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PubMed1999

Heterogeneous Nucleation of n-Butanol Vapor on Submicrometer Particles of SiO2 and TiO2.

Condensation of a supersaturated vapor of n-butanol on monodisperse submicrometer particles is investigated in a flow cloud chamber (FCC). The size dependence of critical supersaturation in the range of 20 to 90 nm is experimentally determined. Two types of aerosol, SiO2 and TiO2, are tested. The results show that both aerosols induce heterogeneous nucleation better than perfectly wetted particles. The experimental critical supersaturation is smaller than that predicted by the Fletcher version of Volmer theory of heterogeneous nucleation even with the line tension and surface diffusion taken into account and has a size dependence in qualitative agreement with that theoretically predicted but to a lesser degree. The discrepancy can not be fully accounted for by the effects of line tension and surface diffusion and the existing theory concerning the curvature-dependent physical properties. The law of corresponding states was extended to the heterogeneous nucleation, and a simple correlation was observed. We conclude that the macroscopic theory of heterogeneous nucleation leads to a prediction of critical supersaturation higher than that experimentally measured. Copyright 1999 Academic Press.

Journal Article↗
PubMed1993

Two-dimensional diffusion of amphiphiles in phospholipid monolayers at the air-water interface.

Steady-state and time-resolved fluorescence spectroscopy has been used to examine lateral diffusion in dipalmitoyl-L-alpha-phosphatidylcholine (DPPC) and dimyristoyl-L-alpha-phosphatidylcholine (DMPC) monolayers at the air-water interface, by studying the fluorescence quenching of a pyrene-labeled phospholipid (pyrene-DPPE) by two amphiphilic quenchers. Steady-state fluorescence measurements revealed pyrene-DPPE to be homogeneously distributed in the DMPC lipid matrix for all measured surface pressures and only in the liquid-expanded (LE) phase of the DPPC monolayer. Time-resolved fluorescence decays for pyrene-DPPE in DMPC and DPPC (LE phase) in the absence of quencher were best described by a single-exponential function, also suggesting a homogeneous distribution of pyrene-DPPE within the monolayer films. Addition of quencher to the monolayer film produced nonexponential decay behavior, which is adequately described by the continuum theory of diffusion-controlled quenching in a two-dimensional environment. Steady-state fluorescence measurements yielded lateral diffusion coefficients significantly larger than those obtained from time-resolved data. The difference in these values was ascribed to the influence of static quenching in the case of the steady-state measurements. The lateral diffusion coefficients obtained in the DMPC monolayers were found to decrease with increasing surface pressure, reflecting a decrease in monolayer fluidity with compression.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2005

Three-dimensional localization and optical imaging of objects in turbid media with independent component analysis.

A new approach for optical imaging and localization of objects in turbid media that makes use of the independent component analysis (ICA) from information theory is demonstrated. Experimental arrangement realizes a multisource illumination of a turbid medium with embedded objects and a multidetector acquisition of transmitted light on the medium boundary. The resulting spatial diversity and multiple angular observations provide robust data for three-dimensional localization and characterization of absorbing and scattering inhomogeneities embedded in a turbid medium. ICA of the perturbations in the spatial intensity distribution on the medium boundary sorts out the embedded objects, and their locations are obtained from Green's function analysis based on any appropriate light propagation model. Imaging experiments were carried out on two highly scattering samples of thickness approximately 50 times the transport mean-free path of the respective medium. One turbid medium had two embedded absorptive objects, and the other had four scattering objects. An independent component separation of the signal, in conjunction with diffusive photon migration theory, was used to locate the embedded inhomogeneities. In both cases, improved lateral and axial localizations of the objects over the result obtained by use of common photon migration reconstruction algorithms were achieved. The approach is applicable to different medium geometries, can be used with any suitable photon propagation model, and is amenable to near-real-time imaging applications.

Algorithms↗
PubMed1987

Effect of innovation characteristics on pharmacists' use of written patient medication information.

