Dong Hun Lee

The propagation of MHD waves depends on a local Alfven speed and ambient geometry. The dynamical properties of MHD waves in the plasmasphere and magnetosphere are investigated by assuming a realistic Alfven speed profile in a dipole field. The WKB approximation is used to determine the cutoff boundaries and estimate the wave dispersion over a whole meridional plane. It is found that most wave energy may be transmitted effectively into the inner magnetosphere near the equatorial region, since the

Tin selenides with layered crystal structures, SnSe and SnSe 2, were synthesized by a solid-state method and electrochemically tested for use as Li-ion battery anodes. The phase change mechanisms of these compounds were thoroughly evaluated by ex situ X-ray diffraction and Se K-edge extended X-ray absorption fine structure techniques. SnSe showed better electrochemical reversibility of Li insertion/extraction than SnSe 2, which was attributed to remarkable conversion/recombination reactions of t

Impulsively excited ULF waves are studied in the three‐dimensional dipole magnetosphere. The properties of coupled compressional and transverse wave fields are found to depend on the longitudinal size of the impulse which is assumed at the magnetopause. The distribution of energy density and the wave spectra are shown for different meridians. We study how compressional waves propagate in the three‐dimensional space and excite the corresponding field line resonances, and how the impulse produces

ULF pulsations have been numerically studied in a new three‐dimensional dipole model, which allows a realistic Alfven speed profile for the plasmasphere and outer magnetosphere in the tailward region. This model includes more realistic boundary conditions at the outer boundary, allowing for partial reflection at the magnetopause and escape of wave energy down the tail. We investigate how Pi2 modes develop in time when an impulse associated with the substorm onset is assumed. It is shown that dis

The properties of the coupling of compressional and transverse ULF waves strongly depend on the azimuthal wavenumber m . We investigate these effects in a numerical model of ULF wave propagation in a dipolar magnetosphere. As the azimuthal wave number m becomes larger, the frequencies of the global modes are increased, each coupling location is shifted toward the plasmapause, and the wave energy of global compressional modes in the magnetosphere is confined to a smaller region near the magnetopa

Dynamics of compressional MHD wave propagation is theoretically studied in the dayside and nightside magnetosphere. In order to analytically examine the MHD wave equation, we adopt the quantum mechanical approach which is often used in the problem of the Schrödinger's equation. The wave solutions are obtained for dayside and nightside Alfven speed profiles, respectively, without any arbitrary boundary condition at the magnetopause or the bow shock. The result shows that the previous cavity/waveg

We present a theoretical study on how Pi 2 pulsations are excited in the magnetosphere. When impulsive disturbances associated with the substorm onset are assumed at the tailward region, their propagation toward the sunward direction is investigated with a wave equation. In order to examine the effect of the plasmapause on the initial disturbances, we analytically solve the wave equation based on the model of a reasonable Alfven speed profile. The exact solution shows that virtual resonant state

Linear frequency modulation (LFM) signals have been widely used for target detection in active sonar systems due to their robustness to reverberation. However, LFM active sonar requires a large number of reference signals for detecting targets moving with unknown speeds. To obtain more accurate detection results, more reference signals are required, resulting in an increased computational burden and memory size. To cope up with this problem, we propose a new fast target detection method that is

Pc1‐2 ULF waves are strongly associated with the presence of various ions in the magnetosphere. We investigate the role of heavy ion resonances in nonuniform plasmas near the equatorial region. By adopting the invariant imbedding method, the coupled plasma wave equations are solved in an exact manner to calculate the resonant absorption at the ion‐ion hybrid resonance. Our results show that irreversible mode conversion occurs at the resonance, which absorbs the fast wave energy. It is found that

A scanning tunneling microscope was used to study the ionization of single Mn acceptors in GaAs(110). The ionization state switches when the GaAs valence band is bent across a Mn acceptor level. This produces a ringlike feature in STM images, whose diameter depends on the tunneling conditions and distance to charged arsenic vacancies. By varying the latter, we could tune the ionization switching, as well as quantify the contributions from tip- and vacancy-induced band bending.

Fire in energy storage systems, such as lithium-ion batteries, has been raised as a serious concern due to the difficulty of suppressing it. Fluorine-based non-flammable agents used as internal substances leaked through the fine pores of the polymer outer shell, leading to a degradation of fire extinguishing performance. To improve the durability of the fire suppression microcapsules and the stability of the ouster shell, a complex coacervation was used, which could be microencapsulated at a low

This chapter contains sections titled: Introduction Plasmapause Effect on Compressional Mode Ionospheric Effects Effects of Longitudinal Asymmetry on Field Line Resonance Discussion and Summary

Magnetohydrodynamic (MHD) wave properties in inhomogeneous plasmas such as the magnetosphere are complicated by existence of local cutoff, coupling, and dissipation. We study the transport of MHD waves when compressional waves are assumed to propagate into the plasmasphere from the outer magnetosphere. By assuming a region of the Alfven speed crest, which approximates the plasmapause region, we investigate how the initial compressional MHD wave energy is reflected, absorbed, and delivered across