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Adaptability to unstructured objects and the avoidance of target damage are critical challenges for flexible grippers in fruit-picking robots. Most existing flexible grippers have many problems in terms of control complexity, stability and cost. This paper proposes a flexible finger design method that considers contact behavior. The new approach incorporates topological design of contact targets and introduces contact stress constraints to directly obtain a flexible finger structure with low contact stress and good adaptability. The study explores the effects of design parameters, including virtual spring stiffness, volume fraction, design domain size, and discretization, on the outcomes of the flexible finger topology optimization. Two flexible finger structures were selected for comparative analysis. The experimental results verified the effectiveness of the design method and the maximum contact stress was reduced by about 70%. An adaptive two-finger gripper was developed. This design allows the gripper to achieve damage-free grasping without additional sensors and control systems. The adaptive and contact performances of the grippers with different driving modes were analyzed. Practical grasping tests were also performed, including evaluation of adaptive performance, stability, and maximum grasping weight. The results indicate that gripper 2 with flexible finger 2 excelled in contact stress and adaptive wrapping, making it well-suited for grasping unstructured and fragile objects. This paper provides valuable insights for the design and application of flexible grippers for picking robots, offering a promising solution to enhance adaptability while minimizing target damage. [ABSTRACT FROM AUTHOR]

As a considerable number of Chinese students suffer from test anxiety, we aimed to find a solution to test anxiety in Chinese students. We conducted an empirical study, in which we replicated the experiment in Min et al. (2022)’s study [1], to examine predictors of test anxiety and whether studying in North America could alleviate test anxiety with N = 85 participants. As predicted, Chinese students studying in North America had less test anxiety than studying in other countries. In addition, older Chinese students were more likely to have high test anxiety.

Axially loaded beam-like structures, such as beam segments and piers of cable-stayed bridges, are widely used in civil engineering. This paper presents a study on the linear and nonlinear vibration of an axially loaded Timoshenko beam with elastic supports. The governing equations of the system are derived using Timoshenko beam theory and von Kármán geometric nonlinearity within the framework of Hamilton's principle. A transition parameter is introduced to describe the direction of the axial internal force during the beam's deformation. Galerkin's method is employed to reduce the nonlinear partial differential equations, from which linear solutions can be obtained. Nonlinear discretized equations are solved using the incremental harmonic balance (IHB) method. Frequency-response curves of the beam system are tracked by pseudo arc-length continuation, and Floquet's theory is used to determine the system's stability. Numerical examples are presented to validate the proposed solutions, comparing the results with the literature and the Runge-Kutta method. The effects of the transition parameter, elastic support's stiffness, and supported position are investigated for both linear and nonlinear vibration of the axially loaded Timoshenko beam. Of particular interest is the significance of the transition parameter, especially for a Timoshenko beam subjected to extreme axial compression with a small slenderness ratio. The present analysis provides critical insights into the design and analysis of such axially loaded structures in various civil engineering applications. [ABSTRACT FROM AUTHOR]

The rapidly increasing demand for heavy vehicles in the transportation sector has led to more severe road damage and significantly higher road maintenance costs. Investigation of active suspension system incorporating vehicle–road interaction (VRI) can provide effective means to reduce the road damage and improve the ride comfort of vehicles. In this paper, an active vehicle suspension controller based on the strongly stable and robust linear–quadratic regulator (LQR) principle is developed for the time-varying VRI system. The coupled system is modeled by a quarter-car traveling on the road modeled by an Euler–Bernoulli beam resting on a viscoelastic foundation. Two types of road irregularities, deterministic sine wave and random, are considered in the numerical studies. A time-frozen technique, by which the linear time-varying system is converted to a time sequence of time-invariant systems, is applied to solve for the coupled responses. Three variables, the dynamic tire load, vehicle body acceleration, and suspension relative displacement, are used to assess the effectiveness of the LQR-based controller in comparison to the passive suspension system. The performance of the active control is investigated for different vehicle speeds, vehicle loads, and road profiles. Numerical studies show that the controller can effectively reduce the road damage and improve the ride comfort, with a slight increase in the suspension relative displacement. This work lays a useful foundation in the problem formulation and system parameter influences for future vehicle suspension design and road damage mitigation including VRI. [ABSTRACT FROM AUTHOR]

We successfully modulate the spectral shift of ultralong room temperature phosphorescence by extending the molecular conjugation of phosphorescence units and colorful afterglow can be achieved from the phosphorescence units. Four phosphorescence units (BCz-2, BCz-1, PyCz and BrPyCz) were comprehensively compared in this work. Doping these phosphorescence units into PMMA, we found that their phosphorescence bands were red shifted sequentially from 490 nm and 550 nm to 627 nm and 629 nm. It is true that the ultralong phosphorescence of phosphorescence units in toluene solution at 77 K and in a polymer film is assigned to their monomer phosphorescence (intrinsic T1 decay). Compared with BCz-2 and BCz-1, PyCz and BrPyCz give out red afterglow because pyrene has the largest molecular conjugation. As PyCz@PMMA emits weak red afterglow at room temperature, we propose two methods to enhance room temperature red afterglow of PyCz, including using of rigid polymer PVA and incorporation of a bromine atom. Intense red afterglow can be observed for PyCz@PVA at room temperature because the rigid environment of PVA greatly suppresses the nonradiative relaxation pathways of triplet excitons. Interestingly, bromination on the benzene ring of PyCz (namely BrPyCz) significantly promotes intersystem crossing (ISC) efficiency and red afterglow of BrPyCz@PMMA is further boosted at room temperature but hardly alters the T1 energy level so their ultralong phosphorescence band positions are kept unchanged. TD-DFT results verify that extension of molecular conjugation reduces energy levels of T1 (2.61 eV, 2.32 eV, 2.03 eV and 2.03 eV) and directly results in a red shift of monomer phosphorescence of BCz-2, BCz-1 and (Br)PyCz. To our best knowledge, this study may be a significant work in precisely tuning the organic phosphorescence color of phosphorescence units and may give some suggestions for development of organic phosphorescence. [ABSTRACT FROM AUTHOR]