• 대한조선학회논문집
• /
• 제52권6호
• /
• pp.460-470
• /
• 2015

In general ships and FPSOs, roll damping is very small and consequently roll motion is very large at the roll resonance frequency. Proper evaluation of the roll damping coefficient at the resonance frequency is an important task in the study of roll motion and usually it is done by the analysis of free roll decay tests. The relative decrement method based on energy relation has been used mainly for the evaluation of roll damping coefficient from the roll decay test so far. As another method, the logarithmic decrement method based on equivalent linear decay assumption can be used for the same purpose and it is relatively simple. In this paper, both of the relative decrement method and the logarithmic decrement method are used for the evaluation of roll damping coefficient including quadratic damping from the free roll decay tests, and their results are cross-checked for verifying the obtained damping coefficients. Through applications to a box-type floating body equiped with bilge keels, it is shown that the two methods give almost the same damping coefficients in a practical view point and the cross-check of their results is to be a good tool to prevent a possible error. And also the quantitative effects of the bilge keels on the roll damping of box-type floating body are shown and discussed.

• Nuclear Engineering and Technology
• /
• 제21권1호
• /
• pp.48-55
• /
• 1989

본 논고에서는 국내의 PWR 및 CANDU 사용후 핵연료로부터 발생하는 붕괴열의 장기적인 거동을 보다 손쉽게 분석하기 위하여 붕귀열을 추정할 수 있는 간단한 근사식을 도출하였다. 근사식의 장기적인 붕괴열 추정에서 ORIGEN 2코드 결과와의 차이를 줄이고 중요한 변수 조건하에서도 붕괴열을 추정할 수 있도록 하기 위하여 민감도 분석을 수행하였다. 그 결과로서 얻어진 근사식은 사용후 핵연료의 이력자료중 중요변수인 연도를 포함함으로써 3~500년정도의 냉각시간 범위내에서는 임의의 연소도를 가진 사용후 핵연료의 붕괴열이라도 추정할 수 있게 되었다. 그리고 대표적으로 30, 37 및 40 GWD/MTU등의 연소도를 갖는 사용후 핵연료의 붕괴열 추정에 있어서는 1년부터 $10^{5}$ 년까지의 냉각시간에 따라 ORIGEN2 ,코드의 결과와 $\pm$10%이내의 차이를 보이고 있어 사용후 핵연료 관리를 위한 관련시설의 열적설계 및 평가 등과 같은 공학적 목적에 유용하게 사용될 수 있을 것이다.

• 대한치과교정학회지
• /
• 제54권3호
• /
• pp.153-159
• /
• 2024

Objective: This study aimed to assess the effects of commonly consumed hot drinks on the force decay of orthodontic elastomeric chains. Methods: This in vitro experimental study evaluated 375 pieces of elastomeric chains with six rings placed on a jig. Four rings were stretched by 23.5 mm corresponding to the approximate distance between the canine and the second premolar. Fifteen pieces served as reference samples at time zero, and 360 pieces were randomized into four groups: control, hot water, hot tea, and hot coffee. Each group was further divided into six subgroups (n = 15) according to the different exposure periods. The specimens in the experimental groups were exposed to the respective solutions at 65.5℃ four times per day for 90 seconds at 5-second intervals. The control group was exposed to artificial saliva at 37℃. The force decay of the samples was measured at 1, 2, 7, 14, 21, and 28 days using a universal testing machine. Data were analyzed using repeated-measures analysis of variance. Results: Maximum force decay occurred on day 1 in all groups. The minimum force was recorded in the control group, followed by the tea, coffee, and hot water groups on day 1. At the other time points, the minimum force was observed in the tea group, followed by the control, coffee, and hot water groups. Conclusions: Patients can consume hot drinks without concern about any adverse effect on force decay of the orthodontic elastomeric chains.

• Journal of Microbiology and Biotechnology
• /
• 제21권4호
• /
• pp.347-358
• /
• 2011

Fomitopsis palustris, a brown-rot basidiomycete, causes the most destructive type of decay in wooden structures. In spite of its great economic importance, very little information is available at the molecular level regarding its complex decay process. To address this, we generated over 3,000 expressed sequence tags (ESTs) from a cDNA library constructed from F. palustris. Clustering of 3,095 high-quality ESTs resulted in a set of 1,403 putative unigenes comprising 485 contigs and 918 singlets. Homology searches based on BlastX analysis revealed that 78% of the F. palustris unigenes had a significant match to proteins deposited in the nonredundant databases. A subset of F. palustris unigenes showed similarity to the carbohydrateactive enzymes (CAZymes), including a range of glycosyl hydrolase (GH) family proteins. Some of these CAZyme-encoded genes were previously undescribed for F. palustris but predicted to have potential roles in biodegradation of wood. Among them, we identified and characterized a gene (FpCel45A) encoding the GH family 45 endoglucanase. Moreover, we also provided functional classification of 473 (34%) of F. palustris unigenes using the Gene Ontology hierarchy. The annotated EST data sets and related analysis may be useful in providing an initial insight into the genetic background of F. palustris.

