Friday, June 27, 2008

Physicist Playing Cards

Last Christmas, my daughter Katherine gave me a unique and fascinating present: Physicist Playing Cards. Each card features a picture of an eminent physicist. You can order the cards from the American Institute of Physics at http://store.aip.org. Two decks are available: one of historical physicists, and one of modern physicists. I browsed through the deck of historical physicists and found ten cards that have relevance to biology and medicine. These ten physicists, each a Nobel Prize winner, contributed greatly to the application of physics to the life sciences. Many of these physicists are mentioned in the 4th Edition of Intermediate Physics for Medicine and Biology (the appropriate page is given in parentheses).

Queen of Diamonds: Marie Curie, pioneer in the study of radiation (p. 489).

Ace of Diamonds: Wilhelm Roentgen, discoverer of X-rays (p. 440).

Nine of Clubs: William Bragg, analyzed crystal structures using X-ray diffraction (p. 466).

Three of Hearts: Felix Bloch, co-discoverer of nuclear magnetic resonance (p. 519).

Ten of Hearts: Henri Becquerel, discoverer of radioactivity (p. 472).

King of Hearts: Edward Purcell, co-discoverer of nuclear magnetic resonance (p. 519).

Ace of Hearts: Pierre Curie, discoverer of the piezoelectric effect (p. 216).

Eight of Spades: Frederic Joliot, co-creator of the first artificial radioisotope (none).

Nine of Spades: Max von Laue, discoverer of X-ray diffraction (none).

Queen of Spades: Irene Joliot Curie, co-creator of the first artificial radioisotope (none).

Friday, June 20, 2008

The Electrocardiogram

When I teach biological physics, we spend at least one class discussing the electrocardiogram (ECG, sometimes called the EKG for the German term Elektrokardiogramm). The 4th Edition of Intermediate Physics for Medicine and Biology covers the ECG in Chapter 7, but students often need additional practice on interpreting the signals from heart arrhythmias. As homework, I require my students to go to the website http://www.skillstat.com/ECG_sim_demo.html and play the ECG simulator game. It tests the students' knowledge of ECGs in a fun, interactive way. The same website has units on cardiac anatomy, a cardiac dictionary, and cardiac trivia games.

I have found that a plastic model of the heart is useful for teaching cardiac anatomy. I own a "Danny Smith Heart," which clearly shows all the heart valves, vessels, chambers, and other anatomical features. Unfortunately, these plastic models tend to be expensive. Other good websites about the heart are http://www.visibleheart.com/, http://en.ecgpedia.org/wiki/Main_Page, and http://www.texasheartinstitute.org/HIC/Topics/inde x.cfm. There is also a good online video that explains the ECG.

The 1924 Nobel Prize in Physiology or Medicine was awarded to the Dutch physiologist Willem Einthoven (1860-1927) "for his discovery of the mechanism of the electrocardiogram." The notation of the P, QRS, and T waves (see Fig. 7.17 of our textbook) was developed by Einthoven, as was his interpretation of the ECG using "Einthoven's triangle" (see Fig. 7.19, and page 188). Einthoven's work is an excellent example of how physics can applied successfully to medicine and biology.

Friday, June 13, 2008

http://medicalphysicsweb.org

Readers of the 4th Edition of Intermediate Physics for Medicine and Biology who are particularly interested in Medical Physics will find the website http://medicalphysicsweb.org interesting. This "community website" is maintained by the Institute of Physics, the United Kingdom's professional organization for physicists. The IOP created several community websites to "promote innovation, growth and networking, ...[and to] provide both a valuable information source and an international forum within which community members can share and exchange their views."

Medicalphysicsweb provides "a mix of in-depth news, analysis, opinion and primary research papers across the key disciplines of medical physics." The site contains editorials, job postings, a buyer's guide, featured journal articles, and research and industry news. Students who are studying from Intermediate Physics for Medicine and Biology will find this website an easy and free way to become familiar with Medical Physics as a profession. You can become a member (no cost, but there is a registration procedure) and receive a weekly "What's New" newsletter. I highly recommend it.

Friday, June 6, 2008

The "Big Three" Partial Differential Equations of Physics

Often a mathematical physics class will focus on the "big three" partial differential equations of physics: the diffusion equation, the wave equation, and Laplace's equation. The 4th edition of Intermediate Physics for Medicine and Biology provides a gentle introduction to each of these equations. You won't find much mathematical theory; Russ Hobbie and I are concerned primarily with exploring their relevance to biology and medicine.

The diffusion equation (Eq. 4.24) is the topic of chapter 4. Diffusion is not covered in many physics classes, but is crucially important to biology. The diffusion equation is also known by another name: the heat equation. Problem 24 of chapter 4 explores an extension of this topic: a "reaction-diffusion" equation that governs the nonlinear propagation of calcium waves.

The wave equation (Eq. 13.5) was not discussed much in previous editions of Intermediate Physics for Medicine and Biology, but it is an essential topic in the 4th edition's new chapter 13 on sound and ultrasound. Here we meet classic wave behavior, such as the relationship between wavelength and frequency, the difference between propagating and standing waves, reflection, and the Doppler effect.

Laplace's equation (the displayed equation before Eq. 7.44a) is encountered in chapter 7 on the electrocardiogram. We don't talk as much about solutions to Laplace's equation as we do the diffusion and wave equations, but it plays a fundamental role in electrostatics, and appears when discussing steady-state solutions to the diffusion equation.

What other important partial differential equations are introduced in our book? The Navier-Stokes equation, governing fluid flow, is analyzed in problem 28 of chapter 1. The Helmholtz equation is presented under its pseudonyms: the cable equation (chapter 6) and the linearized Poisson-Boltzmann equation (chapter 9). Schrödinger's equation, the basic equation of quantum mechanics, is mentioned in the introduction to chapter 3, but is never written down.