Generation and quality improvement of 3D models from silhouettes of 2D images

The shape-from-silhouette (SFS) method has been widely used in 3D shape reconstruction. It uses silhouettes of a series of 2D images captured from multiple viewpoints of an object to generate a 3D model that describes the visual hull of the object. The SFS method faces an inherent problem that virtual features appear all over the model. In addition, concavities on the object may wrongly be modeled as convex shapes because they are invisible on image silhouettes. The purpose of this study is to propose a method to generate a 3D model from silhouettes of multiple images and propose a quality improvement method to overcome the above-mentioned problems. The 3D modeling method focuses on accurate evaluation of 3D points intersected by all polyhedra from different views and the removal of poor meshes on triangulation. The quality improvement method is essentially an iterative procedure, which for smoothing the model and eliminating virtual features and artifacts, while preserving the consistency of all silhouettes. The proposed method is to be used for product presentations in e-commerce, in which the 3D model must be covered with color texture of an object. Several examples are presented to illustrate the capability of the proposed method.     

Fe-Mn-Si-Cr-Ni-C系形状记忆合金时效效果的研究

通过SEM分析，研究了时效后不同成分Fe-Mn-Si-Cr-Ni-C系形状记忆合金形状记忆效应和微观组织，在1123K时效时，超低碳合金1的形状回复率随时效时间的增加一直呈直线上升的趋势，含碳0．18％合金2的形状回复率随时效时间的增加而增加，在300min达到最大值后将随时间的进一步增加而缓慢下降，SEM分析发现在合金2的晶界和晶内析出富铬，富锰和富硅的合金碳化物，而合金1仅在晶界有第二相析出，且第二相成分不同于合金2中的，合金2中第二相粒子的长大速度显著高于合金1中第二相粒子的长大速度，且数量也多得多，通过时效强化奥氏体基体，可显著提高合金的形状记忆效应。     

High glass-transition polyurethane-carbon black electro-active shape memory nanocomposite for aerospace systems

Carbon black conductive filler material, 2–40% by weight was added to specially designed polyurethane polymer to prepare shape memory polymer nanocomposites. The synthesised polyurethane (PU) has exhibited a high glass transition temperature of 85°C compared to the reported values in published literatures. The polymer was characterised for its chemical, electrical, thermal and mechanical properties. The stiffness, load-bearing capacity and electrical conductivity were observed to improve with increased carbon loading. It was found to be capable of responding to thermal as well as electrical stimuli. The shape recovery efficiency was found to be 94% for thermal and 98% for electrical stimuli which is among the highest for PU reported so far.

This review was submitted as part of the 2019 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged.     

Image focus volume enhancement in shape from focus systems

Three-dimensional object reconstructions is an active research area in digital imaging. In shape from focus approach, erroneous focus measurements result in inaccuracy in the depth map reconstruction of 2D object. Conventionally, to enhance the image focus volume, focus values are aggregated within a window, which is a linear filtering approach. Owing to the inherent limitation of linear process, optimal results may not be obtained. In order to overcome this limitation, a non-linear filtering approach is proposed to enhance the image focus volume for accurate depth estimation. The noisy focus values are restored in two steps. First, noisy focus values are detected using min–max operators. In order to increase the dynamic range between the minimum and the maximum focus values within the window, an appropriate power law function is designed. In second step, only the noisy measurements are replaced with the estimated ones. A refined depth map is obtained from the updated focus volume. This process continues until the difference between the previous and the current depth maps becomes very small. The performance of the proposed non-linear filtering approach is obtained for various synthetic and real objects. The results highlight the depth map estimates of the proposed approach more accurate while preserving object edges. Comparative analysis demonstrates the effectiveness of the proposed approach.     

脉冲电场对FeMnSiCr形状记忆合金凝固组织及形状记忆效应的影响

研究了脉冲电场对FeMnSiCr合金凝固组织和形状记忆效应的影响.发现脉冲电场作用于FeMnSiCr合金凝固过程将使合金凝固组织的晶粒得到细化,分析认为柱状晶的存在使形状记忆效应明显提高.在脉冲电压为250V、频率为3Hz的条件下,贴近极冷区,FeMnSiCr合金的形状记忆效应最好.     

A random parameters probit model of urban and rural intersection crashes

Intersections are hazardous locations and many studies have been conducted to identify the factors contributing to the frequency and severity of intersection crashes. However, little attention has been devoted to investigating the differences between crashes at urban and rural intersections, which have different road, traffic and environmental characteristics. By applying a random parameters probit model to the data from the Canadian Province of Alberta between 2008 and 2012, we find that urban intersection crashes are more likely to be associated with hit and run behaviours, roads with higher traffic volume, wet surfaces, four lanes and skewed intersections, and crashes on weekdays and off-peak hours, whereas rural crashes are likely to be associated with increases in fatalities and injuries, roads with higher speed limits, special road features, exit and entrance terminals, gravel, curvature and two lanes, crashes during weekends, peak hours and night-time, run-off-road crashes, and police visit to crash scene. Hence, road safety professionals in urban and rural areas should consider these differences when designing and implementing counter-measures to improve intersection safety, especially their safety audits and reviews, enforcement activities and education campaigns, to target the more vulnerable times and locations in the different areas.     

