absence of supporting electrolyte and for any values of diffusion coefficients of the substrate and the product of an electrode process is presented. The treatment applies to any reasonable combination of the charge numbers of the substrate, its counterion, and the product. A way to incorporate the activation polarization into the model is also demonstrated. It has been shown that the height, position, and shape of the migrational voltammogram are affected by the ratio of the product to substrate diffusivity (theta). In particular, for the electrode processes with sign retention, unequal diffusivities of electroactive species influence both characteristic points of the voltammogram (the limiting current and the half-wave potential). For charge neutralization processes (uncharged product), the changes in theta parameter are accompanied only by a shift in the half-wave potential. The most dramatic changes in the I-E relation can be observed for the charge reversal processes. In this case, a consecutive increase in theta results in the transition of the voltammogram shape from rapid exponential growth (theta < 1), through ramp shape (theta = 1), to common wave shape (theta > 1). On the basis of the expressions derived for the limiting current (exact and linearized), a possibility of the determination of the diffusion coefficient of the electrode reaction product is demonstrated. In addition, the ranges of theta where the assumption of equal diffusivities of the substrate and the product is obeyed within an insignificant error have been determined quantitatively. The theory has been experimentally verified using voltammetric oxidation of hexacyanoferrate(II).

Journal Article↗
PubMed1986

Fluid shear as a possible mechanism for platelet diffusivity in flowing blood.

Platelet transport theory is based on convection diffusion and describes adequately the influence of wall shear rate, platelet concentration and axial (down stream) position. Until now, the influence of the predominant factors affecting platelet adherence, the hematocrit and the red cell size, was not included in this theory. Their role remained hidden in the platelet diffusivity (Dw), which was assumed to be related to the shear rate (gamma) expressed in s-1 by a power law function Dw = m gamma n, in which m and n were thought to be constants. We have determined platelet diffusivity directly from platelet adherence to subendothelium as a function of axial distance in an in vitro perfusion system. Our results indicate that m is a constant with a value of (1.05 +/- 0.05) 10(-9) cm2 s-1 and that n is a function of the hematocrit (h) which is best approximated by a quadratic equation n = 0.297 + 1.29 h - 0.90 h2. The effect of red cell size was introduced by correcting the hematocrit containing factors in this quadratic equation for the square of the red cell diameter. This correction was made on the basis of theoretical considerations. The theoretically derived platelet adherence correlated closely with the previous experimental data regarding the effect of red cell size in which we found that the hemodynamic effect of red cells on platelet adherence decreases with decreasing red cell diameter.

Biomechanical Phenomena↗
PubMed1992

The uses of theory in health advocacy: policies and programs.

This paper illustrates the utility of theory for health educators who advocate for health promotion policies and programs. It describes how diffusion of innovation and other social science theories were employed by a statewide coalition called the Health Promotion and Education Council of Virginia in its effort to reduce premature and preventable death and disability in the state. To this end the Council sought legislative action to accelerate the diffusion of health promotion throughout the state. Discussing elements of diffusion theory such as working through opinion leaders, creating information-exchange relationships, and tailoring the attributes of the innovation to achieve its objectives, the paper reviews the process through which the Council became an effective advocate, and the strategies it devised to communicate the innovation of health promotion to legislators. The legislation that was generated by the work of the legislative study committee and future uses of theory are also discussed.

Diffusion of Innovation↗
PubMed2004

Pair contact process with diffusion: failure of master equation field theory.

We demonstrate that the "microscopic" field theory representation, directly derived from the corresponding master equation, fails to adequately capture the continuous nonequilibrium phase transition of the pair contact process with diffusion (PCPD). The ensuing renormalization group (RG) flow equations do not allow for a stable fixed point in the parameter region that is accessible by the physical initial conditions. There exists a stable RG fixed point outside this regime, but the resulting scaling exponents, in conjunction with the predicted particle anticorrelations at the critical point, would be in contradiction with the positivity of the equal-time mean-square particle number fluctuations. We conclude that a more coarse-grained effective field theory approach is required to elucidate the critical properties of the PCPD.

Journal Article↗
PubMed1986

Theory of the rotational contribution to facilitated diffusion.

Gros and others have recently shown experimentally that the facilitated diffusion of protons carried by a form of haemoglobin is enhanced by rotational diffusion of the carrier, whereas facilitated diffusion of oxygen by the same carrier is not. In this paper the theory of facilitated transport by rotating carriers is developed from first principles. The theory confirms Gros's findings that (i) the rotational contribution appears only when the angle of rotational diffusion over the average time the proton remains bound is small and (ii) under these conditions rotation enhances the normal translational contribution by a factor 1/2 at the lowest carrier concentrations. The theory also shows that there must be a rotational boundary layer.

Binding Sites↗
PubMedDate not supplied

Diffusion of an innovation: adoption of MRI.

"Diffusion of Innovation" is a marketing theory that predicts the pattern of adoption of new products, with specific characteristics of the product determining the rate of adoption. This article attempts to determine whether MRI fits the predicted pattern. A computer Medline search to assess the number of articles printed on MRI shows that MRI is being adopted more slowly than CT, but like CT, MRI is following the pattern predicted by the Diffusion Theory.

