Theoretical and experimental investigation of the resonance responses and chaotic dynamics of a bistable laminated composite shell in the dynamic snap-through mode

The dynamic model of a bistable laminated composite shell simply supported by four corners is further developed to investigate the resonance responses and chaotic behaviors.The existence of the 1:1 resonance relationship between two order vibration modes of the system is verified.The resonance response of this class of bistable structures in the dynamic snap-through mode is investigated,and the four-dimensional(4D)nonlinear modulation equations are derived based on the 1:1 internal resonance relationship by means of the multiple scales method.The Hopf bifurcation and instability interval of the amplitude frequency and force amplitude curves are analyzed.The discussion focuses on investigating the effects of key parameters,e.g.,excitation amplitude,damping coefficient,and detuning parameters,on the resonance responses.The numerical simulations show that the foundation excitation and the degree of coupling between the vibration modes exert a substantial effect on the chaotic dynamics of the system.Furthermore,the significant motions under particular excitation conditions are visualized by bifurcation diagrams,time histories,phase portraits,three-dimensional(3D)phase portraits,and Poincare maps.Finally,the vibration experiment is carried out to study the amplitude frequency responses and bifurcation characteristics for the bistable laminated composite shell,yielding results that are qualitatively consistent with the theoretical results.

Vacancy healing for stable perovskite solar cells via bifunctional potassium tartrate

Perovskite solar cell has gained widespread attention as a promising technology for renewable energy.However, their commercial viability has been hampered by their long-term stability and potential Pb leakage. Herein, we demonstrate a bifunctional passivator of the potassium tartrate(PT) to address both challenges. PT minimizes the Pb leakage in perovskites and also heals cationic vacancy defects, resulting in improved device performance and stability. Benefiting from PT modification, the power conversion efficiency(PCE) is improved to 23.26% and the Pb leakage in unencapsulated films is significantly reduced to 9.79 ppm. Furthermore, the corresponding device exhibits no significant decay in PCE after tracking at the maximum power point(MPP) for 2000 h under illumination(LED source, 100 mW cm^(-2)).

钠离子电池工程化——机遇与挑战

当前,在应对全球能源枯竭与环境恶化之际,可持续且环境友好的可再生能源正迎来重要的发展机遇。以二次电池为代表的电化学储能技术(EES),可实现绿色新能源安全且经济有效的存储和转化,被视为平抑可再生能源间歇性并实现稳定并网输入的最佳解决方案。钠离子电池(SIB),受益于钠资源的丰富性及低成本,是下一代大规模电化学存储系统最具应用前景的选择之一。本文详细讨论了锂离子电池(LIB)和钠离子电池在不同应用场景下的主要区别,并描述了当前对钠离子电池的理解。通过比较锂离子电池、铅酸电池(LAB)和钠离子电池之间的技术发展情况,进一步揭示钠离子电池的优势。本文以基于钠离子电池技术所取得的商业化成就为文章亮点,重点介绍了五家钠离子电池企业和相应的钠离子电池产品,以及各自的钠离子电池化学与技术。最后,讨论了下一代钠离子电池商业化的前景与挑战。

康复机器人与智能辅助系统的研究进展

我国正面临日益严重的老龄化问题和数量庞大的残疾人群,康复机器人与智能辅助系统的研究开发和应用有望为解决养老、失能辅助和康复问题提供部分技术手段.康复机器人与智能辅助系统涉及医学、信息、机械、电子、材料、力学等多个学科领域,其研究与开发也面临诸多挑战和困难,本文从"康复机器人及多种康复训练模式"、"智能辅助系统与生机电技术"、"康复与辅助相关的多模态传感与控制方法"、"外骨骼和可穿戴系统、智能假肢与人机安全性"等方面介绍和讨论康复机器人和智能辅助系统的问题和研究进展,以期为未来康复机器人和智能辅助系统的研究与开发提供些许借鉴.

