Hermetically-coated superparamagnetic Fe2O3 particles with SiO2 nanofilms

Magnetic nanoparticles are frequently coated with SiO2to improve their functionality and bio-compatibility in a range of biomedical and polymer nanocomposile applications. In this paper, a scalable flame aerosol technology is used to produce highly dispersible, superparamagnetic iron oxide nanoparticles hermetically coaled with silica to retain full magnetization performance. Iron oxide particles were produced by flame spray pyrolysis (FSP) of iron acelylacetonale in xylene/acetonitrile solutions, and the resulting aerosol was in situ coaled with SiO2 by oxidation of swirling hexamethlydisiloxane vapor. The process allows independent control of the core Fe2O3, particle properties and the thickness of their silica coaling film. This ensures that the non-magnetic SiO2 layer can be closely controlled and minimized. The optimal SiO2 content for complete (hermetic) encapsulation of the magnetic core particles was determined by isopropanol chemisorption. The magnetization of Fe2O3 coated with about 2 nm thin SiO2 layers was nearly identical lo that of uncoated, pure Fe2O3 nanoparlicles.

Hermetically coated superparamagnetic Fe2O3 particles with SiO2 nanofilms

Magnetic nanoparticles are frequently coated with SiO2 to improve their functionality and biocom-patibility in a range of biomedical and polymer nanocomposite applications. In this paper, a scalable flame aerosol technology is used to produce highly dispersible, superparamagnetic iron oxide nanoparticles hermetically coated with silica to retain full magnetization performance. Iron oxide particles were produced by flame spray pyrolysis of iron acetylacetonate in xylene/acetonitrile solutions and the resulting aerosol was in situ coated with silicon dioxide by oxidation of swirling hexamethlydisiloxane vapor. The process allows independent control of the core Fe2O3 (maghemite) particle properties and the thickness of their silica coating film. This ensures that the nonmagnetic SiO2 layer can be closely controlled and minimized. The optimal SiO2 content for complete (hermetic) encapsulation of the magnetic core particles was determined by isopropanol chemisorption. The magnetization of Fe 2O3 coated with about 2 nm thin SiO2 layers was nearly identical to that of uncoated, pure Fe2O3 nanoparticles. © 2009 American Chemical Society.

Design, fabrication and characterization of spatial mode selector in silicon

We demonstrate the design, fabrication and experimental characterization of the spatial mode selector that transmit only the second silicon waveguide mode. Nanofabrication results and near field measurements are presented. © 2009 Optical Society of America.

Design, fabrication and characterization of spatial mode selector in silicon

We demonstrate the design, fabrication and experimental characterization of the spatial mode selector that transmit only the second silicon waveguide mode. Nanofabrication results and near field measurements are presented. © 2009 Optical Society of America.

Synchronization in a coupled architecture of microelectromechanical oscillators

There has been much recent interest in engineering the phenomenon of synchronization in coupled micro-/nano-scale oscillators for applications ranging from precision time and frequency references to new approaches to information processing. This paper presents descriptive modelling detail and further experimental validation of the phenomenon of mutual synchronization in coupled MEMS oscillators building upon recent experimental validation of this concept by the present authors. In particular, the underlying dependence of the observation of synchronization on system parameters is studied through numerical and analytical modelling while considering essential nonlinearities in both the resonator and circuit domain. Experimental results demonstrating synchronized response are elaborated based on the realization of electrically coupled MEMS resonator based square-wave oscillators. The experimental results on frequency entrainment are found to be in general agreement with results obtained through analytical modeling and numerical simulation. The concept presented here is scalable and could be used to investigate the dynamics of large-arrays of coupled MEMS oscillators. © 2014 AIP Publishing LLC.

Structure, magnetization, and low-temperature spin dynamic behavior of zincblende Mn-rich Mn(Ga)As nanoclusters embedded in GaAs

We have fabricated a set of samples of zincblende Mn-rich Mn(Ga)As clusters embedded in GaAs matrices by annealing (Ga,Mn)As films with different nominal Mn content at 650 degrees C. For the samples with Mn content no more than 4.5%, the Curie temperature reaches nearly 360 K. However, when Mn content is higher than 5.4%, the samples exhibit a spin-glass-like behavior. We suggest that these different magnetic properties are caused by the competing result of dipolar and Ruderman-Kittel-Kasuya-Yosida interaction among clusters. The low-temperature spin dynamic behavior, especially the relaxation effect, shows the extreme creeping effect which is reflected by the time constant tau of similar to 10(11) s at 10 K. We explain this phenomenon by the hierarchical model based on the mean-field approach. We also explain the memory effect by the relationship between the correlation function and the susceptibility.

