Experimental observation of extremely weak optical scattering from an interlocking carbon nanotube array

We experimentally demonstrate a nearly wavelength-independent optical reflection from an extremely rough carbon nanotube sample. The sample is made of a vertically aligned nanotube array, is a super dark material, and exhibits a near-perfect blackbody emission at T=450 K-600 K. No other material exhibits such optical properties, i.e., ultralow reflectance accompanied by a lack of wavelength scaling behavior. This observation is a result of the lowest ever measured reflectance (R=0.0003) of the sample over a broad infrared wavelength of 3 μm < λ < 13 μm. This discovery may be attributed to the unique interlocking surface of the nanotube array, consisting of both a global, large scale and a short-range randomness.     

Effect of a hard coat layer on buckle delamination of thin ITO layers on a compliant elasto-plastic substrate: An experimental–numerical approach

Layer buckling and delamination is a common interfacial failure phenomenon in thin film multi-layer structures that are used in flexible display applications. Typically, the substrate is coated on both sides with a hybrid coating, called a hard coat (HC), which acts as a gas barrier and also increases the scratch resistance. In this paper 250 nm thick indium tin oxide (ITO) layers have been deposited on a 200 μm thick high temperature aromatic polyester substrate (Arylite^TM), with and without a 3 μm HC. In order to study the influence of this HC layer on delamination phenomena, two-point bending experiments are performed from which buckle width and height values are measured after straightening of the sample. An analytical model and a finite element (FE) model are developed to estimate the adhesion properties from the measured buckle geometries. In the numerical model, the initiation and propagation of the delamination process is described by cohesive zone elements, of which the parameters are extracted from response surface model (RSM) results. Furthermore, the numerical model is used to illustrate the significant change in buckle geometry upon load reversal, i.e. from loaded to straightened state, which is governed by the elasto-plastic behavior of the substrate material. It is concluded that the addition of a HC layer significantly decreases the adhesion of the ITO layer. The latter is determined as function of the actual mode angle.     

Stable 4 W CW solid-state green source pumped by fibre-coupled diode-laser arrays

Abstract

A high-power Nd:YAG laser end-pumped by a fibre-coupled diode-laser array system is described. When operated at 1 μm, the device produced 10 W of output power in the TEM₀₀ transverse mode with a slope efficiency of 43%. The system was operated using both 600 μm and 400 μm core, 0·37 N.A. multimode fibres for delivery of the pump radiation, and also with Nd:YVO₄ as the gain material. By intracavity doubling with KTP, 4 W of non-chaotic two-mode 0·5 μm output was obtained.     

The effect of moisture on buckle delamination of thin inorganic layers on a polymer substrate

Moisture-induced buckle delamination of thin inorganic layers on a polymer substrate was studied. Moisture has been found to have a significant effect on the failure mode. Experimentally, an increase in the buckle width, height and the total buckle delamination length with time and humidity was observed. Moreover, a transition from straight to telephone-cord buckle pattern was taken place in a humid environment. Applying only a uniaxial compressive strain on the thin layers did not result in the transition from straight to telephone-cord. For a compliant substrate the transition from straight to telephone-cord buckle occurred at significantly higher ratio of residual strain over critical buckling strain than for a rigid substrate. A simple model for buckling was applied. Using the energy release rate, the interfacial toughness was investigated as a function of relative humidity.     

Observations of how drivers fasten their seatbelts in relation to various startup tasks

Observational data were collected to determine the percentage of drivers that followed various seatbelt buckling sequences. Observers scored the buckling sequence and recorded the time between various startup events and fastening the seatbelt of 1600 drivers in two urban areas, Pinellas County, Florida, and Halifax, Nova Scotia, Canada. The results indicated that most drivers waited to buckle their seatbelt until after they started their vehicle or placed it into gear, with a substantial proportion buckling after placing the vehicle in motion. These results suggest that a salient second seatbelt reminder that was initiated 30 s after placing the vehicle in gear would only be experienced by persons who do not buckle their seatbelt and less than 1% of drivers who buckle their seatbelt more than 29 s after placing the vehicle in gear.     

Experimental study on buckle evolution of thin inorganic layers on a polymer substrate

In this paper the behavior of a 250 nm and a 350 nm thick Indium tin oxide (ITO) layers deposited on a 200 μm thick high temperature aromatic polyester substrate (Arylite™) and spin coated with a 3 μm silica-acrylate hybrid coating (Hard Coat) is discussed. In-situ optical microscopy of the layered structures under uniaxial compressive strain was used to determine the buckle delamination rate at different applied strains. The effect of applied uniaxial compressive strain and layer thickness on the evolution of buckle width and height was investigated. The biaxial-residual stress, uniaxial compressive stress, poor adhesion at the interface and Poisson’s ratio are believed to be responsible for the formation of telephone-cord buckling.     