时效工艺对Fe-14Mn-5Si-8Cr-4Ni-0.2C合金形状记忆效应的影响

研究了时效工艺对Fe-14Mn-5Si-8Cr-4Ni-0.2C合金形状记忆效应和微观组织的影响，研究结果表明，变形后再时效对合金形状记忆效应的提高比不变形直接时效的显著得多，变形后时效将合金的形状回复率提高了190％，而直接时效只提高了83％，经SEM和TEM分析发现，同样时效时间下，与直接时效相比，变形后再时效一方面不仅减少了碳化物的析出数量，抑制了碳化物粒子的长大；另一方面还使第二相粒子主要在晶界上析出，而不是在晶内，正是这两方面的原因导致变形后时效对合金形状记忆效应的提高比不变形直接时效的高得多。     

Polynomial parametrization of nonsingular complete intersection curves

In this paper we give a new method to compute a polynomial parametrization, in case it exists, of an affine nonsingular complete intersection curve. Our method is based on the study of vector fields on nonsingular algebraic curves. In contrast to the existing methods, our algorithm does not use any projection, and no sample point on the curve is needed. It is also important to stress the fact that the algorithm produces a parametrization with coefficients in the ground field.     

发泡CaCO3/杜仲胶形状记忆复合材料的制备与表征

天然杜仲胶的反式有序性结构使其具有较强的结晶能力,交联程度较低时可用作形状记忆材料。本文以热膨胀物理微球Expancel 920DU40为发泡剂制备了发泡CaCO₃/杜仲胶（EUG）形状记忆复合材料,采用SEM、FTIR、DSC、DMA和万能材料试验机等对Expancel 920DU40的组分及受热膨胀特性和不同交联程度的CaCO₃/EUG形状记忆复合材料的结晶熔融行为、微观形貌、形状记忆行为及力学性能进行了表征。结果表明,Expancel 920DU40的外壳为丙烯腈均聚物或与其他单体的共聚物,内部为液态烷烃; CaCO₃/EUG形状记忆复合材料的力学性能与其交联程度和发泡程度有关;随着交联程度的增加,EUG的结晶和熔融温度降低,形变率、形状固定率和形状回复率均降低,当S用量为0.8 g时形状记忆性能最佳;调控交联程度可以获得具备不同形状记忆能力的CaCO₃/EUG形状记忆复合材料。     

An efficient memetic algorithm for 3D shape matching problems

Shape representation plays a vital role in any shape optimization exercise. The ability to identify a shape with good functional properties is dependent on the underlying shape representation scheme, the morphing mechanism and the efficiency of the optimization algorithm. This article presents a novel and efficient methodology for morphing 3D shapes via smart repair of control points. The repaired sequence of control points are subsequently used to define the 3D object using a B-spline surface representation. The control points are evolved within the framework of a memetic algorithm for greater efficiency. While the authors have already proposed an approach for 2D shape matching, this article extends it further to deal with 3D shape matching problems. Three 3D examples and a real customized 3D earplug design have been used as examples to illustrate the performance of the proposed approach and the effectiveness of the repair scheme. Complete details of the problems are presented for future work in this direction.     

大构件相贯线焊接机器人多层多道焊轨迹规划

为了提高大型相贯线焊接构件在使用机器人做埋弧多层多道焊接时的示教和焊接效率,提出了一种焊道轨迹规划方法.设计了一种焊缝填充策略,即各焊层的焊接高度一致,每层中的焊道数与所在层数相同,所有焊道的横截面积相等;推导出多层多道焊的焊道轨迹规划公式,对第二层的第一道焊缝进行示教一次,其余焊道的轨迹即可通过公式求出;按照焊缝搭接的原则,对每个焊道的起弧点的位置进行规划,并详细设计了搭接轨迹的方案.仿真结果显示,该方法能够满足多层多道焊缝填充规划的要求,为机器人焊接时的离线编程提供了理论基础.     

Transverse intersection of invariant manifolds in perturbed multi-symplectic systems

A multi-symplectic system is a PDE with a Hamiltonian structure in both temporal and spatial variables. This article considers spatially periodic perturbations of symmetric multi-symplectic systems. Due to their structure, unperturbed multi-symplectic systems often have families of solitary waves or front solutions, which together with the additional symmetries lead to large invariant manifolds. Periodic perturbations break the translational symmetry in space and might break some of the other symmetries as well. In this article, periodic perturbations of a translation invariant PDE with a one-dimensional symmetry group are considered. It is assumed that the unperturbed PDE has a three-dimensional invariant manifold associated with a solitary wave or front connection of multi-symplectic relative equilibria. Using the momentum associated with the symmetry group, sufficient conditions for the persistence of invariant manifolds and their transversal intersection are derived. In the equivariant case, invariance of the momentum under the perturbation gives the persistence of the full three-dimensional manifold. In this case, there is also a weaker condition for the persistence of a two-dimensional submanifold with a selected value of the momentum. In the non-equivariant case, the condition leads to the persistence of a one-dimensional submanifold with a seleceted value of the momentum and a selected action of the symmetry group. These results are applicable to general Hamiltonian systems with double zero eigenvalue in the linearization due to continuous symmetry. The conditions are illustrated on the example of the defocussing non-linear Schrödinger equations with perturbations which illustrate the three cases. The perturbations are: an equivariant Hamiltonian perturbation which keeps the momentum level sets invariant; an equivariant damped, driven perturbation; and a perturbation which breaks the rotational symmetry.     

