Application of atomic force microscopy in bacterial research

The atomic force microscope (AFM) has evolved from an imaging device into a multifunctional and powerful toolkit for probing the nanostructures and surface components on the exterior of bacterial cells. Currently, the area of application spans a broad range of interesting fields from materials sciences, in which AFM has been used to deposit patterns of thiol‐functionalized molecules onto gold substrates, to biological sciences, in which AFM has been employed to study the undesirable bacterial adhesion to implants and catheters or the essential bacterial adhesion to contaminated soil or aquifers. The unique attribute of AFM is the ability to image bacterial surface features, to measure interaction forces of functionalized probes with these features, and to manipulate these features, for example, by measuring elongation forces under physiological conditions and at high lateral resolution (<1 Å). The first imaging studies showed the morphology of various biomolecules followed by rapid progress in visualizing whole bacterial cells. The AFM technique gradually developed into a lab‐on‐a‐tip allowing more quantitative analysis of bacterial samples in aqueous liquids and non‐contact modes. Recently, force spectroscopy modes, such as chemical force microscopy, single‐cell force spectroscopy, and single‐molecule force spectroscopy, have been used to map the spatial arrangement of chemical groups and electrical charges on bacterial surfaces, to measure cell–cell interactions, and to stretch biomolecules. In this review, we present the fascinating options offered by the rapid advances in AFM with emphasizes on bacterial research and provide a background for the exciting research articles to follow. SCANNING 32: 74–96, 2010. © 2010 Wiley Periodicals, Inc.     

Dynamic behavior of amplitude detection Kelvin force microscopy in ultrahigh vacuum

The acquisition rate of all scanning probe imaging techniques with feedback control is limited by the dynamic response of the control loops. Performance criteria are the control loop bandwidth and the output signal noise power spectral density. Depending on the acceptable noise level, it may be necessary to reduce the sampling frequency below the bandwidth of the control loop. In this work, the frequency response of a vacuum Kelvin force microscope with amplitude detection (AM-KFM) using a digital signal processing (DSP) controller is characterized and optimized. Then, the main noise source and its impact on the output signal is identified. A discussion follows on how the system design can be optimized with respect to output noise. Furthermore, the interaction between Kelvin and distance control loop is studied, confirming the beneficial effect of KFM on topography artefact reduction in the frequency domain. The experimental procedure described here can be generalized to other systems and allows to locate the performance limitations.     

Molecular dynamics of DNA and nucleosomes in solution studied by fast-scanning atomic force microscopy

Nucleosome is a fundamental structural unit of chromatin, and the exposure from or occlusion into chromatin of genomic DNA is closely related to the regulation of gene expression. In this study, we analyzed the molecular dynamics of poly-nucleosomal arrays in solution by fast-scanning atomic force microscopy (AFM) to obtain a visual glimpse of nucleosome dynamics on chromatin fiber at single molecule level. The influence of the high-speed scanning probe on nucleosome dynamics can be neglected since bending elastic energy of DNA molecule showed similar probability distributions at different scan rates. In the sequential images of poly-nucleosomal arrays, the sliding of the nucleosome core particle and the dissociation of histone particle were visualized. The sliding showed limited fluctuation within ∼50 nm along the DNA strand. The histone dissociation occurs by at least two distinct ways: a dissociation of histone octamer or sequential dissociations of tetramers. These observations help us to develop the molecular mechanisms of nucleosome dynamics and also demonstrate the ability of fast-scanning AFM for the analysis of dynamic protein–DNA interaction in sub-seconds time scale.     

