• Macromolecular Research
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• 제16권3호
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• pp.212-217
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• 2008

PVDF ($Kynar^{(R)}$ 761) nanofibers were made by electrospinning with an external voltage of 6-10 kV, a traveling distance of 7-15 cm and a flow rate of 0.4-1 mL/h. Although the mean diameter of the fibers has not changed significantly, the conditions affected the change in diameter distribution. This was attributed to interactions, both attraction and repulsion, between the positive charges on the polymer solutions and the electrically grounded collector. Higher voltages and traveling distance increased the level of attraction between the positive charge on the polymer solution and the electrically grounded collector, resulting in a narrow diameter distribution, In addition, a high flow rate allowed a high population of uniformly charged solutions to travel to the grounded collector, which resulted in a narrow diameter distribution. The optimum conditions for electrospinning of PVDF in DMAc/acetone (3/7 by wt) were a collector voltage of 6 kV, a syringe tip to collector of 7 cm, a flux rate of 0.4 mL/h and 10 kV, 10 cm, 1 mL/h, Since PVDF is widely used as a filtration membrane, it was electrospun on a PET support with a rotating drum as a grounded collector. Surprisingly, some straight nanofibers were separated from the randomly deposited nanofibers. The straight nanofiber area was transparent, while the randomly deposited nanofiber area was opaque. Both straight nanofibers and aligned nanotibers could be obtained by manipulating the PET drum collector. These phenomena were not observed when the support was changed to an Al sheet. This suggests that a pseudo dual collector was generated on the PET sheet. No negative charge was created because the PET sheet was not a conductive material. However, less charge was created when the sheet was not perfectly attached to the metal drum. Hence, the nanotibers jumped from one grounded site to the nearest one, yielding a straight nanofiber.

• 한국추진공학회지
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• 제3권3호
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• pp.9-15
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• 1999

대형로켓엔진을 개발하기 위한 Injector 설계에서 연합된 분무군에 대한 해석은 필수적이다. 본 연구에 서는 운동량이 같은 두 개의 분류가 충돌함으로서 생기는 두 스프레이의 간섭이 질량분포와 액적의 크기/속도분포에 미치는 영향을 조사하였다. 질량채집장치와 PDPA가 실험장치로 사용되었고 물을 실험유체로 사용하였다. 두 스프레이 휀의 운동량비가 1인 경우 두 스프레이 휀의 충돌로 인한 간섭의 영향은 아주 작았다. 마찬가지로 액적의 속도/크기분포도 두 스프레이 휀의 충돌로 인한 간섭영향은 아주 작았으나, 액적의 크기는 2차 충돌로 인하여 충돌점 부근에서 약간 작아졌다. 즉, 추후에 운동량비가 동일한 두 스프레이 휀을 가진 인젝터에 대한 연구시에는 간섭효과를 무시할 수 있음을 알 수 있었다.

• 한국물환경학회지
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• 제39권5호
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• pp.396-412
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• 2023

Species from the mayfly genus Ephemera (Order Ephemeroptera) was assessed for their physical microhabitat suitability (namely E. strigata, E. separigata, and E. orientalis-sachalinensis). Probability distribution models (Exponential, Normal, Lognormal, Logistic, Weibull, Gamma, Beta, and Gumbel) based on the data collected from 23,957 sampling units of 6,787 sites in Korea from 2010 to 2021 were used. Mode and standard deviation calculated from the best-fitting models to species distribution along a water depth gradient were 265 cm and 159 cm in E. orientalis-sachalinensis; 10 cm and 83 cm in E. strigata; 20 cm and 15 cm in E. separigata, respectively. The current velocity gradient was 22 cm/s and 40 cm/s in E. orientalis-sachalinensis; 60 cm/s and 53 cm/s in E. strigata; 82 cm/s and 25 cm/s in E. separigata, respectively. The mean diameter (phi scale) of substrate grains were -3.6 and 2.2 in E. orientalis-sachalinensis; -7.4 and 1.5 in E. strigata; -5.8 and 0.9 in E. separigata, respectively. Habitat suitability range of E. orientalis-sachalinensis was estimated to be 161~369 cm (water depth), 5~44 cm/s (current velocity), -5.2~-2.0 (mean diameter); 3~34 cm (water depth), 36~94 cm/s (current velocity), -8.1~-6.3 (mean diameter) for E. strigata; 12~32 cm (water depth), 63~96 cm/s (current velocity), -6.3~-5.2 (mean diameter) for E. separigata. In relative comparison, E. orientalis-sachalinensis was estimated to be rheophobic, eurybathophilic, and eurypsephophilic; E. strigata to be euryrheophilic, bathophobic, and lithophilic; E. separigata to be stenomesorheophilic, stenobathophobic, stenolithophilic.

