11-20 of 25 results
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Measuring Interstellar Temperature and Ionization Variations Using Observations of Faint Diffuse [OII] Emission
PI Edwin Mierkiewicz
The interstellar medium (ISM) plays a vital role in the ongoing cycle of stellar birth and death as well as galactic evolution. However the role of interstellar matter, from how its properties are influenced by stars to how, in turn, its properties influence star formation is poorly understood.
Within the past decade substantial strides have been made towards unraveling the mysteries of a major ISM component, the widespread warm ionized medium (WIM). The advances were enabled by innovative spectroscopic techniques to detect and study extremely faint interstellar emission lines in the visible spectral region. With such observations it is possible to explore the connection between the Galactic disk and halo as energy and gas are transferred away from massive star-forming regions to large distances from the midplane. An especially exciting development in this area is the evidence for temperature variations and the existence of a previously unrecognized source of heating within the WIM. The emission line of ionized oxygen in the near ultraviolet spectral region (372.7 nm) is key to exploring variations in temperature and ionization state within the gas, and for investigating the role of this additional heating. Our [OII] observations will (1) provide the only opportunity to separate unambiguously variations in temperature from variations in ionization conditions in the warm ionized medium of our Galaxy and (2) confirm whether H-alpha, [NII], and [SII] data can provide reliable temperature information about diffuse ionized gas in our own and other galaxies.Categories: Faculty-Staff
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High Spectral Resolution Observations of Lunar Exospheric Emissions
PI Edwin Mierkiewicz
We are employing high-resolution Fabry-Perot spectroscopy of neutral sodium and potassium emission to investigate the morphology and dynamics of the lunar sodium exosphere. Likely atmosphere source mechanisms are thermal desorption, photo-desorption, ion sputtering, and meteoric impact ablation.
Their relative importance remains uncertain, both with regard to spatial and to temporal trends. Once released, sputtered gases in the lunar atmosphere can be pulled back to the regolith by gravity, escape to space, get pushed away by solar radiation pressure, or become photoionized and swept away by the solar wind. To test hypotheses about the sources, sinks, and escape of the lunar atmosphere, velocity-resolved observations under different lunar phases, altitudes, latitudes, and time histories are being made to help understand factors that link resultant morphologies to sources and solar radiation effects. These observations will help constrain atmospheric and surface-process modeling, and help quantify the source and escape mechanisms.
Categories: Faculty-Staff
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Collaborative Research: Wideband Multi-Beam Antenna Arrays: Low-Complexity Algorithms and Analog-CMOS Implementations
PI Sirani Mututhanthrige Perera
PI Arjuna Habarakada Madanayake
PI Soumyajit Mandal
Explosion of millimeter-wave (mm-wave) bandwidth opens up applications in 5G wireless systems spanning communications, localization, imaging, and radar. This project addresses challenges in mathematics, engineering, and science in developing efficient wideband beamformers based on sparse factorizations of the matrix called-delay Vandermonde matrices (DVM). The proposed highly integrated approach is attractive for mobile applications including 5G smart devices, the internet of things, mobile robotics, unmanned aerial vehicles, and other emerging applications focused on mm-waves.
A multi-beam array receiver is deeply difficult to realize in integrated circuit (IC) form due to the underlying complexity of its signal flow graph. Through the proposed work, mathematical methods based on the theories of i) sparse factorization and complexity of the structured complex DVM with the introduction of a super class for the discrete Fourier transform(which is DVM), and ii) approximation transforms are proved to solve this problem.
The resulting matrices are realized with multi-GHz bandwidths using analog ICs. The novel DVM algorithm solves the longstanding "beam squint" problem, i.e., the fact that the beam direction changes with input frequency, making true wideband operation impossible. Moreover, the proposed multi-beamforming networks in analog IC form will be realized efficiently while addressing precision circuit design, digital calibration, built-in self-test, etc. Besides scientific merits, both minority students and female students will be mentored to pursue careers in the STEM disciplines through the proposed project.
This project was funded by the National Science Foundation (the division of Electrical, Communications, and Cyber Systems) with award numbers 1711625 and 1711395.
Categories: Faculty-Staff
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Cross-Scale Wave Coupling Processes in Kelvin-Helmholtz Structures
PI Heidi Nykyri
Project investigates cross-scale wave coupling processes and their role on ion heating, mixing and diffusion.
One of the pending problems in collisionless plasmas is to understand the plasma heating and transport across three fundamental scales: fluid, ion and electron. The plasma inside Earth’s magnetotail plasma sheet is ~50 times hotter than in the magnetosheath. Furthermore, the specific entropy increases by two orders of magnitude from the magnetosheath to the magnetosphere, which is a signature of a strong non-adiabatic heating. Also, the cold component ions are hotter by ~30 % at the dawnside compared to those measured on the duskside. Our recent statistical study using THEMIS data indicates that the magnetosheath seed population is not responsible for this asymmetry so additional physical mechanisms at the magnetopause or plasma sheet must be at work to explain this asymmetric heating. Recent works suggest that dawn-flank magnetopause boundary is more prone to the fluid-scale Kelvin-Helmholtz instability (KHI) as well as to the ion-scale electromagnetic wave activity, which may help explain the observed plasma sheet asymmetry. Project uses numerical simulations, plasma theory and spacecraft observations to understand relation of small-scale waves to large-scale velocity driven modes and evaluate their role in mixing, diffusion, and heating of ions.
