APS News

FELs, Biological Physics Featured at SESAPS Meeting

The Southeastern Section of the APS (SESAPS) held its 63rd annual meeting, 6-8 November 1997, at Vanderbilt University in Nashville, Tennessee. Invited speakers covered such topics as materials and biophysics research with free electron lasers, nuclear physics, solids and molecular dynamics, optics, physics teaching, astrophysics, high energy physics, chaos in quantum systems, and computational physics in the physics curricula. In addition, Vanderbilt hosted two one-day workshops prior to the meeting, one on radioactive ion beams, and another on condensed matter/free electron laser physics. The Society of Physics Students organized a session for student papers in conjunction with the SESAPS meeting, presenting the Marsh W. White Award for the best paper given at the session.

APS Associate Executive Officer Barrett Ripin spoke on career opportunities for physicists during an interactive Thursday afternoon session, reviewing the current status of the physics job market and outlining short- and long-term strategies being undertaken by the APS to help improve the employability of physicists in various sectors. Later that evening, scientists from Vanderbilt and three other Southeastern universities staged a physics demonstration program. And Laurie McNeil (University of North Carolina, Chapel Hill), chair of the APS Committee on the Status of Women in physics, led session participants in a panel discussion on the topic of balancing family obligations with a physics career on Friday afternoon.

Physics with Intense Radiation

According to Vanderbilt University's Norman Tolk, who spoke at a Friday afternoon session on physics with intense radiation, the Vanderbilt Free Electron Laser's (FEL) tunability, high intensity and short pulse structure make it ideal for (1) studying the electronic and vibrational structure of small and wide band gap semiconductors, and (2) achieving non-thermal wavelength-selective materials alterations. In the first instance, scientists have been able to verify two-photon absorption measurements in Ge. The FEL has also greatly facilitated internal photoemission heterojunction band discontinuity measurements, without the need for complex modeling. With regard to the latter, Tolk has used the FEL to demonstrate strongly wavelength-selective ablation in chemical vapor deposited diamond.

During the same session, Maurizio Ferconi, also of Vanderbilt, described recent attempts to selectively enhance chemical reactions with infrared radiation, which to date have had limited success. The development of new lasers such as the FEL and ultrafast tabletop lasers, and the potential for materials processing and biomedical applications, have rekindled interest in this area. Ferconi's team is implementing state-of-the art computational techniques - using classical and quantum molecular dynamics - to both molecules and solids under intense infrared radiation.

Finally, scientists at the University of Illinois are using "nanoshocks" - tiny but powerful shock waves measuring 100 micrometers in diameter, with a sample thickness of 1 micrometer and a total volume of a few nanograms - to study anthracene, a model molecular crystal, and myoglobin, a molecular nanomachine. Generated by high power picosecond laser pulses in solids via laser ablation, the nanoshock produces large amplitude displacements from the equilibrium geometry. The subsequent ultrafast material relaxation processes are monitored by ultrafast vibrational or visible spectroscopy.

Biological Physics

The use of physical techniques has become very important in understanding the pathophysiology of sickle cell disease, according to Daniel Kim-Shapiro of Wake Forest University, who spoke on Saturday morning. In particular, light scattering and absorption studies have been used to measure the kinetics of sickle cell hemoglobin polymerization and depolymerization (melting). These have led not only to an increased understanding of the disease, which affects about 1 out of 600 people of African descent in the U.S. alone, but has also led to improved treatment strategies. Kim-Shapiro is currently conducting investigations into the phenomenon of polymer melting in sickle cell hemoglobin, which is key to determining whether polymers that reach the lungs melt before they enter the oxygen deficient tissues. Specifically, he has been exploring the kinetics of oxygen binding to the polymers, using time-resolved linear dichroism, followed by laser photolysis.

Multimedia Tools in Physics Teaching

Several sessions were organized around current issues in, and new approaches to, physics teaching, particularly in the area of new computer and mutlimedia tools. On Friday afternoon, Aaron Titus of North Carolina State University addressed the issue of integrating multimedia and physics problems to enhance students' success at solving problems. In a recent study of students' responses on Web-based homework questions, he found that merely presenting a video of motion described in a given physics problem is not the most effective use of multimedia materials. Rather, multimedia-focused problems, where data relevant to solving the problem is embedded in a video or animation, may be the best use of multimedia in physics problem solving.

According to L.W. Martin of North Park University, the updated software package Mathematica 3.0 features a new interface designed to allow more natural entry of traditional mathematical notation, and the entire documentation is electronically searchable, making it ideal for use in upper-level physics courses for students completing assignments, since the mathematics becomes secondary to the physics. As occurred when calculators became widely available, the question remains as to how to use the new tool most effectively to help students learn physics, without distracting them with the computer, and Martin discussed several possible methods for implementing Mathematica into physics courses.

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Editor: Barrett H. Ripin