• Korean Journal of Radiology
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• 제23권1호
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• pp.42-51
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• 2022

Objective: This study aimed to investigate the direction of tissue contraction after microwave ablation in ex vivo bovine liver models. Materials and Methods: Ablation procedures were conducted in a total of 90 sites in ex vivo bovine liver models, including the surface (n = 60) and parenchyma (n = 30), to examine the direction of contraction of the tissue in the peripheral and central regions from the microwave antenna. Three commercially available 2.45-GHz microwave systems (Emprint, Neuwave, and Surblate) were used. For surface ablation, the lengths of two overlapped square markers were measured after 2.5- and 5-minutes ablations (n = 10 ablations for each system for each ablation time). For parenchyma ablation, seven predetermined distances between the markers were measured on the cutting plane after 5- and 10-minutes ablations (n = 5 ablations for each system for each ablation time). The contraction in the radial and longitudinal directions and the sphericity index (SI) of the ablation zones were compared between the three systems using analysis of variance. Results: In the surface ablation experiment, the mean longitudinal contraction ratio and SI from a 5-minutes ablation using the Emprint, Neuwave, and Surblate systems were 28.92% and 1.04, 20.10% and 0.53, and 24.90% and 0.45, respectively (p < 0.001). A positive correlation between longitudinal contraction and SI was noted, and a similar radial contraction was observed. In the parenchyma ablation experiment, the mean longitudinal contraction ratio and SI from a 10-minutes ablation using the three pieces of equipment were 38.60% and 1.06, 32.45% and 0.61, and 28.50% and 0.50, respectively (p < 0.001). There was a significant difference in the longitudinal contraction properties, whereas there was no significant difference in the radial contraction properties. Conclusion: The degree of longitudinal contraction showed significant differences depending on the microwave ablation equipment, which may affect the SI of the ablation zone.

• 한국산학기술학회논문지
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• 제19권12호
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• pp.924-930
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• 2018

본 연구의 목적은 수소연료전지 자동차의 난방부하 대응을 위한 스택 냉각수를 활용하여서, 전동식 히트펌프 시스템에 대한 난방성능 특성을 다양한 운전조건 변화에 대해서 고찰하는 것이다. 냉각수와 냉매(R-134a)와의 열교환을 위해서 판형열교환기를 적용하였고, 전동식 히트펌프 시스템에 적용되는 실내열교환기 입구의 공기온도와 압축기 회전수를 변화시키면서 난방 성능 특성을 분석하였다. 실내열교환기 입구 공기 온도 변화에 대해서 난방 성능은 거의 동일한 결과를 보이고 있는데, 이는 입출구 온도차와 공기 측 밀도의 변화가 균형을 이루었기 때문으로 판단된다. 반면, 히트펌프 시스템 효율(COP)의 경우, 난방 성능은 온도변화에 따라 동일하였지만, 유량 변화로 인하여서, 압축기 소모동력이 감소하였기 때문에, 실내열 교환기 입구 온도가 감소함에 따라서, 시스템 효율은 증가하는 경향을 보이고 있다. 추가적으로, EEV개도가 45%정도까지 열리는 구간에서는, 압축기 소모전력 감소하였기 때문에, 시스템 효율이 증가하였고, 그 이후에는 동일한 시스템 효율을 유지하는 것을 알 수 있었다. 압축기 회전수 변화 시에는 난방성능이 증가하면, 시스템 효율은 감소하는 경향을 보여주고 있다. 이러한 원인은 압축기 회전수 증가에 따른 유량의 증가로 판단된다. 향후, 열원으로 사용하는 냉각수에 대한 운전조건을 변화시켜가면서, 난방성능 특성을 분석하여, 전동식 히트펌프의 난방부하 대응을 위한 제어 방안을 연구하고자 한다.

