Organization of cell assemblies in the hippocampus

Neurons can produce action potentials with high temporal precision. A fundamental issue is whether, and how, this capability is used in information processing. According to the 'cell assembly' hypothesis, transient synchrony of anatomically distributed groups of neurons underlies processing of both external sensory input and internal cognitive mechanisms. Accordingly, neuron populations should be arranged into groups whose synchrony exceeds that predicted by common modulation by sensory input. Here we find that the spike times of hippocampal pyramidal cells can be predicted more accurately by using the spike times of simultaneously recorded neurons in addition to the animals location in space. This improvement remained when the spatial prediction was refined with a spatially dependent theta phase modulation. The time window in which spike times are best predicted from simultaneous peer activity is 10-30 ms, suggesting that cell assemblies are synchronized at this timescale. Because this temporal window matches the membrane time constant of pyramidal neurons, the period of the hippocampal gamma oscillation and the time window for synaptic plasticity, we propose that cooperative activity at this timescale is optimal for information transmission and storage in cortical circuits.     

浅谈建筑情感空间的设计

"情感"经常被用于表达建筑、表达空间,说明由于社会的进步,时代的发展,人们关注更多的是自己所生存空间的舒适程度,这种舒适程度要求设计师在设计过程中不仅要考虑最基本的设计因素,而且要考虑人们的情感因素,考虑人们的心理接受,其设计原则必须满足人体尺度和人文尺度两大方面,以满足人类发展的需要.     

Analysis of regulatory architectures in BST

Based on the data envelopment analysis (DEA) theory, the optimal pathway of metabolic reaction networks in biochemical systems is studied. After calculating the mixed-integer linear programming (MILP) model given by Bailey et al. twice, the decision making units (DMU) and the prediction model of DEA are constructed, where the inputs are levels of manipulated parameters (enzyme) and outputs are concentrations of metabolites. When the metabolic networks are reconstructed, the data are obtained by calculating MILP framework twice and the optimal levels of the manipulated parameter at different regular loops are predicted, thus simplifying the calculations of Bailey's.     

论纤维集合体的电阻

首先建立了纤维块体在具有一对极板的试盒中纵向和横向压缩时导电情况的物理模型.据此物理模型用“无规行走”问题方法建立起数学模型,推导出纤维块体导电阻率ρ与填充率f的关系式.此式的变化趋势,跟实侧电阻率显示值随f的变化相符合.沿极板纵向压缩与横向压缩对纤维块体来说是等价的.ρ随f变化的原因在于纤维块体被压缩过程中纤维块体的导电通道数逐渐增多,每条通道的平均有效长度逐渐缩短.ρ_1～f图线呈拉长S状,中段近似直,f=0.15～0.45间用直线横拟误差不大.     

Determining the composition of the Earth

A long-standing question in the planetary sciences asks what the Earth is made of. For historical reasons, volatile-depleted primitive materials similar to current chondritic meteorites were long considered to provide the 'building blocks' of the terrestrial planets. But material from the Earth, Mars, comets and various meteorites have Mg/Si and Al/Si ratios, oxygen-isotope ratios, osmium-isotope ratios and D/H, Ar/H2O and Kr/Xe ratios such that no primitive material similar to the Earth's mantle is currently represented in our meteorite collections. The 'building blocks' of the Earth must instead be composed of unsampled 'Earth chondrite' or 'Earth achondrite'.     

颗粒聚集体的崩塌性质研究

考察和分析了一般颗粒物质堆积体中崩塌的主要特征，概述了目前对颗粒物质崩塌研究所涉及的相关模型以及理论，并对其适用范围和局限性进行了分析，指出了他们的成功之处及不足，提出了对颗粒物质堆积体崩塌机理进行深入研究的一些思路。     

定位检测破损燃料组件的堆芯啜吸法

破损燃料组件定位检测系统是为了确保反应堆安全运行、及时处理燃料包壳破损事故的安全重要设备.根据目前国际上对有元件盒反应堆采用的堆芯啜吸法,即在反应堆换料期间或发生燃料包壳破损事故时,停堆后直接从仍在堆芯位置的元件盒中取样,进行放射性测量和分析,从而鉴别出有破损的燃料组件的方法,作者设计了200MW低温核供热堆破损燃料组件定位检测系统.该设计既有国际同类设备的先进水平,又结合了低温核供热堆的特点和我国国情,保证了200MW低温核供热堆的安全.     