一种高效和可扩展的OCSP系统

证书状态查询是PKI中的一个关键问题,OCSP是解决这个问题的一种重要机制。本文分析了OCSP协议的技术细节,并在此基础上设计了一种高效的、可扩展的OCSP系统。文中对该系统的关键技术和其自身的安全性问题进行了详细的论述。最后,给出了关于OCSP机制的一些未决问题以及某些思考。

语义Web中描述逻辑本体的可伸缩推理和非一致处理

随着Web信息的与日俱增，使用机器处理这种信息成为一种必然的趋势。语义Web应运而生，成为当前研究的热点之一。它以本体为核心，为不同领域提供共享的词汇，以便机器处理Web信息。表达本体的标准语言OWL以描述逻辑为基础。OWL本体的推理可伸缩性差，难以适应规模较大的本体应用，因此推理可伸缩性问题是一个重要的实际问题。此外，OWL本体是一个逻辑系统，在生成、维护和集成等过程中，都很容易出现非一致现象，导致标准的推理机制不能正常运作。因此本体非一致问题是另一个重要的实际问题。针对上述两个实际问题，本文分别在实现可伸缩推理、修复非一致本体、以及进行非一致容忍推理三个方面提出了解决办法。 [可伸缩推理方面] 本文提出了一种本体断言公理集的划分方法，使本体推理能够在独立的划分子集中进行，以此提高本体推理的可伸缩性。 [本体修复方面] 本文提出了一种计算具有最小删除代价的本体子集的方法；通过删除这种本体子集，可以恢复本体的一致性。该方法将计算上述本体子集的问题归约为在命题逻辑程序中计算某种最优模型的问题，以调用现有的可满足性问题求解器来解决。 [非一致容忍推理方面] 本文将命题逻辑中字典序推理方法应用到描述逻辑中，以提供针对非一致本体的查询机制。本文还提出了一种在描述逻辑本体中进行字典序推理的方法。该方法将字典序结论的判定问题归约为命题可满足性判定问题，以调用现有的可满足性问题求解器来解决。

l-ucon: towards layered access control with ucon

IEEE; IEEE Computer Society; IEEE Technical Committee on Scalable Computing (TCSC)

Layer-by-layer assembly of viral capsid for cell adhesion

Cowpea mosaic virus (CPMV)-based thin films are biologically active for cell culture. Using layer-by-layer assembly of CPMV and poly(diallyldimethylammonium chloride), quantitatively scalable biomolecular surfaces were constructed, which were well characterized using quartz crystal microbalance, UV-vis and atomic force microscopy. The surface coverage of CPMV nanoparticles depended on the adsorption time and pH of the virus solution, with a greater amount of CPMV adsorption occurring near its isoelectric point. It was found that the adhesion and proliferation of NIH-3T3 fibroblasts can be controlled by the coverage of viral particles using this multilayer technique.

Applications of scanning probe microscopy in intrinsically conducting polymer research

The applications of scanning probe microscopy (SPM) in intrinsically conducting polymer research is briefly reviewed, including morphology observation, nanofabrication, microcosmic electrical property measurements, electrochemistry researches, in-situ measurements of film thickness change, and so on. At the same time, some important variations of SPM and the related techniques are briefly introduced. Finally, the future development of SPM in the study of intrinsically conducting polymers is prospected.

Direct patterning of rhodamine 6G molecules on mica by dip-pen nanolithography

Dip-pen nanolithography (DPN) has been developed to pattern monolayer film of various molecules on suitable substrate through the controlled movement of ink-coated atomic force microscopy (AFM) tip, which makes DPN a potentially powerful tool for making the functional nanoscale devices. In this paper, the direct patterning of rhodamine 6G on mica by dip-pen nanolithography was demonstrated. R6G features patterned on the mica was successfully achieved with different tip movement which can be programmed by Nanoscript(TM) language. From the AFM image of R6G patterns, we know that R6G molecule is flatly binding to the mica surface through electrostatic interaction, thus stable R6G nanostructures could be formed on mica. The influence of translation speed and contact time on DPN was discussed. The method can be extended to direct patterning of many other organic molecules, and should open many opportunities for miniaturized optical device and site-specific biological staining.

