• 대한전자공학회논문지SD
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• 제40권11호
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• pp.83-94
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• 2003

본 논문에서는 빠른 정착시간을 갖는 전류셀(Current Cell) 매트릭스의 구조와 출력의 Gain error를 보정할 수 있는 Self calibration current bias 회로의 기능을 가진 고성능 10-bit D/A 변환기를 제안한다. 매트릭스 구조 회로의 복잡성으로 인한 지연시간의 증가 및 전력 소모를 최소화하기 위해 상위 6MSB(Most Significant Bit)전류원 매트릭스와 하위 4LSB(Least Significant Bit)전류원 매트릭스로 구성된 2단 매트릭스 구조로 설계되어 있다. 이러한 6＋4 분할 구조를 사용함으로써 전류 원이 차지하는 면적과 Thermometer decoder 부분의 논리회로를 가장 최적화 시켜 회로의 복잡성과 Chip 사이즈를 줄일 수 있었고 낮은 Glitch 특성을 갖는 저 전력 D/A 변환기를 구현하였다. 또한 self Calibration이 가능한 Current Bias를 설계함으로서 이전 D/A 변환기들의 칩 외부에 구현하던 Termination 저항을 칩 내부에 구현하고 출력의 선형성 및 정확성을 배가시켰다. 본 연구에서는 3.3V의 공급전압을 가지는 0.35㎛ 2-poly 4-metal N-well CMOS 공정을 사용하였고, 모의 실험결과에서 선형성이 매우 우수한 출력을 확인하였다. 또한 소비전력은 45m W로 다른 10bit D/A 변환기에 비해 매우 낮음을 확인 할 수 있었다. 실제 제작된 칩은 Spectrum analyzer에 의한 측정결과에서 100㎒ 샘플링 클럭 주파수와 10㎒ 입력 신호 주파수에서 SFDR은 약 65㏈로 측정되었고, INL과 DNL은 각각 0.5 LSB 이하로 나타났다. 유효 칩 면적은 Power Guard ring을 포함하여 1350㎛ × 750 ㎛ 의 면적을 갖는다.

• 대한전자공학회논문지SD
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• 제39권7호
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• pp.57-65
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• 2002

본 논문에서는 CMOS로 구현된 2.5v 10-bit 300MSPS의 D/A 변환기를 제안하였다. 이를 위해 전체구조는 고속동작에 유리한 전류구동 방식의 8+2 분할 타입으로 상위 8-bit은 Thermometer Code 기법을 이용한 전류셀 매트릭스(Current Cell Matrix)로, 하위 2-bit은 이진 가중 전류열(Binary Weighted Current Array)로 설계하였다. 우수한 다이내믹 특성 및 고속 동작을 만족시키기 위해 낮은 글리치 에너지를 갖는 새로운 전류셀과 BDD(Binary Decision Diagram)에 의한 논리합성 기법을 활용한 새로운 역 Thermometer Decoder를 제안하였다. 제안된 DAC는 $0.25{\mu}m$, 1-Poly, 5-Metal, n-well CMOS 공정으로 제작되었으며, 유효 칩 면적은 $1.56mm^2$이고, 2.5V의 전원전압에서 84mW의 전력소모를 나타내었다. 모의실험 및 측정을 통해 최대 글리치 에너지는 0.9pVsec@fs=100MHz, 15pVsec@fs=300MHz로 나타났다. 또한 출력 주파수가 1MHz, 샘플링 주파수가 300MHz에서의 INL과 DNL은 약 ${\pm}$1.5LSB 이내로, SFDR은 45dB로 측정되었다.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제28권6호
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• pp.456-463
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• 2002

Distraction osteogenesis is a well-established clinical treatment for limb length discrepancy and skeletal deformities. Appropriate mechanical tension-stress is believed not to break the callus but rather to stimulate osteogenesis. In contrast to fracture healing, the mode of bone formation in distraction osteogenesis is primarily intramembranous ossification. Although the biomechanical, histological, and ultrastructural changes associated with distraction osteogenesis have been widely described, the basic biology of the process is still not well known. Moreover, the molecular mechanisms in distraction osteogenesis remain largely unclear. Recent studies have implicated the growth factor cascade is likely to play an important role in distraction. And current reserch suggested that mechanical tension-stress modulates cell shape and phenotype, and stimulates the expression of the mRNA for bone matrix proteins. This article presents the hypotheses and current research that have furthered knowledge of the molecular biology that govern distraction osteogenesis. The gene regulation of growth factors and extracellular matrix proteins during distraction osteogenesis are discussed in this article. It is believed that understanding the biomolecular mechanisms that mediate distraction osteogenesis may guide the development of targeted strategies designed to improve distraction osteogenesis and accelerate bone healing.

