posted on March 25, 2013 by Webmaster
Robert Truehaft, JPL
Tuesday, March 26, 2013 4:30 p.m. Galileo- Pryne – Harvey Mudd College
When trees are cut down, they release their carbon to the atmosphere in CO2. After fossil fuels, deforestation is the second largest anthropogenic contributor to atmospheric CO2. Tropical forests contain about 50% of Earth’s forested biomass, and they account for most deforestation. The degree to which a forest is storing carbon or releasing it to the atmosphere can be remotely sensed by measurements of the forest 3-dimensional distribution of vegetation, particularly in the vertical direction. For example, taller forests store more carbon than shorter ones. 3-dimensional structure measurements made regionally and globally can help to identify patterns of carbon sequestration and release, which affect the global carbon cycle. Measurement of the distribution of vegetation in the vertical direction has only within the last 20 years been possible with the technologies of interferometric synthetic aperture radar (InSAR) and laser ranging (lidar). InSAR and lidar measurements are made by transmitting electromagnetic waves from air or space, which scatter off the vegetated surfaces and return back to the transmitter. The time it takes for a signal to return is related to the vegetation’s height above the surface, that important vertical component. This talk explains the InSAR and lidar measurements, focusing on the basic electromagnetism needed to estimate structural characteristics from the electromagnetic returns. For InSAR, the difference between the arrival time of a scattered signal at two ends of a baseline is the principal vertical indicator. For lidar, the time delay between transmit and receive is related to the altitude of vegetation above the surface. This talk also shows the interface between the physics of electromagnetic scattering and the biology of carbon storage in biomass. It further suggests the possibility of applying physics modes of analysis (e.g. Fourier analysis) to biomass measurement.
posted on February 28, 2013 by Webmaster
David Weld – UC Santa Barbara
Tuesday, March 5, 2013 4:30 p.m. Galileo- Pryne, Harvey Mudd College
Ultracold neutral atoms trapped in optical lattices represent a new frontier for the investigation of outstanding problems in many-body quantum mechanics. These systems promise to bring the precision and control of atomic physics to bear on important problems in condensed matter physics, from nonequilibrium spin dynamics to d-wave superconductivity. The ambit of this fast-growing field is expanding from measurement to control, and from statics to dynamics. Breakthroughs in the ability to exert full spatiotemporal control over the evolution of cold atomic gases will enable a new generation of experiments at the boundary between condensed matter and atomic physics.
At UCSB we are building two experimental platforms (based around ultracold lithium and strontium) which will enable the creation and study of new, highly tunable, and strongly correlated phases of matter. Experimental goals of the lithium platform include quantum simulation of condensed matter Hamiltonians, the demonstration of effective time-reversal in a lattice-trapped gas, and the study of dynamical pseudospin ordering in higher-dimensional tilted lattices. The rich electronic structure of strontium may enable the creation of chiral spin liquids and states exhibiting SU(10) magnetism, and the ultra-narrow intercombination transition along with the negligible scattering length of the heaviest stable strontium isotope are particularly appealing for quantum sensing experiments.
posted on February 21, 2013 by Webmaster
Stephon Alexander, Dartmouth University
Tuesday, February 26, 2013 4:30 pm Millikan Lab – Room 134
posted on February 18, 2013 by Webmaster
Jing Xu – UC Merced
Tuesday, February 19, 2013 4:30 pm Millikan Lab – Room 134
Experimental biophysicists build instruments to study nature’s nano-machines. Molecular motors are nano-machines and are crucial for life: they transport materials in cells. Motor-based transport is inherently a many body problem, and exhibits complex behavior yet to be understood. An analytic model for multiple motor transport has been proposed, but has remained untested. In this talk, I will discuss the construction of a single beam gradient optical trap in my laboratory. I will also discuss planned measurements using this optical trap, aimed at experimentally testing the current model and driving theory development.
posted on February 6, 2013 by Webmaster
Prof. Douglas Natelson, Rice University
Monday, February 11, 2013 4:30 pm Millikan Lab – Room 134
We are all familiar with the idea that driving current through a conductor generates heat. However, when we consider the flow of current at the nanometer scale, we see that the transport of electrons is, in general, a complicated quantum mechanical process, and ideas familiar from thermal equilibrium (e.g., “temperature”) become challenging to define. I will talk about my group’s recent experiments, where we combine clever nanofabrication with electronic and optical techniques to address this question. We use metal electrodes separated at the nanometer scale to push current through molecules. These electrodes act like optical antennas, allowing us to use optical spectroscopy to watch the vibrational modes of those molecules. We can see current-driven vibrational heating, giving us new information about the flow of energy at these scales.
posted on January 29, 2013 by Webmaster
Brian Anderson, University of Arizona
Turbulent fluid flows are found throughout nature, and studied in numerous disciplines, yet a deep physical understanding of the nature of turbulence stubbornly remains “the most important unsolved problem of classical physics” [attributed to Feynman]. But turbulence is not just a classical phenomenon: it has long been studied in superfluid helium, where quantum mechanics and the presence of quantized vortices offer simplifications to characterizing turbulent flows. Nevertheless, the nature of turbulence still remains elusive. For two-dimensional (2D) flows in quantum fluids, however, there are significant prospects for the development of a clear understanding of the relationships between statistical signatures of turbulence, microscopic dynamics of quantum vortices, and other elements of turbulence. In this talk, I will discuss the study of 2D quantum turbulence in atomic Bose-Einstein condensates (BECs), beginning with introductions to the fascinating worlds of two-dimensional turbulence, vortices, and BECs. I will then focus on recent experimental research at the University of Arizona, and associated numerical and theoretical work, investigating 2D quantum turbulence and vortex dynamics in BECs. Although we remain far from a full understanding of turbulence, it is hoped that these studies of 2D quantum turbulence in BECs may shed important new light on at least this one interesting facet of turbulence.
