Experimental Study on the Electrochemical Performance of PEMFC under Different Assembly Forces

Proton exchange membrane fuel cell(PEMFC)is of paramount significance to the development of clean energy.The components of PEMFC are assembled using many pairs of nuts and bolts.The assembly champing bolt torque is critical to the electrochemical performance and mechanical stability of PEMFC.In this paper,a PEMFC with the threechannel serpentine flow field was used and studied.The different assembly clamping bolt torques were applied to the PEMFC in three uniform assembly bolt torque and six non-uniform assembly bolt torque conditions,respectively.And then,the electrochemical performance experiments were performed to study the effect of the assembly bolt torque on the electrochemical performance.The test results show that the assembly bolt torque significantly affected the electrochemical performance of the PEMFC.In uniform assembly bolt torque conditions,the maximal power density increased initially as the assembly bolt torque increased,and then decreased on further increasing the assembly torque.It existed the optimum assembly torque which was found to be 3.0 N·m in this work.In non-uniform assembly clamping bolt torque conditions,the optimum electrochemical performance appeared in the condition where the assembly torque of each bolt was closer to be 3.0 N·m.This could be due to the change of the contact resistance between the gas diffusion layer and bipolar plate and mass transport resistance for the hydrogen and oxygen towards the catalyst layers.This work could optimize the assembly force conditions and provide useful information for the practical PEMFC stack assembly.

Force Feedback Coupling with Dynamics for Physical Simulation of Product Assembly and Operation Performance

Most existing force feedback methods are still difficult to meet the requirements of real-time force calculation in virtual assembly and operation with complex objects. In addition, there is often an assumption that the controlled objects are completely flee and the target object is only completely fixed or flee, thus, the dynamics of the kinematic chain where the controlled objects are located are neglected during the physical simulation of the product manipulation with force feedback interaction. This paper proposes a physical simulation method of product assembly and operation manipulation based on statistically learned contact force prediction model and the coupling of force feedback and dynamics. In the proposed method, based on hidden Markov model （HMM） and local weighting learning （LWL）, contact force prediction model is constructed, which can estimate the contact force in real time during interaction. Based on computational load balance model, the computing resources are dynamically assigned and the dynamics integral step is optimized. In addition, smoothing process is performed to the force feedback on the synchronization points. Consequently, we can solve the coupling and synchronization problems of high-frequency feedback force servo. low-frequency dynamics solver servo and scene rendering servo, and realize highly stable and accurate force feedback in the physical simulation of product assembly and operation manipulation. This research proposes a physical simulation method of product assembly and operation manipulation.

Ground demonstration system based on in-orbit assembly oriented manipulator flexible force control

To eliminate the load weight limit of carrier rockets and reduce the burden on support structures,in-orbit assembly is a key technology to make design of scattering a large diameter telescope into submirror modules,which requires smooth operation of assembly robots,and flexible force control technology is necessary. A ground demonstration system is presented for in-orbit assembly focusing on flexible force control. A six-dimensional force/torque sensor and its data acquisition system are used to compensate for gravity. For translation and rotation,an algorithm for flexible control is proposed. A ground transportation demonstration verifies accuracy and smoothness of flexible force control,and the transportation and assembly task is completed automatically. The proposed system is suitable for the development of in-orbit assembly robots.

Mechanical-force-promoted peptide assembly: a general method

A general method was developed for promoting peptide assembly and protein polymerization to form nanoscale patterns on various surfaces with an atomic force microscope(AFM) operated in a liquid. By scanning solid surfaces with an AFM tip, we showed that peptide monomers assemble at a higher rate in the tip-scanned area compared to other regions. The promotion is attributed to the mechanical force applied by the scanning tip. This kind of mechanical-force-promoted assembly was also observed with different peptides on various substrates. The force promoting peptide assembly provides a simple and practical solution for preparing and building peptide and protein architectures for future nanodevices.