基于迭代共享的SMS交换结构调度算法

以往SMS(Switch-Memory-Switch)交换结构调度算法因实现复杂度过高而难以应用在高速环境中.该文提出了一种基于迭代共享的并行迭代调度算法(IS-RRM).通过在迭代过程中同时解决信元的到达和离开冲突,避免了传统算法构造DTC(Departure-Time-Compatible)二分图所需的复杂开销;利用迭代共享技术,使不同时刻到达的信元共享相对较长一段时间的迭代资源,大大减少了单位时隙所需要的迭代次数,降低了调度器的实现复杂度.仿真表明: 在端口数为32时,在每个时隙中仅需采用10次迭代, IS-RRM算法便能够取得小于10-8的信元丢失率. IS-RRM算法具有良好的鲁棒性,在突发到达和非均匀到达模型下均能取得良好的性能.     

Visualizing columnar architectures using high-field fMRI

Among the many neuroimaging tools available for studying human brain functions, functional magnetic resonance imaging (fMRI) is the most widely used today. One advantage of fMRI over other imaging techniques is its relatively high spatial resolution. High-resolution fMRI, with its superb signal-to-noise ratio and improved tissue-vessel specificity, has strengthened the capability of fMRI and allowed mapping of fine cortical architectures in the human brain. In this review, I will first explain the factors limiting the spatial specificity of the blood oxygenation level-dependent (BOLD) effect, based on which most of fMRI experiments are conducted, and the measures dealing with these factors, and then briefly introduce several high-resolution (sub-millimeter) studies on the functional organization of human primary visual cortex (V1), including mapping of ocular dominance columns, mapping of temporal frequency dependent domains and direct demonstration of tuning to stimulus orientation.     

Visualizing columnar architectures using high-field fMRI

Among the many neuroimaging tools available for studying human brain functions, functional magnetic resonance imaging (fMRI) is the most widely used today. One advantage of fMRI over other imaging techniques is its relatively high spatial resolution. High-resolution fMRI, with its superb signal-to-noise ratio and improved tissue-vessel specificity, has strengthened the capability of fMRI and allowed mapping of fine cortical architectures in the human brain. In this review, I will first explain the factors limiting the spatial specificity of the blood oxygenation level-dependent (BOLD) effect, based on which most of fMRI experiments are conducted, and the measures dealing with these factors, and then briefly introduce several high-resolution (sub-millimeter) studies on the functional organization of human primary visual cortex (V1), including mapping of ocular dominance columns, mapping of temporal frequency dependent domains and direct demonstration of tuning to stimulus orientation.     

由递推关系式确定数列的阶

在一些由递推关系式所决定的数列中,通常需要对数列的阶进行估计。由于数列的显式表达式一般很难求出,因此要判定它们的阶并不是一件容易的事。本文对两种不同类型的递推关系式采用不同的方法得到数列极限的细致刻画。     

由递推关系式确定数列的阶

在一些由递推关系式所决定的数列中,通常需要对数列的阶进行估计.由于数列的显式表达式一般很难求出,因此要判定它们的阶并不是一件容易的事.本文对两种不同类型的递推关系式采用不同的方法得到数列极限的细致刻画.     