There is increasing pressure on pharmacists to provide written medication information in patients. Unfortunately, recent evidence indicates that this practice has not yet been extensively adopted. Pharmacists' reluctance can be explained partially by Diffusion of Innovations Theory which states that the characteristics of an innovation (i.e. relative advantage, compatibility with needs, experience and values, complexity and trialability) can affect its rate of adoption within a community. This theory was tested in a group of Michigan community pharmacists who recently purchased medication information sheets developed by the Michigan Pharmacists Association. Results were compared with a randomly selected sample of similar pharmacists who had not yet purchased the kit. Study findings support the theory that the adoption of an innovation (i.e. use of written information) is affected by the adopters' perception of certain innovation characteristics. The most influential factor in the adoption of the written information sheets was the extent that they were compatible with the pharmacists' business needs, professional values, and past experiences with providing written information to patients. The most important deterrent to adoption of the sheets appeared to be the perceived complexity in implementation at the practice site.

Communication↗
PubMed1992

Studies on the structure of actin gels using time correlation spectroscopy of fluorescent beads.

Fluorescence correlation spectroscopy (FCS) has been used to measure the diffusion of fluorescently labeled beads in solutions of polymerized actin or buffer. The results, obtained at actin concentrations of 1 mg/ml, show that small beads (0.09 micron in diameter) diffuse nearly as rapidly in the actin gel as in buffer, whereas the largest beads tested (0.5 micron in diameter) are immobilized. Measured autocorrelation times for motions of beads with intermediate sizes show that the diffusion is retarded (relative to buffer) and that the time behavior cannot be represented as a single diffusive process. In addition to the retarded diffusion observed over distances > 1 micron, 0.23-micron beads also show a faster motion over smaller distances. Based on the measured rate of this faster motion, we estimate that the beads may be constrained within a cage approximately 0.67 micron on a side, equal to a filament length of approximately 250 subunits. Fluorescence correlation spectroscopy measurements made in the same small spot (radius of 1.4 microns) of the gel vary over time. From the variations of both the autocorrelation functions and the mean fluorescence, we conclude that, corresponding to a spatial scale of 1.4 microns, the actin gel is a dynamic structure with slow rearrangement of the gel occurring over periods of 20-50 s at 21-22 degrees C. This rearrangement may result from local reorganization of the actin matrix. Data for the retardation of beads by the actin gel are consistent with a detailed theory of the diffusion of particles through solutions of rigid rods that have longitudinal diffusion coefficients much less than that of the particles (Ogston, A. G., B. N. Preston, and J. D. Wells. 1973. Proc. R. Soc. Lond. A. 333:297-316).

Actins↗
PubMed1979

Effect of surface potential on the intramembrane electrical field measured with carotenoid spectral shift in chromatophores from Rhodopseudomonas sphaeroides.

Changes in the surface potential, the electrical potential difference between the membrane surface and the bulk aqueous phase were measured with the carotenoid spectral shift which indicates the change of electrical field in the membrane. Chromatophores were prepared from a non-sulfur purple bacterium, Rhodopseudomonas sphaeroides, in a low-salt buffer. Surface potential was changed by addition of salt or by pH jump as predicted by the Gouy-Chapman diffuse double layer theory. When a salf was added at neutral pH, the shift of carotenoid spectrum to shorter wavelength, corresponding to an increase in electrical potential at the outside surface, was observed. The salts of divalent cations (MgSO4, MgCl-2, CaCl2) were effective at concentrations lower than those of monovalent cation salts (NACl, KCl, Na2SO4) by a factor of about 50. Among the salts of monoor divalent cation used, little ionic species-dependent difference was observed in the low-concentration range except that due to the valence of cations. The pH dependence of the salt-induced carotenoid change was explained in terms of the change in surface charge density, which was about 0 at pH 5--5.5 and had negative values at higher pH values. The dependence of the pH jump-induced absorbance change on the salt concentration was also consistent with the change in the charge density. The surface potential change by the salt addition, which was calibrated by H+ diffusion potential, was about 90 mV at the maximum. From the difference between the effective concentrations with salts of mono- and divalent cations at pH 7.8, the surface charge density of (-1.9 +/- 0.5) . 10(-3) elementary charge per A2, and the surface potential of about -100 mV in the presence of about 0.1 mM divalent cation of 5 mM monovalent cation were calculated.

