Towards Accurate Data-free Quantization for Diffusion Models

In this paper, we propose an accurate data-free post-training quantization framework of diffusion models (ADP-DM) for efficient image generation. Conventional data-free quantization methods learn shared quantization functions for tensor discretization regardless of the generation timesteps, while the activation distribution differs significantly across various timesteps. The calibration images are acquired in random timesteps which fail to provide sufficient information for generalizable quantization function learning. Both issues cause sizable quantization errors with obvious image generation performance degradation. On the contrary, we design group-wise quantization functions for activation discretization in different timesteps and sample the optimal timestep for informative calibration image generation, so that our quantized diffusion model can reduce the discretization errors with negligible computational overhead. Specifically, we partition the timesteps according to the importance weights of quantization functions in different groups, which are optimized by differentiable search algorithms. We also select the optimal timestep for calibration image generation by structural risk minimizing principle in order to enhance the generalization ability in the deployment of quantized diffusion model. Extensive experimental results show that our method outperforms the state-of-the-art post-training quantization of diffusion model by a sizable margin with similar computational cost

Groundwater Recharge and Hydrogeochemical Evolution in Leizhou Peninsula, China

An analysis of the stable isotopes and the major ions in the surface water and groundwater in the Leizhou Peninsula was performed to identify the sources and recharge mechanisms of the groundwater. In this study, 70 water samples were collected from rivers, a lake, and pumping wells. The surface water was considered to have a lower salinity than the groundwater in the region of study. The regression equations for δD and δ18O for the surface water and the groundwater are similar to those for precipitation, indicating meteoric origins. The δD and δ18O levels in the groundwater ranged from −60‰; to −25‰; and −8.6‰; to −2.5‰, respectively, and were lower than the stable isotope levels from the winter and spring precipitation. The groundwater in the southern area was classified as the Ca2+-Mg2+-HCO3--type, whereas the groundwater in the northern area included three types (Na+-Cl−-type, Ca2+-Mg2+-HCO3--type, and Ca2+-Mg2+-Cl−-type), indicating rapid and frequent water-rock exchange in the region. A reasonable conclusion is that the groundwater chemistry is dominated by rock weathering and rainwater of local origin, which are influenced by seawater carried by the Asian monsoon

Image Reconstruction Modeling, Simulation and Experimental Study on Wood Fibrous Paper

Modeling of paper fibrous network is necessary and meaningful. This paper presents a method for modeling and Young’s modulus calculation of wood paper, based on the morphology of fibrous network. Sixteen groups of eucalyptus pulp paper sheets were prepared with different processing parameters. Samples were cut for Scanning Electron Microscope (SEM) images capture, with which structural models of fibrous networks were constructed through digital image processing technology. A reconstructing algorithm is proposed in this paper, which mainly includes “skeleton” extraction and simplification. Two-dimensional line-body fibrous models were established and served as represent volume element models, based on which tensile behavior was simulated in ABAQUS. Young’s modulus of paper sheets was then calculated while tensile test was carried out. Porosity of paper sheets prepared is calculated by hypothetical formula, counted in SEM images and measured by medium saturation method. Porosity of structural models is attained through model-image conversion. Consistency of morphology between reconstructed models and SEM images is assessed. Comparison of properties between paper sheets and models majorly focuses on porosity, Young’s modulus, and their relationship with paper-making process parameters. Patterns of process parameters’ influence on paper’s porosity and elastic modulus are analyzed on the premise that results in simulation and experiments agree to each other