• 구강회복응용과학지
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• 제18권4호
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• pp.277-288
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• 2002

Seven finite element models were constructed in mandible having single screw-type implant fixture connected to the premolar superstructure, in order to evaluate how the length, diameter and platform shape of a screw-type fixture influence the stress in the supporting tissue around fixtures. Each finite element model was varied in terms of length, diameter, and platform shape of the fixture. In each model, 250N of vertical load was placed on the central pit of an occlusal plane and 250N of oblique load placed on the buccal cusp. The stress distribution in the supporting tissue and the other components was analysed using 2-dimensional finite element analysis and the maximum von Mises stress in each reference area was compared. Under lateral loading, the stress was larger at the abutment/fixture interface, and in the crestal bone, compared to the stress pattern under vertical loading. The amount of stress at the superstructure was similar regardless of the length, diameter and platform shape of a fixture. Around the longer fixture, the stress was decreased at the bone crest and subjacent cancellous bone and increased in the cancellous bone area apical to the fixture. Around the wider fixture, the stress was decreased at the abutment/fixture interface, and the bone crest and increased in the cancellous bone area apical to the fixture. Around the fixture having wider platform, less stress was produced at the abutment/fixture interface and the upper part of the cortical bone, compared to the fixture having standard platform. In conclusion, the stress distribution of the supporting tissue was affected by length, diameter, and platform shape of a fixture, and the fixture which was larger in diameter and length could reduce the stress in the supporting tissues at the bone-fixture interface and bone crest area.

• 한국산학기술학회논문지
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• 제21권4호
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• pp.317-323
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• 2020

본 연구에서는 수막설비에 사용되는 워터커튼 노즐의 형상 인자 변화에 따른 분사압력과 방사유량 그리고 액적의 평균크기의 상관관계를 분석하였다. 이를 위해서 노즐의 내부 직경과 폭을 변화한 총 5개(D5W3, D5W6, D5W8, D4W6 그리고 D7W6) 각각의 노즐을 제작하였으며, 액적 측정 실험 장치를 구성하여 노즐의 수력직경 변화에 따른 유량 계수와 액적의 분포 상수를 반복실험을 통하여 산출하였다. 그 결과 유량계수는 노즐의 직경과 폭이 증가함에 따라 수력직경의 0.79 지수승과 62.8의 상수값에 비례하여 증가하는 것으로 나타났으며, 평균 액적의 크기는 분사 압력의 -0.235 지수승의 크기로 감소하였다. 특히, 본 연구에서 정의한 액적의 분포상수는 수력 직경의 0.258 지수승과 244.21의 크기에 비례하여 증가하는 것으로 나타났으며, 동일 워터커튼 노즐에 대해서 분사압력의 크기가 증가할수록 평균 액적의 크기가 감소하는 것을 검증하였다. 본 연구 결과는 수막설비용 노즐의 형상 설계에 따른 유동 특성을 예측하기 위한 노즐의 분사압력, 방사유량 그리고 평균 액적크기의 설계 자료로 활용이 유용할 것으로 판단된다.

• The Korean Journal of Ecology
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• 제16권3호
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• pp.317-327
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• 1993

Stands profiles, yearly changes in growth of annual rings, age and diameter structure, and spatial distribution pattern of individuals in the Pinus densiflora stands around the Yeocheon industrial complex were investigated. Growth of annual ring in Pinus densiflora, which survived when vegetation of this area was damaged by air pollutants, was suppressed for about 10 years since 1974 when factories in this area began to operate, but since then such suppressed growth tended to be recovered. It was supposed that the suppresed growth was originated from air pollution and that improvement of growth since the suppressed period was due to the release from competition with them by death of neighbouring trees and the resuction of the amount of air pollutants. Physiognomy of Pinus densiflora stands showed mosaic pattern composed of different patches. Spatial distribution pattern of individuals an stand profiles were similar to those of Pinus densiflora stands regenerated after natural and artificial disturbances. In an age distribution diagram, age of Pinus densiflora population ranged from 1 to 33 years, Among these individuals were recrited corresponded to the suppresed period of growth of annual ring in Pinus densiflora survived when the vegetation was damaged by air pollution. On the other hand, from the result of analysis of frequency distribution diagram of diameter, it was postulated that even if whis Pinus densiflora community can be maintained as it is for the time being, it might be changed to Quercus community with the lapse of time. Regeneration; Pinus densiflora; Air pollution; Annual ring; Age structure; Diameter structure; Quercus spp. In these analyses, factors for individual recognition and species recognition were suggested.

