There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

http://nathan.instras.com/ResearchProposalDB/doc-109.pdf

A review on polymer nanofibers by electrospinning and their applications in nanocomposites

Electrospinning is a highly versatile method to process solutions or melts, mainly of polymers, into continuous fibers with diameters ranging from a few micrometers to a few nanometers. This technique is applicable to virtually every soluble or fusible polymer. The polymers can be chemically modified and can also be tailored with additives ranging from simple carbon-black particles to complex species such as enzymes, viruses, and bacteria. Electrospinning appears to be straightforward, but is a rather intricate process that depends on a multitude of molecular, process, and technical parameters. The method provides access to entirely new materials, which may have complex chemical structures. Electrospinning is not only a focus of intense academic investigation; the technique is already being applied in many technological areas.

Electrospinning: A Fascinating Method for the Preparation of Ultrathin Fibers

TiO(2) is one of the most studied compounds in materials science. Owing to some outstanding properties it is used for instance in photocatalysis, dye-sensitized solar cells, and biomedical devices. In 1999, first reports showed the feasibility to grow highly ordered arrays of TiO(2) nanotubes by a simple but optimized electrochemical anodization of a titanium metal sheet. This finding stimulated intense research activities that focused on growth, modification, properties, and applications of these one-dimensional nanostructures. This review attempts to cover all these aspects, including underlying principles and key functional features of TiO(2), in a comprehensive way and also indicates potential future directions of the field.

TiO2 nanotubes: synthesis and applications.

[23] M. DeLong, Optoelectronic Materials Laboratory/Physics Department,University of Utah, Salt Lake City, USA.[24] S. Setayesh, D. Marsitzky, K. Mullen, Macromolecules 2000, 33, 2016.[25] D. Sainova, T. Miteva, H. G. Nothofer, U. Scherf, I. Glowacki, J. Ulanski,H. Fujikawa, D. Neher, Appl. Phys. Lett. 2000, 76, 1810.[26] T. Pauck, H. Bassler, J. Grimme, U. Scherf, K. Mullen, Chem. Phys. 1996,210, 219.

Nanostructured Fibers via Electrospinning

We have developed a simple technique for the fabrication of polymer nanotubes with a monodisperse size distribution and uniform orientation. When either a polymer melt or solution is placed on a substrate with high surface energy, it will spread to form a thin film, known as a precursor film, similar to the behavior of low molar mass liquids ([1][1], [2][2]).

Similar wetting phenomena occur if porous templates are brought into contact with polymer solutions or melts: A thin surface film will cover the pore walls in the initial stages of wetting. This is because the cohesive driving forces for complete filling are much weaker than the adhesive forces. Wall wetting and complete filling of the pores thus take place on different time scales. The latter is prevented by thermal quenching in the case of melts or by solvent evaporation in the case of solutions, thus preserving a nanotube structure. If the template is of monodisperse size distribution, aligned or ordered, so are the nanotubes, and ordered polymer nanotube arrays can be obtained if the template is removed. Any melt-processible polymer, such as polytetrafluoroethylene (PTFE), blends, or multicomponent solutions can be formed into nanotubes with a wall thickness of a few tens of nanometers. Owing to its versatility, this approach should be a promising route toward functionalized polymer nanotubes.

We used ordered porous alumina and oxidized macroporous silicon templates with narrow pore size distribution ([3][3]). Extended regular pore arrays were prepared by lithography. The pores are well-defined, straight, with a smooth inner surface and with diameters DP between 300 and 900 nm. To process melts, we placed the polymer on a pore array at a temperature well above its glass transition temperature, in the case of amorphous polymers, or its melting point, in the case of partially crystalline polymers. The liquid polymer forms a thin wetting film covering the entire pore surface on a time scale ranging from a few minutes to half an hour. Polymer solutions were dropped on the templates at ambient conditions (fig. S1A) ([4][4]). The resulting nanotubes obtained from either method had wall thicknesses between 20 and 50 nm and lengths of up to 100 μm. Oligomers as well as polymers with molecular masses Mn up to several hundreds of thousands of grams per mol were processed. [Figure 1][5]depicts nanotubes formed from several polymers by melt-wetting. The tip of a polystyrene (PS) nanotube ( Mn ∼ 850,000 g/mol) formed in an alumina template was uncovered by etching the alumina substrate with aqueous potassium hydroxide ([Fig. 1][5]A) ([4][4]). [Figure 1][5]B shows the same sample after the complete removal of the template. [Figure 1][5]C depicts an array of aligned PTFE nanotubes obtained by wetting an alumina template and [Fig. 1][5]D a highly ordered array of polymethyl methacrylate (PMMA; Mn ∼ 80,000 g/mol) nanotubes prepared by wetting a macroporous silicon template. After selectively dissolving the template, the remaining nanotube array still exhibits its hexagonal long-range order.

![Figure 1][6] 

Figure 1 
Scanning electron micrographs of nanotubes obtained by melt-wetting. ( A ) Damaged tip of a PS nanotube ( Mn ∼ 850,000 g/mol) protruding from a porous alumina membrane. The substrate, on which the pore array was located, has been removed to uncover the tube tips. ( B ) Ordered array of tubes from the same PS sample after complete removal of the template. ( C ) Array of aligned PTFE tubes. ( D ) PMMA tubes with long-range hexagonal order obtained by wetting of a macroporous silicon pore array after complete removal of the template.