• 대한원격탐사학회지
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• 제28권1호
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• pp.159-169
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• 2012

본 연구의 목적은 산림생태계 분포 모델인 HyTAG모델(Hydrological and Thermal Analogy Group)과 기능 모델인 MC1 모델(MAPSS-CENTURY 1) 그리고 사회 환경적 지표를 이용하여 기후변화가 한반도 산림생태계에 미치는 영향을 파악하는 것이다. HyTAG의 식생유형분포 변화 빈도와 방향으로부터 산림식생의 민감성과 적응성을 정량화하였다. 또한 MC1으로부터 추정되는 순일차생산량 및 토양탄소저장량의 변이 및 경향으로부터 산림기능의 민감성과 적응성을 정량화하였다. 사회 환경적 지표로는 재정자주도 또는 산림관련 공무원 수 등과 같은 통계자료를 포함하였다. 모든 지표들을 정규화하고 취약성 평가식에 적용하여 취약성 결과를 도출하였다. 취약성 평가의 시간적 범위는 현재(1971-2000)와 미래(2021-2050)로 구분하였다. 국가 기후변화 정책의 우선순위를 판단하기 위해 지표 별 공간 분포 지도를 작성하고 행정구역간의 취약성을 비교한 결과, 지역별로 취약성의 차이가 있는 것으로 나타났다. 이러한 취약성 차이는 적응능력에 따라 가장 크게 좌우되는 것으로 판단되었다. 본 연구의 취약성 평가 방법 및 결과는 산림 경영적 측면에서 의사결정 시스템 개발과 기후변화에 대한 적응정책 수립의 판단 자료로 활용될 것이다.

• Journal of Radiation Protection and Research
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• 제45권2호
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• pp.76-80
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• 2020

Background: To improve the measurement accuracy of liquid-scintillation counting for activity standardization, it is necessary to significantly reduce the background caused by thermal noise or after-pulses. We have therefore improved a movable 3 photomultiplier (3PM)-γ coincidence-counting method using the logical sum of three double coincidences for β events. Materials and Methods: We designed a new data-acquisition system in which β events are obtained by counting the logical sum of three double coincidences. The change in β-detection efficiency can be derived by moving three photomultiplier tubes sequentially from the liquid-scintillation vial. The validity of the method was investigated by activity measurement of ¹³⁴Cs calibrated at the Korea Research Institute of Standards and Science (KRISS) with 4π(PC)β-γ(NaI(Tl)) coincidence counting using a proportional counter (PC) for the β detector. Results and Discussion: Measurements were taken over 14 counting intervals for each liquidscintillation sample by displacing three photomultiplier tubes up to 45 mm from the sample. The dead time in each β- and γ-counting channel was adjusted to be a non-extending type of 20 ㎲. The background ranged about 1.2-3.3 s^-1, such that the contributions of thermal noise or after-pulses were negligible. As the β-detection unit was moved away from the sample, the β-detection efficiencies varied between 0.54 and 0.81. The result obtained by the method at the reference date was 396.3 ± 1.7 kBq/g. This is consistent with the KRISS-certified value of 396.0 ± 2.0 kBq/g within the uncertainty range. Conclusion: The movable 3PM-γ method developed in the present work not only succeeded in reducing background counts to negligible levels but enabled β-detection efficiency to be varied by a geometrical method to apply the efficiency extrapolation method. Compared with our earlier work shown in the study of Hwang et al. [2], the measurement accuracy has much improved. Consequently, the method developed in this study is an improved method suitable for activity standardization of β-γ emitters.

• Asian-Australasian Journal of Animal Sciences
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• 제17권11호
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• pp.1615-1634
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• 2004

