Photorefractive Polymers: Amalgamation of Organic Chemistry, Solid State Physics and Optics

Mohammad Samiullah
Physics Department, Truman State University

In recent years, considerable progress has been made in developing organic materials for Opto-electronics and photonics, driven by the prospect of manufacturing flexible, low-cost devices. In many organic photoconductors the refractive index may be modified by an exposure to low power laser light. The interference of laser beams is used to create a modulated refractive index inside these materials, which serves as a dynamic diffraction grating for a number of applications such as holography, optical phase conjugation, image processing, data storage and real-time parallel information processing. I will review the basics of the photorefractive effect and the organic materials where photorefractive effect has been observed. I will then present a model that incorporates the elementary electronic processes in organic polymers, in order to better understand the emergence of the photorefractive effect in these materials.

Level: Intermediate

Truman alumnus, Brian Ruzicka, had two papers published in the past year in the prestigious physics journal Physical Review Letters: Brian A. Ruzicka, Lalani K. Werake, Guowei Xu, Jacob B. Khurgin, E. Ya. Sherman, Judy Z. Wu, and Hui Zhao, “Second-Harmonic Generation Induced by Electric Currents in GaAs”, Phys. Rev. Lett. 108, 077403 (2012) and Lalani K. Werake, Brian A. Ruzicka, and Hui Zhao, “Observation of Intrinsic Inverse Spin Hall Effect”, Phys. Rev. Lett. 106, 107205 (2011). Congratulations Brian!

A Wonderful Coincidence: Carnegie, Einstein, Hubble, and Lemaitre

Gary L. Cameron
Department of History, Iowa State University

In the first three decades of the 20th century, four men discovered inconsistencies in current world views. A wealthy and ruthless Scottish-American capitalist found that supporting the arts and sciences had value beyond making personal wealth and power. A German-Swiss patent clerk discovered inconsistencies in Newtonian physics and solved them with a revolutionary new idea. An American astronomer from Missouri used Carnegie’s steel and fortune to explore inconsistencies in astronomical observation and theory. A Belgian mathematician explored inconsistencies in the ‘New Physics’ and uncovered an astounding result with implications for the entire universe, confirmed by astronomical observations unknown to him at the time. Four important historical figures, Carnegie, Einstein, Hubble, and Lemaitre, each from a very different world, came together coincidentally between 1900 and 1930 to completely change humanity’s world views of the universe as a whole.

Level: Intermediate

Kevin Satzinger, current Truman Physics senior, was co-author on an article that just came out in Nanotechnology, “High spatial resolution Kelvin probe force microscopy with coaxial probes,” based on his previous summer REU work.

Building a Dynamic Nucleon-Nucleon Interaction

Jonathan Morris (Truman alum)
Department of Science, St Louis Community College at Forest Park

Since Yukawa’s meson hypothesis in 1935, nuclear theorists have been trying to understand the fundamental interaction between nucleons. This Nucleon-Nucleon (NN) potential has resisted attempts at clarification. One reason for this is that the underlaying substructure of the nucleons (QCD) cannot (yet) easily be used to predict nucleon-nucleon scattering observables. This means that physicists “on the ground,” so to speak, must often rely on phenomenological nucleon-nucleon interaction models to do microscopic calculations of nuclear structure. All of the currently used NN potentials employ the static approximation, wherein the particles which mediate the nuclear force are assumed to transfer no energy. In this talk I will discuss our refitting of the Reid Soft Core potential with the inclusion of dynamic pions which explicitly transfer energy. I then show that this new dynamic potential leads to very different in-medium behavior of nucleons. In particular it shows some promise in clarifying the long outstanding problem of nuclear saturation.

Level: Advanced

MEMS for Accelerators and Plasmas

Scott Kovaleski
Department of Electrical and Computer Engineering, University of Missouri—Columbia

Accelerators and plasma sources are generally thought of as large, power hungry systems. Linear accelerators are from a few meters to kilometers long, fusion plasmas require mega-amperes of current, and plasma etching requires kilowatts of radio-frequency power, for example. Microelectromechanical systems (MEMS) can be used to develop charged particle accelerators and plasma sources that are simple, compact, and low power. In most cases, the devices we are developing at the University of Missouri are based on lithium niobate piezoelectric transformers. These simple devices take a low voltage radio-frequency input signal to excite an orthogonal vibration mode via the inverse piezoelectric effect. This vibration can then produce a high voltage via the piezoelectric effect. These compact MEMS devices have been used to produce plasma ion sources for high specific impulse micro-spacecraft propulsion. We have also developed simple electrostatic accelerators that have yielded bremsstrahlung x-ray emission to energies >100 keV. These same high voltage accelerators are being developed to produce neutrons for active interrogation, radioactive source replacement, and other nuclear safeguards applications. This talk will focus on the theory of operation and design of piezoelectric transformers with lithium niobate, and will present some applications of and results from these sources.