Recent Advances in Directed Assembly of Nanowires or Nanotubes

Nanowires and nanotubes of diverse material compositions,properties and/or functions have been produced or fabricated through various bottom-up or top-down approaches.These nanowires or nanotubes have also been utilized as potential building blocks for functional nanodevices.The key for the integration of those nanowire or nanotube based devices is to assemble these one dimensional nanomaterials to specific locations using techniques that are highly controllable and scalable.Ideally such techniques should enable assembly of highly uniform nanowire/nanotube arrays with precise control of density,location,dimension or even material types of nanowires/nanotubes.Numerous assembly techniques are being developed that can quickly align and assemble large quantities of one type or multiple types of nanowires through parallel processes,including flow-assisted alignment,Langmuir-Blodgett assembly,bubble-blown technique,electric/magnetic-field directed assembly,contact/roll printing,knocking-down,etc..With these assembling techniques,applications of nanowire/nanotube based devices such as flexible electronics and sensors have been demonstrated.This paper delivers an overall review of directed nanowire/nanotube assembling approaches and analyzes advantages and limitations of each method.The future research directions have also been discussed.

Dielectrophoretic force distribution of growing microwires

The Dielectropheretic assembly of electrically functional microwires from nanopartical suspensions is introduced. Meanwhile growth mechanism of the microwires is discussed. The agglomeration is based on the polarization and mobility of particles caused by alternating electric fields, commonly referred to as dielectrophoresis (DEP). The spatial distributions of the electric potential, field and dieletrophoretic force are analytically calculated in terms of AC electrokinetics. The calculated results show that the electrophoretic force, very strong near the apex of the microwire, drops abruptly with increasing distance. The electrophoretic force near the apex of the microwire agrees well with the fact that the nanoparticles are highly concentrated at the end of the tip and subsequently aggregate to extend the wire in the direction of the field gradient.

Method of Spectrophotometric Microanalysis Based on HRP/PET Self-assembly Film

Horseradish peroxidase monolayer was assembled on the surface of PET-CO2 substrate. The reaction kinetics of HRP/PET film and H2O2 in micro reactor was studied using improved spectrophotometer. The relative activity of self-assembly HRP/PET film still remains above 80% after storing for 150 days at 4℃. When applied to determination of H2O2 in sample, the recoveries of H2O2 are 96.5%~101.1%.

The Effect of Tire Design Parameters on the Force Transmissibility

A finite element modeling technique is employed in this paper to predict the force transmissibility of tire-cavity-wheel assembly under a free-fixed condition. The tire and wheel force transmissibility is factor in structure borne road noise performance. In order to improve structure borne noise, it is required to lower the 1st peak frequency of force transmissibility. This paper presents an application of finite element analysis modeling along with experimental verification to predict the force transmissibility of tire and wheel assembly. The results of finite element analysis for force transmissibility are shown to be in good agreement with the results from the indoor test. In order to improve structure borne noise, it is required to lower the 1st peak frequency of force transmissibility. And, the effect of the tire design parameters such as the density and modulus of a rubber and the cord stiffness on the force transmissibility is discussed. It is found that the prediction of the force transmissibility model using finite element analysis will be useful for the improvement of the road noise performance of passenger car tire.

Anisotropic formation mechanism and nanomechanics for the self-assembly process of cross-β peptides

Nanostructures self-assembled by cross-β peptides with ordered structures and advantageous mechanical properties have many potential applications in biomaterials and nanotechnologies. Quantifying the intra-and inter-molecular driving forces for peptide self-assembly at the atomistic level is essential for understanding the formation mechanism and nanomechanics of various morphologies of self-assembled peptides. We investigate the thermodynamics of the intra-and inter-sheet structure formations in the self-assembly process of cross-β peptide KⅢIK by means of steered molecular dynamics simulation combined with umbrella sampling. It is found that the mechanical properties of the intra-and inter-sheet structures are highly anisotropic with their intermolecular bond stiffness at the temperature of 300 K being 5.58 N/m and 0.32 N/m, respectively. This mechanical anisotropy comes from the fact that the intra-sheet structure is stabilized by enthalpy but the inter-sheet structure is stabilized by entropy. Moreover, the formation process of KⅢIK intra-sheet structure is cooperatively driven by the van der Waals （VDW） interaction between the hydrophobic side chains and the electrostatic interaction between the hydrophilic backbones, but that of the inter-sheet structure is primarily driven by the VDW interaction between the hydrophobic side chains. Although only peptide KⅢIK is studied, the qualitative conclusions on the formation mechanism should also apply to other cross-β peptides.

