Friday, November 22
12:00 PM, C215 ESC
Barry WalkerUniversity of Delaware
Atoms and Molecules in Ultra-Intense Laser Fields
Ultrahigh intensity lasers can generate peak powers greater than one-hundred trillion Watts. The electric and magnetic fields in these intense laser pulses exceed the summed power generated by all the power plants in the world (a paltry, ten-trillion Watts). Everyday light intensities are well understood thanks in part to approximations such as the non-relativistic Schrödinger equation. With proper credit to the effort of many hard working students, our experimental data and theory modeling have begun to reveal the general picture of the important physics behind the “not-everyday” ultrahigh laser field – matter interaction, including what approximations can be made. Beyond the fundamental physics, it is important to realize the applications of intense lasers. Strong laser fields are, for example, the only way we can generate attosecond (10^-18 second), coherent x-rays. Attosecond x-rays are significant as they promise the ability to probe and quantify the next level of dynamics in quantum systems. We will conclude with a discussion of the ultimate limit for these new light sources in the ultrahigh intensity regime.
Following BA degrees in both Chemistry and Physics at Point Loma Nazarene University, Barry Walker earned a PhD in Physics at SUNY Stony Brook in New York, and did post-doctoral research with Kent Wilson at UC San Diego. He then joined the faculty of Physics & Astronomy at the University of Delaware, where he is a Professor, and where he has served as the Director of Undergraduate Programs and as Associate Department Chair. He is a Fellow of the American Physical Society, a former Visiting Fellow at JILA at the University of Colorado, and has served on the committees of both the American Physical Society and the Optical Society of America. His research expertise is in experimental and theoretical optical science, light matter interactions, and ultrafast opto-electronic technology. Most recently, his interests involve “ultra” high intensity laser fields.
Friday, December 6
12:00 PM, C215 ESC
Angel GarciaLos Alamos National Laboratory
Proteins under Pressure
Proteins are heteropolymers that self-assemble into a compact ordered structure known as the folded state. Although the folded state is a compact state, proteins will unfold under high hydrostatic pressure. This effect seems contradictory, given that high pressures should drive the system toward lower volume states. However, pressure denaturation can be easily explained in terms of the pressure effects of hydrophobic interactions (i.e., how non polar molecules interact with water). We use molecular simulations to model the pressure folding/unfolding equilibrium of small peptides that form alpha helices, beta sheets, and a model protein (the trp-cage mini protein). These calculations show a rich P-T stability diagram in which a protein can unfold at high pressures, or can unfold upon cooling (cold denature) at elevated pressures. I will describe the role of the interactions of water with proteins in describing these effects. The simulation results in small, model proteins will be used to interpret experimental data in larger, complex protein systems.
We welcome anyone who wish to attend, and typically serve refreshments ten minutes before the colloquium begins. Speakers generally keep their presentation accessible to undergraduate physics students.