• 한국정밀공학회지
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• 제30권3호
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• pp.254-259
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• 2013

Ball screw system is widely used as a precision mechanical linear actuator that translates rotational motion to linear motion for its high efficiency, great stiffness and long life. Recently, according to the requirements of high accuracy and stiffness, the pre-load on the ball screw which means of remove the backlash in the ball screw is usually used. Because of the preload which means the frictional resistance between the screw and nut, becomes a dominating heat source and it generates thermal deformation of ball screw which is the reason for low accuracy of the positioning decision. There are several methods to solve the problem that includes temperature control, thermal stable design and error compensation. In the past years, researchers focused on the error compensation technique for its ability to correct ball screw error effectively rather than the capabilities of careful machine design and manufacturing. Significant amounts of researches have been done to real-time error compensation. But in this paper, we developed a series of cooling methods to get thermal equilibrium in the ball screw system. So we find the optimum cooling type for improving positioning error which caused by thermal deformation in the ball screw system.

• Membrane and Water Treatment
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• 제6권5호
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• pp.423-437
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• 2015

Polyvinylidene fluoride/fullerene nanoparticle (PVDF/$C_{60}$) composite microfiltration (MF) membranes were fabricated by a non-solvent induced phase separation (NIPS) using N, N-dimethylacetamide (DMAc) as solvent and deionized water (DI) as coagulation solution. Polyvinylpyrrolidone (PVP) was added to the casting solution to form membrane pores. $C_{60}$ was added in increments of 0.2% from 0.0% to 1.0% to produce six different membrane types: one pristine PVDF membrane type with no $C_{60}$ added as control, and five composite membrane types with varying $C_{60}$ concentrations of 0.2, 0.4, 0.6, 0.8 and 1.0%, respectively. The mechanical strength, morphology, pore size and distribution, hydrophilicity, surface property, permeation performance, and fouling resistance of the six membranes types were characterized using respective analytical methods. The results indicate that membranes containing $C_{60}$ have higher surface porosity and pore density than the pristine membrane. The presence of numerous pores on the membrane caused weaker mechanical strength, but the water flux of the composite membranes increased in spite of their smaller size. Initial flux and surface roughness reached the maximum point among the composite membranes when the $C_{60}$ concentration was 0.6 wt.%.

• Pediatric Infection and Vaccine
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• 제23권3호
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• pp.223-228
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• 2016

국내 Shigella 감염은 대부분 Shigella sonnei 에 의해 발생하나 드물게 Shigella flexneri 에 의한 집단 감염이 보고되고 있다. 항생제 사용률이 높은 국내에서 extended-spectrum ${\beta}-lactamase$ (ESBL) 생성 S. sonnei 감염에 대한 보고는 있었으나 ESBL을 생성하는 S. flexneri 에 대한 예는 지금까지 없었다. 저자들은 국내 한 어린이집에 다니는 소아 2명에게서 CTX-M-14 유형 ESBL 생성 S. flexneri type 2a 감염 증례를 경험하였으며 이는 국내에서 ESBL을 생성하는 S. flexneri 감염의 첫 증례이다. 앞으로 국내에서도 Shigella 감염 시 ESBL 균주의 가능성을 고려하고 적극적인 역학조사와 경험적 항생제 투여에 대한 신중한 선택이 필요할 수 있을 것으로 생각된다.

• Journal of Advanced Marine Engineering and Technology
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• 제40권6호
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• pp.504-509
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• 2016

이중관 벨로우즈는 우수한 성형성과 내식성을 고려하여 오스테나이트계 스테인리스강인 STS 316L 소재를 사용하여 2겹으로 내부 및 외부 벨로우즈를 각각 제작한 후 다양한 조건과 용접 방법을 적용하여 이중관 벨로우즈를 제작한다. 하지만 제품의 성형 또는 사용시 균열이나 파단에 가장 취약한 부분이 용접부이기 때문에 제품의 신뢰성을 획득하기 위하여 각각의 용접부에 대한 미세조직을 관찰하여 결함 발생 여부를 측정해야 한다. 본 연구에서는 다양한 용접 공정을 거쳐 제작된 벨로우즈의 용접부를 검사하고 미세조직을 분석하여 최적의 용접 조건을 도출하였다. 또한 용접부의 경도 측정을 통해 모재와 용접부 그리고 열영향부 등 용접영역의 기계적 특성을 평가하였다.

