• 한국산학기술학회논문지
• /
• 제11권8호
• /
• pp.3106-3111
• /
• 2010

본 연구에서는 천연가스의 온도를 $-40^{\circ}C$까지 냉각시키기 위해서 프로판을 냉매로 사용한 1단 냉동과 2단 냉동 사이의 비교연구를 수행하였다. 열역학 모델식으로는 Peng-Robinson 상태방정식을 적용하였으며, 냉동 사이클의 전산모사를 위해서 Invensys사의 PRO/II with PROVISION 8.3을 활용하였다. 본 연구에서로부터 2단 압축 냉동 사이클을 최적화한 결과 1단 압축 냉동 사이클에 비해서 압축기의 소요동력을 33.5% 가량 줄일 수 있었다.

• 한국결정성장학회지
• /
• 제8권1호
• /
• pp.83-90
• /
• 1998

Li, K과 Na-흑연 층간화합물의 stage 전이 특성을 탄소층사이에 존재하는 intercalants의 deintercalation 메카니즘을 고려하여 제시하였다. 온도와 압력을 조절하여 합성된 Li-GICs(graphite intercalation compounds)를 분위기하에서 자발적으로 분해시켰다. 이들 화합물을 XRD 분석한 결과 1, 2 stage의 d001-값이 각각 3.71, 7.06 $\AA$으로 나타났다. 분위기하에서 Li-GiCs를 deintercalation 반응을 시킨 6주 후에 잔유화합물이 형성됨을 알 수 있었다. 또한, two-bulb 법으로 K-GICs를 합성하였으며, K-GDICs(graphite deintercalation compounds)의 구조적 안정성과 stage 전이에 대하여 조사하였다. X-선회절 결과로부터 K-GDICs는 10주 동안 안정한 K-흑연 잔유 화합물을 형성하였다. 그리고 고온, 고압법을 이용하여 합성된 1, 2stage의 Na-GICs의 deintercalation 반응과 열적 안정성에 대한 온도 의존성에 대하여 논하였다. 열적 안정성과 관련하여 Na-GICs의 구조변화를 XRD에 의하여 확인하였다. 이들 과정에 따르면 stage 전이는 무질서한 stage를 가진 GDICs의 불규칙적인 deintercalation에 의하여 형성됨을 제시할 수 있었다.

• 반도체공학회 논문지
• /
• 제2권3호
• /
• pp.6-12
• /
• 2024

본 논문에서는 130nm CMOS 공정을 이용하여 제작된 2.4GHz 차동 캐스코드 전력 증폭기에 대한 연구를 제시하고 있다. 이 전력증폭기는 무선 전력 전송 응용을 위해 설계되었으며, 단일 종단 출력을 위한 발룬 트랜스포머 설계로 구성된 두 개의 차동 스테이지를 갖추고 있다. 출력 단 뿐만 아닌 각 단 사이의 전력 매칭을 위해 발룬 트랜스포머를 활용하고 있으며, 온도 보상이 가능한 바이어스 회로를 추가하여 2.4GHz 주파수 대역에서 안정적인 바이어스 전압을 유지한다. 이를 통해 TT/40℃에서 출력 전력은 21.75 dBm 이고 전력부가효율은 40.9%를 달성한다.

• 한국식품조리과학회지
• /
• 제20권1호
• /
• pp.34-41
• /
• 2004

The retention rate of riboflavin in two cooked vegetable salads (spinach salad and sesame leaf salad) were examined at every cooking stage, holding temperature and holding time, with various cooking methods, and a better food preparation method developed. The riboflavin contents of the samples were analyzed by HPLC, with fluoresence detection. The changes in the pH and water contents of the samples were measured during the holding stage at various temperatures and times. There were significant differences in the riboflavin contents during the various preparation and cooking processes, such as trimming, washing, boiling and parching etc. The retention rates of the riboflavin with the various holding methods and cooking temperature were also significantly different. The boiling process caused large losses of riboflavin: in the cases of spinach salad and sesame leaf salad these were 78％ and 52％ respectively. The pH and water contents showed faster change during 0-6 hours than during 6-12 hours.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2001년도 추계학술대회 논문집
• /
• pp.208-211
• /
• 2001

In the drawing from round billet to non-circular section there are two different processes through solid hole die(HD) and the other cassette roller dies(CRD). The CRD process has several cassette type rollers and a billet is able to move through the given gaps between two profiled rollers. The objective of this study is based on the analysis and evaluation of two aforementioned processes using experiments and finite element simulation. In order to simulate the multi-stage drawing process from circular sectioned billet to rounded square section, the finite element analysis is applied to the process using a commercially available DEFORM-3D code. Two types of experimental drawing tests through designed and manufactured dies for pure copper and aluminum alloy are carried out at room temperature. The analysis included comparison of material properties before and after drawing of each process and also provide some useful information by a FEM simulation.

