• 자원ㆍ환경경제연구
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• 제9권5호
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• pp.903-924
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• 2000

This paper examines the alternative method to measure the state of overall economic activity. The macroeconomic variables, used for business cycle, take more than a month after a period for collection and aggregation. The electricity generation data is compiled in mechanical ways just after the period. Based on this fact, we develop the two stage estimation method for coincident economic indicators in order to detect the business cycle in an earlier period, using Stock-Watson's Dynamic Factor Model. Using monthly data from 1970 to 1999, it is found that the experimental coincidence economic indicators are well-fitted to data and also that the estimates of two stage estimation method have good explanatory power, equivalent to the experimental coincidence economic indicators. While the RMSE of coincidence economic indicators is found to be 1.27%, that of the experimental coincidence economic indicators is found to be 1.31% and that of the two stage estimation method is around 1.44%. If we take consideration into the fact that it measures the business cycle in one month earlier, we come to the conclusion that the two stage estimation is of great use.

• 한국산학기술학회논문지
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• 제15권5호
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• pp.3327-3335
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• 2014

본 연구에서는 천연가스의 냉각을 위한 프로판을 냉매로 사용한 단일 및 다단 냉동 사이클에 대한 소요 에너지를 비교하였다. 이를 위해서 천연가스의 온도를$ -37.00^{\circ}C$까지 냉각시키기 위해서 프로판을 냉매로 사용하여 1단 압축 및 2단, 3단, 4단 압축을 이용한 냉동 사이클에 대한 비교 연구를 수행하였다. 전산모사를 위해 한국가스공사로부터 제공받은 천연가스 조성을 적용하였으며, 열역학 모델식으로는 Peng-Robinson 상태방정식을 적용하였다. 냉동기 압축 단수가 증가할수록 응축기의 heatduty는 점점 줄어드는 것을 알 수 있었다. 4단 압축공정의 경우 1단 압축공정에 비해 응축기의 heatduty는 약 20.36% 정도 감소하였으며 냉매의 총 순환 유량은 약 14.53% 감소하였다. 또한 4단 압축공정의 경우 1단 압축공정에 비해 압축기의 총 소요 동력은 약 41.61% 감소함을 알 수 있었다.

• 한국수소및신에너지학회논문집
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• 제30권5호
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• pp.395-400
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• 2019

Comparative studies between single- and two-stage refrigeration cycle using propane as a refrigerant have been performed for a vapor recompression refrigeration cycle. PRO/II with PROVISION release 10.2 from AVEVA company was used, and the Soave-Redlich-Kwong equation of state model with Twu's alpha function was selected for the modeling and optimization of the refrigeration cycle for the reliquefaction of BOG coming out from the LPG storage tank. In two-stage refrigeraton cycle, 24.8% of compressor power was reduced compared to that of single-stage refrigeration cycle through the optimization works.

• 대한의생명과학회지
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• 제13권1호
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• pp.61-69
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• 2007

The cycle of the seminiferous epithelium and the development of spermatids of Apodemus agrarius coreae were observed using a light microscope. The cycle of the seminiferous epithelium was divided into 10 stages, and developing spermatids were subdivided into 10 steps. The Golgi phases occurs the first two steps ($St_1,\;St_2$), and the cap phases had the next two consecutive steps ($St_3$ and $St_4$). The acrosomal phases consisted of steps $5{\sim}8$ ($St_5-St_8$), and the remaining two steps consisted the maturation ($St_9$) and spermiation ($St_{10}$) phases, respectively. Type Ad spetmatogonia are appeared in all stages (I-X). Type Ap spermatogonia appeared from stage I and II, In spermatogonia from stage III, IV and V, and B spermatogonia from stages VI. The leptotene spermatocytes appeared from stage VII, zygotene from stages I, II, VIII, IX and X, pachytene from stage III to VIII, diplotene in stage IX, and meiotic figures and secondary spermatocytes in stage X. These data are considered in relation to interspecific differences in sperm morphology.

• 설비공학논문집
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• 제19권9호
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• pp.630-639
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• 2007

A $CO_2$ cycle shows large throttling loss during the expansion process. The application of an expander into the $CO_2$ cycle can reduce the throttling loss and then improve system performance. In this study, the performance of a transcritical $CO_2$ cycle with an expander was analytically investigated in order to improve the cooling performance of the system. The expander was applied to the single-stage and two-stage compression cycles. The performance was analyzed with the variations of compressor frequency, outdoor temperature, and expander efficiency. The single-stage and two-stage compression cycles with the expander showed COP improvement of 25% and 32%, respectively, over the single-stage cycle with an EEV.

