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Physics & Astronomy Colloquium
Thursdays, 3:30 p.m.
Call us at: (323) 343-2100
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Spring Quarter 2016 Schedule

Location: BIOS 244
Refreshments - 3:00 p.m., Colloquium - 3:15 p.m


No Colloquium

Cesar Chavez Holiday
(Campus Closed)


Dr. Joe Kovalik
Senior Engineer
Jet Propulsion Laboratory, California Institute of Technology, Pasadena CA

"Free Space Optical Communications"

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Abstract: Free Space Optical Communications offer a means to increase data rates for space missions while reducing Size, Weight, and Power (SWAP) which is critical for spaceflight.  This talk will discuss the fundamentals of free space communications and present past and planned flight demonstrations.


Massimo Tinto
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA

"Earth- and (future) Space-based Observations of Gravitational Waves"

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Abstract: The direct observation of a gravitational wave (GW) signal from the coalescence of two in-spiraling black-holes, announced by LIGO on Thursday, February 11, 2016, represents one of the greatest triumphs in experimental physics today and the beginning of a new era for astronomy.

Ground-based detectors such as LIGO are sensitive to the kHz GW band, with the seismic noise-wall preventing them from being sensitive below ~ 10 Hz. Astronomical observations in the mHz band, where GW signals are expected to be stronger and larger in number, can only be made in space by flying a GW interferometer. Such a detector will observe GWs emitted by sources whose dynamic time-scales are significantly longer than those characterizing signals detectable on Earth, and will enhance the capabilities of ground-based detectors by first observing signals that would then become detectable on Earth at later times in their dynamic evolutions.

After giving a brief introduction to gravitational waves and their sources, and the LIGO results, I will describe the current efforts underway in the US and abroad for flying a space-based GW interferometer together with the existing programmatic and technological challenges.


Dr. Warren Skidmore
Thirty Meter Telescope International Observatory

"The Thirty Meter Telescope. The Next Generation of Ground Based Telescope. What, Why and How"


Abstract: I’ll talk about the TMT project, the exciting scientific questions that drive the building of a giant telescope, how the observatory is designed to support a range of scientific studies that span the universe from asteroids to the first luminous structures in the universe and about the engineering solutions that have been developed to overcome the problems of constructing and operating a giant diffraction limited observatory.


Lamar Glover
California State University, Los Angeles

"Study of Light Scattering Points on Test-Mass Mirrors in Gravitational Wave Observatories"

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Abstract: The sensitivity of Gravitational Wave observatories is limited by the thermal noise and scatter on the test-mass mirror dielectric coatings, which directly relates to the reach of its detection radius into the Universe. The LIGO mirrors, when illuminated by the standing beam, look similar to a photographic image of a star cluster. Thus, we studied photographs of the LIGO mirrors with "daophot", a tool designed to identify stars from photographs along with determining their structure.  "Daophot" ignored the smear of actual dirt on the mirror and extracted hundreds of thousands of weaker, point-like scatterers, uniformly distributed across the mirror surface.  The amplitude distribution implies that these scatterers are distributed through the depth of the coating.  The sheer number of the observed scatterers implies a fundamental, thermodynamic origin.  Theoretical material science consideration indicates that these scatterers are nucleation centers and are also the likely source of the mirror dissipation and thermal noise, which could potentially lead towards a mitigation strategy and an increase of the detection radius of GW observatories.


Matthew Thompson
Lead Scientist, Tri Alpha Energy

"On the Path to Aneutronic Fusion"

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Abstract:Tri Alpha Energy's purpose is to deliver world-changing clean fusion energy technology as fast as possible.  Starting with the end in mind – a fusion solution that delivers practical science, engineering integration and competitive economics – Tri Alpha Energy developed a unique approach combining advanced particle accelerator and plasma physics.  The C-2U experiment at Tri Alpha Energy seeks to test these ideas by studying the evolution of advanced beam-driven field-reversed configuration (FRC) plasmas sustained by neutral beam (NB) injection for 5+ ms.  C-2U is an upgrade to the earlier C-2 [1] experiment with an improved neutral beam injection (NBI) system which can deliver a total of 10+ MW of hydrogen beam power, by far the largest ever used in a compact toroid plasma experiment.  This increase in beam power, combined with our earlier innovations in FRC stabilization, successfully produced high-performance, advanced beam-driven FRCs sustained for times significantly longer than the characteristic plasma decay times.  This accomplishment represents a significant advance towards the scientific validation of the FRC-based approach to fusion. This presentation will provide an overview of the C-2U device and recent experimental advances.
[1] M.W. Binderbauer et. al, Phys. Rev. Lett 105, 045003 (2010)