Fabrication and evaluation of chitosan–gelatin based buckling implant for retinal detachment surgery

The traditional nonabsorbable silicone buckling implant (buckle) may cause some long-term complications when it is used in the retinal detachment surgery. In this study we fabricated a chitosan–gelatin based buckling implant to replace the traditional one. We evaluated its biocompatibility with human scleral fibroblasts (HSF) in vitro and its cytotoxicity with L929 cell. To evaluate elasticity and hardness of the blends buckle, the mechanical properties of the chitosan–gelatin buckle were compared with the traditional silicone buckle. The light and electron microscopy coupled with immunocytochemistry demonstrated that chitosan–gelatin blends supported the survival and growth of primarily cultured HSF without significant cytotoxic effects. MTT analysis and cell cycle analysis indicated that chitosan–gelatin blends promoted the proliferation of HSF. A preliminary in vivo implantation test indicated that chitosan–gelatin buckling implant were compatible with the surrounding tissue. The results collectively demonstrated that chitosan–gelatin blends could be a candidate biodegradable material for scleral buckling surgery.     

Ultrasmall microlens array based on vertically aligned carbon nanofibers

An ultrasmall tunable microlens with a diameter of 1.5 μm is fabricated using nematic liquid crystals (electrically tunable medium) and vertically aligned carbon nanofibers (CNFs, electrodes). Individual CNFs are grown at the center of circular dielectric regions. This allows the CNFs to produce a more Gaussian electric field profile and hence more uniformity in lens array switching.     

Evaluation of thin film adhesion to a compliant substrate by the analysis of progressive buckling in the fragmentation test

The interface toughness of a thin coating/compliant substrate system is estimated based on the evolution of coating buckle patterns in the fragmentation test. The linear density of coating buckles as a function of applied strain is determined experimentally for a SiO_x coating deposited on a polyethylene terephthalate film. A three-dimensional non-linear finite element model is developed to simulate the process of buckle formation in a single narrow coating strip. The elastic energy released during buckling-driven delamination is obtained from the energy balance in the system before and after the buckling event. Both the interface adhesion and the total energy release rate, which includes the plastic dissipation in the substrate during debonding, are evaluated. The apparent interfacial toughness, equal to 15 J/m² at the onset of buckling, is found to increase with strain. This is tentatively explained by the probabilistic features of the buckle accumulation process, reflected also in the random locations of buckles evolving towards a log-normal distribution of buckle spacings at high strains.     

采用定向SiC纳米线烧结制备高强多孔 SiC陶瓷

利用直接墨水打印方法制备了由定向SiC纳米线交错叠层组成的具备网络状孔隙结构的高强SiC多孔陶瓷.制备的碳化硅多孔陶瓷具有高的通孔结构和完全由定向SiC纳米线组装而成的结构特征.研究了烧结温度对定向SiC纳米线多孔陶瓷的微观结构、相组成演变及力学性能的影响.研究结果表明:烧结温度低于1900℃时,SiC纳米线能保持高长...     

Development of an experimental bench to reproduce the tow buckling defect appearing during the complex shape forming of structural flax based woven composite reinforcements

This work investigates the tow buckling defect that may take place during the forming of complex shapes. The defect is studied independently of the process with a device specially designed. A specific instrumentation was associated to the device. Structure light interferometry was chosen to measure the elevation of the tows exhibiting the buckling defect all along its growth. The device and its instrumentation were validated in this work and a preliminary study was performed to investigate the origin of the tow buckle’s appearance and its growth kinematic. The growth kinematic of the buckle’s appearance consisting on a double simultaneous rotation of the tow exhibiting the buckle around the Z and the Y axis was established. It was shown that the in-plane bending of the tow is a key parameter that can probably be considered as a preliminary criterion that conditions the appearance and the growth of the tow buckling defect.     

Global buckling load of a nonlinearly elastic bar

Summary The nonlinear buckling of an elastic bar with softening characteristic is studied. It is found that, under large disturbances, the bar may buckle under loads well below the linear buckling load.     

Silicon rice-straw array emitters and their superior electron field emission

Free standing and vertically aligned silicon rice-straw- like array emitters were fabricated by modified electroless metal deposition (EMD), using HF-H(2)O(2) as an etching solution to reduce the emitter density and to make the emitter end of the formed silicon rice-straw arrays shaper than those formed by conventional EMD. These silicon rice-straw array emitters can be turned on at E(0) = 4.7 V/μm, yielding an EFE (electron field emission) current density of J(e) = 139 μA/cm(2) in an applied field of 12.8 V/μm. According to a simple simulation, the excellent EFE performance of the silicon rice-straw array emitters originates in not only the favorable distribution of emitter arrays, but also the shape of the emitter apexes. The modified-EMD method is easily scaled up without expensive equipment, so silicon rice-straw array emitters are a promising alternative to silicon-based field emitters.     

An experimental study of the influence of film edges and imperfections on buckling morphologies of quenched iron films

Iron films, quenched by silicone oil during deposition, have been prepared on glass substrates by a DC-magnetron sputtering method. The role of film edges and imperfections on the morphologies of buckle driven delaminations in the films has been investigated. The buckling patterns are found to initiate usually from areas such as the film edges, spreading fronts of silicone oil and other imperfections in the films. When the buckling patterns grow near the fronts of silicone oil, they tend to form disordered telephone cord buckle networks. When the patterns initiate from the film edges, they generally have first a straight-sided shape perpendicular to the edges, and then propagate a few micrometers apart in bifurcation or telephone cord structure. The growth of the buckling patterns can be well controlled by introducing some imperfections into the glass substrates before deposition.     

