Repository Community:

An efficient reinforcement learning action strategy for topology optimization: application to muffler design

2026-01-31T15:00:00Z

Title: An efficient reinforcement learning action strategy for topology optimization: application to muffler design Author(s): Oh, Kee Seung; Kim, Yoon Young; Chung, Hayoung; Oh, Joo Hwan Abstract: Despite the growing interest in applying reinforcement learning (RL) to design optimization, its high computational cost limits its applicability to problems involving expensive function evaluations. In this study, we propose an efficient RL action strategy specifically designed for acoustic topology optimization. The key idea is to assign action values (Q-values) to each element individually and select material-filled elements in descending order of their Q-values until the target volume fraction is met, instead of evaluating Q-values for complete combinations of elements that satisfy the volume constraint. This formulation decouples the learning complexity from the combinatorial explosion of candidate layouts, making the training of the Q-value-estimating neural network more efficient and thus the RL-based approach is more suitable for topology optimization problems requiring fine meshes. As a representative application, we consider the design of a muffler's internal layout to maximize sound transmission loss-a problem where conventional gradient-based methods often fail to achieve near-global optimal solutions. By integrating the proposed method with finite element simulations and a reward function shaped by transmission loss at one or more target frequencies, the RL agent learns policies that directly determine the material distribution for single- or multi-frequency objectives. The resulting muffler designs, based on a two-dimensional finite element model, exhibit near-global optimal performance and outperform those generated by conventional gradient-based methods. The advantages of the proposed approach over standard RL-based topology optimization methods are also clearly demonstrated.

A nanoporous Ni(OH)2 interlinked Co3O4 heterojunction: a novel approach to chromium(vi) detection

2026-03-31T15:00:00Z

Title: A nanoporous Ni(OH)2 interlinked Co3O4 heterojunction: a novel approach to chromium(vi) detection Author(s): Darabdhara, Gitashree; Baruah, Manash J.; Saikia, Eramoni; Gohain, Shivanee Borpatra; Bayan, Rajarshi; Kemprai, Rahul; Gogoi, Dipankoj; Park, Young-Bin; Das, Biraj; Sharma, Mukesh Abstract: The present study broadly explores the synthesis, structural characteristics, and electrochemical performance of a nanoporous Ni(OH)2/Co3O4 heterojunction engineered for efficient enzymatic sensing of hexavalent chromium Cr(vi). The synthesized heterostructure consists of a porous Ni(OH)2/Co3O4 matrix (nanopores, with dimensions approximately ranging from 6 to 10 nm) intimately coupled with evenly dispersed Co3O4 nanocrystals, forming a well-integrated interface that enables strong synergistic redox coupling and rapid electron transport across the junction. The nanoporous framework significantly increases the electrochemically active surface area offering abundant catalytically active sites and facilitates improved transport of electrolytes. Simultaneously, the heterojunction ensures continuous conductive pathways, thereby minimizing charge-transfer resistance and enhancing overall electron mobility. The combined structural and electronic advantages translate into markedly improved sensitivity, catalytic activity, and operational stability for enzymatic Cr(vi) detection with a limit of detection (LOD) of 39 nM. Overall, the results underscore the significant role of heterojunction engineering in enhancing the performance of metal hydroxide-oxide materials for advanced environmental sensing applications.

Partial Bodyweight-Supported Squats Elicit Eccentric Contraction of the Thigh Muscles

2026-03-31T15:00:00Z

Title: Partial Bodyweight-Supported Squats Elicit Eccentric Contraction of the Thigh Muscles Author(s): Seo, Eunyoung; Kim, Olga V.; Kim, Chansu; Gemechu, Duguma Teshome; Kim, Keun-Tae; Kang, Sang Hoon; Lee, Song Joo Abstract: Purpose The study aimed to investigate how different levels of supporting forces during the squat exercise at a self-selected speed, along with different knee angles, affect fascicle length, pennation angle, and muscle activation for healthy young individuals. Methods Twelve healthy subjects participated in the study to measure fascicle length and pennation angle of the vastus lateralis (VL) at 0°, 60°, and 80° knee flexion. Leg muscle activities and the ground reaction force (GRF) were measured during squats using a squat aid machine with three supporting force levels. Results VL fascicle length and pennation angle at 0° knee flexion were significantly lower than at 60° and 80° flexion across all force levels (p < 0.05). Moreover, the leg muscles’ mean maximum electromyography and the three-direction normalized GRFs measured on both the squat aid machine and the subjects’ feet showed no significant variations across supporting forces. Conclusion Our findings indicate that squat exercise has the potential to induce eccentric contraction by increasing fascicle length and muscle activation and decreasing pennation angle, regardless of the supporting force level. Therefore, a squat aid machine for squats is recommended as a safe and effective approach to enhance muscle force through eccentric contractions.

Compensatory Kinematic Analysis in Various Directions After Chronic Stroke

2026-03-31T15:00:00Z

Title: Compensatory Kinematic Analysis in Various Directions After Chronic Stroke Author(s): Lee, Aenon; Casaña, José; Kang, Sang Hoon; Cruz-Montecinos, Carlos; López-Bueno, Rubén; Suso-Martí, Luis; Calatayud, Joaquín