Bulletin of the American Physical Society
2018 Joint Fall Meeting of the Texas Sections of APS, AAPT and Zone 13 of the SPS
Volume 63, Number 18
Friday–Saturday, October 19–20, 2018; University of Houston, Houston, Texas
Session C01: Biophysics and Soft Matter I |
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Chair: Greg Morrison, University of Houston Room: Science and Engineering Classroom (SEC) 102 |
Friday, October 19, 2018 2:25PM - 2:37PM |
C01.00001: A new design of an electrostatic quadrupole quadruplet focusing lens system for low MeV multi-ion micro-beam H. Arya, V. A. Chirayath, M. Jin, A. H. Weiss, G. Glass, Y. Chi The progress in the understanding of ion induced damage of cellular matrix has lagged behind the development of techniques in heavy ion therapy (HIT). In order to fill this gap, we have initiated an inter-university effort for the construction of a new sub-micron ion beam to perform fine controlled radiobiological studies with a variety of ions (with energies up to 4.5 MeV/charge(q)). In this work, we present our new design of an electrostatic quadrupole quadruplet (EQQ) lens system that will be used for the production of the sub-micron beam. Its demagnification factor (Df) is 33 at a working distance (Dw) of 98 mm for 3MeV/q ion beams with an emittance of 0.2 μm-mrad at the object aperture. Compared to the EQQ tested under similar input beam conditions at the Columbia University (CU) micro beam1, our Df is 8 times higher at comparable Dw. Our design achieves a comparable focusing performance to the separated EQ triplet (EQT) lens system1 (Df ~ 38 and Dw ~ 126 mm), but with a compact lens design and fewer quadrupoles. Our study also shows that EQQ has chromatic aberration very similar to and better spherical aberration than that of EQT. The simulations were done using SIMION 8.1® and GICOSY that were bench marked by reproducing the measured beam parameters of the CU micro beam1. |
Friday, October 19, 2018 2:37PM - 2:49PM |
C01.00002: Temperature Dependence of Proton NMR Relaxation Times at Earth's MagneticField Fatemeh Khashami, Peter J Niedbalski, David Clark, Christopher Parish, Yusef Maleki, Alan Paul Zanders, Qing Wang, Lloyd Lumata In this study, we have investigated the spin-lattice relaxation time (T1) of water-glycerol mixtures at the earth's magnetic field. The water 1H T1's at differing ratios of water-glycerol contents were measured at different temperatures ranging from 253.15 K to 353.15 K. Our results indicate that, water 1H T1 increases linearly with temperature. The addition of higher glycerol content into the mixture decreases the slope of this linear relationship and, disrupts the linearity of this behavior at low temperatures. Our experimental results are compared to the theoretical predictions in light of the Bloembergen-Pound-Purcell (BPP) theory, where a remarkable agreement between the theory and the experiment is observed. |
Friday, October 19, 2018 2:49PM - 3:01PM |
C01.00003: Dynamic Nuclear Polarization: Increasing MRI Signals by >10,000-fold Lloyd Lumata Dynamic nuclear polarization (DNP) via the dissolution method is an emerging physics technique that amplifies the nuclear magnetic resonance (NMR) or imaging (MRI) signals by several thousand-fold. The MRI signal amplification works via microwave-driven transfer of the high electron spin alignment to the nuclear spins at high magnetic field and low temperature. The frozen hyperpolarized samples are then dissolved into hyperpolarized liquids at physiologically tolerable temperatures for in vivo metabolic imaging applications. In this talk, the current DNP instrumental advances and applications to cancer imaging diagnostics will be discussed. In particular, the optimization methods to maximize MRI signal enhancements by >10,000-fold will be discussed in light of its applications in tracking abnormal metabolism in aggressive cancers. |
Friday, October 19, 2018 3:01PM - 3:13PM |
C01.00004: Graph-Based Ginzburg-Landau Energy Functional Theory For Soft Matter Yossi Eliaz, Margaret S Cheung We consider a binary mixture of particles in equilibrium, and a nonequilibrium actomyosin network for investigating the phases and the mechanism of collective self-assembly. In our simulations, binary mixture becomes phase-separated above a critical temperature. Next, we study a dynamical system of actomyosin networks which undergo contraction and gelation. We developed a graph theory based model that examines and predicts the generic features in the dynamics and thermodynamics of self-assembly. First we translate a complex biophysical system into a graph, then extracting meaningful reaction coordinates and order parameters from the graph. We capture phase separation in a binary mixture when using its bipartite graph’s Min-Cut as an order parameter in a Landau Free Energy Functional. For actomyosin networks, we construct the graph from the adjacency matrix of the actin filaments’ monomers. Establishing this renormalization framework allows to build graphs from cytoskeleton super resolution experiments and to link together analytical, simulated, and experimental data. |
Friday, October 19, 2018 3:13PM - 3:25PM |
C01.00005: Abstract Withdrawn
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Friday, October 19, 2018 3:25PM - 3:37PM |
C01.00006: Resolving the Interfaces in C60-SubPC Organic Solar Cells Using Molecular Dynamics Simulations Jacob Tinnin, Pengzhi Zhang, Eitan Geva, Barry Dunietz, Margaret S Cheung Organic photovoltaic cells (OPVs) are still associated with relative low efficiencies despite recent advances. As the performance depends on the molecular dynamics (MD) and structure, it is crucial to understand this relationship at a quantitative level. To do this we analyzed the well-studied dyad of boron subphthalocyanine chloride (SubPC) and C60 using MD simulations to understand the effects of device fabrication scheme on the materials interfaces. We developed order parameters to resolve the interface at the molecular level. Using importance sampling, we find an additional interfacial geometry over the two primary configurations addressed in the previous studies. In addition, we show that, due to an energy barrier between basins, the population of structures depends on the initial set-up which is used to differentiate between the fabrication schemes. We expect that the insight we provide will enhance efforts to design effective OPVs. |
Friday, October 19, 2018 3:37PM - 3:49PM |
C01.00007: Molecular Mechanisms of the Interhead Coordination by Interhead Tension in Cytoplasmic Dyneins Qian Wang, Biman Jana, Michael Diehl, Margaret Cheung, Anatoly Kolomeisky, José Onuchic Cytoplasmic dyneins play a major role in retrograde cellular transport along microtubule filaments. Dyneins are multidomain motor proteins with two heads that coordinate their motion via their interhead tension. Compared with the leading head, the trailing head has a higher detachment rate from microtubules, facilitating the movement. However, the molecular mechanism of such coordination is unknown. To elucidate this mechanism, we performed molecular dynamics simulations on a cytoplasmic dynein to probe the effect of the interhead tension on the structure. The tension creates a torque that influences the head rotating about its stalk. The conformation of the stalk switches from the α registry to the β registry during the rotation, weakening the binding affinity to microtubules. The directions of the tension and the torque of the leading head are opposite to those of the trailing head, breaking the structural symmetry between the heads. The leading head transitions less often to the β registry than the trailing head. The former thus has a greater binding affinity to the microtubule than the latter. |
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