天然高分子改性阳离子絮凝剂的性能

以天然玉米芯粉为原料与阳离子醚化剂和碱性催化剂的混合物进行反应合成了一种新型的阳离子絮凝剂．分别选用高岭土、硅藻土两种体系研究其絮凝性能，实验结果表明，天然高分子改性阳离子絮凝剂的絮凝性能明显优于六水氯化铝和国产的聚丙烯酰胺，具有最佳用量范围宽、pH应用范围广、无毒性残留等优点。     

非奇异M矩阵的判定

给出了Ｍ矩阵的几个新的判定准则，这些准则具有简单、方便的特点，且与已有的判定准则相比，具有更为广泛的适用范围。     

Image reconstructions of helical assemblies of the HIV-1 CA protein

The type 1 human immunodeficiency virus (HIV-1) contains a conical capsid comprising approximately 1,500 CA protein subunits, which organizes the viral RNA genome for uncoating and replication in a new host cell. In vitro, CA spontaneously assembles into helical tubes and cones that resemble authentic viral capsids. Here we describe electron cryo-microscopy and image reconstructions of CA tubes from six different helical families. In spite of their polymorphism, all tubes are composed of hexameric rings of CA arranged with approximate local p6 lattice symmetry. Crystal structures of the two CA domains were 'docked' into the reconstructed density, which showed that the amino-terminal domains form the hexameric rings and the carboxy-terminal dimerization domains connect each ring to six neighbours. We propose a molecular model for the HIV-1 capsid that follows the principles of a fullerene cone, in which the body of the cone is composed of curved hexagonal arrays of CA rings and the ends are closed by inclusion of 12 pentagonal 'defects'.     

Assembly of hybrid photonic architectures from nanophotonic constituents

The assembly of hybrid nanophotonic devices from different fundamental photonic entities--such as single molecules, nanocrystals, semiconductor quantum dots, nanowires and metal nanoparticles--can yield functionalities that exceed those of the individual subunits. Combining these photonic elements requires nanometre-scale fabrication precision and potentially involves a material diversity that is incompatible with standard nanotechnological processes. Although merging these different systems on a single hybrid platform is at present challenging, it promises improved performance and novel devices. Particularly rapid progress is seen in the combination of plasmonic-dielectric constituents with quantum emitters that can be assembled on demand into fundamental model systems for future optical elements.     

Kinase-regulated quantal assemblies and kiss-and-run recycling of caveolae

A functional genomics approach has revealed that caveolae/raft-mediated endocytosis is subject to regulation by a large number of kinases. Here we explore the role of some of these kinases in caveolae dynamics. We discover that caveolae operate using principles different from classical membrane trafficking. First, each caveolar coat contains a set number (one 'quantum') of caveolin-1 molecules. Second, caveolae are either stored as in stationary multi-caveolar structures at the plasma membrane, or undergo continuous cycles of fission and fusion with the plasma membrane in a small volume beneath the surface, without disassembling the caveolar coat. Third, a switch mechanism shifts caveolae from this localized cycle to long-range cytoplasmic transport. We have identified six kinases that regulate different steps of the caveolar cycle. Our observations reveal new principles in caveolae trafficking and suggest that the dynamic properties of caveolae and their transport competence are regulated by different kinases operating at several levels.     

Determining the position of the cell division plane

Proper positioning of the cell division plane during mitosis is essential for determining the size and position of the two daughter cells--a critical step during development and cell differentiation. A bipolar microtubule array has been proposed to be a minimum requirement for furrow positioning in mammalian cells, with furrows forming at the site of microtubule plus-end overlap between the spindle poles. Observations in other species have suggested, however, that this may not be true. Here we show, by inducing mammalian tissue cells with monopolar spindles to enter anaphase, that furrow formation in cultured mammalian cells does not require a bipolar spindle. Unexpectedly, cytokinesis occurs at high frequency in monopolar cells. Division always occurs at a cortical position distal to the chromosomes. Analysis of microtubules during cytokinesis in cells with monopolar and bipolar spindles shows that a subpopulation of stable microtubules extends past chromosomes and binds to the cell cortex at the site of furrow formation. Our data are consistent with a model in which chromosomes supply microtubules with factors that promote microtubule stability and furrowing.