• 제목/요약/키워드: Dendritic

검색결과 768건 처리시간 0.032초

선단과냉을 고려한 이원합금의 주상 수지상응고 모델 (A model for columnar-dendritic solidification of binary alloys accounting for dendrite tip undercooling)

  • 유호선
    • 대한기계학회논문집B
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    • 제22권5호
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    • pp.698-707
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    • 1998
  • A simplified model for predicting microsegregation during columnar-dendritic solidification of binary alloys is developed, in which back diffusion, dendrite arm coarsening and dendrite tip undercooling are simultaneously incorporated. The inclusion of tip undercooling is accomplished by modifying the initial conditions of the existing solute diffusion model, in such forms that tip undercooling depresses the beginning of solidification below the liquidus temperature, and that the secondary arm spacing evolves in accordance with the minimum undercooling theory. Sample calculations for the well-known benchmark system show that the present predictions not only consist with the extablished limiting cases, but also agree favorably with the available experimental data within a reasonable tolerance. In particular, a typical decreasing trend in the eutectic fraction at high cooling rates is successfully resolved. Comparison of the individual and combined effects of characteristic parameters in reference with the limiting cases reveals the interactions among parameters. Every parameter plays the role of reducing the eutectic fraction, and the degree of influence depends primarily on the cooling rate. Coarsening enhances the effect of tip undercooling, while suppressing that of back diffusion. A vigorous back diffusion seems to restrain the apperance of the undercooling effect. Overall, each contribution of the three parameters to microsegregation is estimated to be of the same order, which suffices to justify the present study.

저탄소성 용접금속의 응고균열에 미치는 탄소함량의 영향 (The effect of carbon content on hot cracking of low carbon steel weld)

  • 정호신;엄동석
    • Journal of Welding and Joining
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    • 제6권4호
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    • pp.16-26
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    • 1988
  • The effect of carbon content on hot cracking of welded carbon steel was investigated Eight steel plates whose carbon content range from 0.02 to 0.23 percent were welded by autogeous gas tungsten are process. Constant strain was applied to the hot crack test specimen under the strain rate of 0.15 mm per second during welding. The hot cracking susceptibility ws high in the rnage of 0.02-0.05 and 0.12-0.23 percent carbon contents. The critical carbon content immune to hot cracking is in the range from 0.07 to 0.12 percent carbon. By electron probe microanalyser, amanganese segregation was not seen significantly in the whole carbon range. But segregation of silicon was higher in the region of low carbon contents. However, sulphur was segregated remarkably in the region betwen 0.18 and 0.23 percent carbon by peritectic reaction. Very smal lamount of dnedritic structure was observed in the region from 0.02 to 0.05 percent carbon by peritectic reaction. Very small amount of dendritic structure was observed in the region from 0.02 to 0.05 percent carbon but the predominant solidification structure was smooth by cellular growth. The higher the carbon content is, the more the columnar dendritic structure was observed.

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국내 인공댐호의 물리적 환경인자에 의한 호수특성 고찰에 관한 연구 (Studies on the Phisical Environmental Factor Analysis for Water Quality Management in Man-made Lake of Korea)

  • 김좌관;홍욱희
    • 한국환경과학회지
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    • 제1권2호
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    • pp.49-57
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    • 1992
  • First, We classified man-made lakes in Korea as 4-type lakes, that is, there were River-run lakes, Dendritic lakes, Reservoir-lakes, River-mouth lakes, We studied on the environmental factors of 3-type lakes except River-mouth lakes, compared these lakes with natural lakes in foreign country. Environmental factors were watershed area, lake storage, mean depth, hydraulic retention time. As a results, 3-type lakes in Korea had remarkable differences one another according to above-mentioned environmental factors. First, We recognized that River-run lakes had higher nutrient loading according to having wider watershed area than natural lakes, and had lower algal growth rate according to shorter hydraulic retention time than natural lakes. Dendritic lake had higher nutrient loading than natural lakes, longer retention time than River-run lake. Reservoir-lakes had environmental factors between Dentritic lakes and River-run lakes. Therefore, If this studies had no quantitative results about various factors, We recognized that man-made lakes in korea had different environmental factors as compared with natural lakes, and had clear classification among 3-type lakes.

