The Sontag Endowment for Physics Fund

posted on February 2, 2014 by

Thanks to a generous million dollar gift from Rick and Susan Sontag, The Sontag Endowment for Physics Fund will support extended, focused student research projects during the summer, a hallmark of the Pomona College Physics and Astronomy Department.  Read about this wonderful gift and the donors in the official Pomona College press release.

Seeing Molecules in Color: Science and Commercialization in Resonance Force Microscopy

posted on April 18, 2013 by

Sung Park, CEO Molecular Vista, PO ’81

Will Morrison, PO ’12 

Tuesday, April 23, 2013 4:30 p.m. Millikan Lab – Room 134

We introduce the science behind a new kind of atomic force microscope (AFM).  This “Molecular Resonance Force Microscope” (RFM) measures optical resonances entirely through mechanical vibrations in the AFM tip.  Forces can be measured from resonant e-fields, near field, and stimulated Raman scattering, all concurrent with high resolution topographical data, suggesting potential applications that range from studying the dynamics and structure of bio-molecules to nanoplasmonics.  The presentation will give a short overview of AFM technology to build a foundation for discussing RFM, followed by a description of the new tool and some preliminary data, endeavoring simultaneously to convey some of the unique experience and perspective of doing science and developing an instrument at a small startup.

Coarse-grained Simulations of Ion-Containing Polymers

posted on April 18, 2013 by

Amalie Frischknecht, ‘92  –  Sandia

Tuesday, April 16, 2013 4:30 p.m. Millikan Lab – Room 134

Ionomers are polymers containing a small fraction of covalently bound ionic groups.  They are of interest in electrochemical applications such as electrolytes for batteries and membranes for fuel cells.  In particular, a single-ion conducting polymer electrolyte made of ionomers would be safer and have higher efficiency than currently-used liquid electrolytes.  However, melt ionomeric materials do not have sufficiently high conductivities for practical application.  This is most likely because the ions tend to form aggregates, leading to slow ion transport. A key question is therefore how molecular structure affects the ionic aggregation and ion dynamics. To probe these structure-property relationships, we have performed coarse-grained molecular dynamics simulations of a simple model of ionomers, designed to capture the most important physics in these systems. We find that the ions aggregate into clusters in all of the simulations, but the cluster morphology depends strongly on the polymer architecture. The structure calculated from the MD simulations compares favorably with x-ray scattering data.   Furthermore, the simulations give a detailed picture of the sizes, shapes, and composition of the ionic aggregates, which is difficult to extract from experiment.  We also study the dynamics of the ions, and find that ion transport occurs mainly by cluster rearrangements.  The highest conductivity occurs for ionomers with percolated ionic clusters.

Atomically Thin Photodetectors: The Ideal Semi-Metal vs. the Insurmountable Insulator

posted on April 8, 2013 by

Nathaniel Gabor, MIT

Tuesday, April 9, 2013 4:30 p.m. Galileo- Pryne – Harvey Mudd College

Graphene, an atomically thin sheet of hexagonally oriented carbon, is a zero band gap conductor (semi-metal) that exhibits extraordinary electronic behavior and broadband optical absorption. Hexagonal boron nitride, which shares a similar structure to that of graphene, is a highly insulating electronic material that does not absorb any light in the visible spectrum. By combining graphene and boron nitride into ultrathin vertical stacks, we can fabricate new optoelectronic devices that demonstrate highly sensitive optical response, yet are only as thick as the width of a DNA molecule. In this talk, I will discuss how stacking these atomically thin materials allows us to explore new types of optoelectronic devices that may ultimately lead to more efficient light energy harvesting technologies.

Planet Formation and the Solar System

posted on April 1, 2013 by

Hilke Schlichting, Caltech

Tuesday, April 2, 2013 4:30 p.m. Millikan Lab – Room 134

In my talk, I will discuss recent insights that we have gained into planet formation form our solar system. I will talk about the Kuiper belt, located at the outskirts of our planetary system, which provides a snapshot of earlier stages of planet formation and is therefore an ideal laboratory for testing planet formation theories. I will show how we can use the Kuiper belt size distribution to gain new insights into runaway growth during planet formation and how we can use it to constrain the initial sizes of planetesimals that are the building blocks of planets.

The Physics in the Forest: Remote Sensing of Tropical Forests with Interferometric SAR and Lidar.

posted on March 25, 2013 by

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.

Cold Atom Quantum Simulation

posted on February 28, 2013 by

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.

Molecular Motor Biophysics: Hardware Instrumentation and Nonlinear Physics

posted on February 18, 2013 by

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.

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