• Journal of the Mineralogical Society of Korea
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• v.13 no.4
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• pp.186-195
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• 2000

To study phosphate adsorption on kaolinite, $^{31}$ P MAS NMR(magic angle spinning nuclear magnetic resonance spectroscopy)has been used for kaolinite reacted in 0.1 M phosphate solutions at pH’s from 3 to 11. There are at least 3 different forms of phosphate on kaolinite. One is the phosphate physically adsorbed on kaolinite surface (outer-sphere complexes) or species left after vacuum-filtering. The second is the phosphate adsorbed by ligand exchange (inner-sphere complexes), and the third is Al-phosphate precipitates which are pH dependent. Most of the inner-spherer complexes and surface precipitates are mainly on hydroxided Al(aluminol) rather than hydroxided Si(silanol). These are pertinent with the results obtained from the phosphate adsorption experiments on silica gel and ${\gamma}$-Al$_2$O$_3$ as model compounds, respectively. The two peaks with more negative chemical shifts(more shielded) than the ortho-phosphate peak (positive chemical shift) are assigned to be the inner-sphere complexes and surface precipitates. The $^{31}$ P chemical shifts of the Al-phosphate precipitates are more negative than those of inner-sphere complexes at a given pH due to the larger number of P-O-Al linkages per tetrahedron. The chemical shifts of both the inner-sphere complexes and surface precipitates are more negative than those of inner-sphere complexes at a given pH due to the larger number of P-O-Al linkages per tetrahedron. The chemical shifts of both the inner-sphere complexes and surface precipitates become progressively less shielded with increasing pH. For the inner-sphere complexes, decreasing phosphate protonation combined with peak averaging by rapid proton exchange among phosphate tetrahedra with different numbers of protons is though to be the reason for the peak change. The decreasing shielding with increasing pH for surface precipitates is probably due to the decreasing average number of P-O-Al linkages per tetrahedron combined with decreasing protonation like inner-sphere complexes.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.6
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• pp.528-535
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• 2004

Ultrasonic Vibrator is designed to achieve the maximum vibration amplitude at 30 kHz by in-cluding a horn (diameter, 40 mm), mechanical vibration amplifier at the top of the ultrasonic vibrator in the system and making the complete system resonate. In addition, it is experimentally visualized by particle imaging velocimetry (PIV) that the acoustic streaming velocity in the gap is at maximum when the gap between the ultrasonic vibrator and stationary plate agrees with the multiples of half-wavelength of the ultrasonic wave. This fact results from the resonance of the sound wave and the theoretical analysis of that is also accomplished and verified by experiment. It is observed that the magnitude of the acoustic streaming dependent upon the gap between the ultrasonic vibrator and stationary plate possibly changes due to the measurement of the average velocity fields of the acoustic streaming induced by the ultrasonic vibration at resonance and non-resonance. There exists extremely small average velocity at non-resonant gaps while the relatively large average velocity exists at resonant gaps compared with non-resonant gaps. It also reveals that there should be larger axial turbulent intensity at the hub region of the vibrator and at the edge of it in the resonant gap where the air streaming velocity is maximized and the flow phenomena is conspicuous than that at the other region. Because the variation of the acoustic streaming velocity at resonant gap is more distinctive than that at non-resonant gap, shear stress increases more in the resonant gap and is also maximized at the center region of the vibrator except the local position of center (r〓0). At the non-resonant gap there should be low values of vorticity distribution, but in contrast to the non-resonant gap, high and negative values of it exist at the center region of the vibrator with respect to the radial direction and in the vicinity of the middle region with respect to the axial direction. Acoustic streaming is noise-free due to the ultrasonic vibration and maintenance-free because of the absence of moving parts. Moreover, the proposed method by acoustic streaming can be utilized to the nano and micro-electro mechanical systems as a driving mechanism in addition to the augmentation of the streaming velocity.

• Journal of the Korean Magnetics Society
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• v.21 no.4
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• pp.121-126
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• 2011

Spin dynamics of magnetic tunnel junctions with free and fixed reference layers is investigated by ferromagnetic resonance micromagnetic simulations. First, in magnetic tunnel junctions with an exchange biased synthetic ferrimagnetic reference layer, a magnetization direction of each layer and the tunneling magnetoresistance are calculated for a DC magnetic field. To investigate the spin exciting modes in magnetic tunnel junctions, we simulate the ferromagnetic resonance frequency spectra with small RF magnetic fields. Exciting modes of the tunneling magnetoresistance calculated by an included angle between free and reference layers is interpreted from those of each layer. Spin exciting modes are different according to a signs of the DC magnetic field. In a negative magnetic field, FMR frequency spectra of free and reference layers are well elucidated by the modified Kittel's equation. However, in a positive magnetic field, there is no simple analytic solution related to FMR frequency spectra due to the coupled modes. Since ferromagnetic layers in magnetic tunnel junctions are interactive each other, careful considerations of the reference and fixed layer as well as the free layer are required for understanding on the spin dynamics of magnetic tunnel junctions with an exchange biased synthetic ferrimagnetic reference layer.

