Special thanks go to Dr. Ranjith Wijesinghe, Assistant Professor of Physics and Astronomy at Ball State University in Muncie, Indiana. This semester, Ranjith is teaching APHYS 316 (Medical Physics 2) using Intermediate Physics for Medicine and Biology. As he prepares his class lectures, Ranjith emails me all the mistakes he finds in our book, which I dutifully add to the errata. I can keep track of what the class is covering by the location of the errors Ranjith finds. In mid January the class was studying Fourier series, and he found a missing "sin" in Eq. 11.26d. By early February they were analyzing images, and Ranjith noticed some missing text in the figure associated with Problem 12.7. Then in mid February they began studying ultrasound, and eagle-eyed Ranjith emailed me that the derivative in Eq. 13.2 should be a partial derivative. I'm expecting some newly-discovered typo in Chapter 14 next week.

Actually, Ranjith is an old friend of mine. We were graduate students together at Vanderbilt University in the late 1980s, and both worked in the lab of John Wikswo. I took care of the crayfish (which have some giant axons that are useful for studying action currents) and Ranjith looked after the frogs (whose sciatic nerve is an excellent model for analyzing the compound action potential). After leaving Vanderbilt, Ranjith was a postdoc at Tulane University with Paul Nunez, an expert in electroencephalography and author of the acclaimed textbook Electric Fields of the Brain: The Neurophysics of EEG. While a member of Nunez's group, Ranjith coauthored several papers, including "EEG coherency.1. Statistics, reference electrode, volume conduction, Laplacians, cortical imaging, and interpretation at multiple scales" in the journal Electroencephalography and Clinical Neurophysiology (Volume 103, Pages 499-515, 1997). According to Google Scholar, this landmark paper has been cited 277 times, which is quite an accomplishment (and is more citations than my most cited paper has).

I hope Ranjith keeps on sending me errors he finds, and I encourage other careful readers to do so too. And a big HELLO! to Ball State students taking Medical Physics 2. The true measure of a textbook is what the students think of it. I hope you all find it useful, and best of luck to you as the end of the semester approaches. Don't give Dr. Wijesinghe too hard a time in class. If he finishes early one day and you have a few minutes to spare, ask him for some old stories from graduate school. He has a few, if he will tell you!