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Process evaluation in a multisite, primary obesity-prevention trial in American Indian schoolchildren.

We describe the development, implementation, and use of the process evaluation component of a multisite, primary obesity prevention trial for American Indian schoolchildren. We describe the development and pilot testing of the instruments, provide some examples of the criteria for instrument selection, and provide examples of how process evaluation results were used to document and refine intervention components. The theoretical and applied framework of the process evaluation was based on diffusion theory, social learning theory, and the desire for triangulation of multiple modes of data collection. The primary objectives of the process evaluation were to systematically document the training process, content, and implementation of 4 components of the intervention. The process evaluation was developed and implemented collaboratively so that it met the needs of both the evaluators and those who would be implementing the intervention components. Process evaluation results revealed that observation and structured interviews provided the most informative data; however, these methods were the most expensive and time consuming and required the highest level of skill to undertake. Although the literature is full of idealism regarding the uses of process evaluation for formative and summative purposes, in reality, many persons are sensitive to having their work evaluated in such an in-depth, context-based manner as is described. For this reason, use of structured, quantitative, highly objective tools may be more effective than qualitative methods, which appear to be more dependent on the skills and biases of the researcher and the context in which they are used.

Asian People↗

The rate of compensatory evolution.

A two-locus model is presented to analyze the evolution of compensatory mutations occurring in stems of RNA secondary structures. Single mutations are assumed to be deleterious but harmless (neutral) in appropriate combinations. In proceeding under mutation pressure, natural selection and genetic drift from one fitness peak to another one, a population must therefore pass through a valley of intermediate deleterious states of individual fitness. The expected time for this transition is calculated using diffusion theory. The rate of compensatory evolution, kappa c, is then defined as the inverse of the expected transition time. When selection against deleterious single mutations is strong, kappa c becomes independent on the recombination fraction r between the two loci. Recombination generally reduces the rate of compensatory evolution because it breaks up favorable combinations of double mutants. For complete linkage, kappa c is given by the rate at which favorable combinations of double mutants are produced by compensatory mutation. For r > O, kappa c decreases exponentially with r. In contrast, kappa c becomes independent of r for weak selection. We discuss the dynamics of evolutionary substitutions of compensatory mutants in relation of WRIGHT's shifting balance theory of evolution and use our results to analyze the substitution process in helices of mRNA secondary structures.

Evolution, Molecular↗

Genetic drift in an infinite population. The pseudohitchhiking model.

Selected substitutions at one locus can induce stochastic dynamics that resemble genetic drift at a closely linked neutral locus. The pseudohitchhiking model is a one-locus model that approximates these effects and can be used to describe the major consequences of linked selection. As the changes in neutral allele frequencies when hitchhiking are rapid, diffusion theory is not appropriate for studying neutral dynamics. A stationary distribution and some results on substitution processes are presented that use the theory of continuous-time Markov processes with discontinuous sample paths. The coalescent of the pseudohitchhiking model is shown to have a random number of branches at each node, which leads to a frequency spectrum that is different from that of the equilibrium neutral model. If genetic draft, the name given to these induced stochastic effects, is a more important stochastic force than genetic drift, then a number of paradoxes that have plagued population genetics disappear.

Crossing Over, Genetic↗

Mutation-selection balance with stochastic selection.

Diffusion theory has been used to analyze a model of mutation-selection balance in which the selection process is assumed to be stochastic in time. The limiting outcome of the mutation-stochastic selection process is determined qualitatively by the geometric mean fitnesses of the genotypes, and the conditions for fixation or polymorphism are similar to those that determine the outcome of the mutation-selection process when selection is constant. However, in the case of a completely recessive allele, detailed numerical study of the polymorphism associated with stochastic selection has shown that the average allele frequency maintained is greater than the equilibrium frequency expected when selection is constant, even when the geometric mean fitness of the recessive homozygotes is identical in the stochastic and deterministic models. Thus, allele frequencies in natural populations that are too high to be plausibly explained by a balance between mutation and constant selection can be accounted for if selection is stochastic.

Alleles↗

An evaluation of the effectiveness of a planned diffusion process: the Smoke-Free Class of 2000 project in Texas.