Bacterial Chromatophores↗
PubMed1990

Use of tracers to measure flow within single microvessels.

Most techniques for making quantitative measurements of flow within single microvessels rely on tracers which are injected upstream of the microvessel and monitored noninvasively (e.g., optical densitometry) at selected sites along the microvessel. This study examines theoretically the measurement of average flow velocity (v) within individual microvessels from tracer flow data at monitoring sites. Starting with a fundamental convection-diffusion equation, the theory considers tracers which can distribute across both plasma and red cell phases. An integral analysis indicates that v = delta zeta/delta tau, where delta zeta is the distance between monitoring sites, and delta tau is the tracer transit or "residence" time needed to traverse that distance. The residence time which arises explicitly requires measurement of the flow-weighted average tracer concentration at each monitoring site. Because noninvasive tracer measurements provide indices of the unweighted average tracer concentration, a velocity measurement error, delta(zeta), arises, delta(zeta) is quantified in relation to the axial location of the measurement site, the velocity profile, the tracer Peclet number, and the radial distribution of tracer at the vessel inlet. delta(zeta) does not vanish when tracer enters a microvessel with a radially uniform concentration profile, but does vanish past a critical distance, Lc, from the microvessel entrance. The critical distance can be estimated using Lc/d = 0.05(vd)/D (d. vessel diameter; v, average flow velocity; D, tracer diffusivity). Accordingly, tracer data can be used to quantify flow velocity within a microvessel provided the microvessel length allows for monitoring tracer flow beyond the estimated Lc value. This study serves as a necessary precursor to analyses of plasma-phase tracers used to measure microvascular plasma flow.

Blood Flow Velocity↗
PubMedDate not supplied

Heart health promotion: predisposition, capacity and implementation in Ontario Public Health Units, 1994-96.

The Canadian Heart Health Initiative-Ontario Project (CHHIOP) investigates predisposition and capacity in Ontario public health departments to implement community-based heart health promotion activities. The research draws upon diffusion of innovations theory and recent work on ecological approaches to health promotion within which public health agencies are seen to play a central role. Mail-back surveys were completed by heart health staff in all 42 health departments in 1994 and 1996. Predisposition and capacity were measured as the importance and effectiveness ascribed to 18 organizational practices supportive of community heart health activities. Level of implementation was reported for 74 activities spanning a range of risk factors and settings. Predisposition, capacity and implementation scores increased between 1994 and 1996. The findings confirm positive correlations between predisposition and capacity and between capacity and implementation.

Attitude of Health Personnel↗
PubMedDate not supplied

Enhancing the effectiveness of HIV/AIDS prevention programs targeted to unique population groups in Thailand: lessons learned from applying concepts of diffusion of innovation and social marketing.

Diffusion of innovations theory and social marketing theory have been criticized for their limited applicability in influencing unique population groups (e.g., female commercial sex workers (CSWs) working in low-class brothels). This study investigated the applicability of these two theoretical frameworks in outreach efforts directed to unique populations at high risk for HIV/AIDS in Bangkok, Thailand. Further, this study examined Thai cultural characteristics that influence communication about HIV/AIDS prevention. The results suggest that certain concepts and strategies drawn from the two frameworks were used more or less by effective outreach programs, providing several policy-relevant lessons. Cultural constraints, such as the lack of visibility of the disease and traditional sexual practices, influenced communication about HIV/AIDS prevention.