面向人机融合的智能动力下肢假肢研究现状与挑战

智能动力下肢假肢在残疾人生活中起着越来越重要的作用.解决人-智能假肢-环境融合中的关键科学问题是实现假肢穿戴者安全、流畅运动的必要条件.本文针对此问题,综述了面向人机融合的智能动力下肢假肢研究,包括智能动力下肢假肢的仿生结构和控制方法、人体运动意图识别、复杂环境下的人-智能假肢融合、以及用于下肢假肢的感知替代和反馈,深入探讨了智能动力下肢假肢人机融合研究中所面临的挑战和问题,最后,本文对该领域的未来发展方向进行了展望和总结.

水下多级微结构液气界面的稳定性和可恢复性研究

微结构表面浸没水下所形成的液气界面对减阻等应用具有重要意义.液气界面的稳定存在是结构功能表面发挥作用的前提.因此,如何增强液气界面的稳定性以抵抗浸润转变过程,以及在液气界面失稳之后,如何实现去浸润过程以提高液气界面的可恢复性能,均具有重要的科学研究意义和实际应用价值,也是国内外研究关注的热点问题.本文针对具有多级微结构的固体表面,研究其在浸没水下后形成的液气界面的稳定性和可恢复性.通过激光扫描共聚焦显微镜对不同压强下液气界面的失稳过程和降压后的恢复过程进行原位观察,实验结果和基于最小自由能原理的理论分析相吻合.本文揭示了多级微结构抵抗浸润转变以及提高液气界面可恢复性能的机理:侧壁上的次级结构(纳米颗粒、多层翅片)通过增加液气界面在壁面的表观前进接触角增强了液气界面的稳定性;底面的次级结构(纳米颗粒和封闭式次级结构)可以维持纳米尺寸气核的存在,有利于水中溶解气体向微结构内扩散,最终使液气界面恢复.本文的研究为通过设计多级微结构表面来获得具有较强稳定性和可恢复性的液气界面提供了思路.

一种从离散模拟到连续介质弹性模拟的过渡方法

提出了一种从离散分子动力学模拟(MD)到连续介质弹性有限元计算分析(FEA)的过渡方法,简称MD-FEA方法.首先通过MD计算获得晶体材料原子的移动位置,然后根据晶体结构的周期性特征构造连续介质假设下的有限单元变形模型,进一步结合材料的力学行为本构关系获得应变和应力场.为了检验MD-FEA方法的有效性,将该方法应用于详细分析Al-Ni软硬组合两相材料纳米柱体的拉伸变形问题和基底材料为Al球形压头材料为金刚石的纳米压痕问题.采用MD-FEA方法获得了上述两种问题的应力-应变场,并将计算结果分别与传统MD方法中通过变形梯度计算的原子应变以及原子的位力应力进行了比较,详细讨论了用MDFEA方法计算的应力-应变场与传统MD原子应变和位力应力的区别,并对MD-FEA方法的有效性及其相较于传统MD方法所具有的优势进行了探讨.结论显示, MD-FEA方法与传统MD方法在应力-应变变化平缓的区域得到的结果接近,但在变化剧烈的区域以及材料的表/界面区域, MD-FEA方法能够得到更加精确的结果.同时, MD-FEA方法避免了传统MD方法中,需要人为选取截断半径以及加权函数所导致的误差.另外,当应变较大时, MD-FEA方法计算的小应变与传统MD方法计算的格林应变存在一定差异,因此, MD-FEA方法更适合应变较小的情形.

维度调控策略提升铂基纳米晶氧还原催化研究进展（英文）

燃料电池技术的商业化进程主要受制于其阴极动力学缓慢的氧还原反应(ORR)所需的高铂量电催化剂,因此急需开发更高活性的电催化剂。过去十年里,人们在提高铂基催化剂ORR活性的研究取得了极大进展。本文概述了通过结构调控提升铂基纳米晶氧还原电催化性能的最新进展,依据纳米晶的空间维度展开讨论,同时列举各类电催化材料的优缺点。基于理论和实验结果,本文重点讨论铂基纳米晶应用于氧还原电催化的构效关系,以及其对下一代电催化材料结构设计方面的潜在指导意义。最后,我们对此领域未来的研究方向做了展望。

