• 한국초전도ㆍ저온공학회논문지
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• 제19권3호
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• pp.27-32
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• 2017

The effects of artificial holes on the trapped magnetic fields and magnetic levitation forces of very large single-grain $Y_{1.5}Ba_2Cu_3O_{7-y}$ (Y1.5) bulk superconductors were studied. Artificial holes were made for Y1.5 powder compacts by die pressing using cylindrical dies with a diameter of 30 mm or 40 m, or rectangular dies with a side length of 50 mm. The single grain Y1.5 bulk superconductors (25 mm, 33 mm in diameter and 42 mm in side length) with artificial holes were fabricated using a top-seeded melt growth (TSMG) process for the die-pressed Y1.5 powder compacts. The magnetic levitation forces at 77 K of the 25 mm single grain Y1.5 samples with one (diameters of 4.2 mm) or six artificial holes (diameters of 2.5 mm) were 10-17% higher than that of the Y1.5 sample without artificial holes. The trapped magnetic fields at 77 K of the Y1.5 samples with artificial holes were also 9.6-18% higher than that of the Y1.5 sample without artificial holes. The 33 mm and 42 mm single grain Y1.5 samples with artificial holes (2.5 mm and 4.2 mm in diameter) also showed trapped magnetic fields 10-13% higher than that of the Y1.5 samples without artificial holes in spite of the reduced superconducting volume fraction due to the presence of artificial holes. The property enhancement in the large single grain Y1.5 bulk superconductors appears to be attributed to the formation of the pore-free regions near the artificial holes and the homogeneous oxygen distribution in the large Y123 grains.

• Journal of Magnetics
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• 제16권2호
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• pp.181-185
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• 2011

To improve trapped field characteristics of a high temperature superconducting (HTS) bulk, a technique to implement artificial holes has been studied. The artificial holes, filled up with epoxy or metal, may provide better cooling channel and enhance mechanical strength of the HTS bulk. Although many useful researches based on experiments have been reported, a numerical approach is still limited because of several reasons that include: 1) highly non-linear electromagnetic properties of HTS; and 2) difficulty in modeling of randomly scattered "small" artificial holes. In this paper, a 2-D finite element method with iteration is adopted to analyze trapped field characteristics of HTS bulk with artificial holes. The validity of the calculation is verified by comparison between measurement and calculation of a trapped field in a $40{\times}40\;mm$ square and 3.1 mm thick HTS bulk having 16 artificial holes with diameter of 0.7 mm. The effects of sizes and array patterns of artificial holes on distribution of trapped field within HTS bulk are numerically investigated using suggested method.

• 한국초전도ㆍ저온공학회논문지
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• 제14권3호
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• pp.1-4
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• 2012

Effects of artificial holes on the cooling efficiency of single grain YBCO bulk superconductors were studied. Single grain YBCO bulk superconductors without artificial holes, with six 2.4 mm holes and six holes filled with Bi-Pb-Cd-Sn metal solder were fabricated by a top-seeded melt growth process for powder compacts with/without holes. Simulation for the cooling rate to a liquid nitrogen temperature (77 K) of YBCO samples was carried out using a finite element method (FEM) and the results are compared with the actual cooling rates of samples in liquid nitrogen. The simulated cooling times for the YBCO sample without holes, with six holes and with six holes filled with the metal solder were 80, 47 and 75 sec. respectively, which are similar to the actual cooling times of 84, 52 and 78 sec. estimated for the same samples cooled in liquid nitrogen. The shorter cooling time of the sample with artificial holes are attributed to the increased surface areas associated with the presence of artificial holes. The metal filling into the holes did not give any remarkable effect on the cooling efficiency.

• Progress in Superconductivity
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• 제11권1호
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• pp.52-56
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• 2009

Temperature distributions and thermal stresses were calculated and analyzed to investigate the effect of the artificial holes to the transient behaviors of the superconductors which was cooled in liquid nitrogen. Three dimensional finite element method was used to calculated the transient temperature and thermal stresses in the superconductors. The cooling speed of the superconductors with holes is faster than those without holes. Because the thermal stresses calculated in the superconductors can be relaxed by the distributed holes, the volume of the peak tensile stress decreases during the cooling in liquid nitrogen. If optimal metal, which can maintain the relaxation of thermal stresses, is used to fill and reinforce the artificial holes, the probability of failure of the superconductors may be decreased by the decrease of volume of peak tensile stress.

• 구강회복응용과학지
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• 제21권2호
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• pp.143-151
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• 2005

The purpose of this study was to evaluate the most effective method for repairing the exfoliated resin teeth. The specimens were divided into five groups according to repair method and presence of retention holes. The groups were as follows Group1 : Control group Group2 : Sprinkle method with no retention holes Group3 : Sprinkle method with retention holes Group4 : Flask method with no retention holes Group5 : Flask method with retention holes The results were as follows. 1. According to shear bond strength, the value decreased in the order of group1, group5, group3, group2, group4 and there were significant difference between, each group except between group1 and groups5, group2 and group3, group2 and group4(p < 0.05). 2. According to observations of the exfoliation surface, group2 and 4 showed more failure in the denture base resin and repair resin interface, but in group1, 3 and 5 there were more mixed failures. From the results above, there were no significant difference between repair methods without retention holes. But when comparing groups with retention holes, the flask method showed significantly improved results compared to the sprinkle method. Especially, group5 showed similar results as the control group.

