• Korean Journal of Radiology
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• 제22권7호
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• pp.1194-1202
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• 2021

Objective: To investigate the age-dependent changes in regional cerebral blood flow (CBF) in healthy adults by fitting mathematical models to imaging data. Materials and Methods: In this prospective study, 90 healthy adults underwent pseudo-continuous arterial spin labeling imaging of the brain. Regional CBF values were extracted from the arterial spin labeling images of each subject. Multivariable regression with the Akaike information criterion, link test, and F test (Ramsey's regression equation specification error test) was performed for 7 models in every brain region to determine the best mathematical model for fitting the relationship between CBF and age. Results: Of all 87 brain regions, 68 brain regions were best fitted by cubic models, 9 brain regions were best fitted by quadratic models, and 10 brain regions were best fitted by linear models. In most brain regions (global gray matter and the other 65 brain regions), CBF decreased nonlinearly with aging, and the rate of CBF reduction decreased with aging, gradually approaching 0 after approximately 60. CBF in some regions of the frontal, parietal, and occipital lobes increased nonlinearly with aging before age 30, approximately, and decreased nonlinearly with aging for the rest of life. Conclusion: In adults, the age-related perfusion patterns in most brain regions were best fitted by the cubic models, and age-dependent CBF changes were nonlinear.

• 한국항공운항학회지
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• 제19권4호
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• pp.51-57
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• 2011

The spin-up and the spring-back are most severe load cases in the aircraft landing gear design. These load cases are caused by reciprocal action of complex physical phenomenon such as the friction between a tire and ground, inertia of the rotation of a tire and the flexibility of a landing gear structure. Generally, the empirical formula or the theoretical formula is used to calculate the spin-up and spring-back load in the early stage of the development program of the aircraft landing gear. After the materialization of the design of a landing gear, spin-up and spring-back load are acquired by the free drop test. In this study, the spin-up and the spring-back load of the rubber shock absorber type KC-100 nose landing gear are calculated by the explicit finite element analysis. Through this analysis, more accurate and realistic spin-up and spring back loads could be applied to the early phase of the development of the aircraft landing gear.

• 한국항공우주학회지
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• 제35권1호
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• pp.79-86
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• 2007

회전 발사체용 마그너스 효과 풍동실험 측정장치를 개발하였다. 국방과학연구소 풍동실험실에서는 고속풍동실험에 앞서 지상기능시험과 마그너스 저속풍동실험을 수행하였으며 마그너스 모형은 분당 약 6,000~10,000 회전하였으며, 속도 100 m/sec에서 측정한 마그너스 효과는 무차원 회전특성인자에 대해 선형적인 변화특성을 보였다. 동일형상 모형에 대해 미국 AEDC-4T 풍동에서 기 수행하였던 마그너스 측정결과와의 비교검토를 수행하였다.

• KEPCO Journal on Electric Power and Energy
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• 제4권1호
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• pp.19-24
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• 2018

가스터빈 동익에 대한 지속적인 국산화 개발이 추진되어, 국내 정밀 주조 기술을 향상시키고, 동익의 유지 보수 비용을 낮추는 등의 직간접적인 긍정적 효과를 가져왔지만, 여전히 국산화 개발품이 발전소에서 안정적인 실사용이 가능한지에 대한 우려가 존재한다. 향상된 소재와 주조기술을 바탕으로 조직학적, 기계적 성질에서 충분한 품질을 확보하였더라도, 개발품을 대상으로 다양한 신뢰성 검증이 요구되는 이유이다. 고속회전시험기는 로터, 디스크 등의 회전체에 원심력을 가하여, 이에 따른 제품의 특성을 분석하기 위한 시험장비로 일반적으로 과속도시험을 통한 최종적인 품질검사에 주로 사용된다. 본 논문에서는 전력연구원에 구축된 고속회전시험기를 활용한 가스터빈 동익에 대한 과속도시험을 포함한 저주기피로시험 사례를 중심으로 신뢰성 시험 및 평가 결과를 기술하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제25회 추계학술대회논문집
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• pp.479-483
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• 2005