Adolescent↗
PubMed1998

Electrostatic enhancement of diffusion-controlled protein-protein association: comparison of theory and experiment on barnase and barstar.

The electrostatic enhancement of the association rate of barnase and barstar is calculated using a transition-state theory like expression and atomic-detail modeling of the protein molecules. This expression predicts that the rate enhancement is simply the average Boltzmann factor in the region of configurational space where association occurs instantaneously in the diffusion-controlled limit. Based on experimental evidence, this "transition state" is defined by configurations in which, relative to the stereospecifically bound complex, the two proteins are shifted apart by approximately 8 A (so a layer of water can be accommodated in the interface) and the two binding surfaces are rotated away by 0 degrees to 3 degrees. The values of the average Boltzmann factor, calculated by solving the Poisson-Boltzmann equation, for the wild-type complex and 16 complexes with single mutations are found to correlate well with experimental results for the electrostatic rate enhancement. The predicted rate enhancement is found to be somewhat insensitive to the precise definition of the transition state, due to the long-range nature of electrostatic interactions. The experimental ionic strength dependence of the rate enhancement is also reasonably reproduced.

Bacterial Proteins↗
PubMed1999

Monitoring the dissemination of an educational protocol on pediatric asthma in family practice: a test of associations between dissemination variables.

Many asthma education programs aim at reducing morbidity. Now that effective programs are available, the next step is the nationwide dissemination to achieve morbidity reduction. A dissemination of a tested program has been undertaken in Dutch primary care, guided by the Diffusion of Innovation theory. It was hypothesized that greater awareness and concern and/or receptivity about asthma self-management would make it more likely that family physicians would adopt the program. Family physicians were considered more likely to adopt the program if they saw it as an improvement on their current way of providing education, as easy to use, and as having observable outcomes. It was expected that once the program had been adopted, and as it was being implemented, it would increasingly be perceived by its users as successful. Finally, more perceived success of performance was expected to be related to continued use. Both longitudinal and cross-sectional data largely confirmed the hypotheses.

Adult↗
PubMed2006

Prescribing antiepileptics for the elderly: differences between guideline recommendations and clinical practice.

The incidence of epilepsy in patients aged >60 years is higher than in any other period of life. Yet, until recently, what was known about the treatment of older patients with epilepsy has been inferred from studies in younger patients. A growing body of clinical evidence focused exclusively on the elderly suggests that, while some issues are similar for older and younger adults, older patients with epilepsy may require even more attention regarding antiepileptic drug (AED) selection than younger patients. This article reviews published guidelines and recommendations to identify explicit recommendations for use of specific AEDs in the elderly, and assesses the extent to which those recommendations have been adopted in clinical practice. We found that while one systematically derived guideline stated that lamotrigine may be a good choice for older patients because of its favourable adverse effect profile, only clinical recommendations based on expert opinion explicitly identified AEDs that are more and less appropriate for use in the elderly. Examination of published studies describing recent AED-prescribing patterns suggests that clinical recommendations have been, at best, slowly adopted. This observation is exemplified by the fact that older patients newly diagnosed with epilepsy are still prescribed phenobarbital--a drug identified as suboptimal in 1985. In order to better understand the delay in adopting clinical recommendations, we examine these findings in light of diffusion of innovations theory, a theory that has been used to understand dissemination of other new medical technologies. According to this theory, while it is too early to suggest that use of second-generation AEDs in the elderly has been delayed, the continued use of phenobarbital in older patients newly diagnosed with epilepsy represents a serious delay in adoption of recent guidelines. Delays may be related to lack of knowledge by primary care clinicians and emergency room physicians (who frequently treat older patients with epilepsy), lack of 'opinion leaders' in primary care and perhaps general neurology, clinicians' focus on seizure control as the primary endpoint in treating patients with epilepsy, and difficulties in changing long-standing prescribing patterns. Research targeting barriers to more appropriate prescribing is needed to determine appropriate strategies for changing AED prescribing practices in the elderly.

