共查询到19条相似文献,搜索用时 109 毫秒
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已知光敏蛋白菌紫质LB膜具有类似于视觉系统感受野的对光微分响应。利用这个特性,本文组装了一对人工视皮层条型简单细胞感受野,并测定了其朝向选择特性及ON-区闪光融合频率响应特性。在此基础上,用这一对人工感受野组成了猫视皮层细胞双眼汇聚功能模拟系统,并模拟了猫视皮层细胞双眼汇聚功能。 相似文献
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生黑醋菌可以将D-山梨醇转化为L-山梨塘,用微生物将D-山梨醇氧化为L-山梨糖是维生素C生产的一个重要部分,目前工业上用的都是游离菌批式生产工艺。由于固定化活细胞作为生物催化剂具有生产的连续性和稳定性.操作简便.产物易于分离纯化等优点[1],已有不少实验室研究甩固定化微生物细胞将D-山梨醇转化为L-山梨糖[1-6],国内也有用海藻酸固定化生黑醋菌Acetobacteriummelanogenum的报道[2,3]。用海藻酸钙[1-3]、聚丙烯酰胺[4]、铝处理的海藻酸钙[5]、水合聚丙烯酰胺与海藻酸钙混合固定化的微生物细胞[6]转化D-山梨醇成为L-山梨糖,都有因机械强度差,而不适合在搅拌式发酵罐中生产的弱点。聚乙烯醇制备的固定化微生物细胞具有机械强度好、类似于橡皮的弹性、成低等特性[7]。因此,我们选择聚乙烯醇作为固定化生黑醋菌的材料。 相似文献
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高产花色苷玫瑰茄细胞系的筛选 总被引:10,自引:0,他引:10
花色苷在植物中呈现粉红、红、紫红、紫等颜色,可以用作食品、药品及化妆品的着色剂,亦有药用价值。作为食品添加剂,颜色较合成色素自然,且安全无毒性。早在1987年,Mizukami[1]就建议用植物细胞培养物生产花色苷类代替合成色素。所有的植物培养细胞都是异源性的。各细胞之间产花色苷的能力相差很大[2].因为产花色苷的细胞系带有颜色标记,所以容易识别并通过肉眼选择即可获得高产花色苷的细胞系。筛选的方法很多,如平板饲喂法[3]、小细胞团法[4]、细胞块法[5]、肉眼观察直接挑选法及细胞分栋器法[6]等。高产系花色苷的含量可增加几倍到几十倍,而且产量稳定。本文采用平板法及小细胞团法筛选高产花色苷的玫瑰茄(Hibiscus sabdariffa L.)细胞系。 相似文献
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在真菌的反硝化作用中,一种细胞色素P-450起着一氧化氮还原酶的作用,被称为细胞色素P-450nor[1]。最近的研究发现:真菌细胞色素P-450nor有三种类型。除了缣孢菌(Fusarium oxysporum)P+450nor(即F.P-450nor)外。还有两种存在于柱孢菌(Cylindrocarpon tonkinense).即C. P-450norl和2[2]。
F.P-450nox和C.P-450norl能以NADH为直接的电子供体,使NO还原生成N2O。C. P-450nor2不仅能直接利用NADH。而且能直接利用NADPH.还原NO生成N2O。F. P-450nor基因已被克隆和测序[3-4]。本文测定了C.P-450nor2的eDNA编码区全序列,3’非编码区部分序列和5’引导序列。 相似文献
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链霉菌中表达了透明颤菌血红蛋白(VHb),表明VHb对放线紫素的产生和菌体的生长有促进作用[2].pIJ702质粒上带有与次生代谢有关的酪氨酸酶基因(mel)[3],mel由ORF438启动子(PORF438)带动转录[4].本文尝试利用PORF4328表达vgb. 相似文献
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Tony Lindeberg 《PloS one》2013,8(7)
The brain is able to maintain a stable perception although the visual stimuli vary substantially on the retina due to geometric transformations and lighting variations in the environment. This paper presents a theory for achieving basic invariance properties already at the level of receptive fields. Specifically, the presented framework comprises (i) local scaling transformations caused by objects of different size and at different distances to the observer, (ii) locally linearized image deformations caused by variations in the viewing direction in relation to the object, (iii) locally linearized relative motions between the object and the observer and (iv) local multiplicative intensity transformations caused by illumination variations. The receptive field model can be derived by necessity from symmetry properties of the environment and leads to predictions about receptive field profiles in good agreement with receptive field profiles measured by cell recordings in mammalian vision. Indeed, the receptive field profiles in the retina, LGN and V1 are close to ideal to what is motivated by the idealized requirements. By complementing receptive field measurements with selection mechanisms over the parameters in the receptive field families, it is shown how true invariance of receptive field responses can be obtained under scaling transformations, affine transformations and Galilean transformations. Thereby, the framework provides a mathematically well-founded and biologically plausible model for how basic invariance properties can be achieved already at the level of receptive fields and support invariant recognition of objects and events under variations in viewpoint, retinal size, object motion and illumination. The theory can explain the different shapes of receptive field profiles found in biological vision, which are tuned to different sizes and orientations in the image domain as well as to different image velocities in space-time, from a requirement that the visual system should be invariant to the natural types of image transformations that occur in its environment. 相似文献
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Seminal work in the early nineties revealed that the visual receptive field of neurons in cat primary visual cortex can change in location and size when artificial scotomas are applied. Recent work now suggests that these single neuron receptive field dynamics also pertain to the neuronal population receptive field (pRF) that can be measured in humans with functional magnetic resonance imaging (fMRI). To examine this further, we estimated the pRF in twelve healthy participants while masking the central portion of the visual field. We found that the pRF changes in location and size for two differently sized artificial scotomas, and that these pRF dynamics are most likely due to a combination of the neuronal receptive field position and size scatter as well as modulatory feedback signals from extrastriate visual areas. 相似文献
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The integration of local image features into global shapes was investigated in monkeys and humans using fMRI. An adaptation paradigm was used, in which stimulus selectivity was deduced by changes in the course of adaptation of a pattern of randomly oriented elements. Accordingly, we observed stronger activity when orientation changes in the adapting stimulus resulted in a collinear contour than a different random pattern. This selectivity to collinear contours was observed not only in higher visual areas that are implicated in shape processing, but also in early visual areas where selectivity depended on the receptive field size. These findings suggest that unified shape perception in both monkeys and humans involves multiple visual areas that may integrate local elements to global shapes at different spatial scales. 相似文献