• Investigative Magnetic Resonance Imaging
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• v.7 no.1
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• pp.47-55
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• 2003

Purpose : Cortical dysplasia is known to be of variety of MR imaging findings. We attempted to classify MR imaging findings of cortical dysplasia into several types and to correlate those with histopathologic grades and subtypes. Materials and Methods : Preoperative MR images of 97 patients with pathologically-proven cortical dysplasia were retrospectively reviewed with knowledge of the diagnosis and operative sites. The patients were divided into MR-positive and MR-negative groups based on the presence or absence of MR imaging abnormalities. In MR-positive group, MR imaging features were arbitrarily classified into four types (atrophic, cortical-band, inward-rounding, and nonspecific types) on the basis of size of the gyrus and adjacent CSF space, cortical thickness, signal intensity of the subcortical white matter, and blurring of the gray-white matter junction. The pathologic findings were also retrospectively reviewed without knowledge of MR imaging findings and divided into three grades (mild, moderate, and severe) and two subtypes (nonballoon-cell and balloon-cell). Pathologic grades and subtypes we re compared between MR-positive and MR-negative groups. Four MR types of the MR-positive group were correlated with the pathologic grades and subtypes. Results : MR-positive and MR-negative groups consisted of 39 (40%) and 58 (60%) patients, respectively. Of the MR-positive group, atrophic type was seen in 13 patients (33 %), cortical-band type in 9 (23%), inward-rounding type in 9 (23%), and nonspecific type in 8 (21%). There was no significant difference in the pathologic grades between MR-positive and MR-negative groups, although MR-positive group tended to have higher pathologic grades than MR-negative group did. Balloon-cell subtype was found significantly higher in MR-positive group than in MR-negative group (p<0 .05): 21% (8/39) versus 5% (3/58). The inward-rounding type corresponded to the pathologically severe grade and balloon-cell subtype in 78% (7/9) and 56% (5/9) of the patients, respectively, while the atrophic type to the mild grade and nonballoon-cell subtype in 77% (10/13) and 100% (13/13), respectively. Conclusion : A variety of MR imaging abnormalities were found in 40% of the patients with cortical dysplasia and those were classified into four types (atrophic, cortical-band, inward-rounding, and nonspecific types), of which the inward-rounding type correlated well with the pathologically severe grade and balloon-cell subtype, whereas the atrophic type with the mild grade and nonballoon-cell subtype.

• Journal of the Korean Institute of Telematics and Electronics
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• v.19 no.5
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• pp.20-25
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• 1982

A realization method of the microwave oscillator is proposed by the inherently stable transistor with a cavily resonator feedback loop. The real Part of the output impedance of the inherently stable bipolar transistor can be made to be negative at the resonance frequency by the high-Q cavity feedback loop, and the oscillation condition can be obtained with the matching section of the load. In this work the microwave transistor oscillator is realized with a silicon bipolar transistor HXTR 2101 and a reentrani cavity, and characteristic of the output power 10m Watts at 2.33 GHz osc. frequency can be verified experimentally.

• Journal of Korean Neurosurgical Society
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• v.41 no.2
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• pp.118-119
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• 2007

We report a rare case of Wallenberg's lateral medullary syndrome caused by prone position for spine surgery. A 48-year old man developed Wallenberg's syndrome characterized by involuntary myoclonic movements, ataxia on his left side, hyperalgia and cold sensation on his right side after prone position for general anesthesia for the spinal stenosis L3-L4, L4-L5. Brain computed tomography scan was immediately performed and showed negative findings, but magnetic resonance image [MRI] demonstrated brain infarction on the left medulla. Emergent heparinization was performed and his motor power and sensation returned to normal and discharged with stable and satisfactory recovery after 16 days.

• Applied Microscopy
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• v.48 no.1
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• pp.1-5
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• 2018

Cryo-transmission electron microscopy (cryo-TEM) allows us to perform structural analysis of a analyses of large protein complexes, which are difficult to analyze using X-ray crystallography or nuclear magnetic resonance. The most common examples of proteins used are ribosomes and proteasomes. In this paper, we briefly describe the advantage of cryo-TEM and the process of two-dimensional classification by considering a human proteasome as an example.

• Journal of Korean Neurosurgical Society
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• v.49 no.6
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• pp.373-376
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• 2011

We report a case of a non traumatic spinal subdural hematoma or subarachnoid hematoma manifesting as lumbago, leg pain and bladder dysfunction that showed angiographically occult vascular malformation (AOVM). Although the spinal angiogram did not reveal any vascular abnormality, the follow-up magnetic resonance image showed AOVM. Complete surgical removal was performed due to the aggravated bladder dysfunction. This case highlights the need to consider bleeding due to spinal AOVM, even when angiography is negative.

• Journal of Korean Neurosurgical Society
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• v.42 no.2
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• pp.129-131
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• 2007

Intracranial epithelioid hemangioendothelioma is extremely rare. We report a case of intracranial epithelioid hemangioendothelioma which developed in a 55-year-old man who presented with dysarthria for two weeks. The brain computed tomography scan and magnetic resonance image showed masses which had fat component at the left frontal convexity and at left posterior parietal area. Excisional biopsy at the left frontal convexity confirmed epithelioid hemangioendothelioma which is immunopositive for CD31, supporting endothelial differentiation, and negative for CD68, SMA and HMB-45.

• Journal of Korean Neurosurgical Society
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• v.44 no.6
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• pp.385-388
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• 2008

We herein describe the case of a focal spontaneous spinal epidural abscess who was initially diagnosed to have a free fragment of a lumbar disc. A 71-year-old woman presented with history of low back and right leg pain. Magnetic resonance imaging suggested a peripherally enhancing free fragment extending down from S1 nerve root axilla. Preoperative laboratory investigation showed elevation of c-reactive protein (CRP), erythrocyte sedimentation rate (ESR) levels. She was taken for surgery and a fluctuating mass at the axilla of S1 nerve was found. When the mass was probed with a dissector, a dark yellow, thick pus drained out. Pus cultures were negative. Patients who present with extreme low back plus leg pain and increased leucocyte count, ESR and CRP levels should raise the suspicion of an infection of a vertebral body or spinal epidural space.