New strain hardening model for sheet metal forming and its applications : 판재 성형 및 적용을 위한 새로운 가공경화 모델

Pham, Quoc Tuan 경북대학교 대학원 2017 국내석사

This study presents a new strain hardening model named as Kim-Tuan model for perfectly describing the flow curve of sheet metals at a wide range of strain. Studied materials in this work are aluminium 5052-O, Advanced High Strength Steel DP980 and commercially pure titanium sheet that are candidates of three metallurgical microstructure: body-centred-cubic (BCC), face-centred-cubic (FCC) and hexagonal-closed-packing (HCP). As a benefit of Kim-Tuan hardening model, the slope of flow curve or the work hardening rate of different materials based on proposed model shows a high agreement with the experimental observation in tensile test. The extrapolation of these calculated flow curves provides the prediction of post-necking behaviour of Kim-Tuan model for tested materials. Furthermore, the post-necking predictions of Kim-Tuan hardening model were matched well with the stress-strain data obtained from hydraulic bulge tests of all tested materials in this study. Additionally, in comparing with the conventional hardening model such as Swift or Voce model, proposed hardening model improves the accuracy of finite element model on simulating the tensile test of AL5052-O sheet. In other issue, proposed hardening model generates a correct prediction of forming limit for CP Ti sheet in comparing with experimental data obtained from punch-stretching test. It is concluded that the Kim-Tuan hardening model is a good choice for studying the large strain problems of sheet metal forming by both mean of analytical and numerical aspects. 이 연구는 광범위의 변형률에 대해 금속판재의 유동 곡선을 완벽하게 설명하기 위한 새로운 가공 경화 모델, 즉 Kim-Tuan 모델을 보여준다. 이 연구에서 실험한 부재는 Al5052-O, Advanced High Strength Steel DP980, 마지막으로 3가지 금속 미세구조를 보여주고 상업적으로 순수한 티타늄 판이다. 여기서 3가지 금속 미세구조는 체심입방구조(BCC), 면심입방구조(FCC), 그리고 육방밀집구조를 말한다. Kim-Tuan 경화 모델의 한가지 장점으로서, 유동 곡선의 기울기나 제시된 모델에 기초한 다른 부재들의 가공 경화율은 인장실험에서 도출한 실험내용과 높은 일치율을 보여준다. 계산된 유동 곡선에 대한 외삽법은 실험한 부재에 대해 Kim-Tuan 모델의 네킹현상 이후의 행동양식을 예측하는데 도움을 준다. 뿐만 아니라, Kim-Tuan 가공 경화 모델의 네킹 이후의 행동 양식에 대한 예측은 이 연구에서 수압팽출실험을 거친 시편들에서 얻어낸 응력-변형률 데이터와 잘 들어 맞는다. 추가적으로, Swift 나 Voce 모델과 같은 전통적인 가공경화 모델과 비교해 봤을때, 제시된 가공 경화 모델은 Al5052-O 판의 인장실험을 모의실험하는데 FE model보다 향상된 정확도를 제공한다. 다시 말해서, 제시된 가공경화 모델은 FLD 시험에서 얻은 실험값과 비교해 봤을때, CP Ti 판의 성형한도에 대한 정확한 예측을 만들어 준다. 결론적으로, Kim-Tuan 가공경화 모델은 높은 변형률에 대한 판재성형학을 연구하는데 훌륭한 선택사항이 될 것이다.

Constitutive modeling of anisotropic sheet metals subjected to large strain forming processes : 대변형을 고려한 이방성 판재의 구성모델링