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혈관면역모세포 T세포 림프종의 세침흡인 세포소견 -짧은 증례 보고- (Fine Needle Aspiration Cytological Findings of Angioimmunoblastic T-cell Lymphoma -A Brief Case Report -)

  • 정지한;최현주;강석진;강창석;이교영;유진영
    • 대한세포병리학회지
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    • 제17권2호
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    • pp.159-161
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    • 2006
  • Recently, we experienced a case of Angioimmunoblastic T-cell lymphom (AITL) in a 60-year-old man presented with lymphadenopathy, which is first cytological report in Korea. The cytological features showed a heterogeneous population of small to medium-sized lymphocytes, immunoblasts, and plasma cells. Characteristically, there were also a distinct population of follicular dendritic cells admixed with lymphoid cells, forming the so-called dendritic cell-lymphocyte complexes. Histological features showed the classic morphologic features of AITL. Recognition of the characteristic cytological features can suggest the possibility of AITL.

Morphologic Evidence of Anti-Tumor Specificity of T Cells Activated by Denritic Cells Derived from Peripheral Blood Mononuclear Cells of Thyroid Cancer Patients

  • Lee, Dae-Heui
    • The Korean Journal of Physiology and Pharmacology
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    • 제16권4호
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    • pp.243-247
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    • 2012
  • Recent studies suggest that immunization with autologous dendritic cells (DCs) results in protective immunity and rejection of established tumors in various human malignancies. The purpose of this study is to determine whether DCs are generated from peripheral blood mononuclear cells (PBMNs) by using cytokines such as F1t-3 ligand (FL), granulocyte macrophage-colony stimulating factor (GM-CSF), IL-4, and TNF-${\alpha}$, and whether cytotoxic T cells activated against the thyroid cancer tissues by the DCs. Peripheral blood was obtained from 2 patients with thyroid cancer. DCs were established from PBMNs by culturing in the presence of FL, GM-CSF, IL-4, and TNF-${\alpha}$ for 14 days. At day 14, the differentiated DCs was analyzed morphologically. The immunophenotypic features of DCs such as CDla, CD83, and CD86 were analyzed by immunofluorelescence microscopy. At day 18, DCs and T cells were incubated with thyroid cancer tissues or normal thyroid tissues for additional 4 days, respectively. DCs generated from the PBMNs showed the typical morphology of DCs. Activated cytotoxic T lymphocytes (CTLs) were observed also. DCs and the CTLs were attached to the cancer tissues on scanning electron microscope. The DCs activated the CTLs, which able to specifically attack the thyroid cancer. This study provides morphologic evidence that the coculture of T cells/cancer tissues activated the T cells and differentiated CTLs. The CTLs tightly adhered to cancer tissues and lysed cancer tissues vigorously. Therefore DCs could be used as potential vaccines in the immunotherapy.

금속이온 착체에 의한 G4-48PyP 덴드리머 LB막의 전기적 특성 (Electrical Properties of G4-48PyP Dendrimer LB Films complex with Metal Ions)

  • 정상범;유승엽;박재철;권영수
    • 한국전기전자재료학회:학술대회논문집
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    • 한국전기전자재료학회 2002년도 하계학술대회 논문집 Vol.3 No.2
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    • pp.769-772
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    • 2002
  • Dendrimers are well-defined macromolecules exhibiting a tree-like structure, first derived by the cascade molecule approach. Peculiar features of the dendritic geometry are the large number of end groups as well as the shape persistence in higher generations, approaching spherical geometry. And one of the most peculiar characteristics of dendritic macromolecules is their controlled molecular structure and orientation, which means that they have a practical application in achieving a highly organized molecular arrangement. We attempted to fabricate a dendrimer LB films containing 48 pyridinepropanol functional end group. As the pyridinepropanol functional group could form a complex structure with metal ions. We investigated the surface activity of dendrimer films at air-water interface compared with pure dendrimer and its complex with $Fe^{2+}$ ions into subphase. We though that metal ions are contributed to networking or branching reaction between dendrimers. And we expected that it can result in the differences on the electrical properties. We have studied the electrical properties of the ultra thin dendrimer LB films investigated by the current-voltage characteristics of metal dendrimer LB films/metal (MIM) structure.

