Melanopsin and rod-cone photoreceptive systems account for all major accessory visual functions in mice

In the mammalian retina, besides the conventional rod-cone system, a melanopsin-associated photoreceptive system exists that conveys photic information for accessory visual functions such as pupillary light reflex and circadian photo-entrainment. On ablation of the melanopsin gene, retinal ganglion cells that normally express melanopsin are no longer intrinsically photosensitive. Furthermore, pupil reflex, light-induced phase delays of the circadian clock and period lengthening of the circadian rhythm in constant light are all partially impaired. Here, we investigated whether additional photoreceptive systems participate in these responses. Using mice lacking rods and cones, we measured the action spectrum for phase-shifting the circadian rhythm of locomotor behaviour. This spectrum matches that for the pupillary light reflex in mice of the same genotype, and that for the intrinsic photosensitivity of the melanopsin-expressing retinal ganglion cells. We have also generated mice lacking melanopsin coupled with disabled rod and cone phototransduction mechanisms. These animals have an intact retina but fail to show any significant pupil reflex, to entrain to light/dark cycles, and to show any masking response to light. Thus, the rod-cone and melanopsin systems together seem to provide all of the photic input for these accessory visual functions.     

教师是计算机辅助教学—CAI课件建设的主体

现代教育技术工作的出发点及归宿都应落实在实现教育过程最优化和提高教学质量上,要实现这个目标,仅仅依靠电教人员的努力是不够的,必须有广大教师的积极参与,因为教师是教学的主体,必须充分发挥教师在多媒体CAI课件建设中的主导作用.     

倾斜入射地震下结构-地基的透射边界

为正确反映结构-地基动力相互作用,消除传统固定边界模型将地震能量全部陷入计算模型的不合理现象,该文提出倾斜入射地震下结构-地基动力反应分析的有限元模型及其透射边界.有限元模型由主网格、自由场网格和侧边透射层网格组成,地震以入射平面波形式输入,以入射波运动作为非惯性参考坐标系建立相对运动的动力方程.结构-地基实际反应为相对运动与入射波动之和,算例表明透射边界模型能有效地透射倾斜入射地震下结构-地基动力反应的辐射分量.     

论投影型视觉媒体在教学中的应用

随着科学技术的迅猛发展,一些新兴的媒体技术正在迅速出现并飞速发展,但一些传统的媒体技术如投影型视觉媒体却有它独有的特点,在教学中有其不可替代的作用,继续为教育教学服务.     

连续输入的SOM算法的权值收敛性

研究了自组织映射（SOM）算法的权值收敛性问题,提出了一个连续状态下的目标函数,由这个目标函数出发利用Robbins-Monro算法证明了连续状态下的自组织映射的权值将收敛到一个稳定值,其结果适应于任意有限维的情形。     

课堂教学如何突出学生的主体地位--"情绪状态"一节课教学的实践与思考

学生是学习的主体，然而在以往的“情绪”一节的教学实践中，受惯性的教学价值观，目标，内容，模式及评价支配，并未真正突出学生的主体地位，在改革了的“情绪”教学中，围绕“唯知”转向“人格发展”，进行了一系列教学实践重心的转移，较好地突出了学生的主体价值与主体精神。     

数字图像压缩编码技术综述

本文阐述了数字图像压缩编码的必要性,介绍了几种常见数字图像压缩编码方法的原理及其适用的场合和特点,并对数字图像编码新技术做了简单介绍。     

汽车变速器输入轴塑性成形工艺

输入轴是汽车变速器中重要零件,针对其特殊结构提出一火加热和轧锻结合的塑性复合加工工艺,即采用圆柱坯料只进行一次加热,依次采用楔横轧和锻造工艺加工塑性成形输入轴。本文分别设计楔横轧和锻造模具,并进行相关实验。在锻造工艺中轴部圆角采用挤压方案成形,避免其出现折叠缺陷。阶梯轴作为两步工艺的中间产品,其在复合工艺过程中起到承上启下的作用,分别对阶梯轴锥角和轴长进行实验与分析,确定参数的最佳选取范围,并最终通过复合工艺加工成形输入轴。输入轴齿形填充饱满,各部分无缺陷。     

