• Korean Journal of Mathematics
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• 제16권3호
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• pp.281-290
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• 2008

The purpose of this paper, GM modules are defined as a generalization of AGR rings. Also, from the faithful GM-property, we get a commutativity of rings. Finally, for a nearring R, we will introduce MR groups, and also derive some properties of GM modules and MR groups.

• 대한수학회지
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• 제42권6호
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• pp.1153-1167
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• 2005

In this paper, all rings and all near-rings R are associative, all modules are right R-modules. For a near-ring R, we consider representations of R as R-groups. We start with a study of AGR rings and their properties. Next, for any right R-module M, we define a new concept GM module and investigate the commutative property of faithful GM modules and some characterizations of GM modules. Similarly, for any near-ring R, we introduce an R-group with MR-property and some properties of MR groups.

• Investigative Magnetic Resonance Imaging
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• 제7권1호
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• pp.47-55
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• 2003

목적 : 뇌피질 이형성증의 다양한 자기공명영상소견을 유형별로 분류하고 병리적 등급 및 유형과의 연관성을 분석한다. 대상 및 방법 : 수술 후 병리적으로 뇌피질 이형성증이 확진된 97명을 대상으로 하였다. 수술 전 MR 영상을 후향적으로 분석하였으며, 이상 소견의 유무에 따라 MR 양성군과 MR 음성군으로 나누었다. MR 양성군에서는 뇌회와 인접지주막하 공간의 크기, 뇌피질 두께, 피질하백질의 신호 강도, 뇌피질과 백질 경계부의 명확성에 의하여 MR 이상 소견을 분류하였다. 병리적 소견 역시 영상 소견을 모르는 상태에서 후향적으로 분석하였으며, 경도, 중등도, 고도와 비풍선세포형, 풍선세포형으로 나누었다. MR 양성군과 음성군 사이에서 그리고 MR 양성군의 네 가지 유형 내에서 각각 병리적 등급 및 유형의 차이가 있는지 분석하였다. 결과: MR 양성군과 음성군은 각각 39 (40%) 명, 58 (60%) 명이었다. MR 양성군 중 위축형은 13 (33%)명, 피질띠형은 9 (23%)명, 내측 만곡형은 9 (23%)명, 그리고 비특이적 형태는 8 (21%)명이었다. MR 양성군과 음성군 사이에서 병리적 등급은 의미 있는 차이가 없었으나, MR음성군에 비하여 MR 양성군에서 고도의 병리적 등급의 빈도가 높은 경향을 보였으며 또한 풍선 세포형의 빈도 역시 유의하게 높았다. (5% Vs 2l%, p＜0.05). 특히 MR 양성군 중에 내측 만곡형은 고도의 병리적 등급과 풍선세포형의 빈도가 각각 78% (7/9), 56% (5/9)인 반면에, 위축형은 경도의 등급과 비풍선세포형의 빈도가 각각 77% (10/13), 100%(13/13)이었다. 결론: 뇌피질이형성증 환자의 MR 영상에서 반 이하에서만 이상 소견을 발견할 수 있었고, 특히 내측 만곡형은 병리적으로 고도의 등급 및 풍선세포형, 그리고 위축형은 경도의 등급 및 비풍선세포형과 높은 연관성을 보여 주었다.

• Korean Journal of Radiology
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• 제2권2호
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• pp.80-86
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• 2001

Objective: To assess the potential clinical utility of in-vivo 31P magnetic resonance spectroscopy (MRS) in patients with various malignant and benign breast lesions. Materials and Methods: Seventeen patients with untreated primary malignant breast lesions (group I), eight patients with untreated benign breast lesions (group II) and seven normal breasts (group III) were included in this study. In-vivo 31P MRS was performed using a 1.5 Tesla MR scanner. Because of the characteristics of the coil, the volume of the tumor had to exceed 12 cc (3×2×2 cm), with a superoinferior diameter at least 3 cm. Mean and standard deviations of each metabolite were calculated and metabolite ratios, such as PME/PCr, PDE/PCr, T-ATP/PCr and PCr/T-ATP were calculated and statistically analyzed. Results: Significant differences in PME were noted between groups I and III (p=0.0213), and between groups II and III (p=0.0213). The metabolite ratios which showed significant differences were PME/PCr (between groups II and III) (p=0.0201), PDE/PCr (between groups I and III, and between groups II and III) (p=0.0172), T-ATP/PCr (between groups II and III) (p=0.0287), and PCr/T-ATP (between groups II and III) (p=0.0287). There were no significant parameters between groups I and II. Conclusion: In-vivo 31P MRS is not helpful for establishing a differential diagnosis between benign and malignant breast lesions, at least with relatively large lesions greater than 3 cm in one or more dimensions.

• Korea-Australia Rheology Journal
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• 제20권2호
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• pp.45-50
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• 2008

This paper presents an experimental approach to study the effect of friction on magnerorheological (MR) fluids. Both steady and dynamic modes were employed to investigate MR fluid behaviors. The experimental results indicate that the total MR effects are dominated by two factors: magnetic force and friction force. Conventionally, the magnetic force contribution to MR effect has been intensively studied while the friction force effect has attracted less attention. This study provides a method to quantitatively predict the friction contribution to the total MR effect. It may be used to effectively analyze enhanced MR effects reported by other groups. Also, it might provide good guidance to develop high-efficiency MR fluids.