Pham, Quoc Tuan 경북대학교 대학원 2020 국내박사

Constitutive models of sheet metal are conventionally established based on experimental data obtained from several standardized testing methods such as uniaxial tensile test, biaxial tensile test, in-plane shear test. In industrial forming processes, deformation of sheet materials exceeds the maximum strain observed in the standard tests. Thus, the use of the constitutive models, which are developed up on the standardized tests, in finite element analysis for real parts has limitations. This thesis aims to be a contribution to the further development of sheet metal modeling until large strains in several aspects of plasticity including hardening law, yield function, and forming limits. In this thesis, a new strain hardening law named Kim-Tuan hardening law is developed by combining Swift and Voce models in a novel way to provide a good description of flow stresses in both pre- and post-necking ranges simultaneously. The hardening law contains four parameters which are simply calibrated by a common curve fitting method to minimize the different between the hardening law and the experimental data obtained from uniaxial tensile test. Comparing with bulge test data, the extrapolation of the calibrated hardening law provides a relevant prediction for flow stresses at large strains of various aluminum alloys and advanced high strength steel sheets. In addition, adopting the proposed hardening law in a reverse finite element method to identify the hardening law of several sheet metals reduces the number of iterations in the process. Besides the uniaxial tensile test, calibrating a hardening law in large strain ranges requires the usage of an additional test, for example, bulge test or in-plane shear test. Bsed on curve fitting method, this thesis proposes an alternative procedure for this goal using the measured forming limit at plane strain forming mode, $FLC_0$ coupling with uniaxial tensile test data. In this a fitting routine, the measured $FLC_0$ is introduced into the cost function to constrain the post-necking prediction of hardening law to the reality; while, the usage of uniaxial tensile test data ensures the accuracy of pre-necking evaluation, as usual. It is found that employing the developed procedure decreases the variation of predicted flow stresses according to the selection of hardening models. Several modeling strategies have been proposed in the literature to describe the distortion of subsequent yield surface of sheet metals, especially for HCP structure materials. However, the validation of these methods is limited to the final stage of homogeneous deformation observed in uniaxial tensile tests. In the present study, the evolution of yield surface is further modeled using an isotropic-distortional hardening approach up to larger strain range. In the approach, the evolution of the Yld2000-2d function is modelled as a function of equivalent plastic work, which leads to a better description of material responses of pure titanium sheets subjected to different forming processes. Calculation of forming limit curve (FLC) of sheet metals involves a representative hardening law and yield function. A simple and effective method is presented to estimate the level of limited strain in the plane strain mode, $FLC_0$. The presented method is applied to characterize the role of the hardening law and yield function on the level of the theoretically calculated FLC of sheet metals. It is found that the hardening law strongly influences the $FLC_0$ level, while the yield function is a key factor that influences the shape of the theoretical FLC. 금속 판재의 구성모델은 일반적으로 표준 규격으로 정해진 인장시험, 이축인장시험 그리고 평면전단시험을 기반으로 개발되어졌다. 대부분의 산업용 성형 공정에는 표준 시험에서 관찰 된 것보다 훨씬 큰 변형률이 요구된다. 따라서, 표준 시험을 기반으로 개발된 구성모델을 실제 제품에 대한 유한요소해석에 사용하는 데에는 한계가 있다. 본 논문은 경화식, 항복함수 및 성형한계도를 포함한 소성의 여러 측면에서 대변형까지의 금속 판재의 거동을 표현하는 모델개발에 기여하는 것을 목표로 한다. 본 논문에서는, Swift와 Voce 모델을 기반으로 판재의 인장시험에서 얻어지는 초기넥킹(pre-necking) 및 후-넥킹(post-necking)의 영역에서 동시에 유동 응력을 잘 모사하는 Kim-Tuan 식으로 알려진 저자에 의해 개발된 새로운 경화식을 소개한다. 개발된 경화식은 인장시험에서 얻은 응력과 식으로 계산된 응력의 차이를 최소로 하는 최소자승법을 이용한 커브 피팅 방법으로 간단하게 구할 수 있는 4개의 재료상수를 포함한다. 개발된 식의 유효성을 검증하기 위해 대변형 구간의 데이터를 얻을 수 있는 유압벌지실험을 여러 등급의 알루미늄으로 수행하였으며, 최적화된 파라미터로 얻어진 경화식의 외삽된 결과 실험결과와 잘 일치함을 보였다. 또한, 대변형 영역에서의 파라미터 최적화를 위해서는 단축인장뿐만 아니라, 유압벌지실험 또는 평면 전단시험도 필요하다. 본 논문은 커브피팅 방법에 기초하여 측정된 성형한계도에서 평면변형모드인 $FLC_0$ 값과 인장시험 데이터와 함께 예측하는 방법을 제안한다. 측정된 $FLC_0$ 는 커브피팅 루틴에서 경화함수의 후넥킹 예측을 제한하는 비용함수로 사용된다. 반면에, 단축인장시험의 데이터는 초기넥킹 예측 평가의 정확성을 보장한다. 개발된 파라미터 최적화 절차의 도입은 경화모델의 선택에 따라 예측된 유동응력의 변화가 줄어드는 것을 보여준다. HCP 구조를 가지는 금속 판재의 초기항복 이후에 항복곡면이 왜곡되는 현상을 설명하기 위하여 다양한 모델링 방법이 여러 논문들에서 제안되었다. 그러나, 이들 방법의 검증은 단축인장시험에서 관찰되는 균질 변형의 최종 단계로 제한된다. 최근 연구에서는, 항복곡면의 변화는 더 큰 변형 범위까지 등방성-왜곡 경화모델(isotropic-distortional hardening model) 을 사용하여 모델링되었다. 이 방법은, Yld2000-2d 함수와 등가소성일(equivalent plastic work) 사용하며, 다양한 성형 공정에서의 순티타늄 판재의 재료 거동을 잘 설명한다. 금속판재의 성형한계도의 계산은 경화함수와 항복함수를 포함한다. 평면변형 모드인 $FLC_0$에서 변형의 한계을 평가하기 위한 단순하고 효과적인 방법을 소개한다. 제시된 방법은 이론적으로 계산된 판재의 FLC에서 경화법칙 및 항복함수의 역할을 평가하기 위해 적용됐다. 경화법칙이 $FLC_0$에 강한 영향을 미치는 반면에, 항복함수는 FLC의 형상에 중요한 역할을 하는 것으로 확인됐다.