Direct patterning of negative nanostructures on self-assembled monolayers of 16-mercaptohexadecanoic acid on Au(111) substrate via dip-pen nanolithography

Both bare and self-assembled monolayer (SAM) protected gold substrate could be etched by allyl bromide according to atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometric (ICPMS) analysis results. With this allyl bromide ink material, negative nanopatterns could be fabricated directly by dip-pen nanolithography (DPN) on SAMs of 16-mercaptohexadecanoic acid (MHA) on Au(111) substrate. A tip-promoted etching mechanism was proposed where the gold-reactive ink could penetrate the MHA resist film through tip-induced defects resulting in local corrosive removal of the gold substrate. The fabrication mechanism was also confirmed by electrochemical characterization, energy dispersive spectroscopy (EDS) analysis and fabrication of positive nanopatterns via a used DPN tip.

基于网络数据库的分子结构式的动态显示

讨论了在网络数据库环境中动态显示分子结构式的问题。数据库中存储分子的结构信息,在检索时动态生成分子结构式图,图形格式为SVG。SVG是一种矢量图形格式,又是一种基于XML的置标语言。用SVG可以动态创建分子结构式图形,而且文件是文本文件,体积小,易于编辑和信息交换。文中给出了从数据库中提取数据,动态生成分子结构式图形的方法。

基于机械力与电场的AFM纳米操作/加工研究

纳米技术是在纳米尺度上研究物质的特性和相互作用，以及利用这些特性的多学科交叉的新兴科学技术。纳米加工技术是对纳米技术的重要应用，它使人类在纳米尺度上进行结构和器件的制造成为可能。基于原子力显微镜(AFM)的纳米加工是近20年来发展的技术，由于AFM具有许多新颖的技术特点(如高分辨率，可操控等)，因而基于AFM的纳米加工技术成为纳米科学研究的新热点。 本论文以纳米制造为背景，围绕基于AFM的纳米加工技术所涉及的科学问题，重点开展了基于机械力的AFM纳米操作和基于电场的AFM纳米加工的理论方法和实现技术研究。在这些研究的基础上，开展了基于纳观机械力的刻划、纳米颗粒的排列、碳纳米管的装配实验研究，开展了基于微观电场的氧化点、氧化线、氧化文字的加工实验研究，以及微观电场氧化切割、焊接加工方法的研究。 本文的主要内容包括：交互式纳米操作系统的构建，基于机械力的AFM纳米操作研究，基于电场的AFM纳米加工研究，基于机械力与电场的AFM纳米操作/加工实验研究。具体如下： 在商用AFM的基础上，研究并搭建了具有力觉与视觉反馈的交互式纳米操作系统。通过该系统操作者可以实时感觉到操作中作用在AFM针尖的纳观力并控制针尖的运动，还可以实时观察到模拟出的针尖操作过程，因而显著提高了纳米操作的直观性、可靠性及效率。 在基于机械力的AFM纳米操作研究方面，为了理解纳观环境下普遍存在的黏附力特性，对AFM的力曲线进行了分析并给出了详细解释；通过研究探针悬臂的形变，提出了探针所受三维作用力的建模方法，以此模型获得了操作中的纳观力信息；基于多刚体动力学理论提出了碳纳米管的二连杆动力学建模方法，并对碳纳米管在操作中的弯曲特性进行了仿真分析。这些研究为基于机械力的AFM纳米操作提供了理论指导。 在基于电场的AFM纳米加工方面，研究了微观电场在样本表面的分布，建立了电场氧化加工中电场分布模型，以此模型分析了氧化物特性与电场分布的关系；对氧化加工中氧化物生长过程进行了动力学分析，得到了氧化物生长的理论模型；系统地研究了氧化加工中各因素(偏压，加工速度，针尖－样本距离等)对氧化结构生成的影响，总结了氧化物的生成与各因素的关系，验证了理论分析的结果，提高了电场氧化加工的重复性及可控性。这些研究为基于电场的AFM纳米加工提供了理论及实验依据。 在基于机械力与电场的AFM纳米操作/加工理论研究的基础上，进行了相关的实验研究。通过基于机械力的AFM纳米操作方法实现了在样本表面刻划文字，纳米颗粒的排列，碳纳米管的操作及装配；通过基于电场的AFM纳米加工方法实现了在样本表面加工氧化点，氧化线及氧化文字等纳米结构。利用电场氧化加工方法还实现了对碳纳米管的定点切割与焊接，拓展了AFM纳米加工的应用领域。这些实验研究验证了系统的操作及装配性能，证明了电场加工的有效性及具有潜在的应用前景。 本文的研究工作为制造纳米结构、纳米器件提供了一条可行的技术途径，对AFM纳米加工技术的进一步发展具有一定的理论参考及实践指导意义。