Time discretization effect on the nonlinear vibration of embedded SWBNNT conveying viscous fluid

In this study, the effect of time discretization on the nonlinear transverse vibration and instability of single-walled boron nitride nanotube (SWBNNT) conveying viscous fluid is investigated based on the nonlocal piezoelasticity theory. SWBNNT is considered as an Euler–Bernoulli beam and is subjected to combined mechanical loading, thermal changes and electrical field. The elastic medium is simulated as Winkler and Pasternak foundation. The interaction between the inner viscous fluid and SWBNNT is obtained using Navier–Stokes equation. The axial inertia is neglected and a new approach is introduced to decouple the mechanical and electrical fields considering charge equation. Motion equations are derived by Hamilton’s principle using the Von-Kármán nonlinearity theory. In the first approach, time and space domains are discretized using the method of multiple scale (MMS) and Galerkin procedure respectively, and in the second one differential quadrature method (DQM) is utilized to space discretization. Good agreement is shown between the results of first and second approach. Numerical results indicate the significant effects of aspect ratio, elastic medium and nonlocality on the frequency and instability of the SWBNNT.     

精神交互体验设计方法的现象学阐释

目的 研究体验设计中的精神维度,在人机交互、人际交互的基础上提出精神交互的概念,并阐述精神交互体验的特点,分析精神交互体验的实例,论述全触点设计思维。方法 运用现象学方法,悬置人机交互、人际交互的各种接触方式,还原出交互体验的本质是精神交互。结论 产品和服务设计中的人机交互体验、人际交互体验,最终都指向精神交互体验。精神交互的特点是交互双方超越时空限制、在彼此的精神目光中永恒在场。精神交互使有限的触点变成了无限的全触点,为体验设计方法的深化提供了新的视野。     

Double wavelet analysis of modulation phenomena in nonstationary dynamics

A new method based on the double wavelet transform is proposed for the analysis of features related to the interaction of modes in nonstationary dynamics of systems with several time scales. Examples are presented, which illustrate new possibilities offered by the proposed method in determining the characteristics of amplitude and frequency modulation from the time series of complex oscillatory processes.     

Label-free parallel screening of combinatorial triazine libraries using reflectometric interference spectroscopy

The parallel reflectometric interference spectroscopy is presented as a label-free optical detection method. A new setup was adapted to accommodate sample carriers in a 96-well microplate. It allows for the first time simultaneous plate imaging by a CCD camera for the parallel detection of specific biomolecular interaction in the microplate wells at heterogeneous phase using direct optical monitoring. The detection of binding events with time resolution enables a highly parallel functional biomolecular interaction analysis (BIA). The combination of this new screening setup with combinatorial solid-phase synthesis is performed in the wells of glass-bottom microplates to accomplish the synthesis and the screening platform within one device. As a model system for a solid-phase substance library, synthesis of a triazine library and the subsequent BIA with four different antibodies were carried out. The presented setup enables a time resolution of 18 s with a total screening time of less than 35 min including baseline adjustment, BIA, and regeneration of the screening device for 96 samples in parallel. The binding studies reveal a fast classification of the different monoclonal and polyclonal antibodies and enable the detection of triazines with high binding affinity. The presented prototype is the first parallelized optical label-free detection system for biomolecular interaction analysis that is suitable for a high-throughput screening based on the 96-well microplate format.     

An interaction energy integral method for computation of mixed-mode stress intensity factors along non-planar crack fronts in three dimensions

A new interaction energy integral method for extracting mixed-mode stress intensity factors along the fronts of non-planar, three-dimensional cracks is described. In the method, interaction energy contour integrals are defined and expressed in domain form. The mixed-mode stress intensity factors are obtained by evaluating the domain integrals as a post-processing step in the finite element method. To assess the accuracy of the method, two benchmark problems are considered. The first problem is that of an arc crack in an infinitely extended solid subjected to equibiaxial tension. The second is that of a lens-shaped crack embedded in an infinite solid subjected to hydrostatic tension. Excellent agreement is obtained between the numerical and corresponding analytical results obtained from the literature.     

