Multicomponent polymeric engineering materials

The great advances made in polymeric structural materials over the past decade have led to their replacement of conventional materials in a wide range of uses including high-performance aerospace applications. This shift in choice of materials is based on economic advantages, simplified fabrication, freedom from corrosion, and lower weight. The trend toward use of polymeric materials will grow as the materials science of this new technology is developed. Better insight into such fundamental problems as the mechanisms by which forces are transferred to the polymer molecule, the surface interactions between polymer phases or polymer and fiber, and the molecular processes by which energy is absorbed during fracture will greatly stimulate the development of this field.     

Hierarchical structure in polymeric materials

The diversity of monomers available for synthesis of high polymers makes it possible to prepare a wide variety of long-chain macromolecular compounds. It is instructive to consider a hierarchical organization of structure in polymers at four successive levels--the molecular, nano-, micro-, and macrolevels--and to examine how interactions at and between these various levels of structure have important and often quite specific influences. Examples are drawn from semicrystalline polymers with flexible chains, liquid-crystalline polymers composed of rigid macromolecules, and amorphous polymers. Structural hierarchies in biocomposite systems are also discussed, particularly in soft connective tissues such as tendon and intervertebral disk.     

Functional materials based on self-assembly of polymeric supramolecules

Self-assembly of polymeric supramolecules is a powerful tool for producing functional materials that combine several properties and may respond to external conditions. We illustrate the concept using a comb-shaped architecture. Examples include the hexagonal self-organization of conjugated conducting polymers and the polarized luminance in solid-state films of rodlike polymers obtained by removing the hydrogen-bonded side chains from the aligned thermotropic smectic phase. Hierarchically structured materials obtained by applying different self-organization and recognition principles and directed assembly form a basis for tunable nanoporous materials, smart membranes, preparation of nano-objects, and anisotropic properties, such as proton conductivity.     

Chain length recognition: core-shell supramolecular assembly from oppositely charged block copolymers

Molecular recognition based on length was found to occur between oppositely charged pairs of flexible and randomly coiled block copolymers in an aqueous milieu. Matched pairs with the same block lengths of polyanions and polycations exclusively formed even in mixtures with different block lengths. These assemblies of the charged segments with matched chain lengths then formed larger core-shell-type supramolecular assemblies with an extremely narrow size distribution due to the strict phase separation between core- and shell-forming segments.     

Community structure of corals and reef fishes at multiple scales

Distributions of numerical abundance and resource use among species are fundamental aspects of community structure. Here we characterize these patterns for tropical reef fishes and corals across a 10,000-kilometer biodiversity gradient. Numerical abundance and resource-use distributions have similar shapes, but they emerge at markedly different scales. These results are consistent with a controversial null hypothesis regarding community structure, according to which abundance distributions arise from the interplay of multiple stochastic environmental and demographic factors. Our findings underscore the importance of robust conservation strategies that are appropriately scaled to the broad suite of environmental processes that help sustain biodiversity.     

