# TREND 2014

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**August 8, 2014**

**On this page... TREND 2014 Presentations **

**Role of substrate topography on actin organization and dynamics in tumor associated fibroblasts****The impact of imperfect information on network attack****Synchronized chaos in diffusively coupled optical feedback networks****Understanding the dynamics of soap bubble pinch-off****Supersymmetric quantum mechanics and reflectionless potentials****Modeling and characterization of soliton trains in an electron beam****Electromagnetic cavities as an analog to chaos regularization of quantum tunneling rates****Non-equilibrium dynamics in ultracold interacting atoms****High current stabilization circuit for ultracold atom trap****Guiding sensor arrays for Lagrangian data assimilation in a point vortex flow****Granular Impact Dynamics: Effect of intruder shape**

**Winners of TREND Fair 2014**

**Best Overall Project: **

**"Electromagnetic cavities as an analog to chaos regularization of quantum tunneling rates" by Rachel Owen, Western Washington University**

**Two projects were equally deserving to receive the award for Runner-Up for Best Overall Project: **

**"Modeling and characterization of soliton trains in an electron beam," Jared Ginsberg, Cornell University
"Non-equilibrium dynamics in ultracold interacting atoms," Sergio Smith, Howard University**

**Role of substrate topography on actin organization and dynamics in tumor associated fibroblasts**

**(Presentation, Poster) **

**Kevin Belnap, Brigham Young University**

**Advisor: Dr. Arpitah Upadhyaya**

**Fibroblast cells are critical to the support of most tissues because they secrete the proteins necessary for the development of the extracellular matrix (ECM). In the case of pancreatic cancer, tumor associated fibroblasts (TAF) have been shown to support high tumor density and cancer metastasis. While the correlation of TAFs with pancreatic tumors is well demonstrated, the source of their malignant contribution remains unclear. Therefore, understanding how these cells interact with their environments is critical. Of particular interest are the cytoskeletal dynamics of actin filaments and acting binding proteins (ABP). Using fluorescence microscopy, and a fluorescently labeled ABP called palladin as a marker, we identified actin stress fibers in the cell. By exposing the cells to substrates of varied topography, we demonstrated the mechanosensitivity of the fibroblasts. While the exact mode of cell sensation is unknown, we explore different analysis methods to study cytoskeletal structure and motion, which may lead to future understanding of this process. **

** **

**The impact of imperfect information on network attack**

**Jesus Caloca, Boise State University**

**Andrew Melchionna, University of Rochester**

**Advisors: Profs. Tom Antonsen, Michelle Girvan, and Ed Ott**

**A complex network can be used as an effective basis for modelling systems in which connectivity is important. Examples include the World-Wide-Web, social associations of individuals, and genetic regulatory networks. We study the effect of attacks on the percolation of complex networks, where the assumed purpose of the attack is to reduce the size of the largest connected component of the network. We consider attacks which consist of successive removal of network nodes, and we evaluate the impact of the attacker having imperfect information about the network (i.e., false and/or missing network links). We observe that dynamical importance and betweenness centrality-based attacks are surprisingly robust to the presence of a moderate amount of imperfect information and are more effective compared to simpler degree-based attacks. **

**Synchronized chaos in diffusively coupled optical feedback networks**

**(Presentation, Poster) **

**Katherine Coppess, University of Michigan**

**Brianna Mork, Gustavus Adolphus College**

**Advisors: Profs. Tom Muprhy and Raj Roy**

**Synchronization in oscillator networks, where two or more oscillators evolve in unison, has important applications in communications, power distribution, electronics, and biology. To experimentally investigate synchrony in small networks, four identical optoelectronic oscillators are coupled together to form a configurable network with several adjustable parameters, allowing for the exploration of different dynamics and synchronization states. Keeping other parameters constant, feedback and coupling strengths are varied for multiple topologies to investigate the synchrony of the network under both periodic and chaotic conditions. We simulate and experimentally demonstrate stable stats of synchrony between oscillators in the network. We compare experimental and simulated results with symmetry analysis predictions of topology-dependent states of global and cluster synchrony. **

