凹壁不稳定性流动的数值计算

凹壁结构在工业应用的多个领域中都是很常见的,由于离心力不稳定性,流体流过凹壁面附近时可能会产生G?rtler涡。为了研究这些涡的特性及对流场产生的影响,采用CFD技术对曲率半径为2 m的弯曲渠道的流动过程进行数值模拟。用有限体积法对模型进行空间离散,采用大涡模拟中Smagorinsky-Lilly模型进行计算。通过与实验结果进行对比发现,计算结果能较准确的反应G?rtler涡随流动的发展过程。在此基础上进行的分析表明:在速度3 m/s,湍流度0.35%的进口条件下,沿流向流过一段距离后,在靠近凹壁的边界层中产生了G?rtler涡;涡轴平行于流动方向并且相邻涡轴之间的距离保持不变;随着涡在展向和法向空间的增长,速度等值线出现"蘑菇状"结构;靠近出口位置"蘑菇状"结构破裂,流动发生转捩。     

Unsupervised MRI segmentation of brain tissues using a local linear model and level set

Real-world magnetic resonance imaging of the brain is affected by intensity nonuniformity (INU) phenomena which makes it difficult to fully automate the segmentation process. This difficult task is accomplished in this work by using a new method with two original features: (1) each brain tissue class is locally modeled using a local linear region representative, which allows us to account for the INU in an implicit way and to more accurately position the region's boundaries; and (2) the region models are embedded in the level set framework, so that the spatial coherence of the segmentation can be controlled in a natural way. Our new method has been tested on the ground-truthed Internet Brain Segmentation Repository (IBSR) database and gave promising results, with Tanimoto indexes ranging from 0.61 to 0.79 for the classification of the white matter and from 0.72 to 0.84 for the gray matter. To our knowledge, this is the first time a region-based level set model has been used to perform the segmentation of real-world MRI brain scans with convincing results.     

A joint shape evolution approach to medical image segmentation using expectation-maximization algorithm

This study proposes an expectation–maximization (EM)-based curve evolution algorithm for segmentation of magnetic resonance brain images. In the proposed algorithm, the evolution curve is constrained not only by a shape-based statistical model but also by a hidden variable model from image observation. The hidden variable model herein is defined by the local voxel labeling, which is unknown and estimated by the expected likelihood function derived from the image data and prior anatomical knowledge. In the M-step, the shapes of the structures are estimated jointly by encoding the hidden variable model and the statistical prior model obtained from the training stage. In the E-step, the expected observation likelihood and the prior distribution of the hidden variables are estimated. In experiments, the proposed automatic segmentation algorithm is applied to multiple gray nuclei structures such as caudate, putamens and thalamus of three-dimensional magnetic resonance imaging in volunteers and patients. As for the robustness and accuracy of the segmentation algorithm, the results of the proposed EM-joint shape-based algorithm outperformed those obtained using the statistical shape model-based techniques in the same framework and a current state-of-the-art region competition level set method.     

The low-temperature phase of Kac-Ising models

We analyze the low-temperature phase of ferromagnetic Kax-Ising models in dimensionsd2. We show that if the range of interactions is ^–1, then two disjoint translation-invariant Gibbs states exist if the inverse temperature satisfies –1^N, where =d(1–)/(2d+2)(d+1), for any >0. The proof involves the blocking procedure usual for Kac models and also a contour representation for the resulting long-range (almost) continuous-spin system which is suitable for the use of a variant of the Peierls argument.     

应用微型计算机分析和设计液压缓冲装置

本文提供了一种用微型计算机绘制高分辨率图形的方法。本方法用于分析各种液压缓冲装置动态特性时,只要列出数学模型,不用求解复杂的微分方程就能直接画出特性曲线;用于缓冲装置的设计时,可以方便地进行调参,确定最佳参数。还提出了在微型计算机上设计理想的抛物线型、阶梯型缓冲柱塞的简单方法。     

基于傅立叶描述符优化形变轮廓插值的步态识别研究

针对现有步态识别算法在步态周期变化时不能很好地保留瞬时信息的问题,提出了一种基于傅里叶描述符优化形变轮廓插值方法。首先,对人类轮廓的周期性形变进行建模;然后,将基于傅里叶系数乘积的新度量作为闭合曲线之间的距离度量,并利用帧插值方法近似识别半周期的起始帧和结束帧;最后,利用步态距离完成最终的步态分类。在OU-ISIR和CASIA步态数据库上的识别精度可分别高达99%、87.34%,分析结果表明,提出的算法在步态周期变化时依然能保留瞬时信息,对行走速度上的轻微变化具有更好的鲁棒性,并且大大降低了整体计算复杂度。     

