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PubMed2003

Differential adoption of pharmacotherapy recommendations for type 2 diabetes by generalists and specialists.

Newer, multimedication (novel) regimens provide better glycemic control for many type 2 diabetics when sulfonylurea monotherapy (traditional) becomes ineffective. Because better glycemic control is associated with decreased likelihood of complications and lower utilization and cost of care, the authors examined change in prescribing patterns for veterans with type 2 diabetes between FY 97 and 99. They classified medication regimens as traditional and novel based on the combination of diabetes medications patients received at the end of each year. Multivariate logistic regression analyses controlling for disease severity indicated that patients were more likely to receive novel regimens over time, but those seen only in primary care were less likely to receive novel regimens than those previously seen by a specialist. Geographic differences and differences in how recommendations were implemented by generalists and specialists suggest that diffusion of innovations theory may help explain variations in practice and guide interventions designed to translate research into practice.

Aged↗
PubMed2004

Formulation of photon diffusion from spherical bioluminescent sources in an infinite homogeneous medium.

BACKGROUND: The bioluminescent enzyme firefly luciferase (Luc) or variants of green fluorescent protein (GFP) in transformed cells can be effectively used to reveal molecular and cellular features of neoplasia in vivo. Tumor cell growth and regression in response to various therapies can be evaluated by using bioluminescent imaging. In bioluminescent imaging, light propagates in highly scattering tissue, and the diffusion approximation is sufficiently accurate to predict the imaging signal around the biological tissue. The numerical solutions to the diffusion equation take large amounts of computational time, and the studies for its analytic solutions have attracted more attention in biomedical engineering applications. METHODS: Biological tissue is a turbid medium that both scatters and absorbs photons. An accurate model for the propagation of photons through tissue can be adopted from transport theory, and its diffusion approximation is applied to predict the imaging signal around the biological tissue. The solution to the diffusion equation is formulated by the convolution between its Green's function and source term. The formulation of photon diffusion from spherical bioluminescent sources in an infinite homogeneous medium can be obtained to accelerate the forward simulation of bioluminescent phenomena. RESULTS: The closed form solutions have been derived for the time-dependent diffusion equation and the steady-state diffusion equation with solid and hollow spherical sources in a homogeneous medium, respectively. Meanwhile, the relationship between solutions with a solid sphere source and ones with a surface sphere source is obtained. CONCLUSION: We have formulated solutions for the diffusion equation with solid and hollow spherical sources in an infinite homogeneous medium. These solutions have been verified by Monte Carlo simulation for use in biomedical optical imaging studies. The closed form solution is highly accurate and more computationally efficient in biomedical engineering applications. By using our analytic solutions for spherical sources, we can better predict bioluminescent signals and better understand both the potential for, and the limitations of, bioluminescent tomography in an idealized case. The formulas are particularly valuable for furthering the development of bioluminescent tomography.

Computer Simulation↗
PubMed2006

Barriers and facilitators to replicating an evidence-based palliative care model.

Recognition of the difficulties involved in replicating evidence- based interventions is well documented in the literature within the medical field. Promising research findings are often not translated into practice, and if they are, there is a significant time gap between study conclusion and practice adoption. The purpose of this article is to describe the barriers and facilitators encountered by two managed care organizations while replicating an evidence-based end of life in-home palliative care model. Using Diffusion of Innovation Theory as a theoretical framework, results from focus groups and interviews with the project's clinical, administrative and research teams are presented and recommendations made for improving translational efforts. The process of replicating the end of life in-home palliative care model clearly illustrated the key elements required for successfully diffusing innovation. These key elements include marketing and communication, leadership, organizational support and training and mentorship. This qualitative process study provides clear, real world perspectives of the myriad of challenges encountered in replicating an evidence-based project.

Diffusion of Innovation↗
PubMed1981

Competitive membrane adsorption of Na+, K+, and Ca2+ in smooth muscle cells.

A theory for Na+, K+ and Ca2+ competitive adsorption to a charged membrane is used to explain a number of experimental observations in smooth muscle. Adsorption is described by Langmuir isotherms for mono- and divalent cations which in turn are coupled in a self-consistent way to the bulk solution through the diffuse double layer theory and the Boltzman equations. We found that the dissociation constants for binding of Na+, K+ and Ca2+ in guinea pig taenia coli are ca. 0.009, 1.0, and 4 X 10(-8) M, respectively. Furthermore, the effect of a Ca2+ pump that maintains free surface Ca2+ concentration constant is investigated. A decrease in intracellular Na+ content results in an increased Ca2+ uptake; part of this uptake is due to an increase in surface-bound Ca2+ in an intracellular compartment which is in contact with the myofilaments. Variations in the amount of charge available to bind Ca2+ and the surface charge density are studied and their effect interpreted in terms of different pharmacological agents.

