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Biomedical subjects

V C Rogers

Publications and source records attributed to V C Rogers.

16 recordsLinked to original sources
PubMed1997

Radon penetration of concrete slab cracks, joints, pipe penetrations, and sealants.

Radon movement through 12 test slabs with different cracks, pipe penetrations, cold joints, masonry blocks, sealants, and tensile stresses characterized the importance of these anomalous structural domains. Diffusive and advective radon transport were measured with steady-state air pressure differences controlled throughout the deltaP = 0 to 60 Pa range. Diffusion coefficients (deltaP = 0) initially averaged 6.5 x 10(-8) m2 s(-1) among nine slabs with only 8% standard deviation, but increased due to drying by 0.16% per day over a 2-y period to an average of 2.0 x 10(-7) m2 s(-1). An asphalt coating reduced diffusion sixfold but an acrylic surface sealant had no effect. Diffusion was 42 times higher in solid masonry blocks than in concrete and was not affected by small cracks. Advective transport (deltaP < or = 60 Pa) was negligible for the slabs (10(-16) m2 permeability), pipe penetrations, and caulked gaps, but was significant for cracks, disturbed pipe penetrations, cold joints, masonry blocks, and concrete under tensile stress. Crack areas calculated to be as small as 10(-7) m2 significantly increased radon advection. Algebraic expressions predict air velocity and effective crack width from enhanced radon transport and air pressures. Masonry blocks, open cracks, and slab cold joints enhance radon penetration but stressed slabs, undisturbed pipe penetrations, and sealed cracks may not.

Adsorption↗
PubMed1997

Raetrad model extensions for radon entry into multi-level buildings with basements or crawl spaces.

The RAETRAD model was generalized to characterize radon generation and movement from soils and building materials into multi-level buildings with basements or crawl spaces. With the generalization, the model retains its original simplicity and ease of use. The model calculates radon entry rates that are consistent with measurements published for basement test structures at Colorado State University, confirming approximately equal contributions from diffusion and pressure-driven air flow at indoor-outdoor air pressure differences of deltaP(i-o) = -3.5 Pa. About one-fourth of the diffusive radon entry comes from concrete slabs and three-fourths comes from the surrounding soils. Calculated radon entry rates with and without a barrier over floor-wall shrinkage cracks generally agree with Colorado State University measurements when a sustained pressure of deltaP(i-o) = -2 Pa is used to represent calm wind (<1 m s(-1)) conditions. Calculated radon distributions in a 2-level house also are consistent with published measurements and equations.

Air Pollution, Indoor↗
PubMed1995

Radon diffusion coefficients for aged residential concretes.

This note reports radon gas pore diffusion coefficient measurements for residential concretes from Florida, ranging in age from 12 y to 45 y. The coefficients ranged from 1.5 x 10(-7) m2 s-1 to 5.5 x 10(-7) m2 s-1. On the average, these values are about a factor of 1.6 higher than average values previously reported for new residential concretes in Florida.

Air Pollutants, Radioactive↗
PubMed1994

Radon diffusion coefficients for residential concretes.

Radon gas diffusion through concrete can be a significant mechanism for radon entry into dwellings. Measurements of radon diffusion coefficients in the pores of residential concretes ranged from 2.1 x 10(-8) m2 s-1 to 5.2 x 10(-7) m2 s-1. The pore diffusion coefficients generally increased with the water-cement ratio of the concrete and decreased with its density. A least-squares regression of the diffusion coefficients on concrete density gave an r value of -0.73.

Air Pollutants, Radioactive↗
PubMed1994

The RAETRAD model of radon generation and transport from soils into slab-on-grade houses.

