3790 research outputs found
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George Eliot in Romantic Biofiction
Get PDFBook review of The Honeymoon, by Dinitia Smith, published 2016 by Other PressPublishe
Spectral properties and associated plasma energization by magnetosonic waves in the Earth's magnetosphere: Particle-in-cell simulations
Get PDFIn this paper, we perform a 1-D particle-in-cell (PIC) simulation model consisting of three species, cold electrons, cold ions, and energetic ion ring, to investigate spectral structures of magnetosonic waves excited by ring distribution protons in the Earth's magnetosphere, and dynamics of charged particles during the excitation of magnetosonic waves. As the wave normal angle decreases, the spectral range of excited magnetosonic waves becomes broader with upper frequency limit extending beyond the lower hybrid resonant frequency, and the discrete spectra tends to merge into a continuous one. This dependence on wave normal angle is consistent with the linear theory. The effects of magnetosonic waves on the background cold plasma populations also vary with wave normal angle. For exactly perpendicular magnetosonic waves (parallel wave number k(parallel to) = 0), there is no energization in the parallel direction for both background cold protons and electrons due to the negligible fluctuating electric field component in the parallel direction. In contrast, the perpendicular energization of background plasmas is rather significant, where cold protons follow unmagnetized motion while cold electrons follow drift motion due to wave electric fields. For magnetosonic waves with a finite k(parallel to), there exists a nonnegligible parallel fluctuating electric field, leading to a significant and rapid energization in the parallel direction for cold electrons. These cold electrons can also be efficiently energized in the perpendicular direction due to the interaction with the magnetosonic wave fields in the perpendicular direction. However, cold protons can be only heated in the perpendicular direction, which is likely caused by the higher-order resonances with magnetosonic waves. The potential impacts of magnetosonic waves on the energization of the background cold plasmas in the Earth's inner magnetosphere are also discussed in this paper.Publishe
How Writing Contributes to Learning: New Findings from a National Study and Their Local Application
No full textAnderson, P., Anson, C. M., Fish, T., Gonyea, R. M., Marshall, M., Menefee-Libey, W., Paine, C., Blake, L. P., Weaver, S. (2017). How writing contributes to learning: New findings from a national study and their local application. Peer Review, (19)1. https://www.aacu.org/peerreview/2017/Winter/AndersonPublishedYe
Ticks and Tick-Borne Illnesses of Alabama
Get PDFPresentation to a hunter education class on ticks and tick-borne illnesses, their risks, and related preventative/avoidance measures. Also includes a summary of Auburn University's research efforts and preliminary results.Analyses in progressN
The ion temperature gradient: An intrinsic property of Earth's magnetotail
Get PDFAlthough the ion temperature gradient along (X-GSM) and across (Z(GSM)) the Earth's magnetotail, which plays a key role in generating the cross-tail current and establishing pressure balance with the lobes, has been extensively observed by spacecraft, the mechanism responsible for its formation is still unknown. We use multispacecraft observations and three-dimensional (3-D) global hybrid simulations to reveal this mechanism. Using THEMIS (Time History of Events and Macroscale Interactions during Substorms), Geotail, and ARTEMIS (Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun) observations during individual, near-simultaneous plasma sheet crossings from 10 to 60 R-E, we demonstrate that the ion temperature Z(GSM) profile is bell-shaped at different geocentric distances. This Z(GSM) profile is also prevalent in statistics of similar to 200 THEMIS current sheet crossings in the near-Earth region. Using 3-D global hybrid simulations, we show that mapping of the X-GSM gradient of ion temperature along magnetic field lines produces such a bell-shaped profile. The ion temperature mapping along magnetic field lines in the magnetotail enables construction of two-dimensional distributions of these quantities from vertical (north-south) spacecraft crossings. Our findings suggest that the ion temperature gradient is an intrinsic property of the magnetotail that should be considered in kinetic descriptions of the magnetotail current sheet. Toward this goal, we use theoretical approaches to incorporate the temperature gradient into kinetic current sheet models, making them more realistic.PublishedYe
The ion temperature gradient: An intrinsic property of Earth's magnetotail
