Physics Department

C o l l o q u i a

Winter 2008

 

Colloquia are at 4pm, Thursdays, in 100 Willamette Hall and are preceded by coffee, tea, and cookies at 3:40 in the Wilamette Atrium.

Speakers: Information, including maps and directions to the Physics Department, can be found here (compiled by Graham Kribs, Fall term).

Raghuveer Parthasarathy is the organizer of the Winter 2008 colloquia.

Colloquium Schedule

Date

Speaker

   
Jan. 10, 2008 Ray Vandiver -- Oregon Museum of Science and Industry (OMSI); URL: [1] ,

Presenting cutting edge topics in an informal science setting -- Abstract

Host: Stan Micklavzina

   
Jan. 17, 2008 Ethan Minot -- Oregon State University, Department of Physics; URL: [1]

Charge sensing in biological environments with carbon nanotube devices -- Abstract

Host: Raghuveer Parthasarathy

   
Jan. 24, 2008 Dan Blair -- Georgetown University, Department of Physics ; URL: [1]

Colloids in action: Microscopic insights into clogging and jamming -- Abstract

Host: Raghuveer Parthasarathy

   
Jan. 31, 2008 Russ Donnelly -- University of Oregon, Department of Physics; URL: [1]

The making of absolute zero -- Abstract

Host: Raghuveer Parthasarathy

   
Feb. 7, 2008 Matt Anderson -- San Diego State University; URL: [1]

Better check your pulse! Femtosecond lasers, pulse shaping, and measurement. -- Abstract

Host: Graduate Students

   
Feb. 14, 2008 Darrell Schroeter -- Reed College; URL: [1]

Flatland -- Abstract

Host: Raghuveer Parthasarathy

   
Feb. 21, 2008 Brad Johnson -- Western Washington University ; URL: [1]

Thermal-Cycling and Memory Functions in the Ising Model: New Tricks from an Old Dog -- Abstract

Host: Raghuveer Parthasarathy

   
Feb. 28, 2008 Chris Fuchs -- Perimeter Institute for Theoretical Physics; URL: [1]

Charting the Shape of Hilbert Space: A Bit of Quantum Foundations at the Perimeter Institute -- Abstract

Host: Mike Raymer

   
Mar. 6, 2008 Xiao-Min Lin -- Argonne National Laboratory; URL: [1]

Synthesis and Assembly: Building Functional Nanocrystal Superlattices -- Abstract

Host: Raghuveer Parthasarathy

Mar. 13, 2008 Marcia Levitus -- Arizona State University, Department of Chemistry and Biochemistry and Department of Physics; URL: [1]

Applications of Fluorescence Correlation Spectroscopy to the Study of Nucleic Acid Conformational Dynamics -- Abstract

Host: Raghuveer Parthasarathy

 

 

Raghuveer Parthasarathy, Department of Physics , University of Oregon

Contact:  raghu [at] physics.uoregon.edu

Last updated: December 20, 2007

 

 

Abstracts

 

Ray Vandiver -- Presenting cutting edge topics in an informal science setting

Science centers confront a significant challenge in developing effective strategies for introducing more difficult and abstract concepts for the general public. OMSI's current work on the topic of nanotechnology will provide the case study to demonstrate tactics used by the informal science education community.

 

Ethan Minot -- Charge sensing in biological environments with carbon nanotube devices

Carbon nanotubes have remarkable properties, including one-dimensional electronic subbands, unusual sensitivity to strain and magnetic-field, and enormous mechanical strength. After discussing experiments that measure these fundamental properties [1,2], I will focus on applications of carbon nanotube devices in the fields of medicine and molecular biology. Semiconducting carbon nanotubes are extremely sensitive to their electrostatic environment. We use this property to build single-nanotube sensors in liquid environments that detect bio-molecule adsorption in real time via changes in device conductivity [3,4]. I will discuss future directions for biosensor research, such as single molecule sensitivity.