Effects of herbal drug extracts on Memory and neurotransmitter levels in mice and rats / : Pham Tuan Linh

Pham Tuan Linh 충남대학교 대학원 2002 국내석사

베트남 다문화가정 아동의 사회적 지지가 학교적응에 미치는 영향 : 또래관계 및 적응유연성의 매개효과를 중심으로 : Focusing on the Mediating effect of Peer relation and Resilience

Hoang Tuan Ngoc 인제대학교 일반대학원 2017 국내박사

ABSTRACT The effects of Social support of Vietnamese multicultural Children on School Adjustment - Focusing on the Mediating effect of Peer relation and Resilience - HOANG TUAN NGOC (Advisor: Prof. Lee, Sun Woo) Department of Social Welfare Graduate School, Inje University In this research, dependent variable was school adjustment, independent variable was social support, and mediator variables were peer relation and resilience. The main purpose of this research is to investigate the variable structural causal relationship and direct effect and indirect effect. Quota sampling technique was performed by conducting survey of 200 Vietnamese multicultural family children in elementary school of 1-6 grades in Korean. Questionnaire survey was used on this research. To verify the research hypothesis SPSS and Amos program were used as analytical methods to demonstrate the main effects, mediation effects, direct effects. The result analysis for this study problem can be summarized as follows. First, social support was primarily predicted by the positive effect of school adjustment. Second, social support was primarily predicted by the positive effect of peer relation. Third, social support was primarily predicted by the positive effect of resilience. Fourth, peer relation was not primarily predicted by the effect of school adjustment. Fifth, resilience was primarily predicted by the positive effect of peer relation. Sixth, peer relation as primarily predicted by the positive effect of resilience. Seventh, the regression analysis technique of SEM model was used to determine the directed dependencies among a set of social support, peer relation and school adjustment. Significantly direct effect(β=.541, p<.01), indirect effect(β=.249, p<.05), total effect(β=.790, p<.01. In this analysis the mediation of peer relation and resilience on the effect of social support on school adjustment was found. Eighth, the regression analysis technique of SEM model was used to determine the directed dependencies among a set of social support, peer relation and school adjustment. Significantly direct effect p<.01), indirect effect, total effect. In this analysis the mediation of resilience on the effect of social support on school adjustment was found. Based on these findings, recommendations can be drawn as follows: First, social support was found effecting on school adjustment. Thus, the parent should pay attention on the children and spend time talking and sharing the communication with their children. The Social welfare agencies, the multicultural support center should provide the necessary assistance to Vietnamese multicultural family in education their children. And also, the teacher should be enhance knowledge and skill in teaching and understanding about multicultural family children by training. Second, the mediation of peer relation on the effect of social support on school adjustment