Get PDFAlthough the ion temperature gradient along (X GSM) and across (Z GSM) the Earth's magnetotail, which plays a key role in generating the cross‐tail current and establishing pressure balance with the lobes, has been extensively observed by spacecraft, the mechanism responsible for its formation is still unknown. We use multispacecraft observations and three‐dimensional (3‐D) global hybrid simulations to reveal this mechanism. Using THEMIS (Time History of Events and Macroscale Interactions during Substorms), Geotail, and ARTEMIS (Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun) observations during individual, near‐simultaneous plasma sheet crossings from 10 to 60 R E , we demonstrate that the ion temperature Z GSM profile is bell‐shaped at different geocentric distances. This Z GSM profile is also prevalent in statistics of ~200 THEMIS current sheet crossings in the near‐Earth region. Using 3‐D global hybrid simulations, we show that mapping of the X GSM gradient of ion temperature along magnetic field lines produces such a bell‐shaped profile. The ion temperature mapping along magnetic field lines in the magnetotail enables construction of two‐dimensional distributions of these quantities from vertical (north‐south) spacecraft crossings. Our findings suggest that the ion temperature gradient is an intrinsic property of the magnetotail that should be considered in kinetic descriptions of the magnetotail current sheet. Toward this goal, we use theoretical approaches to incorporate the temperature gradient into kinetic current sheet models, making them more realistic.Publishe
Proton velocity ring-driven instabilities and their dependence on the ring speed: Linear theory
Get PDFLinear dispersion theory is used to study the Alfven-cyclotron, mirror and ion Bernstein instabilities driven by a tenuous (1%) warm proton ring velocity distribution with a ring speed, v(r), varying between 2v(A) and 10v(A), where v(A) is the Alfven speed. Relatively cool background protons and electrons are assumed. The modeled ring velocity distributions are unstable to both the Alfven-cyclotron and ion Bernstein instabilities whose maximum growth rates are roughly a linear function of the ring speed. The mirror mode, which has real frequency omega(r)=0, becomes the fastest growing mode for sufficiently large v(r)/v(A). The mirror and Bernstein instabilities have maximum growth at propagation oblique to the background magnetic field and become more field-aligned with an increasing ring speed. Considering its largest growth rate, the mirror mode, in addition to the Alfven-cyclotron mode, can cause pitch angle diffusion of the ring protons when the ring speed becomes sufficiently large. Moreover, because the parallel phase speed, v(vertical bar ph), becomes sufficiently small relative to v(r), the low-frequency Bernstein waves can also aid the pitch angle scattering of the ring protons for large v(r). Potential implications of including these two instabilities at oblique propagation on heliospheric pickup ion dynamics are discussed.Publishe
Ion Bernstein instability as a possible source for oxygen ion cyclotron harmonic waves
Get PDFThis paper demonstrates that an ion Bernstein instability can be a possible source for recently reported electromagnetic waves with frequencies at or near the singly ionized oxygen ion cyclotron frequency, Omega(+)(O), and its harmonics. The particle measurements during strong wave activity revealed a relatively high concentration of oxygen ions (similar to 15%) whose phase space density exhibits a local peak at energy similar to 20 keV. Given that the electron plasma-to-cyclotron frequency ratio is omega(pe)/Omega(e) greater than or similar to 1, this energy corresponds to the particle speed v/v(A) . greater than or similar to 0.3, where v(A) is the oxygen Alfven speed. Using the observational key plasma parameters, a simplified ion velocity distribution is constructed, where the local peak in the oxygen ion velocity distribution is represented by an isotropic shell distribution. Kinetic linear dispersion theory then predicts unstable Bernstein modes at or near the harmonics of Omega(+)(O) and at propagation quasi-perpendicular to the background magnetic field, B-0. If the cold ions are mostly protons, these unstable modes are characterized by a low compressibility (vertical bar delta B-parallel to vertical bar(2)/vertical bar delta B vertical bar(2) less than or similar to 0.01), a small phase speed (v(ph) similar to 0.2v(A)), a relatively small ratio of the electric field energy to the magnetic field energy (between 10(-4) and 10(-3)), and the Poynting vector directed almost parallel to B-0. These linear properties are overall in good agreement with the properties of the observed waves. We demonstrate that superposition of the predicted unstable Bernstein modes at quasi-perpendicular propagation can produce the observed polarization properties, including the minimum variance direction on average almost parallel to B-0.Publishe
Enhancing Diversity in Undergraduate Science: Self-Efficacy Drives Performance Gains with Active Learning
Get PDFEfforts to retain underrepresented minority (URM) students in science, technology, engineering, and mathematics (STEM) have shown only limited success in higher education, due in part to a persistent achievement gap between students from historically underrepresented and well-represented backgrounds. To test the hypothesis that active learning disproportionately benefits URM students, we quantified the effects of traditional versus active learning on student academic performance, science self-efficacy, and sense of social belonging in a large (more than 250 students) introductory STEM course. A transition to active learning closed the gap in learning gains between non-URM and URM students and led to an increase in science self-efficacy for all students. Sense of social belonging also increased significantly with active learning, but only for non-URM students. Through structural equation modeling, we demonstrate that, for URM students, the increase in self-efficacy mediated the positive effect of active-learning pedagogy on two metrics of student performance. Our results add to a growing body of research that supports varied and inclusive teaching as one pathway to a diversified STEM workforce.PublishedYe