基于时域声辐射模态的结构噪声主动控制研究

以简支矩形板为例，提出了利用时域声辐射模态进行声辐射研究，并从物理和数学意义上对时域声辐射模态进行了解释。研究表明时域声辐射模态既与时间无关，也互相独立，使得计算和控制声功率得以简化。针对瞬时声功率主要由第一阶辐射模态的声功率所决定的特点，在时域里进行结构噪声的主动控制研究，通过抵消第一阶辐射模态的声功率使得总的声功率得以有效降低。在此基础上，建立基于最小二乘算法的自适应反馈控制系统，进行仿真计算，结果证明了主动控制策略是有效的。     

On the modelling of thermo-unelastic periodic composites: Microlocal parameter theory

Summary In this paper a new high efficiency C-O grid coupled with the potential flow solver based on the finite volume technique is given. It significantly reduces the CPU time and increases the computational efficiency. In order to improve the accuracy of traditional potential method a shock point operator is used to account for entropy correction. Some calculated results of 2D inviscid, viscous/inviscid interaction and 3D inviscid flow indicate that nonisentropic potential method produces results closer to Euler solution as well as experimental data, while its computational efforts are nearly the same as the usual isentropic potential method.With 9 Figures     

Preliminary Study on Quantitative Research Methods of Discussion-based Teaching: CAD/CAM Course

Computer-aided design and manufacturing,or CAD/CAM,in a narrow sense,is the use of a computer for component design and machining. As a specialized course for students,CAD/CAM course is a required course for undergraduates majoring in mechanical engineering and related engineering majors and also the core technical skills to be mastered during the undergraduate study. Based on the teaching practices of CAD/CAM course,this paper tries to introduce the discussion-based method in curriculum design and the implementation of the course,and enhance the interaction between teachers and students through using new information interaction tools such as We Chat group and course homepage to stimulate students' interest,and also expand the learning space and time. Thus,the problems students have will be solved in real time. In this study,for the first time,the statistical methods are used to record detailed the speaking time,keywords and the frequency of teachers and students' interaction,and also carries out quantitative analysis in order to explore the interactive patterns between teacher and students in discussion-based teaching,so as to improve communication and learning efficiency between teacher and students. Meanwhile,this paper also discussed the advantages and the disadvantages of using discussion-based teaching in the hope that it can provide reference for the following discussion-based teaching of CAD/CAM course in mechanical or related engineering majors.     

耦合有限元物质点法及其在流固耦合问题中的应用

有限元法在求解大变形问题时会遇到网格畸变和时间步长严重减小的问题。物质点法在大变形问题中无网格扭曲问题,且粒子代表了物质流动,无需界面追踪算法。但在小变形问题中,物质点法的精度和效率均低于有限元法。该课题组针对冲击侵彻问题提出的耦合有限元物质点法分别采用有限元法和物质点法模拟小变形和大变形物体,物体间的相互作用通过接触算法实现,既保留了有限元针对小变形问题高精度高效率的特点,又避免了材料大变形给有限元法带来的网格扭曲和时间步长严重减小的问题,还可以自动追踪界面。在流固耦合问题中,固体变形较小而流体变形较大,因此也适合用耦合有限元物质点法求解。该文简要介绍了耦合有限元物质点法的基本原理,并将其应用于流固耦合问题中,取得了较好的效果,表明耦合有限元物质点法是分析流固耦合问题的一种有效的方法。     

无人驾驶车多种空间人类移动性交互设计研究

目的探讨无人驾驶车在智能交通系统、大数据、人工智能等技术支持下,对人类移动性的范式拓展与设计思考,研究新型人类移动性下无人驾驶车的交互设计方法。方法采用文献调查法、田野调查法和用户参与式设计方法进行分析研究。结果无人驾驶车对人类移动性的拓展包含信息转化,时空维度转换,固有信息与即生信息、转化信息构成了人类新的社交网络以及移动性的内容知识图谱。链接物资流、信息流和资金流的人类移动性构建在多种空间的灵活信息架构中。结论新型人类移动性的无人驾驶车交互设计,将交互内容、功能、媒介的设计,与人类移动性的数据采集、数据处理、数据应用相映射,交互模型中人的身份变得多元,人类群体移动性的交互模式形成新的交互行为逻辑,交互环境由人工智能数字环境和人类智能非数字环境共同构成混合智能的交互样态,信息架构基于自动驾驶形成自适应用户自产生内容UGC前馈和无人驾驶车专业生产内容PGC反馈的智能信息,新的人类移动性催生出由交互载体、功能、内容三要素构成的新的人机交互范式。     

