Chromatic visual evoked potential responses in preschool children

The purpose of the study was to analyze chromatic visual evoked potential (VEP) responses to isoluminant red-green (R-G) and blue-yellow (B-Y) stimuli in 30 preschool children (1.5-6 years). The predominant part of the response consisted of a positive (P) wave, which showed age-related latency changes (linear decrease). P wave latency was shorter when using 21° compared to 7° R-G (p=0.004) and B-Y (p=0.044) stimulus and also when using 21° R-G compared to 21° B-Y stimulus (P=0.000). P wave amplitude did not show age-related changes. However, a lower amplitude was recorded when using 7° R-G stimulus (p=0.0013) and also when using B-Y compared to R-G stimulus. We may conclude that chromatic VEP to R-G and B-Y stimuli is reliably recorded in preschool children and that P wave to R-G stimulation shows a higher amplitude and shorter latency than to B-Y stimulus.     

P-GMAW熔池双面视觉传感与图像处理

视觉是手工焊接最重要的信息获取手段,为了模拟这一过程,建立了一套脉冲熔化极气体保护焊(P-CMAW)的双面实时视觉传感系统.利用被动光源视觉传感方法,研究了P-GMAW正反面熔池成像的滤光方法、成像时间、成像机理.结果表明,利用中心波长为665 nm的窄带滤光片在脉冲基值结束期间取像,可以获取清晰的P-GMAW正面熔池图像;利用中性减光技术,可以获取清晰的反面熔池图像.分析表明,正反面成像的主要光源均来自于熔池的自身辐射,因此,成像质量可靠.针对不同的熔池图像特征,提出了相应的图像处理算法,实现了正反面熔池边界的提取.     

The dynamics of the Bulgarian newspaper industry in a period of transition: organizational adaptation, structural inertia and political change

The alignment strategies of state-owned Bulgarian newspaperenterprises are examined in light of the theoretical insightsprovided by adaptation and selection perspectives of organizationalevolution. Building on the distinction between core and periphery,I argue that the impact of internal restructuring is closelytied to the location of change in the organizational structure.The results indicate that newspaper enterprises that attemptedto reorganize their core structures became liable to pressuresof environmental selection. The lack of real structural reformsin Bulgarian society between 1987 and 1990 was used to explainthe unsuccessful adaptation attempts made by newspapers thatimplemented only peripheral adjustments.     

一种带有连续变化分辨率的中央凹视觉处理方法研究

针对以往中央凹视觉处理过程中,中央凹区域太小,分辨率下降过快,难以满足模式识别、跟踪等问题。基于可分解映射,提出一种带有连续变化分辨率的中央凹视觉处理方法。实验结果表明:在保持中央凹图像数据量不变的基础上,该方法可以提供更大的中央凹区域。     

Characterizing contrast adaptation in a population of cat primary visual cortical neurons using Fisher information

When cat V1/V2 cells are adapted to contrast at their optimal orientation, a reduction in gain and/or a shift in the contrast response function is found. We investigated how these factors combine at the population level to affect the accuracy for detecting variations in contrast. Using the contrast response function parameters from a physiologically measured population, we model the population accuracy (using Fisher information) for contrast discrimination. Adaptation at 16%, 32%, and 100% contrast causes a shift in peak accuracy. Despite an overall drop in firing rate over the whole population, accuracy is enhanced around the adapted contrast and at higher contrasts, leading to greater efficiency of contrast coding at these levels. The estimated contrast discrimination threshold curve becomes elevated and shifted toward higher contrasts after adaptation, as has been found previously in human psychophysical experiments.     

Invariant operators for processing the results of measurements with a finite-dimensional image for increased reliability

An operator for processing data from a specific experiment is considered to transform the data into an output function. The requirement for this function to be independent of the way of presenting the input data is formalized. Some well-known methods for processing information with a finite-dimensional image are investigated for invariance.Translated from Izmeritel'naya Tekhnika, No. 6, pp. 5–6, June, 1994.     

