A laser ablation method for the synthesis of crystalline semiconductor nanowires

A method combining laser ablation cluster formation and vapor-liquid-solid (VLS) growth was developed for the synthesis of semiconductor nanowires. In this process, laser ablation was used to prepare nanometer-diameter catalyst clusters that define the size of wires produced by VLS growth. This approach was used to prepare bulk quantities of uniform single-crystal silicon and germanium nanowires with diameters of 6 to 20 and 3 to 9 nanometers, respectively, and lengths ranging from 1 to 30 micrometers. Studies carried out with different conditions and catalyst materials confirmed the central details of the growth mechanism and suggest that well-established phase diagrams can be used to predict rationally catalyst materials and growth conditions for the preparation of nanowires.     

Virus-enabled synthesis and assembly of nanowires for lithium ion battery electrodes

The selection and assembly of materials are central issues in the development of smaller, more flexible batteries. Cobalt oxide has shown excellent electrochemical cycling properties and is thus under consideration as an electrode for advanced lithium batteries. We used viruses to synthesize and assemble nanowires of cobalt oxide at room temperature. By incorporating gold-binding peptides into the filament coat, we formed hybrid gold-cobalt oxide wires that improved battery capacity. Combining virus-templated synthesis at the peptide level and methods for controlling two-dimensional assembly of viruses on polyelectrolyte multilayers provides a systematic platform for integrating these nanomaterials to form thin, flexible lithium ion batteries.     

Fabrication and magnetic properties of arrays of metallic nanowires

Arrays of ferromagnetic nickel and cobalt nanowires have been fabricated by electrochemical deposition of the metals into templates with nanometer-sized pores prepared by nuclear track etching. These systems display distinctive characteristics because of their one-dimensional microstructure. The preferred magnetization direction is perpendicular to the film plane. Enhanced coercivities as high as 680 oersteds and remnant magnetization up to 90 percent have also been observed.     

Encoding electronic properties by synthesis of axial modulation-doped silicon nanowires

We describe the successful synthesis of modulation-doped silicon nanowires by achieving pure axial elongation without radial overcoating during the growth process. Scanning gate microscopy shows that the key properties of the modulated structures-including the number, size, and period of the differentially doped regions-are defined in a controllable manner during synthesis, and moreover, that feature sizes to less than 50 nanometers are possible. Electronic devices fabricated with designed modulation-doped nanowire structures demonstrate their potential for lithography-independent address decoders and tunable, coupled quantum dots in which changes in electronic properties are encoded by synthesis rather than created by conventional lithography-based techniques.     

造林树种苗木定向培育理论探讨

为解决苗木培育的技术难题 ,作者提出了苗木定向培育的概念 .苗木定向培育 ,是根据造林地立地条件主要限制因子对苗木的要求 ,在苗木培育过程中采取相应调控技术措施 ,使苗木在形态、生理及活力等方面满足造林需要 ,做到适地适树造林 .我们以困难立地条件下造林用苗为目标 ,阐述了苗木定向培育技术体系 ,通过不同的育苗技术措施 ,如抗性基因与种源选择、林木种子处理技术、苗木抗逆性调控技术、苗木活力保护技术与管理技术等措施 ,为做到适地适苗造林提供理论依据     

利用VBA提高农业信息资源建设的工作效率和质量

农业倩息资源建设过程中,经常会遇到批量查找、替换和标注等重复性强且繁琐的操作,自动化语言VBA作为一种与微软办公套件可以协同工作的工具,可以成为农业信息资源建设过程中采集、编码和审核等重要环节的得力助手.通过探索VBA在农业信息采集、整理、加工中的应用,以实例的方式展示了VBA协助不同格式农业信息的快速整理、格式的统一和禁用农药的批量查找和标注,提高农业信息整合的工作效率和质量的应用.     