Assembly of Oligoglycine Layers on Mica Surface

Assembly of [Gly7-NHCH2-]4C, [Gly7-NHCH2-]3C CH3 and [Gly4NH(CH2)5-]2 peptides on mica surface in aqueous so-lution was studied. The peptides are capable of forming atomically smooth (2.65-4.3 nm in height) layers assembled as polyglycine II. Monomers in the layers are situated normally to the surface. Formation of analogous flat 2D structures also takes place in solution but much more slowly than on mica surface, i.e. negatively charged surface plays an active role promoting the assembly.

Unveiling the nanoscale architectures and dynamics of protein assembly with in situ atomic force microscopy

Proteins play a vital role in different biological processes by forming complexes through precise folding with exclusive inter-and intra-molecular interactions.Understanding the structural and regulatory mechanisms underlying protein complex formation provides insights into biophysical processes.Furthermore,the principle of protein assembly gives guidelines for new biomimetic materials with potential appli-cations in medicine,energy,and nanotechnology.Atomic force microscopy(AFM)is a powerful tool for investigating protein assembly and interactions across spatial scales(single molecules to cells)and temporal scales(milliseconds to days).It has significantly contributed to understanding nanoscale architectures,inter-and intra-molecular interactions,and regulatory elements that determine protein structures,assemblies,and functions.This review describes recent advancements in elucidating protein assemblies with in situ AFM.We discuss the structures,diffusions,interac-tions,and assembly dynamics of proteins captured by conventional and high-speed AFM in near-native environments and recent AFM developments in the multimodal high-resolution imaging,bimodal imaging,live cell imaging,and machine-learning-enhanced data analysis.These approaches show the significance of broadening the horizons of AFM and enable unprecedented explorations of protein assembly for biomaterial design and biomedical research.

Collaborative force and shape control for large composite fuselage panels assembly

This study proposed a force and shape collaborative control method that combined method of influence coefficients(MIC)and the elitist nondominated sorting genetic algorithm(NSGA-II)to reduce the shape deviation caused by manufacturing errors,gravity deformation,and fixturing errors and improve the shape accuracy of the assembled large composite fuselage panel.This study used a multi-point flexible assembly system driven by hexapod parallel robots.The proposed method simultaneously considers the shape deviation and assembly load of the panel.First,a multi-point flexible assembly system driven by hexapod parallel robots was introduced,with the relevant variables defined in the control process.In addition,the corresponding mathematical model was constructed.Subsequently,MIC was used to establish the prediction models between the displacements of actuators and displacements of panel shape control points,deformation loads applied by the actuators.Following the modeling,the shape deviation of the panel and the assembly load were used as the optimization objectives,and the displacements of actuators were optimized using NSGA-II.Finally,a typical composite fuselage panel case study was considered to demonstrate the effectiveness of the proposed method.

Mechanical force-induced assembly of one-dimensional nanomaterials

There have been intensive and continuous research efforts in large-scale controlled assembly of one-dimensional(1D)nanomaterials,since this is the most effective and promising route toward advanced functional systems including integrated nano-circuits and flexible electronic devices.To date,numerous assembly approaches have been reported,showing considerable progresses in developing a variety of 1D nanomaterial assemblies and integrated systems with outstanding performance.However,obstacles and challenges remain ahead.Here,in this review,we summarize most widely studied assembly approaches such as Langmuir-Blodgett technique,substrate release/stretching,substrate rubbing and blown bubble films,depending on three types of external forces:compressive,tensile and shear forces.We highlight the important roles of these mechanical forces in aligning 1D nanomaterials such as semiconducting nanowires and carbon nanotubes,and discuss each approach on their effectiveness in achieving high-degree alignment,distinct characteristics and major limitations.Finally,we point out possible research directions in this field including rational control on the orientation,density and registration,toward scale-up and cost-effective manufacturing,as well as novel assembled systems based on 1D heterojunctions and hybrid structures.