• Journal of Microbiology and Biotechnology
• /
• 제27권10호
• /
• pp.1808-1819
• /
• 2017

Knowledge on the functional characteristics and temporal variation of anaerobic bacterial populations is important for better understanding of the microbial process of two-stage anaerobic reactors. However, owing to the high diversity of anaerobic bacteria, close attention should be prioritized to the frequently abundant bacteria that were defined as core bacteria and putatively functionally important. In this study, using MiSeq sequencing technology, the core bacterial community of 98 operational taxonomic units (OTUs) was determined in a two-stage upflow blanket filter reactor treating pharmaceutical wastewater. The core bacterial community accounted for 61.66% of the total sequences and accurately predicted the sample location in the principal coordinates analysis scatter plot as the total bacterial OTUs did. The core bacterial community in the first-stage (FS) and second-stage (SS) reactors were generally distinct, in that the FS core bacterial community was indicated to be more related to a higher-level fermentation process, and the SS core bacterial community contained more microbes in syntrophic cooperation with methanogens. Moreover, the different responses of the FS and SS core bacterial communities to the temperature shock and influent disturbance caused by solid contamination were fully investigated. Co-occurring analysis at the Order level implied that Bacteroidales, Selenomonadales, Anaerolineales, Syneristales, and Thermotogales might play key roles in anaerobic digestion due to their high abundance and tight correlation with other microbes. These findings advance our knowledge about the core bacterial community and its temporal variability for future comparative research and improvement of the two-stage anaerobic system operation.

• International Journal of Automotive Technology
• /
• 제7권3호
• /
• pp.261-267
• /
• 2006

Understanding the mechanism of carbon oxidation is important for the successful modeling of diesel particulate filter regeneration. Carbon oxidation characteristics were investigated by temperature programmed oxidation(TPO) method as well as constant temperature oxidation(CTO) with a flow reactor including porous bed. The activation energy of carbon oxidation was increasing with temperature and had two different constant values in the early and the later stage of the oxidation process respectively in TPO experiment. Kinetic constants were derived and the reaction mechanisms were assumed from the experimental results and a simple reaction scheme was proposed, which approximately predicted the overall oxidation process in TPO as well as CTO.

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2005년도 제31회 KOSCO SYMPOSIUM 논문집
• /
• pp.120-131
• /
• 2005

The evaporation characteristics of single and multicomponent droplets hanging at the tip of a quartz fiber are studied experimentally at the different environmental conditions under normal gravity. Heptane and Hexadecane are selected as two fuels with different evaporation rates and boiling temperatures. At the first step, the evaporation of single component droplet of both fuels has been examined separately. At the next step the evaporation of several blends of these two fuels, as a binary component droplet, has been studied. The temperature and pressure range is selected between 400 and 700 $^{\circ}C$, and 0.1 and 2.5 MPa, respectively. High temperature environment has been provided by a falling electrical furnace. The initial diameter of droplet was in range of 1.1 and 1.3 mm. The evaporation process was recorded by a high speed CCD camera. The results of binary droplet evaporation show the three staged evaporation. In the the first stage the more volatile component evaporates. The droplet temperature rises after an almost non evaporating period and in the third stage a quasi linear evaporation takes place. The evaporation of the binary droplet at low pressure is accompanied with bubble formation and droplet fragmentation and leads to incomplete microexplosion. The component concentration affects the evaporation behavior of the first two stages. The bubble formation and droplet distortion does not appear at high environment pressure. Nomenclature

• 소성∙가공
• /
• 제7권6호
• /
• pp.620-630
• /
• 1998

Conventional hot forging and thixoforging of Al 7075 alloy have been compared with respect to microstructures, formability and hardness. Two distinctive temperature-strain rate ranges for hot forging of Al 7075 alloy were observed from the results of simple compression tests with strain rates of 10-3∼101 sec-1 in the temperatures between $250^{\circ}C$ and $500^{\circ}C.$ In the dynamic recovery range (low temperature-high strain rate range) multi-stage forging was necessary to form a complex shape part due to the lack of formability. In the high temperature-low strain rate range, in which dynamic recrystallization takes place a complex shaped park could be formed by single-stage forging. About 50% cold working in the SIMA process was necessary to get a fine and homogeneous microstructures. Microstructural study suggest that thixoforged Al 7075 part has fine grains and homogeneous microstructures. Its hardness number is almost same to that of conventional hot forged part after aging treatment.

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 1999년도 제19회 KOSCO SYMPOSIUM 논문집
• /
• pp.241-249
• /
• 1999

Soot particle temperatures in co-flow diffusion flames have been measured using a two-color pyrometry at the pressure of 0.2 MPa(2 atm). The measured soot particle temperatures along with the integrated soot volume fractions are analyzed to understand soot formation characteristics. At 0.2 MPa, the addition of small amount of air into ethylene do not change the soot particle temperature in soot formation regions. This result showed that the increase of soot formation with addition of air is mostly due to the chemical effect of the added air, such as the increased role of C3 chemistry during the early stage of soot inception process. The addition of sufficient air into ethylene, however, changes soot particle temperatures and the understanding of soot formation characteristics becomes complicated. Measured soot particle temperatures also showed that there is no significant temperature effect for the synergistic effect of ethylene/propane mixture on soot formation.