Opsin expression: new mechanism for modulating colour vision

Each cone photoreceptor in the retina responds to light in a limited range of wavelengths, giving it a spectral phenotype. This phenotype is determined by the most prevalent of the photoreceptor's visual-pigment proteins (opsins) and is assumed to remain unchanged during an animal's lifetime. Here we show that in the Pacific pink salmon, Oncorhynchus gorbuscha, single cones can switch their spectral phenotype from ultraviolet to blue by regulating the production of the appropriate opsins as the fish grow older. This photoreceptor plasticity may operate to modulate colour vision as the salmon's lifestyle changes.     

Polymorphism of the long-wavelength cone in normal human colour vision

Colour vision is based on the presence of multiple classes of cone each of which contains a different type of photopigment. Colour matching tests have long revealed that the normal human has three cone types. Results from these tests have also been used to provide estimates of cone spectral sensitivities. There are significant variations in colour matches made by individuals whose colour vision is classified as normal. Some of this is due to individual differences in preretinal absorption and photopigment density, but some is also believed to arise because there is variation in the spectral positioning of the cone pigments among those who have normal colour vision. We have used a sensitive colour matching test to examine the magnitude and nature of this individual variation and here report evidence for the existence of two different long-wavelength cone mechanisms in normal humans. The different patterns of colour matches made by male and female subjects indicate these two mechanisms are inherited as an X-chromosome linked trait.     

MEGF10 and MEGF11 mediate homotypic interactions required for mosaic spacing of retinal neurons

In many parts of the nervous system, neuronal somata display orderly spatial arrangements. In the retina, neurons of numerous individual subtypes form regular arrays called mosaics: they are less likely to be near neighbours of the same subtype than would occur by chance, resulting in 'exclusion zones' that separate them. Mosaic arrangements provide a mechanism to distribute each cell type evenly across the retina, ensuring that all parts of the visual field have access to a full set of processing elements. Remarkably, mosaics are independent of each other: although a neuron of one subtype is unlikely to be adjacent to another of the same subtype, there is no restriction on its spatial relationship to neighbouring neurons of other subtypes. This independence has led to the hypothesis that molecular cues expressed by specific subtypes pattern mosaics by mediating homotypic (within-subtype) short-range repulsive interactions. So far, however, no molecules have been identified that show such activity, so this hypothesis remains untested. Here we demonstrate in mouse that two related transmembrane proteins, MEGF10 and MEGF11, have critical roles in the formation of mosaics by two retinal interneuron subtypes, starburst amacrine cells and horizontal cells. MEGF10 and 11 and their invertebrate relatives Caenorhabditis elegans CED-1 and Drosophila Draper have hitherto been studied primarily as receptors necessary for engulfment of debris following apoptosis or axonal injury. Our results demonstrate that members of this gene family can also serve as subtype-specific ligands that pattern neuronal arrays.     

Stochastic gene expression out-of-steady-state in the cyanobacterial circadian clock

Recent advances in measuring gene expression at the single-cell level have highlighted the stochastic nature of messenger RNA and protein synthesis. Stochastic gene expression creates a source of variability in the abundance of cellular components, even among isogenic cells exposed to an identical environment. Recent integrated experimental and modelling studies have shed light on the molecular sources of this variability. However, many of these studies focus on systems that have reached a steady state and therefore do not address a large class of dynamic phenomena including oscillatory gene expression. Here we develop a general protocol for analysing and predicting stochastic gene expression in systems that never reach steady states. We use this framework to analyse experimentally stochastic expression of genes driven by the Synechococcus elongatus circadian clock. We find that, although the average expression at two points in the circadian cycle separated by 12 hours is identical, the variability at these two time points can be different. We show that this is a general feature of out-of-steady-state systems. We demonstrate how intrinsic noise sources, owing to random births and deaths of mRNAs and proteins, or extrinsic noise sources, which introduce fluctuations in rate constants, affect the cell-to-cell variability. To distinguish experimentally between these sources, we measured how the correlation between expression fluctuations of two identical genes is modulated during the circadian cycle. This quantitative framework is generally applicable to any out-of-steady-state system and will be necessary for understanding the fidelity of dynamic cellular systems.     

