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Results for “diffusion theory”

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PubMed2003

Smoking among university students in Canada and South Korea: linking diffusion theory with consumer susceptibility to interpersonal influence.

This research examines the relationship between consumer susceptibility to interpersonal influence (CSII) and smoking diffusion patterns in Canada and South Korea. It is hypothesized that individuals with higher susceptibility to interpersonal influence are more likely to follow the dominant trend with regard to smoking behavior. Among South Korean females, smoking prevalence has been increasing and, in line with this trend, smokers were found to have a higher susceptibility to interpersonal influence than non-smokers. Among Canadians and among South Korean males, smoking has been in decline and, in line with this trend, non-smokers were found to have a higher susceptibility to interpersonal influence than smokers. Implications for social marketers and health professionals are discussed.

Adolescent↗
PubMed1993

The advance of Muller's ratchet in a haploid asexual population: approximate solutions based on diffusion theory.

Asexual populations experiencing random genetic drift can accumulate an increasing number of deleterious mutations, a process called Muller's ratchet. We present here diffusion approximations for the rate at which Muller's ratchet advances in asexual haploid populations. The most important parameter of this process is n0 = N e-U/s, where N is population size, U the genomic mutation rate and s the selection coefficient. In a very large population, n0 is the equilibrium size of the mutation-free class. We examined the case n0 > 1 and developed one approximation for intermediate values of N and s and one for large values of N and s. For intermediate values, the expected time at which the ratchet advances increases linearly with n0. For large values, the time increases in a more or less exponential fashion with n0. In addition to n0, s is also an important determinant of the speed of the ratchet. If N and s are intermediate and n0 is fixed, we find that increasing s accelerates the ratchet. In contrast, for a given n0, but large N and s, increasing s slows the ratchet. Except when s is small, results based on our approximations fit well those from computer simulations.

Computer Simulation↗
PubMed2006

Quantification of bioluminescence images of point source objects using diffusion theory models.

A simple approach for estimating the location and power of a bioluminescent point source inside tissue is reported. The strategy consists of using a diffuse reflectance image at the emission wavelength to determine the optical properties of the tissue. Following this, bioluminescence images are modelled using a single point source and the optical properties from the reflectance image, and the depth and power are iteratively adjusted to find the best agreement with the experimental image. The forward models for light propagation are based on the diffusion approximation, with appropriate boundary conditions. The method was tested using Monte Carlo simulations, Intralipid tissue-simulating phantoms and ex vivo chicken muscle. Monte Carlo data showed that depth could be recovered within 6% for depth 4-12 mm, and the corresponding relative source power within 12%. In Intralipid, the depth could be estimated within 8% for depth 4-12 mm, and the relative source power, within 20%. For ex vivo tissue samples, source depths of 4.5 and 10 mm and their relative powers were correctly identified.

Algorithms↗
PubMed1994

Basic optothermal diffusion theory for interstitial laser photocoagulation.

A theoretical basis for interstitial laser photocoagulation (ILP) practiced with point-emitting fiber tips has been established by solving the bioheat transfer equation, using basic Green's function methods, for steady and instantaneous point sources of both optical energy and direct heat. Three combination optical and thermal parameters have been identified that strongly influence temperature distributions during ILP. These are defined here as optothermal heat capacities and an optothermal diffusion length, all of which characterize how a thermal diffusion temperature profile is flattened and reduced when optical diffusion is added. Relevance and limitations of this theory for practical ILP are discussed. A useful result is a mathematical verification of previous empirical observations that point optical sources heat tissues less than point heat sources of the same power. A comparison of normalized theoretical temperature transients with published measurements suggests that in normal liver, blood perfusion cooling may exceed thermal conduction by a factor of 5.6 +/- 1.7.

Biophysical Phenomena↗
PubMedDate not supplied

Concepts of diffusion theory and a graphic approach to the description of the epidemic flow of contagious disease.

Concepts used to analyze sociological, geographic, and economic processes were adapted to an examination of the diffusion of contagious disease. The example used in applying these concepts was an epidemic of variola minor which continued for 12 months in an area of 1,006 square kilometers centered on the city of Bragança Paulista, Sao Paulo State (Brazil). A graphic procedure is proposed that depicts aspects of the epidemic flow of person-to-person transmission. Spatial, temporal, and sociological characteristics of the epidemic flow are disclosed in sequential diagrams. They represent geographic areas as well as schools and agglomerates of households affected by the epidemic at a given time, the mode of diffusion, and the source of the infection. The procedure yielded indirect evidence of the role of school pupils as introducers of variola minor into households and school classes. All subdivisions of the city, six of the seven rural districts, and four of the five elementary schools were affected through hierarchical (between-areas) diffusion. Subsequently, there was neighborhood (within-area) diffusion, and this resulted in new interactions between areas.

Brazil↗
PubMed2005

Diffusion theory and telemedicine adoption by Kansas health-care providers: critical factors in telemedicine adoption for improved patient access.

Twenty counties in Kansas were randomly selected from those designated as rural on the basis of their populations. A sample of 356 physicians and physicians' assistants in these counties was chosen. A postal survey was sent to the identified providers up to three times. One hundred and eighty-six of the questionnaires were returned (a response rate of 52%). In all, 76% of the respondents were physicians, 76% were men and 42% were family practitioners. Practitioners were classified as adopters or non-adopters of telemedicine, based on their report of whether they had ever referred one or more patients for a health-care consultation via telemedicine. Of the 167 participants who marked this item, 30 (18%) were adopters and 137 (82%) were non-adopters. Among the adopters, 16 (53%) said that they expected to use telemedicine with about the same frequency or more often in the future. In contrast, 61 (45%) non-adopters reported that they did not expect to refer patients by telemedicine in the future and 51 (37%) were unsure. Neither age (r = 0.16, P = 0.44) nor gender (chi2 = 2.35, P = 0.13) was related to the adoption variable or the number of referrals made to telemedicine clinics. The results suggest that adopters and non-adopters of telemedicine perceive its value very differently, and that an opportunity exists to promote the concept to non-adopters more effectively.

Age Factors↗