• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.99-99
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• 2013

In this talk, I will present two research works in progress, which are: i) mapping of piezoelectric polarization and associated charge density distribution in the heteroepitaxial InGaN/GaN multi-quantum well (MQW) structure of a light emitting diode (LED) by using inline electron holography and ii) in-situ observation of the polarization switching process of an ferroelectric Pb(Zr1-x,Tix)O3 (PZT) thin film capacitor under an applied electric field in transmission electron microscope (TEM). In the first part, I will show that strain as well as total charge density distributions can be mapped quantitatively across all the functional layers constituting a LED, including n-type GaN, InGaN/GaN MQWs, and p-type GaN with sub-nm spatial resolution (~0.8 nm) by using inline electron holography. The experimentally obtained strain maps were verified by comparison with finite element method simulations and confirmed that not only InGaN QWs (2.5 nm in thickness) but also GaN QBs (10 nm in thickness) in the MQW structure are strained complementary to accommodate the lattice misfit strain. Because of this complementary strain of GaN QBs, the strain gradient and also (piezoelectric) polarization gradient across the MQW changes more steeply than expected, resulting in more polarization charge density at the MQW interfaces than the typically expected value from the spontaneous polarization mismatch alone. By quantitative and comparative analysis of the total charge density map with the polarization charge map, we can clarify what extent of the polarization charges are compensated by the electrons supplied from the n-doped GaN QBs. Comparison with the simulated energy band diagrams with various screening parameters show that only 60% of the net polarization charges are compensated by the electrons from the GaN QBs, which results in the internal field of ~2.0 MV cm-1 across each pair of GaN/InGaN of the MQW structure. In the second part of my talk, I will present in-situ observations of the polarization switching process of a planar Ni/PZT/SrRuO3 capacitor using TEM. We observed the preferential, but asymmetric, nucleation and forward growth of switched c-domains at the PZT/electrode interfaces arising from the built-in electric field beneath each interface. The subsequent sideways growth was inhibited by the depolarization field due to the imperfect charge compensation at the counter electrode and preexisting a-domain walls, leading to asymmetric switching. It was found that the preexisting a-domains split into fine a- and c-domains constituting a $90^{\circ}$ stripe domain pattern during the $180^{\circ}$ polarization switching process, revealing that these domains also actively participated in the out-of-plane polarization switching. The real-time observations uncovered the origin of the switching asymmetry and further clarified the importance of charged domain walls and the interfaces with electrodes in the ferroelectric switching processes.

• Journal of Veterinary Clinics
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• v.26 no.6
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• pp.650-654
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• 2009

A 1-week-old, male Korean native calf with acute clinical signs of depression, mild diarrhea, ataxia, recumbency and tremor was referred to Chonbuk Veterinary Medical Center of Chonbuk National University. Vision loss and cornea edema were also observed on physical examination. The patient had been deteriorated with nystagumus, strabisumus and opisthtonus. Blood cell count test and blood biochemistry test revealed remarkable leukocytosis, and hypoalbuminemia and increased blood urea nitrogen. No remarkable findings were observed on radiography. On magnetic resonance imaging study, there were enlarge lateral, third, and forth ventricles. The cortical grey and subcortical white matter of left temporal lobe showed hypointense on T1-weighted images and hyperintense on T2-weighted images, and slightly enhanced on contrast-enhanced T1-weighted images. Escherichia coli strain was identified from cerebrospinal fluid sample. Palliative treatment was attempted but the neonatal calve was expired three days after admission. Severe multifocal fibrino-suppurative meningitis with Escherichia coli infection was confirmed histopathologically.

