Advances in atomic force microscopy

This article reviews the progress of atomic force microscopy (AFM) in ultra-high vacuum, starting with its invention and covering most of the recent developments. Today, dynamic force microscopy allows to image surfaces of conductors \emph{and} insulators in vacuum with atomic resolution. The mostly used technique for atomic resolution AFM in vacuum is frequency modulation AFM (FM-AFM). This technique, as well as other dynamic AFM methods, are explained in detail in this article. In the last few years many groups have expanded the empirical knowledge and deepened the theoretical understanding of FM-AFM. Consequently, the spatial resolution and ease of use have been increased dramatically. Vacuum AFM opens up new classes of experiments, ranging from imaging of insulators with true atomic resolution to the measurement of forces between individual atoms.Comment: In press (Reviews of Modern Physics, scheduled for July 2003), 86 pages, 44 figure

System integration in multidatabases

This paper presents an exploratory approach to the development of a tool for integrating existing databases. The intent is to meet specific requirements and to achieve flexibility through the creation of an "open" system. The methodology assumes an integration model which captures the essential characteristics of a distributed system within a knowledge base. The model and the underlying knowledge base may be used to represent the distributed environment and to define requirements for the shared use of heterogeneous databases. An interactive method is proposed which allows the user to proceed in an iterative fashion in specifying system attributes and resolving design conflicts. The project is at present in the definition phase; current work is aimed at the identification of generic multidatabase services, and their abstraction in a form amenable for storage in the knowledge base

Microalgae on display: a microfluidic pixel-based irradiance assay for photosynthetic growth

Microalgal biofuel is an emerging sustainable energy resource. Photosynthetic growth is heavily dependent on irradiance, therefore photobioreactor design optimization requires comprehensive screening of irradiance variables, such as intensity, time variance and spectral composition. Here we present a microfluidic irradiance assay which leverages liquid crystal display technology to provide multiplexed screening of irradiance conditions on growth. An array of 238 microreactors are operated in parallel with identical chemical environments. The approach is demonstrated by performing three irradiance assays. The first assay evaluates the effect of intensity on growth, quantifying saturating intensity. The second assay quantifies the influence of time-varied intensity and the threshold frequency for growth. Lastly, the coupled influence of red-blue spectral composition and intensity is assessed. Each multiplexed assay is completed within three days. In contrast, completing the same number of experiments using conventional incubation flasks would require several years. Not only does our approach enable more rapid screening, but the short optical path avoids self-shading issues inherent to flask based systems.This work was possible through support from a Strategic Grant from the Natural Science and Engineering Research Council of Canada (NSERC), the University of Toronto Connaught Global Challenges Program in Bio-Inspired Ideas for Sustainable Energy and on-going support from the NSERC Discovery Grant Program. The authors gratefully acknowledge two individual awards received, namely the University of Toronto McLean Senior Fellowship (DS) and the NSERC Post-graduate Scholarship (PJG). Funding from the Canada Foundation for Innovation (CFI) provided infrastructure essential to this work