• 한국정보과학회논문지:데이타베이스
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• 제32권6호
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• pp.641-649
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• 2005

오늘날 인터넷의 발달과 함께 XML이 많이 사용됨에 따라, XML 저장소와 질의 처리에 관한 연구가 활발하게 이뤄지고 있다. XML에서는 경로 질의를 사용하는데, 이러한 경로 질의를 효과적으로 처리하기 위하여 여러 가지 색인 기법들이 연구되었다. 최근에는 구조 조인 기법이 각광을 받고 있다. 구조 조인 기법은 엘리먼트들의 포함 관계를 살펴 질의를 처리한다. 특히 문서 전체에 대한 탐색을 하지 않고 해당하는 엘리먼트들의 역색인 리스트만을 비교하여 질의 처리를 수행하는 장점을 갖는다. 하지만 구조 조인 기법은 실제 질의 결과에 포함되지 않는 불필요한 엘리먼트들도 탐색해야 하는 비효율성을 가진다. 따라서 본 논문에서는 구조 조인 기법의 성능을 개선하는 레벨 구조 조인 기법을 제안한다. 제안하는 기법은 경로 질의 내 엘리먼트 사이의 관계 정보와 XML 문서 내의 엘리먼트들의 레벨 분포 정보를 이용한다. 이를 통해 구조 조인을 수행할 때, 비교되는 역색인 리스트 내의 모든 엘리먼트들이 아닌, 특정 레벨에 해당하는 엘리먼트들만을 이용하여 비교를 수행함으로써 질의 처리의 속도를 향상시킬 수 있다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.193-194
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• 2006

A solid freeform fabrication (SFF) system using selective laser sintering (SLS) is currently recognized as a leading process and SLS extends the applications to machinery and automobiles due to the variousmaterials employed. In order to develop a more elaborate and rapid system for fabricating large objects compared to existing SLS, this study employs a new selective dual-laser sintering (SDLS) process. Also, this paper will address development of an SFF system which employs the dual laser system and the unique scanning device. Experiments were performed to evaluate the effect of a scanning path and fabrication parameters on sintering process and to fabricate the various 3D objects using polymer powder.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2005년도 춘계학술대회 논문집
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• pp.395-400
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• 2005

Nano-scale fabrication of silicon substrate based on the use of atomic force microscopy (AFM) was demonstrated. A specially designed cantilever with diamond tip, allowing the formation of damaged layer on silicon substrate by a simple scratching process, has been applied instead of conventional silicon cantilever for scanning. A thin damaged layer forms in the substrate at the diamond tip-sample junction along scanning path of the tip. The damaged layer withstands against wet chemical etching in aqueous KOH solution. Diamond tip acts as a patterning tool like mask film for lithography process. Hence these sequential processes, called tribo-nanolithography, TNL, can fabricate 2D or 3D micro structures in nanometer range. This study demonstrates the novel fabrication processes of the micro cantilever and diamond tip as a tool for TNL using micro-patterning, wet chemical etching and CVD. The developed TNL tools show outstanding machinability against single crystal silicon wafer. Hence, they are expected to have a possibility for industrial applications as a micro-to-nano machining tool.

• 전자공학회논문지S
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• 제35S권7호
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• pp.86-94
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• 1998

The rosette-scan seeker is a device mounted on the infrared guided missile. It offers the positions and iamges of target to missiles servo system by scanning a space about target in rosette pattern with a single detector. An instantaneous field of view (IFOV), which is a diameter of a detector moving along the path of the rosette pattern, has the property that its smaller size provide the less interference of background signals and detector noise. If its size is too small to voer the total field of view (TFOV), however, it produces the invisible regions in the TFOV. In this case, the invisible regions cause the performance of the seeker to deteriorate. For full scan-coverage, it is necessary to design the small IFOV without the invisible regions in the TFOV, as possible. In this paper, we propose the new method of designing the smaller IFOV than the conventional method and verify full coverage of the scanned region. By comparing the nose equivalent flux density (NEFD) of the proposed method with the that of the conventional one, we confirm that the former is better than the latter in terms of performance.

• 한국정밀공학회지
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• 제23권8호
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• pp.39-46
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• 2006

Nano-scale fabrication of silicon substrate based on the use of atomic force microscopy (AFM) was demonstrated. A specially designed cantilever with diamond tip, allowing the formation of damaged layer on silicon substrate by a simple scratching process, has been applied instead of conventional silicon cantilever for scanning. A thin mask layer forms in the substrate at the diamond tip-sample junction along scanning path of the tip. The mask layer withstands against wet chemical etching in aqueous KOH solution. Diamond tip acts as a patterning tool like mask film for lithography process. Hence these sequential processes, called tribo-nanolithography, TNL, can fabricate 2D or 3D micro structures in nanometer range. This study demonstrates the novel fabrication processes of the micro cantilever and diamond tip as a tool for TNL using micro-patterning, wet chemical etching and CVD. The developed TNL tools show outstanding machinability against single crystal silicon wafer. Hence, they are expected to have a possibility for industrial applications as a micro-to-nano machining tool.