• Korean Journal of Radiology
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• 제21권9호
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• pp.1065-1076
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• 2020

Objective: To determine the prognostic value of MRI-based tumor regression grading (mrTRG) in rectal cancer compared with pathological tumor regression grading (pTRG), and to assess the effect of diffusion-weighted imaging (DWI) on interobserver agreement for evaluating mrTRG. Materials and Methods: Between 2007 and 2016, we retrospectively enrolled 321 patients (male:female = 208:113; mean age, 60.2 years) with rectal cancer who underwent both pre-chemoradiotherapy (CRT) and post-CRT MRI. Two radiologists independently determined mrTRG using a 5-point grading system with and without DWI in a one-month interval. Two pathologists graded pTRG using a 5-point grading system in consensus. Kaplan-Meier estimation and Cox-proportional hazard models were used for survival analysis. Cohen's kappa analysis was used to determine interobserver agreement. Results: According to mrTRG on MRI with DWI, there were 6 mrTRG 1, 48 mrTRG 2, 109 mrTRG 3, 152 mrTRG 4, and 6 mrTRG 5. By pTRG, there were 7 pTRG 1, 59 pTRG 2, 180 pTRG 3, 73 pTRG 4, and 2 pTRG 5. A 5-year overall survival (OS) was significantly different according to the 5-point grading mrTRG (p = 0.024) and pTRG (p = 0.038). The 5-year disease-free survival (DFS) was significantly different among the five mrTRG groups (p = 0.039), but not among the five pTRG groups (p = 0.072). OS and DFS were significantly different according to post-CRT MR variables: extramural venous invasion after CRT (hazard ratio = 2.259 for OS, hazard ratio = 5.011 for DFS) and extramesorectal lymph node (hazard ratio = 2.610 for DFS). For mrTRG, k value between the two radiologists was 0.309 (fair agreement) without DWI and slightly improved to 0.376 with DWI. Conclusion: mrTRG may predict OS and DFS comparably or even better compared to pTRG. The addition of DWI on T2-weighted MRI may improve interobserver agreement on mrTRG.

• Tribology and Lubricants
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• 제27권4호
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• pp.213-217
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• 2011

In this study, friction characteristics using elastomeric actuator with Magneto-rheological (MR) materials are identified. Typically, Magneto-rheological materials are divided into two groups by MR fluid in fluid state and MR elastomer in solid state like rubber. The stiffness characteristics of Magneto-rheological material can be changed as magnetic field is applied. MR fluid has been applied to various industry fields such as to brake, clutch, damper, engine mount and etc. However, MR fluid has been used under the sealed condition to prevent leaking issues. In order to overcome these problems, MR elastomer that has same property as MR fluid has been developed and studied. MR elastomer mainly consists of polymer material such as natural rubber or silicon rubber with particles that can be polarized with magnetic field. And it is called as a smart material since its stiffness and damping characteristics can be changed. In this study, MR elastomer is produced and pin-on-disc tests are carried out to identify the friction characteristics of the material. Several test conditions are applied to evaluate the feasibility to use as a smart actuator in the field of vibration control.

• 보험의학회지
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• 제30권2호
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• pp.12-15
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• 2011

Background: The beneficial effects of implantable cardioverter defibrillators (ICDs) in primary and secondary prevention patients are well established. However, data on potential differences between both groups in mortality are scarce. The aim of this study was to assess extra risk differences between primary and secondary prevention ICD recipients. Methods: Comparative mortality figures were calculated from a source article using mortality analysis methods. Results: Mortality ratio (MR) of primary and secondary prevention ICD recipients were 393% and 373%. Excess death rates (EDR) of both groups were 42 and 38 per 1,000. Discussion: MR and EDR were higher in primary prevention group. But, there was no significant difference.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 추계학술대회 논문집
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• pp.92-93
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• 2013

In this study, Shock Absorption performance of Magneto-rheological elastomer(MRE) is identified through the drop impact test. Magneto-rheological materials are divided into two groups by MR fluid in fluid state and MR elastomer in solid state like rubber. The stiffness characteristics of Magneto-rheological material can be changed as magnetic field is applied. The impact loads in MR elastomer were measured under weight of impactor. Experiment results are shown through the experiments to confirm the effect of shock absorption of MR elastomer. Thus, the MR elastomer can be applied to shock absorber used in area that shock occurs.

• 대한자기공명의과학회:학술대회논문집
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• 대한자기공명의과학회 2003년도 제8차 학술대회 초록집
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• pp.98-98
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• 2003

We will present various MR findings of hyperacute ischemic stroke with our own experiences in the management of the patients according to the findings. 대상 및 방법： A total of 441 patients were underwent 'acute stroke MR' imaging protocol between Mar. 2001 and Jun. 2003. The protocol included initial T2-weighted image (WI), diffusion WI (DWI, b=2000), time-of-flight (TOF) MR angiography (MRA), and pefusion WI(PWI), and follow-up T2WI, DWI, TOF MRA, and neck vessel contrast-enhanced MRA obtained three to five days after the insult. Among them, we retrospectively reviewed the MR findings and clinical courses of 193 patients with anterior circulation territorial infarction. Those ICA and MCA lesions were divided into six and five groups respectively according to the level and mechanism of the occlusion. PWI findings can be another factor in the management planning.