• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2012년도 추계학술대회 논문집
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• pp.458-463
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• 2012

This case study refers to resonance with vertical pumps. Vibration problem occurring after the inverter was installed for speed control. Its problem was appeared any revolution under rated speed. Vibration data was acquired during normal operation and transient state. We examined FRF on its resonance in field and also analyzed a result by finite element method. There was carried out the retrofit in field which was based on these results for solving problem.

• Journal of electromagnetic engineering and science
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• 제15권2호
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• pp.104-110
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• 2015

As civil infrastructures continue to deteriorate, the demand for structural health monitoring (SHM) has increased. Despite its outstanding capability for damage identification, many conventional SHM techniques are restricted to huge structures because of their wired system for data and power transmission. Although wireless data transmission using radio-frequency techniques has emerged vis-$\grave{a}$-vis wireless sensors in SHM, the power supply issue is still unsolved. Normal batteries cannot support civil infrastructure for no longer than a few decades. In this study, we develop a magnetic resonance-based wireless power transmission system, and its performance is validated in three different mediums: air, unreinforced concrete, and reinforced concrete. The effect of concrete and steel rebars is analyzed.

• 동력기계공학회지
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• 제4권4호
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• pp.59-64
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• 2000

Especially, demands for the noise reduction of mold transformer has been becoming an common issue because it has been used mainly at the residence area such as building and ship. So, this paper investigates the noise source and countermeasure of mold transformer radiated high noise abnormally. The result of impact hammering test for core of transformer ascertains the core resonance by harmonics of line frequency and high noise can be reduced to avoid core resonance by changing torque strength of tie rod. Magnetic field analysis is performed to identify the reason that noise of V-phase is higher than U and W-phase in the normal condition. It is the cause that flux density and magnetic force of V-phase is higher than the other phase respectively.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1921-1926
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• 2004

The tone generation mechanism and aeroacoustic characteristics have been investigated for flow over open cavities using direct acoustic numerical simulations. Physically the tone generation mechanism of open cavity is more complicated when flow instabilities are excited by the correlation effects of flow parameters. From non-dimensional parameter studies in very low Mach number range, it is shown that characteristics of cavity resonance inherently involve typical acoustic pattern at each discrete tone frequency, and especially in laminar flow the fundamental tone frequency is determined within flow instability criterion of laminar shear layer as well as cavity geometry, length to depth ratio.

• 한국자기공명학회논문지
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• 제6권2호
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• pp.142-154
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• 2002

One of the oldest, still unsolved, and often ignored problems in magnetic resonance remains the issue of how to observe undistorted, normal one-dimensional spectra where the frequencies and their relative intensities represent faithfully the distribution of spins and sites in the sample within the magnet. Often distortions in these parameters are accepted, as the price of sensitivity enhancement, or because it is unclear just how these distortions might be avoided. Surprisingly enough, the problem is exacerbated by the use of modern techniques of pulsed Fourier transform NMR. Noise spectroscopy is an approach to solving the problem of distorted NMR spectra, which is largely under appreciated; it promises virtually "unlimited" distortionless bandwidths without costly hardware investments. Nonetheless, its exploitation remains limited. We will discuss why noise spectroscopy belongs in the arsenal of tricks spectroscopists should be aware of, show examples where its use is essential if accurate, quantitative NMR is to be expected, and discuss some recent approaches which extend its applicability yet further, particularly in solid state NMR and in applications to quadrupolar nuclear spins.

• 대한족부족관절학회지
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• 제25권1호
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• pp.1-5
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• 2021

Physical examination and surgical findings and symptoms are often inconsistent with magnetic resonance imaging (MRI) findings when diagnosing chronic ankle lateral ligament instability, and confirmed surgical findings are used as the gold standard in most clinical studies. Anterior drawer testing is considered unreliable because normal findings are highly variable, and its accuracy ranges from 50% to 100%. Furthermore, radiographic stress imaging, such as in anterior drawer stress view, is performed under manual stress or using a stress device, and its findings also vary widely and confuse when interpreting stress views. The average accuracy of MRI findings is around 85% (range, 66%~91.7%), and thus, cannot be used as a primary indicator for surgery. For patients with suspected lateral ankle ligament instability, based on symptoms and physical examination findings, MRI may be useful for identifying lesions in ankle joints and for differentiating them from other conditions.

