Model reduction for nonlinear multiscale parabolic problems using dynamic mode decomposition

In this article, a model reduction technique is presented to solve nonlinear multiscale parabolic problems using dynamic mode decomposition. The multiple scales and nonlinearity bring great challenges for simulating the problems. To overcome this difficulty, we develop a model reduction method for the nonlinear multiscale dynamic problems by integrating constraint energy minimizing generalized multiscale finite element method (CEM-GMsFEM) with dynamic mode decomposition (DMD). CEM-GMsFEM has shown great efficiency to solve linear multiscale problems in a coarse space. However, using CEM-GMsFEM to directly solve multiscale nonlinear parabolic models involves dynamically computing the residual and the Jacobian on a fine grid. This may be very computationally expensive because the evaluation of the nonlinear term is implemented in a high-dimensional fine scale space. As a data-driven method, DMD can use observation data and give an explicit expression to accurately describe the underlying nonlinear dynamic system. To efficiently compute the multiscale nonlinear parabolic problems, we propose a CEM-DMD model reduction by combing CEM-GMsFEM and DMD. The CEM-DMD reduced model is a coarsen linear model, which avoids the nonlinear solver in the fine space. It is crucial to judiciously choose observation in DMD. Only proper observation can render an accurate DMD model. In the context of CEM-DMD, we introduce two different observations: fine scale observation and coarse scale observation. In the construction of DMD model, the coarse scale observation requires much less computation than the fine scale observation. The CEM-DMD model using the coarse scale observation gives a complete coarse model for the nonlinear multiscale dynamic systems and significantly improves the computation efficiency. To show the performance of the CEM-DMD using the different observations, we present a few numerical results for the nonlinear multiscale parabolic problems in heterogeneous porous media.     

脉冲风洞短时测力信号的延拓与动态载荷辨识方法

研究了一种可快速辨识脉冲风洞中试验模型所受动态载荷的方法。给出了载荷、系统单位脉冲响应函数、天平输出三者的时域离散化模型,指出后者是前两者线性卷积的截断;将天平短时振荡输出延拓为完整的线性卷积结果,对前两者补零延拓,将上述模型转化为圆周卷积形式,进而通过离散傅里叶变换得到三者的频域离散化模型,求解频域模型得到载荷。通过单自由度系统简单载荷、多自由度系统复杂载荷两个数值模拟算例验证了该方法仅需对测量信号低通滤波即可准确辨识出载荷;经风洞试验,验证了方法的准确性和实用性。     

基于卷积神经网络的刀具磨损在线监测

为了提高刀具磨损在线监测的精度和泛化性能,提出一种基于卷积神经网络的刀具磨损量在线监测模型。利用时域传感器信号对刀具磨损量进行定量分析,避免数据预处理带来的信息丢失;采用深度网络自适应地提取特征,取代传统的人工特征提取过程,并通过加深网络进一步挖掘信号中隐藏的微小特征。实验结果表明,该模型对刀具后刀面磨损量监测效果较好,可以有效避免人为特征提取的局限,精度和泛化性都有一定程度的提高。与相关研究的对比也证实了其可行性和有效性。     

Towards a multi-physics modelling framework for thrombolysis under the influence of blood flow

Thrombolytic therapy is an effective means of treating thromboembolic diseases but can also give rise to life-threatening side effects. The infusion of a high drug concentration can provoke internal bleeding while an insufficient dose can lead to artery reocclusion. It is hoped that mathematical modelling of the process of clot lysis can lead to a better understanding and improvement of thrombolytic therapy. To this end, a multi-physics continuum model has been developed to simulate the dissolution of clot over time upon the addition of tissue plasminogen activator (tPA). The transport of tPA and other lytic proteins is modelled by a set of reaction–diffusion–convection equations, while blood flow is described by volume-averaged continuity and momentum equations. The clot is modelled as a fibrous porous medium with its properties being determined as a function of the fibrin fibre radius and voidage of the clot. A unique feature of the model is that it is capable of simulating the entire lytic process from the initial phase of lysis of an occlusive thrombus (diffusion-limited transport), the process of recanalization, to post-canalization thrombolysis under the influence of convective blood flow. The model has been used to examine the dissolution of a fully occluding clot in a simplified artery at different pressure drops. Our predicted lytic front velocities during the initial stage of lysis agree well with experimental and computational results reported by others. Following canalization, clot lysis patterns are strongly influenced by local flow patterns, which are symmetric at low pressure drops, but asymmetric at higher pressure drops, which give rise to larger recirculation regions and extended areas of intense drug accumulation.     