Preparation and characterization of 3-mercaptopropyl trimethoxysilane self-assembled monolayers

Silane coupling regent （3-mercaptopropyl trimethoxysilane （MPTS）） was prepared on the single-crystal silicon substrate to form 2-dimensional self-assembled monolayers （SAMs）. The growth behavior of SAMs formed from 3-MPTS was investigated using atomic force microscopy （AFM）, contact angle measurements, ellipsometry, and X-ray photoelectron spectroscopy （XPS）. The formation behavior of MPTS SAMs was investigated by a series of AFM images and the roughness of MPTS SAMs on silicon substrates with the assembling time from 1 min to 24 h. The water contact angle measurements indicated the growth behavior of MPTS that correlated with the AFM measurements at different immersion times, too. The chemical states of the typical elements in the MPTS SAMs were analyzed using X-ray photoelectron spectroscopy. The results show that MPTS is self-assembled on the substrate.

In situ AFM investigation of dual-mode self-assembling peptide

Nanostructures/patterns formed by biomolecules can produce different physicochemical properties in terms of hydrophobicity, zeta-potential, color, etc., which play paramount roles in life. Peptides, as the main bio-building blocks, can form nanostructures with different functions,either in solutions or on interfaces. Previously, we synthesized a short peptide with the inspiration of an Alzheimer’s disease-related peptide: amyloid β peptide(A-p),namely GAV-9, which can epitaxially self-assemble into regular nanofilaments on liquid-solid interfaces, and it was found that both the hydrophobicity and charge state of the interfaces can significantly influence its assembling behavior. It was also reported that another A-β-containing dipeptide, FF,can self-assemble into nanostructures in solutions. Owing to the close relationship between these two short peptides, it is interesting to conjugate them into a de novo peptide with two separated structural domains and study its self-assembling behavior. To this end, herein we have synthesized the GAV-FF peptide with a sequence of NH2-VGGAVVAGVFF-CONH2 and verified its selfassembling property using the in situ liquid-phase atomic force microscopy. The results show that the GAV-FF peptide can self-assemble into nanofilaments both in solutions and on aqueous-solid interfaces, but with different morphologies. The FF domain accelerates the template-assisted self-assembling(TASA) process of the GAV domain, which in return enhances the solubility of FF in aqueous solutions and further participates in the fibrillization of FF. The current results could help deepen the understanding of the aggregation mechanism of diseaserelated peptides and could also shed light on the strategies to create artificial bio-functional nanostructures/patterns,which hold a significant potential for biomedical applications.

Nano-tribological characteristics of lanthanum-based thin films on sulfonated self-assembled monolayer of 3-mercaptopropyl trimethoxysilane

Silane coupling reagent （3-mercaptopropyl trimethoxysilane （MPTS）） was prepared on silicon substrate to form two-dimensional Self-Assembled Monolayer （SAM） and the terminal -SH group in the film was in situ oxidized to -SO3H group to endow the film with good chemisorption ability. Thus, lanthanum-based thin films were deposited on oxidized MPTS-SAM to form rare earth composite thin films （RE thin films）, making use of the chemisorption ability of the -SO3H group. Atomic Force Microscope （AFM）, X-ray Photoelectron Spectrometry （XPS）, and contact angle measurements were used to characterize the RE thin films. Adhesive force and friction force of the RE thin films and silicon substrate were measured under various applied normal loads and scanning speed of AFM tip. The results showed that the friction force increased with applied normal loads and scanning speed of AFM tip. To study the effect of capillary force, tests were performed in various relative humidities. The results showed that the adhesive force of silicon substrate increased with relative humidity and the adhesive force of RE thin films only increased slightly with relative humidity. Research showed that surfaces with higher hydrophobic property reveal lowered adhesive and friction forces.

