Physics designed to shock

July 23, 2003

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. Some of the exciting topics that will be presented at this conference include:

**Shock Waves: A New Medical Tool (Special Session)**

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.

*Targeting cancer* In this symposium, Dr. Charles Lin, Massachusetts General Hospital and Harvard University, discusses shock waves generated by short laser pulses that can kill living cells containing absorbing nanoparticles. Nanoparticles 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.

*How shocks force tissue* Professor Hyojin Kim of Chungnam University will describe a new approach to understanding the molecular basis for shock compression of biological systems, the "energy landscape" approach. He will present data where shock waves are used to study large amplitude motions of proteins and will discuss the first observation of viscoelasticity in shocked proteins.

*Needle-free drug delivery* Dr. Apostolos Doukas of the Wellman Laboratories of Photomedicine, Massachusetts General Hospital, Harvard Medical School, discusses using shock waves to deliver drugs through the skin without needles and to deliver genetic materials into living cells.

(Figure 1 [pdf] shows a protein from a shock compression point-of-view. It is full of internal space that can be squeezed out by shock compression.)

**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. A highlight of the conference will be a symposium on the properties of fluid hydrogen at very high pressures and temperatures.

Hydrogen is the simplest and most abundant atom in the universe. Fusion of hydrogen (or its isotope deuterium, known as heavy hydrogen) into helium powers the stars, and is the fuel for the hoped-for fusion power of the future here on Earth. Its properties under high shock compression near 100 GPa (a million times atmospheric pressure or about 15 million psi) and 10000 degrees K have been a subject of intense experimental and theoretical effort for most of the past decade. Despite this, a controversy still exists as to its equation of state (the relationship between pressure, density, and temperature). Resolving this issue is important for basic condensed matter physics and the design of laser-driven fusion experiments. The symposium will feature lectures by leading experimentalists and theoreticians from the U.S. and Russia on progress and challenges in understanding the surprisingly complex behavior of hydrogen at extreme conditions.

**Instantaneous Freezing of Water**

Daniel Dolan, a graduate student at Washington State University (and now on the staff of Sandia National Laboratory) has obtained the first pictures of freezing of water on a sub-microsecond time scale. In this case the water was induced to freeze by subjecting it to pressures up to 36,000 atmospheres and taking pictures through quartz windows. The "ice" condenses not as the familiar crystals, but apparently as filaments of "Ice 7", as shown in Figure 2(pdf).

**Special Review Lectures**

There will be a series of plenary lectures presented by the some of the most reknowned scientists working in this exotic field.
-end-


American Physical Society

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