• Current Optics and Photonics
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• 제3권1호
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• pp.16-21
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• 2019

We present a broad-bandwidth comb-spacing-swept source (CSWS) based on a differential polarization delay line (DPDL) for interferometric three-dimensional (3D) imaging. The comb spacing of the CSWS is repeatedly swept by the tunable DPDL in the multiwavelength source to provide depth-scanning optical coherence tomography (OCT). As the polarization differential delay of the DPDL is tuned from 5 to 15 ps, the comb spacing along the wavelength continuously varies from 1.6 to 0.53 nm, respectively. The wavelength range of various semiconductor optical amplifiers and the cavity feedback ratio of the tunable fiber coupler are experimentally selected to obtain optimal conditions for a broader 3-dB bandwidth of the multiwavelength spectrum and thus provide a higher axial resolution of $35{\mu}m$ in interferometric OCT imaging. The proposed CSWS-OCT has a simple imaging interferometer configuration without reference-path scanning and a simple imaging process without the complex Fourier transform. 3D surface images of a via-hole structure on a printed circuit board and the top surface of a coin were acquired.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.636-639
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• 2003

It is difficult to machine below 10 micrometers by conventional machining methods, such as micro-EDM. However, ultra micro machining using focused ion beam(FIB) is able to machine to 50 nanometers. In addition, 3 dimensional structures can be made by a combination of FIB and CVD to the level of 10 nanometers. Die ＆ moulds techniques are better than one-to-one machining techniques in the mass production of ultra size structures, in regards to production costs. In this case, the machining precision of die ＆ moulds affects produced parts. Also, it is advantageous to machine die ＆ moulds to the 10 micrometer level by FIB technique rather than other techniques. In this paper, the grooving characteristics for die ＆ mould materials by FIB were carried out experimentally in order to compare the machining characteristics of FIB with conventional machining methods. The results showed that the machining parameters and the scanning path of FIB affects the precision. The machined width and depth of the groove varied depending on the required depth due to the redeposition of the sputtered ion material accumulating on both the bottom and the side of the wall.

• The Journal of Advanced Prosthodontics
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• 제14권5호
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• pp.294-304
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• 2022

PURPOSE. The purpose of this study was to evaluate the influence of different palatal vault configurations on the accuracy and scan speed of intraoral scans (IO) of completely edentulous arches. MATERIALS AND METHODS. Three different virtual models of a completely edentulous maxillary arch with different palatal vault heights- Cl I moderate (U-shaped), Cl II deep (steep) and Cl III shallow (flat)-were digitally designed using CAD software (Meshmixer; Autodesk, USA) and 3D-printed using SLA-based 3D-printer (XFAB; DWS, Italy) (n = 30; 10 specimens per group). Each model was scanned using intraoral scanner (Trios 3; 3Shape^TM, Denmark). Scanning time was recorded for all samples. Scanning accuracy (trueness and precision) were evaluated using digital subtraction technique using Geomagic Control X v2020 (Geomagic; 3DSystems, USA). One-way analysis of variance (ANOVA) test was used to detect differences in scanning time, trueness and precision among the test groups. Statistical significance was set at α = .05. RESULTS. The scan process could not be completed for Class II group and manufacturer's recommended technique had to be modified. ANOVA revealed no statistically significant difference in trueness and precision values among the test groups (P=.959 and P=.658, respectively). Deep palatal vault (Cl II) showed significantly longer scan time compared to Cl I and III. CONCLUSION. The selection of scan protocol in complex cases such as deep palatal vault is of utmost importance. The modified, adopted longer path scan protocol of deep vault cases resulted in increased scan time when compared to the other two groups.

• 한국주조공학회지
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• 제30권1호
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• pp.34-45
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• 2010

The effects of alloy elements and cooling rate on the solidification path and the formation behavior of $\beta$ phase in Fe-containing Al-Si alloys were studied based on the thermodynamic analysis and the pertinent experiments. The thermodynamic calculation was systematically performed by using Thermo-Calc program. For the thermodynamic analysis in high alloy region of Al-Si-Fe ternary system, a thermodynamic database for Thermo-Calc was correctly updated and revised by the collected up-to-date references. For the thermodynamic-based prediction of various solidification paths in Fe-containing Al-Si system, liquidus projection of Al-Si-Fe ternary system, including isotherms, invariant, monovariant, bivariant reactions and equilibrium temperatures, was calculated and analyzed as functions of composition and temperature. The calculated results were compared to the experimental results using various casting specimens. In order to analyze various solidification sequences as functions of Si and Fe content, 4 representative alloy compositions, low Fe content in both low and high Si contents and high Fe content again in both low and high Si contents, were designed in this study. For better understanding of the influence of cooling rate on the formation behavior of $\beta$ phase, 4 alloys were solidified under furnace and rapidly cooled conditions. Cooling curves of solidified alloys were recorded by thermal analysis. Various important solidification events were evaluated using the first derivative-cooling curves. Microstructures of the casting samples were studied by the combined analysis of optical microscopy (OM) and scanning electron microscopy (SEM).

• 폴리머
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• 제29권2호
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• pp.146-150
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• 2005

본 연구는 수십 마이크로미터 크기의 임의의 3차원 형상제작을 위한 이광자 광중합에 의한 나노 입체 리소그래피(nano-stereolithography) 공정개발에 관한 것이다. 본 연구에서 제안한 공정은 3차원 CAD 파일을 이용하여 형상의 윤곽선을 고화시켜서 연속적으로 적층하여 구조물을 제작하는 공정으로 기존의 리소그래피 공정과 달리 복잡한 형상제작이 가능하다. 형상제작은 펨토초 레이저를 이용하여 이광자 흡수 색소가 첨가된 아크릴레이트 계열의 단량체에 이광자 중합반응으로 제작하였으며 선 폭 정밀도는 150 nm수준이었다. 이광자 광중합법으로 윤곽선을 고화시켜 쉘(shell) 형태로 3차원 형상을 제작할 때에는 기계적 강성이 약하여 고화 후에 용매로 중합반응이 일어나지 않는 부분을 제거할 때 변형이 쉽게 발생하게 된다. 본 연구에서는 이러한 문제점을 해결하고자 윤곽 쉘 두께를 증가시켜 윤곽선을 중첩으로 제작하는 이중 윤곽선 스캐닝 방법(double contour scanning)을 시도하였으며 이를 통하여 제작된 형상의 강도가 향상됨을 확인할 수 있었다.