规整化最小二乘子空间相交测向技术探讨

在浅海条件下,子空间相交的方法可以消除多途效应的影响,实现水平长阵的准确目标方位估计,获得比常规波束形成算法更优的性能。然而,该算法在数值计算稳定性上存在问题。在最小二乘子空间相交算法的基础上,提出一种Tikhonov规整化的最小二乘子空间相交算法,该算法在原解向量的基础上,施加了一个滤波因子,滤除了小特征值对应的解向量,使算法的数值计算稳定性大大提高,从而也提高了算法的检测性能。试验数据处理结果表明,该算法是有效的。     

基于容量比较法的卧式罐容量表计算方法研究

在卧式罐容量计量容量比较法原理的基础上,讨论了由有限的卧式罐离散(V-H)点计算出全高度量程范围内任意点的容积值的4种计算方法。并以30m³卧式罐为对象进行了试验研究。试验结果表明:Lagrange插值方法、分段线性插值方法、三次多项式拟合方法和三次样条插值方法在中间液位区间的计算结果较为一致;三次样条插值方法计算结果与试验值偏差最小,最大偏差值23.0L,而且稳定性较好;Lagrange插值方法、分段线性插值方法和三次多项式拟合方法在低液位高度或高液位高度的偏差比中间液位区间的计算偏差大;但是在低液位高度和高液位高度区间,由于多节点时边沿振荡原因,Lagrange插值方法的计算偏差大于三次样条插值方法。     

约束态相变中TiNi形状记忆合金的马氏体自拉伸过程

研究了约束态加热过程中产生的回复力对TiNi形状记忆合金剩余马氏体的影响．结果表明，产生的回复力使剩余马氏体发生了塑性变形，使逆相变温度升高，剩余马氏体分数和其逆相变温度之间存在特定的函数关系．但是，外部约束条件的变化对马氏体的自拉伸过程所造成的剩余马氏体分数与其逆相变温度之间的关系影响很小．     

基于混杂系统Q学习最优控制的信号灯控制方法

采用混杂切换系统Q学习最优控制方法实现了单交叉口信号灯优化控制.提出了应用强化学习中的Q学习进行混杂系统切换控制的方法,并将该方法应用于解决交叉口信号灯控制问题.首先建立了交叉口混杂切换系统模型,在确定信号灯控制行为集的基础上,应用Q学习算法决定最优的控制策略,进而得出交叉口信号灯最佳切换信号.采用Paramics微观交通仿真软件进行了仿真,结果验证了采用该方法实现混杂切换系统优化控制问题的可行性和有效性.     

Fe-18Mn-5Si-8Cr-5Ni-0.1N形状记忆合金组织和性能的研究

研究了Fe-18Mn-5Si8Cr-5Ni-0.1N形状记忆合金的形状记忆效应、回复应力、耐蚀性能.结果表明,在Fe-18Mn-5Si-8Cr-5Ni合金中加入0.1%的氮,对合金的形状记忆效应不利,但当预变形量小于4.5%时,降低幅度较小,在14%～18%左右.在变形量小于4.5%时,含氮合金加热时的回复应力高于未加氮的合金的回复应力;当变形量大于4.5%时,含氮合金的回复应力低于未加氮的合金的回复应力,两种合金的加热时最大回复应力的最大值相近(90 MPa左右).又由于氮具有强烈的固溶强化作用,大大强化了基体,使得合金在冷却过程中因回复应力导致的塑性变形量和二次相变量减小,从而导致合金冷却到室温的回复应力显著提高,当预变形量为6%时,含氮合金的室温回复应力最大,比未加氮的合金的最大室温回复应力高约21%.同时,氮的加入有利于提高合金的耐蚀性能.     

A smart repair embedded memetic algorithm for 2D shape matching problems

Shape representation plays a major role in any shape optimization exercise. The ability to identify a shape with good performance is dependent on both the flexibility of the shape representation scheme and the efficiency of the optimization algorithm. In this article, a memetic algorithm is presented for 2D shape matching problems. The shape is represented using B-splines, in which the control points representing the shape are repaired and subsequently evolved within the optimization framework. The underlying memetic algorithm is a multi-feature hybrid that combines the strength of a real coded genetic algorithm, differential evolution and a local search. The efficiency of the proposed algorithm is illustrated using three test problems, wherein the shapes were identified using a mere 5000 function evaluations. Extension of the approach to deal with problems of unknown shape complexity is also presented in the article.