基于内隐测量的APP交互流程可用性评估方法

目的 研究内隐测量用于交互流程评估的普遍方法，选取适合的参考指标建立评估标准，旨在提出一套完整且通用的评估策略。方法 以带有拍摄功能的宠物社交类APP为载体，提出两种不同的交互流程，建立交互原型，并提取两套原型中差异较大的流程进行对比实验，采用眼动仪收集被测的无意识行为，依据首次注视时间、兴趣区域注视率，注视点图等指标分析实验数据，并与外显测量结果相结合，衡量用户操作情况以及APP的交互性能。结果 根据实验和数据分析，得出以拍摄界面为主页是更适合宠物社交APP的交互方式。结论 内隐测量评估作为一种新兴的产品可用性评估方式，不仅在交互界面设计评估上得到了广泛的应用，还可作为产品交互流程的评估方法，并具有深度挖掘的意义。     

不同任务模式下APP三种交互框架的可用性比较

目的 APP的交互框架能够有效引导用户操作,交互框架的选择需要与产品中最主要的任务模式进行匹配,本研究为探究不同任务模式下三种交互框架的可用性表现差异。方法采用手机APP原型模拟任务的方法,考察了被试在使用标签式、侧边展开式、宫格式这三种典型交互框架来完成切换任务和沉浸任务时的反应时、任务难度评分以及偏好评价,并探究了搜索目标位于不同系列位置时被试完成切换任务的反应时和任务难度评分。结果 (1)对于切换任务模式,被试使用标签式的绩效和主观评价都优于其它交互框架,而使用侧边展开式的任务完成绩效和主观评价最差;(2)当进行切换任务时,搜索目标位于首屏界面下半部分时绩效最佳,其次是位于首屏界面上半部分,而搜索目标位于需要下滑滚动的位置时最差;(3)对于沉浸任务模式,被试使用三种交互框架从绩效和主观评价上都无显著差异。结论交互框架的行为绩效与主观评价会受到任务模式的影响,因此在选择APP最佳的交互框架时应根据APP的主要任务模式来决定。     

Variable thermal singularity boundary elements in the study of neighbouring singularities

Two new boundary elements are presented for the simulation of variable order thermal singularities in two dimensions. The first can model the variable order temperature derivative and heat flux singularities at one end of the element. The second element can simulate the temperature derivative and heat flux singularities at both the ends of the element simultaneously. These elements are useful for studying the interaction of variable order thermal neighbouring singularities. They are employed here for the computation of stress intensity factors in the crack–crack interaction problems under thermal load. To improve the accuracy of such computations a modified crack closure integral based method is adapted. Examples of mode I and mode II centre crack, two collinear neighbouring cracks, kinked crack in a plate, and tee joint with a kinked edge crack under thermal or thermal and mechanical loading are studied to illustrate the usefulness of these elements in the study of neighbouring thermal singularities. Copyright © 2001 John Wiley & Sons, Ltd.     

New multifrequency method for the determination of the dissipation factor of capacitors and of the time constant of resistors

A new method for the simultaneous determination of the dissipation factor of capacitors and of the time constant of resistors by a multifrequency method is presented. This method is based on the measurement of impedance ratios at two or more frequencies. A bridge is set up with a programmable two-channel ac voltage source and the impedances to be compared. The impedance ratios are determined by synchronous sampling procedures and application of discrete Fourier transform. In a first experiment, a high-grade gas-filled 1 nF standard capacitor was compared with a stable 1 M/spl Omega/ ac resistor at frequencies between 31 Hz and 666 Hz. The estimated standard uncertainties (k=1) are 0.6/spl middot/10/sup -6/ for the dissipation factor of the capacitor and 0.4 ns for the time constant of the ac resistor.     

Porphyrin assembly on beta-cyclodextrin for selective sensing and detection of a zinc ion based on the dual emission fluorescence ratio

In the present paper, a new cyclodextrin/porphyrin supramolecular sensitizer for zinc ion has been proposed based on the porphyrin dual fluorescence emission ratio. In aqueous solution, meso-tetraphenylporphyrin shows weak fluorescence, while in the presence of alkylated beta-cyclodextrin, it exhibits significant fluorescence enhancement by forming a cyclodextrin/porphyrin inclusion complex. Furthermore, the formation of a supramolecular complex causes a remarkable increase of the porphyrin metalation rate following the porphyrin fluorescence emission changes at two different emission wavelengths. The fluorescence emission of tetraphenylporphyrin at 656-nm bands decreases while that at 606 nm increases upon zinc ion interaction. Thus, the inclusion complex can behave as a ratiometric fluorescent sensor. Theoretically derivative equations for fluorescent ratiometry have been proposed for the first time. The feasibility of the proposed method is demonstrated by the performance of fluorometric detection of zinc ion. With the optimum conditions described, zinc ion in aqueous solution can be determined from 5.0 x 10(-7) to 2.5 x 10(-4) M. As the porphyrin electronic absorption and fluorescence emission are located in the visible range, and the fluorescence changes upon zinc ion interaction show high selectivity over biologically relevant cations, the inclusion complex could be used for biomedical application.     

