一种视皮层非经典感受野的模型

根据视觉信息加工过程中视皮层细胞非经典感受野对中心感受野区域具有抑制作用的生物机制,提出了一种模拟该机制的模型.用Gabor能量作为感受野响应,以高斯差分函数为基础构造两个具有方向的半椭圆环来作为非经典感受野区域,设计中心感受野与周边抑制区域的相位差权重函数来模拟非经典感受野的抑制机制.实验结果与这种生理特性相一致.     

Depth is encoded in the visual cortex by a specialized receptive field structure

Binocular neurons in the visual cortex are thought to perform the first stage of processing for the fine stereoscopic depth discrimination exhibited by animals with frontally located eyes. Because lateral separation of the eyes gives a slightly different view to each eye, there are small variations in position (disparities), mainly along the horizontal dimension, between corresponding features in the two retinal images. The visual system uses these disparities to gauge depth. We studied neurons in the cat's visual cortex to determine whether the visual system uses the anisotropy in the range of horizontal and vertical disparities. We report here that there is a corresponding anisotropy in the cortical representation of binocular information: receptive-field profiles for left and right eyes are matched for cells that are tuned to horizontal orientations of image contours. For neurons tuned to vertical orientations, left and right receptive fields are predominantly dissimilar. Therefore, a major modification is required of the conventional notion of disparity processing. The modified scheme allows a unified encoding of monocular form and binocular disparity information.     

A receptor that mediates the post-mating switch in Drosophila reproductive behaviour

Mating in many species induces a dramatic switch in female reproductive behaviour. In most insects, this switch is triggered by factors present in the male's seminal fluid. How these factors exert such profound effects in females is unknown. Here we identify a receptor for the Drosophila melanogaster sex peptide (SP, also known as Acp70A), the primary trigger of post-mating responses in this species. Females that lack the sex peptide receptor (SPR, also known as CG16752), either entirely or only in the nervous system, fail to respond to SP and continue to show virgin behaviours even after mating. SPR is expressed in the female's reproductive tract and central nervous system. The behavioural functions of SPR map to the subset of neurons that also express the fruitless gene, a key determinant of sex-specific reproductive behaviour. SPR is highly conserved across insects, opening up the prospect of new strategies to control the reproductive and host-seeking behaviours of agricultural pests and human disease vectors.     

Ultra-fine frequency tuning revealed in single neurons of human auditory cortex

Just-noticeable differences of physical parameters are often limited by the resolution of the peripheral sensory apparatus. Thus, two-point discrimination in vision is limited by the size of individual photoreceptors. Frequency selectivity is a basic property of neurons in the mammalian auditory pathway. However, just-noticeable differences of frequency are substantially smaller than the bandwidth of the peripheral sensors. Here we report that frequency tuning in single neurons recorded from human auditory cortex in response to random-chord stimuli is far narrower than that typically described in any other mammalian species (besides bats), and substantially exceeds that attributed to the human auditory periphery. Interestingly, simple spectral filter models failed to predict the neuronal responses to natural stimuli, including speech and music. Thus, natural sounds engage additional processing mechanisms beyond the exquisite frequency tuning probed by the random-chord stimuli.     

双臂质量不同音叉振动周期与频率的研究

在分析音叉受迫振动的基础上,利用周期测定仪测定周期快捷方便的优点,将负载分别加在音叉某一臂上的不同位置,研究音叉的振动周期和频率与所加负载在音叉不同位置的关系,得到了随着位置的不同,音叉的频率与周期为非线性变化。当在音叉某一位置不变而逐渐增加负载质量,发现周期与质量为线性关系,并为正相关,而频率与质量为线性关系,但为负相关,而且正相关与负相关的线性相关系数很高。其结果揭示了振动周期和频率与音叉双臂质量不同时的关系。     

Dynamic receptive field plasticity in rat spinal cord dorsal horn following C-primary afferent input

The central terminals of cutaneous primary afferent neurons are spatially ordered in the dorsal horn in a highly organized fashion such that a point-to-point map represents the body surface. This afferent terminal somatotopic map correlates with the map of the receptive fields of the cells on which they terminate. The location, size and modality of the cutaneous receptive fields of dorsal horn neurons necessarily depend upon the anatomical presence of afferent nerve fibres which deliver information from the periphery, directly or indirectly, to the cells. However the receptive field size and modality of a cell do not depend only on anatomical connections. Excitatory and inhibitory interneurons, descending influences and facilitations or depressions of synaptic contacts can alter receptive field properties. Here we show that prolonged and substantial cutaneous receptive field changes can be produced by brief inputs from peripheral unmyelinated afferent fibres.     