BBU(Base Bleed Unit)는 155mm 탄에 부착되어 비행 중에 형성되는 탄저부 항력(Base drag)을 감소시켜 사거리를 연장시키는 무기 체계로 국내에서는 2000년 이후 양산화 되었다. 본 연구는 항력감소제용 저연소속도 추진제의 원료 조성 변화를 통한 공정 Lead time 단축으로 생산성을 향상시키는데 목적이 있으며 개발 과정은 추진제 및 연소방지제의 조성시험을 통한 기본적인 특성 확인을 거친 후 Spin Test 와 실제 발사시험을 통해서 최종 성능을 확인하는 순서로 진행하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.398-400
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• 2004

The three-dimensional woven fabric C/SiC composites blisk turbine rotor model was evaluated. The spin tests of the blisk model were performed to measure strain distributions at the room temperature. The rotational strength of the blisk model could be improved by the fiber addition. But, there are still more researches to be done.

• 한국항공우주학회지
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• 제39권10호
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• pp.912-918
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• 2011

본 연구의 목적은 풍동실험을 통해 회전발사체에서 발생하는 동적 롤댐핑 특성을 실험적으로 측정하는데 있었으며, 이를 위해 약 12,000 rpm으로 회전하는 회전발사체 실험모형에 작용하는 롤댐핑 특성의 측정을 위한 고속풍동실험을 국방과학연구소 삼중음속풍동에서 수행하였다. 실험시의 마하수는 0.7~1.05까지의 천음속 영역이었으며 이때의 받음각 구간은 -4~+10 deg이었다. 풍동실험 측정기법의 유효성 평가를 위해 동일형상 모형에 대해 기 수행하였던 롤댐핑 측정결과와의 비교검토를 수행하였다.

• Journal of Magnetics
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• 제16권2호
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• pp.169-172
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• 2011

This study reports an alternative method for measuring the magnetoresistance of unpatterned magnetic tunnel junctions similar to the current-in-plane tunneling (CIPT) method. Instead of using microprobes, a series of point contacts with different spacings are coated on the top surface of the junctions and R-H loops at various spacings are then measured by the usual four-point probe method. The values of magnetoresistance and resistance-area products can be obtained by fitting the measured data to the CIPT theoretical model. The test results of two types of junctions were highly similar to those obtained from standard CIPT tools. The proposed method may help to accelerate the process for evaluating the quality of magnetic tunnel junctions when commercial CIPT tools are not accessible.

• Journal of Information Processing Systems
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• 제14권4호
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• pp.941-947
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• 2018

Since the amplitudes of spin echo train in nuclear magnetic resonance logging (NMRL) are small and the signal to noise ratio (SNR) is also very low, this paper puts forward an improved de-noising algorithm based on wavelet transformation. The steps of this improved algorithm are designed and realized based on the characteristics of spin echo train in NMRL. To test this improved de-noising algorithm, a 32 points forward model of big porosity is build, the signal of spin echo sequence with adjustable SNR are generated by this forward model in an experiment, then the median filtering, wavelet hard threshold de-noising, wavelet soft threshold de-noising and the improved de-noising algorithm are compared to de-noising these signals, the filtering effects of these four algorithms are analyzed while the SNR and the root mean square error (RMSE) are also calculated out. The results of this experiment show that the improved de-noising algorithm can improve SNR from 10 to 27.57, which is very useful to enhance signal and de-nosing noise for spin echo train in NMRL.

• Bulletin of the Korean Chemical Society
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• 제33권3호
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• pp.803-808
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• 2012

We have implemented two-component spin-orbit relativistic effective core potential (SOREP) methods in an all-electron relativistic program DIRAC. This extends the capacity of the two-component SOREP method to many ground and excited state calculations in a single program. As the test cases, geometries and energies of the small halogen molecules were studied. Several two-component methods are compared by using spin-orbit and scalar relativistic effective core potentials. For the $I_2$ molecule, excitation energies of low-lying excited states agree well with those from corresponding all-electron methods. Efficiencies in SOREP calculations enhanced by using symmetries are also discussed briefly.