• 한국산학기술학회논문지
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• 제15권3호
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• pp.1749-1755
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• 2014

진동해머에 의해 시공되는 말뚝의 해석기법을 개발하고 매개변수연구를 수행하여 개발된 해석기법의 신뢰성을 평가해보았다. 편심모멘트와 진동수에 따른 매개변수해석을 통해 구한 가속도를 비교분석해 본 결과 최대가속도의 크기는 대략적으로 편심모멘트에 비례하였으며 진동수의 제곱에 비례하였다. 또한 변위진폭은 편심모멘트에 비례하는 결과를 나타내었고 진동수에는 거의 영향을 받지 않았는데 이러한 경향은 공운전시의 거동특성과 유사하다. 매개변수해석을 통해 구한 동적 하중전이곡선을 비교해 볼 때 편심모멘트와 진동수의 크기에 관계없이 최대 동적단위선단저항력의 크기는 동일하였으며 최대 동적단위주면마찰력의 크기는 편심모멘트에 영향을 받으나 진동수와는 무관하였다. 매개변수해석결과를 종합적으로 비교분석해 볼 때 개발된 해석기법은 합리적인 해석결과를 보인다고 볼 수 있다.

• 한국세라믹학회지
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• 제38권10호
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• pp.936-941
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• 2001

5.31 mol% ${Y_2}{O_3}$-4.45 mo1% ${Nb_2}{O_5}$-90.31 mo1% $ZrO_2$에 ${Al_2}{O_3}$를 첨가한 복합체를 제조하여 알루미나 입도가 복합체의 균열 전파 저항성에 미치는 영향을 조사하였다. $ZrO_2/{Al_2}{O_3}$ 복합체에서는 R-cuve 거동이 관찰되었으며 0.2, $2.8{\mu}m$ ${Al_2}{O_3}$가 20 vol%가 첨가된 복합체의 인성값은 각각 7.9, $8.8MPam^{1/2}$이었다. 파괴인성값의 차이는 ${Al_2}{O_3}$ 입도 크기에 의존하는 $ZrO_2/{Al_2}{O_3}$ 복합체 내의 정방정 $ZrO_2$의 결정립 크기 차이에 의한 것으로 추정된다.

• 한국자원식물학회지
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• 제19권6호
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• pp.706-715
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• 2006

Nitrate reductase deficient (NR) mutant lines were selected indirectly by their resistance to 100mM chlorate in cell cultures of P. parviflora. A total of 585 chlorate resistant lines were confirmed by a second passage on a high concentration of chlorate. Frequency of spontaneous mutation was $9.7{\times}10^{-7}$ in 3 month old suspension-cultured cells, and in non-selective media containing amino acids as sole nitrogen source. The frequency of mutation could be increased up to 11-fold by culture for 12 months. Out of 40 randomly selected calli, 22 were fully deficient in NR. The rest of the clones contained a decreased level of NR activity. Further characterization was carried out in 13 mutant lines which were fully deficient in NR and in 5 mutant lines containing residual (0-7.0%) NR activity, as compared to wild-type cells cultured on the same medium. The $NR^-$ mutants were tentatively classified as defective in the NR apoenzyme (nia-type; 11 mutant lines including the 5 with residual NR activity) or in the molybdenum cofactor (cnx-type; 7 mutant lines) by the XDH activity. The cnx-type could be further classified into two groups. In one group (5 mutant lines) of these, the NR activity could be partially restored by nonphysiologically high (1.0mM) molybdate in the culture medium. Both types of $NR^-$ mutants were unable to grow on minimal medium containing nitrate as sole nitrogen source, but grew well on amino acids. They also proved to be extremely sensitive to the standard medium ($MSP_1$) containing nitrate and ammonium. Shoot regeneration was obtained only in the $NR^-$ mutants, which contained residual NR activity, but they so far have failed to grow into plants.