• 전기의세계
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• 제18권6호
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• pp.9-22
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• 1969

This thesis has suggested a method of applying the Maximum Principle of Pontryagin to the optimal control of distributive electrical networks. In general, electrical networks consist of branches, nodes, sources and loads. The effective values of steady state currents and voltages are independent of time but only expressed as the functions of position. Moreover, most of the node voltages and branch currents are not predetermined, that is, initially unknown, and their inherent loop characteristics satisfy only Kirchhoff's current and voltage laws. The Maximum Principle, however, needs the initial fixed values of all state variables for its standand way of application. In spite of this inconsistency this thesis has undertaken to suggest a new approach to the successful solution of the above mentioned networks by introducing scaling factors and a state variable change technique which transform the boundary-value unknown problem into the boundary-value partially fixed and partially free problem. For the examples of applying the method suggested, the control problems for minimizing copper quantity in a distribution line have been solved with voltage drop constraint imposed on. In the case of uniform load distribution it has been shown that the optimal wire diameter of the distribution line is reciprocally proportional to the root of distance. For the same load pattern as above the wire diameter giving the minimum copper loss in the distribution line has been shown to be reciprocally proportional to distance.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2021년도 봄 학술논문 발표대회
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• pp.195-196
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• 2021

The pore distribution of the cement mortar mixed with carbon nanotubes was found to have a large number of pores at (370~80)㎛, and the distribution ratio was larger as the carbon nanotubes were mixed. However, the pores with a fine particle diameter of (10-0.5) ㎛ were found to be larger as the carbon nanotubes were incorporated. However, the distribution of pores of the test specimens of conductive cement mortar with deterioration damage was found to be distributed in a number of particle diameters of (500 to 100) ㎛ and (10 to 0.5) ㎛. It is judged that the particle diameter of the internal pores increased due to the damage. However, as the mixing ratio of the test specimen with carbon nanotubes increased, the distribution of voids was relatively lower than that of plain, and it was judged to have excellent resistance to deterioration damage.

• 한국대기환경학회지
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• 제19권2호
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• pp.167-177
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• 2003

The number size distribution of urban aerosols ranging from 0.02 to 20 ${\mu}{\textrm}{m}$ in diameter was measured by using a scanning mobility particle sizer (SMPS) system and an aerodynamic particle sizer spectrometer (APS) at Seoul from November 30,2001 to January 14, 2002. The gaseous species such as CO, NO, NO$_2$, and $O_3$ were also continuously monitored. The daily average concentration of urban aerosols sorted into three groups (0.02~0.1 ${\mu}{\textrm}{m}$, 0.1~1 ${\mu}{\textrm}{m}$ and 1~10 ${\mu}{\textrm}{m}$) and the typical number, surface, and volume distributions of urban aerosols were discussed in this paper. The weekly variation of aerosol concentration was compared with those of gaseous concentrations. relative humidity, and visibility. The results showed that the particle number concentration seemed to increase in the morning and the number concentration of fine particles less than 1 fm in diameter seemed to increase when the concentrations of CO, NO, and NO$_2$ were high. The number concentration of fine particles was relatively high when the relative humidity was greater than 70％ during the increasing period of relative humidity. The visibility was weakly correlated with the concentration of aerosols ranging 0.1 to 1 ${\mu}{\textrm}{m}$, and the number size distribution for high visibility episode was apparently different from that for low visibility episode.

• 한국환경보건학회지
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• 제30권3호
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• pp.253-258
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• 2004

Synthetic organic polyelectrolytes can be used to condition sludges to enhance their dewaterability. Intermittent aerobic digestion is an useful digestion technology and has many advantages like neutral pH, low installation cost and easiness to operation. The objectives of this study were to investigate the dewaterability of intemittent aerobic digestion sludge and to find the relationship between dewaterability and particle size distribution change under the conditioning of intermittent aerobic digestion sludge by cationic polyelectrolyte. Digested sludge from intermittent aerobic digestion was used and cationic polyacrylamide polymer was added as a conditioner. CST(capillary suction time), TTF(time-to-filtration) were tested as a dewaterability index and the number of particle distribution was analyzed using particle size analyzer. The results indicate that cationic polyelectrolytes is useful to enhance dewaterability of intermittent aerobic digestion sludge. Mean particle diameter was increased as polymer dosage increased and its value was reached up to 100 mm on the condition of optimal cationic polymer dosage. CST and TTF are well correlated with mean particle diameter when the weighting order is 1.7. By the optimal conditioning with cationic polymer, particles in the filtrate are also reduced significantly and this means that conditioning is helpful to main stream by reducing SS loading from return flow.