Adsorption↗
PubMed1981

Effect of nonspecific forces and finite receptor number on rate constants of ligand--cell bound-receptor interactions.

We develop a theory of ligand diffusion in the presence of a central potential toward or away from receptor patches that are uniformly distributed over a spherical cell. The current onto the receptors is reduced to less than that onto the sphere by a factor that is a nonlinear function of the number of free receptors, their size, and their potential energy. Similarly, under conditions defined by the theory, the dissociation rate from a receptor is reduced by the probability of rebinding to some other receptor on the same cell. This complicates the kinetic analysis, leading to the possibility of an occupancy-dependent dissociation rate, but has no effect on the interpretation of thermodynamic data.

Cell Membrane↗
PubMed2006

Diffusion of innovations: anatomical informatics and iPods.

Over the course of many centuries, evolving scientific methods and technologies have advanced the study of anatomy. More recently, such dissemination of innovations has been formally studied in multidisciplinary psychosocial contexts, yielding useful knowledge about underlying principles and processes. We review these precepts and show how diffusion of innovations theory and principles apply to the development and dissemination of anatomical information methods and resources. We consider the factors affecting the late-20th-century dissemination of personal computers and World Wide Web hypermedia into widespread use in anatomical research and instruction. We report on the results of a small experiment in applied diffusion, the development and Internet-based distribution of learning resources for a popular, widely distributed personal media player. With these wearable microcomputer devices already in use by a variety of students, new opportunities exist for widespread dissemination of anatomical information. The continuing evolution of wearable computing devices underscores the need for maintaining anatomical information transportability via standardized data formats.

Anatomy↗
PubMed2000

Mechanism and characteristics of protein release from lactitol-based cross-linked hydrogel.

Lactitol-based cross-linked hydrogel was synthesized, and model proteins (alpha-chymotrypsin, beta-lactoglobulin, bovine serum albumin (BSA), and gamma-globulin) were incorporated into the cross-linked hydrogel. The larger-molecular-weight proteins have lower diffusivity (D(e)) in the hydrogel. Increasing temperature accelerated the diffusion rate of proteins; however, the diffusion did not follow the Arrhenius equation at temperatures above 37 degrees C. The swelling ratio of the hydrogel was slightly decreased after heating for 2 h at 37 and 45 degrees C, and significantly reduced after 1 h at 60 degrees C. Therefore, diffusion of beta-lactoglobulin and BSA may be decreased by hydrogel shrinking at temperature over 37 degrees C. The model proteins have high affinities to buffer solution compared to the hydrogel network structure, resulting in high partition coefficients (K > 1) which do not affect the calculation of D(e) values. Incorporated protein release follows the theory of hindered diffusion.

Animals↗
PubMed2005

Self-consistent generalized Langevin equation for colloidal mixtures.

A self-consistent theory of collective and tracer diffusion in colloidal mixtures is presented. This theory is based on exact results for the partial intermediate scattering functions derived within the framework of the generalized Langevin equation formalism, plus a number of conceptually simple and sensible approximations. The first of these consists of a Vineyard-like approximation between collective and tracer diffusion, which writes the collective dynamics in terms of the memory function related to tracer diffusion. The second consists of interpolating this only unknown memory function between its two exact limits at small and large wave vectors; for this, a phenomenologically determined, but not arbitrary, interpolating function is introduced: a Lorentzian with its inflection point located at the first minimum of the partial static structure factor. The small wave-vector exact limit involves a time-dependent friction function, for which we take a general approximate result, previously derived within the generalized Langevin equation formalism. This general result expresses the time-dependent friction function in terms of the partial intermediate scattering functions, thus closing the system of equations into a fully self-consistent scheme. This extends to mixtures a recently proposed self-consistent theory developed for monodisperse suspensions [Yeomans-Reyna and Medina-Noyola, Phys. Rev. E 64, 066114 (2001)]. As an illustration of its quantitative accuracy, its application to a simple model of a binary dispersion in the absence of hydrodynamic interactions is reported.

Journal Article↗
PubMed2006

Nickel and lead sequestration in manganese oxide-coated montmorillonite.