The first year of the Texas Triagency Coalition Smoke-Free Class of 2000 project (SFC2000) in Texas was evaluated using a descriptive model developed from diffusion theory. Tobacco-prevention education (TPE) materials were to be made available to all first grade teachers within the state. A random sample survey of 213 teachers indicated that 96 (44.7%) had received the materials. Adoption and implementation were high. By May of 1989, 64.2% of those teachers receiving materials had adopted and already implemented the program, and 25.3% had adopted and intended to use the materials. Almost all (96.8%) of those teachers who received the kit indicated that they would maintain the first grade program in the coming school year. Of respondents to a 1 year follow-up survey, 41.1% used it the first year only, 27.3% used it both years, 12.5% used it only in year 2 and 18.2% did not use it either year. Of those receiving the kits, 48% indicated that they had not previously taught TPE and thus were introduced to the concept of TPE through the SFC2000 kits. Receptivity was highest (over 90% agreement) for including TPE in elementary school curricula, with fewer teachers strongly agreeing with items tapping personal involvement with TPE. This evaluation of a statewide component of a national initiative reinforces the need to consider the dissemination and implementation of materials when planning large-scale interventions and evaluating their impact.

Adult↗

Persistence of microsatellite arrays in finite populations.

Given that most microsatellite arrays are of no obvious functional significance, it is natural to ask how long these sequences persist during evolution. The expected persistence time was calculated for microsatellite arrays undergoing replication slippage and random genetic drift using diffusion theory and Monte Carlo simulation. In each of the three models of replication slippage compared, copy number changes involve only single steps. In one model, the rates of addition or loss of repeat units are constant; in the other two models, they are dependent on array length in a linear or quadratic way. For all three models, it was found that persistence time of microsatellite loci increases with population size in a sublinear fashion. A heuristic argument is presented as to why this result holds true for a more general class of mutation mechanisms, including models that incorporate base substitutions in addition to replication slippage. This suggests that the approximately 30% deficiency of microsatellite loci on chromosome X (relative to autosomes) that has been well documented for several mammalian species cannot be explained by the fact that the X chromosome has a smaller effective population size than do autosomes, as has been hypothesized.

Computer Simulation↗

Dissolution of metal tritides in a simulated lung fluid.

Metal tritides including titanium tritide (Ti 3Hx) and erbium tritide (Er 3Hx) have been used as components of neutron generators. The current understanding of metal tritides and their radiation dosimetry for internal exposure is very limited, and the ICRP Publication 30 does not provide for tritium dosimetry in metal tritide form. However, a few papers in the literature suggest that the solubility of metal tritides could be low. The current radiation protection guidelines for metal tritide particles are based on the assumption that their biological behavior is similar to tritiated water, which could be easily absorbed into body fluid. Therefore, these particles could have relatively short biological half-lives (10 d). If the solubility is low, the biological half-life of metal tritide particles and the dosimetry of an inhalation exposure to these particles could be quite different from tritiated water. This paper describes experiments on the dissolution rate of titanium tritide particles in a simulated lung fluid. Titanium tritide particles with mean sizes of 103 microm (coarse) and 0.95 microm (fine) were used. The results showed that the coarse particles dissolved much more slowly than the fine particles. The long-term dissolution half times were 361 and 33 d for the coarse and fine particles, respectively. Dissolution data of the fine particles were consistent with the diffusion theory. The dissolution half times were longer than the 10-d biological half time for tritiated water in the body. This finding has significant implications for the current health protection guidelines, including annual limits of intakes and derived air concentrations.

Body Fluids↗

Noninvasive functional imaging of human brain using light.

Analysis of photon transit time for low-power light passing into the head, and through both skull and brain, of human subjects allowed for tomographic imaging of cerebral hemoglobin oxygenation based on photon diffusion theory. In healthy adults, imaging of changes in hemoglobin saturation during hand movement revealed focal, contralateral increases in motor cortex oxygenation with spatial agreement to activation maps determined by functional magnetic resonance imaging; in ill neonates, imaging of hemoglobin saturation revealed focal regions of low oxygenation after acute stroke, with spatial overlap to injury location determined by computed tomography scan. Because such slow optical changes occur over seconds and co-localize with magnetic resonance imaging vascular signals whereas fast activation-related optical changes occur over milliseconds and co-localize with EEG electrical signals, optical methods offer a single modality for exploring the spatio-temporal relationship between electrical and vascular responses in the brain in vivo, as well as for mapping cortical activation and oxygenation at the bedside in real-time for clinical monitoring.