• ETRI Journal
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• 제46권2호
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• pp.263-276
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• 2024

Different diseases occur in the brain. For instance, hereditary and progressive diseases affect and degenerate the white matter. Although addressing, diagnosing, and treating complex abnormalities in the brain is challenging, different strategies have been presented with significant advances in medical research. With state-of-art developments in artificial intelligence, new techniques are being applied to brain magnetic resonance images. Deep learning has been recently used for the segmentation and classification of brain images. In this study, we classified normal and pathological brain images using pretrained deep models through transfer learning. The EfficientNet-B5 model reached the highest accuracy of 98.39% on real data, 91.96% on augmented data, and 100% on pathological data. To verify the reliability of the model, fivefold cross-validation and a two-tier cross-test were applied. The results suggest that the proposed method performs reasonably on the classification of brain magnetic resonance images.

• 대한방사선기술학회지:방사선기술과학
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• 제42권5호
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• pp.351-356
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• 2019

This study aimed to determine whether there was a difference in measurements between North American Symptomatic Carotid Endarterectomy Trial(NASCET) and Warfarin-Aspirin Symptomatic Intracranial Disease(WASID) methods that measure the middle cerebral artery stenosis in Digital Subtraction Angiography (DSA) and Magnetic Resonance Angiography (MRA). It involved 24 patients who had completed both DSA and MRA among patients with Middle Cerebral Artery (MCA) stenosis. The Middle Cerebral Artery (MCA) stenosis was measured using the NASCET and WASID methods through a retrospective analysis. For the NASCET and WASID methods, they performed measurements on normal blood vessels located far from and close to the stenosis, respectively. The mean value and standard deviation of the Digital Subtraction Angiography (DSA) measured by the NASCET method were 59.23% and 13.27%. On the other hand, those of the Digital Subtraction Angiography (DSA) measured by the WASID method were 66.64% and 12.47%. And, the mean value and standard deviation of the Magnetic Resonance Angiography (MRA) measured by the NASCET method were 49.82% and 12.06%. By contrast, those of the Magnetic Resonance Angiography (MRA) measured by the WASID method were 56.63% and 10.67%. All the p-values obtained by the Pearson and Spearman correlation tests in the Digital Subtraction Angiography (DSA) and the Magnetic Resonance Angiography (MRA) were <0.01. In conclusion, this study suggests that both the NASCET and WASID methods to measure the middle cerebral artery stenosis in the Digital Subtraction Angiography (DSA) and the Magnetic Resonance Angiography (MRA) can be used if they are not used interchangeably.

• 대한의생명과학회지
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• 제10권2호
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• pp.115-120
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• 2004

To investigate the correlation between the magnetic resonance imaging (MRI) of cerebral fat embolism that is induced by injecting oleic acid into 10 cats, and a pathologic diagnosis. Using a microcatheter, 30 ${mu}ell$ of oleic acid was injected into the internal carotid artery of 10 cats. MR T2-weighted image (T2WI), diffusion-weighted image (DWI) and Gadolinium-enhanced T1-weighted image (Gd-enhanced T1WI) were obtained after 30 minutes and 2 hours of embolization. After 30 minutes of the embolization, lesions of very high signal intensity were detected by T2WI in 6 cats, and of slightly high signal intensity in 2 cats; in the remaining 2 cats, signal intensity was normal. DWI showed lesions of very high intensity in 9 cats and of slightly high intensity in one cat. According to the findings of light microscopic examination, infarcted lesions mainly involved the gray matter, but also some white matter. A magnetic resonance imaging diagnosis for cerebral fat embolism that was induced by oleic acid through the internal carotid artery in cats showed high signal intensity on the T2WI and the DWI within an initial 2 hours, and with a well enhancement on the Gd-enhanced T1WI. Considering cellular edema, cerebrovascular injury and extracellular space widening, we assumed pathologically that cytotoxic and vasogenic edema exists at the same time.

• 한국전기전자재료학회논문지
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• 제21권4호
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• pp.335-340
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• 2008

In this study, novel structured thin ultrasonic rotary motor has been proposed. Ultrasonic motors are based on an elliptical motion on the surface of elastic body. Thin brass plate was used as a cross shaped vibrator and eight ceramic plates were attached on upper side and bottom side of the brass plate. From the thin stator, elliptical displacements of the four contact tips were obtained. To find the optimal size of the stator, motions of the motors were simulated using ATILA by changing length, width and thickness of the ceramics. The stators had commonly three resonance peaks and contact tips of the stator moved on tangential or normal trajectories at these resonance peaks. The maximum displacements at the resonance peaks were compared. As results, maximum displacements of the contact tips were obtained at the length of 16 mm, width of 6 mm and thickness of 0.4 mm. Changes of the resonance frequencies were inversely proportional to the length of ceramic and proportional to the width of ceramic. The motor was fabricated by using the designed stator. And, the characteristics of the motor were compared with the simulated results. When the motor was fabricated with these results, speed fo 935 rpm was obtained by input voltage of 25 Vrms at 93.5 kHz.