Micro-Friction of Diazoresin/Polyacrylic Acid Self-Assembly Films in Water with Atomic Force Microscopy

Ultrathin films composed of diazoresin（DR）and polyacrylic acid（PAA）were fabricated.The surface morphology of the films in water was measured using an atomic force microscopy（AFM）.The self-assembly technique makes the surface rather flat and uniform.The friction force and its dependence on the velocity differ from the surface charge of the thin films.The friction force of repulsive DR/PAA film increases linearly with velocity and has lower values than that of attractive DR film over the full range of velocity.As the velocity increases,the attractive friction of DR film first decreases to a minimum at a velocity of 2 line/s and then increases all the way.When the surface is repulsive to the friction substrate,the friction of thin films that is determined by hydrated lubrication of polymer chains that is ultralubricated;when it is adhesive to the friction substrate,the friction is mainly contributed from the elastic deformation of adsorbed polymer chains in the low velocity region and from viscous sliding in the presence of hydrated-layer lubrication of the polymer chains in the higher velocity region.

高速列车轴装制动盘螺栓轴力影响因素探究

制动盘紧固螺栓作为影响制动盘服役性能的关键零部件,其可靠性直接影响列车的运行安全。制动盘复杂的服役工况使得螺栓轴力时刻发生变化,研究制动盘在新造组装和后续服役过程中的螺栓轴力变化,对于指导结构设计、制造和运用有重要价值。针对某250 km/h高速列车轴装制动盘紧固螺栓,利用有限元仿真方法研究紧固件装配位置误差、制动热变形及定心环结构这三个因素对制动盘螺栓轴力的影响。结果表明:螺栓和套筒之间存在装配误差时,极端情况会使螺栓平均轴向应力增大10.6 MPa;在紧急制动工况下,制动热载荷会使螺栓发生0.112 mm的弯曲变形,制动过程中螺栓轴向应力最大增幅达20%;在垂向冲击载荷作用下,使用带定心环结构的制动盘可使螺栓径向弯曲变形量减小25%,轴向应力波动也有所降低。新造制动盘和服役后制动盘螺栓轴力的实测结果表明,装配误差会使制动盘螺栓轴力存在离散性,在服役一段时间后螺栓轴力也会发生变化。通过控制装配精度、使用定心环结构等方法可减小螺栓应力波动、降低服役失效风险。

面对面角接触球轴承装置热力耦合仿真分析

在研究轴承时为了方便计算简化模型,一般将组合装置中的两个轴承简化成一个轴承进行分析,这样会带来一定的误差,因此这里分析了面对面球轴承组合装置中两个轴承的热特性耦合。这里首先分析了角接触球轴承的摩擦力矩,根据混合润滑机理,考虑了混合热阻影响,计算了轴承在发生摩擦时生成的热量,通过ANSYS的APDL命令流将进行参数化建模,建立了面对面轴承组合装置仿真模型,再利用APDL命令流循环计算出组合装置不同时刻下的温度场和在不同时刻温度场下的热膨胀诱导的力,从而分析出组合装置中的两个轴承预紧力和发热量的时变耦合特性。实验结果表明,这里模型与实验数据吻合,验证了本模型的正确性。

弹簧刚度对敏感波纹密封件特性影响的分析

对某些特殊性能的波纹管,可以采取在波纹管内腔或外部配置圆柱螺旋弹簧的方式。本文通过对弹簧数据、p-w曲线特性数据的分析,包括均布力刚度、压力灵敏度、重复性误差、迟滞误差、最大量程等数据,同时通过Ansys软件对密封组件进行受力分析,探究弹簧对测量类敏感类波纹管组件的影响。结果表明,加入弹簧后,波纹管组件特性有改善,均布力刚度下降,压力灵敏度升高,重复性误差、迟滞误差、最大量程等减小,并且通过选择合适刚度的弹簧,可以使组件性能达到最佳。