**Understanding the dynamics of soap bubble pinch-off**

**(Presentation, Poster) **

**Courtney Cromartie, University of Maryland**

**Advisor: Prof. Dan Lathrop**

**In topology, any change producing additional sides or a break in the surface is usually associated with a singularity. We sought to better understand the topological changes that occur when a soap bubble is pinched off the main film body until it breaks or pops. While on the molecular scale these are not true singularities, the topological changes during bubble pinch-off indicate two singularity-like events: the first when the internal walls of the soap film meet to form a solid column of soap solution, and the second when the column of solution physically separates from the main film body. We developed an apparatus to consistently produce similarly sized bubbles in an enclosed space. Using high-speed camera footage, we documented the full process from bubble formation to destruction. From these images, we used edge-tracing software to determine the geometry associated with various stages of the process. We used dimensional analysis to better understand the forces (e.g., surface tension, kinetic energy) at play in the soap solution that drive the first singularity-like event.**

**Supersymmetric quantum mechanics and reflectionless potentials**

**(Presentation, Poster) **

**Kahlil Dixon, Howard University**

**Advisor: Dr. Victor Galitski**

**In the following presentation, I will review some of the consequences of supersymmetric quantum mechanics. This includes a discussion of supersymmetric Hamiltonian formalism, as well as a discussion of scattering properties and how symmetric potential functions can share these properties. Results from using this formulism with the particle in a box and quantum oscillator examples were studied. Examples of super potential functions that correspond with non-trivial reflectionless potentials are given, in addition to a general discussion of supersymmetry and topological boundary modes.**

**(Work supported in part by NSF through the PFC@JQI)**

**Modeling and characterization of soliton trains in an electron beam**

**Jared Ginsberg, Cornell University**

**Advisors: Dr. Brian Beaudoin and Prof. Rami Kishek**

**I have studied and characterized large amplitude perturbations in high brightness electron beams. The development of solitons from such perturbations is compared with analytical results using numerical differential equation solving techniques within Mathematica. Solitons are waves that behave like particles in that neither time evolution nor collisions with other solitons change their size, shape, or velocity. Electron beam solitons, though predicted theoretically decades ago, were only first observed in recent experiments at the University of Maryland Electron Ring (UMER). In UMER, an induction cell uses a potential difference to create a relatively narrow energy perturbation on a long, rectangular electron beam. Sufficiently strong perturbations develop into trains of ~5 solitons moving in unison along this beam over a ~30 microsecond beam lifetime. It is the solitons in these trains for which I will describe the relative velocities and spacing, and for which I present comparisons of experimental data and numerical results. **

**Electromagnetic cavities as an analog to chaos regularization of quantum tunneling rates**

**(Presentation, Poster) **

**Rachel Owen, Western Washington University**

**Advisor: Dr. John Rodgers**

**For two-dimensional, symmetric, double-well potentials separated byb a tunneling barrier, it has been shown theoretically that quantum mechanical tunneling rates are dependent on the shape of the well in the limit of small quantum wavelength. Shapes that support chaotic wave functions produce statistically smaller fluctuations in the tunneling rate than classical (integrable) wells. This effect is called "regularization" of tunneling rates and can be analyzed by examining the splitting in energy level between symmetric and antisymmetric wave functions. Utilizing the similarity in the wave natures of a quantum mechanical particle in a symmetric double-well and transverse electromagnetic waves in a 2-D cavity, we investigate chaos regularization in coupled microwave cavities, both numerically and experimentally. The difference between the antisymmetric and symmetric eigenstate frequencies squared and evanescent electromagnetic wave propagation in a cutoff tunnel is shown to be analagous to energy splitting and quantum mechanical tunneling, respectively. This analogy allows investigation of regularization in various microwave cavities and, by extension to a lab-scale model, the behavior of complex quantum mechanical systems. **