Communication↗
PubMed1982

Intergovernmental relations in physician education and health planning: state adoption decisions and the impact of federal programs.

This study seeks to explain states' adoptions of programs in health planning and in physician education. It also seeks to further understanding of the impact of federal health planning and education programs on the states. Several theories and models are employed in analyzing the actions of state decision-makers. These include incremental theory, models of the diffusion of innovations, economic resources theory, and a theory of competitive partisanship. The data utilized in this research were principally derived from intensive interviews with "key" state actors and from historical, documentary materials. Only minimal federal impact appears on states' goals in physician education and health planning. Rather, there is evidence of considerable innovativeness among the states prior to Federal program initiatives. A problem-generated search for solutions seems to be a major source of this innovation. Finally, federal program implementation requirements appear to be a major source of federal--state conflict and opposition.

Diffusion of Innovation↗
PubMed1981

Cell, membrane, and diffusion-an essay in bio-theory.

The Cell Theory is criticised and an alternative version proposed. It is suggested that the notion of a sponge-like, spongioform, cell (7) might be preferable to the classical notion of a membrane-bound cell. This would allow consideration of the probability that cells behave like sponges and procure their material and metabolite requirements entrained in a convected flow of water past their internal membrane systems. I shall consider some deductive consequences of this alternative in a companion article (1). The Cell Theory, however, formulated on the basis of a membrane-bound cell, specifically excludes the possibility of convective flow in and out of cells. For that reason, the metaphysical and historical foundations of Cell Theory are re-examined, the cases for the physicochemical viewpoint as against the teleological viewpoint further discussed, and the relationship of them to the notions of 'cell', 'membrane', and 'diffusion' looked into all over again. It is concluded that there is more evidence, from light and electron microscopy, for a spongioform cell than for a balloon cell.

Cell Biology↗
PubMed2003

Dependence of plastoquinol diffusion on the shape, size, and density of integral thylakoid proteins.

The diffusion of plastoquinol in the chloroplast thylakoid membrane is modelled using Monte Carlo techniques. The integral proteins are seen as obstacles to diffusion, and features of percolation theory emerge. Thus, the diffusion coefficient diminishes with increasing distance and there is a critical threshold of protein concentration, above which the long-range diffusion coefficient is zero. The area occupied by proteins in vivo is assessed and appears to be around this threshold, as determined from calculations assuming randomly distributed noninteracting proteins. Slight changes in the protein arrangement lead to pronounced changes in diffusion behaviour under such conditions. Mobility of the proteins increases the protein occupancy threshold, while boundary lipids impermeable to PQ diffusion decrease it. Further, the obstruction of plastoquinone/plastoquinol binding sites in a random arrangement is evaluated.

Binding Sites↗
PubMed1996

Hindered diffusion in agarose gels: test of effective medium model.

The diffusivities of uncharged macromolecules in gels (D) are typically lower than in free solution (D infinity), because of a combination of hydrodynamic and steric factors. To examine these factors, we measured D and D infinity for dilute solutions of several fluorescein-labeled macromolecules, using an image-based fluorescence recovery after photobleaching technique. Test macromolecules with Stokes-Einstein radii (rs) of 2.1-6.2 nm, including three globular proteins (bovine serum albumin, ovalbumin, lactalbumin) and four narrow fractions of Ficoll, were studied in agarose gels with agarose volume fractions (phi) of 0.038-0.073. The gels were characterized by measuring the hydraulic permeability of supported agarose membranes, allowing calculation of the Darcy permeability (kappa) for each gel sample. It was found that kappa, which is a measure of the intrinsic hydraulic conductance of the gel, decreased by an order of magnitude as phi was increased over the range indicated. The diffusivity ratio D/D infinity, which varied from 0.20 to 0.63, decreased with increases in rs or phi. Thus as expected, diffusional hindrances were the most severe for large macromolecules and/or relatively concentrated gels. According to a recently proposed theory for hindered diffusion through fibrous media, the diffusivity ratio is given by the product of a hydrodynamic factor (F) and a steric factor (S). The functional form is D/D infinity = F(rs/k1/2) S(f), where f = [(rs+rf)/rf]2 phi and rf is the fiber radius. Values of D/D infinity calculated from this effective medium theory, without use of adjustable parameters, were in much better agreement with the measured values than were predictions based on other approaches. The strengths and limitations of the effective medium theory for predicting diffusivities in gels are discussed.

Animals↗
PubMed1998

Marketing innovations to nurses, Part 2: Marketing's role in the adoption of innovations.

This article is the second in a two-part series concerning marketing techniques to enhance nurses' adoption of innovations. Introducing and getting staff to implement new policies and procedures constitute an important part of the WOC nurse's role. The application of Rogers' Diffusion of innovation Theory provides WOC nurses with a framework to introduce innovations into the clinical setting and to change subsequent practice patterns. This article introduces the WOC nurse to marketing principles needed to successfully introduce a practice innovation to nurse colleagues; it also builds upon Rogers' Diffusion of Innovation Theory and presents a sample marketing plan as a template for marketing innovations in the clinical setting.

Critical Care↗