Aged↗
PubMed2003

Modeling the dynamics of the solvated SL1 domain of HIV-1 genomic RNA.

A mode-coupling solution of the Smoluchowski diffusion equation (MCD theory), designed to describe the dynamics of wobbling macromolecules in water, is applied to a macromolecular bead model including water beads in the nearest layers. The necessary statistical averages are evaluated by time averaging along a molecular dynamics (MD) trajectory where both solute and water are introduced as atomistic models. The cross peaks in (1)H nuclear Overhauser effect spectroscopy (NOESY) NMR spectra that are routinely measured to determine biological structures are here calculated for the mutated 23 nucleotides stem-loop fragment of the SL1 domain in the HIV-1(Lai) genomic RNA. The calculations are in acceptable agreement with experiments without requiring any screening of the hydrodynamic interactions. The screening of hydrodynamics was necessary in previous MCD calculations obtained by using the same full atomistic MD trajectory, but a nonsolvated frictional model.

Base Sequence↗
PubMed2005

Clinical nurse educators as agents for change: increasing research utilization.

The purpose of this study was to examine the determinants of research utilization among clinical nurse educators. The primary goal for clinical nurse educators is the facilitation of professional development of practicing nurses. Responsibilities include promoting best practice by mentoring others, acting as an information source, and assisting in the development of policies and procedures based on available research evidence. Using Rogers' (Diffusion of Innovations, 4th edn., The Free Press, New York) diffusion of innovations theory as a theoretical foundation, we conducted a secondary analysis to test a predictive model of research utilization using linear regression. Results show that educators report significantly higher research use than staff nurses and managers. Predictors of research utilization include attitude toward research, awareness of information based on research, and involvement in research activities. Localite communication predicted conceptual research use and mass media predicted symbolic use, lending support to the idea that overall, instrumental, conceptual, and symbolic research utilization are conceptually different from one another. Our findings show that the research utilization behaviors of clinical nurse educators position them to facilitate evidence-based nursing practice in organizations. We discuss the theoretical, conceptual, and nursing role implications of our findings for nursing practice, education, and research. Suggestions for future research includes studying actual use of research findings of clinical nurse educators and designing intervention studies that assesses the effectiveness of clinical nurse educators as facilitators of research utilization in organizations.

Adult↗
PubMed2003

Modeling skin permeability to hydrophilic and hydrophobic solutes based on four permeation pathways.

Barrier properties of skin originate from low permeability of stratum corneum. The objective of this paper is to compile fundamentally-based analytical expressions that can be used to predict skin permeability to hydrophilic as well as hydrophobic solutes. Solute permeation through four possible routes in stratum corneum including free-volume diffusion through lipid bilayers, lateral diffusion along lipid bilayers, diffusion through pores, and diffusion through shunts was analyzed. Contribution of free-volume diffusion through lipid bilayers was determined using Scaled Particle Theory. This theory relates solute partition and diffusion coefficients to the work required to create cavities in a lipid bilayers to allow solute incorporation and motion. Contribution of lateral lipid diffusion was determined from the literature data. Contribution of pores was estimated using hindered transport theory. This theory assumes that hydrophilic solutes permeate across the skin through imperfections in the lipid bilayers modeled as pores. Finally, contribution of shunts was determined using a simple diffusion model. The model yielded a series of equations to predict skin permeability based on solute radius and octanol-water partition coefficient. Predictions of the model compare well with the experimental data.

Hydrophobic and Hydrophilic Interactions↗
PubMed2003

The identification of factors linked to the potential acceptance of transgenic biopharmaceuticals: an exploratory study.