**Non-equilibrium dynamics in ultracold interacting atoms**

**(Presentation, Poster) **

**Sergio Smith, Howard University**

**Advisor: Dr. Michael Foss-Feig**

**Counter-propagating lasers may be used to create a lattice of standing electromagnetic waves, or an optical lattice. Ultracold atoms within the lattice become trapped within discrete regions of high interaction between the atoms and light, known as potential wells. While the potential in these wells is classically too high to allow the atoms to move from one to the next, atoms may "tunnel" to neighboring wells. Movement between sites is affected by interactions with other atoms. This research as concerned with creating computer simulations of the evolution of non-equilibrium distributions of atoms in a lattice and examining the effect of the interaction between atoms on the rate of tunneling. **

**(Work supported in part by NSF through the PFC@JQI) **

**High current stabilization circuit for ultracold atom trap**

**(Presentation, Poster) **

**Smita Speer, Howard University**

**Advisor: Dr. Ryan Price**

**Bose-Einstein condensates (BECs) are created through laser cooling and magnetic evaporative cooling of a dense group of atoms to temperatures close to 0 degrees Kelvin. Our ultracold atoms group studies the properties and behavior of BECs within magneto-optical and magnetic traps in our lab. Electromagnetic coils in our lab are used to produce magnetic fields to contain and interact with the Rubidium atoms; fluctuations in the current-carrying coils results in the production of magnetic field noise that interferes with the experiment. My research focused on creating a configuration of operational amplifiers (op amps) designed to filter and stabilize the current and reduce the noise present in our ultracold atom traps. In order to withstand current between -30 and 30 amps, we integrated our op amp configuration with a printed circuit board to protect the op amp, as well as to actively regulate the current to a precision of 0.1mA. Our op amps are attached to aluminum heat sinks and liquid cooling plates, and they are housed in an aluminum rack. Future work on this system will include tests for increased current and magnetic field stability, as well as precision of current control. **

**(Work supported in part by NSF through the PFC@JQI)**

**Guiding sensor arrays for Lagrangian data assimilation in a point vortex flow**

**(Presentation) **

**Storm Weiner, University of California - Berkeley**

**Advisor: Prof. Derek Paley**

**We use a two point-vortex model to develop a sensor control system for estimating geophysical flows. The vortex state is estimated by assimilating position measurements using an Ensemble Kalman Filter and a full nonlinear model. Lyapunov control laws are explored using the first order self-propelled particle model. The efficacy of different collective motion states of the sensors will be explored. Following ideas from (DeVries 2013), we expect that trajectories which explore the topologically distinct regions of phase space will yield accurate estimations of the multi-vortex state. Using various geometrical M-functions, this schema can be adapted to nonintegrable vortex systems and other, more complicated, flow models. Our goal is to develop a cooperative, dynamic sensory array which can outperform lagrangian sensors. These methods can be applied to climate, weather, and pollution monitoring systems.**

**Granular Impact Dynamics: Effect of intruder shape**

**(Presentation, Poster)**

**Shola Wylie, Mount Holyoke College**

**Advisor: Prof. Wolfgang Losert**

**When an object impacts a granular material, the particles collectively exert a force that stops the intruder. In previous studies, a universal scaling law that relates the total drop height to the final depth has been used to describe these impacts. While this scaling law accurately describes the motion of many spherical intruder-particle interactions, it has yet to be systematically proven for impacts with non-spherical intruders. Previous work conducted by different labs has produced models that predict a modified scaling law for non-spherical intruders. This work has yet to be experimentally proven for three dimensional intruder-particle interactions. We examine how the motions of the intruder and the particles change with intruder shape and how the scaling law can be modified to account for such differences. To investigate the effect of intruder shape, we used a novel imaging technique that allows us to capture the interior of a three-dimensional granular system under impact. Using this technique, we can measure microscopic properties of the grain trajectories to determine their effect on the macroscopic intruder depth. **