Aerosol chemical and optical properties during the Mt. Zirkel Visibility Study.

Aerosol chemical and optical properties were measured near the Mt. Zirkel Wilderness Area in northwestern Colorado. Six-hour PM2.5 (particles with aerodynamic diameters less than 2.5 microm) mass concentrations and PM2.5 dry particle light scattering at 550 nm averaged 4.6 microg m(-3) and 8.6 Mm(-1), respectively. Sulfates, organic carbon, and geological material were the principle components of particle mass and light scattering. Hygroscopic growth was consistent with that expected for ammonium sulfate aerosols. Size distributions derived from three-wavelength (i.e., 450, 550, and 700 nm) nephelometer data were similar to those measured in other remote areas of the western USA. Quasi-dry chemical light scattering efficiencies derived using Mie theory were 3.6 m2 g(-1) for organic carbon, 2.5 m2 g(-1) for sulfates (ammonium sulfate and ammonium bisulfate), 2.6 m2 g(-1) for ammonium nitrate, and 1.76 m2 g(-1) for geological material. These values are lower than but consistent with previously reported results. Realistic efficiencies could not be derived using the multiple linear regression (MLR) approach.

Titanium endosteal dental implants in the mandibles of beagle dogs: a 2 year study.

Forty of 44 vented endosteal blade implants were well tolerated by the mandibular tissues of beagle dogs, as demonstrated clinically, radiographically, and histologically. Infection and inflammation were not observed. The epithelium did not invade along the neck of the implants more than 2 mm. below the mandibular crest. After 3 to 6 months, except for increasing density of bone at the metal interface, no distinct pattern of reaction could be discerned histologically. Except for heavy collagenous investment in three dogs, there was no sign of the implants being treated as sterile foreign bodies. In this study, histology did not provide good criteria for evaluating the failure of vented endosteal blade implants. In four implants which failed, the most reliable signs of failure were increased mobility and/or sulcus depth around the neck of the abutments. Radiographic evaluation of implants provided the best means of determining bone resorption. Bone resorption was apparent 3 to 6 months after implantation, did not appear to be progressive, and did not indicate implant failure or impending implant failure in those animals in which it occurred. Radiolucent areas observed in 29 of the specimens contained connective tissue, marrow spaces, thin bone trabeculae, and nonpathologic tissues. Although in some of the dogs stress on implants did not cause failure, there is a need for further experimentation involving vented endosteal blades subjected to occlusal loading.

Multiple scattering calculations for technology.

A many-flux (discrete ordinate) radiative transfer calculation procedure is described with the goal of making the mathematics easy to learn and use. The major approximation is the neglect of polarization. Emission within the scattering medium is not included, and the formulas are restricted to a scattering medium bounded by parallel planes. The boundary conditions allow for a variety of kinds of illumination, and the surface reflection coefficients at the boundaries of the scattering medium are accurately determined. A comparison is made with the two-flux (Kubelka-Munk) and four-flux calculation methods, and this leads to empirical expressions for the scattering and absorption coefficients in these simple theories, which make them give nearly the same results as exact theories. These empirical expressions provide a very simple method for estimating the absolute reflectance and transmittance of turbid media and greatly increase the utility of the two-flux and four-flux calculation methods. The two-flux equations give excellent results provided the absorption is small compared to scattering and the optical thickness is greater than 5. A comparison with experimental data taken with collimated illumination shows that the four-flux equations give good results at any optical thickness even if the absorption is strong.