Adaptation and perceptual norms in color vision

Many perceptual dimensions are thought to be represented relative to an average value or norm. Models of norm-based coding assume that the norm appears psychologically neutral because it reflects a neutral response in the underlying neural code. We tested this assumption in human color vision by asking how judgments of "white" are affected as neural responses are altered by adaptation. The adapting color was varied to determine the stimulus level that did not bias the observer's subjective white point. This level represents a response norm at the stages at which sensitivity is regulated by the adaptation, and we show that these response norms correspond to the perceptually neutral stimulus and that they can account for how the perception of white varies both across different observers and within the same observer at different locations in the visual field. We also show that individual differences in perceived white are reduced when observers are exposed to a common white adapting stimulus, suggesting that the perceptual differences are due in part to differences in how neural responses are normalized. These results suggest a close link between the norms for appearance and coding in color vision and illustrate a general paradigm for exploring this link in other perceptual domains.     

Modulation frequency and orientation tuning of second-order texture mechanisms

Modulation frequency and orientation tuning of second-order mechanisms underlying the detection of modulation in local spatial-frequency information are assessed by using an oblique-masking paradigm. Stimuli were Gabor-filtered noise patterns in which the local carrier spatial frequency was modulated about an average value of 4.7 cycles per degree (cpd) according to sinusoidal function. Thresholds were determined for spatial-frequency modulated test patterns (0.2 and 0.8 cpd) with fixed vertical carrier and modulation orientations presented alone and in the presence of spatiotemporally superimposed masks. Mask modulation frequency (0.1, 0.2, 0.4, 0.8, or 1.6 cpd), modulation orientation (0 degree, 45 degrees, or 90 degrees relative to vertical), and carrier orientation (18.5 degrees or 90 degrees relative to vertical) were manipulated independently while the mask modulation amplitude remained fixed at 0.25. Manipulating the modulation frequency of the mask revealed some modulation frequency specificity, particularly at lower test modulation frequencies. Spatial-frequency modulated masks produced threshold elevations regardless of the local carrier orientation. However, there was no evidence of threshold elevation when the mask modulation orientation was orthogonal to that of the test pattern. These results suggest a second-order texture mechanism that is tuned to both modulation frequency and modulation orientation but is not selective in terms of the orientation of first-order inputs.     

Measurement method of asphalt pavement mean texture depth based on multi-line laser and binocular vision

A new measuring method of mean texture depth of asphalt pavement is proposed based on the technology of multi-line laser and binocular vision. The developed method is incorporated with the profile method and the digital image technology. A three-dimensional mathematical model is established based on the triangulation measuring principle in order to implement the three-dimensional reconstruction of asphalt surface profile. Image processing technology helps locate the exact coordinates of each point on the model. In addition, the techniques of multi-line laser pairing and epipolar restriction are introduced for the image matching between multi-line laser and binocular vision. Through the model and the spatial equations obtained, the values of the mean profile depth of asphalt pavement can be figured out. According to the profile method, an integrated calculation procedure of texture depth is established. A set of sand patch field tests are implemented to verify the reliability of the developed method.     

Integration of differing chromaticities in early and midlevel spatial vision

Using Glass patterns composed of isoluminant dots we have investigated the segregation and integration of chromatic information by the visual system. By measuring pattern detection when the chromaticities of the two elements forming a dot pair are varied (intradipole variation), we characterize integration at an early level of spatial processing. By measuring pattern detection for dot pairs where the within-pair chromaticity is the same but the among-pair chromaticities are varied (interdipole variation) we characterize integration and segregation for a more global, midlevel, spatial processing mechanism. Using isoluminant patterns in which all dots have the same chromaticity, we find that (i) detection thresholds are similar to those for luminance-defined dots, and (ii) an equivalent-contrast metric approximately equates thresholds for various chromaticities, including those along both the cardinal and the intermediate axes of an opponent-color space. When intradipole chromaticity is varied we observe that (i) the ability of visual mechanisms to extract oriented dot pairs decreases with increasing chromaticity differences, and (ii) average bandwidths are similar for cardinal and intermediate directions. For pattern detection with interdipole chromatic variation the visual system does not segregate noise dot pairs from correlated dot pairs on the basis of chromatic differences alone, and appears to integrate oriented dot pairs of differing chromaticities in forming a global percept, even for large color differences. Isoluminant Glass patterns with translational and concentric correlations give similar results. The results are compared with those obtained for contrast variation in luminance-defined Glass Patterns and are discussed in terms of current multistage models of color processing by the visual system.     