文字视觉语言的力量——平面设计中文字个性化的视觉表现形式

以平面设计中文字个性化的视觉表现形式为切入点,论述了如何取得文字编排的视觉语言个性化与视觉传达功能的兼容并蓄.分析了文字编排创意的具体表现技巧及个性特征,文字视觉语言个性化与实际应用的关系.指出文字个性化表现必须关注其自身的表现内涵,方能有效发挥其视觉语言的作用.     

关于力学系统的随机变分计算

首先建立力学系统随机运动的等时和非等时变分；其次给出描述力学系统带多维参数随机运动的几类重要Ｇａｕｓｓ场的变分表示，最后举例说明本结果的应用。     

Mismatch between the population and meltwater changes creates opportunities and risks for global glacier-fed basins

Mountain glaciers are indispensable suppliers of freshwater for human sustenance in extensive cold and arid areas of the world [1-3].However,due to pronounced c...     

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。     

随机运输问题的对偶森林迭代算法

本算法从一个对偶森林向另一个对偶森林迭代。在非退化的情况下,每步迭代都使对 偶目标函数值严格增加,并在有限步内达到最优值,每步迭代最多只需解一个一维非线 性方程。在“宇宙６８０００”机上,对此算法进行了两个包括６００个以上变量的大型问题计 算,计算结果表明算法是可行有效的。     

随机波动率模型的等价鞅测度

研究了随机波动率模型的等价鞅测度.利用动态规划方法通过效用无差别定价构造了最小熵鞅测度,并给出了极小鞅测度和方差最优鞅测度,验证了这些鞅测度是不同的.     

Messenger RNA for the coat protein of tobacco mosaic virus.

TMV RNA is not an efficient template for translation of the viral coat protein, in spite of containing nucleotide sequences coding for the protein. Efficient translation requires the prior synthesis within infected cells of a smaller RNA carrying only a portion of the information encoded in the whole genome.     

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.     

Seismological evidence for mosaic structure of the surface of the Earth's inner core

The transition from the Earth's solid inner core to liquid outer core is the location where the inner core grows and from which compositional convection in the outer core originates. Most seismological models of the Earth describe the inner-core boundary as sharp and simple, although experimental data requiring the presence of a thin transition layer at the bottom of the outer core have been reported. The density jump at the inner-core boundary--an important parameter determining gravitational energy release and constraining the compositional difference between the inner and outer core-is also not well known. Estimates of this density jump obtained using free-oscillation eigenfrequencies give low values of 0.25-1.0 g cm(-3), whereas a method using the amplitude ratio of core-reflected phases yielded values of 0.6-1.8 g cm(-3) (refs 14, 15, 16-17). Here we analyse properties of waves precritically reflected from the Earth's inner core (PKiKP phases) that show significant variability in amplitude, consistent high-frequency content and stable travel times with respect to a standard Earth model. We infer that the data are best explained by a mosaic structure of the inner core's surface. Such a mosaic may be composed of patches in which the transition from solid inner to liquid outer core includes a thin partially liquid layer interspersed with patches containing a sharp transition.     

地质建模中基于响应面代理的不确定性研究

针对应用随机地质建模技术进行不确定性分析中的难点问题,提出了使用响应面代理模型进行不确定分析的
方法及其研究流程;分析了此方法应用过程中的关键点,即根据地质特征,充分考虑各建模环节的不确定性,开展敏感
性参数分析,应用响应面方法建立代理模型,生成训练/验证模型及应用代理模型进行结果预测时采样算法的要求。基
于代理模型的预测结果,可方便地得到定量评价参数相对真实的概率分布。在此基础之上,筛选对应于某一概率下的
随机地质模型,有助于进一步定量评价油田开发风险与潜力,为开发方案的编制及优化服务。