Amorphous hydrous manganese oxide (HMO) is an important mineral in soils and sediments influencing the mobility and bioavailability of metal contaminants. In this study, nickel and lead sorption to discrete HMO and HMO-coated montmorillonite was investigated mechanistically. The effect of pH and concentration revealed that when normalized to the mass of oxide present, the HMO-coated montmorillonite behaved similarly to the discrete Mn oxide, where both ions sorbed onto HMO-coated montmorillonite as inner-sphere complexes. Ni coordinated to the vacancy sites in the Mn oxide structure, while Pb formed bidentate corner-sharing complexes. These coordination environments were observed not only as a function of loading, pH, and ionic strength, but also in long-term studies where sorption increased by as much as 100% (from 6x10(-4) to 1.2x10(-3) mol Ni/g HMO-coated montmorillonite). In this slower sorption process, intraparticle diffusion, the internal surface sites along microporous walls appear to be no different than external ones. Best fit diffusivities ranged from 10(-12) to 10(-13) cm2/s for Ni and 10(-17) to 10(-20) cm2/s for Pb. The significant difference in the diffusivities for the two ions is consistent with site activation theory, where theoretical surface diffusivities were predicted and given their error were in agreement with experimental results. Mn oxides sequester heavy metals in the environment.

Adsorption↗
PubMed2005

Implementation of an innovative health service a "real-world" diffusion study.

BACKGROUND: Although reporting on the healthcare-setting level of continuance or discontinuance of an intervention once a trial is completed has been recommended, such "real-world" diffusion studies are rare. The present example was made possible by funding to explore opportunities for post-trial implementation of an innovative health counseling intervention for cardiovascular prevention in The Netherlands. METHODS: Between 2001 and 2004, in a longitudinal case study, we compared two healthcare settings: a cardiology outpatient clinic and general practices. Rogers' diffusion of innovations theory served as the theoretical background. Information was extracted from minutes of meetings and informal conversations with health counselors, and checked by the project manager. Additional data were collected from physicians with a short questionnaire. RESULTS: Implementation of the health counseling intervention was successful in the cardiology outpatient clinic, but was unsuccessful in the general practices. Success was related to a centralized diffusion system, stronger "change agent" efforts, avoidance of post-trial interruption of service delivery, easily achievable "reinventions," and positive physician perceptions of the service (i.e., not complex and compatible with current practice routines). Support came from changes in the organization of care that created opportunities for, instead of competition with, the innovative service. However, coincidental events may also have played a part. CONCLUSIONS: Our findings confirm the importance of most theoretically predicted individual and organizational diffusion variables. This implies that the implementation of innovative healthcare services requires attention at both levels.

Ambulatory Care↗
PubMed2003

Self-consistent theory of collective Brownian dynamics: theory versus simulation.

A recently developed theory of collective diffusion in colloidal suspensions is tested regarding the quantitative accuracy of its description of the dynamics of monodisperse model colloidal systems without hydrodynamic interactions. The idea is to exhibit the isolated effects of the direct interactions, which constitute the main microscopic relaxation mechanism, in the absence of other effects, such as hydrodynamic interactions. Here we compare the numerical solution of the fully self-consistent theory with the results of Brownian dynamics simulation of the van Hove function G(r,t) and/or the intermediate scattering function F(k,t) of four simple model systems. Two of them are representative of short-ranged soft-core repulsive interactions [(sigma/r)(mu), with mu>>1], in two and in three dimensions. The other two involve long-ranged repulsive forces in two (dipolar, r(-3) potential) and in three (screened Coulomb, or repulsive Yukawa interactions) dimensions. We find that the theory, without any sort of adjustable parameters or rescaling prescriptions, provides an excellent approximate description of the collective dynamics of these model systems, particularly in the short- and intermediate-time regimes. We also compare our results with those of the single exponential approximation and with the competing mode-mode coupling theory.

Journal Article↗
PubMedDate not supplied

Opening the black box: measuring hospital information technology capability.

Recently, health care investment in information technology (IT) has experienced a significant increase. Paralleling this increase has been an increase in IT capabilities. Despite the interest in and promises of IT in the health care setting, there is a paucity of empirical research that has attempted to define an organizational measure of IT capability. The dearth of research has contributed to the traditional belief that IT is perceived as a "black box," whereby organizational resources enter the box as "inputs" and are somehow transformed into positive outcomes for an organization. However, for positive outcomes to be realized, these outcomes must be measurable. This research uses a stakeholder perspective to develop a theoretically specified measure of IT capability. A latent construct, IT munificence, is proposed using tenets from diffusion of innovation theory and strategic contingency theory. The construct is tested using a sample of 1,545 acute care hospitals located in the United States. IT munificence fits the study data well, supporting the hypothesis that IT munificence represents a strategy of hospital IT capability.

Diffusion of Innovation↗
PubMed2006

Modeling growth from the vapor and thermal annealing on micro- and nanopatterned substrates.

