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The APS Topical Group on Shock Compression of Condensed Matter held its biennial conference in Portland, Oregon, from July 20-25. Topics included the targeting and destruction of cancer cells, needle- free drug delivery, making solid hydrogen, progress toward fusion, and watching the instantaneous freezing of water. Among the plenary speakers was this year's recipient of the Shock Compression Science Award, Jim Asay (Washington State University), who spoke about how shock waves can be tailored for investigation of specific properties of materials under extreme compression, such as occurs in meteor impact, the interior of large planets, or in large explosions.
Shock compression studies examine the effects of shock waves on materials of scientific and engineering importance. Shocks can be produced by high-speed impacts or intense explosions. Study of shock waves began as a part of the nuclear weapons program, but the benefits from this new field of science have been far-reaching.
A New Medical Tool. Understanding shock waves in biology and medicine is a new challenge and a new opportunity for shock compression science. Biological tissues are fundamentally different and considerably more complicated than the liquids and solids normally studied by shock compression. Laser surgeries generate shock waves in living tissues, causing both mechanical and chemical changes. The shock waves can compress biological molecules and change the pH and ionic strength of the aqueous media, and can result in wanted and unwanted chemical and biological effects including irreversible damage via denaturing proteins, tearing tissues and killing living cells.
In a special symposium on medical applications for shockwaves, Charles Lin of Massachusetts General Hospital and Harvard University, discussed how shock waves generated by short laser pulses can kill living cells containing absorbing nanoparticles. Nano- particles can be tailored for a variety of uses including selective uptake by cancer cells, allowing targeted cell killing without the use of poisonous chemotherapy agents.
In the same session, Hyojin Kim of Chungnam University described a new approach to understanding the molecular basis for shock compression of biological systems, the "energy landscape" approach. He presented data in which shock waves are used to study large amplitude motions of proteins and discussed the first observation of viscoelasticity in shocked proteins. And Apostolos Doukas of the Wellman Laboratories of Photomedicine, Massachusetts General Hospital, Harvard Medical School, discussed using shock waves to deliver drugs through the skin without needles and to deliver genetic materials into living cells.
Hydrogen Compressed to a Solid. Understanding highly compressed hydrogen is vital in efforts to achieve laser-driven fusion, processes in stars and the role of hydrogen in more everyday settings. Discovery of the properties of highly compressed hydrogen has been a major goal and source of competition in the international shock wave community. Another highlight of the SCCM conference was a symposium on the properties of fluid hydrogen at very high pressures and temperatures.
The symposium featured lectures by leading experimentalists and theoreticians from the US and Russia on progress and challenges in understanding the surprisingly complex behavior of hydrogen at extreme conditions.
--Compiled by David Harris