森林水源涵养功能的多尺度内涵、过程及计量方法

近年来国内森林生态系统服务功能研究较多,但应用价值不高,其科学性受到诸多质疑.从森林水源涵养功能的多尺度内涵、过程以及其计量方法出发,对国内外研究动态和发展趋势进行了总结分析,重新审视森林水源涵养功能的研究意义,探讨森林水源涵养功能的多尺度特征.从森林水源涵养功能作用的空间尺度上看,其拦蓄洪水削减洪峰的功能仅在较小尺度上有效,而调节径流的功能只有当森林土壤的入渗量超过蒸散量时,才可能有更多地下水补给河道径流,进而增加旱季河道流量.同时森林水源涵养功能也具有明显的时间尺度特征,具体表现为在次降水事件中,由于蒸散发量较小,森林水源涵养功能的物质量等于森林不同层次的截留量,在功能上表现为拦蓄降水;在长时间尺度上,由于林地蒸散要耗去大量水分,森林水源涵养功能的物质量等于森林不同层次的截留量减去林地蒸散发量,在功能上表现为净化水质和调节径流.大多数研究仅对单一林分的个别层次蓄水功能进行研究,缺乏流域尺度或者更大空间尺度的森林水源涵养功能研究.建议从区域降尺度到流域或将坡面尺度上推到流域,集中在流域尺度解决森林水源涵养空间异质性将是解决森林水源涵养功能尺度外推的有效办法.就目前国内流行的森林水源涵养功能计量方法而言,其与尺度及研究目的有较大相关性,在研究中应根据研究目的、研究尺度和可获取的数据情况选择合适的计量方法.研究突出了不同尺度作用下森林水文过程的复杂性及重要性,并结合森林与水关系的争论问题,分析目前国内对森林水源涵养功能研究的一些误区,提出森林水源涵养功能研究的一些关键科学问题及未来可能的发展方向,主要包括:1)明确界定森林水源涵养功能的边界,探索森林水源涵养功能计量的新方法;2)加强不同时空尺度关联的森林水源涵养功能研究,包括正确评价森林水源涵养功能的时空变异规律,森林生态系统水源涵养功能的尺度效应,森林水源涵养与下游水生态安全,森林水源涵养研究范式转变等核心问题.     

A review of methods to evaluate crop model performance at multiple and changing spatial scales

Precision Agriculture - Crop models are useful tools because they can help understand many complex processes by simulating them. They are mainly designed at a specific spatial scale, the field. But...     

Fluorometric detection of enzyme activity with synthetic supramolecular pores

The reversible blockage of synthetic pores formed by rigid-rod beta barrels, either by substrates or products, was used to sense a variety of enzymatic reactions in high-throughput format with "naked-eye" fluorescent detection. Improvement of sensor sensitivity beyond three orders of magnitude by straightforward internal mutations underscores the functional plasticity of rigid-rod beta barrels. Such detectors of enzyme activity with the aforementioned characteristics are needed in areas as diverse as proteomics and environmentally benign organic synthesis.     

三江平原典型湿地的多尺度人为干扰格局研究

采用多尺度滑动窗口算法,分析三江平原典型湿地的人为干扰空间格局,确定土地利用类型在建三江湿地生态系统中的受人为干扰度(pd)及干扰邻近度(pdd)。结果表明:1)2001—2006年间研究区土地利用类型的变化对多尺度的干扰格局分布有极大影响,耕地干扰比例高达37.94%。2)人为干扰度类型c1、c2在水域、林地和沼泽分布较广,干扰值较小;而水田和旱地占干扰度c7、c8的74.38%和61.76%,说明耕地是建三江区湿地生态系统主要人为干扰源。3)多尺度干扰邻近度证明人为干扰是在一定尺度上发生,当pd0.4或pd0.7且pddpd时,人为干扰对周边土地利用类型必定产生影响。     

不同尺度土壤性质空间变异研究进展

综述了近年来不同尺度(田间尺度,小区尺度和微尺度)上土壤性质(土壤水分、养分、理化性质及生物学性质等)空间变异研究的进展。探讨了土壤性质空间变异的原因,影响因素及研究方法,并对土壤空间变异研究前景进行了展望。     

带脉冲的高阶线性时标微分方程的振动性（英文）

研究了带强迫项的一阶时标脉冲微分方程的振动性,得到几个时标方程的解具有振动性的判定条件,并举例说明了脉冲对时标系统解振动性的重要性.     

Temporal frequency of subthreshold oscillations scales with entorhinal grid cell field spacing

Grid cells in layer II of rat entorhinal cortex fire to spatial locations in a repeating hexagonal grid, with smaller spacing between grid fields for neurons in more dorsal anatomical locations. Data from in vitro whole-cell patch recordings showed differences in frequency of subthreshold membrane potential oscillations in entorhinal neurons that correspond to different positions along the dorsal-to-ventral axis, supporting a model of physiological mechanisms for grid cell responses.     