• Journal of Cardiovascular Imaging
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• v.31 no.4
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• pp.191-199
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• 2023

BACKGROUND: Assessment of left ventricular (LV) function plays a pivotal role in the management of patients with valvular heart disease, including those caused by rheumatic heart disease. Noninvasive LV pressure-strain loop analysis is emerging as a new echocardiographic method to evaluate global LV systolic function, integrating longitudinal strain by speckle-tracking analysis and noninvasively measured blood pressure to estimate myocardial work. The aim of this study was to characterize global LV myocardial work efficiency in patients with severe rheumatic mitral stenosis (MS) with preserved ejection fraction (EF). METHODS: We retrospectively included adult patients with severe rheumatic MS with preserved EF (> 50%) and sinus rhythm. Healthy individuals without structural heart disease were included as a control group. Global LV myocardial work efficiency was estimated with a proprietary algorithm from speckle-tracking strain analyses, as well as noninvasive blood pressure measurements. RESULTS: A total of 45 individuals with isolated severe rheumatic MS with sinus rhythm and 45 healthy individuals were included. In healthy individuals without structural heart disease, the mean global LV myocardial work efficiency was 96% (standard deviation [SD], 2), Compared with healthy individuals, median global LV myocardial work efficiency was significantly worse in MS patients (89%; SD, 4; p < 0.001) although the LVEF was similar. CONCLUSIONS: Individuals with isolated severe rheumatic MS and preserved EF, had global LV myocardial work efficiencies lower than normal controls.

• Nuclear Medicine and Molecular Imaging
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• v.43 no.5
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• pp.487-494
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• 2009

Purpose: Small size of recombinant scFv antibody has many advantages such as rapid blood clearances and improved targeting antibodies to tumor region. On the other hand owing to small size, number of amino group is insufficient in conjugation with chelator and fluorescence labeling. This study is to introduce poly lysine tag to the C-terminal end of scFv lym-1 sequence for fluorescence chelator conjugation. Materials and Methods: Poly lysine scFv lym-1 gene, cloned into pET-22b (+) vector, was expressed in E. coli BL21 (DE3) strain. Antibody purification was performed with Ni-NTA column and then size exclusion column chromatography. Expression and purification levels of poly lysine tagged scFv lym-1 antibody were confirmed by western blot analysis. I-124, I-125, I-131 and Tc-99m were used for radiolabeling of purified poly lysine scFv lym-1. Flow cytometry analysis of FIT( conjugated poly lysine scFv lym-1 was performed for confirmation of immunoreactivity of human Burkitt's lymphoma cells. Results: Poly lysine scFv lym-1 antibody was purified through two steps and identified as molecular weight of 48 KDa. Radiolabeling yields of I-124, I-125, I-131 and Tc-99m into poly lysine scFv lym-1 were >99%, >99%, >95% and >99%, respectively. Flow cytometry analysis of poly lysine scFv and scFv lym-1 was showed similar immunoreactivity to human Burkitt's lymphoma cells. Conclusion: Poly lysine tag was useful for the sufficient number of amino groups to scFv lym-1 antibody for chelator conjugation with minimizing loss of immunoreactivity.

• Geophysics and Geophysical Exploration
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• v.25 no.4
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• pp.214-216
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• 2022

Distributed acoustic sensing (DAS), an increasingly growing acquisition technique in the oil and gas exploration and seismology fields, has been used to record seismic signals using optical cables as receivers. With the development of imaging methods for DAS data, full waveform inversion (FWI) is been applied to DAS data to obtain high-resolution property models such as P- and S-velocity. However, because the DAS systems measure strain from the phase distortion between two points along optical cables, DAS data must be transformed from strain to particle velocity for FWI algorithms. In this study, a plane-wave FWI algorithm based on the relationship between strain and horizontal particle velocity in the plane-wave assumption is proposed to apply FWI to DAS data. Under the plane-wave assumption, strain equals the horizontal particle velocity, which is scaled by the velocity at the receiver position. This relationship was confirmed using a numerical experiment. Furthermore, 4-layer and modified Marmousi-2 velocity models were used to verify the applicability of the proposed FWI algorithm in various survey environments. The proposed FWI was implemented in land and marine survey environments and provided high-resolution P- and S-velocity models.

• Smart Structures and Systems
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• v.16 no.4
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• pp.667-681
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• 2015

The scour induced by strong currents and wave action decreases the embedded length of monopiles and leads to a decrease of their structural stability. The objective of this study is the development and consideration of scour-monitoring techniques for offshore monopile foundations. Tests on physical models are carried out with a model monopile and geo-materials prepared in a cylindrical tank. A strain gauge, two coupled ultrasonic transducers, and ten electrodes are used for monitoring the scour. The natural frequency, ultrasonic reflection images, and electrical resistivity profiles are obtained at various scour depths. The experimental results show that the natural frequency of the model monopile decreases with an increase in the scour depth and that the ultrasonic reflection images clearly detect the scour shape and scour depth. In addition, the electrical resistivity decreases with an increase in scour depth. This study suggests that natural frequency measurement, ultrasonic reflection imaging, and electrical resistivity profiling may be used as effective tools to monitor the scour around an offshore monopile foundation.