机器人立体视觉模块的故障诊断

针对机器人的视觉模块，提出了一种故障诊断的算法．该方法根据极线几何理论，利用基本矩阵离线地得到故障诊断的期望范围，再根据匹配像素点是否落在期望范围内判断视觉模块当前是否存在故障．与常规方法相比，不需要增加额外的传感器，且占用系统资源较少，具有相当好的实时性．实验证明，利用该方法进行故障诊断的错判率和漏检率均在3％以下。     

Role for a cortical input to hippocampal area CA1 in the consolidation of a long-term memory

A dialogue between the hippocampus and the neocortex is thought to underlie the formation, consolidation and retrieval of episodic memories, although the nature of this cortico-hippocampal communication is poorly understood. Using selective electrolytic lesions in rats, here we examined the role of the direct entorhinal projection (temporoammonic, TA) to the hippocampal area CA1 in short-term (24 hours) and long-term (four weeks) spatial memory in the Morris water maze. When short-term memory was examined, both sham- and TA-lesioned animals showed a significant preference for the target quadrant. When re-tested four weeks later, sham-lesioned animals exhibited long-term memory; in contrast, the TA-lesioned animals no longer showed target quadrant preference. Many long-lasting memories require a process called consolidation, which involves the exchange of information between the cortex and hippocampus. The disruption of long-term memory by the TA lesion could reflect a requirement for TA input during either the acquisition or consolidation of long-term memory. To distinguish between these possibilities, we trained animals, verified their spatial memory 24 hours later, and then subjected trained animals to TA lesions. TA-lesioned animals still exhibited a deficit in long-term memory, indicating a disruption of consolidation. Animals in which the TA lesion was delayed by three weeks, however, showed a significant preference for the target quadrant, indicating that the memory had already been adequately consolidated at the time of the delayed lesion. These results indicate that, after learning, ongoing cortical input conveyed by the TA path is required to consolidate long-term spatial memory.     

输入输出系统噪信比的计算

为改进噪信比的计算方法,利用系统相关函数的Ｚ变换和逆Ｚ变换关系,导出了系统噪信比的计算公式,它使得噪信比可以直接通过系统模型和噪声模型传递函数的复积分得到。同时,给出了这个复积分的递推计算式,避免了复积分留数的复杂运算,简化了用数字仿真确定噪信比的计算量。并将这一方法推广用于计算多变量系统的噪信比。数值例子说明给出方法是有效的。     

评价企业科技投入效益的几个模型

在分析我国企业科技投入过低状况的基础上,从投入项目的经济效益和社会效益角度,提出了评价企业科技投入效益的几个模型.经济效益主要考虑利润,社会效益主要考虑项目对社会的贡献和项目实施后对就业、技术进步等的影响和效果.     

Bicycle-pedal model for the first step in the vision process.

Computer simulation of the molecular dynamics of retinal during its photoisomerisation inside a restrictive active site gives a detailed model for the sequence of events in the first step of the vision process. It is proposed that the prelumirhodopsin intermediate contains a strained all-trans retinal molecule produced directly and rapidly from the 11-cis, 12-s-trans conformation in rhodopsin by a bicycle-pedal isomerisation. The model reproduces the main experimental observations and explains how the protein makes the photoisomerisation path unique.     

