• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 A
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• pp.486-488
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• 1996

A dc-dc converter which transfers l2-48W of power(regulated output voltage 24V) across a large, variable air gap(1-2cm) has been designed. This converter employs double resonance to compensate the large leakage inductance of the primary and secondary of the transcutaneous transformer. To maximize the effect of resonance, a constant frequency, duty cycle control method is used. The duty cycle control presents advantages over a frequency control in terms of increase in dc voltage gain and reduction of the primary current. The analysis and design procedure for the proposed scheme is presented and the performance result is simulated and verified experimentally.

• Bulletin of the Korean Chemical Society
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• 제34권10호
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• pp.2983-2988
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• 2013

Second-order rate constants ($k_N$) have been measured spectrophotometrically for the reactions of 4-chloro-2-nitrophenyl X-substituted-benzoates (1a-1h) with a series of cyclic secondary amines in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The Hammett plot for the reactions of 1a-1h with piperidine consists of two intersecting straight lines, while the Yukawa-Tsuno plot exhibits an excellent linear correlation with ${\rho}_X $ = 1.25 and r = 0.58, indicating that the nonlinear Hammett plot is not due to a change in the rate-determining step (RDS) but is caused by ground-state stabilization through resonance interactions for substrates possessing an electron-withdrawing group in the benzoyl moiety. The Br${\o}$nsted-type plot for the reactions of 4-chloro-2-nitrophenyl benzoate (1d) with a series of cyclic secondary amines curves downward with ${\beta}_2$ = 0.85, ${\beta}_1$ = 0.24, and $pK_a{^o}$ = 10.5, implying that a change in RDS occurs from the $k_2$ step to the $k_1$ process as the $pK_a$ of the conjugate acid of the amine exceeds 10.5. Dissection of $k_N$ into the microscopic rate constants $k_1$ and $k_2/k_{-1}$ ratio associated with the reaction of 1d reveals that $k_2$ is dependent on the amine basicity, which is contrary to generally held views.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제45권1호
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• pp.29-33
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• 2019

Objectives: Bone density seems to be an important factor affecting implant stability. The relationship between bone density and primary and secondary stability remains under debate. The aim of this study was to compare primary and secondary stability measured by resonance frequency analysis (RFA) between different bone types and to compare implant stability at different time points during 3 months of follow-up. Materials and Methods: Our study included 65 implants (BioHorizons Implant Systems) with 3.8 or 4.6 mm diameter and 9 or 10.5 mm length in 59 patients. Bone quality was assessed by Lekholm-Zarb classification. After implant insertion, stability was measured by an Osstell device using RFA at three follow-up visits (immediately, 1 month, and 3 months after implant insertion). ANOVA test was used to compare primary and secondary stability between different bone types and between the three time points for each density type. Results: There were 9 patients in type I, 18 patients in type II, 20 patients in type III, and 12 patients in type IV. Three implants failed, 1 in type I and 2 in type IV. Stability values decreased in the first month but increased during the following two months in all bone types. Statistical analysis showed no significant difference between RFA values of different bone types at each follow-up or between stability values of each bone type at different time points. Conclusion: According to our results, implant stability was not affected by bone density. It is difficult to reach a certain conclusion about the effect of bone density on implant stability as stability is affected by numerous factors.

• Journal of Breast Cancer
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• 제21권4호
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• pp.453-462
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• 2018