A review was undertaken to obtain information on the sustainability of pig free-range production systems including the management, performance and health of pigs in the system. Modern outdoor rearing systems requires simple portable and flexible housing with low cost fencing. Local pig breeds and outdoor-adapted breeds for certain environment are generally more suitable for free-range systems. Free-range farms should be located in a low rainfall area and paddocks should be relatively flat, with light topsoil overlying free-draining subsoil with the absence of sharp stones that can cause foot damage. Huts or shelters are crucial for protecting pigs from direct sun burn and heat stress, especially when shade from trees and other facilities is not available. Pigs commonly graze on strip pastures and are rotated between paddocks. The zones of thermal comfort for the sow and piglet differ markedly; between 12-22$^{\circ}C$ for the sow and 30-37$^{\circ}C$ for piglets. Offering wallows for free-range pigs meets their behavioural requirements, and also overcomes the effects of high ambient temperatures on feed intake. Pigs can increase their evaporative heat loss via an increase in the proportion of wet skin by using a wallow, or through water drips and spray. Mud from wallows can also coat the skin of pigs, preventing sunburn. Under grazing conditions, it is difficult to control the fibre intake of pigs although a high energy, low fibre diet can be used. In some countries outdoor sows are fitted with nose rings to prevent them from uprooting the grass. This reduces nutrient leaching of the land due to less rooting. In general, free-range pigs have a higher mortality compared to intensively housed pigs. Many factors can contribute to the death of the piglet including crushing, disease, heat stress and poor nutrition. With successful management, free-range pigs can have similar production to door pigs, although the growth rate of the litters is affected by season. Piglets grow quicker indoors during the cold season compared to outdoor systems. Pigs reared outdoors show calmer behaviour. Aggressive interactions during feeding are lower compared to indoor pigs while outdoor sows are more active than indoor sows. Outdoor pigs have a higher parasite burden, which increases the nutrient requirement for maintenance and reduces their feed utilization efficiency. Parasite infections in free-range pigs also risks the image of free-range pork as a clean and safe product. Diseases can be controlled to a certain degree by grazing management. Frequent rotation is required although most farmers are keeping their pigs for a longer period before rotating. The concept of using pasture species to minimise nematode infections in grazing pigs looks promising. Plants that can be grown locally and used as part of the normal feeding regime are most likely to be acceptable to farmers, particularly organic farmers. However, one of the key concerns from the public for free-range pig production system is the impact on the environment. In the past, the pigs were held in the same paddock at a high stocking rate, which resulted in damage to the vegetation, nutrient loading in the soil, nitrate leaching and gas emission. To avoid this, outdoor pigs should be integrated in the cropping pasture system, the stock should be mobile and stocking rate related to the amount of feed given to the animals.

• 대한기계학회논문집B
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• 제37권6호
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• pp.583-590
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• 2013

가변 방사율 라디에이터는 우주환경에서 작동하는 장비의 온도가 낮을 때는 방사율이 낮아져 시스템의 외부로의 열 손실을 줄이고, 반대로 온도가 높은 때는 방사율이 높아져 장비의 열을 외부로 방출할 수 있어 효율적인 열제어가 가능하게 한다. 가변 방사율 소재로 보편적으로 이용하고 있는 것 중 하나인 감온변색 장치(thermochromics device)는 추가적인 장비 필요 없이 열제어가 가능하기 때문에 효율적이고 고장이 발생하지 않는 장점을 가지고 있다. 본 연구는 이와 같은 이유로 감온변색 장치의 소재 중 하나인 LSMO($La_{1-x}Sr_xMnO_3$)채택하여 졸-겔(sol-gel)방법을 이용하여 제작하고, 제작된 샘플의 가변방사 성능을 실험적으로 규명하였다. 또한, 진공환경과 극저온 환경에 반복 노출시켜 시편이 극심한 환경 변화 이후에도 방사율 값이 일정함을 확인하여 우주적합성을 판단하였다.

• 에너지공학
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• 제12권1호
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• pp.11-16
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• 2003

지상 정적 상태에 있는 항공기내 연료온도의 변화가 유한차분식에 의하여 해석되었다. 수정 Dufort-Frankel 기법의 explicit 방법에 의해 수치계산이 수행되었다. 항공기는 지상 정적상태에서 1% hot day 대기조건에 따른 태양의 복사 및 바람의 속도와 함께 반복되는 일일주기의 공기온도에 노출되어 있다고 가정되었다. 항공기는 난류유동장내에 있는 것으로 가정되었다. 항공기 표면과 외부대기사이의 열전달을 계산하기 위하여 Eckert에 의해 제안된 평판위의 난류 열전달계수가 사용되었다. 본 해석에 사용된 지배방정식은 연료에 대한 에너지방정식이다. 본 해석으로부터, 주익탱크의 연료온도가 다른 탱크들 가운데 가장 높게 나타났으며 온도변화율 또한 가장 크게 나타났다. 본 온도해석에 대한 결과는 여러 비행임무에 있어서 항공기내의 연료온도 변화 해석을 위한 초기치로서 사용될 수 있다. 또한, 본 해석방법은 항공기 열에너지 관리시스템의 해석 및 설계에 사용될 수 있다.