was found. To enhance the relationship with peer there should have some programme for sharing and understand each culture background. Third, the mediation of resilience on the effect of social support on school adjustment was found. To enhance the resilience of Vietnamese multicultural family children there should be have the connection of parent, teacher's help. Key words : Vietnamese multicultural children, Social Support, School Adjustment, Peer relation, Resilience. Mediate Effect, Structural Equation Model 국문초록 베트남 다문화가정 아동의 사회적 지지가 학교적응에 미치는 영향 -또래관계 및 적응유연성의 매개효과를 중심으로- 황준옥 (지도교수 이선우) 인제대학교 대학원 사회복지학과 본 연구는 베트남 다문화가정 아동의 사회적 지지, 학교적응, 또래관 계, 적응유연성 간의 구조적 인과관계를 규명하고, 또래관계와 적응유연 성의 매개효과를 파악하는데 목적이 있다. 먼저 베트남 다문화가정 아동 의 사회적 지지가 학교적응에 미치는 영향을 검증하였다. 다음으로 베트 남 다문화가정 아동의 사회적 지지가 학교적응에 미치는 영향에서 또래 관계와 적응유연성 변인에 대한 매개효과를 검증하였다. 본 연구는 한국 에서 초등학교에 다니는 베트남 다문화 가정 아동 200명을 조사 대상으 로 실시하였고 조사대상지역으로 서울, 부산, 울산 대도시 외에도 중·소 도시 김해, 진주, 포항, 창원 등 7개 도시가 포함되었다. 설문지를 통한 설문 조사를 실시하였다. 분석방법은 연구가설을 검증하기 위한 SPSS 프 로그램과 AMOS 프로그램을 활용하였으며, 이를 통해 매개효과를 검증하 였다. 본 연구의 주요결과는 다음과 같다. 첫째, 사회적 지지가 높을수록 학교적응 수준이 높았다. 둘째, 사회적 지지가 높을수록 또래관계가 좋았다. 셋째, 사회적 지지가 높을수록 적 응유연성이 높았다. 넷째, 또래관계가 좋을수록 학교적응 수준이 높았다. 다섯째, 적응유연성이 높을수록 학교적응 수준이 높았다. 여섯째, 또래관 계가 좋을수록 적응유연성이 높았다. 구조방정식 모형에서 독립변인들 각각이 종속변인에 미치는 영향력을 볼 수 있는 것과 같이 잠재변인들의 직접효과를 알 수 있을 뿐만 아니라 간접효과와 총효과의 크기를 파악할 수 있다. 사회적 지지가 학교적응에 미치는 직접효과, 간접효과와 총효과는 모두 통계적으로 유의하게 나타 났다. 총효과는 직접효과와 간접효과의 합이며, 간접효과는 사회적 지지 가 또래관계와 적응유연성을 매개하여 학교적응에 미치는 영향을 의미한 다. 구체적으로 학교적응에 대한 사회적 지지의 간접효과는 사회적 지지 -> 또래관계-> 학교적응, 사회적 지지->적응유연성-> 학교적응, 사회적 지지->또래관계->적응유연성-> 학교적응의 세 가지 간접효과의 합으로 볼 수 있다. 사회적 지지가 학교적응에 미치는 효과가 매개변수인 또래 관계와 적응유연성이 투입되었을 때 사회적 지지와 학교적응에 대한 영 향력이 유의미함에 따라 또래관계와 적응유연성이 부분매개 한다고 볼 수 있다. 이처럼 부분매개효과를 보인다는 것은 또래관계와 적응유연성 이 매개변수로 투입되는 경우 사회적 지지와 학교적응에 미치는 영향에 서 간접경로에 의한 매개효과만 통계적으로 유의하다는 것이다. 베트남 다문화가정 아동의 사회적 지지와 학교적응의 관계에서 또래관계의 매개 효과를 확인해 본 결과 또래관계는 부분매개효과를 가지는 것으로 나타 났다. 이것으로 아동이 사회적 지지는 학교적응에 직접적인 영향을 주기 도 하지만 또래관계를 통해 학교적응에 영향을 준다는 것을 의미한다. 또한, 베트남 다문화가정 아동의 사회적 지지와 학교적응의 관계에서 적 응유연성의 매개효과를 확인해 본 결과 적응유연성은 부분매개효과를 가 지는 것으로 나타났다. 이것은 아동의 사회적 지지는 학교적응에 직접적인 영향을 주기도 하지만 적응유연성을 통해 학교적응에 영향을 준다는 것을 의미한다. 일곱째, 또래관계는 사회적 지지가 학교적응에 미치는 영향을 매개하였다. 여덟째, 적응유연성은 사회적 지지가 학교적응에 미 치는 영향을 매개하였다. 이러한 연구결과를 바탕으로 한 본 연구의 제언은 다음과 같이 제시할 수 있다. 첫째, 아동에 대한 사회적 지지가 학교적응에 영향을 미치는 것으로 나타난 결과를 고려할 때, 아동이 학교에 잘 적응하기 위해서는 부모가 자녀들의 이야기를 주의 깊게 들어줘서 자녀들이 부모와의 대화를 만족 스럽게 느낄 수 있도록 하는 것이 중요하다. 그러기 위해서는 캠핑, 전 통문화체험 등 가족이 함께할 수 있는 프로그램을 통하여 아동에게 부모 의 지지가 잘 전달 될 수 있도록 할 필요가 있다. 또한, 아동에 대한 교 사의 지지가 잘 전달 될 수 있게 하려면 교사들이 다문화에 대한 이해를 질적·양적으로 높일 필요가 있다. 질적으로 높이기 위해서는 다문화교 육 전담인원을 배치하는 제도적 보완이 필요하고, 양적으로 높이기 위해 서는 다문화와 관련된 교육이나 연수로 적극적으로 하는 교사의 의지가 필요하다. 둘째, 사회적 지지가 또래관계를 통해서 학교적응에 영향을 미치는 것 으로 나타난 결과를 고려할 때 아동이 또래관계를 향상시키기 위해서는 일반아동이 가지고 있는 다문화 가정과 다문화 사회에 대한 인식변화를 통해 다문화 감수성을 높여야 한다. 이러한 다문화 감수성 향상을 위해 서 교육청과 학교에서 관련된 프로그램을 필수 교육과정으로 지정하여 일반 아동과 베트남 다문화가정의 아동이 진정으로 함께 할 수 있는 교 육을 만들게 되면 긍정적인 또래관계 또한 자연스럽게 형성될 수 있을 것이다. 셋째, 사회적 지지가 적응 유연성을 통해서 학교적응에 영향을 미치는 것으로 나타난 결과를 고려할 때 적응유연성을 높이기 위해서는 아동에 대한 상담 프로그램이 필요하다. 이러한 상담은 가정에서 부모와 또는 학교에서 교사와 일상적으로 진행할 수 있는 데 아동에게 적절한 상담은 아동의 사회적 지지, 또래관계, 적응유연성을 동시에 높여주어 다문화 가정 아동의 학교적응에 긍정적인 영향을 최대화시킬 것이다. 핵심어 : 베트남 다문화가정 아동, 사회적 지지, 학교적응, 또래관계, 적응유연성, 구조방적식, 매개효과.