We propose a -dimensional mesoscopic model to describe the most relevant physical processes that take place while depositing and/or annealing micro- and nanopatterned solid substrates. The model assumes that a collimated incident beam impinges over the growing substrate; scattering effects in the vapor and reemission processes are introduced in a phenomenological way as an isotropic flow. Surface diffusion is included as the main relaxation process at the micro- or nanoscale. The stochastic model is built following population dynamics considerations; both stochastic simulations and the deterministic limit are analyzed. Numerical aspects regarding its implementation are also discussed. We study the shape-preserving growth mode, the coupling between shadowing effects and random fluctuations, and the spatial structure of noises using numerical simulations. We report important deviations from linear theories of surface diffusion when the interfaces are not compatible with the small slope approximation, including spontaneous formation of overhangs and nonexponential decay of pattern amplitudes. We discuss the dependence of stationary states with respect to the boundary conditions imposed on the system.

Journal Article↗
PubMed1999

Community-based promotion of breast screening using small group education.

Small Group Education (SGE) to promote breast cancer screening was implemented in a community-wide program. Based on diffusion of innovations theory, SGE initially was directed toward women at higher occupation and education levels and then progressively shifted toward more vulnerable populations of women at risk of not getting screening. During the four-year intervention, 116 volunteers led SGE presentations, with 8,184 women participating in 740 groups at work sites, organizations, residences, and churches. High participation in SGE and positive participant responses suggest that delivery of SGE using a social diffusion model was an effective method for reaching women throughout the community.

Adult↗
PubMed1994

Characterization of the calcium-binding site that regulates association of protein kinase C with phospholipid bilayers.

Association of calcium-dependent isotypes of protein kinase C (PKC) with a phospholipid bilayer is regulated by a single Ca(2+)-binding site. The dependence of PKC association with phosphatidylserine-containing membranes on the concentration of Ca2+ is linear in the submicro- to submillimolar range. The Ca(2+)-regulated association of PKC with the membrane is sensitive to the factors that alter the diffuse double-layer potential produced by anionic lipids such as phosphatidylserine (PS). This indicates that the Ca(2+)-binding site on the membrane-bound enzyme senses a higher concentration of Ca2+ than is present in bulk solution. This is a consequence of the accumulation of Ca2+ in the layer adjacent to the plane of the membrane by the double-layer potential. Calculations based on the Gouy-Chapman-Stern theory of the diffuse double layer yielded a unique value of the Ca2+ dissociation constant for the Ca(2+)-PKC-bilayer complex equal to approximately 700 nM. The soluble form of the enzyme has a 3.5 order of magnitude lower affinity for Ca2+. The free energy of interaction between the Ca(2+)- and PS-binding sites is large (approximately 5 kcal/mol). In contrast, the interaction between the diacylglycerol-binding site and either the Ca(2+)- or PS-binding site appears to be weak.

Amino Acid Sequence↗
PubMed1983

Interaction between calcium ions and surface charge as it relates to calcium currents.

Calcium ions affect the gating of Ca currents. Surface charge is involved but to what extent is unknown. We have examined this, using isolated nerve cell bodies of Helix aspersa and the combined microelectrode-suction pipette method for voltage-clamp and internal perfusion. We found that Ba and Sr currents produced by substitution of these ions for extracellular Ca ions are activated at less positive potentials than Ca currents. Mg ions do not permeate the Ca channel and changes in [Mg]o produce shifts in the activation-potential curves that are comparable to the effects of changes in [Ba]o or [Sr]o. Inactivation of Ba currents also occurs at less positive potentials. Perfusion intracellularly with EGTA reduced inactivation of Ca currents as a function of potential, but did not shift the inactivation-potential curve. Hence, Ca current-dependent inactivation which is blocked by intracellular EGTA probably does not involve a similar change of intracellular surface potential. The voltage shifts of activation and inactivation produced by extracellular divalent cations used singly or in mixtures can be described by the Gouy-Chapman theory for the diffuse double layer with binding (Gilbert & Ehrenstein, 1969; McLaughlin, Szabo & Eisenman, 1971). From the surface potential values and the Boltzman distribution, we have computed surface concentrations that predict the following experimental observations: 1) saturation of current-concentration relationships when surface potential is changing maximally; 2) the increase in peak current when Ca ions are replaced by Sr or Ba ions; and 3) the greater inhibitory effect of Mg on IBa than ICa. Theory indicates that surface charge cannot be screened completely even at 1 M [Mg]o and thus that Ca channel properties must be evaluated in the light of surface charge effects. For example, after correction for surface charge effects the relative permeabilities of Ca, Ba and Sr ions are equivalent. In the presence of Co ions, however, Ca ions are more permeable than Ba ions suggesting a channel binding site may be involved.

Animals↗