电容器组负荷开关电场与气流场仿真分析

基于电场数值分析理论,采用二维轴对称电场和拉普拉斯方程描述电容器组负荷开关灭弧室内电场,仿真分析分合闸过程中负荷开关的电场分布,计算电场强度随开距的变化情况;仿真分析合闸过程中的预击穿特性;同时,使用有粘气流场的二维可压缩的N-S方程组描述开关内部气流场,计算分闸情况下负荷开关内部的气流场分布情况,并通过耦合计算得到负荷开关不同条件下的介质恢复强度曲线.     

A single population of olfactory sensory neurons mediates an innate avoidance behaviour in Drosophila

All animals exhibit innate behaviours in response to specific sensory stimuli that are likely to result from the activation of developmentally programmed neural circuits. Here we observe that Drosophila exhibit robust avoidance to odours released by stressed flies. Gas chromatography and mass spectrometry identifies one component of this 'Drosophila stress odorant (dSO)' as CO2. CO2 elicits avoidance behaviour, at levels as low as 0.1%. We used two-photon imaging with the Ca2+-sensitive fluorescent protein G-CaMP to map the primary sensory neurons governing avoidance to CO2. CO2 activates only a single glomerulus in the antennal lobe, the V glomerulus; moreover, this glomerulus is not activated by any of 26 other odorants tested. Inhibition of synaptic transmission in sensory neurons that innervate the V glomerulus, using a temperature-sensitive Shibire gene (Shi(ts)), blocks the avoidance response to CO2. Inhibition of synaptic release in the vast majority of other olfactory receptor neurons has no effect on this behaviour. These data demonstrate that the activation of a single population of sensory neurons innervating one glomerulus is responsible for an innate avoidance behaviour in Drosophila.     

Segregation of efferent connections and receptive field properties in visual area V2 of the macaque

V2 is a visual area of the macaque monkey which is at the second level in a recently proposed hierarchy of cortical visual areas. Histochemical staining for cytochrome oxidase (CO) in V2 reveals a pattern of alternate thick and thin CO-rich stripes separated by CO-sparse interstripes. These subregions receive distinct inputs from neurones in CO-rich and CO-sparse zones arrayed within the superficial layers of V1 (refs 4, 5). Are output projections from V2 to higher visual areas also segregated? Using an anatomical double-label paradigm, we have now demonstrated that V2 cells projecting to two of its major target areas, MT and V4 (refs 6, 7), are arranged in stripe-like clusters which are largely segregated from one another and which are closely related to the pattern of CO stripes. Concomitant electrophysiological recordings from V2 indicate that groups of cells having similar receptive field properties are clustered within the subregions defined by these anatomical techniques.     

电磁场中变频率谐振子的不变量和传播子以及波函数

本文依靠一特定的正则变换,用相空间路径积分方法,求得电磁场中变频率谐振子的不变量和传播子以及波函数。     

Construction of a genetic toggle switch in Escherichia coli

It has been proposed' that gene-regulatory circuits with virtually any desired property can be constructed from networks of simple regulatory elements. These properties, which include multistability and oscillations, have been found in specialized gene circuits such as the bacteriophage lambda switch and the Cyanobacteria circadian oscillator. However, these behaviours have not been demonstrated in networks of non-specialized regulatory components. Here we present the construction of a genetic toggle switch-a synthetic, bistable gene-regulatory network-in Escherichia coli and provide a simple theory that predicts the conditions necessary for bistability. The toggle is constructed from any two repressible promoters arranged in a mutually inhibitory network. It is flipped between stable states using transient chemical or thermal induction and exhibits a nearly ideal switching threshold. As a practical device, the toggle switch forms a synthetic, addressable cellular memory unit and has implications for biotechnology, biocomputing and gene therapy.     