• 대한화장품학회지
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• 제38권3호
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• pp.263-273
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• 2012

최근 연구에서 잠재적 피부 색소침착 경감제로서 파라-쿠마린산(PCA)의 주목되는 특성이 발견되었다. 본 연구의 목적은 이 물질의 자외선 차단 효과를 탐구하는 것이다. 자외선에 노출된 HaCaT 세포의 생존율에 대한 PCA의 영향을 in vitro에서 조사하고, 자외선 흡수 스펙트럼이 유사한 방향성 아미노산 대사물들의 작용과 비교하였다. In vivo시험으로는 PCA 크림(1.5 %)과 크림 베이스를 SKH-1 무모 쥐의 등 피부에 도포하고 UVB에 의한 염증 반응으로 나타나는 피부색(홍반) 및 두께 변화(부종)를 측정하였다. 크림 도포-자외선 조사는 2일 간격으로 총 12회 반복하였다. HaCaT 세포를 UVB에 노출시켰을 때 광량 의존적으로 세포 생존율이 감소하였다. 자외선 노출(10 mJ $cm^{-2}$)에 의한 세포 생존율감소는 100 ${\mu}M$의 PCA, cinnamic acid, urocanic acid, 그리고 indole acrylic acid에 의해 각각 39, 27, 39, 31 %가 억제되었다. 무모 쥐의 등 부위에 도포된 PCA크림(10 ${\mu}g\;cm^{-2}$)은 자외선(150 mJ $cm^{-2}$)-노출 피부의 색 지수, 즉 $L^*$, $a^*$ 및 $b^*$ 값, 그리고 두께의 변화를 각각 59, 50, 58, 53 %씩 억제하였다. 본 연구의 결과는 PCA의 멜라닌 생성 억제 작용을 밝힌 선행 연구와 함께 PCA가 자외선에 노출된 피부의 색소 이상 침착과 염증 반응을 막아줄 수 있음을 시사하였다.

• 한국생물공학회:학술대회논문집
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• 한국생물공학회 2000년도 추계학술발표대회 및 bio-venture fair
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• pp.421-424
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• 2000

Cartilage injuries are frequent nowadays. The previous surgical treatment of cartilage defect was limited. Another approach in the treatment of cartilage injuries is the use of reconstitute cartilage consisting of chondrocytes cultured in suitable biodegradable scaffolds. Current studies have demonstrated the compatibility of chondrocytes with different biomaterials and the chondrogenesis in various types of porous scaffolds. The cell ingrowth into the porous scaffolds is modulated by initial cell loading efficiency. Therefore, well-interconnected pore structure and even pore distribution of the scaffolds are essential for efficient cell seeding. According to our previous work, well-interconnected macroporous scaffolds can be prepared by gas-foaming/salt-leaching method using ammonium bicarbonate salt as porogen additives. In this work, primary chondrocytes were cultured in PLGA 65/35 scaffolds fabricated by using our method. Cells seeded in the scaffolds showed well distribution by agitated seeding method. Histochemical staining of proteoglycans present in the scaffolds was used to visualize the chondrocyte ingrowth in the scaffolds. At 3 weeks, the population of chondrocytes was increased for the most part of the scaffolds, and extra cellular matrix (ECM) secretion was increased as culture periods progressed.

• 한국전산유체공학회지
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• 제19권1호
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• pp.27-33
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• 2014

A new and efficient implicit scheme is proposed to obtain a steady-state solution in time integration and the comparison of characteristics with the approximation ways for the implicit method to solve the incompressible Navier-Stokes equations is provided. The conservative, finite-volume cell-vertex upwind scheme and artificial compressibility method using dual time stepping for time accuracy is applied in this paper. The numerical results obtained indicate that the direct application of Jacobian matrix to the Lower and upper sweeps of implicit LU-SGS leads to better performance as well as convergence regardless of CFL number and true time step than explicit scheme and approximation of Jacobian matrix. The flow simulation around box in uniform flow with unstructured meshes is demonstrated to check the validity of the current formulation.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 하계학술대회 논문집
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• pp.889-892
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• 2000

