Minimum-time optimal control of robotic manipulators based on Hamel’s integrators

Meccanica - In this paper, we develop a framework of time optimization path planning for robotic manipulators surrounded by static obstacles. Our approach is based on the recursive dynamics method...     

Effect of Y2O3 on microstructural characteristics and wear resistance of cobalt‐based composite coatings produced on TA15 titanium alloy surface by laser cladding

The effects of Y₂O₃ on the microstructure, phase composition of the coatings, microhardness and wear resistance of cobalt‐based composite coatings prepared by laser cladding were investigated. The TA15 titanium alloy was selected as substrate which the cobalt‐based composite powder with different content of Y₂O₃ was cladded on. The microstructure of the coatings was observed by scanning electron microscope (SEM) and metallurgical microscope. The phase structure of the coatings was determined by X‐ray diffraction (XRD), and the microhardness and wear resistance of the coatings were measured by hardness tester and wear testing machine. The results show that the rare earth oxide Y₂O₃ can refine and purify the microstructure of the coatings, reduce the porosities and cracks and improve compactness of the coatings. Moreover the addition of Y₂O₃ improves the microhardness of the coatings and reduces the friction coefficient, thus improving the wear property of the coatings. And the wear resistance of the coating with Y₂O₃ has improved about 50 times; the highest value of microhardness in the coating is HV1181.1. And 0.8 wt% content of Y₂O₃ in the coating is the best choice for improving the microhardness and wear resistance of the coating. It is feasible to improve the microstructure and tribological properties of laser cladding coatings by adding of Y₂O₃. Copyright © 2014 John Wiley & Sons, Ltd.     

次临界能源包层严重事故缓解系统

针对中国工程物理研究院混合堆次临界能源包层,提出了一种新型的严重事故缓解系统——工程通道注水系统,采用通道注水的方法直接导出燃料区衰变热,同时与非能动安全壳冷却系统结合,实现燃料区非能动长期冷却的建立,阻止燃料区熔化进程发展,保证次临界能源包层的完整性。在保守假设条件下,当燃料区温度达到1220℃时,工程通道注水系统投入运行即可完成严重事故缓解功能。     

医用物理学课程翻转课堂的教学改革与实践

在2018级临床医学专业医用物理学课程中进行翻转课堂试点教学,对学生考试成绩进行了统计与分析,在学时减半的情况下,进行翻转课堂教学班级的平均分略高于传统教学班级的平均分.翻转课堂为先进的教学方法,主要培养学生自主学习能力,调动学生学习的积极性,可以大范围推广使用.     

Strain Hardening and Strain Softening of Reversibly Cross-linked Supramolecular Polymer Networks

The large amplitude oscillatory shear behavior of metallo-supramolecular polymer networks formed by adding bis-Pd(II) cross-linkers to poly(4-vinylpyridine) (PVP) in dimethyl sulfoxide (DMSO) solution is reported. The influence of scanning frequency, dissociation rate of cross-linkers, concentration of cross-linkers, and concentration of PVP solution on the large amplitude oscillatory shear behavior is explored. In semidilute unentangled PVP solutions, above a critical scanning frequency, strain hardening of both storage moduli and loss moduli is observed. In the semidilute entangled regime of PVP solution, however, strain softening is observed for samples with faster cross-linkers (k(d) ～ 1450 s(-1)), whereas strain hardening is observed for samples with slower cross-linkers (k(d) ～ 17 s(-1)). The mechanism of strain hardening is attributed primarily to a strain-induced increase in the number of elastically active chains, with possible contributions from non-Gaussian stretching of polymer chains at strains approaching network fracture. The divergent strain softening of samples with faster cross-linkers in semidilute entangled PVP solutions, relative to the strain hardening of samples with slower cross-linkers, is consistent with observed shear thinning/shear thickening behavior reported previously and is attributed to the fact that the average time that a cross-linker remains detached is too short to permit the local relaxation of polymer chain segments that is necessary for a net conversion of elastically inactive to elastically active cross-linkers. These and other observations paint a picture in which strain softening and shear thinning arise from the same set of molecular mechanisms, conceptually uniting the two nonlinear responses for this system.     

不同色浆质量分数的水性聚氨酯涂料对聚氯乙烯表皮低温爆破性能的影响

本文制备了一系列不同色浆质量分数的水性聚氨酯涂料,并将其喷涂在汽车仪表板聚氯乙烯(PVC)表皮的背面形成复合材料。 用旋转流变仪表征了涂料的粘度以评价其喷涂性能;用差示扫描量热仪表征了材料的玻璃化转变温度(T_g);利用万能材料试验机表征了材料在-30 ℃条件下的拉伸性能及抗撕裂性能;用动态热机械分析仪表征了材料的损耗比随温度的变化。 结果表明:不同色浆质量分数的涂料都能喷涂,含有涂层材料PVC表皮在-30 ℃低温爆破性能与涂层材料的T_g、低温拉伸性能、抗撕裂性能的关系并不大,而与涂层材料的阻尼性能直接相关。 材料的阻尼性能越好,其低温爆破性能越好。     

求解全局最优问题的多重点样本水平值估计的相对熵算法

研究有界闭箱约束下的全局最优化问题,利用相对熵及广义方差函数方程的最大根与全局最小值之间的等价关系,设计求解全局最优值的积分型水平值估计算法.对采用重点样本采样技巧产生的函数值按一定规则进行聚类,从而在各聚类中产生的若干新重点样本,结合相对熵算法,构造出多重点样本进行全局搜索的新算法.该算法的优点在于每次迭代选用当前较好的函数值信息,以达到随机搜索到更好的函数值信息.同时多重点样本可有利挖掘出更好的全局信息.一系列的数值实验表明该算法是非常有效的.     

Luminescent properties and the morphology of SrMoO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> powders synthesized <Emphasis Type="Italic">via</Emphasis> combining sol-gel and solid-state route

SrMoO₄:Eu³⁺ red phosphors were prepared by combining sol-gel and solid-state route. Citric acid and ethylenediaminetetraacetic acid (EDTA), employed as the chelating agents, were added to the aqueous solutions of metal nitrates. X-ray diffraction (XRD) and photoluminescent spectra techniques (PL) were used to characterize the resultant powders. The results indicated the obtained SrMoO₄:Eu³⁺ phosphors were fine powders with a particle size of 50 nm. The effects of synthesizing conditions were also investigated and optimized, which included the synthesis temperature and the activator concentration on the luminescent intensity. Compared with SrMoO₄:Eu³⁺ phosphors prepared by Solid-state reaction SrMoO₄:Eu³⁺ phosphors prepared by combining sol-gel and solid-state route showed appropriate particle size and a higher emission intensity.     

Effects of noise on the outer synchronization of two unidirectionally coupled complex dynamical networks

We study the effect of noise on the outer synchronization between two unidirectionally coupled complex networks and find analytically that outer synchronization could be achieved via white-noise-based coupling. It is also demonstrated that, if two networks have both conventional linear coupling and white-noise-based coupling, the critical deterministic coupling strength between two complex networks for synchronization transition decreases with an increase in the intensity of noise. We provide numerical results to illustrate the feasibility and effectiveness of the theoretical results.