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Adhesion of CD40-stimulated Germinal Center B Cells to HK Cells Employs the CD11a/CD18-CD54 Interactions

  • Lee, Joonhee;Choe, Jongseon
    • IMMUNE NETWORK
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    • 제3권3호
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    • pp.176-181
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    • 2003
  • Background: The molecular basis of follicular dendritic cells (FDC)-germinal center (GC) B cell interaction is largely unknown, although this cellular interaction is thought to be important for the whole process of GC B cell differentiation. Methods: Using FDC-like cells, HK, and highly purified GC B cells, we attempted to identify the molecules that play critical roles in the interactions between FDC and B cells. GC B cells were co-cultured with HK cells and soluble CD154 in the presence or absence of various function-blocking monoclonal antibodies to examine their effect on GC B cell binding to HK cells and B cell proliferation. Results: Anti-CD11a and anti-CD54 antibodies inhibited GC B cell binding to HK cells while anti-CD49d and anti-CD106 antibodies did not. GC B cell proliferation was not impaired by the disruption of GC B cell-HK cell adherence. Conclusion: Our results suggest that CD11a/CD18-CD54 interactions play an important roles in the initial binding of GC B cells to FDC and diffusible growth factors from FDC may be responsible the massive proliferation of GC B cells.

Non-blinking dendritic crystals from C-dot solution

  • Mewada, Ashmi;Vishwakarma, Ritesh;Patil, Bhushan;Phadke, Chinmay;Kalita, Golap;Sharon, Maheshwar;Sharon, Madhuri
    • Carbon letters
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    • 제16권3호
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    • pp.211-214
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    • 2015
  • Bio-imaging and drug carriers for delivery have created a huge demand for crystals. Crystals are fascinating materials that have been grown for a long time but obtaining biocompatible fluorescent crystals is a challenging task. We report on the growth of fluorescent crystals using a carbon dot (C-dot) solution by a hydrothermal process. The crystallization pattern of these C-dots exhibited a unique dendritic structure having a feather-like morphology. The growth temperature and pressure were maintained at 60℃ and 200 mmHg, respectively, for crystal growth. A green fluorescence (under UV light) that was observed in the C-dot solution was retained in the crystals formed from the solution. Cytotoxicity studies on Vero cells revealed the crystals to be extremely biocompatible. These fluorescent crystals are extremely well suited for biomedical and optoelectronic applications.

역확산을 고려한 이원합금의 비평형 수지상응고 해석 (Analysis on the non-equilibrium dendritic solidification of a binary alloy with back diffusion)

  • 정재동;유호선;이준식
    • 대한기계학회논문집B
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    • 제20권10호
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    • pp.3361-3370
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    • 1996
  • Micro-Macro approach is conducted for the mixture solidification to handle the closely linked phenomena of microscopic solute redistribution and macroscopic solidification behavior. For this purpose, present work combines the efficiency of mixture theory for macro part and the capability of microscopic analysis of two-phase model for micro part. The micro part of present study is verified by comparison with experiment of Al-4.9 mass% Cu alloy. The effect of back diffusion on the macroscopic variables such as temperature and liquid concentration, is appreciable. The effect, however, is considerable on the mixture concentration and eutectic fraction which are indices of macro and micro segregation, respectively. According to the diffusion time, the behavior near the cooling wall where relatively rapid solidification permits short solutal diffusion time, approaches Scheil equation limit and inner part approaches lever rule limit.

테일러-갤러킨 유한요소법에 의한 하도추적 모형의 적용 -홍수시 하천 유량 모의- (Application of Channel Routing Model by Taylor-Galerkin Finite Element Method -Modeling of Flow in Flood-)

  • 이해균
    • 한국콘텐츠학회논문지
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    • 제11권1호
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    • pp.404-410
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    • 2011
  • 1차원 개수로 부정류의 수치 해석을 위하여 Taylor-Galerkin 기법의 유한요소법을 St. Venant 방정식의 차분에 적용하였다. 단일 수로에서 수문의 닫힘에 의한 배수문제와 3개 이상 하도가 만나는 합류점을 포함하는 수지상(dendritic) 하천 네트워크에 적용하고 그 결과를 기존에 제시된 유한차분법, 유한요소법 등의 수치기법과 비교하였으며 매우 잘 일치함을 확인하였다. 본 연구에서 적용한 기법은 연속방정식과 운동량방정식을 순차적으로 해석해 나가기 때문에 적용이 간편하며, 최종적으로 삼대각 행렬과 합류점의 적합조건을 위한 최소한의 요소를 포함하기 때문에 삼대각 행렬의 연산 방법을 적용할 수 있어 계산 측면에서 빠르고 안정적이다. 또한, 행렬의 저장을 위한 메모리 측면에서 경제적이다.