Level: Advanced

Magnetic Patterns in Superconductors and Ferromagnets

Ruslan Prozorov
The Ames Laboratory and Department of Physics & Astronomy, Iowa State University

Conventional thermodynamics fails when dealing with finite samples that develop patterns, such as ferromagnetic domains or the intermediate state in type-I superconductors. The notion of the ground state has to be replaced by a more vague minimum energy state when the latter has to be calculated in the entire space taking into account stray fields and energy of the domain walls. However, macroscopic measurements are always conducted on the finite samples and yield integrals of the quantities of interest, so the interpretation of the results requires knowledge of the pattern structure. It turns out that these patterns can be highly unusual and their prediction requires non-standard approaches. Various nontrivial phenomena, such as topological hysteresis [1], suprafroth [2] and topological time-reversal symmetry breaking may be observed. I will present direct time-resolved magneto-optical imaging of magnetic patterns in ferromagnets and superconductors and show that some well-established theories, such as Landau’s theory of the intermediate state, have to be revisited. On the other hand, magnetic patterns may be used as model systems to study, for example, the physics of froths [2]. I will conclude with a proposition for the theorists to predict the “minimum energy pattern” using the “generators,” such as iterative function systems or the wavelets.

[1] R. Prozorov, “Equilibrium topology of the intermediate state in type-I superconductors of different shapes”, Phys. Rev. Lett. 98, 257001 (2007).

[2] R. Prozorov, A. F. Fidler, J. Hoberg, P. C. Canfield, “Suprafroth in type-I superconductors”, Nature Physics 4, 327 (2008)

Level: Intermediate

Perspective on the Japanese Fukushima Nuclear Power Plant Disaster

William H. Miller
Nuclear Science and Engineering Institute, University of Missouri – Columbia

On March 11, 2011, at 14:46 (JST), a severe earthquake measuring 9.0 on the Richter Scale occurred 112 miles (180 km) off the coast of the Fukushima Daiichi Nuclear Power Station – the largest Japan has ever experienced. It caused all of the operating units (units 1, 2, and 3) to automatically scram on seismic reactor protection system trips. The earthquake caused a loss of all off-site electrical power sources to the site. The emergency diesel generators automatically started and provided AC power to emergency systems. Forty-one minutes after the earthquake, at 15:27, the first of a series of seven tsunamis arrived at the site. The maximum tsunami height impacting the site was estimated to be 46 to 49 feet (14 to 15 meters). This exceeded the design basis tsunami height of 18.7 feet (5.7 meters) and was above the site grade levels of 32.8 feet (10 meters) at units. All AC power was lost to units 1-4 by 15:41 when a tsunami overwhelmed the site and flooded some of the emergency diesel generators and switchgear rooms. This presentation will discuss what happened at Fukushima and its current status, and will review the media response to the radiological consequences.

Level: Introductory

Investigating the Earliest Phases of Massive Star Formation

Esteban D. Araya
Department of Physics, Western Illinois University

Massive stars – stars with more than eight times the mass of the Sun – are responsible for the enrichment of the interstellar medium with heavy elements and the existence of extraordinary physical objects such as neutron stars and black holes. In this talk I will review some of our current work on the study of massive star formation. In particular, the formation of massive stars within molecular filaments and the discovery of periodic maser flares of several molecular species, which possibly trace periodic accretion events onto young massive binaries.

Level: Intermediate

Mutation, Speciation and Phase Transitions on a Neutral Landscape

Sonya Bahar
Department of Physics and Astronomy, University of Missouri—St Louis

I will discuss how clustering can occur in a neutral fitness landscape in a computational evolutionary model. This clustering simulates sympatric speciation: the organisms cluster phenotypically, but are not spatially separated. Moreover, clustering occurs not only in the case of assortative mating, but also in the case of bacteria-like splitting. Clustering is not observed in a control case where organisms can mate randomly. The population size and the number of clusters undergo phase-transition-like behavior as the maximum mutation size is varied. These results bear comparison with more mathematical studies of clustering on neutral landscapes in the context of branching and annihilating random walks, and have implications for the current debate over the value of “neutral” models in ecology and evolution.

Level: Intermediate