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Full-Text Articles in Physics
Evidence For Electron Energization Accompanying Spontaneous Formation Of Ion Acceleration Regions In Expanding Plasmas, Evan M. Aguirre, Rikard Bodin, Neng Yin, Timothy N. Good, Earl E. Scime
Evidence For Electron Energization Accompanying Spontaneous Formation Of Ion Acceleration Regions In Expanding Plasmas, Evan M. Aguirre, Rikard Bodin, Neng Yin, Timothy N. Good, Earl E. Scime
Physics and Astronomy Faculty Publications
We report experiments conducted in an expanding argon plasma generated in the inductive mode of a helicon source in the Hot hELIcon eXperiment–Large Experiment on Instabilities and Anisotropies facility. As the neutral gas pressure increases, the supersonic ion acceleration weakens. Increasing neutral pressure also alters the radial profile of electron temperature, density, and plasma potential upstream of the plasma expansion region. Langmuir probe measurements of the electron energy probability function (EEPF) show that heating of electrons at the plasma edge by RF fields diminishes with increasing gas pressure, yielding a plasma with a centrally peaked electron temperature, and flat potential …
Testing A Thermodynamic Approach To Collective Animal Behavior In Laboratory Fish Schools, Julia A. Giannini, James G. Puckett
Testing A Thermodynamic Approach To Collective Animal Behavior In Laboratory Fish Schools, Julia A. Giannini, James G. Puckett
Physics and Astronomy Faculty Publications
Collective behaviors displayed by groups of social animals are observed frequently in nature. Understanding and predicting the behavior of complex biological systems is dependent on developing effective descriptions and models. While collective animal systems are characteristically nonequilibrium, we can employ concepts from equilibrium statistical mechanics to motivate the measurement of material-like properties in laboratory animal aggregates. Here, we present results from a new set of experiments that utilize high speed footage of two-dimensional schooling events, particle tracking, and projected static and dynamic light fields to observe and control the behavior of negatively phototaxic fish schools (Hemigrammus bleheri). First, …
Additive Modulation Of Dna-Dna Interactions By Interstitial Ions, Wei Meng, Raju Timsina, Abby Bull, Kurt Andresen, Xiangyun Qiu
Additive Modulation Of Dna-Dna Interactions By Interstitial Ions, Wei Meng, Raju Timsina, Abby Bull, Kurt Andresen, Xiangyun Qiu
Physics and Astronomy Faculty Publications
Quantitative understanding of biomolecular electrostatics, particularly involving multivalent ions and highly charged surfaces, remains lacking. Ion-modulated interactions between nucleic acids provide a model system in which electrostatics plays a dominant role. Using ordered DNA arrays neutralized by spherical cobalt3+ hexammine and Mg2+ ions, we investigate how the interstitial ions modulate DNA-DNA interactions. Using methods of ion counting, osmotic stress, and x-ray diffraction, we systematically determine thermodynamic quantities, including ion chemical potentials, ion partition, DNA osmotic pressure and force, and DNA-DNA spacing. Analyses of the multidimensional data provide quantitative insights into their interdependencies. The key finding of this study is that …
Similarities Between Insect Swarms And Isothermal Globular Clusters, Dan Gorbonos, Kasper Van Der Vaart, Michael Sinhuber, James G. Puckett, Andrew M. Reynolds, Nicholas T. Ouellette, Nir S. Gov
Similarities Between Insect Swarms And Isothermal Globular Clusters, Dan Gorbonos, Kasper Van Der Vaart, Michael Sinhuber, James G. Puckett, Andrew M. Reynolds, Nicholas T. Ouellette, Nir S. Gov
Physics and Astronomy Faculty Publications
Previous work has suggested that disordered swarms of flying insects can be well modeled as self-gravitating systems, as long as the “gravitational” interaction is adaptive. Motivated by this work, we compare the predictions of the classic, mean-field King model for isothermal globular clusters to observations of insect swarms. Detailed numerical simulations of regular and adaptive gravity allow us to expose the features of the swarms' density and velocity profiles that are due to long-range interactions and are captured by the King model phenomenology, and those that are due to adaptivity and short-range repulsion. Our results provide further support for adaptive …