十字型刚架中轴压柱面外稳定性设计方法研究

出于使用功能的考虑,在多高层结构中多层楼板抽空后形成通高区.在通高区内,外筒框架柱无任何面外支撑,其面外失稳常常控制结构的设计.该文针对通高区多层群柱的基本组成单元--两层两跨的十字型刚架中轴压柱的面外稳定性能进行了研究,提出了其面外稳定性设计方法.首先,剖析了十字型刚架中轴压柱发生面外失稳的主要影响因素,并按照面外支...     

Two distinct buckling modes in carbon nanotube bending

By using controlled SPM manipulation, carbon nanotubes have been continuously bent into a series of increasing angles, and two distinct buckling modes corresponding to "abrupt" and "gradual" buckle formation were observed through recording the height increment at the bend site during the loading process. Molecular dynamics simulation also found the two buckling modes in different types of carbon nanotubes, and their atomistic mechanism was revealed. Finally, the dependence of the critical buckling condition on diameters of carbon nanotubes was tentatively studied.     

氧化锌透明陶瓷光学透过模型构建与实验验证

本研究以ZnO透明陶瓷为研究对象, 基于Mie理论及Rayleigh-Debye近似散射理论, 建立了单轴六方晶系透明陶瓷的双折射散射与其直线光学透过率之间关联的理论模型, 阐明了ZnO透明陶瓷光学直线透过率随晶粒尺寸减小、陶瓷织构度的提升而增大的关系。采用强磁场下的注浆成型工艺结合优化放电等离子体烧结参数, 实现了ZnO透明陶瓷显微结构的有效调控, 使得制备的ZnO透明陶瓷符合模型要求。实验结果表明: 当ZnO陶瓷平均晶粒尺寸从1.72 μm减小至0.66 μm时, 其600 nm处的直线透过率从5.1%提高到12.9%; 对于亚微米级ZnO陶瓷(平均晶粒尺寸0.35 μm), 当陶瓷织构度从4.0%提高到24.7%时(XRD计算), 样品光学直线透过率从21.6%提升到36.6%。所获得实验结果与构建的理论模型计算结果吻合, 证实了所构建的模型。     

穿越平移断层海底埋地管道屈曲失效分析EI北大核心CSCD

长输海底管道常不可避免地穿过地震断层,地震断层活动可能导致管道发生扭曲、皱折甚至断裂,极大威胁管道安全。采用创新性的向量式有限元方法 (VFIFE)分析穿越地震断层海底管道屈曲失效行为,首先推导考虑材料非线性的VFIFE空间壳单元计算公式,提出适用壳单元的非线性管土耦合模型,然后重点解决了海底管道屈曲及屈曲传播过程中存在的内壁自碰撞接触问题,编制了Fortran计算程序和相应后处理程序。通过文献对比证明了模型的正确性。开展了平移断层作用下空载状态海底管道屈曲失效过程模拟,分析了穿越角度、土体性质和水压大小对海底管道屈曲失效行为的影响,结果表明:海底管道径厚比小,用钢等级高,周围土体强度低,具有更高的抵抗断层位移载荷能力;较低外压和平移断层联合作用下,管道变形呈S形,屈曲失效由断层位移引起的过度弯曲主导,失效模式是第二个弯曲处或者两个弯曲处的受压侧出现明显内陷,截面变形呈椭圆形;穿越角度越小,屈曲失效的临界断层位移越小;周围土体强度越高(砂土>黏土>淤泥夹砂),管道弯曲变形越严重,屈曲失效的临界断层位移越小;较高外压和平移断层联合作用下,屈曲失效由外压主导,主要模式是第一个弯曲处或者第二个弯曲处首先出现压溃,然后发生屈曲传播现象;不同水压和平移断层位移组合下海底管道破坏程度不一,压溃位置、屈曲传播方向和范围、截面变形呈现不同模式。结果可用于指导穿越地震断层海底管道抗震设计和止屈防护研究。     

Buckling Of Thin Film Thermoelectrics

This work investigates buckling behavior of thin film thermoelectrics subjected to a temperature gradient. Both a single-layer thermoelectric film and multilayered structures are studied. The multilayered structure consists of a p-type and n-type thermocouple separated by an insulating layer with or without additional supporting membrane layers. The temperatures, and thermoelectrically induced stresses and membrane forces are first presented. The elastic stability theories of homogeneous plates and laminated composites are subsequently used to determine the temperature differential between the hot and cold junctions that causes buckling of the thin film structures. The numerical results show that a single-layer thermoelectric film could buckle at a temperature differential of around 10 K for large length-to-thickness ratios. The multilayered thermoelectric thin film structures exhibit significantly higher buckling temperature differentials due to reduced overall length-to-thickness ratios.