多尺度YOLO人脸年龄估计方法研究

通过观察人脸估计年龄较为常见，但如何准确预测年龄则是一个难题。为提高人脸图像年龄估计的准确率，提出一种基于YOLO（You Only Look Once）模型的目标检测方法。将多尺度回归思想应用于卷积神经网络（Convolutional Neural Network，CNN），通过多尺度卷积改善模型对小尺寸目标的提取能力，结合特征通道分权重思想，改善特征提取操作中特征信息丢失的问题，构造决策树回归得到年龄估计。这种方法在人脸年龄图像库FG-NET上获得平均绝对误差（MAE）3.43，在GROUP数据集获得区间匹配度（AEM）62.4%。实验结果表明，通过多尺度特征回归以及通道权重分配，可以较为准确地进行人脸信息检测，并由此建立鲁棒性更强的人脸年龄估计模型。     

基于卷积神经网络的构件分类策略的研究

为了提高软件复用过程中构件检索的效率，分析了软件构件分类技术的优缺点以及构件特征，从构件刻面信息的角度，采用卷积神经网络技术，提出一种基于卷积神经网络的构件分类策略；利用卷积神经网络对构件刻面特征进行提取，减少人为因素，提高刻面信息提取精确性，并训练出基于卷积神经网络的构件分类模型，通过具体的实验，来论证该模型的准确性，以达到提高构件检索效率的目的。     

Changes in kernel properties,in situ gelatinization,and physicochemical properties of waxy rice with inhibition of starch branching enzyme during cooking

The kernel properties, gelatinisation and physicochemical properties of rice were investigated in a waxy rice Guang-ling-xiang-nuo (GLXN) and its transgenic line GLXN-RNAi with inhibition of starch branching enzyme I/IIb. The volume swelling, water content and leached material of cooked kernels increased with increasing cooking time, but they were lower in GLXN-RNAi than in GLXN. The kernels of GLXN-RNAi were more difficultly gelatinised and disrupted than those of GLXN during cooking. The starch in the exterior of GLXN-RNAi endosperm was not completely gelatinised. The C_A-type starch of GLXN-RNAi was more resistant to cooking than A-type starch of GLXN. The cooked kernels of GLXN-RNAi had lower rapidly digestible starch and greater slowly digestible starch than those of GLXN. Brown rice flour had higher peak, hot, final and setback viscosities and lower breakdown viscosity in GLXN than GLXN-RNAi. These results indicated that GLXN-RNAi kernels exhibited great potential in applications as health foods.     

A high-throughput maize kernel traits scorer based on line-scan imaging

Maize kernel traits such as kernel length, kernel width and kernel number determine kernel weight and, consequently, maize yield. Therefore, the measurement of kernel traits is important for maize breeding and the evaluation of maize yield. The conventional method for measuring kernel traits is still manual, which is time consuming, costly and subjective. In this study, a novel maize kernel traits scorer (MKTS) was developed for the automatic measurement of 12 maize kernel traits based on line-scan imaging, image processing, and automatic control techniques. Here, total of 615 samples were measured to evaluate the system performance. The results showed that the MKTS was capable of evaluating maize kernel traits with the mean absolute percentage error of the manual and automatic measurements less than 5% and the measurement efficiency of approximately 72 s for the measurement of 6 ears. In conclusion, this high-throughput scorer will provide maize scientists with a novel tool to assist in maize functional genetics and maize breeding.     

A smoothed particle hydrodynamics and coarse‐grained molecular dynamics hybrid technique for modelling elastic particles and breakable capsules under various flow conditions

In this work, a hybrid numerical approach, which combines elements of SPH and coarse‐grained molecular dynamics, is used to investigate the effect of various flow conditions to deformable and breakable shell‐structures such as capsules, vesicles or biological cells. Copyright © 2014 John Wiley & Sons, Ltd.     

LTI连续时间系统零状态响应的求解方法

目前国内很多"信号与系统"的教材中讨论了LTI连续时间系统零状态响应的一些求解方法,本文根据现有的信号与系统教材中连续时间系统零状态响应的求解方法,分别从利用冲激响应与激励的卷积、微分方程和变换域三方面求解零状态响应,并给出了实例说明了其正确性。