• 태양에너지
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• 제15권1호
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• pp.29-38
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• 1995

본 연구는 $H_2O/LiBr$와 $NH_3/H_2O$계를 사용하는 2단2원 흡수식 사이클의 특성에 관한 연구이다. 이 사이클은 2개의 단효용 사이클로 이루어져 있으며, 저온단의 흡수기와 응축기에서 얻어진 열을 고온단의 증발기에서 이용하는 사이클로서 저온단의 증발기 및 응축기의 온도, 재생기 온도, 열교환 온도차를 파라메터로 하여 계산한 결과 다음과 같은 결론을 얻었다. 2단2원사이클의 성립범위를 확인하였으며 본 계산조건에서 $50{\sim}70^{\circ}C$의 승온폭을 얻을 수 있었다. 또한 $50^{\circ}C$의 난방온도를 얻기위한 최적재생온도는 $105^{\circ}C$, 최대 COP를 얻기위한 저온측사이클의 응축압력은 $16^{\circ}C$, 그리고 이 조건에서 저온측 사이클의 응축압력을 단효용 사이클의 경우보다 낮게 억제하는 것이 가능함을 알았다.

• Journal of Electrical Engineering and Technology
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• 제11권1호
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• pp.143-149
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• 2016

The two-stage converter is widely used in traditional DC/AC inverter. It has several disadvantages such as complex topology, large volume and high loss. In order to overcome these shortcomings, a novel half load-cycle worked dual SEPIC single-stage inverter, which is based on the analysis of the relationship between input and output voltages of SEPIC converters operating in the discontinuous conduction mode (DCM), is presented in this paper. The traditional single-stage inverter has remarkable advantages in small and medium power applications, but it can’t realize boost DC/AC output directly. Besides one pre-boost DC/DC converter is needed between the DC source and the traditional single-stage inverter. A novel DC/AC inverter without pre-boost DC/DC converter, which is comprised of two SEPIC converters, is studied. The output of dual SEPIC converters is connected with anti-parallel and half load-cycle control is used to realize boost and buck DC/AC output directly and work properly, whatever the DC input voltage is higher or lower than the AC output voltage. The working principle, parameter selection and the control strategy of the inverters are analyzed in this paper. Simulation and experiment results verify the feasibility of the new inverter.

• 대한기계학회논문집B
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• 제36권1호
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• pp.17-24
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• 2012

본 연구에서는 효율적인 냉방시스템의 성능특성을 연구하기 위하여 2단압축을 이용한 이산화탄소 냉방사이클의 성능에 대하여 해석적 연구를 진행하였다. 2단압축을 이용한 플래쉬 중간냉각(flash intercooler)과 플래쉬 가스 바이패스(flash gas bypass) 사이클에 대한 해석적 모델을 개발하였으며 실내온도, 실외온도, 그리고 1단 및 2단 EEV 개도를 변화시켰다. 그 결과 FI와 FGB 사이클의 성능계수는 실외온도를 변화시켰을 경우 각각 28.5%, 22.1% 정도 감소하였으며, 실내온도 변화에 따른 이단압축 사이클의 성능변화는 단단압축 사이클에 비하여 적은 것으로 나타났다. 또한 저단 및 고단 EEV 개도를 변경하였을 경우 성능은 각각 13.5%, 6.9% 그리고 0.9%, 2.6% 정도 증가하는 것으로 나타나 고단 EEV 개도보다 저단의 EEV 개도의 변화가 시스템의 성능에 미치는 영향이 큰 것으로 확인되었다. FI 사이클은 다양한 운전조건에서 시스템의 성능이 가장 높게 나타나는 것을 확인할 수 있었다.

• Journal of Advanced Marine Engineering and Technology
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• 제22권6호
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• pp.782-791
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• 1998

This paper presents a computer simulation of five types of triple effect absorption cycles employ-ing the refrigerant absorbent combinations of NH3/LiNO3 low-pressure type NH3/LiNO3+H2O/LiBr binary two-stage type series flow cycle and two types of parallel flow cycle for H2O/LiBr. The absorption systems is investigated through cycle simulation to obtain the system characteristics with the cooling water inlet temperature approach temperature of absorber loss temperature of absorber and chilled water outlet temperature. The most important characteristic temperature of absorber and chilled water outlet temperature. The most important characteristic of NH3/LiNO3 low-pressure type and a NH3/LINO3+H2O/LiBr binary two-stage type is that it obtains a coefficient of performance higher than the sum of the performance coefficients of its part operating independently. As a result of this analysis the optimum designs and operating conditions were determined based on the operating conditions and the coefficient of performance.

• 한국식품영양학회지
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• 제25권1호
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• pp.205-213
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• 2012

This study investigated the life cycle of menus and made suggestions on the appropriate time for when new menus should be developed. For this purpose, a total of 636 customers who visited 'T' Restaurant more than 25 times in the past three years were used for analysis. After estimating product life cycles based on sales and selling period, an empirical study was conducted. In terms of product life cycle, a growth stage was observed in the category of pasta and pizza in both stores A and B, whereas sales in the rice category stayed constant. Regarding trend in seasonal sales, a big difference was detected between the two stores. While store A was already in the decline stage of the life cycle in all menu categories, store B remained in the growth stage. In terms of menu life cycle, the product life cycle of long-lived products was observed in the pasta category in both stores A and B. While the pizza category was in the growth stage, the product life cycle of long-lived products was observed in the rice category. It is expected that the results of this study could be useful in development of new menus and product life cycle management to fulfill diverse customer needs in the dining-out business.