A technique for in situ X-ray computed tomography of deformation-induced cavitation in thermoplastics

Deformation-induced cavitation influences the mechanical response of polymeric materials, but acquiring in situ measurements of the spatial evolution of cavities has typically necessitated the use of synchrotron radiation sources. The objective of this study is to develop and demonstrate a method allowing for in situ measurements of deformation-induced cavitation in axisymmetric polymer specimens, using a home-laboratory X-ray computed tomography setup. The method is demonstrated by assessing deformation-induced cavitation of mineral-filled PVC in a repeated loading-unloading experiment. A temporal resolution of about 3 s is obtained by exploiting the axisymmetry of notched round tensile specimens. The evolution of relative density was captured throughout the experiment, revealing an interplay between void nucleation and void growth. Combined with surface deformation measurements obtained by digital image correlation, the present technique yields data suitable for calibration and validation of material models.     

Uniqueness of Solution to Systems of Elliptic Operators and Application to Asymptotic Synchronization of Linear Dissipative Systems II: Case of Multiple Feedback Dampings

In this paper, the authors consider the asymptotic synchronization of a linear dissipative system with multiple feedback dampings. They ?rst show that under the observability of a scalar equation, Kalman’s rank condition is su?cient for the uniqueness of solution to a complex system of elliptic equations with mixedobservations. The authors then establish a general theory on the asymptotic stability and the asymptotic synchronization for the corresponding evolutional system subjected to mixed dampings of various natures. Some classic models are presented to illustrate the ?eld of applications of the abstract theory.     

Bursting synchronization in networks with long-range coupling mediated by a diffusing chemical substance

Many networks of physical and biological interest are characterized by a long-range coupling mediated by a chemical which diffuses through a medium in which oscillators are embedded. We considered a one-dimensional model for this effect for which the diffusion is fast enough so as to be implemented through a coupling whose intensity decays exponentially with the lattice distance. In particular, we analyzed the bursting synchronization of neurons described by two timescales (spiking and bursting activity), and coupled through such a long-range interaction network. One of the advantages of the model is that one can pass from a local (Laplacian) type of coupling to a global (all-to-all) one by varying a single parameter in the interaction term. We characterized bursting synchronization using an order parameter which undergoes a transition as the coupling parameters are changed through a critical value. We also investigated the role of an external time-periodic signal on the bursting synchronization properties of the network. We show potential applications in the control of pathological rhythms in biological neural networks.     

Error evaluation for Zernike polynomials fitting based phase compensation of digital holographic microscopy

Combining the experimental research with the simulation calculation, the error evaluation for Zernike polynomials fitting (ZPF) based phase compensation of digital holographic microscopy (DHM) is performed. The obtained results show that the reconstructed phase with high precision can be obtained by ZPF phase compensation algorithm. Moreover, the phase error for ZPF based phase compensation algorithm increases with both the variation of object height and object transverse area, the larger variation of object height, the larger of phase error, and the larger of object transverse area, the faster increase of RMS phase error. To decrease the error of ZPF phase compensation algorithm, it is required to ensure one of the variations of object height and object transverse area to be a small value. Importantly, the proposed method supplies a useful tool for the error evaluation of phase compensation algorithm.     

Experimental investigation of the effect of temperature on the strength of polyimide contact structures

A new photogrammetry based measurement technique for contact areas in line contact structures is developed. From the data collected by this technique, a method for measuring the contact strength of contact structures in high temperature applications is proposed. The contact strength of a line contact structure of polyimide at different temperatures is measured; the results show that the increase in temperature decreases the contact strength of the structure. The effect of temperature on the contact strength is studied by investigating the occurrence and evolution of yielding core within the structure at different temperatures. The decrease in the yield strength and elastic modulus of the polyimide material at high temperature induces core yielding at lower loads and eases the propagation of core yielding to the surface.     

