I began using scanning electron microscopes to solve problems encountered in the fabrication of x-ray diffraction gratings. Since these diffraction gratings consist of very regular lines and spaces, and produce high contrast images from the SEM. my microscopy work often points out problems with the microscope.

One time, for example, I went to the university SEM lab I often use, and was advised that the microscope was down that day due to major field problems. This lab often had problems with stray fields for reasons no one could explain. Usually I was the only one to complain about stray field distortions since they are most obvious when imaging straight lines at high magnification, but on this occasion, the problem was serious and obvious to all.

The microscope had just been serviced and as the lens coils had been replaced, they were expected to be the cause. The service technician was called in and determined that neither the coils nor the microscope electronics were the problem.

What is combinatorial chemistry? Combinatorial chemistry is quickly becoming a very popular technique for organic synthesis in the pharmaceutical and biotechnology fields. Basically, combinatorial methods allow one to obtain thousands of derivatives of chemical compounds in a very quick and efficient manner. The method begins when a molecule of interest is attached to resin beads. Once the molecule is attached, a number of reactions can be run on the beads. The beads can be split up into several subsets, and different reactions can be run on each of the subsets. Because the beads are in the solid phase, it is extremely easy to separate the beads from the liquid layer after the reactions have completed.

Despite the potential of the technique, electron tomography has yet to be widely used by biologists. This is in part related to the rather daunting list of equipment and expertise that are required. Thanks to continuing advances in theory and instrumentation, tomography is now more feasible for the non-specialist. One barrier that has essentially disappeared is the expense of computational resources. In view of this progress, it is time to give more attention to practical issues that need to be considered when embarking on a tomographic project. The following recommendations and comments are derived from experience gained during two long-term collaborative projects.

LaserJets, like many other printers, print in lines per inch (Ipi). The lines represent in digital image printing lines of pixels. If the pixels are printed squarely than each square area (of a width equal to that of the actual line width) must be printed with a desired amount of ink variations in order to generate the gray levels (see John Russ’ book for a nice illustration on how this is done in a LaserJet). LaserJets and Inkjets use dots as the smallest printed entity.