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At least 379 records · Page 21Linked to original sources

Flow properties of driven-diffusive lattice gases: theory and computer simulation.

We develop n-cluster mean-field theories (1 < or = n < or = 4) for calculating the flux and the gap distribution in the nonequilibrium steady states of the Katz-Lebowitz-Spohn model of the driven diffusive lattice gas, with attractive and repulsive interparticle interactions, in both one and two dimensions for arbitrary particle densities, temperature as well as the driving field. We compare our theoretical results with the corresponding numerical data we have obtained from the computer simulations to demonstrate the level of accuracy of our theoretical predictions. We also compare our results with those for some other prototype models, notably particle-hopping models of vehicular traffic, to demonstrate the qualitative features we have observed in the Katz-Lebowitz-Spohn model, emphasizing, in particular, the consequences of repulsive interparticle interactions.

Journal Article↗

Activation energies for quantum diffusion of hydrogen in metals and on metal surfaces using delocalized nuclei within the density-functional theory.

Hydrogen diffusion on the Cu(001) surface and in bulk Nb and Ta is studied in the quantum regime using first-principles electronic-structure calculations. We present, for the first time, a direct density-functional calculation of the activation energy required to establish the quantum-mechanically delocalized hydrogen coincidence configuration and of the corresponding tunneling matrix element. For the two bulk systems a direct comparison can be made with nuclear magnetic resonance data, and we find excellent agreement for both the coincidence energy and the tunneling matrix element.

Journal Article↗

A theory of quantum diffusion localization.

The quantum localization of chaotically diffusive classical motion is reviewed, using the kicked rotator as a simple but instructive example. The specific quantum steady state, which results from statistical relaxation in the discrete spectrum, is described in some detail. A new phenomenological theory of quantum dynamical relaxation is presented and compared with the previously existing theory.

Journal Article↗

Diffusion of innovations theory and work-site AIDS programs.

Four case studies of the adoption of work-site AIDS programs are investigated, two of which were modifications of the Centers for Disease Control and Prevention's Business Responds to AIDS (BRTA) program. AIDS work-site programs were mainly initiated by the four study companies as a result of the efforts of a champion (defined as an individual who gains attention and resources for an issue in a system) or the occurrence of a tragic event, such as a company employee contracting AIDS. The BRTA program is an innovation that has not yet reached critical mass, which is the point after which further rates of adoption occur rapidly in a self-sustaining process.

Acquired Immunodeficiency Syndrome↗

Diffusion of innovation theory for clinical change.

Maximising the adoption of evidence-based practice has been argued to be a major factor in determining healthcare outcomes. However, there are gaps between evidence-based recommendations and current care. Bridging the evidence gap will not be achieved simply by informing clinicians about the evidence. One theoretical approach to understanding how change may be achieved is Rogers' diffusion model. He argues that certain characteristics of the innovation itself may facilitate its adoption. Other factors influencing acceptance include promotion by influential role models, the degree of complexity of the change, compatibility with existing values and needs, and the ability to test and modify the new procedure before adopting it. The diffusion model may provide valuable insights into why some practices change and others do not, as well as guiding those who try to effect adoption of best-evidence practice.

Communication↗

Boundary conditions for- single-ion diffusion.

We have constructed a theory for diffusion through the pore of a single-ion channel by taking a limit of a random walk around a cycle of states. Similar to Levitt's theory of single-ion diffusion, one obtains boundary conditions for the Nernst-Planck equation that guarantee that the pore is occupied by at most one ion. Two of the terms in the boundary conditions are identical to those given by Levitt. However, the construction gives rise to a third term not found in Levitt's theory. With this term, the channel spends exponentially distributed intervals in the empty state. Ion sample paths have been simulated to help visualize trajectories near the channel entrances, with and without the new term. We use the modified Levitt theory to fit several potential profiles to the conductance data of Russell et al. In particular, we have analyzed the profile for Na+ in gramicidin calculated by Roux and Karplus. The peak-to-peak amplitude of their result must be reduced to at most 35% of its original value to fit the data. But with this reduction, excellent fits are obtained.

Computer Simulation↗

Grounding a new information technology implementation framework in behavioral science: a systematic analysis of the literature on IT use.

Many interventions to improve the success of information technology (IT) implementations are grounded in behavioral science, using theories, and models to identify conditions and determinants of successful use. However, each model in the IT literature has evolved to address specific theoretical problems of particular disciplinary concerns, and each model has been tested and has evolved using, in most cases, a more or less restricted set of IT implementation procedures. Functionally, this limits the perspective for taking into account the multiple factors at the individual, group, and organizational levels that influence use behavior. While a rich body of literature has emerged, employing prominent models such as the Technology Adoption Model, Social-Cognitive Theory, and Diffusion of Innovation Theory, the complexity of defining a suitable multi-level intervention has largely been overlooked. A gap exists between the implementation of IT and the integration of theories and models that can be utilized to develop multi-level approaches to identify factors that impede usage behavior. We present a novel framework that is intended to guide synthesis of more than one theoretical perspective for the purpose of planning multi-level interventions to enhance IT use. This integrative framework is adapted from PRECEDE/PROCEDE, a conceptual framework used by health planners in hundreds of published studies to direct interventions that account for the multiple determinants of behavior. Since we claim that the literature on IT use behavior does not now include a multi-level approach, we undertook a systematic literature analysis to confirm this assertion. Our framework facilitated organizing this literature synthesis and our analysis was aimed at determining if the IT implementation approaches in the published literature were characterized by an approach that considered at least two levels of IT usage determinants. We found that while 61% of studies mentioned or referred to theory, none considered two or more levels. In other words, although the researchers employ behavioral theory, they omit two fundamental propositions: (1) IT usage is influenced by multiple factors and (2) interventions must be multi-dimensional. Our literature synthesis may provide additional insight into the reason for high failure rates associated with underutilized systems, and underscores the need to move beyond the current dominant approach that employs a single model to guide IT implementation plans that aim to address factors associated with IT acceptance and subsequent positive use behavior.

Attitude to Computers↗

New developments in the theory of the diffuse double layer.

The role of ion size effects in determining diffuse layer properties is considered. Monte Carlo data relevant to this question are reviewed. Then the integral equation approach to the problem is considered with an emphasis on attempts to derive an analytical equation for the potential drop across the diffuse layer. An empirical model for ion size effects is described that allows one to estimate not only the diffuse layer potential drop but also the diffuse layer capacity, the ionic surface excesses, and the potential distribution in the diffuse layer. It is demonstrated that the resulting model can easily be applied by experimentalists to the analysis of experimental data for double layer phenomena in electrochemistry and colloid science.

Journal Article↗

Basic theory for the diffusive sampling of radon.

From the closed-form solution of the Fickian equation describing the uptake of radon by a diffusive sampler, the following are calculated: 1) the optimal estimate of the time-weighted average radon concentration; 2) the effect of the geometry of the diffusive sampler on performance; 3) the maximum sampling time consistent with a predetermined maximum error in the estimated time-weighted average concentration of radon; and 4) the effects of temperature and pressure on the performance of the sampler. It is shown that the maximum sampling error can be greatly reduced by dividing the adsorbent bed into two layers placed in series and by using a weighted average of the uptakes on the two layers.

Air Pollutants, Radioactive↗