We have investigated the Pt doping effect on structural and electrochemical properties of amorphous vanadium oxide film, grown by radio frequency magnetron sputtering. Room temperature charge-discharge measurements based on a half-cell with a constant current clearly indicated that the Pt doping could improve the cyclibility of V$_2$O$_{5}$ cathode film. Using glancing angle x-ray diffraction (GXRD) and high resolution transmission electron microscopy (HRTEM) analysis, we found that the Pt doping with l0W r.f. power induce more random amorphous structure than undoped V$_2$O$_{5}$ film. As the r.f. power of Pt increases, large amount of Pt incorporates into amorphous V$_2$O$_{5}$ and makes PtOx microcrystalline phase in amorphous matrix. This result suggests that the semicondcuting PtOx microcrystalline phase in amorphous matrix lead to a drastically faded cyclibility of 50W Pt doped V$_2$O$_{5}$ cathode film. Possible explanations are given to describe the Pt doping effect on cyclibility of vanadium oxide cathode film.de film.

• 한국전기전자재료학회논문지
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• 제13권9호
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• pp.751-757
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• 2000

The r.f. power effect for Pt doping is investigated on structural and electrochemical properties of amorphous vanadium oxide(V$_2$O$_{5}$) film, grown by direct current (d.c.) magnetron sputtering. Room temperature charge-discharge measurements based on a half-cell with a constant current clearly indicated that the Pt doping could improve the cyclibility of V$_2$O$_{5}$ cathode film. Using glancing angle x-ray diffraction(GXRD) and high-resolution transmission electron microscopy (HRTEM) analysis, we found that the Pt doping with 10W r.f. power induces more random amorphous structure than undoped V$_2$O$_{5}$ film. As the r.f. power of Pt target increases. large amount of Pt atoms incorporates into the amorphous V$_2$O$_{5}$ film and makes $\alpha$-PtO$_2$microcrystalline phase in the amorphous V$_2$O$_{5}$ matrix. These results suggest that the semiconducting $\alpha$-PtO$_2$ microcrystalline phase in amorphous matrix lead to a drastically faded cyclibility of 50W Pt doped V$_2$O$_{5}$ cathode film. Possible explanations are given to describe the Pt doping effect on cyclibillity of the amorphous V$_2$O$_{5}$ cathode film battery. film battery.

• 대한의용생체공학회:의공학회지
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• 제39권5호
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• pp.188-207
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• 2018

Recently, three-dimensional (3D) printing of biological tissues and organ has become an attractive interdisciplinary research topic that combines a broad range of fields including engineering, biomaterials science, cell biology, physics, and medicine. The 3D bioprinting can be used to produce complex tissue engineering scaffolds based on computer designs obtained from patient-specific anatomical data. It is a powerful tool for building structures by printing cells together with matrix materials and biochemical factors in spatially predefined positions within confined 3D structures. In the field of the 3D bioprinting, three major categories of the 3D bioprinting include the stereolithography-based, inkjet-based, and dispensing-based bioprinting. Some of them have made significant process. Each technique has its own advantages and limitations. Compared with non-biological printing, the 3D bioprinting should consider additional complexities: biocompatibility, degradability of printing materials, cell types, cell growth, cell viability, and cell proliferation factors. Numerous 3D bioprinting technologies have been proposed, and some of them have been making great progress in printing several tissues including multilayered skin, cartilaginous structures, bone, vasculature even heart and liver. This review summarizes basic principles and key aspects of some frequently utilized printing technologies, and introduces current challenges, and prospects in the 3D bioprinting.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제32권6호
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• pp.524-529
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• 2006

For the repairing of bone defect, autogenous or allogenic bone grafting remains the standard. However, these methods have numerous disadvantages including limited amount, donor site morbidity and spread of diseases. Tissue engineering technique by culturing stem cells may allow for a smart solution for this problem. Adipose tissue contains mesenchymal stem cells that can be differentiate into bone, cartilage, fat or muscle by exposing them to specific growth conditions. In this study, the authors procured the stem cell from buccal fat pad and differentiate them into osteoblast and are to examine the bone induction capacity. Buccal fat-derived cells (BFDC) were obtained from human buccal fat pad and cultured. BFDC were analyzed for presence of stem cell by immunofluorescent staining against CD-34, CD-105 and STRO-1. After BFDC were differentiated in osteogenic medium for three passages, their ability to differentiate into osteogenic pathway were checked by alkaline phosphatase (ALP) staining, Alizarin red staining and RT-PCR for osteocalcin (OC) gene expression. Immunofluorescent and biochemical assays demonstrated that BFDC might be a distinguished stem cells and mineralization was accompanied by increased activity or expression of ALP and OC. And calcium phosphate deposition was also detected in their extracelluar matrix. The current study supports the presence of stem cells within the buccal fat pad and the potential implications for human bone tissue engineering for maxillofacial reconstruction.