Categories: Faculty-Staff
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Experimental Identification of Plasma Wave Modes in Vicinity of KH Vortices and in Plasma ’Mixing’ Regions in Low Latitude Boundary Layer (Ion scales)
PI Heidi Nykyri
Project uses Cluster spacecraft data to identify ion-scale waves within Kelvin-Helmholtz waves.
Project uses Cluster spacecraft data to identify ion-scale waves within Kelvin-Helmholtz waves.Categories: Faculty-Staff
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Statistical correlation study between solar wind, magnetosheath and plasma sheet properties
PI Heidi Nykyri
CO-I Xuanye Ma
Statistical study of the solar wind, magnetosheath, and magnetospheric plasma properties usinng 8+ years of THEMIS data.
The study will utilize recently developed statistical tool developed under Nykyri's NSF CAREER grant to present 8+ years of THEMIS spacecraft data in the coordinate system that takes into account the motion of the magnetopause and bow shock and will organize THEMIS observations into spatial bins with respect to physical boundaries under prevailing solar wind conditions. The study will address how do the plasma sheet properties such as number density, temperature, electron to ion temperature ratio and specific entropy vary during a) Parker-Spiral, Ortho-parker spiral, Northward and Southward IMF, and b) during high and slow solar wind speed, and how are these correlated with corresponding magnetosheath properties?
Categories: Faculty-Staff
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NSF Career Award: Effects of Magnetosheath properties on the dynamics and plasma transport produced by the Kelvin-Helmholtz Instability and on the Plasma Sheet Anisotropies
PI Heidi Nykyri
Project investigates impact of magnetosheath properties on Kelvin-Helmholtz instability
The magnetosheath processes will be studied by doing a statistical study of the magnetosheath properties using THEMIS data and by utilizing global hybrid (fluid electrons, particle ions) simulations. In addition, the MHD-scale KHI will be compared with hybrid and particle simulations of the instability.
Categories: Faculty-Staff
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Turbulence and Structure in the Magnetospheric Cusps: Cluster spacecraft observations
PI Heidi Nykyri
Project analyzes the structure, origin of fluctuations and high-energy particles in the high-altitude cusp regions
Project uses Cluster data and high-resolution local 3-D MHD simulations with test particles to determine the structure and origin of high-energy particles in the high-altitude cuspCategories: Faculty-Staff
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Magnetospheric Multi-Scale (MMS) Observations and simulations of high-energy electrons in the dayside magnetosheath
PI Heidi Nykyri
CO-I Brandon Burkholder
CO-I Xuanye Ma
The key objective of this study is to better understand the source and cause of high-energy electrons observed by the MMS in the dayside magnetosheath.
The key objective of this study is to better understand the source and cause of high-energy electrons observed by the MMS in the dayside magnetosheath. The Magnetospheric Multi-Scale (MMS) mission is a four-spacecraft constellation orbiting in formation around Earth with a main goal to study the microphysics of magnetic reconnection at the dayside magnetopause. Recent MMS observations showed high energy (40 keV) electrons leaking into the magnetosheath. However, the dominant leaking mechanism has not been fully understood. Global Lyon-Fedder-Mobarry (LFM) with test particle simulations suggest that low latitude reconnection and the nonlinear Kelvin-Helmholtz (KH) instability can cause the leak of high energy electrons into the magnetosheath. But it is important to notice that many of the electrons leaking events were observed close to Fall Equinox when the MMS orbit has a significant y-component and the z_GSM coordinate can be substantial (up to ~7 R_E). Therefore, MMS high-energy electron events may have a high-latitude source. For instance, it is well demonstrated that magnetic reconnection between the Interplanetary Magnetic Field (IMF) and Earth's magnetic field surrounding the cusps can lead to the formation of cusp diamagnetic cavities (Nykyri et al., JGR 2011a,b; Adamson et al., angeo 2011), extended regions of decreased magnetic field, which can be filled with higher energy (>30 keV) electrons, protons and O+ ions. Cluster observations revealed 90-degree pitch angle electrons in the cavity, strongly suggestive of a local acceleration mechanism (Walsh, angeo 2010; Nykyri et al, JASTP 2012). Test particle simulations in a high-resolution 3D cusp model uncovered that trapped particles in the diamagnetic cavities can be accelerated when their drift paths go through regions of "reconnection quasi-potential" (Nykyri et al, JASTP 2012). Once the IMF orientation changes it is possible for trapped particles in the cavity to end up into the loss cone and "leak out" of the cavity. A systematic approach to our science objective addresses the following compelling science questions by synergy using MMS observational data and numerical simulation.
Categories: Faculty-Staff
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Science and engineering proof of concept study for the Next generation Space Weather Prediction mission and space weather model development
PI Heidi Nykyri
Project analyzes astrodynamics (transfer trajectories) and spacecraft constellation stability about all Lagrange points for Mercury, Venus, Earth, Mars system for the "next generation" space weather prediction mission, and develops a solar wind model which will use data from this mission
Project analyzes astrodynamics and constellation stability for the "next generation" space weather prediction mission, and develops a solar wind model which will use data from this missionCategories: Faculty-Staff
11-20 of 25 results