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Ruijie Hao

Publications and source records attributed to Ruijie Hao.

2 recordsLinked to original sources

Flow-based Policy With Distributional Reinforcement Learning in Trajectory Optimization

Reinforcement Learning (RL) has proven highly effective in addressing complex control and decision-making tasks. However, in most traditional RL algorithms, the policy is typically parameterized as a diagonal Gaussian distribution, which constrains the policy from capturing multimodal distributions, making it difficult to cover the full range of optimal solutions in multi-solution problems, and the return is reduced to a mean value, losing its multimodal nature and thus providing insufficient guidance for policy updates. In response to these problems, we propose a RL algorithm termed flow-based policy with distributional RL (FP-DRL). This algorithm models the policy using flow matching, which offers both computational efficiency and the capacity to fit complex distributions. Additionally, it employs a distributional RL approach to model and optimize the entire return distribution, thereby more effectively guiding multimodal policy updates and improving agent performance. Experimental trails on MuJoCo benchmarks demonstrate that the FP-DRL algorithm achieves state-of-the-art (SOTA) performance in most MuJoCo control tasks while exhibiting superior representation capability of the flow policy.

cs.LG

Mechanisms of Dual-Band Emission in Sb-Doped Rare-Earth Phosphates Revealed

The Sb$^{3+}$ ion has garnered significant interest due to its effectiveness in boosting the optical properties of host materials. Among the interesting phenomena is the commonly observed dual-band emission, which has often been interpreted by adopting the phenomenological model that explains the dual-band emission (``ultraviolet band'' and ``visible band'') in Sb-doped $L$PO$_{4}$ ($L$ = Sc, Y, Lu). However, the model for Sb-doped $L$PO$_{4}$ series itself has not been well understood theoretically. In this work, we employ first-principles calculations combined with group-theory analysis to clarify the underlying physical mechanism behind dual-band emission in Sb-doped $L$PO$_{4}$ series. We demonstrate that the dual-band arises from two excited-state equilibrium structures, one exhibits a relatively small distortion with respect to the ground-state equilibrium structure, while the other displays a significantly larger distortion, characteristic of an ``off-center'' configuration. The deviations from the ground-state configuration are dominated by two distinct vibrational modes, $b_2$ and $e$ modes, involving the Jahn-Teller effect and the pseudo Jahn-Teller effect, respectively. Furthermore, charge transition levels and energy barriers calculated using the climbing image nudged elastic band (CI-NEB) method have aided in understanding the relaxation between the two excited-state configurations and the property changes across the Sc, Y, and Lu series. These insights provide a basis for understanding the exotic properties of Sb$^{3+}$ in other hosts and may facilitate the design of optical materials in a broader range of systems involving Sb$^{3+}$ ions.

cond-mat.mtrl-sci