• 한국전자통신학회논문지
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• 제11권4호
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• pp.411-420
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• 2016

석탄과 석유를 대신할 새로운 대체 에너지의 연구 및 개발은 지난 수년간 계속해서 연구되고 있다. 최근엔 유한 에너지 가격 상승으로 인하여 무공해 신재생 에너지의 관심이 증가하고 있다. 특히 기존에 활발히 연구되고 상용화된 신재생 에너지 분야 중 태양에너지는 태양광 에너지에 주된 연구가 이루어져 있다. 그러나 태양광 에너지의 효율성은 이미 포화상태에 도달하였다. 이에 본 논문에서는 태양광이 아닌 태양열 에너지를 활용할 수 있는 태양광 추적형 파라볼릭 집열장치를 제안한다. 제안하는 태양열 집열장치는 효과적으로 태양열을 집열하기 위하여 파라볼릭 형태로 제안하고, 계절 및 시기에 따른 태양의 위치변화를 감지할 수 있도록 5축 센서 방식의 태양광 추적형 트래킹 기술을 결합한 태양열 집열장치의 프로토타입을 제안한다. 또한 집열장치의 효율적인 관리를 위하여 관리자 인터페이스를 설계 및 구현한다.

• Journal of Power Electronics
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• 제14권2호
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• pp.271-281
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• 2014

Fluctuating wind conditions necessitate the use of a variable speed wind turbine (VSWT) with a AC/DC/AC converter scheme in order to harvest the maximum power from the wind and to decouple the synchronous generator voltage and frequency from the grid voltage and frequency. In this paper, a combination of a three phase diode bridge rectifier (DBR) and a modified topology of the diode clamped multilevel inverter (DCMLI) has been considered as an AC/DC/AC converter. A control strategy has been proposed for the DCMLI to achieve the objective of grid interface of a wind power system together with local load compensation. A novel fixed frequency current control method is proposed for the DCMLI based on the level shifted multi carrier PWM for achieving the required control objectives with equal and uniform switching frequency operation for better control and thermal management with the modified DCMLI. The condition of the controller gain is derived to ensure the operation of the DCMLI at the fixed frequency of the carrier. The converter current injected into the distribution grid is controlled in accordance with the wind power availability. In addition, load compensation is performed as an added facility in order to free the source currents being fed from the grid of harmonic distortion, unbalance and a low power factor even though the load may be unbalanced, non-linear and of a poor power factor. The results are validated using PSCAD/EMTDC simulation studies.

• 한국대기환경학회지
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• 제22권4호
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• pp.468-476
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• 2006

Hazardous air pollutants (HAPs) have high toxicity and bioaccurnulation potentials into human body even inbsmall amount (levels of ng/$m^3$). As the levels of HAPs might be controversial, it has been become essential to establish the analysis method for correct results. In this study, various analysis methods of VOCs and Aldehydes were compared in order to select the proper methods in our condition. Sampling and analysis method of VOCs were followed to EPA TO-14a and TO-17. VOCs were collected in absorption tube and separated by thermal desorption unit then analyzed by GC/MSD. Aldehydes were sampled in DNPH-cartridge and extracted into solution then analyzed by HPLC as the same condition of EPA TO-13a. This study also shows the results of QA/QC system of selected methods. Some experiments could be improving the data assurance blank test, calibration check, repetition precision check, the determination of detection limit and reproducibility of the retention time. Precisions of VOCs and aldehydes were ranged in 2$\sim$9% and 1$\sim$4% RSD, respectively. Recovery rate of VOCs showed variable ranges from 60 to 133.5%. MDL of VOCs and aldehydes were 0.044$\sim$0.284 ppb and 0.14$\sim$1.02 ng, respectively.