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The spectral reflectance and transmittance over the wavelength range of 250-700 nm were evaluated for leaves of 20 deciduous tree species and leaf sheaths of five isogenic wax variants of Sorghum bicolor differing in visible reflectance due to cuticular waxes. Using the sorghum sheath reflectance and cuticle surface characteristics as a model, it was concluded that tree leaf reflectance above 0.06 was likely due to the presence of variously-shaped fine epicuticular wax structures on the leaf surface. Increasing the density of sub-micron wax structures corresponded to an enhanced ultraviolet (UV) reflectance over the PAR reflectance of a given leaf surface-either S. bicolor sheath or tree leaf. Amorphous globular epicuticular wax structures did not appear to scatter UV as well as wax filaments or vertical plates in varying patterns even when the dimensions of the structures were similar. Further work is needed to clarify this relationship and the influence of cellular pigments on subsurface contributions to the reflectance.

1143Ammonia (NH 3 ) emissions vary considerably among farms as influenced by climate and management. Because emission measurement is difficult and expensive, process-based models provide an alternative for estimating whole farm emissions. A model that simulates the processes of NH 3 formation, speciation, aqueous-gas partitioning, and mass transfer was developed and incorporated in a whole farm simulation model (the Integrated Farm System Model). Farm sources included manure on the floor of the housing facility, manure in storage (if used), fieldapplied manure, and deposits on pasture (if grazing is used). In a comprehensive evaluation of the model, simulated daily, seasonal, and annual emissions compared well with data measured over 2 yr for five free stall barns and two manure storages on dairy farms in the eastern United States. In a further comparison with published data, simulated and measured barn emissions were similar over differing barn designs, protein feeding levels, and seasons of the year. Simulated emissions from manure storage were also highly correlated with published emission data across locations, seasons, and different storage covers. For field applied manure, the range in simulated annual emissions normally bounded reported mean values for different manure dry matter contents and application methods. Emissions from pastures measured in northern Europe across seasons and fertilization levels were also represented well by the model. After this evaluation, simulations of a representative dairy farm in Pennsylvania illustrated the effects of animal housing and manure management on whole farm emissions and their interactions with greenhouse gas emissions, nitrate leaching, production costs, and farm profitability.

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In vivo tissue responses were compared for three commercially available polypropylene suburethral slings that differ markedly in fabric structure and in size of resulting interstices and pores. All three elicited the same basic inflammatory response; however, individual fabric structures produced distinct differences in tissue formation within each mesh. The presence of numerous, closely spaced, small diameter filaments prevented formation of extensive fibrous connective tissue within two slings (ObTape and IVS Tunneller mesh). The much larger diameter monofilament and open knit structure of the Monarc sling permitted the most extensive fibrous tissue integration. These differences may be of interest to physicians considering clinical use.

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[1] A major limitation in predicting the ultraviolet-B (UVB) irradiance on organisms is the difficulty in determining the UVB under partly cloudy sky conditions. This study developed models for estimating the diffuse fraction of ultraviolet-A (UVA) and UVB radiation under partly cloudy skies based on National Weather Service (NWS) cloud cover measurements and Department of Agriculture (USDA) UVB Radiation Monitoring and Research Network UV radiation measurements made from 1997 through 1999 at nine locations in the United States. The UVB diffuse fraction and the difference between clear and partly cloudy sky diffuse fraction were empirically modeled as a function of solar zenith angle and cloud fraction with a resulting mean bias error (MBE) of 0.019 and 0.014, respectively, and a root mean squared error (RMSE) of 0.069 and 0.079, respectively. A semiempirical model was also evaluated where the diffuse fraction was treated as the summation of clear and overcast sky diffuse fractions, respectively, weighted by the probability of the Sun's direct beam being obstructed or not for a given cloud cover fraction. This model MBE was less than 0.01 of both the UVA and UVB wave bands, while the RMSE was 0.035 within the UVB wave band and À0.030 in the UVA wave band. Model errors were greatest for low solar zenith angles and high cloud fractions in the UVB. The cloud fraction measurements used in these models only include clouds up to 3.6 km. Consequently, they should only be used when the cloud information has the same characteristics.