From micro- to nanofabrication with soft materials

Soft materials are finding applications in areas ranging from microfluidic device technology to nanofabrication. We review recent work in these areas, discuss the motivation for device fabrication with soft materials, and describe applications of soft materials. In particular, we discuss active microfluidic devices for cell sorting and biochemical assays, replication-molded optics with subdiffraction limit features, and nanometer-scale resonators and wires formed from single-molecule DNA templates as examples of how the special properties of soft materials address outstanding problems in device fabrication.     

Assembling materials with DNA as the guide

DNA's remarkable molecular recognition properties and structural features make it one of the most promising templates to pattern materials with nanoscale precision. The emerging field of DNA nanotechnology strips this molecule from any preconceived biological role and exploits its simple code to generate addressable nanostructures in one, two, and three dimensions. These structures have been used to precisely position proteins, nanoparticles, transition metals, and other functional components into deliberately designed patterns. They can also act as templates for the growth of nanowires, aid in the structural determination of proteins, and provide new platforms for genomics applications. The field of DNA nanotechnology is growing in a number of directions, carrying with it the promise to substantially affect materials science and biology.     

Actinide topological insulator materials with strong interaction

Topological band insulators have recently been discovered in spin-orbit coupled two-and three-dimensional systems. We theoretically predict a class of topological insulators where interaction effects play a dominant role. In actinide elements, simple rocksalt compounds formed by Pu and Am lie on the boundary between metals and insulators. We show that interaction drives a quantum phase transition to a topological insulator phase with a single Dirac cone on the surface. These putative topological insulators may provide a setting for both applied and fundamental investigation.     

东方百合鳞片结合叶片切段培养快繁技术

以东方百合西伯利亚品种为材料,在试验基础上形成了鳞片切块—不定芽分化—叶片切段—分化丛芽—壮苗—生根培养—移栽小植株的东方百合快繁技术。适宜的鳞片分化培养基为MS 1 mg/L BA 0.5 mg/LNAA 0.05 mg/L GA3,适宜的叶片切段分化培养基为MS 1 mg/L BA 1 mg/L NAA,适宜的壮苗培养基为MS 1 mg/L BA 0.5 mg/L NAA 0.1 mg/L GA3,适宜的生根培养基为MS 0.75 mg/L NAA。鳞片培养时以外部或中部鳞片的中下部切块较好,叶片切段培养以叶片中下部切取1.5~3 cm长度的叶段为宜,鳞片或叶片接种时近轴面向上放置优于远轴面向上放置。     

带脉冲和时滞的时标双向联想记忆Cohen-Grossberg神经网络的稳定性分析(英文)

讨论了一类带脉冲和时滞的含有可变系数的时标双向联想记忆Cohen-Grossberg神经网络的稳定性.利用Lyapunov泛函和Halanay不等式,获得了这类神经网络的平衡点的存在性、全局指数稳定性、全局指数鲁棒稳定性,表明脉冲对于系统的指数稳定性和鲁棒稳定性起了重要的作用.最后以实例说明了理论结果的有效性.     

Restriction fragment length polymorphisms associated with water use efficiency in tomato

Improvement of crop water use efficiency (WUE) has not been successful because evaluation for this component of drought resistance is unreliable in field-grown plants. The composition of stable isotopes of plant carbon (delta(13)C) was earlier shown to be an excellent indicator of WUE in tomato and other species. It is now reported that delta(13)C can be satisfactorily predicted from three restriction fragment length polymorphisms (RFLPs), which are genetic markers for discrete DNA sequences within the genome. An additive type of gene action was observed for all three RFLP markers, and for one of them there also was a significant nonadditive component. Combining the delta(13)C and RFLP technologies may aid in identifying genes associated with WUE and in studying mechanisms contributing to WUE. These technologies will also be useful for crop improvement.