• Journal of Ecology and Environment
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• 제38권4호
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• pp.415-424
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• 2015

This research was conducted to reveal the characteristics of breeding ecology of oriental scops owl (Otus sunia stictonotus) inhabiting in South Korea according to the nest types during the breeding season from march to October for two years (2011 and 2012). Oriental scops owl nested in woodpecker's nest holes (46.1%), natural tree holes (38.5%), and artificial wood boxes (15.4%). These nests were located on following trees: Zelkova serrata, Paulownia coreana, Celtis sinensis, Salix chaenomeloides, Salix babylonica, Fraxinus rhynchophylla, Robinia pseudoacacia and Platanus occidentalis. The hatching success was 91.4%, fledging success was 83.0%, and breeding success was 75.9%. The factors of the breeding failure were falling (57.1%), abandonment (28.6%), hatching failure (7.1%), and others with unknown cause of death (7.1%). According to nest types, the fledging success (69.2%) of woodpecker's nest holes were low and the hatching success (79.2%) of natural tree holes were also low due to hatching failure and abandonment. However, hatching success, fledging success, breeding success were high in the artificial nests as all the eggs hatched and succeeded in fledging. Therefore, we suggested that artificial nests can cover the weaknesses of natural nests as well as increasing the breeding success. However, long-term research on installation place, height, and hole sizes of the artificial nest are required in order to clearly reveal the effects on the breeding success of oriental scops owl.

• Progress in Superconductivity
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• 제9권1호
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• pp.107-110
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• 2007

Bi/CNT composite and resin/CNT were chosen to improve the mechanical properties of $YBa_2Cu_3O_7$(YBCO) superconductor. In order to elucidate the effects of Bi/CNT composite and resin/CNT in YBCO superconductors, melt texture superconductor were impregnated by mixed compound of Bi and CNT into the artificial holes parallel to the c-axis, which were drilled on the YBCO superconductor. Various amount of Bi/CNT and resin/CNT were impregnated to YBCO superconductor with different holes diameters. Typical artificial holes diameters were 0.5, 0.7, and 1.0 mm respectively. Result of three-point bending test measurement, the bending strength with resin/CNT impregnation was improved up to 59.64 MPa as compared with 50.79 MPa of resin/CNT free bulk. Resin/CNT impregnation has been found to be one of the effective ways in improving the mechanical properties of bulk superconductor.

• 전기학회논문지
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• 제62권5호
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• pp.657-662
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• 2013

A size-reduced high frequency mixer designed by adopting artificial dielectric substrate is described in this work. The artificial dielectric substrate is composed by stacking the lower substrate in which a lot of metalized via-holes exist, and upper substrate on which microstrip lines are realized. The effective dielectric constant increases due to the inserted lots of via-holes, and this may be applied to size-reduction of high frequency circuits. In this work, in order to present an application example of size-reduction for active high frequency circuits using the artificial dielectric substrate, a 8GHz single gate mixer is miniaturized and measured. It is described that the basic circuit elements for mixers such as hybrid, low pass filter, and matching networks can be replaced by the artificial dielectric substrate for size-reduction. The final mixer has 55% of size compared to the normal one. The measured average conversion gain is around 3dB which is almost similar result as the normal circuit.

• 한국초전도ㆍ저온공학회논문지
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• 제11권2호
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• pp.15-19
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• 2009

Bulk $YBa_2Cu_3O_{7-{\delta}}$ (YBCO) superconductor was manufactured with the top-seeded melt grown method. The 9, 16, and 25 holes, as small as 0.7mm in diameter, parallel to the c-axis were mechanically drilled. Magnetic flux mapping and levitation force were measured and compared to estimate the influence of multiple holes on the magnetic properties of YBCO superconductor at 77K. According to the measurements, the maximum magnetic flux density obtained from the plain sample was 2.48kG, while the maximum magnetic flux density of the sample with 25 holes was low as around 2.29kG. The levitation force measured on the sample with 9 holes increased from 91N to 105N. The levitation force measured on the samples with 9 holes is relatively higher than the plain sample without any holes. In this case, increase of the levitation force in the perforated samples could be explained by enhancement of the cooling efficiency more effectively. We investigated that the magnetic properties of YBCO superconductor were strongly influenced by the artificial holes.

• 대한의용생체공학회:의공학회지
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• 제25권6호
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• pp.489-496
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• 2004

혈액이 케뉼라를 통과할 때 생리적인 범위를 벋어나는 기계적인 하중이나 전단응력을 받게 되며, 그 결과로 용혈의 발생기전이 되는 ADP(Adenosine Diphospate)를 증가 시키게 된다. 저자는 수치해석적인 방법을 이용하여 사이드 홀을 가진 케뉼라의 3차원 유동을 해석하였다. 연구의 대상이 되는 케뉼라는 환자의 대퇴정맥에 삽입되어 혈액을 배출하는 배액 케뉼라이다. 이러한 배액 케뉼라는 배출 성능을 높이기 위해 일반적으로 사이드 홀을 장착한다. 4개, 12개, 20개인 사이드 홀을 가진 케뉼라에 대하여 경우에 대하여, 각각 엇갈림 배열, 직렬 배열. 변형된 직렬배열을 적용하여, 총 9가지 서로 다른 모델을 시뮬레이션 해보았으며 이것을 사이드 홀이 없는 케뉼라와 더불어 비교하였다. 유량, 벽면전단응력(Wail Shear Stress. WSS), 전단율(Shear Rate. SR) 값을 구하여 분석하므로 사이드 홀의 영향을 알아보았다. 연구를 통하여 사이드 홀의 개수와 배열이 모두 혈류 역학적인 변수들에 영향을 주는 것을 확인하였다. 유량이 사이드 홀의 개수에 비례하지 않는 것을 확인 하였고 사이드 홀의 개수가 많을 수로 평균 전단율을 줄이는 것을 확인 하였다.