• Molecules and Cells
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• v.43 no.10
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• pp.880-888
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• 2020

Inherited peripheral neuropathy is a heterogeneous group of peripheral neurodegenerative disorders including Charcot-Marie-Tooth disease. Many peripheral neuropathies often accompany impaired axonal construction and function. To study the molecular and cellular basis of axon-defective peripheral neuropathy, we explore the possibility of using Caenorhabditis elegans, a powerful nematode model equipped with a variety of genetics and imaging tools. In search of potential candidates of C. elegans peripheral neuropathy models, we monitored the movement and the body posture patterns of 26 C. elegans strains with disruption of genes associated with various peripheral neuropathies and compiled a database of their phenotypes. Our assay showed that movement features of the worms with mutations in HSPB1, MFN2, DYNC1H1, and KIF1B human homologues are significantly different from the control strain, suggesting they are viable candidates for C. elegans peripheral neuropathy models.

• International Journal of Vascular Biomedical Engineering
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• v.1 no.1
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• pp.3-12
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• 2003

Ultrasonic pulsed Doppler velocimetry has become a standard international method of classifying carotid disease. Because the measured angle adjusted velocity increases as the Doppler angle increases, examinations should be performed at a convenient standard Doppler examination angle. An angle of 60 degrees is achievable throughout most examinations. Multiple Doppler viewing angles allow the acquisition of velocity vectors during the cardiac cycle, revealing the complex velocity patterns. Ultrasonic velocimetry (whether Doppler or time domain) is based on changes in the phase of the ultrasound echo. Other examinations can be done based on the echo phase. Slow motions of organs such as the brain can be used to monitor changes in edema. Measurements of tissue strain due to the pulsatile filling of the arterioles. This plethysmographic imaging method can display differences in tissue perfusion because of different tissue types and changes in autonomic activity.

• Smart Structures and Systems
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• v.5 no.4
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• pp.469-482
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• 2009

The emerging sensor-based structural health monitoring (SHM) technology has a potential for cost-effective maintenance of aging civil infrastructure systems. The author proposes to integrate continuous and global monitoring using on-structure sensors with targeted local non-destructive evaluation (NDE). Significant technical challenges arise, however, from the lack of cost-effective sensors for monitoring spatially large structures, as well as reliable methods for interpreting sensor data into structural health conditions. This paper reviews recent efforts and advances made in addressing these challenges, with example sensor hardware and health monitoring software developed in the author's research center. The hardware includes a novel fiber optic accelerometer, a vision-based displacement sensor, a distributed strain sensor, and a microwave imaging NDE device. The health monitoring software includes a number of system identification methods such as the neural networks, extended Kalman filter, and nonlinear damping identificaiton based on structural dynamic response measurement. These methods have been experimentally validated through seismic shaking table tests of a realistic bridge model and tested in a number of instrumented bridges and buildings.

• Parasites, Hosts and Diseases
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• v.60 no.5
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• pp.367-370
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• 2022

Fascioliasis is a parasitic infection caused by liver flukes. Although several cases have been reported in Korea, phylogenetic analysis of isolates is lacking. In this study, a 66-year-old woman with right upper quadrant (RUQ) abdominal pain was diagnosed as fascioliasis involving abdominal muscle by imaging study. She received praziquantel treatment, but symptoms were not improved. Lateral movement of the abscess lesion was followed. Trematode parasite was surgically removed from the patient's rectus abdominis muscle. The fluke was identified as Fasciola hepatica based on sequence analysis of 18S rDNA. To determine the phylogenetic position of this Fasciola strain (named Korean Fasciola 1; KF1), the cox1 gene (273 bp) was analyzed and compared with the genes of 17 F. hepatica strains isolated from cows, sheep, goats, and humans from various countries. Phylogenetic analysis showed that KF1 was closely related with the isolates from China goat.