Adult↗

Time-resolved experiments on light diffusion in anisotropic random media

Multiple light scattering in isotropic and anisotropic media is studied experimentally with an optical gating technique, as commonly used in fluorescence spectroscopy. The experimental setup permits an accurate analysis of the propagation of a short light pulse through disordered or partially ordered media. The diffusion constant of some isotropic systems is reported, and the anisotropy in the diffusion constant for light diffusion through liquid crystals is observed. For the time-resolved data, good agreement with diffusion theory is found in all cases, including the liquid crystal in the nematic phase.

Journal Article↗

Absorption and scattering perturbations in homogeneous and layered diffusive media probed by time-resolved reflectance at null source-detector separation.

We characterize the capability of time-resolved reflectance measurements at small source-detector separation (less than 5 mm) to localize small inhomogeneities embedded in an otherwise homogeneous or layered diffusive medium. By considering both absorption and scattering inhomogeneities, we demonstrate the improvement of this approach in terms of contrast and spatial resolution, as compared to more typical set-ups involving larger source-detection separations (few centimeters). Simulations are performed exploiting an analytical perturbation approach to diffusion theory and a four-layer heterogeneous time-resolved Monte Carlo code, considering realistic tissue geometries. Exhaustive investigation in the parameters space is reported.

Absorption↗

Multiscale mixing efficiencies for steady sources.

Multiscale mixing efficiencies for passive scalar advection are defined in terms of the suppression of variance weighted at various length scales. We consider scalars maintained by temporally steady but spatially inhomogeneous sources, stirred by statistically homogeneous and isotropic incompressible flows including fully developed turbulence. The mixing efficiencies are rigorously bounded in terms of the Péclet number and specific quantitative features of the source. Scaling exponents for the bounds at high Péclet number depend on the spectrum of length scales in the source, indicating that molecular diffusion plays a more important quantitative role than that implied by classical eddy diffusion theories.

Journal Article↗

Breakdown of wave diffusion in 2D due to loops.

The validity of the diffusion approximation for the intensity of multiply scattered waves is tested with numerical simulations in a strongly scattering 2D medium of finite extent. We show that the diffusion equation underestimates the intensity and attribute this to both the neglect of recurrent scattering paths and interference within diffusion theory. We present a theory to quantify this discrepancy based on counting all possible scattering paths between point scatterers. Interference phenomena, due to loop paths, are incorporated in a way similar to coherent backscattering.

Journal Article↗

Time-resolved reflectance at null source-detector separation: improving contrast and resolution in diffuse optical imaging.

We propose a novel approach to imaging in diffusive media based on time-resolved reflectance measurements at null source-detector separation. This approach yields better spatial resolution and contrast as compared to the classical approach, which typically employs a separation of 20-40 mm. Results are obtained by an analytical perturbation approach to diffusion theory and on Monte Carlo simulations. Practical implementation with state-of-the-art technology and performance of a complementary approach based on the use of small but not null source-detector separation are also discussed.

Journal Article↗

Bulk flow in ferrofluids in a uniform rotating magnetic field.

Direct measurements of the bulk flow of a ferrofluid in a uniform rotating magnetic field were obtained using the ultrasonic velocity profile method. The fluid was observed to corotate with the field in a rigid-body-like fashion throughout the bulk of the container, except near the air-fluid interface, where it was observed to counterrotate. The results were found in qualitative agreement with the spin diffusion theory of Zaitsev and Shliomis [J. Appl. Mech. Tech. Phys. 10, 696 (1969)]10.1007/BF00907424.

Journal Article↗

Passive nitrate transport by root plasma membrane vesicles exhibits an acidic optimal pH like the H(+)-ATPase.

