695 research outputs found
Collage Diffusion
We seek to give users precise control over diffusion-based image generation
by modeling complex scenes as sequences of layers, which define the desired
spatial arrangement and visual attributes of objects in the scene. Collage
Diffusion harmonizes the input layers to make objects fit together -- the key
challenge involves minimizing changes in the positions and key visual
attributes of the input layers while allowing other attributes to change in the
harmonization process. We ensure that objects are generated in the correct
locations by modifying text-image cross-attention with the layers' alpha masks.
We preserve key visual attributes of input layers by learning specialized text
representations per layer and by extending ControlNet to operate on layers.
Layer input allows users to control the extent of image harmonization on a
per-object basis, and users can even iteratively edit individual objects in
generated images while keeping other objects fixed. By leveraging the rich
information present in layer input, Collage Diffusion generates globally
harmonized images that maintain desired object characteristics better than
prior approaches
SIMULATING OZONE EFFECTS ON FOREST PRODUCTIVITY: INTERACTIONS AMONG LEAFâ, CANOPYâ, AND STANDâLEVEL PROCESSES
Ozone pollution in the lower atmosphere is known to have adverse effects on forest vegetation, but the degree to which mature forests are impacted has been very difficult to assess directly. In this study, we combined leafâlevel ozone response data from independent ozone fumigation studies with a forest ecosystem model in order simulate the effects of ambient ozone on mature hardwood forests. Reductions in leaf carbon gain were determined as a linear function of ozone flux to the leaf interior, calculated as the product of ozone concentration and leaf stomatal conductance. This relationship was applied to individual canopy layers within the model in order to allow interaction with standâ and canopyâlevel factors such as light attenuation, leaf morphology, soil water limitations, and vertical ozone gradients.
The resulting model was applied to 64 locations across the northeastern United States using ambient ozone data from 1987 to 1992. Predicted declines in annual net primary production ranged from 3 to 16% with greatest reductions in southern portions of the region where ozone levels were highest, and on soils with high waterâholding capacity where drought stress was absent. Reductions in predicted wood growth were slightly greater (3â22%) because wood is a lower carbon allocation priority in the model than leaf and root growth. Interannual variation in predicted ozone effects was small due to concurrent fluctuations in ozone and climate. Periods of high ozone often coincided with hot, dry weather conditions, causing reduced stomatal conductance and ozone uptake. Withinâcanopy ozone concentration gradients had little effect on predicted growth reductions because concentrations remained high through upper canopy layers where net carbon assimilation and ozone uptake were greatest.
Sensitivity analyses indicate a tradeâoff between model sensitivity to available soil water and foliar nitrogen and demonstrate uncertainties regarding several assumptions used in the model. Uncertainties surrounding ozone effects on stomatal function and plant water use efficiency were found to have important implications on current predictions. Field measurements of ozone effects on mature forests will be needed before the accuracy of model predictions can be fully assessed
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