频域分段相干累加法在P码直捕系统中的应用

论文提出将频域分段相干累加法应用于P码直捕系统。首先对算法进行了介绍,然后给出了应用此算法的P码直捕的实现方案,分析了在高动态环境下其对硬件资源及工作速度的要求,研究表明应用频域分段相干累加法的P码直捕系统能够适应高动态环境,且大大节省了硬件资源。     

Receptor binding redefined by a structural switch in a mutant human insulin

Crystal structures of insulin have been determined in various distinct forms, the relevance of which to receptor recognition has long been the subject of speculation. Recently the crystal structure of an inactive insulin analogue has been determined and, surprisingly, found to have a conformation identical to native insulin. On this basis Dodson and colleagues have suggested that the known insulin crystal structures reflect an inactive conformation, and that a change in conformation is required for activity--specifically, the carboxy terminal residues of the B-chain are proposed to separate from the amino terminal residues of the A-chain. Here we report the solution structure of an active insulin mutant, determined by two-dimensional NMR, which supports this hypothesis. In the mutant, the carboxy terminal beta-turn and beta-strand of the B-chain are destabilized and do not pack across the rest of the molecule. We suggest that analogous detachment of the carboxy terminal region of the B-chain occurs in native insulin on binding to its receptor. Our finding that partial unfolding of the B-chain exposes an alternative protein surface rationalizes the receptor-binding properties of a series of anomalous insulin analogues, including a mutant insulin associated with diabetes mellitus in man.     

黔南坳陷节理发育特征及其对构造应力场转换的指示

通过野外地质调查,统计和分析黔南坳陷节理产状、几何样式及序列关系等,探讨古构造应力场特征.结果表明:根据节理切割及其与断层的先后关系,可将黔南坳陷节理组分为5个序列,NNE与SEE向X型平面共轭剪节理在加里东末期首先发育,在燕山晚期发育NW-NE方向共轭剪节理和NNE-NEE方向共轭剪节理,且前者发育时间先于后者, EW向节理在喜马拉雅期形成;构造应力场主方向经历了NEE-NS-NE-EW的先逆时针后顺时针的应力场转换;燕山期和喜马拉雅期在黔南坳陷构造应力场转换中起着重要作用.     

Interaction between microbubble and elastic microvessel in low frequency ultrasound field using finite element method

The interaction between microbubble and elastic microvessel wall has been hypothesized to be important in the mechanisms of therapeutic ultrasound applications.In this study,a 2D axisymmetric finite element numerical model is established to study the interaction between elastic microvessel wall and oscillating microbubble in low frequency ultrasound field using fluid solid interaction method.The numerical results show that the bubble oscillation induces the vessel wall dilation and depression.The von Mises stress distribution over the microvessel wall is heterogeneous and the maximum value of the midpoint on the inner vessel wall could reach 0.23 MPa and 1.32 MPa under PNP 0.2 MPa and 0.5 MPa,respectively.When the bubble collapses,the circumferential stress decreases rapidly and the transmural pressure increases dramatically.Noticeably,the circumferential stress becomes compressive with the maximum magnitude 1.83 MPa under PNP 0.5 MPa,larger than the maximum tension value.It is possible that the rapid compression stress during bubble collapse plays important role in mechanical effect on microvessel wall endothelial lining disruption.     

观文矿区地下暗河中天然电场选频法的探测研究

天然电场选频法在地下暗河的勘探中有抗干扰能力强、方便、快速、资料直观易解释等独特的优点.简述了天然电场选频法的基本工作原理以及该方法在工作中注意的问题,在分析水文地质条件的基础上,运用天然电场选频的方法,对观文矿区内地下暗河进行了探测研究,并根据探测结果与地质构造特征,初步确定了探测区的4条地下暗河,为+ 875运输巷...