从自然形象到艺术形象的升华——谈风景写生的概括与提炼

艺术作品中的艺术形象是画家对客观自然进行高度概括和提炼的结果,也是画家艺术思想、审美理想和价值观念等主观精神的集中反映。笔者通过对视像的空间构成、基本特征、色彩关系等诸因素的概括与提炼的论述,认为这些因素是自然形象升华为艺术形象的关键所在。     

Transient fluid–structure interaction with non-matching spatial and temporal discretizations

This paper presents a review of spatial and temporal discretization schemes for unsteady flow interacting with structure. Two types of spatial coupling schemes are analyzed: (i) point-to-element projection and (ii) common-refinement based projection. It is shown that the point-to-element projection schemes may yield inaccurate load transfer from the source fluid mesh to the target solid mesh, leading to a weak instability in the form of spurious oscillations and overshoots in the interface solution. The common-refinement scheme resolves this problem by providing an accurate transfer of discrete interface conditions across non-matching meshes. With respect to the temporal discretization, three coupling techniques are assessed: (i) conventional sequential staggered (CSS); (ii) generalized serial staggered (GSS) and (iii) combined interface boundary condition (CIBC). Traditionally, continuity of velocity and traction along interfaces are satisfied through algebraic interface conditions applied in a sequential fashion, which is often referred to as staggered computation. In existing partitioned staggered procedures, the interface conditions may undermine stability and accuracy of coupled fluid–structure simulations. By utilizing the CIBC technique on the velocity and traction boundary conditions, a staggered coupling procedure can be constructed with similar order of accuracy and stability as standalone computations. The effectiveness of spatial and temporal coupling schemes is investigated with the aid of simple 1D examples and new 2D subsonic flow-shell aeroelastic simulations.     

Processing, microstructure and mechanical properties of nickel particles embedded aluminium matrix composite

Nickel particles were embedded into an Al matrix by friction stir processing (FSP) to produce metal particle reinforced composite. FSP resulted in uniform dispersion of nickel particles with excellent interfacial bonding with the Al matrix and also lead to significant grain refinement of the matrix. The novelty of the process is that the composite was processed in one step without any pretreatment being given to the constituents and no harmful intermetallic formed. The novel feature of the composite is that it shows a three fold increase in the yield strength while appreciable amount of ductility is retained. The hardness also improved significantly. The fracture surface showed a ductile failure mode and also revealed the superior bonding between the particles and the matrix. Electron backscattered diffraction (EBSD) and transmission electron microscopy analysis revealed a dynamically recrystallized equiaxed microstructure. A gradual increase in misorientation from sub-grain to high-angle boundaries is observed from EBSD analysis pointing towards a continuous type dynamic recrystallization mechanism.     

Effects of modification on microstructure and properties of ultrahigh carbon (1.9 wt.% C) steel

The effects of a modifier that contains Rare Earths (RE), low melting point alloy (Al-Bi-Sb) and Ca-Si alloy on an ultrahigh carbon steel containing 1.9 wt.% C were studied. Microstructure characterization was carried out with optical microscopy (OM) and scanning electronic microscopy (SEM) combined with energy-dispersive spectrometry (EDS). Upon modification, the continuous eutectic carbide network structure was broken up and changed to a partly isolated and finer blocky structure in the as-cast alloy. Differential scanning calorimetry (DSC) revealed that the eutectoid temperature increased and the eutectic temperature decreased for the modified alloy. Modification also improved the impact toughness of the tempered steel, with a significant increase from 6.5 to 12.6 J cm⁻², despite the hardness remaining around 66 HRC. Furthermore, in pure sliding under loads of 20, 60 and 100 N for 600 s against a zirconia ball, the modified alloy shows slightly higher friction coefficient at all loads than the non-modified one. In addition, the friction coefficient for the steel specimen decreased with load from 20 N to 100 N attributing to a reduction in metallic wear and the formation of a thicker oxide film on the surfaces.     