Cauchy-type integrals and integral equations with logarithmic singularities

Summary The Gauss-type quadrature methods with a logarithmic weight function can be extended to the evaluation of Cauchy-type integrals and to the solution of Cauchy-type integral equations by reduction of the latter to a linear system of algebraic equations. This system is obtained by applying the integral equation at properly selected collocation points. The poles of the integrand lying in the integration interval were treated as lying outside this interval. The efficiency of the method, both in evaluating integrals and solving integral equations, is exhibited by a numerical example. Finally, an application of the method to a crack problem of plane elasticity is made.     

Morphological mechanisms and kinetics of large-strain plastic deformation and evolution of texture in semicrystalline polymers

The development of deformation-induced texture in high-density polyethylene is described from the point of view of a micromechanically based composite computer model of crystalline lamellae associated with attached amorphous layers. The predictions of the model are compared and contrasted with detailed recent experimental observations of this process by WAXS, SAXS, TEM, atomic force microscopy, light microscopy and a whole host of conventional and unconventional means of mechanical probing. A separate set of experiments probing the rate controlling process of chain slip in quasi-single-crystalline nylon-6 are also presented together with implications related to the kinetics of long-range dislocation motion in such highly textured solids.     

Stress singularities in anisotropic three-material wedges and junctions with applications

This paper presents the general solutions of stress singularity in anisotropic three-material wedges and junctions. The influencing factors on the strength of stress singularity are the material constants, the fiber orientation and three wedge angles. Most emphasis has been placed on the roles of the intermediate material played in the structural design. The results can be applied to control the damage initiation and growth near the edge of the angle-ply or cross-ply laminated composite, such as the use of epoxy pocket (Chan, Composites Engineering Handbook, Marcel Dekker, Inc., New York, 1997, p. 309). By selecting appropriate stiffness and geometry of the interphase material, the damage resistance and durability of the structures can be improved.     

Microstructural features, texture and strengthening mechanisms of nanostructured AA6063 alloy processed by powder metallurgy

Nanostructured AA6063 (NS-Al) powder with an average grain size of ∼100 nm was synthesized by high-energy attrition milling of gas-atomized AA6063 powder followed by hot extrusion. The microstructural features of the consolidated specimen were studied by transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques and compared with those of coarse-grained AA6063 (CG-Al) produced by hot powder extrusion of gas-atomized powder (without using mechanical milling). The consolidated NS-Al alloy consisted of elongated ultrafine grains (aspect ratio of ∼2.9) and equiaxed nanostructured grains. A high fraction (∼78%) of high-angle grain boundaries with average misorientation angle of 33° was noticed. Microtexture evaluation by plotting pole-figures and orientation distribution function (ODF) analysis showed Copper and P texture components for both the consolidated Al alloys. Tensile test at room temperature and microhardness measurement revealed that a significant improvement in the strength of AA6063 alloy is obtained through refinement of the grain structure. The strengthening mechanisms are discussed based on the dislocation-based models. The role of high-angle and low-angle grain boundaries on the strengthening mechanisms is discussed.     

含PID控制器的迟滞非线性控制系统的主共振及奇异性

针对含PID控制器的迟滞非线性闭环控制系统,用Backlash神经网络模型逼近系统迟滞非线性部分,建立动力学模型。研究了系统在简谐激励下的主共振,利用平均法得到了系统的分岔方程,并用奇异性理论进行了分析,得到了转迁集和分岔图。另外还研究了系统参数对开折参数和分岔参数的影响,从而为系统参数的选择提供理论指导。     

Numerical solution of integral equations with logarithmic-, Cauchy- and Hadamard-type singularities

This study presents an extension of the piecewise quadratic polynomial technique to solve singular integral equations with logarithmic- and Hadamard-type singularities. For completeness and continuity, the evaluation of the weights for logarithmic-, Cauchy- and Hadamard-type singularities are given explicitly. Numerical results concerning logarithmic- and Hadamard-type singular integral equations are compared with the known solutions. The solution of Cauchy-type singular integral equations was discussed in detail in a previous study by Miller and Keer. © 1998 John Wiley & Sons, Ltd.     

Free vibrations of continuous beams with singularities in inertia and stiffness distribution

The free vibrations of continuous beams with singularities in inertia and stiffness distribution are presented in this paper. Simple closed-form mathematical expressions for the mode shapes of vibrations are obtained using Galerkin's approach. Several numerical examples of structures with known exact solutions are presented to show the accuracy of the method. Also, examples of a simple beam with intermediate elastic translational and rotational supports carrying point and rotational mass, a two-span continuous beam with variable moment of inertia and mass distribution and a single-span beam with fixed end and overhanging cantilever are presented to show the applicability of the method     

Crack tip stress singularities and dislocation interactions with anisotropic viscoelastic bimaterial interfaces

The time evolution of the force on a dislocation and the near tip stress field of a semi-infinite crack, lying at an angle towards the welded interface of a bimaterial and just touching it, is studied. The bimaterial consists of viscoelastic media with the most general anisotropy. Applying the Laplace transform to the field equations gives similar relations to those considered in [3], provided that appropriate elastic coefficients are replaced by their Laplace-transformed viscoelastic counterparts. Numerical methods are then used for the inversion of both the Laplace and Mellin transforms and numerical results for near crack tip stress fields are presented along with asymptotic ones for small and large times. Corresponding results are presented for the force on a dislocation. For simple anisotropies a relation between the force on a dislocation and the time dependence of appropriate crack tip stresses is established.     