1. Minot, Yaish, Sazonova, Park, Brink and McEuen, Phys. Rev. Lett. 90, 156401 (2003)
2. Minot, Yaish, Sazonova, and McEuen, Nature 428, 536 (2004)
3. Minot, Janssens, Heller, Heering, Dekker and Lemay, Appl. Phys. Lett., 91 093507 (2007)
4. Heller, Janssens, Mannik, Minot, Lemay and Dekker, Nano Letters (2007)

 

Daniel Blair -- Colloids in action: Microscopic insights into clogging and jamming

Suspensions of colloidal particles are astounding model systems used to study a variety of fundamentally important problems in soft matter physics. The versatility of colloids is due in large part to the increasing sophistication of their synthesis, and the relative physical simplicity of their interactions. This talk will discuss recent experimental results on two soft-matter topics that utilize colloidal particles; clogging during flow and jamming in glasses.

I will first present results from microfluidic studies of clogging in model porous media. By using simple imaging techniques, and a minimal geometric model, I will describe the physical origins of clogging in microfluidic devices. These results demonstrate that the aggregation of micron sized particles, in a low Reynolds number flow, is dominated by single particle interactions and not collective phenomena. In the second half of the talk, I will discuss the microscopic response of colloidal glasses to a macroscopically applied compressive stress. Using time resolved laser scanning confocal microscopy, I identify and track the motion of thousands of colloidal particles in real space over very long times. With this technique, and ideas garnered from metallic glasses, the complete local strain tensor for each particle is determined. I will demonstrate that highly localized, correlated shear and compression transformations are necessary for colloidal glasses to approach a maximally jammed state.

 

Russ Donnelly -- The making of Absolute Zero

Absolute Zero is a two hour TV documentary history of the field of low temperature physics. It has been produced by Windfall Films in London and premiered on BBC Channel 4 in July to enthusiastic reviews. It is being translated into several languages for broadcast to EU countries through the French television station ARTE. It wias be featured on NOVA here in the US the evenings of January 8 and 15. I will explain how the idea was conceived and how, through seven years of hard work, it actually got accomplished. For more information, our website is www.absolutezerocampaign.org. The new interactive NOVA website is at http://www.pbs.org/wgbh/nova/zero/.

 

Matt Anderson -- Better check your pulse! Femtosecond lasers, pulse shaping, and measurement

For the past several decades, ultrafast lasers have been at the forefront of optical physics research. These lasers have attracted such attention for four primary reasons: 1) The pulses are exceedingly short, a few femtoseconds, which permits access to events that occur on the fastest time scales, such as molecular vibrations; 2) The pulses are high in peak power, since the photons are squeezed into such a short temporal window. Indeed, tabletop systems can approach intensities equivalent to focusing the entire solar flux hitting the earth onto the head of a pin; 3) The spectrum is extremely broad, up to several hundred nanometers, permitting a whole host of possibilities for spectral control and measurement; And 4) The spectrum contains a million regularly spaced spectral modes which can be used to make the world's most precise clocks, such as the 2005 Nobel Prize winning work of Ted Hänsch and John Hall.

SDSU’s femtosecond laser started generating ultrashort pulses of light on Jan. 31, 2001. Since that time, we have been concentrating on various ideas in pulse shaping, including both temporal shaping and spatial shaping, and pulse measurement, using the SPIDER characterization technique. We demonstrated that complex pulse shapes can be generated, and when combined with pulse measurement in a feedback loop, controlled and optimized in real time. In this talk I will give an introduction to femtosecond lasers, pulse shaping and measurement, highlight some advances made by others, and tell you about the great work my Master's and Bachelor's students have been doing over the past several years in San Diego.

 

Darrell Schroeter -- Flatland

In three dimensions, there are only two possibilities for the quantum statistics that particles obey: they are either bosons or fermions. In two dimensions, the possibilities are much richer; notably, particles that obey a continuum of quantum statistics are possible. These particles, which obey fractional statistics, are called anyons. Anyons are known to exist in the fractional quantum Hall effect (FQHE) and may also arise in a class of Mott insulators known as spin liquids. I will present an exactly-solvable model [1] for which the ground state is a chiral spin liquid, a state whose excitations obey fractional statistics.