Ependymal cells of chordate larvae are stem-like cells that form the adult nervous system

In ascidian tunicates, the metamorphic transition from larva to adult is accompanied by dynamic changes in the body plan. For instance, the central nervous system (CNS) is subjected to extensive rearrangement because its regulating larval organs are lost and new adult organs are created. To understand how the adult CNS is reconstructed, we traced the fate of larval CNS cells during ascidian metamorphosis by using transgenic animals and imaging technologies with photoconvertible fluorescent proteins. Here we show that most parts of the ascidian larval CNS, except for the tail nerve cord, are maintained during metamorphosis and recruited to form the adult CNS. We also show that most of the larval neurons disappear and only a subset of cholinergic motor neurons and glutamatergic neurons are retained. Finally, we demonstrate that ependymal cells of the larval CNS contribute to the construction of the adult CNS and that some differentiate into neurons in the adult CNS. An unexpected role of ependymal cells highlighted by this study is that they serve as neural stem-like cells to reconstruct the adult nervous network during chordate metamorphosis. Consequently, the plasticity of non-neuronal ependymal cells and neuronal cells in chordates should be re-examined by future studies.     

Transient cells of the developing mammalian telencephalon are peptide-immunoreactive neurons

In the development of the mammalian telencephalon, the genesis of neurons destined for the various layers of the cerebral cortex is preceded by the generation of a population of cells that comes to reside in the subplate and marginal zones (see ref. 2 for nomenclature). In the cat, these cells are present in large numbers during development, when their location is correlated with the arrival and accumulation of ingrowing axonal systems and with synapses. However, as the brain matures, the cells disappear and the white matter and layer 1 of the adult emerge. Their disappearance occurs in concert with the invasion of the cortical plate by the axonal systems and with the elimination of the synapses from the subplate. Here we report that the subplate cells have properties typical of mature neurons. They have the ultrastructural appearance of neurons and receive synaptic contacts. They also have long projections and are immunoreactive for MAP2 (microtubule associated protein 2). Further, subpopulations are immunoreactive for one of several neuropeptides. These observations suggest that during the fetal and early postnatal development of the mammalian telencephalon the subplate cells function as neurons in synaptic circuitry that disappears by adulthood.     

Oligopotent stem cells are distributed throughout the mammalian ocular surface

The integrity of the cornea, the most anterior part of the eye, is indispensable for vision. Forty-five million individuals worldwide are bilaterally blind and another 135 million have severely impaired vision in both eyes because of loss of corneal transparency; treatments range from local medications to corneal transplants, and more recently to stem cell therapy. The corneal epithelium is a squamous epithelium that is constantly renewing, with a vertical turnover of 7 to 14 days in many mammals. Identification of slow cycling cells (label-retaining cells) in the limbus of the mouse has led to the notion that the limbus is the niche for the stem cells responsible for the long-term renewal of the cornea; hence, the corneal epithelium is supposedly renewed by cells generated at and migrating from the limbus, in marked opposition to other squamous epithelia in which each resident stem cell has in charge a limited area of epithelium. Here we show that the corneal epithelium of the mouse can be serially transplanted, is self-maintained and contains oligopotent stem cells with the capacity to generate goblet cells if provided with a conjunctival environment. Furthermore, the entire ocular surface of the pig, including the cornea, contains oligopotent stem cells (holoclones) with the capacity to generate individual colonies of corneal and conjunctival cells. Therefore, the limbus is not the only niche for corneal stem cells and corneal renewal is not different from other squamous epithelia. We propose a model that unifies our observations with the literature and explains why the limbal region is enriched in stem cells.     

Self-reactive gamma delta T cells are eliminated in the thymus

The genes encoding a gamma delta T-cell receptor specific for a major histocompatibility complex class I molecule encoded by the TIa locus have been inserted into the mouse germ line. In mice that do not express the TIa-encoded determinant, transgenic gamma delta T cells are a functional component of the CD4-CD8- 'double-negative' T cells in the thymus and peripheral lymphoid organs. In mice that express the TIa-encoded determinant, there are no transgenic gamma delta T cells in peripheral lymphoid organs, and there are no thymocytes expressing normal levels of the transgenic gamma delta T-cell receptor.