The wetting technique can be easily extended to prepare functionalized nanotubes, for example, palladium/polymer composite nanotubes. We first wetted the porous templates with a solution containing poly-l-lactide (PLLA) and palladium(II)acetate under ambient conditions. After evaporation of the solvent dichloromethane, a PLLA/palladium(II)acetate film covered the pore walls. The template was subsequently annealed in vacuum at temperatures of up to 300°C to degrade PLLA ([5][7]) and to reduce Pd. In a second wetting step, molten PS was added, so that Pd/PS composite tubes were formed (fig. S1B). Energy-dispersive x-ray microanalysis verified the presence of Pd (fig. S1C), and selected area electron diffraction of single composite tubes revealed that it was metallic with a typical crystallite size of 2 to 3 nm (fig. S1D). As demonstrated by this example, template-wetting should have an outstanding potential in providing customized nanotubes for a broad range of applications in nanoscience.

1. [↵][8]1. P. G. de Gennes
 , Rev. Mod. Phys. 57, 827 (1985).
 [OpenUrl][9][CrossRef][10][Web of Science][11]

2. [↵][12]S. F. Kistler, in Wettability , Surfactant Science Series , vol. 49, J. C. Berg, Ed. (Dekker, New York, 1993), chap. 6.
 

3. [↵][13]1. R. B. Wehrspohn, 2. J. Schilling
 , MRS Bull. 8, 623 (2001).
 [OpenUrl][14]

4. [↵][15]Materials and methods are available as supporting mate rial on Science Online.
 

5. [↵][16]1. M. Bognitzki 2. et al.
 , Adv. Mater. 12, 637 (2000).
 [OpenUrl][17]

6. Support from the Deutsche Forschungsgemeinschaft (WE 2637/1-1 and WE 496/19-1) and transmission electron microscopy investigations by C. Dietzsch are gratefully acknowledged. Supporting Online Material [www.sciencemag.org/cgi/content/full/296/5575/1997/DC1][18] Materials and Methods Fig. S1

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 [6]: pending:yes
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 [9]: {openurl}?query=rft.jtitle%253DReviews%2Bof%2BModern%2BPhysics%26rft.stitle%253DRev.%2BMod.%2BPhys.%26rft.issn%253D1539-0756%26rft.volume%253D57%26rft.spage%253D827%26rft_id%253Dinfo%253Adoi%252F10.1103%252FRevModPhys.57.827%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx
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 [12]: #xref-ref-2-1 "View reference 2 in text"
 [13]: #xref-ref-3-1 "View reference 3 in text"
 [14]: {openurl}?query=rft.jtitle%253DMRS%2BBull.%26rft.volume%253D8%26rft.spage%253D623%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx
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 [17]: {openurl}?query=rft.jtitle%253DAdv.%2BMater.%26rft.volume%253D12%26rft.spage%253D637%26rft.atitle%253DADV%2BMATER%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx
 [18]: http://www.sciencemag.org/cgi/content/full/296/5575/1997/DC1

/pdf/polymer-nanotubes-by-wetting-of-ordered-porous-templates-2py17nlryz.pdf

Polymer nanotubes by wetting of ordered porous templates.

The wetting of porous templates with polymer melts and solutions or polymer-containing mixtures is a simple and versatile method for the preparation of tubular structures with diameters ranging from a few tens of nanometers to micrometers. The tube walls can be made of a multitude of materials, some of which have thus far been altogether impossible to use or very limited in their ability to be incorporated into nanostuctures. Template wetting also makes it possible to modify the nanotubes in a variety of ways, for example through the controlled generation of pores or the embedding of nanoparticles into the walls. This method offers a promising approach to functionalized nanotube-template hybrid systems and free-standing nanotubes.

Nanotubes by template wetting: a modular assembly system.

Nanoporous anodic aluminium oxide has traditionally been made in one of two ways: mild anodization or hard anodization. The first method produces self-ordered pore structures, but it is slow and only works for a narrow range of processing conditions; the second method, which is widely used in the aluminium industry, is faster, but it produces films with disordered pore structures. Here we report a novel approach termed "pulse anodization" that combines the advantages of the mild and hard anodization processes. By designing the pulse sequences it is possible to control both the composition and pore structure of the anodic aluminium oxide films while maintaining high throughput. We use pulse anodization to delaminate a single as-prepared anodic film into a stack of well-defined nanoporous alumina membrane sheets, and also to fabricate novel three-dimensional nanostructures.

/pdf/structural-engineering-of-nanoporous-anodic-aluminium-oxide-l6wyh896sf.pdf

Structural engineering of nanoporous anodic aluminium oxide by pulse anodization of aluminium

The aim was to prepare fibers with diameters below the micrometer range characterized by specific bulk morphologies and surface topologies Such materials are of interest for various applications including reinforcement, sensors or filtration as well as the formation of functional tubes by the use of fiber templates We were able to manufacture highly structured submicrometer fibers by electrospinning from ternary solutions using polylactide (PLA) and polyvinylpyrrolidone (PVP) as polymer model components Co-continuous phase morphologies resulted from phase separation processes taking place during fiber formation In a subsequent step, specific surface topologies or fine pores were generated by selective removal of one of the components

Martin Steinhart

Papers

Nanostructured Fibers via Electrospinning

Polymer nanotubes by wetting of ordered porous templates.

Nanotubes by template wetting: a modular assembly system.

Structural engineering of nanoporous anodic aluminium oxide by pulse anodization of aluminium

Preparation of Fibers With Nanoscaled Morphologies: Electrospinning of Polymer Blends