Tilted lamellae in an affinely deformed 3D macrolattice and elliptical features in small‐angle scattering

Lamellar reflections in small‐angle X‐ray and neutron scattering patterns of uniaxially drawn semicrystalline polymers appear to fall on elliptical or hyperbolic arcs. We attribute this to a 3D lattice of tilted lamellae, a macrolattice. Affine deformation of this lattice, such as during uniaxial draw, moves and spreads the reflections along elliptical arcs, and nonaffine deformation, such as during rolling, moves and spreads the reflections along an arc that deviates from an ellipse. Discrete reflections are the product of two functions: the elliptical trace that is the Fourier transform of the affinely deformed lattice and the radial streak that is the Fourier transform of the individual lamella in the reciprocal space. Four‐point patterns are obtained if the lamellar‐surface normal is tilted away from the fiber‐axis, and two‐point patterns if it is not. This model is used to discuss the transformation between four‐ and two‐point patterns and other changes in lamellar morphology that occur during drawing and annealing of oriented semicrystalline polymers. The deformation of the macrolattice of crystalline lamellae, need not be correlated to the tilt of the lamellae. The tilt of the lamellae is shown to be important. It reflects the cross‐sectional area mismatch at the lamellar surface between crystalline stems and amorphous chains segments, and this indicates the internal strain in the interfibrillar amorphous regions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1277–1286, 2006     

A-weighted sound pressure level as a loudness/annoyance indicator for environmental sounds - Could it be improved?

A system is introduced with the purpose of showing how an auditory perception system may be built up to include the basic quantities on loudness domain. The quantities are the critical bands, the power law, and the weighting. The power law seems to be the most crucial basis for hypothesizing a loudness function. It has been shown that the power law could be applied as such by assuming the auditory perception system to have two essentially different stimuli: the intensity (sound pressure level) and pure pressure. These physically different quantities seem to be combined in the root of the power law, and in this study the roots are determined from equal-loudness contours. A loudness function is derived on the basis of this finding. By adding the weighting, a method has been constructed for assessing loudness. After defining the weighting, the equal-loudness contours are constructed and are seen to be virtually identical to the contours in ISO 226. It has also been found that the equations for deriving the contours in this standard and in the new ISO 226 may be incorrect, because there is no definition of a sensible loudness function. Finally, it is deduced that the derived weighting must be unequivocal for an auditory perception system (depending solely on the otologically representative group). Finally, the A-weighting (as part of an A-weighted sound pressure level) as such is reasonably similar to the weighting derived in this study. Therefore, this weighting is not the main problem when assessing sounds in respect to loudness. The A-weighting is thus chosen as the weighting for the indicator derived in the study for assessing environmental sounds.     

基于物体轮廓和前向预测的自适应窗匹配

针对用窗方法进行视差估计的问题,在详细分析了不同情况下窗大小对亮度差平方和（SSD）影响的基础上,根据立体图像内容的特点和自然界物体的性质,提出了基于物体轮廓和前向预测的自适应窗匹配方法,用于立体图像对对应像素点的视差估计,对一维亮度信号的仿真分析清楚地展示了该算法能在图像的各像素点迅速合理地调整窗大小,从而达到几乎在每一像素点的匹配窗尺寸参数都是最优的目标,与以前提出的自适应窗匹配法比较,该算法复杂度更低,最后,对立体图像信号的处理证明了同样的结果。     

A lateral differential confocal microscopy for accurate detection and localization of edge contours

Common path noise and disturbance in light source and ambient lighting affect detection accuracy of edge contours greatly in optical microscopy. In order to solve this problem, a lateral differential confocal microscopy is proposed based on principle of lateral difference and confocal microscopy. The approach proposed uses confocal dual-receiving light path arrangement and real-time heterodyne subtraction of two signals with lateral offsets by a differential detector to improve the system′s accuracy and detection sensitivity. Theoretical analyses have been presented. In addition, a simple prototype system has been built based on theoretical analyses. Related experiments have been performed under laboratory conditions. Different from former image processing methods, common path noise and additive disturbance in light source and ambient lighting are eliminated before they are recorded. Theoretical analyses and experimental results indicate a more accurate and sensitive result.