具有优异甲醇耐受性的Rh掺杂Pd Cu有序金属间化合物纳米粒子增强氧还原电催化

由于阴极催化剂有限的活性和耐久性以及甲醇渗透到阴极所导致的催化剂中毒问题,直接甲醇燃料电池(DMFCs)仍面临严峻的挑战。本文报道了一类新型的具有有序金属间结构的Rh掺杂PdCu纳米颗粒用于提高阴极氧还原反应(ORR)的活性、耐久性和甲醇耐受性。通过结合Rh原子掺杂以及有序金属间结构两者的优点,在碱性条件下,Rh掺杂Pd Cu金属间化合物催化剂在0.9 V电位下对氧还原质量活性相比商业Pt/C提高7.4倍。这种独特的结构还使其表现出出色的ORR耐久性,在连续20000个循环后的半波电位和质量活性几乎不变。此外,在苛刻的中毒环境下,仍可以保持Rh掺杂PdCu金属间化合物电催化剂高的氧还原催化活性。

提升基于钙钛矿的叠层太阳能电池稳定性的策略

近年来,基于有机无机金属卤化物钙钛矿的叠层太阳能电池引起了巨大的研究热潮。但是,不稳定性限制了其商业化。适用于顶部子电池的宽带隙钙钛矿存在相不稳定性,而适用于底部子电池的窄带隙钙钛矿存在空气不稳定性。首先,我们总结了提升基于钙钛矿的叠层太阳能电池稳定性的最新进展。然后,我们系统地分析了导致宽带隙钙钛矿的相不稳定性和窄带隙钙钛矿的空气不稳定性的原因,并为解决这些不稳定性问题总结了合理的策略。我们也简短地总结了中间层带来的不稳定性以及相应的解决措施。最后,我们回顾了钙钛矿材料固有的本征不稳定性和相应的改进方法,这对于将来发展更稳定的叠层太阳能电池中是必要的。我们认为随着对钙钛矿子电池的理解越来越深入,基于钙钛矿的叠层电池特别是钙钛矿/硅叠层电池将会迅速商业化。

湍流预混燃烧中的非各向同性速度统计与涡面结构

尽管统计局部各向同性假设已广泛用于湍流理论和建模,但湍流预混火焰的局部释热会令附近流体密度与黏性发生突变,进而使湍流流场呈现非各向同性统计。我们将涡面场方法推广于湍流预混燃烧,用于表征非各向同性涡面结构。发现未燃侧的小尺度缠绕扭曲涡管在火焰区受到热膨胀的拉伸作用,在已燃侧融合为大尺度块状结构。结合拟涡能输运方程和雷诺应力Lumley三角形,分析发现从未燃侧到已燃侧速度场非各向同性程度逐步增加,且涡面几何结构的变化与速度场局部非各向同性统计高度相关。

Highly Reversible Li–Se Batteries with Ultra-Lightweight N,S-Codoped Graphene Blocking Layer

The desire for practical utilization of rechargeable lithium batteries with high energy density has motivated attempts to develop new electrode materials and battery systems. Here, without additional binders we present a simple vacuum filtration method to synthesize nitrogen and sulfur codoped graphene(N,S-G) blocking layer, which is ultra-lightweight, conductive, and free standing. When the N,S-G membrane was inserted between the catholyte and separator, the lithium–selenium(Li–Se)batteries exhibited a high reversible discharge capacity of 330.7 mAh g^(-1) at 1 C(1 C = 675 mA g^(-1)) after 500 cycles and high rate performance(over 310 mAh g^(-1) at 4 C) even at an active material loading as high as ～5 mg cm^(-2). This excellent performance can be ascribed to homogenous dispersion of the liquid active material in the electrode, good Li^+-ion conductivity, fast electronic transport in the conductive graphene framework, andstrong chemical confinement of polyselenides by nitrogen and sulfur atoms. More importantly, it is a promising strategy for enhancing the energy density of Li–Se batteries by using the catholyte with a lightweight heteroatom doping carbon matrix.