The net initial passive flux (J(Ni)) in reconstituted plasma membrane (PM) vesicles from maize (Zea mays) root cells was measured as recently described (P. Pouliquin, J.-P. Grouzis, R. Gibrat ¿1999 Biophys J 76: 360-373). J(Ni) in control liposomes responded to membrane potential or to NO(3)(-) as expected from the Goldman-Hodgkin-Katz diffusion theory. J(Ni) in reconstituted PM vesicles exhibited an additional component (J(Nif)), which was saturable (K(m) for NO(3)(-) approximately 3 mM, with J(Nifmax) corresponding to 60 x 10(-9) mol m(-2) s(-1) at the native PM level) and selective (NO(3)(-) = ClO(3)(-) > Br(-) > Cl(-) = NO(2)(-); relative fluxes at 5 mM: 1:0.34:0.19). J(Nif) was totally inhibited by La(3+) and the arginine reagent phenylglyoxal. J(Nif) was voltage dependent, with an optimum voltage at 105 mV at pH 6.5. The activation energy of J(Nif) was high (129 kJ mol(-1)), close to that of the H(+)-ATPase (155 kJ mol(-1)), and J(Nif) displayed the same acidic optimal pH (pH 6.5) as that of the H(+) pump. This is the first example, to our knowledge, of a secondary transport at the plant PM with such a feature. Several properties of the NO(3)(-) uniport seem poorly compatible with that reported for plant anion channels and to be attributable instead to a classical carrier. The physiological relevance of these findings is suggested.

Biological Transport↗

In vivo reflectance of blood and tissue as a function of light wavelength.

Light reflectance from soft tissue has been utilized in noninvasive clinical measurement devices such as the photoplethysmograph and the reflectance pulse oximeter. Incident light on the skin travels into the underlying layers and is in part reflected back to the surface. This paper describes the reflectance of light from in vivo tissue for wavelengths in the range from 420 to 940 nm, based on photon diffusion theory and on experimental results from studies of 17 subjects. The results show a minimum reflectance and a peak sensitivity to the blood pulsations in the wavelength range from 510 to 590 nm. Skin pigmentation is seen to attenuate reflectance rather than altering the character of the modulation spectra. Based on the model introduced in this paper, the dependence of modulation spectra on mean blood fractional volume as well as wavelength is also described theoretically, and corroborated by further experimental data at 570 and 630 nm. At these latter wavelengths, the signal-to-noise ratio was calculated for the blood volume pulsation signal in the presence of physiological noise. The median for calculated ratios of reflectance modulation by blood pulsation and ratios of signal to noise between the two wavelengths were 13.1 and 7.5, respectively, for 93 sites in nine subjects. These results are seen to be consistent with the theory.

Blood Volume↗

Successive order scattering transport approximation for laser light propagation in whole blood medium.

An analytical solution method of the radiative transport equation, describing light scattering distribution in whole blood, is derived by applying successive order scattering approximation and transport approximation. By separating coherent components of scattered fluxes, the transport equation can be represented in terms of each order scattering flux, and the equations for each order scattering flux have a simplified integration term of scattering contribution that usually makes the solution complicated or even impossible. Also, actual phase function can be used for calculation of angular dependent scattering distribution that is approximated by the sum of the zeroth- and first-order Legendre polynomial in diffusion theory, or the sum of isotropic and coherent components in transport approximation. The method is then used to calculate reflectance from a half-space blood medium. It is found that first-order scattering flux alone produces a good agreement with experimental data and higher-order scattering fluxes are negligible in whole blood.

Anisotropy↗

A comparative study of photoacoustic and reflectance methods for determination of epidermal melanin content.

Although epidermal melanin content has been quantified non-invasively using visible reflectance spectroscopy (VRS), there is currently no way to determine melanin distribution in the epidermis. We have developed a photoacoustic probe that uses a Q-switched, frequency-doubled Nd:YAG (neodymium, yttrium, aluminum, garnet) laser operating at 532 nm to generate acoustic pulses in skin in vivo. The probe contained a piezoelectric element that detected photoacoustic waves that were then analyzed for epidermal melanin content using a photoacoustic melanin index (PAMI). Melanin content was compared between results of photoacoustics and VRS. Spectra from human skin were fitted to a model based on diffusion theory that included parameters for epidermal thickness, melanin content, hair color and density, and dermal blood content. Ten human subjects with skin phototypes I-VI were tested using the photoacoustic probe and VRS. A plot of PAMI v. VRS showed a good linear fit with r2=0.85. Photoacoustic and VRS measurements are shown for a human subject with vitiligo, indicating that melanin was almost completely absent. We present preliminary modeling for photoacoustic probe design and analysis necessary for depth profiling of epidermal melanin.

Acoustics↗