posted on November 26, 2012 by Webmaster
Marcus Roper, UCLA
Tuesday, November 27, 2012 4:30 pm Millikan Lab – Room 134
Fungi are the most diverse of all eukaryotic organisms and enjoy extraordinary ecological success as decomposers, pathogens and mutualists. Focusing on two problems of recent interest, I will discuss how this success may rest on their ability to solve hard physical problems:
#1. The forcibly launched spores of ascomycete fungi must eject through a boundary layer of nearly still air in order to reach dispersive air flows. Because of their microscopic size, singly ejected spores are almost immediately brought to rest by fluid drag. However, by coordinating the ejection of thousands or hundreds of thousands of spores, fungi such as the devastating plant pathogen Sclerotinia sclerotiorum, are able to create a flow of air that carries spores across the boundary layer and around any intervening obstacles.
#2. Time permitting, I will then show how the fungal mycelium itself is hydraulically engineered to create mixing flows of nuclei during growth. I hypothesize that these mixing flows are an adaptation that makes fungi very tolerant of chimerism: the presence of genetically different nuclei within the same organism. Chimeric fungi are known to be more adaptable and infectious than non-chimeric individuals, and are also thought to be key intermediate stages in the evolution of new species.
posted on October 10, 2012 by Webmaster
Justin M. Brown, University of California, Berkeley
Tuesday, October 9, 2012 4:30 pm Millikan Lab – Room 134
Gravity and quantum mechanics are expected to unify at the Planck scale described by an exceeding large energy of 1019 GeV. This regime is far from the reach of the highest energy colliders, but tests of fundamental symmetries provide an avenue to explore physics at this scale from the low energy world. Proposed theories of quantum gravity suggest possible breaking of Lorentz and CPT symmetry that have so far been unobserved. I present results from my recent graduate work that improved the existing limits of a Lorentz- and CPT-violating background field coupling to the neutron spin by a factor of 30. In a tabletop setup, polarized atomic vapors of K and 3He form a comagnetometer to suppress magnetic fields but remain sensitive to non-magnetic spin couplings. A distinctive feature of our apparatus is a rotating platform for frequent reversals of the comagnetometer with respect to the celestial frame. Rotating the apparatus introduces several systematic effects, the largest of which is the rotation of the earth. I will highlight continuing improvements to the experiment including transfer to the South Pole in December to eliminate the Earth’s rotation background entirely.
posted on September 27, 2012 by Webmaster
Eric Kort (’04), JPL – NASA
Thursday, September 27, 2012 at 4:30 pm in Millikan Laboratory – Room 134 (Refreshments at 4:15 pm)
Abstract: Human activities have significantly perturbed our planet’s atmospheric composition, with major consequences for our present and future Climate. In particular, higher levels of long-lived greenhouse gases such as CO2, CH4, and N2O are playing a driving role in the climate change occurring today. To better understand both the present climate and possible future climate scenarios, it is critical to observe atmospheric concentrations and distributions of these gases and improve our knowledge of current human and natural emissions levels. In this talk, I will first discuss observation made from an aircraft travelling from pole-to-pole and focus on some surprises we found in the Arctic. Moving from the global to urban scale, I’ll then focus on carbon emissions from cities, which presently represent the single largest human contribution to climate change. Despite the large contribution of urban areas to the total greenhouse gas emission rate, there presently exists no method for robustly quantifying emissions changes, be they growth or reduction. I’ll discuss the Megacity Carbon pilot project, which aims to develop and demonstrate an observing system that will be able to monitor megacity carbon emissions. This entails both earth- & space-based observations, including the expansion of an observing network in the Los Angeles basin, with a potential site situated at Pomona College.
posted on September 25, 2012 by Webmaster
Philip Muirhead, Caltech
Tuesday, September 25, 2012 at 4:30 pm, Galileo-Pryne at Harvey Mudd College (Refreshments at 4:15 pm)
Abstract: With the success of NASA’s Kepler Spacecraft, extrasolar planet science has entered a new era. Prior to Kepler’s launch exoplanet science was primarily concerned with gas-giant exoplanets, since gas giants comprised the majority of discoveries, numbering in the hundreds. NASA’s Kepler Mission has since discovered thousands of exoplanets with many of them terrestrial-sized. Of particular interest are terrestrial exoplanets orbiting low-mass stars, which are roughly 1/10 to 1/2 the mass of Sun. Low-mass stars dominate stellar populations, so understanding the prevalence of terrestrial exoplanets orbiting low-mass stars, life-harboring or otherwise, is crucial to understanding their prevalence in the Universe. I will present a ground-based observation program to characterize low-mass stars with exoplanets discovered by the Kepler Spacecraft, and our identification of the three smallest exoplanets detected to date: Kepler 41 b, c and d (formerly KOI 961 b, c and d). The program uses a fully-cryogenic infrared spectrograph built by myself and others and deployed on the 200-inch Hale Telescope at Palomar Observatory in Southern California.