UCLA

Speaker:
Troy Carter
UCLA

Abstract:
I will give an overview of the challenges associated with harnessing nuclear fusion as a terrestrial power source and the progress that has been made in research in this area. In particular, I will discuss turbulence in magnetically-confined plasmas and how transport associated with this turbulence limits the confinement achievable in current and planned experiments. I will present recent UCLA research that has helped advance our understanding of the basic physics of turbulence and turbulent transport in magnetized plasmas.

Speaker:
P.U.P.A. Gilbert
University of Wisconsin

Abstract:
Mapping the Amorphous-to-crystalline transitions in CaCO3 biominerals with 20-nm resolution One of the most fascinating aspects of calcite biominerals is their intricate and curved morphology, quite different from the rhombohedral crystal habit of geologic calcite. These morphologies, as well as space-filling and greater resistance to fracture, are achieved via amorphous precursor mineral phases (1). In this talk we will show that in sea urchin larval spicules two distinct phase transitions occur, 12 and 23 (2). Both transitions are regulated by inhibiting proteins, which introduce activation barriers between states otherwise spontaneously transforming because they are energetically downhill (3). 1. Y Politi, RA Metzler, M Abrecht, B Gilbert, FH Wilt, I Sagi, L Addadi, S Weiner, and PUPA Gilbert. Mechanism of transformation of amorphous calcium carbonate into calcite in the sea urchin larval spicule. Procs. Natl. Acad. Sci. USA 105, 17362-17366, 2008. 2. AV Radha, TZ Forbes, CE Killian, PUPA Gilbert, and A Navrotsky. Transformation and crystallization energetics of synthetic and biogenic amorphous calcium carbonate. Procs. Natl. Acad. Sci. USA 107, 16438–16443, 2010. 3. YUT Gong, CE Killian, IC Olson, NP Appathurai, RA Metzler, AL Amasino, FH Wilt, PUPA Gilbert. Phase Transitions in Sea Urchin Larval Spicules. Under review.

Speaker:
Michael Jura
UCLA

Abstract:
Knowing that extrasolar planetary systems are common, we would like to learn whether the Earth is normal or distinctive. Bulk Earth is 94% composed of O, Mg, Si and Fe and very deficient compared to the Sun in volatiles such as C and N. With our recent observations of white dwarf stars that have recently accreted tidally-disrupted minor planets that are about 300 km in diameter, we find a similar compositional pattern in extrasolar asteroids. While there must be individual exceptions, in aggregate, the studied extrasolar asteroids also are as “dry”; they probably formed interior to a snow line. Although the current sample is tiny, it appears that bulk Earth is compositionally normal for a rocky body. In the future, we may learn whether extrasolar planetesimals have undergone differentiation, a fundamentally important process in the history of our own planet.

Speaker:
German Prieto
Universidad de los Andes, Bogotá, Colombia

Abstract:
The physical mechanism of intermediate-depth earthquakes is still under debate. In contrast to conditions in the crust and shallow lithosphere, at temperatures and pressures corresponding to depths >50 km one would expect rocks to yield by creep or flow and not by brittle failure, so there has to be a physical mechanism that allows for brittle or brittle-like failure for intermediate-depth earthquakes. Two such mechanisms have been proposed: dehydration embrittlement and thermal shear runaway. Earthquake nests represent a region with high earthquake concentration that is isolated from nearby activity. I will discuss general observations on the three famous intermediate-depth earthquake nests – Vrancea, Hindu-Kush and Bucaramanga. The emphasis will be on the Bucaramanga nest (Colombia) and how high-resolution seismological observations (tectonic setting, precise earthquake locations, focal mechanisms, stress drops, etc.) may provide key constraints on the mechanism responsible. Given the nature and characteristics of this nest, it can be thought as natural laboratory for understanding the physics of intermediate-depth earthquakes.