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  1. Abstract

    Laser powder-bed fusion (L-PBF) additive manufacturing presents ample opportunities to produce net-shape parts. The complex laser-powder interactions result in high cooling rates that often lead to unique microstructures and excellent mechanical properties. Refractory high-entropy alloys show great potential for high-temperature applications but are notoriously difficult to process by additive processes due to their sensitivity to cracking and defects, such as un-melted powders and keyholes. Here, we present a method based on a normalized model-based processing diagram to achieve a nearly defect-free TiZrNbTa alloy via in-situ alloying of elemental powders during L-PBF. Compared to its as-cast counterpart, the as-printed TiZrNbTa exhibits comparable mechanical properties but with enhanced elastic isotropy. This method has good potential for other refractory alloy systems based on in-situ alloying of elemental powders, thereby creating new opportunities to rapidly expand the collection of processable refractory materials via L-PBF.

     
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    Free, publicly-accessible full text available December 1, 2025
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  5. Overcoming challenges and transitioning from school to work is particularly problematic for individuals who are deaf or hard of hearing, presenting significant issues for both the labor market and vocational training institutions. Due to the lack of research addressing the career maturity and distinctive obstacles faced by this population, this paper endeavors to investigate performance disparities within the machining field. The specific focus is on assessing whether hearing loss may impact students' machining performance. Considering the essential human capabilities for perception in machining, especially in industrial settings, encompass a range of faculties including visualization, hearing, and tactile senses. Thus, addressing concerns related to accommodating individuals with disabilities is important, prompting inquiries into optimizing training programs and quantifying potential disparities in learning or schooling outcomes, behavioral patterns, and overall performance in future careers. The conducted studies involved multiple participants, including hearing, deaf, and hard-of-hearing students with various machining training backgrounds. The investigation will delve into data concerning the qualities of manual machining outputs and the subject’s self-rating feedback. The outcomes from this study are expected not only to allow to obtain more insights into human behavior in machining operations, but also to identify key differences between machinist trainees who exhibit no underlying hearing problems and ones who are deaf/hard of hearing. The findings of this work provide valuable takeaways concerning machinists with hearing loss, revealing little to no effect of hearing loss on trainee performance, alleviating concerns about potential performance weaknesses. The outcomes from this study have shown that trainee experience seems to relate directly to machining proficiency, regardless of hearing loss. 
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    Free, publicly-accessible full text available June 23, 2025
  6. This letter aims to develop a new learning-based flocking control framework that ensures inter-agent free collision. To achieve this goal, a leader-following flocking control based on a deep Q-network (DQN) is designed to comply with the three Reynolds’ flocking rules. However, due to the inherent conflict between the navigation attraction and inter-agent repulsion in the leader-following flocking scenario, there exists a potential risk of inter-agent collisions, particularly with limited training episodes. Failure to prevent such collision not only caused penalties in training but could lead to damage when the proposed control framework is executed on hardware. To address this issue, a control barrier function (CBF) is incorporated into the learning strategy to ensure collision-free flocking behavior. Moreover, the proposed learning framework with CBF enhances training efficiency and reduces the complexity of reward function design and tuning. Simulation results demonstrate the effectiveness and benefits of the proposed learning methodology and control framework. 
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  7. Flocking control for multi-agent automated vehicles has attracted more research interest recently. However, one significant challenge is that the common use of point-shaped virtual leaders giving uniform navigations is unsuitable for vehicle motions with varying relative positions and orientations on multi-lane roads, particularly on curved sections. Considering the practical movements of multi-agent ground vehicles, this paper proposes a novel type of polyline-shaped leader(s) that aligns with multi-lane roads. Specifically, the polyline-shaped leader is composed of line segments that consider road curvatures, different lanes, and the flocking lattice configuration. Moreover, an artificial flow guidance method is applied to provide the direction of velocity references to ensure vehicles move within their respective lanes during the formed flocking. Simulation results demonstrate that the proposed approach can successfully regulate vehicles to drive in their lanes in coordinated motion, which gives fewer structural deviations on curved roads compared to the case with the point-shaped leader. 
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  8. Free, publicly-accessible full text available May 1, 2025
  9. Although many methods of ground vehicle dynamics control have been widely studied, their robustness against undesirable oscillatory coupling behaviors of planar and roll dynamics is not fully explored. To address this issue, a hierarchical multiple-input-multiple-output (MIMO) decoupling controller is proposed in this study. Based on the hierarchical control configuration, the coupled vehicle roll and planar dynamics are resolved in the high-level control, and a control allocation is utilized for tracking control in the low-level control. The decoupled internal dynamics and nominal stability are then analyzed and proved. Moreover, by using the vehicle yaw rate and load transfer ratio, a control trigger with dynamic weighting is designed to guarantee the feasibility of the MIMO decoupling control and smooth control efforts. Through the co-simulation between CarSim and MATLAB/Simulink, the feasibility and effectiveness of the proposed controller are verified. 
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  10. Free, publicly-accessible full text available July 1, 2025