基于结构特征的路面裂纹病害检测算法

提出一种新颖的图像分解算法,用于复杂背景下的路面病害图像,可以获得较为清晰的裂纹病害信息。通过对含有局部线性特征的裂纹图像进行形态分析,建立与结构特征相匹配的基底,利用局部Ridgelet函数作为稀疏表示的基底,图像中的结构信息作为一种组成成分被提取出来,同时运用全变差正则化方法对提取的结构信息加以正则化约束,使得提取结果更加精细化。实验结果表明利用该算法提取的裂纹病害信息符合人眼的观测结果。     

H2-Ni电池用纳米锆溶胶中硅含量分析方法

运用N2O-C2H2火焰原子吸收光谱法进行氢镍(H2-Ni)蓄电池材料用纳米锆溶胶中硅含量分析方法的研究。介绍硅的最佳分析条件,并在样品测定中对干扰因素进行了综合考虑。实验表明,该方法具有灵敏度高、干扰小、操作步骤简单、容易掌握、分析周期短等特点。样品硅含量的分析其相对标准偏差均小于1.0%(n=10),标准加入回收率在97.0%～102.0%(n=6);达到了实验室仪器分析技术与分析质量的控制要求。     

刻线边缘表面重构及其边缘粗糙度测量

给出了一种边缘粗糙度(LER)三维参数评估的方法。采用原子力显微镜(AFM)测量了刻线单侧边缘形貌,根据AFM的工作机理和测量特点重构边缘表面,采用回归分析方法确定了边缘表面的评价基准面。结合集成电路中光刻工艺的具体需求,提出了能够反映边缘表面形貌特征的三维LER表征参数。结合实例,计算了所提出的部分LER参数,分析了LER标准差参数的测量精度。     

Atomic multicast protocol for intrusion-tolerance based on trusted timely computing base

Distributed architecture is often adopted for the intrusion-tolerance system currently. However, this distributed intrusion-tolerance system has a consensus problem. To solve this problem, this article explores a distributed intrusion-tolerance system of hybrid time model based on trusted timely computing base (TTCB) and implement an atomic multicast protocol using TTCB services. The TTCB is a trust secure real-time component inside the server, with a well defined interface and separated from the operation system. It is in the synchronous communication environment, while the application layer in the server works asynchronously. By the atomic multicast protocol, it can be achieved that when the servers are over twice the number of faulty servers, the consensus can be satisfied. The performance evaluations show that the proposed protocol can yield larger good throughput with a lower unavailability.     

玻色-爱因斯坦凝聚原子与Schr?dinger猫态相互作用系统中的压缩特性

利用全量子理论,研究了玻色-爱因斯坦凝聚原子与Schr?dinger猫态相互作用系统中, 光场和原子激光的压缩特性。 结果表明: 在系统中,偶相干态、奇相态分别与玻色-爱因斯坦凝聚原子相互作用,偶相干态、奇相态光场和原子激光均不呈现压缩效应。 而Yurke-Stoler相干态光场和原子激光呈现压缩效应。 在强场 (|a|=1)情况下,三种不同光场的两种压缩现象均不产生。 光场和原子激光的压缩特性主要受初始光强和耦合常数的影响。     

How r-Plane Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Surface Modifications Impact the Growth of Epitaxial (001) CeO<Subscript>2</Subscript> Thin Films

We present evidence that it is the presence or absence of atomic terraces with a specific crystallographic orientation on the (102) Al₂O₃ surface that promotes growth of single-crystal (001) CeO₂ films over polycrystalline (111) CeO₂ films. The CeO₂ film nucleates so that the [010] and [100] directions of the film align parallel and perpendicular to the terrace edges. In the absence of terraces, multidomain (111) CeO₂ films result in which the in-plane orientation of the two domains are rotated by 85.71°, so that a [110] CeO₂ direction aligns parallel to either the or Al₂O₃ direction.     

玉米中微量铅的测定

采用原子分光光度法对玉米中微量铅的测定进行了研究,并对其影响因素、结果进行分析和探讨。通过单因素试验和正交试验确定其最佳条件为:测量波长283.3 nm、改进剂用量0.12 mL、样品灰化时间7 h、试液的pH值为6.5。该方法简单方便,可广泛用于粮食、果蔬中微量铅的测定。