Purpose: This study aimed to compare the diagnostic performance of contrast-enhanced digital mammography (CEDM) and contrast-enhanced magnetic resonance imaging (CEMRI) in preoperative evaluations, and to evaluate the effect of each modality on the surgical management of women with breast cancer. Methods: This single-center, prospective study was approved by the Institutional Review Board, and informed consent was obtained from all patients. From November 2016 to October 2017, 84 patients who were diagnosed with invasive carcinoma (69/84) and ductal carcinoma in situ (15/84), and underwent both CEDM and CEMRI, were enrolled. Imaging findings and surgical management were correlated with pathological results and compared. The diagnostic performance of both modalities in the detection of index and secondary cancers (multifocality and multicentricity), and occult cancer in the contralateral breast, was compared. The authors also evaluated whether CEDM or CEMRI resulted in changes in the surgical management of the affected breast due to imaging-detected findings. Results: Eighty-four women were included in the analysis. Compared with CEMRI, CEDM demonstrated a similar sensitivity (92.9% [78/84] vs. 95.2% [80/84]) in detecting index cancer (p=0.563). For the detection of secondary cancers in the ipsilateral breast and occult cancer in the contralateral breast, no significant differences were found between CEDM and CEMRI (p=0.999 and p=0.999, respectively). Regarding changes in surgical management, CEDM resulted in similar changes compared with CEMRI (30.9% [26/84] vs. 29.7% [25/84], p=0.610). Regarding changes in surgical management due to false-positive findings, no significant differences were found between CEDM and CEMRI (34.6% [9/26] vs. 44.0% [11/25], p=0.782). Conclusion: CEDM demonstrated a diagnostic performance comparable with CEMRI in depicting index cancers, secondary cancers, and occult cancer in the contralateral breast. CEDM demonstrated similar changes in surgical management compared with CEMRI.

• 한국자기공명학회논문지
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• 제19권3호
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• pp.106-111
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• 2015

Helicobacter pylori (H. pylori) survives in acidic and fluctuating pH conditions of the stomach. The pH effect on H. pylori proteins is important for the advanced understanding of its evolution and viability, although this bacterium has the molecular machinery that neutralizes the acidic condition. HP1492 is known as a conserved NifU-like protein from H. pylori. NifU is a nitrogen fixation protein that mediates the transfer of iron-sulfur (Fe-S) cluster to iron-sulfur proteins like ferredoxin. Commonly, the monomeric reduced state of NifU can be converted to the dimeric oxidized state by intermolecular disulfide bond formation. Because it remains unclear that HP1492 actually behaves as known NifU protein, we first found that this protein can adopt both oxidized and reduced forms using size exclusion chromatography. Circular dichroism experiment showed that HP1492 is relatively well-structured at pH 6.5, compared to other pH conditions. On the basis of the backbone resonance assignment of HP1492, we further characterized the residues that are sensitive to pH using NMR spectroscopy. These residues showing large chemical shift changes could be mapped onto the secondary structure of the protein. Our results could provide the foundation for structural and biophysical studies on a wide spectrum of NifU proteins.

• Journal of Korean Neurosurgical Society
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• 제65권3호
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• pp.479-488
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• 2022

Objective : The surgical management of trigeminal neuralgia (TN) caused by petrous apex meningioma (PAM) is still a challenge because of the lesion's deep location and the surrounding complex structures. The authors describe the intradural anterior transpetrosal approach (ATPA) and its effect on the treatment of TN secondary to PAM. Methods : A retrospective analysis of 15 patients with TN secondary to PAM who underwent surgery via the intradural ATPA was conducted. The key techniques, which included drilling off the petrosal apex (PA) and opening the upper wall of Meckel's cave (MC), are described in detail. Results : Total removal of the tumor and complete pain relief (Barrow Neurological Institute I) were achieved in all 15 patients without significant morbidity. Five patients developed new facial numbness postoperatively, which disappeared within three months after surgery. The postoperative magnetic resonance imaging showed temporal lobe swelling in three patients, but no clinical symptoms. One patient had cerebrospinal fluid leakage and was managed with bed rest and temporary lumbar drainage. One patient had an intracranial infection and was treated with antibiotics. By the last follow up, no patients had pain relapse or/and tumor recurrence. It is worth noting that the vascular compression at the root of the trigeminal nerve was found in one patient during the operation. Conclusion : Our experience suggests that drilling off the PA and opening the upper wall of the MC are key elements for a good outcome of the treatment of TN secondary to PAM. The intradural ATPA has the advantages for both tumor resection and pain relief.