[1] Schroeter, Kapit, Thomale, and Gretier, Phys Rev Lett 99, 097202 (2007).

 

Brad Johnson -- Thermal-Cycling and Memory Functions in the Ising Model: New Tricks from an Old Dog

The ubiquitous Ising model provides a rich system for the modeling of a variety of correlated systems. In this talk, I present the results of numerical studies of 2- and 3-dimensional Ising spin systems subjected to thermal cycling from an ordered state to states with a fixed order parameter (<1), but with differing overall morphologies, and back to a quenched state. Interestingly, for systems with initial states generated by thermal disordering above Tc, the initial state of a given order parameter is made up of larger, complex-bounded 'islands' of like-spin (than the case for random disorder with the same overall order parameter) and consequent quenches of the state to T < Tc result in a strong correlation to a particular final average order parameter. The function we find is given by <S> ≈ tanh(B ⋅ Sinit), where Sinit is the order parameter of the initial state, <S>is the average quenched order parameter, and B is a constant that depends upon the morphology of the initial state. The reason for the strong correlation stems from the energies associated with spins at the borders of large clusters. This 'memory effect' does not occur in 3D (due to the larger number of near-neighbors). This research arose as a consequence of phenomena seen in interfacial states of thin-film liquid crystals.

Chris Fuchs -- Charting the Shape of Hilbert Space: A Bit of Quantum Foundations at the Perimeter Institute

As physicists, we have become accustomed to the idea that a theory's content is always most transparent when written in coordinate-free language. But sometimes the choice of a good coordinate system is very useful for settling deep conceptual issues. And this is particularly so for an information-oriented or Bayesian approach to quantum foundations: One good coordinate system may (eventually!) be worth more than a hundred blue-in-the-face arguments. This talk will motivate and chronicle the search for one such coordinate system for the space of quantum states---the so-called Symmetric Informationally Complete Quantum Measurements---which has caught the attention of a handful of us at the Perimeter Institute, a handful of our visitors, and a handful of other colleagues around the world.

 

Xiao-Min Lin -- Synthesis and Assembly: Building Functional Nanocrystal Superlattices

Over the past two decades, there has been significant development in the synthesis and characterization of colloidal nanocrystals. Chemically synthesized nanocyrstals have been used in many applications ranging from biomedical assays, catalysis and electronic and photonic devices. From the material point of view, the most exciting aspect is that nanocrystals can be used as building blocks to create new hierarchical macroscopic materials. Nevertheless, tremendous challenges still lie ahead in understanding both the synthesis and assembly of nanocrystals.

In this talk, I will show that a strongly-binding molecular ligand can alter the nanoparticle growth process, leading to a new, previously unexplored ripening regime. This process affects the particle size, structure and composition. I will show results on the dynamics of the nanocrystal superlattice formation using both colloidal droplet evaporation and Langmuir trough methods. Using in-situ small angle x-ray scattering and optical microscopy, we found that the evaporation kinetics and the concentration of ligand play important roles on the dynamics and structure of superlattices. Ultimately, these techniques allow us to fabricate nanocrystal superlattices with unique electronic and mechanical properties.

Marcia Levitus -- Applications of Fluorescence Correlation Spectroscopy to the Study of Nucleic Acid Conformational Dynamics

Fluorescence correlation spectroscopy (FCS) is a technique based on the measurement of the spontaneous fluctuations of the fluorescence signal of a small number of molecules. Fluorescence fluctuations are typically measured in an optically restricted sub-micron observation volume, and then analyzed statistically to reveal kinetic information about the processes that lead to these fluctuations. Such processes include concentration fluctuations via molecular diffusion, chemical reactions, photophysical processes, etc.

I will present an overview of the technique, and concentrate on the recent applications of FCS to the study of nucleic acid conformational dynamics. Much of the effort in this regard has been focused on dealing with the problem of separating the contributions due to conformational dynamics from those due to molecular diffusion. We have recently developed a new methodology that combines FCS and FRET (fluorescence energy transfer) and allows conformational dynamics to be analyzed independently of the fluctuations caused by diffusion. I will discuss this new approach and present recent experimental applications.