Design, Synthesis, and SAR Studies of Novel Scaffolds for Drug Discovery

Ngoc Pham, Tuan-Anh Kangwon National Univ 2013 국내박사

SECTION 1 Design, Synthesis, and Anti-inflammatory Activity of Novel Unnatural C-S-C and C-NH-C Linked Biflavones Biflavonoids are polyphenolic molecules which belong to flavonoid family and consist of a dimer of flavonoids linked to each other by either a C?C or a C?O?C covalent bond. Many different chemical structures of biflavonoids have been isolated from plants and found to possess interesting biological properties. Ochnaflavone, a naturally occurring biflavonoid mainly found in the medicinal plant Lonicera japonica Thunb. (Caprifoliaceae), strongly exhibit anti-inflammatory activity through multiple mechanisms. Furthermore, several synthetic approaches yielded a series of C-C and C-O-C linked biflavonoids with anti-inflammatory potential. Therefore, biflavonoids might provide a basis for novel anti-inflammatory drugs. As a part of continuing structural elaboration and searching more potent anti-inflammatory agents, a series of unnatural C-S-C and C-NH-C linked biflavones were designed, synthesized and evaluated their anti-inflammatory activities. By using transition metal-catalyzed cross-coupling reactions, a series of unnatural C-S-C and C-NH-C linked biflavones including 4 analogues of ochnaflavone and 17 basic biflavones possessing a different array of flavone-flavone linkage were generated successfully. The initial anti-inflammatory activities of ochnaflavone analogues showed promising results relate to iNOS-mediated NO production inhibition. Especially, penta-O-methyl C-S-C linked ochnaflavone analogue (BFO-1) possesses a dual strong inhibitory activities against COX-2-mediated PEG2 and iNOS-mediated NO production. To date, BFO-1 is the only synthetic biflavone having a dual promising PGE2 and NO inhibitory activities. This novel scaffolds might provide a basis for further SAR studies. Keywords: unnatural biflavone, ochnaflavone, anti-inflammatory activity, C-S-C linkage, C-NH-C linkage, cross-coupling reaction. SECTION 2 Novel Scaffolds With Potent GPR119 Agonistic Activity: Design, Synthesis, and SAR Study GPR119 is a G-protein-coupled receptor predominantly express on pancreatic beta cells and intestinal enteroendocrine cells. GPR119 can be actived by lysophosphatidylcholine (LPC), oleoylethanolamine (OEA), N-oleoyldopamin (OLDA), ovalnil and OEA most probably represents the endogenous ligand. GPR119 agonist stimulates glucose-dependent insulin secretion in vitro and lowers an elevated blood glucose level in vivo. Furthermore, they have been demonstrated to stimulate the release of the incretin (GLP-1 and GIP). Therefore, GPR119 agonist has emerged as a promising target for the treatment of type 2 diabetes and obesity by improving glucose homoeostasis while concurrently slowing gastric emptying, reducing food intake and promoting weight loss. To date, several candidates have been entered clinical trials for treatment of type 2 diabetes. Diverse fused aromatic heterocycle scaffolds were found in the precedent literatures and patents of GPR119 agonists. As a congener of bicyclic heterocycle scaffolds, we were interested in quinazoline and purine heterocycle since they have emerged as promising scaffolds in medicinal chemistry and drug development. We have synthesized and characterized a series of novel 2,4-disubstituted quinazolines. We found that the analogues bearing (2-fluoro-4-methylsulfonyl)phenylamino and azabicyclic amine groups with N-Boc (12a, 12c and 12g) exhibited better EC50 values than that of OEA even though they appeared to be partial agonists. Recently, a SAR study with purine scaffold to discover more potent GPR119 agonists is under progress. A series of purine analogues possessing (2-fluoro-4-methylsulfonyl)phenylamino group and aza(bi)cyclic alcohol or aza(bi)cyclic amine groups were generated. Their human GPR119 agonistic activities will be shown in a near future. Keywords: GPR119 agonist, type 2 diabetes, quinazoline, purine, azabicyclic amine, azabicyclic alcohol