3D star-like atypical hybrid MOF derived single-atom catalyst boosts oxygen reduction catalysis

Developing high-efficiency,stable and non-precious electrocatalysts for oxygen reduction reaction(ORR)is highly important for energy conversion and storage.Single atom catalysts(SACs)show good potential in enhancing ORR,however,the specifical control over the coordination surroundings around single metal center to intrinsically modify the electron structure is still a great challenge.Herein,we demonstrate that a 3 D hybrid MOF composed of cobalt doped ZIF-L and ZIF-8,featuring star morphology with six equal branches,can be used as an advanced precursor for making the Co SACs for greatly boosted ORR.The as-synthesized Co_(SA)-N-C exhibits excellent ORR activity with E_(1/2) of 0.891 V in alkaline medium,outperforming the commercial Pt/C by 39 m V.Moreover,the E_(1/2) of Co_(SA)-N-C(0.790 V)is merely 15 m V,less than that of Pt/C(0.805 V)in acid medium,which is among the best in the reported state-of-the-art SACs.DFT calculations demonstrate that the enhanced ORR performance is assigned to the formation of atomically isolated cobalt atom coordinated three N atoms and one C atom,which is easier to decrease the free energy of rate determining step and accelerate the ORR process than that of traditional cobalt atom coordinated four N atoms.In addition,a primary Zn-air battery with Co_(SA)-N-C cathode reveals a maximum power density of 92.2 m W cm^(-2) at 120.0 m A cm^(-2),far higher than that of commercial catalysts(74.2 m W cm^(-2) at 110.0 m A cm^(-2)).

Advanced Carbon Materials for Non-aqueous Potassium Ion Battery Anodes

Owing to the abundant reserves and low cost, potassium ion batteries(PIBs), as potential alternatives to lithium ion batteries(LIBs) in the field of grid-level electrical energy storage systems, have triggered extensive research interest recently. Taking into consideration of the cost, environmental benignity and sustainability, carbon-based materials are supposed to be a promising choice for PIB anodes. In this perspective, we summarize the carbon-based materials with various microstructures toward PIBs and try to offer comprehensive understanding the underlying mechanism of potassium(K) ion storage. In addition, several strategies including heteroatom doping, morphology engineering, defect engineering, interlayer engineering, and composition engineering are proposed to rationally design the nanostructures of the advanced carbon-based PIB anodes. Finally, we conclude the current challenges and provide our perspectives on the development of high-performance carbon materials for PIB anodes.

Development and Control of Underwater Gliding Robots:A Review

As one of the most effective vehicles for ocean development and exploration,underwater gliding robots(UGRs)have the unique characteristics of low energy consumption and strong endurance.Moreover,by borrowing the motion principles of current underwater robots,a variety of novel UGRs have emerged with improving their maneuverability,concealment,and environmental friendliness,which significantly broadens the ocean applications.In this paper,we provide a comprehensive review of underwater gliding robots,including prototype design and their key technologies.From the perspective of motion characteristics,we categorize the underwater gliding robots in terms of traditional underwater gliders(UGs),hybrid-driven UGs,bio-inspired UGs,thermal UGs,and others.Correspondingly,their buoyancy driven system,dynamic and energy model,and motion control are concluded with detailed analysis.Finally,we have discussed the current critical issues and future development.This review offers valuable insight into the development of next-generation underwater robots well-suited for various oceanic applications,and aims to gain more attention of researchers and engineers to this growing field.

High-index faceted noble metal nanostructures drive renewable energy electrocatalysis

Noble metallic nanocrystals are used in a wide variety of applications,such as catalysis,batteries,and bio-and chemical sensors.Most of the previous studies focus on the preparation of thermodynamically stable nanocrystals enclosed by low-index facets and discuss their corresponding catalytic properties.Recently,researchers have found that the nanocrystals with high-index facets(HIFs)are of more interest for electrocatalysis.Herein,we review recent key progress in the synthesis of noble metallic nanoparticles enclosed with HIFs and their facetdependent electrocatalytic behaviors.First,we introduce the concept of HIFs,and establish the correlation between their surface structure and catalytic activity.Then,we discuss various synthetic approaches for controlling the shapes and composition of the nanocrystals enclosed by HIFs.Afterwards,we showcase the enhanced electrocatalytic performance realized by HIF-based nanostructures.Finally,we provide guidance on how to improve the electrocatalysis by engineering HIFs on noble metallic nanocrystals.