• 한국환경과학회지
• /
• 제7권3호
• /
• pp.301-310
• /
• 1998

Recently, bathes have been suspected to an Important source of indoor exposure to volatile organic compounds(VOCs). Two experiments were conducted to evaluate chloroform exposure and corresponding body burden by exposure routes while bathing. Another experiment was conducted to ekamine the chloro- form dose during dermal exposure and the chloroform decay In breath after dermal exposure. The chioroform dose was determined based on exhaled breath analysis. The ekamine breath concentration measured after normal baths (2.8 Vg/$m^3$) was approxidmately 13 tomes higher that measured prior to normal bathes (0.2 ug/$m^3$). Based on the means of the normalized post exposure chloroform breath concentration. the dermal exposure was estimated to contribute to 74% of total chloroform body burden while bathing. The Internal dose from bathing (Inhalation plus dermal) was comparable to the dose ostimated Srom dally water Ingestion. The rusk associated 10 a weekly, 30-min bath was estimated to be 1 x 10.5, while the rusk firom dally Ingestion of tap water was to be $0.5{\times}0^{-5} for 0.151 and 6.5{\times}10^{-5}$ for 2. 0 1. Chloroform breath concentration Increased gradually during the 60 minute dermal exposure. The breath decay after the dermal exposure showed two-phase mechanism, with early raped decay and the second slow decay. The mathematical model was developed to describe the relationship between water and air chloroform concentrations, with $R^2$ : 0.4 and p<0.02.

• 한국전산유체공학회지
• /
• 제21권1호
• /
• pp.19-29
• /
• 2016

A Prototype Gen-IV Sodium-cooled Fast Reactor which is one of the $4^{th}$ generation nuclear reactors is in development by Korea Atomic Energy Research Institute. The reactor is composed of four main fluid systems which are categorized by its functions, i.e., Primary Heat Transport System, Intermediate Heat Transport System, Decay Heat Removal System and Sodium-Water Reaction Pressure Relief System. The coolant of the reactor is liquid sodium and sodium-to-sodium heat exchangers are installed at the interfaces between two fluid systems, Intermediate Heat Exchangers between the Primary Heat Transport System and the Intermediate Heat Transport System and Decay Heat Exchangers between the Primary Heat Transport System and the Decay Heat Removal System. For the design and performance analysis of the Intermediate Heat Exchanger and the Decay Heat Exchanger, a computer code was written during previous step of research. In this work, the computer code named "SHXSA" has been validated preliminarily by computational fluid dynamics simulations.

• Coupled systems mechanics
• /
• 제9권5호
• /
• pp.455-471
• /
• 2020

This paper presents the results of the study of vertically natural frequency of tractor tires are effected by changing different ground contacts and inflation pressures using the Free Decay Method. The results show that the natural frequencies of the tire are not affected while the vertical acceleration increased strongly due to the increase of inflation pressure when the tire performs free decay vibration on rigid ground. In addition, the number of natural frequency peaks of the tire also increases with increasing tire inflation pressure. On the other hand, the natural frequencies of the tractor tire increases strongly while the vertical acceleration decreases slightly with the increase of tire inflation pressure as the tire performs free decay vibration on soft soil. Further, the natural frequencies of tire-soil system are always higher than that of tire only, and it changed with changing the soil depth. Results also show the natural frequency of tire and tire-soil system is in the range of 3.0 to 10.0 Hz that lie within the most critical natural frequency range of the human body. These findings have to be mentioned and used as design parameters of the tractor suspension system.

• 방사성폐기물학회지
• /
• 제20권2호
• /
• pp.171-183
• /
• 2022

The parent and daughter nuclides in a radioactive decay chain arrive at secular equilibrium once they have a large half-life difference. The characteristics of this equilibrium state can be used to estimate the production time of nuclear materials. In this study, a mathematical model and algorithm that can be applied to radio-chronometry using the radioactive equilibrium relationship were investigated, reviewed, and implemented. A Bateman equation that can analyze the decay of radioactive materials over time was used for the mathematical model. To obtain a differential-based solution of the Bateman equation, an algebraic numerical solution approach and two different matrix exponential functions (Moral and Levy) were implemented. The obtained result was compared with those of commonly used algorithms, such as the Chebyshev rational approximation method and WISE Uranium. The experimental analysis confirmed the similarity of the results. However, the Moral method led to an increasing calculation uncertainty once there was a branching decay, so this aspect must be improved. The time period corresponding to the production of nuclear materials or nuclear activity can be estimated using the proposed algorithm when uranium or its daughter nuclides are included in the target materials for nuclear forensics.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1995년도 하계학술대회 논문집 C
• /
• pp.1156-1158
• /
• 1995

Charge decay, thermally stimulated current(TSC), charging and discharging currents(I) are measured for negatively corona-charged polymers. In this study, we will make an experiment in charge decay on polymer surface, TSC, polarity effect and the others in order to analysis it's mechanism. Especially polyvinylidene fluoride(PVDF) film is the best functional material which has been so far. Therefore, It's worthy of notice to investigate it's characteristic. And then some other functional polymers will be focused on. An experimental result was missed out for the shortage of setting. So, this thesis will be explained on the theory and direction of reseach hereafter.

• Transactions on Electrical and Electronic Materials
• /
• 제7권5호
• /
• pp.235-239
• /
• 2006

Charge dynamics in polymeric materials after aged under ac electric field using the pulsed electroacoustic (PEA) technique is reported. The emphasis is placed on charge decay. The charge dynamics of the ac aged additive free low density polyethylene (LDPE) samples under dc bias differ from the sample without ac ageing, indicating changes brought in by ac ageing. It is believed that a slow decay rate of charge in the ac aged sample is related to the formation of deep traps in the material. However, chemical analysis by infrared spectroscope (FTIR) and Raman microscope reveals no significant chemical changes taken place in the bulk of the material after ac ageing. Further experiments on irradiated LDPE have revealed a similar behaviour, i.e. the charge decay is slower in irradiated samples than that of fresh sample. The findings presented clearly indicate that space charge measurement can be used as a diagnostic tool to monitor ageing in polymeric materials.