Real time and in situ control of the gap size of nanoelectrodes for molecular devices

Molecular electronics is often limited by the lack of a simple method to fabricate nanoelectrodes with controlled gap size. This is partly attributed to the lack of a real time characterization in the fabrication. Here, we report a new method based on an electron induced deposition process operated in scanning electron microscopy that realizes in situ and real time characterization in the nanoelectrode fabrication; thus the gap size can be controlled easily and precisely. It is a clean and nondestructive process for carbon nanotube (CNT) electrodes. The mechanism is detailed. The nanoelectrodes have a pi-conjugated surface due to the deposition of sp(2)-rich amorphous carbon. As an application, DNA molecules are assembled between the CNT electrodes by pi-stacking interaction for current-voltage measurement. Our result provides a feasible route to prepare nanoelectrodes with controlled gap size, and it will be valuable for current efforts in molecular electronics and nanoelectronics.     

一种新的复介电常数自由空间测量技术研究

提出了一种新的复介电常数的自由空间测量方法,该方法将介质周期结构引入到复介电常数的测量中。运用多模网络理论与严格的模匹配技术,系统分析了加损耗样品层的介质周期结构的散射特性,详细研究了样品复介电常数对反射峰幅度和中心频率的影响。该测量方法不仅克服了传统自由空间法的不稳定性和相位模糊性问题,而且具有谐振法可以对低损耗介质精确测量且测量过程简单的优点,为复介电常数的精确测量提供了一种新的测量方法和重要的理论指导。     

一种新型裂尖加强函数的显式动态扩展有限元法

基于扩展有限元方法提出了一种新的裂尖加强函数,与传统三角函数基表征的加强函数相比,该裂尖加强函数通过组合传统的函数基,继承了传统附加函数的特性,同时使得结点的奇异附加自由度减少为2个,减少了总体劲度矩阵的规模,提高了计算效率。通过集中质量矩阵考虑结构的惯性效应,使用显式时间积分方法计算了含裂纹结构的瞬间受载问题,并应用相互作用积分得到裂尖端点处的动态应力强度因子。通过相关算例的对比分析,验证了所提出的裂尖加强函数的有效性,同时表明采用显式时间积分方法进行结构动态响应分析的可行性及准确性。     

Dynamic investigation of laminated composite beams with shear and rotary inertia effect subjected to the moving oscillators using FEM

An algorithm based on the finite element method (FEM) has been developed to study the dynamic response of composite laminated beams subjected to the moving oscillator. The first order shear deformation theory (FSDT) is assumed for the beam model. The algorithm accounts for the complete dynamic interaction between the components of system. The proposed method can also be applied to the general moving mass and the simplified moving force problems. After deriving the governing equations of motion of beam and oscillator, the corresponding equations of motion are integrated by applying the Newmark’s time integration procedures to obtain the system responses in each time step. The numerical results of free vibration and moving force problems analysis of isotropic and composite laminated beams are presented and, whenever possible, compared to the available analytical solution and other numerical results in order to demonstrate the accuracy of the present method. In addition, parametric analysis is carried out over a wide range of velocities and mass, frequency and damping ratios of system components.     

任意随机激励下结构随机振动分析的一种数值方法

应用复化Cotes数值积分方法改进精细积分方法,建立一种新的高效的精细积分方法：C-PTSIM,并基于有限元理论讨论了此方法在任意随机激励下线性结构随机动力响应的应用。采用复化Cotes积分方法计算结构动力响应状态方程一般解的积分项,推导出随机激励下结构动力响应的显式表达式,利用一阶矩和二阶矩运算规律计算结构响应的均值和方差。C-PTSIM方法避免了精细积分过程中系数矩阵求逆问题,有效改善了精细积分在时间步长内载荷线性化假设带来的误差,在不改变时间步长时采用高次数复化积分时获得与更精细步长时同样精度的结果,表明该方法对时间步长的弱敏感性,并能节省大量的计算时间。基于此方法给出结构随机振动响应分析算例,并与其他方法对比,说明了该方法的高效率和高精度。