• 한국철도학회논문집
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• 제8권1호
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• pp.41-50
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• 2005

Steel -Concrete Composite two girder railway bridges applying high performance steel with extra thick plate have economic and aesthetic advantages due to the simplification of manufacturing and construction process. However, steel bridges are seldom adopted in domestic railway bridge, since steel bridges are not efficient as R.C bridges considering dynamic characteristics and noise, etc. While highway bridges do not have lower horizontal bracing and larger interval of diaphragm cross beam, railway bridges install lower horizontal bracings to control the torsion due to heavy eccentrical line load. Accurate finite element analysis were performed with the parameters of existence of bracing and bracing shape, with the cross beam interval and stiffness, etc. To find out the effects of secondary members such as horizontal bracings and diaphragms, static md dynamic analysis have been performed by using finite element method. In this study, few member plate-girder bridges are analyzed with variable span lengths to examine the dynamic behavior and limits of damping. And though lateral bracings are members against torsion, but lateral bracing's absence is no big problem. Time history analysis using mode superposition method makes proof of this result.

• Bulletin of the Korean Chemical Society
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• 제35권7호
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• pp.2081-2085
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• 2014

Second-order rate constants ($k_N$) have been measured spectrophotometrically for the reactions of phenyl 2- pyridyl carbonate (6) with a series of cyclic secondary amines in MeCN at $25.0{\pm}0.1^{\circ}C$. The Br${\o}$nsted-type plot for the reaction of 6 is linear with ${\beta}_{nuc}$ = 0.54, which is typical for reactions reported previously to proceed through a concerted mechanism. Substrate 6 is over $10^3$ times more reactive than 2-pyridyl benzoate (5), although the reactions of 6 and 5 proceed through the same mechanism. A combination of steric hindrance, inductive effect and resonance contribution is responsible for the kinetic results. The reactions of 6 and 5 proceed through a cyclic transition state (TS) in which H-bonding interactions increase the nucleofugality of the leaving group (i.e., 2-pyridiniumoxide). The enhanced nucleofugality forces the reactions of 6 and 5 to proceed through a concerted mechanism. In contrast, the corresponding reaction of 4-nitrophenyl 2-pyridyl carbonate (7) proceeds through a stepwise mechanism with quantitative liberation of 4-nitrophenoxide ion as the leaving group, indicating that replacement of the 4-nitrophenoxy group in 7 by the PhO group in 6 changes the reaction mechanism (i.e., from a stepwise mechanism to a concerted pathway) as well as the leaving group (i.e., from 4-nitrophenoxide to 2-pyridiniumoxide). The strong electron-withdrawing ability of the 4-nitrophenoxy group in 7 inhibits formation of a H-bonded cyclic TS. The presence or absence of a H-bonded cyclic TS governs the reaction mechanism (i.e., a concerted or stepwise mechanism) as well as the leaving group (i.e., 2-pyridiniumoxide or 4-nitrophenoxide).

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 F
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• pp.2508-2511
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• 1999

A non-contact battery charger which transfers energy using magnetic field without any electrical contacts is designed using half-bridge series resonant converter. This converter utilizes series resonance to reduce the undesirable effect of large leakage inductance of the non-contact transformer and ZVS operation can reduce switching losses. In this paper. analysis and design procedure of half-bridge series resonant converter with non-contact transformer is presented. Input voltage is 85VAC ${\sim}$ 270VAC, output voltage and current is 4.1V and 800mA, respectively. Furthermore, a method for calculating the secondary current of the transformer to control battery charging current in constant current charging mode which is required for litium-ion battery is proposed and the performance is verified from experiments.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제49권4호
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• pp.265-271
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• 2000

A non-contact battery charger for cellular phone is designed using half-bridge series resonant converter. This converter utilizes series resonance to reduce the undesirable effect of large leakage inductance of the detachable transformer and ZVS operation can reduce switching loss and switching noise. In this paper, analysis and design procedure of half-bridge series resonant converter with detachable transformer is presented. The input voltage is 85VAC∼270VAC, and the output voltage and current is 4.1V and 800mA, respectively. Furthermore, a method of calculating the secondary current of the transformer to control the battery charging current in the constant current charging mode is proposed. The performance of the charger is verified through experiments.