磁性茶渣炭的简易制备及其活化过硫酸盐降解罗丹明B的性能

以硫酸亚铁(FeSO₄·7H₂O)和红茶渣为原料,采用限氧高温热解技术制备了系列磁性生物炭（Fe-BC_0.72、Fe-BC_0.55、Fe-BC_0.25）并将其用于活化过二硫酸盐（PS）降解罗丹明B（Rh B)）。考察了Fe₃O₄（Fe）与生物炭(BC)的质量比、Fe-BC投加量、过硫酸钾用量、溶液pH、温度等参数对BC-Fe活化PS降解Rh B效果的影响。结果表明,当Fe₃O₄与生物炭(BC)的质量比为0.55、Fe-BC用量为0.021 3 g、PS用量为0.030 2 g,pH为5、反应温度为30 ℃时Fe-BC_0.55对RhB (40 mg·L^-1)的降解效果最佳,反应90 min时的降解率为98.8%。将Fe-BC_0.55磁性分离、循环使用5次,对RhB的降解率为75%。     

String tension and stability of magic tip-suspended nanowires

Multishell helical gold nanowires were recently imaged by electron microscopy. We show theoretically that the contact with the gold tips at either end of the wire plays a crucial role and that local minima in the string tension rather than the total wire free energy determine the nanowire stability. Density functional electronic structure calculations of the simplest and thinnest coaxial gold and silver wires of variable radius and chirality were carried out. We found a string tension minimum for a single-tube gold nanowire that is chiral and consists of seven strands, in striking agreement with observation. In contrast, no such minimum was found for silver, where the s-d competition leading to surface reconstruction is lacking.     

Synthesis and characterization of helical multi-shell gold nanowires

Suspended gold nanowires were made in an ultra-high vacuum. The finest of them was 0.6 nanometer in diameter and 6 nanometers in length. By high-resolution electron microscopy, they were shown to have a multi-shell structure composed of coaxial tubes. Each tube consists of helical atom rows coiled round the wire axis. The difference between the numbers of atom rows in outer and inner shells is seven, resulting in magic shell-closing numbers.     

Control of thickness and orientation of solution-grown silicon nanowires

Bulk quantities of defect-free silicon (Si) nanowires with nearly uniform diameters ranging from 40 to 50 angstroms were grown to a length of several micrometers with a supercritical fluid solution-phase approach. Alkanethiol-coated gold nanocrystals (25 angstroms in diameter) were used as uniform seeds to direct one-dimensional Si crystallization in a solvent heated and pressurized above its critical point. The orientation of the Si nanowires produced with this method could be controlled with reaction pressure. Visible photoluminescence due to quantum confinement effects was observed, as were discrete optical transitions in the ultraviolet-visible absorbance spectra.     

酶定向进化文库的筛选方法

酶工程作为生物技术的主体之一,对农产品加工等的发展具有广泛作用。自然界中的酶往往不能满足 实际生产,因此需要通过模拟自然界中的蛋白质进化,对酶进行改造和突变文库筛选,最终得到符合实际生产的酶。 目前,改造酶的途径主要有定点突变和定向突变两种。突变体文库的建立方法较为成熟,并且建立起的文库库容也 能够达到研究者的要求,但是突变体文库的筛选受现有技术等所局限,成为了定向进化技术的瓶颈。介绍了几种常 用的突变体文库的筛选方法,对它们的原理及特点进行阐述,并对未来的发展方向及趋势进行了总结。     

DNA-templated self-assembly of protein arrays and highly conductive nanowires

A DNA nanostructure consisting of four four-arm junctions oriented with a square aspect ratio was designed and constructed. Programmable self-assembly of 4 x 4 tiles resulted in two distinct lattice morphologies: uniform-width nanoribbons and two-dimensional nanogrids, which both display periodic square cavities. Periodic protein arrays were achieved by templated self-assembly of streptavidin onto the DNA nanogrids containing biotinylated oligonucleotides. On the basis of a two-step metallization procedure, the 4 x 4 nanoribbons acted as an excellent scaffold for the production of highly conductive, uniform-width, silver nanowires.     