Initiation and early growth mechanisms of corrosion fatigue cracks in stainless steels

The mechanism of corrosion fatigue crack initiation in stainless steels was examined in both air and chloride solutions. For a tempered martensitic, a duplex and a soft martensitic steel it is shown that the decrease of the fatigue strength from the value measured in air to that measured in corrosive environments depends primarily upon the stability of the protective film. If the passivity is stable, cracks are found to originate almost exclusively at oxide inclusions. Cracking or debonding were found to occur. For the duplex steel in the vicinity of the inclusion there were pronounced emerging persistent slip bands. They cause localized corrosion attack, thus allowing cracks to be formed more easily. If pitting is superposed, crack nucleation always occurs at the base of the pit. Pit formation and growth rate are accelerated by cyclic loading.     

Further evidence for four mechanisms mediating vision at threshold: sensitivities to complex gratings and aperiodic stimuli

It is now generally accepted that several mechanisms mediate contrast detection at threshold. Many attempts to measure the bandwidths of these mechanisms using subthreshold summation have yielded estimates suggesting very narrow frequency tuning. We have measured thresholds for three classes of stimuli: gratings containing two sinusoidal components, sums of "difference of Gaussian" (DOG) patterns, and square waves. The results of the subthreshold summation experiments with gratings are consistent with those of other studies. All of these thresholds can be predicted by a model requiring only four center-surround-type mechanisms at each retinal locus. These mechanisms have a full bandwidth at a half-height of about 1.75 octaves. Quantitative prediction of sensitivities depends critically upon spatial probability summation. It is this spatial nonlinearity that yields these somewhat conterintuitive results. The much narrower bandwidths inferred by others are due to the assumption of linearity used in their analyses.     

Robust manufacturing inspection and classification with machine vision

This paper presents and compares methods for inspecting products using machine vision systems. This research compares the Mahalanobis Taguchi System (MTS) with a method based on principal component transformation and multi-modal overlap methods, and which is called the Principal component Feature overlap Measure (PFM). In an example application, the PFM achieves significantly higher Signal/Noise-ratios (+80 dB) and equal or better classification performance than MTS with a lower number of classification features (-75%).     

Computer-generated holograms for three-dimensional surface objects with shade and texture

Digitally synthetic holograms of surface model objects are investigated for reconstructing three-dimensional objects with shade and texture. The objects in the proposed techniques are composed of planar surfaces, and a property function defined for each surface provides shape and texture. The field emitted from each surface is independently calculated by a method based on rotational transformation of the property function by use of a fast Fourier transform (FFT) and totaled on the hologram. This technique has led to a reduction in computational cost: FFT operation is required only once for calculating a surface. In addition, another technique based on a theoretical model of the brightness of the reconstructed surfaces enables us to shade the surface of a reconstructed object as designed. Optical reconstructions of holograms synthesized by the proposed techniques are demonstrated.     

The Pickett effect at early age and experiment separating its mechanisms in tension

A new experimental approach that allows separation of the components of the Pickett effect due to surface microcracking and stress-induced shrinkage is developed and demonstrated for early age concrete subjected to tensile loads induced in restrained shrinkage tests. The experiment measures creep of three concree materials subjected to same loads, but under different environments: moist-cover, sealed, and drying conditions. The key features of the experiment are the suppression of shrinkage in the moist-cover test, and the uniform internal drying in the sealed test. The results confirm that the Pickett effect in tension has two sources: stress-induced shrinkage and microcracking. The new approach provides insght to creep, shrinkage, softening, and cracking behaviour under tensile load, and explains behavioral differences between plain and fiber reinforced concrete.     

掺杂与钽条和钽丝组织性能关系的研究

通过金相显微分析、扫描电镜观察、电子探针分析、密度测试、TEM观察和力学性能测试研究了掺杂与钽条和钽丝组织和性能的关系.结果表明:随着掺杂量的增加,钽条晶粒变细,且掺B比掺A细化晶粒的效果更加明显,但随着掺B量的增加烧结变得不充分,钽条密度偏低;随着掺杂量的增加,钽丝的再结晶温度升高,组织晶粒细化,其中掺B比掺A细化效果更加明显;随着掺杂量的增加钽丝室温抗拉强度增加,伸长率则随着掺A量的增加而降低,随着掺B量的增加而升高,且掺B较掺A强化效果明显,B的加入还起到了细晶韧化效果.