Plasmon hybridization reveals the interaction between individual colloidal gold nanoparticles confined in an optical potential well

The understanding of interaction forces between nanoparticles in colloidal suspension is central to a wide range of novel applications and processes in science and industry. However, few methods are available for actual characterization of such forces at the single particle level. Here we demonstrate the first measurements of colloidal interactions between two individual diffusing nanoparticles using a colorimetric assay based on plasmon hybridization, that is, strong near-field coupling between localized surface plasmon resonances. The measurements are possible because individual gold nanoparticle pairs can be loosely confined in an optical potential well created by a laser tweezers. We quantify the degree of plasmon hybridization for a large number of individual particle pairs as a function of increasing salt concentration. The data reveal a considerable heterogeneity at the single particle level but the estimated average surface separations are in excellent agreements with predictions based on the classical theory of Derjaguin, Landau, Verwey, and Overbeek.     

A study of the tensile behaviour of flax tows and their potential for composite processing

To study the potential of flax tows in composite processing as an alternative to flax spun yarns, a flat flax tow consisting of aligned fibre bundles held together by a natural binder was used and characterised in tension under various conditions. The effect of the gauge length was studied on the dry reinforcement. The experimental results showed that the mechanical properties and failure mechanism varied significantly depending on the gauge length and are discussed in relation to the distribution of elementary fibres within the tow. A characteristic length as from which the mechanical properties are stable has been identified. At this length, the effect of the strain rate on the tensile properties was measured and their sensitivity to the strain rate suggests a viscous effect in the behaviour of the flax tow. To approach process conditions such as wet filament winding, a batch of specimens was impregnated with epoxy prior to tensile testing. The tensile properties under wet conditions were found to be close to the properties under dry conditions and shows that the tow can withstand typical processing tensions. Finally, tensile tests on cured-impregnated tows showed interesting mechanical properties for composite application.     

An ideal observer with channels versus feature-independent processing of spatial frequency and orientation in visual search performance

An influential assumption for the front end of models in vision, visual search, and object recognition is an analysis of independent features that correspond to basic image properties, such as motion, shape, and color. Empirically, one common test of independent features (a cue-summation study) measures performance with increasing available cues or features, with improving performance leading to conclusions of summation across independent features. In a study by Shimozaki et al. [J. Vision 2, 354-370 (2002)], both ideal and human observers showed no summation with large stimulus differences, in contrast to independent-feature models and suggesting that stimulus information (as assessed by an ideal observer) might affect cue-summation studies. Extending the previous summation study, observers performed a visual search of four Gabors differing in only orientation, only spatial frequency, or both orientation and spatial frequency, across a range of target-distractor differences. An ideal observer underpredicted human summation for small differences, whereas the independent-orientation and spatial-frequency feature models overpredicted human summation for large differences. An ideal observer with channels jointly tuned to spatial frequency and orientation predicted human performance across both small and large target-distractor differences.     

Cone pigment gene expression in individual photoreceptors and the chromatic topography of the retina

Human trichromatic vision is based on three classes of cones: L, M, and S (long-, middle-, and short-wavelength sensitive, respectively). Individuals can have more than one M and/or more than one L pigment gene on the X chromosome along with an S pigment gene on chromosome 7. In some people the X-linked pigment gene array can include polymorphic variants that encode multiple, spectrally distinct cone photopigment subtypes. A single-cell, polymerase chain reaction approach was used to examine visual pigment gene expression in individual human cone cells and identify them as L or M. The ratio of L:M pigment gene expression was assayed in homogenized retinal tissues taken from the same eyes. Results indicate that there is a close correspondence between the cone ratio determined from counting single cells and the L:M pigment mRNA ratio estimated from homogenized pieces of retina. The results also show that the different pigment genes in one array are often expressed at very different levels, giving rise to unequal numbers of L and M cones. Expression of only one photopigment gene was detected in each cone cell. However, individual males can have more than the classically described three spectrally distinct cone types in their retinas.     

National primary special standard for the unit of chromatic dispersion in optical fibers

The national primary special standard for the unit of chromatic dispersion in optical fibers, a national verification scheme, and results of metrological studies of the standard are described.