Discovery and directed evolution of a glyphosate tolerance gene

The herbicide glyphosate is effectively detoxified by N-acetylation. We screened a collection of microbial isolates and discovered enzymes exhibiting glyphosate N-acetyltransferase (GAT) activity. Kinetic properties of the discovered enzymes were insufficient to confer glyphosate tolerance to transgenic organisms. Eleven iterations of DNA shuffling improved enzyme efficiency by nearly four orders of magnitude from 0.87 mM-1 min-1 to 8320 mM-1 min-1. From the fifth iteration and beyond, GAT enzymes conferred increasing glyphosate tolerance to Escherichia coli, Arabidopsis, tobacco, and maize. Glyphosate acetylation provides an alternative strategy for supporting glyphosate use on crops.     

Fluorous mixture synthesis: a fluorous-tagging strategy for the synthesis and separation of mixtures of organic compounds

The solution-phase synthesis of organic compounds as mixtures rather than in individual pure form offers efficiency advantages that are negated by the difficulty in separating and identifying the components of the final mixture. Here, a strategy for mixture synthesis that addresses these separation and identification problems is presented. A series of organic substrates was tagged with a series of fluorous tags of increasing fluorine content. The compounds were then mixed, and multistep reactions were conducted to make enantiomers or analogs of the natural product mappicine. The resulting tagged products were then demixed by fluorous chromatography (eluting in order of increasing fluorine content) to provide the individual pure components of the mixture, which were detagged to release the final products.     

Search for magnetic monopoles in the lunar sample

An electromagnetic search for magnetic monopoles of the minimum size predicted by Dirac, or of any larger magnitude, has been performed on 8.37 kilograms of lunar surface material. No monopole was found. This experimnent sets new limists on the production cross section for monopoles and on their occurrence in cosmic radiation.     

A new strategy for the synthesis of glycoproteins

Posttranslational modifications of proteins regulate many biological processes, including metabolism, signal transduction, and gene expression. The synthetic challenges associated with generating homogeneous populations of selectively modified proteins, however, have hindered detailed studies of the effects of these modifications on protein structure and function. Here, we report an approach to the cotranslational synthesis of selectively glycosylated proteins in which the modified amino acid is genetically encoded. We show that myoglobin containing beta-N-acetylglucosamine (GlcNAc)-serine at a defined position can be expressed in Escherichia coli in good yield and with high fidelity. The beta-GlcNAc moiety can be recognized by a saccharide-binding protein, or subsequently modified with a galactosyltransferase to build more complex carbohydrates. This approach should be generally applicable to other posttranslational modifications such as protein phosphorylation, acetylation, and methylation.     

A strategy for the chemical synthesis of nanostructures

Highly localized chemical catalysis was carried out on the surface groups of a self-assembled monolayer with a scanning probe device. With the use of a platinum-coated atomic force microscope tip, the terminal azide groups of the monolayer were catalytically hydrogenated with high spatial resolution. The newly created amino groups were then covalently modified to generate new surface structures. By varying the nature of the catalyst and the chemical composition of the surface, it may be possible to synthesize molecular assemblies not readily produced by existing microfabrication techniques.     

SrTiO3纳米线的溶胶-凝胶模板法制备与表征

采用二次阳极氧化法制备多孔阳极氧化铝(AAO)模板,通过溶胶-凝胶模板法在AAO模板的孔洞中制得SrTiO3纳米线,用XRD,EDS,SEM,TEM和SAED对纳米线的结构、成分和形貌进行表征. 结果表明:AAO模板孔洞相互平行,孔径大小均一,所得纳米线长约13 μm,直径约70 nm,含有Al,O,Sr,Ti 4种元素,为立方相多晶结构.     

Preservation of the gene pool of crossbred replacement heifers during directed growing

Directed growing of replacement heifers using various methods of rearing and rated feeding resulted in increase of the live weight and milk yield at first lactation and decrease in the feeding costs.