In this exploratory study, Rogers' diffusion of innovation theory was used to identify which factors are likely to contribute to the potential acceptance of transgenic biopharmaceuticals (TG-Bs). These products are not yet available to the general public. A scale was designed to assess three of five core attributes related to the potential adoption rate of innovations (Rogers 1995), as well as to measure potential acceptance characteristics for biotechnology products. These attributes were relative advantage, compatibility with existing values, and complexity. In addition, two other characteristics were included: knowledge (Gartrell and Gartrell 1979) and perceived risks (Bauer 1960). The survey was completed by 74 consumers (78% response rate) using convenience sampling. The research findings show that Rogers' three core attributes are supported, but that knowledge andperceived risks were excluded from the model. The model for transgenic biopharmaceuticals consists of: 1. Consumer-related benefits (positively correlated to potential adoption). 2. New types of animals (negatively correlated to potential 3. Perceived complexity (negatively correlated to potential adoption). All the scaled items developed for this study were highly significant, which indicates that they can be used successfully by other researchers working in this field. As TG-Bs are a discontinuous innovation, biotechnology companies may need to present the benefits of these products, as well as the ease of their use prior to their launch, in order to increase their potential acceptance by consumers.

Adult↗
PubMed2005

Simulations of concentrated suspensions of rigid fibers: relationship between short-time diffusivities and the long-time rotational diffusion.

Brownian dynamics simulations of the behavior of suspensions of fibers demonstrate that the scaling of the rotational diffusivity with respect to the number density (nL3) is a sensitive function of the thickness and the parameter L2D(R0)/D(T0), where D(R0) is the rotational diffusivity at infinite dilution, D(T0) is the average center-of-mass diffusivity at infinite dilution, and L is the fiber length. Existing theories for the long-time rotational diffusivities of rigid fibers in the semidilute and concentrated regimes fail to accurately account for the relationship with the dilute values of the rotational and translational diffusivities of the various physical models used to simulate the fibers. The concentration regime studied in this work ranges from a number density of nL3 approximately 0-150, which is below the transition from an isotropic to nematic state. The effect of the fiber thickness was studied by performing simulations of rods with aspect ratios (fiber length over diameter) of 25, 50, and 500, as well as performing projections for infinitely thin fibers. The excluded volume of the rods was enforced through the use of short-range potentials. For a rod with an aspect ratio of 50 with a parameter of L2D(R0)/D(T0)=9, which corresponds to a slender-body model of the individual fibers, the rotational diffusivity (D(R)) scales as D(R)/D(R0) approximately (nL3)(-1.9) in the concentration regime of 70 < or = nL3 < or = 150. Similarly with a parameter of L2D(R0)/D(T0)=4, corresponding to a rigid-dumbbell model, the rotational diffusivity scales as D(R)/D(R0) approximately (nL3)(-1.1) over the same range of concentrations. For rods with aspect ratios of 25, it is observed that a difference in the scaling is seen for L2D(R0)/D(T0) approximately < 8, with higher values of this ratio exhibiting essentially the same scaling. Additional values of the ratio L2D(R0)/D(T0) were investigated to determine the overall behavior of the suspension dynamics with respect to this parameter. These findings resolve discrepancies between simulation results for rotational diffusivities reported by previous investigators and provide new insights for the development of an accurate theory for the diffusivity of rigid rods suspended in solution.

Journal Article↗
PubMed2001

Resolution in capillary electrophoresis with nonaqueous methanol as solvent: theoretical prediction and experimental confirmation.

The resolution of the analytes was predicted from their known pKa* values and actual mobilities in nonaqueous methanolic solutions according to theory taking longitudinal diffusion as the only cause for peak dispersion. This leads to an equation of the resolution as a function of the pH*, as both selectivity and efficiency are dependent on the pH of the buffer. The experimentally obtained resolution values were in acceptable agreement with the predicted theoretical ones in most cases. This was demonstrated for substituted benzoic acids as analytes. The pKa* values needed for the calculation of the resolution were derived from the pH* dependence of the effective mobility. The pH* scale in methanol was based on conventional pKa* values of acetic acid and chloroacetic acid taken from the literature.

Benzoates↗