• Journal of Korean Neurosurgical Society
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• 제48권6호
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• pp.506-517
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• 2010

Objective : We investigated whether Disability Evaluation (DE) situations influence patients' neuropsychological test performances and psychopathological characteristics and which variable play a role to establish an explanation model using statistical analysis. Methods : Patients were 536 (56.6%) brain-injured persons who met inclusion and exclusion criteria, classified into the DE group (DE; n = 300, 56.0%) and the non-DE group (NDE; n = 236, 44.0%) according to the neuropsychological testing's purpose. Next, we classified DE subjects into DE cluster 1 (DEC1; 91, 17.0%), DE cluster 2 (DEC2; 125; 23.3%), and DE cluster 3 (DEC3; 84, 15.7%) via two-step cluster analysis, to specify DE characteristics. All patients completed the K-WAIS, K-MAS, K-BNT, SCL-90-R, and MMPI. Results : In comparisons between DE and NDE, the DE group showed lower intelligence quotients and more severe psychopathologic symptoms, as evaluated by the SCL-90-R and MMPI, than the NDE group did. When comparing the intelligence among the DE groups and NDE group, DEC1 group performed worst on intelligence and memory and had most severe psychopathologic symptoms than the NDE group did. The DEC2 group showed modest performance increase over the DEC1 and DEC3, similar to the NDE group. Paradoxically, the DEC3 group performed better than the NDE group did on all variables. Conclusion : The DE group showed minimal "faking bad" patterns. When we divided the DE group into three groups, the DEC1 group showed typical malingering patterns, the DEC2 group showed passive malingering patterns, and the DEC3 group suggested denial of symptoms and resistance to treatment.

• 한국지반신소재학회논문집
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• 제2권3호
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• pp.19-24
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• 2003

폐기물 매립지 바닥층 및 사면에 적용되는 평편 형 및 텍스츄어드 형 고밀도 폴리에틸렌 지오멤브레인의 장기성능이 검토되었다. 특수 설계된 스크래치 장치를 이용하여 인위적으로 지오멤브레인 표면에 결함을 부여하였다. 결함 및 미결함 지오멤브레인의 역학적 및 마찰특성, 화학저항성 및 자외선 저항성 그리고 산화유도시간 등이 검토되었다. 텍스츄어드 형 지오멤브레인의 마찰특성이 평편 형 지오멤브레인 보다 우수함을 알 수 있었다. 끝으로 화학저항성, 자외선 저항성 그리고 산화유도시간 측정결과로부터 결함이 없는 지오멤브레인과 텍스츄어드 형 지오멤브레인의 장기성능이 결함이 있는 지오멤브레인보다 우수함을 알 수 있었다.

• 한국표면공학회지
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• 제50권5호
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• pp.339-344
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• 2017

Highly corrosion resistance performance of CrAlSiN coatings were obtained by applying ultrathin $Al_2O_3$ thin films using atomic layer deposition (ALD) method. CrAlSiN coatings were prepared on Cr adhesion layer/SUS304 substrates by a hybrid coating system of arc ion plating and high power impulse magnetron sputtering (HiPIMS) method. And, ultrathin $Al_2O_3$ passivation layer was deposited on the CrAlSiN/Cr adhesion layer/SUS304 sample to protect CrAlSiN coatings by encapsulating the whole surface defects of coating using ALD. Here, the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy dispersive X-ray spectrometry (EDX) analysis revealed that the ALD $Al_2O_3$ thin films uniformly covered the inner and outer surface of CrAlSiN coatings. Also, the potentiodynamic and potentiostatic polarization test revealed that the corrosion protection properties of CrAlSiN coatings/Cr/SUS304 sample was greatly improved by ALD encapsulation with 50 nm-thick $Al_2O_3$ thin films, which implies that ALD-$Al_2O_3$ passivation layer can be used as an effect barrier layer of corrosion.