A Decentralized Resource Allocation for Small Cells in Heterogeneous Networks

LE ANH TUAN 경희대학교 대학원 2017 국내박사

Small cell networks are envisioned as a promising solution to enhance the capacity and coverage for indoor and cell edge users with less capital expenditure and maintenance cost in the heterogeneous networks (HetNets). To reap the benefits of small cell network deployment, we target optimization-based approaches to employ the resource allocation problems for small cells with various enabling technologies in the future wireless network. Accordingly, the overall small cell network is modeled by an optimization problem. This problem integrates multiple constraints such as transmit powers, backhaul link capacities, radio resources, interference management, and the users' quality of service (QoS) demands into a unified optimization problem. To solve this problem, we exploit the frameworks of the coalitional game, matching theory, and optimization theory to find sub-optimal solutions in a decentralized manner. In this thesis, we particularly investigate two optimization problems for resource allocation in small cells with the cognitive radio and wireless virtualization technologies. These technologies are identified as some of the key emerging technologies for future wireless networks. At first, we consider a resource allocation in the uplink of the cognitive femtocell network (CFN). The goal is to maximize the uplink sum-rate under constraints of intra-tier and inter-tier interference while maintaining the average delay requirement for femtocell users and protecting the macrocell base station. In the solution section, we aim at developing distributed algorithms in which the CFN implementation is self-organized and self-optimized. To this end, we first propose an autonomous framework, in which the femtocell users self-organize into disjoint groups (DJGs). Then, we examine the coalitional game aspects of the subchannel and power allocations in each DJG. We show that the optimization problem can be formulated as a coalitional game in partition form. This game captures realistic inter-coalition effects that are formed by players who are seeking to cooperate and to form coalitions. By using the recursive core method and optimization theory, we develop a distributed algorithm for the power and channel allocations. We prove that the proposed algorithm always converges to a Nash-stable partition. Then, we study resource allocation for small cell networks with the wireless virtualization considering both the backhaul capacity of the infrastructure provider (InP) and the users' QoS requirements. The optimization problem focuses on the profit gained by a mobile virtual network operator (MVNO) which is a middleman who buys physical resource from the InP, bundling them into virtual resources called slides before selling off the service providers. To solve this problem, we propose a distributed solution framework based on Lagrangian relaxation to find a suboptimal decision about slice and transmit power allocations. Furthermore, by exploiting the concept of a matching game, we propose a low complexity solution that makes our proposal much more practical and robust in the virtualized wireless network environment. In all of these scenarios, the proposed frameworks are evaluated based on the simulation results. We show that the proposed frameworks can be implemented in a distributed manner and require a small number of iterations to converge. The experimental results show that the proposed frameworks are better than those of the other frameworks.