Wavelet analysis of stagnation point flow of non-Newtonian nanofluid

The wavelet approach is introduced to study the influence of the natural convection stagnation point flow of the Williamson fluid in the presence of thermophysical and Brownian motion effects. The thermal radiation effects are considered along a permeable stretching surface. The nonlinear problem is simulated numerically by using a novel algorithm based upon the Chebyshev wavelets. It is noticed that the velocity of the Williamson fluid increases for assisting flow cases while decreases for opposing flow cases when the unsteadiness and suction parameters increase, and the magnetic effect on the velocity increases for opposing flow cases while decreases for assisting flow cases. When the thermal radiation parameter, the Dufour number, and Williamson’s fluid parameter increase, the temperature increases for both assisting and opposing flow cases. Meanwhile, the temperature decreases when the Prandtl number increases. The concentration decreases when the Soret parameter increases, while increases when the Schmidt number increases. It is perceived that the assisting force decreases more than the opposing force. The findings endorse the credibility of the proposed algorithm, and could be extended to other nonlinear problems with complex nature.

Ion migration in halide perovskite solar cells:Mechanism,characterization,impact and suppression

Metal halide perovskites are emerging as the most promising candidate for the next-generation Photovoltaics(PV)materials,due to their superior optoelectronic properties and low cost.However,the resulting Perovskite solar cells(PSCs)suffer from poor stability.In particular,the temperature and light activated ionic defects within the perovskite lattice,as well as electric-field-induced migration of ionic defects,make the PSCs unstable at operating condition,even with device encapsulation.There is no doubt that the investigation of ion migration is crucial for the development of PSCs with high intrinsic stability.In this review,we first briefly introduce the origin and pathways of ion migration,and also the essential characterization methods to identify ion migration.Next,we discuss the impact of ion migration on the perovskite films and cells with respect to photoelectric properties and stability.Then,several representative strategies to suppress ion migration are systematically summarized in the context of composition engineering,additive engineering and interface engineering,with an in-depth understanding on the underlying mechanisms which may provide more clues for further fabrication of PSCs with improved stability.Finally,a perspective with some suggestion on future research directions and chemical approaches are provided to alleviate ion migration in perovskite materials and the entire devices.

Droplet impact on wetted structured surfaces

In this study,we numerically investigate the droplet impact onto a thin liquid film deposited on a structured surface with square pillars and cavities.The time evolution of crown geometry is strongly affected by the surface structure.When the thickness of the liquid film is larger than the structure height,the expanding speed of the crown base radius is independent of the structure width.However,if the liquid film thickness is equal to the structure height,the crown base expands slower as the structure width increases.Surface structures have strong effects on the crown height and radius,and can prevent ejected filament from breaking into satellite droplets for certain cases.For the liquid film with the thickness equal to the pillar height,both the crown height and the radius exhibit non-monotonic behaviors as the pillar width increases.There exists one pillar width which produces the smallest crown height and the largest crown radius.

Review ： Controllable Synthesis of Two-Dimensional (2D) MoS2 by Chemical Vapor Deposition Process

Atomically thin MoS_2 has draw n tremendous attention due to its great potential in a range of electronic devices such as photodetectors,field effect transistors( FET),and sensors. In the past few years,numerous methods including mechanical cleavage,liquid exfoliation,chemical vapor deposition( CVD)have been devoted to synthesizing tw o dimensional atomically thin MoS_2. Among these methods,CVD is the most promising method for preparing large-size and highly crystalline MoS_2 monolayers,exhibiting relatively good optical and electrical properties. Nevertheless,there are so many experiment parameters in CVD process that w e should take into account,w hich makes it still a challenge for us to grow large-scale,single-crystalline MoS_2 monolayer films suitable for practical applications. This review systematically summarized some synthetic strategies of MoS_2 by CVD in recent years. We also discussed in detail how these vital factors such as substrates,carrier gases,M o precursors,influenced the process of grow th,w hich w as expected to help us to controllably synthesize high-quality MoS_2 and other kinds of transition metal dichalcogenides including WS_2,VS_2,WSe_2 and so forth.