Sparse intrinsic decomposition and applications

This paper proposes an intrinsic decomposition method from a single RGB-D image. To remedy the highly ill-conditioned problem, the reflectance component is regularized by a sparsity term, which is weighted by a bilateral kernel to exploit non-local structural correlation. As shading images are piece-wise smooth and have sparse gradient fields, the sparse-induced ${\ell }_1$-norm is used to regularize the finite difference of the direct irradiance component, which is the most dominant sub-component of shading and describes the light directly received by the surfaces of the objects from the light source. To derive an efficient algorithm, the proposed model is transformed into an unconstrained minimization of the augmented Lagrangian function, which is then optimized via the alternating direction method. The stability of the proposed method with respect to parameter perturbation and its robustness to noise are investigated by experiments. Quantitative and qualitative evaluation demonstrates that our method has better performance than state-of-the-art methods. Our method can also achieve intrinsic decomposition from a single color image by integrating existed depth estimation methods. We also present a depth refinement method based on our intrinsic decomposition method, which obtains more geometry details without texture artifacts. Other application, e.g., texture editing, also demonstrates the effectiveness of our method.     

RECENT PROGRESS IN INCOMPRESSIBLE REYNOLDSAVERAGED NAVIER-STOKES SOLVERS

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频谱细化及频谱校正技术在激光多普勒测速仪中的应用

提出了对多普勒信号先进行频谱细化,再进行频谱校正的方法,阐述了几种常见的离散频谱细化和频谱校正算法的基本原理,并运用它们对不同频率的理想正弦信号和实测的多普勒信号进行谱仿真和实测研究。理论分析和实验结果表明:频谱细化算法中Goertzel细化算法所需的运算量最少,计算速度最快;频谱校正算法中比值校正算法校正公式简单,运算量少,且校正精度较高;频谱细化和频谱校正技术大大提高了频谱分辨率,将其运用于频谱分析型激光多普勒测速仪中切实可行。     

扩展BPEL4WS实现基于语义的服务流程动态细化

越来越多的企业采用面向服务的架构来构建其信息基础设施,并通过执行Web服务流程来实现其业务逻辑。然而,当前作为工业界标准的服务流程建模语言BPEL4WS只能支持非常有限的运行时动态性,难以适应复杂多变的业务需求。针对这一问题,提出了在BPEL4WS及其执行引擎之上,实现基于语义的服务流程动态细化的机制——在BPEL4WS中增加目标类型的活动以及流程的语义描述；扩展现有BPEL4WS执行引擎使之能够执行带有目标活动的流程,并能够根据目标描述与流程的数据内容,在运行时为目标活动匹配与绑定子流程。     

Efficient local stereo matching algorithm based on fast gradient domain guided image filtering

Guided image filtering (GIF) based cost aggregation or disparity refinement stereo matching algorithms are studied extensively owing to the edge-aware preserved smoothing property. However, GIF suffers from halo artifacts in sharp edges and shows high computational costs on high-resolution images. The performance of GIF in stereo matching would be limited by the above two defects. To solve these problems, a novel fast gradient domain guided image filtering (F-GDGIF) is proposed. To be specific, halo artifacts are effectively alleviated by incorporating an efficient multi-scale edge-aware weighting into GIF. With this multi-scale weighting, edges can be preserved much better. In addition, high computational costs are cut down by sub-sampling strategy, which decreases the computational complexity from O(N) to O(N/s²) (s: sub-sampling ratio) To verify the effectiveness of the algorithm, F-GDGIF is applied to cost aggregation and disparity refinement in stereo matching algorithms respectively. Experiments on the Middlebury evaluation benchmark demonstrate that F-GDGIF based stereo matching method can generate more accuracy disparity maps with low computational cost compared to other GIF based methods.     

Dynamically adaptive real-time disparity estimation hardware using iterative refinement

The computational complexity of disparity estimation algorithms and the need of large size and bandwidth for the external and internal memory make the real-time processing of disparity estimation challenging, especially for High Resolution (HR) images. This paper proposes a hardware-oriented adaptive window size disparity estimation (AWDE) algorithm and its real-time reconfigurable hardware implementation that targets HR video with high quality disparity results. Moreover, an enhanced version of the AWDE implementation that uses iterative refinement (AWDE-IR) is presented. The AWDE and AWDE-IR algorithms dynamically adapt the window size considering the local texture of the image to increase the disparity estimation quality. The proposed reconfigurable hardware architectures of the AWDE and AWDE-IR algorithms enable handling 60 frames per second on a Virtex-5 FPGA at a 1024×768 XGA video resolution for a 128 pixel disparity range.