扫描电化学显微镜在功能材料分析中的应用

扫描电化学显微镜是一种扫描探针技术,利用微电极检测发生在固／液、液／液或者气／液界面反应物或者反应产物的连续变化。这里将对该技术原理进行详细说明。过去我们工作主要都集中在固定化酶的活性成像。最近研究的领域开始拓展到与能源转变相关材料上,如染料敏化太阳能电池和（生物）燃料电池的氧气催化还原。起初的尝试已经扩展到如何扩宽研究材料的范围和成像模式的应用范围。扫描电化学显微镜的反馈和产生～收集模式已被用于研究染料敏化太阳能电池半导体／电解质界面的光激发染料阳离子再生过程。现在开始关注更多的与太阳能的再生,燃料电池或染料敏化太阳能电池相关的复杂反应,这些复杂的反应包括外部质量传输过程、内部质量和电荷传输过程、多孔物质反应中心的本身活性等。     

The attenuated ray transform for connections and Higgs fields

We show that for a simple surface with boundary the attenuated ray transform in the presence of a unitary connection and a skew-Hermitian Higgs field is injective modulo the natural obstruction for functions and vector fields. We also show that the connection and the Higgs field are uniquely determined by the scattering relation modulo a gauge transformation. The proofs involve a Pestov type energy identity for connections together with holomorphic gauge transformations which arrange the curvature of the connection to have definite sign.     

Modification and characterization of artificially patterned enzymatically active surfaces by scanning electrochemical microscopy

This review summarizes the characterization of localized enzymatic activity by scanning electrochemical microscopy (SECM). After introducing the concepts of feedback imaging and generator-collector experiments with enzyme-modified solid surfaces, a comparison of the merits and limitations of both approaches is given and further illustrated by selected applications. They include enzyme-modified patterned monolayers, enzyme-modified polymer microstructures and enzyme-modified metal microstructures. Such configurations are important for the development of miniaturized bioanalytical systems with proteins, such as miniaturized enzyme electrode arrays. SECM has emerged as an ideal tool for prototyping of such systems. It also offers several mechanisms for local surface modifications under conditions compatible with conservation of protein functionality of enzymes and antibodies. The subsequent imaging of the immobilized activity provides direct information about local immobilized enzyme activity. The range of biotechnological applications can be expanded by labeling other biomolecules, such as monoclonal antibodies, with appropriate enzymes. Miniaturized electrochemical enzyme immunoassays that apply the sandwich format and SECM as the detection method are reviewed. They have been performed on microstructured supports after reagent spotting or on agglomerates of surface-modified magnetic microbeads. Finally, current challenges are listed with indications of ongoing research to overcome current limitations by means of instrumental improvements. Received: 19 December 2000 / Revised: 26 February 2001 / Accepted: 2 March 2001     

A uniqueness theorem for an inverse boundary value problem in electrical prospection

We show that a near constant conductivity of a two-dimensional body can be uniquely determined by steady state direct current measurements at the boundary. Mathematically, we show that the coefficient γ in the operator ?.γ? is uniquely determined by its Dirichlet integrals.     

Comparative study of lattice‐Boltzmann and finite volume methods for the simulation of laminar flow through a 4:1 planar contraction

In the present paper, a comparative study of numerical solutions for Newtonian fluids based on the lattice‐Boltzmann method (LBM) and the classical finite volume method (FVM) is presented for the laminar flow through a 4:1 planar contraction at a Reynolds number of value one, Re=1. In this study, the stress field for LBM is directly obtained from the distribution function. The calculations of the stress based on the FVM‐data use the evaluations of velocity gradients with finite differences. The stress field for both LBM and FVM is expressed in the present study in terms of the shear stress and the first normal stress difference. The lateral and axial profiles of the velocity, the shear stress and the first normal stress difference for both methods are investigated. It is shown that the LBM results for the velocity and the stresses are in excellent agreement with the FVM results. Copyright © 2004 John Wiley & Sons, Ltd.     

Inverse boundary value problems at the boundary—continuous dependence

We use the methods of microlocal analysis to give a new proof of a theorem of Kohn and Vogelius, showing that the boundary values of a continuous isotropic conductivity can be recovered from voltage and current measurements at the boundary. Moreover, we prove sharp estimates to establish the continuous dependence of the boundary values of the conductivity on the voltage to current maps.     

Characterization and `Source-Receiver' Continuation of Seismic Reflection Data

In reflection seismology one places sources and receivers on the Earth's surface. The source generates elastic waves in the subsurface, that are reflected where the medium properties, stiffness and density, vary discontinuously. In the field, often, there are obstructions to collect seismic data for all source-receiver pairs desirable or needed for data processing and application of inverse scattering methods. Typically, data are measured on the Earth's surface. We employ the term data continuation to describe the act of computing data that have not been collected in the field. Seismic data are commonly modeled by a scattering operator developed in a high-frequency, single scattering approximation. We initially focus on the determination of the range of the forward scattering operator that models the singular part of the data in the mentioned approximation. This encompasses the analysis of the properties of, and the construction of, a minimal elliptic projector that projects a space of distributions on the data acquisition manifold to the range of the mentioned scattering operator. This projector can be directly used for the purpose of seismic data continuation, and is derived from the global parametrix of a homogeneous pseudodifferential equation the solution of which coincides with the range of the scattering operator. We illustrate the data continuation by a numerical example. This research was supported in part under NSF CMG grant EAR-0417891. Partly supported by a John Simon Guggenheim fellowship.