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Xiaohan Sun

Publications and source records attributed to Xiaohan Sun.

7 recordsLinked to original sources

Local Geometric and Transport Properties of Networks that are Generated from Hyperuniform Point Patterns

Hyperuniformity, which is a type of long-range order that is characterized by the suppression of long-range density fluctuations in comparison to the fluctuations in standard disordered systems, has emerged as a powerful concept to aid in the understanding of diverse natural and engineered phenomena. In the present paper, we harness hyperuniform point patterns to generate a class of disordered, spatially embedded networks that are distinct from both perfectly ordered lattices and uniformly random geometric graphs. We refer to these networks as \emph{hyperuniform-point-pattern-induced (HuPPI) networks}, and we compare them to their counterpart \emph{Poisson-point-pattern-induced (PoPPI) networks}. By computing the local geometric and transport properties of HuPPI networks, we demonstrate how hyperuniformity imparts advantages in both transport efficiency and robustness. Specifically, we show that HuPPI networks have systematically smaller total effective resistances, slightly faster random-walk mixing times, and fewer extreme-curvature edges than PoPPI networks. Counterintuitively, we also find that HuPPI networks simultaneously have more negative mean Ollivier--Ricci curvatures and smaller total effective resistances than PoPPI networks, indicating that edges with moderately negative curvatures need not create severe bottlenecks to transport. Moreover, HuPPI networks are consistently more robust under both random edge removals and curvature-based targeted edge removals, maintaining larger connected components for larger fractions of removed edges than their PoPPI counterparts. We also demonstrate that the network-generation method strongly influences these properties and in particular that it often overshadows differences that arise from underlying point patterns.

cond-mat.dis-nn

From Far and Near: Perceptual Evaluation of Crowd Representations Across Levels of Detail

In this paper, we investigate how users perceive the visual quality of crowd character representations at different levels of detail (LoD) and viewing distances. Each representation, including geometric meshes, image-based impostors, Neural Radiance Fields (NeRFs), and 3D Gaussians, exhibits distinct trade-offs between visual fidelity and computational performance. Our qualitative and quantitative results provide insights to guide the design of perceptually optimized LoD strategies for crowd rendering.

cs.CV

CrowdSplat: Exploring Gaussian Splatting For Crowd Rendering

We present CrowdSplat, a novel approach that leverages 3D Gaussian Splatting for real-time, high-quality crowd rendering. Our method utilizes 3D Gaussian functions to represent animated human characters in diverse poses and outfits, which are extracted from monocular videos. We integrate Level of Detail (LoD) rendering to optimize computational efficiency and quality. The CrowdSplat framework consists of two stages: (1) avatar reconstruction and (2) crowd synthesis. The framework is also optimized for GPU memory usage to enhance scalability. Quantitative and qualitative evaluations show that CrowdSplat achieves good levels of rendering quality, memory efficiency, and computational performance. Through the.se experiments, we demonstrate that CrowdSplat is a viable solution for dynamic, realistic crowd simulation in real-time applications.

cs.CV

Evaluating CrowdSplat: Perceived Level of Detail for Gaussian Crowds

Efficient and realistic crowd rendering is an important element of many real-time graphics applications such as Virtual Reality (VR) and games. To this end, Levels of Detail (LOD) avatar representations such as polygonal meshes, image-based impostors, and point clouds have been proposed and evaluated. More recently, 3D Gaussian Splatting has been explored as a potential method for real-time crowd rendering. In this paper, we present a two-alternative forced choice (2AFC) experiment that aims to determine the perceived quality of 3D Gaussian avatars. Three factors were explored: Motion, LOD (i.e., #Gaussians), and the avatar height in Pixels (corresponding to the viewing distance). Participants viewed pairs of animated 3D Gaussian avatars and were tasked with choosing the most detailed one. Our findings can inform the optimization of LOD strategies in Gaussian-based crowd rendering, thereby helping to achieve efficient rendering while maintaining visual quality in real-time applications.

cs.CV

Stimulated Smith-Purcell emission based on bound states in the continuum

Recent advances in the development of bound states in the continuum offer new strategies to tailor electron-wave interaction and hence control the electron-induced emission. In this article we investigate the design to produce stimulated Smith-Purcell emission with a single open grating. This scheme exploits a strong radiative resonance near a bound state in the continuum, enabling staggering enhancements of multiple diffraction orders of a subwavelength grating under evanescent wave incidence. The interaction between a continuous electron beam and the radiative resonant mode bunches electrons, resulting in coherent oscillation and consequently stimulated Smith-Purcell radiation. Using a higher diffraction order for Smith-Purcell radiation, coherent radiation with low-energy electrons is also allowed. The interaction with a radiative mode that has two propagating space harmonics enables stimulated radiation towards two different directions. This work paves the way to a compact coherent radiation source, which may find application in communications, physics, and biology.

physics.app-ph

High-efficiency waveguide couplers via impedance-tunable transformation optics

We design compact waveguide couplers via impedance-tunable transformation optics. By tuning impedance coefficients in the original space, two-dimensional metallic and dielectric waveguide couplers are designed with a high efficiency. Through tuning refractive index simultaneously, we find that the transformation medium inside a designed metallic waveguide coupler can be a reduced-parameter material for coupling waves between waveguides with arbitrary different cross sections and embedded media. In the design of dielectric waveguide couplers, we apply two different schemes: one is that both core region and its cladding region are contained in a transformed space, the other is only core region contained in the transformed space. The former has a very high efficiency near 100%; the latter is less efficient with a very small decline which can be a simplified candidate in the design of near-perfect dielectric waveguide couplers. The transformation medium for dielectric waveguide couplers can also be reduced-parameter material by selecting appropriate refractive index coefficients. Two-dimensional numerical simulations confirm our design with good performances.

physics.optics

Reflectionless design of optical elements using impedance-tunable coordinate transformation

We report a new strategy to remove the reflections resulted from the finite embedded transformation-optical design by proposing an impedance-tunable coordinate transformation, on which the functions of impedance coefficients can be derived in the original space without changing the refractive index. Based on the new approach, two-dimensional (2D) reflectionless beam compressors/expanders, bends, shifters and splitters are designed using the modified anisotropic medium. It is found that the reflections can be removed in magnetic response materials for TE polarization or dielectric response materials for TM polarization. The numerical simulations confirm that various reflectionless optical elements can be realized in the pure transformation optics. The impedance-tunable coordinate transformation can be generalized to three-dimensional (3D) cases and be applied to other transformation-optical designs.

physics.optics