Structural engineering of transition metal compounds (W, Mo) for high efficiency of electrochromic devices and hydrogen evolution reaction

Nguyen, Tuan Van 중앙대학교 대학원 2023 국내박사

Bioelectrochemical Denitrification: Microbial Characterization and Kinetics in Response to Different Current Densities and Nitrate Concentrations

Tuan, Doan Van 연세대학교 대학원 2014 국내박사

Engineering of Nanocarriers for the Efficient Targeting and Combinational Delivery for Anticancer Treatment

Tran, Tuan-Hiep 영남대학교 대학원 2016 국내박사

Comparison of three different techniques on the efficacy of canal filling material removing using micro computed tomography

Tuan Anh Nguyen Graduate School, Yonsei University 2019 국내석사

Achieving high quality retreatment, the removal of previous filling materials is the first importance. Several techniques have been used to remove sealer and gutta-percha but none of them can completely clean the root canal walls, particularly in the apical third. That’s significant etiological factor for the success of nonsurgical retreatment. Recently studies showed that the passive ultrasonic irrigation (PUI) technique was only more effective than the conventional irrigation technique in removing residual root filling material in cervical and middle third of root canals. However, the action of the PUI may have been reduced in the apical third because the curvature in the root canals limited apical enlargement. Gentlefile Brush (GB) was invented to overcome the disadvantages of previous instruments, base on the effective of centrifuge force to remove the filling material from the apical third. Micro-CT system can evaluate the quality of the preparation and the quality of the endodontic retreatment in 3D manner nondestructively while preserving the specimen. The aim of this study was to assess the quality of endodontic retreatment by three difference techniques after filled with gutta-percha cone and Well-root MTA sealer, by measuring the percentage of volume debris of gutta-percha and sealer remain intracanal for filling artificial molars with Micro-CT. The filling material was removed from 30 plastic teeth by Nickel-titanium (Ni-Ti) rotary retreatment system. Final irrigation was performed with 2 mL of saline and 10 specimens was randomly allocated in conventional group (n = 10). In PUI group, irrigation with ultrasonic was added to the conventional group procedure for 10 specimens. In GB group, irrigation with GB was added to the conventional group procedure for 10 specimens. To measure the volume of the filling material remain after retreatment and the volume of root canal, Micro-CT (3D) images of the filling material were visualized by CT-Vol. When measuring the amount of filling material remain, a gray scale range between 124 and 255 was assigned as volume of the filling material (Vm), and a gray scale range between 0 and 124 was assigned as volume of empty root canal (Vc). The results showed the total mean volume of residual filling material of an artificial tooth after retreatment in conventional group, PUI group and Gentlefile Brush group were 4.84896 mm3, 0.80702 mm3, and 0.05248 mm3, respectively. The volume of filling materials remain in apical area of GB group was significantly lower than conventional group and PUI group (p < 0.05). The volume of filling material remain in middle area and coronal area was significantly higher in conventional group, compare with PUI group and GB group (p < 0.05). In PUI group, the volume of filling materials remain was significant higher in apical area compared with middle area and coronal area (p < 0.05). Observation by stereo microscope demonstrate that the filling material remain stayed on the root canal wall. However, in PUI group, a large amount of filling materials was remained mainly focused in apical area. The findings of this study indicated that the cleaning effect of GB system was superior to those of NiTi Retreatment files and PUI system in apical area. The cleansing effect of the GB is not impeded by the number of curvature of the root canal due to the GB's properties. GB is better than other techniques used in non-surgical retreatment to remove old root canal filling materials.