Optical extensometer and elimination of the effect of out-of-plane motions

A novel optical extensometer is developed to estimate the local uniform strain on planar surface accurately. The proposed system consists of a shared large format lens and two image sensors, which acquire pairs of images of two isolated small regions on the object surface simultaneously. Digital image correlation (DIC) algorithm is applied to determine the relative displacement between gauge points designated on recorded pairs of images. Then local strain can be extracted after dividing the relative displacement by the scale distance. Moreover, a special experimental setup called “correction sheet” is used to eliminate the virtual strain induced by out-of-plane motions. Uni-axial tensile experiments are performed to validate the reliability and resolution of the optical extensometer, and the measurement results demonstrate that the resolution of the optical extensometer achieves 2–3 με.     

Gaussian pre-filtering for uncertainty minimization in digital image correlation using numerically-designed speckle patterns

This paper discusses the effect of pre-processing image blurring on the uncertainty of two-dimensional digital image correlation (DIC) measurements for the specific case of numerically-designed speckle patterns having particles with well-defined and consistent shape, size and spacing. Such patterns are more suitable for large measurement surfaces on large-scale specimens than traditional spray-painted random patterns without well-defined particles. The methodology consists of numerical simulations where Gaussian digital filters with varying standard deviation are applied to a reference speckle pattern. To simplify the pattern application process for large areas and increase contrast to reduce measurement uncertainty, the speckle shape, mean size and on-center spacing were selected to be representative of numerically-designed patterns that can be applied on large surfaces through different techniques (e.g., spray-painting through stencils). Such “designer patterns” are characterized by well-defined regions of non-zero frequency content and non-zero peaks, and are fundamentally different from typical spray-painted patterns whose frequency content exhibits near-zero peaks. The effect of blurring filters is examined for constant, linear, quadratic and cubic displacement fields. Maximum strains between ±250 and ±20,000 µε are simulated, thus covering a relevant range for structural materials subjected to service and ultimate stresses. The robustness of the simulation procedure is verified experimentally using a physical speckle pattern subjected to constant displacements. The stability of the relation between standard deviation of the Gaussian filter and measurement uncertainty is assessed for linear displacement fields at varying image noise levels, subset size, and frequency content of the speckle pattern. It is shown that bias error as well as measurement uncertainty are minimized through Gaussian pre-filtering. This finding does not apply to typical spray-painted patterns without well-defined particles, for which image blurring is only beneficial in reducing bias errors.     

A superhydrophobic magnetic elastomer actuator for droplet motion control

For the fast droplet transportation on an open surface, a new magnetic elastomer with a superhydrophobic surface has been developed. Because the surface is superhydrophobic, the water droplet can easily roll off on the surface. The movement of the droplet was controlled by a deliberate local deformation of the surface of the elastomer induced by magnetic actuation. The direction and speed of the droplet motion was easily controlled by changing the surface topography using magnetic force. We also demonstrate the applicability of the devices as a new type of open‐surface digital microfluidics using a simple chemical reaction. Copyright © 2013 John Wiley & Sons, Ltd.     

Kinetic study of electrochemically induced Michael reaction of1,4-dihydroxyanthraquinone with acetylacetone and benzoylacetone

The electrochemical oxidation of 1,4-dihydroxyanthraquinone has been studied in the presence of acetylacetone and benzoylacetone as nucleophiles in a mixture of ethanol/water by means of cyclic voltammetry as a diagnostic technique.The results indicate the participation of electrochemically produced anthraquinone in the Michael addition reaction with acetylacetone and benzoylacetone to form the corresponding new anthraquinone derivatives.On the basis of the EC mechanism,the observed homogeneous rate constants（kobs）of the reaction of anthraquinone with acetylacetone and benzoylacetone were estimated by comparing the experimental cyclic voltammograms with the digitally simulated results.     

基于无线传感器网络的飞行器测控通信系统测量方案设计

随着航天技术的发展,飞行器测控通信系统需要测量的参数种类和数量不断增加,但同时要求系统在进行方案搭建时满足更高的可靠性、更小的体积和更小的设备质量。为解决这类问题,提出了基于无线传感器网络的飞行器测量方案,方案重点从节点配置、时间同步、网络拓扑、能源供应等方面对方案进行阐述,最后给出了应解决的关键技术攻关方向。