74 Science Research Writing Imaging was performed in the error signal mode, acquiring the defl ection and height signal simultaneously. Th e defl ection signal was minimized by optimizing gains and scan speed. Th e height images presented were recorded in the contact mode. Th e scan speed was roughly linear to the scan size, at 4–8 lines/s for lower magnifi cations (frame size 1–25 µm). Th e applied force was corrected manually to compensate for thermal drift . To achieve reproducible forces, cantilevers were selected from a restricted area of one wafer. Th e dimensions of one tip were measured in a scanning electron microscope to calculate the mechanical properties of the cantilever (Butt et al., 1993). Th e 120-µm-long cantilevers purchased from Olympus Ltd. (Tokyo, Japan) had a force constant of k = 0.1 N/m, and the 200-µm-long cantilevers purchased from Digital Instruments had a force constant of 0.15 N/m. All cantilevers used had oxide-sharpened Si3N4 tips. Sample preparation To minimize contamination of surfaces during exposure to ambient air, sample supports were prepared immediately before use. All buff ers were made with ultrapure water (−18 MDcm−1; Branstead, Boston, MA). Th is water contains fewer hydrocarbons than conventional bidistilled water and fewer macroscopic contaminants, both of which can infl uence the imaging process. Chemicals were grade p.a. and purchased from Sigma Chemie AG (Buchs, Switzerland). Th e buff ers used were Tris-(hydroxymethyl)- aminomethane (from pH 10.2 to pH 7.2), MES (from pH 6.5 to pH 5.5), and citric acid (from pH 5.4 to pH 3.0). Macromolecular samples were checked before use by conventional negative stain electron microscopy (Bremer et al., 1992) and/or by sodium dodecyl sulfate-gel electrophoresis. Th e samples were diluted to a concentration of 5–10 µg/ml in buff er solution (pH 8.2, 20 mM Tris-HCl, 2100 mM; monovalent electrolyte; except for DPPE, which was not further diluted) before adsorption to freshly cleaved mica. Aft er an adsorption time of 10–60 min, the samples were gently washed with the measuring buff er to remove weakly attached membranes. Th is allowed height measurements at low electrolyte concentrations, at which
Methodology — Vocabulary 75 samples adsorb sparsely to mica (Muller et al., 1997a and 1997b). Experiments requiring constant pH were performed at pH 8.2. Th e isoelectric points of bacteriorhodopsin, AQP1, DPPE, and OmpF are 5.2 (Ross et al., 1989), 6.95 (calculated), −10 (Tatulian, 1993), and 4.64 (calculated), respectively. Th us, at this pH, all samples had a net negative charge, except for DPPE, which had a net positive charge. Now do the same in your target articles. We hope you obtain good confi rmation of the model and can now answer the questions in Section 2.1: • How do I start this section? What type of sentence should I begin with? • What type of information should be in this section, and in what order? • How do I end this section? 2.4 Vocabulary In order to complete the information you need to write this section of your paper you now need to fi nd appropriate vocabulary for each part of the model. Th e vocabulary in this section is taken from over 600 research articles in diff erent fi elds, all of which were written by native speakers and published in science journals. Only words/phrases which appear frequently have been included; this means that the vocabulary lists contain words and phrases which are considered normal and acceptable by both writers and editors. In the next section we will look at vocabulary for the following seven areas of the model: 1. PROVIDE A GENERAL INTRODUCTION AND OVERVIEW OF THE MATERIALS/METHODS and GIVE THE SOURCE OF MATERIALS/ EQUIPMENT USED Th is includes phrases such as In this study, most of the samples were tested using a... as well as verbs such as were supplied by. A good list of commonly- used words and expressions will encourage you to include this in your fi rst sentences.