Open Access. Powered by Scholars. Published by Universities.®
Articles 1 - 7 of 7
Full-Text Articles in Physics
Temporal And Spatial Turbulent Spectra Of Mhd Plasma And An Observation Of Variance Anisotropy, D. A. Schaffner, Michael R. Brown, Vyacheslav S. Lukin , '00
Temporal And Spatial Turbulent Spectra Of Mhd Plasma And An Observation Of Variance Anisotropy, D. A. Schaffner, Michael R. Brown, Vyacheslav S. Lukin , '00
Physics & Astronomy Faculty Works
The nature of magnetohydrodynamic (MHD) turbulence is analyzed through both temporal and spatial magnetic fluctuation spectra. A magnetically turbulent plasma is produced in the MHD wind tunnel configuration of the Swarthmore Spheromak Experiment. The power of magnetic fluctuations is projected into directions perpendicular and parallel to a local mean field; the ratio of these quantities shows the presence of variance anisotropy which varies as a function of frequency. Comparisons among magnetic, velocity, and density spectra are also made, demonstrating that the energy of the turbulence observed is primarily seeded by magnetic fields created during plasma production. Direct spatial spectra are …
Columnar Molecular Aggregation In The Aqueous Solutions Of Disodium Cromoglycate, D. M. Agra-Kooijman, G. Singh, A. Lorenz, Peter J. Collings, H.-S. Kitzerow, S. Kumar
Columnar Molecular Aggregation In The Aqueous Solutions Of Disodium Cromoglycate, D. M. Agra-Kooijman, G. Singh, A. Lorenz, Peter J. Collings, H.-S. Kitzerow, S. Kumar
Physics & Astronomy Faculty Works
Stack, chimneylike, and threadlike assemblies have previously been proposed for the structure of disodium cromoglycate (DSCG) aggregates in aqueous solutions. The results of the synchrotron x-ray scattering investigations reported here reveal the formation of simple columnar assemblies with pi-pi stacking at a separation of 3.4 angstrom between the DSCG molecules. Lateral separation between the assemblies is concentration and temperature dependent, varying from similar to 35 to 42 angstrom in the orientationally ordered nematic (N) phase and from 27 to 32 angstrom in the columnar or middle (M) phase having long range lateral positional order. The assemblies' length depends on concentration …
Turbulence Analysis Of An Experimental Flux-Rope Plasma, D. A. Schaffner, Vyacheslav S. Lukin , '00, A. Wan, Michael R. Brown
Turbulence Analysis Of An Experimental Flux-Rope Plasma, D. A. Schaffner, Vyacheslav S. Lukin , '00, A. Wan, Michael R. Brown
Physics & Astronomy Faculty Works
We have previously generated elongated Taylor double-helix flux-rope plasmas in the SSX MHD wind tunnel. These plasmas are remarkable in their rapid relaxation (about one Alfven time) and their description by simple analytical Taylor force-free theory despite their high plasma beta and high internal flow speeds. We report on the turbulent features observed in these plasmas including frequency spectra, autocorrelation function, and probability distribution functions of increments. We discuss here the possibility that the turbulence facilitating access to the final state supports coherent structures and intermittency revealed by non-Gaussian signatures in the statistics. Comparisons to a Hall-MHD simulation of the …
Introductory Physics In Biological Context: An Approach To Improve Introductory Physics For Life Science Students, Catherine Hirshfeld Crouch, K. Heller
Introductory Physics In Biological Context: An Approach To Improve Introductory Physics For Life Science Students, Catherine Hirshfeld Crouch, K. Heller
Physics & Astronomy Faculty Works
We describe restructuring the introductory physics for life science students (IPLS) course to better support these students in using physics to understand their chosen fields. Our courses teach physics using biologically rich contexts. Specifically, we use examples in which fundamental physics contributes significantly to understanding a biological system to make explicit the value of physics to the life sciences. This requires selecting the course content to reflect the topics most relevant to biology while maintaining the fundamental disciplinary structure of physics. In addition to stressing the importance of the fundamental principles of physics, an important goal is developing students' quantitative …