Remediation planning and 222Rn-related construction zoning require knowledge of how close and strong 226Ra sources can be in different foundation soils under different groundwater conditions without excessively elevating indoor 222Rn levels. A two-dimensional numerical-analytical model was developed to simulate (a) 222Rn emanation, decay, and movement by diffusion and advection in soils around houses and in their understructures; and (b) 222Rn accumulation in a single-zone house. The model represents foundation soils and a house in elliptical-cylindrical geometry. 222Rn may diffuse through its floor slab or may enter via idealized cracks and openings. The model was validated with analytical calculations of two-dimensional air pressure fields and with one-dimensional calculations of 222Rn generation with diffusion and diffusion combined with advection. Agreement generally was within < 1% when finite-difference approximations were minimized. Benchmark comparisons with indoor 222Rn measurements in two test-cell structures under passive and depressurized conditions averaged within 11% of measured values, well within measurement uncertainty. The corresponding average bias was only 3%. Larger variations were observed when applying the model to 50 houses. In this application, a negative bias of nearly 50% was observed due to data gaps and to poorly-characterized floor slabs and crack distributions.

Diffusion↗
PubMed1991

Multiphase radon generation and transport in porous materials.

Radon generation and transport in porous materials involve solid, liquid, and gas phases in the processes of emanation, diffusion, advection, absorption, and adsorption. Oversimplifications, such as representing moist soil systems by air-phase emanation and transport models, cause theoretical inconsistencies and biases in resulting calculations. Detailed Rn rate balance equations for solid, liquid, and gas phases were analyzed and combined using phase equilibrium constants to derive a single diffusive-advective rate balance equation in the traditional form. The emanation, diffusion, and permeability coefficients in the new equation have expanded definitions and interpretations to include Rn phase transfer. Radon adsorption was characterized by an exponential moisture dependence, and diffusion and permeability constants utilized previous moisture relationships. Correct boundary and interface conditions were defined, and the unified theoretical approach was applied to field data from a diffusion-dominated system and to laboratory data from an advection-dominated system. Measured 222Rn fluxes and concentrations validated the modeled values within the measurement variability in both applications.

Mathematics↗
PubMed1991

Correlations for predicting air permeabilities and 222Rn diffusion coefficients of soils.

The rate of 222Rn gas transport through earthen materials controls 222Rn releases to the atmosphere and to indoor environments. The key soil-related parameters characterizing 222Rn transport in earthen materials are the 222Rn diffusion coefficient and the soil air permeability. Simple correlations have been developed for predicting the 222Rn diffusion coefficient and the air permeability of soils based on fraction of water saturation, total porosity, and arithmetic mean particle diameter. Correlations are based on 1,073 diffusion coefficient measurements and 137 soil air permeability measurements. The geometric standard deviations between the correlation predictions and the measurements are 1.98 for the diffusion coefficients and 2.31 for the soil air permeabilities.

Air↗
PubMed1991

Psychosocial aspects of treating the HIV-infected dental patient.

As the number of human immunodeficiency virus (HIV)-seropositive individuals and persons diagnosed with clinical acquired immune deficiency syndrome (AIDS) increases, dentists will find it increasingly difficult either to avoid caring for this group of patients or to justify referral. While clinical management alone has posed a new role for dentistry in the HIV epidemic, the psychosocial dimensions of patient care are presenting even more challenging difficulties for the profession. General dentists, especially, have heretofore not faced the need to address the special needs of patients known to have terminal infectious disease. Treating HIV-seropositive and AIDS patients will produce psychosocial difficulties normally not encountered by the dental team. There is a need to understand the psychosocial issues affecting the patient as well as the dental provider, in order to implement changes in our educational approach to future patient management.

Adult↗
PubMed1989

Statistical estimation of analytical data distributions and censored measurements.

A numerical method was developed for estimating the shapes of unknown distributions of analytical data and for estimating the expected values of censored data points. The method is based conceptually on the normal probability plot. Data are ordered and then transformed by using a power function to achieve approximate linearity with respect to a computed normal cumulative probability scale. The exponent used in the power transformation is an index of the distribution shape, which covers a continuum on which normality is defined as d = 1 and log normality is defined as d = 0. Expected transformed values of censored points are computed from a straight line fitted to the transformed, accepted data, and these are then back-transformed to the original distribution. The method gives improved characterization of analytical data distributions, particularly in the distribution extremities. It also avoids the biases from improper handling of censored data arising from measurements near the analytical detection limit. Illustrative applications were computed for atmospheric SO2 data and for mineral concentrations in hamburgers.

Least-Squares Analysis↗