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In acute experiments on unanesthetized curarized cats the intensity functions, response thresholds, inhibition thresholds, and differential sensitivity of 96 neurons in the primary visual projection cortex were investigated by extracellular recording of unit activity during central and peripheral stimulation of their receptive fields. In darkness the neurons had wide threshold and above-threshold reliefs (3–30°). The threshold reliefs of the receptive fields of some cells were found to be V-shaped, whereas others were marked by alternation of zones of increased and reduced excitability. Sensitivity of both excitatory and inhibitory inputs of the receptive field as a rule was greatest in the center. Inhibitory inputs of different cortical neurons were much more standard and less sensitive to light, and they were mainly activated within the intermediate (mesoptic) range of brightnesses. During light adaptation the threshold contour of the receptive field narrows sharply, mainly because of the fall in sensitivity of its peripheral inputs. Compared with the lateral geniculate body and retina, the relative number of low-threshold elements, sensitivity in the system of inhibitory elements, and differential brightness sensitivity are greater in the cortex. The mechanisms of formation of receptive fields of cortical neurons and their modification during changes in the level of adaptation, and also the role of excitatory and inhibitory inputs of the cell in these effects are discussed.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 11, No. 3, pp. 227–235, May–June, 1979. 相似文献
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Tony Lindeberg 《Biological cybernetics》2013,107(6):589-635
A receptive field constitutes a region in the visual field where a visual cell or a visual operator responds to visual stimuli. This paper presents a theory for what types of receptive field profiles can be regarded as natural for an idealized vision system, given a set of structural requirements on the first stages of visual processing that reflect symmetry properties of the surrounding world. These symmetry properties include (i) covariance properties under scale changes, affine image deformations, and Galilean transformations of space–time as occur for real-world image data as well as specific requirements of (ii) temporal causality implying that the future cannot be accessed and (iii) a time-recursive updating mechanism of a limited temporal buffer of the past as is necessary for a genuine real-time system. Fundamental structural requirements are also imposed to ensure (iv) mutual consistency and a proper handling of internal representations at different spatial and temporal scales. It is shown how a set of families of idealized receptive field profiles can be derived by necessity regarding spatial, spatio-chromatic, and spatio-temporal receptive fields in terms of Gaussian kernels, Gaussian derivatives, or closely related operators. Such image filters have been successfully used as a basis for expressing a large number of visual operations in computer vision, regarding feature detection, feature classification, motion estimation, object recognition, spatio-temporal recognition, and shape estimation. Hence, the associated so-called scale-space theory constitutes a both theoretically well-founded and general framework for expressing visual operations. There are very close similarities between receptive field profiles predicted from this scale-space theory and receptive field profiles found by cell recordings in biological vision. Among the family of receptive field profiles derived by necessity from the assumptions, idealized models with very good qualitative agreement are obtained for (i) spatial on-center/off-surround and off-center/on-surround receptive fields in the fovea and the LGN, (ii) simple cells with spatial directional preference in V1, (iii) spatio-chromatic double-opponent neurons in V1, (iv) space–time separable spatio-temporal receptive fields in the LGN and V1, and (v) non-separable space–time tilted receptive fields in V1, all within the same unified theory. In addition, the paper presents a more general framework for relating and interpreting these receptive fields conceptually and possibly predicting new receptive field profiles as well as for pre-wiring covariance under scaling, affine, and Galilean transformations into the representations of visual stimuli. This paper describes the basic structure of the necessity results concerning receptive field profiles regarding the mathematical foundation of the theory and outlines how the proposed theory could be used in further studies and modelling of biological vision. It is also shown how receptive field responses can be interpreted physically, as the superposition of relative variations of surface structure and illumination variations, given a logarithmic brightness scale, and how receptive field measurements will be invariant under multiplicative illumination variations and exposure control mechanisms. 相似文献
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同心圆感受野去抑制特性的数学模拟 总被引:5,自引:1,他引:5
以感受野外周区内各亚区之间的抑制性相互作用为基础,提出了一个能描述视网膜神经节细胞传输特性的数学模型,此模型能很好地解释传统感受野外大范围去抑制区产生的机制。当用来处理亮度对比边缘时,它既能很好地增强边缘对比,又可有效地提升被传统感受野中心/外周拮抗机制所滤除了的区域亮度对比和亮度梯度信息。本文也用不同空间频率的光栅和真实图像检验了模型的空间频率传递特性,并与其它模型进行了比较。 相似文献
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Perfusion of the fourth cerebral ventricle with artificial cerebrospinal fluid, made hypertonic by the addition of 0.89 M sucrose, resulted in no change in the rate of renal sodium excretion. These data lead us to conclude that the putative receptive field in the area of the fourth ventricle which is capable of affecting urinary sodium excretion contains elements that are sodium-specific 相似文献