Nexus/Physics: An Interdisciplinary Repurposing Of Physics For Biologists, E. F. Redish, C. Bauer, K. L. Carleton, T. J. Cooke, M. Cooper, Catherine Hirshfeld Crouch, B. W. Dreyfus, B. D. Geller, J. Giannini, J. S. Gouvea, M. W. Klymkowsky, W. Losert, K. Moore, J. Presson, V. Sawtelle, K. V. Thompson, C. Turpen, R. K.P. Zia
Nexus/Physics: An Interdisciplinary Repurposing Of Physics For Biologists, E. F. Redish, C. Bauer, K. L. Carleton, T. J. Cooke, M. Cooper, Catherine Hirshfeld Crouch, B. W. Dreyfus, B. D. Geller, J. Giannini, J. S. Gouvea, M. W. Klymkowsky, W. Losert, K. Moore, J. Presson, V. Sawtelle, K. V. Thompson, C. Turpen, R. K.P. Zia
Physics & Astronomy Faculty Works
In response to increasing calls for the reform of the undergraduate science curriculum for life science majors and pre-medical students (Bio2010, Scientific Foundations for Future Physicians, Vision & Change), an interdisciplinary team has created NEXUS/Physics: a repurposing of an introductory physics curriculum for the life sciences. The curriculum interacts strongly and supportively with introductory biology and chemistry courses taken by life-science students, with the goal of helping students build general, multi-discipline scientific competencies. NEXUS/Physics stresses interdisciplinary examples and the content differs markedly from traditional introductory physics to facilitate this: it extends the discussion of energy to include interatomic potentials and …
Observation Of Turbulent Intermittency Scaling With Magnetic Helicity In An Mhd Plasma Wind Tunnel, D. A. Schaffner, Adrian H. J. Wan , '15, Michael R. Brown
Observation Of Turbulent Intermittency Scaling With Magnetic Helicity In An Mhd Plasma Wind Tunnel, D. A. Schaffner, Adrian H. J. Wan , '15, Michael R. Brown
Physics & Astronomy Faculty Works
The intermittency in turbulent magnetic field fluctuations has been observed to scale with the amount of magnetic helicity injected into a laboratory plasma. An unstable spheromak injected into the MHD wind tunnel of the Swarthmore Spheromak Experiment displays turbulent magnetic and plasma fluctuations as it relaxes into a Taylor state. The level of intermittency of this turbulence is determined by finding the flatness of the probability distribution function of increments for magnetic pickup coil fluctuations B(t). The intermittency increases with the injected helicity, but spectral indices are unaffected by this variation. While evidence is provided which supports the hypothesis that …
Elasticity-Dependent Self-Assembly Of Micro-Templated Chromonic Liquid Crystal Films, M. A. Lohr, M. Cavallaro Jr., D. A. Beller, K. J. Stebe, R. D. Kamien, Peter J. Collings, A. G. Yodh
Elasticity-Dependent Self-Assembly Of Micro-Templated Chromonic Liquid Crystal Films, M. A. Lohr, M. Cavallaro Jr., D. A. Beller, K. J. Stebe, R. D. Kamien, Peter J. Collings, A. G. Yodh
Physics & Astronomy Faculty Works
We explore micropatterned director structures of aqueous lyotropic chromonic liquid crystal (LCLC) films created on square-lattice cylindrical-micropost substrates. The structures are manipulated by modulating the LCLC mesophases and their elastic properties via concentration through drying. Nematic LCLC films exhibit preferred bistable alignment along the diagonals of the micropost lattice. Columnar LCLC films, dried from nematics, form two distinct director and defect configurations: a diagonally aligned director pattern with local squares of defects, and an off-diagonal configuration with zig-zag defects. The formation of these states appears to be tied to the relative splay and bend free energy costs of the initial …