Jim Fuller
California Institute of Technology, Pasadena, CA

"Saturn Ring Seismology: Complex Interactions Between the Planet, the Rings, and the Moons"

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Abstract: The rich dynamics of the Saturn ring and moon systems offer unique opportunities to study the evolution of the planet and its surrounding bodies. For instance, seismology of Saturn is made possible by the gravitational interaction between Saturn and its rings, in which density waves in the rings are excited at Lindblad resonances with Saturn's oscillation modes. The seismic signatures in the rings suggest the existence of stable stratification in the deep interior of the planet, likely created by composition gradients between the core and envelope due to helium sedimentation and/or core erosion. These structures within the planet influence the tidal interactions which drive the outward migration of Saturn's inner satellites. Rapid migration can occur when moons become locked in resonance with Saturn's oscillation modes, driving the moons outward on a planetary evolution timescale.


John Baez
Department of Mathematics, University of California, Riverside

"My Favorite Number"

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Abstract: The number 24 plays a central role in the mathematics of string theory, thanks to a series of "coincidences" that is just beginning to be understood. One of the first hints of this fact was Euler's bizarre "proof" that
                               1 + 2 + 3 + 4 + ··· = -1/12
which he obtained before Abel declared that "divergent series are the invention of the devil". Euler's formula can now be understood rigorously, and in physics it explains why bosonic strings work best in 26=24+2 dimensions.  Other remarkable facts about then connect string theory, the Leech lattice (the densest way to pack spheres in 24 dimensions), and a huge group called the Monster.


Nicole Yunger Halpern
Institute for Quantum Information and Matter, Caltech

"Quantum Steampunk: Quantum Information Applied to Thermodynamics"

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Abstract: Thermodynamics has shed light on engines, efficiency, and time’s arrow since the Industrial Revolution. Quantum information theory and technologies have bloomed in the past few decades. Information theory provides a toolkit that is transforming our understanding of thermodynamics. Upshots range from fundamental (e.g., how and why do systems thermalize? Can we always distinguish heat from work?) to potentially practical (e.g., nanoscale engines and the thermodynamic value of quantum coherences). I will overview applications of quantum information theory to thermodynamics. Topics include entropies, tradeoffs between work and information, fluctuation theorems, and the impressive control developed recently over quantum-thermodynamics experiments. Cutting-edge mathematical and experimental tools, combined with one of physics’s deepest and oldest theories, are generating insights worthy of science fiction.


Courtney Dressing
NASA Sagan Postdoctoral Fellow, Caltech

"The Frequency and Composition of Small Exoplanets"

Dressing pic

Abstract: Over the past twenty years, ground- and space-based investigations have revealed that our galaxy is teeming with planetary systems and that Earth-sized planets are common. I will focus on the results of the NASA Kepler mission and describe two investigations of the frequency and composition of small planets. First, I analyzed Kepler observations of small stars and measured a cumulative planet occurrence rate of 2.45 +/- 0.22 planets per small star with periods of 0.5-200 days and planet radii of 1-4 Earth radii. Within a conservative habitable zone based on the moist greenhouse inner limit and maximum greenhouse outer limit, I estimated an occurrence rate of 0.15 (+0.18/-0.06) Earth-size planets and 0.09 (+0.10/-0.04) super-Earths per small star habitable zone. Second, I explored the compositional diversity of small planets by using the HARPS-N spectrograph on the Telescopio Nazionale Galileo (TNG) to measure the masses of transiting planets.  Concentrating on the set of small planets with well-constrained radii from space-based observations with Kepler or CoRoT and precise mass estimates from TNG/HARPS-N or Keck/HIRES, I found that all close-in dense exoplanets with masses of approximately 1-6 Earth masses are consistent with the same fixed ratio of iron to rock as the Earth and Venus. Future measurements of the masses and radii of a larger sample of planets receiving a wider range of stellar insolations will reveal whether the fixed compositional model found for these highly-irradiated dense exoplanets extends to the full population of low-mass planets.  

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