• Nuclear Engineering and Technology
• /
• 제26권2호
• /
• pp.277-284
• /
• 1994

폐기물 고화체로부터 주위의 Near-field로의 단일 핵종의 이동에는 많은 연구가 수행되고 있으나, 방사성 핵종 사슬의 이동에 관한 연구는 매우 제한되어 있다. 본 논문에서는 조화 유출되는 방사성 핵종 사슬의 이동을 분석하고, 유한 크기의 다공성 매질에서의 일반적인 비순환 해석해를 제시하였다. 또한 이해를 사용후 핵연료에서 가장 중요한 핵종사슬인 $^{234}$ U$\longrightarrow$$^{230}$ Th$\longrightarrow$$^{226}$ Ra 에 적용하여 보았다. 본 연구는 방사성 폐기물의 처분장 성능평가에 유용하고 중요하게 사용될 것이다.

• 대한수학회지
• /
• 제49권3호
• /
• pp.515-536
• /
• 2012

This work focuses on the general decay stability of nonlinear stochastic differential equations with unbounded delay. A Razumikhin-type theorem is first established to obtain the moment stability but without almost sure stability. Then an improved edition is presented to derive not only the moment stability but also the almost sure stability, while existing Razumikhin-type theorems aim at only the moment stability. By virtue of the $M$-matrix techniques, we further develop the aforementioned Razumikhin-type theorems to be easily implementable. Two examples are given for illustration.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2000년도 춘계학술대회논문집
• /
• pp.1762-1766
• /
• 2000

Estimation of reverberant time is one of important factor for the calculation of absorption ration of absorption material. In general the digital filter bank has been used for the, estimation of decay curve of the sound pressure in a reverberant room. However at low frequency, it is not easy to get a good linear decay curve for the estimation of reverberant time. Now, wavelet transform is applied to this difficult task, a good result has been obtained at low frequency. The decay curve using wavelet filter bank is better than that using digital filter bank at low frequency. At higher frequency, both curves are similar.

• Nuclear Engineering and Technology
• /
• 제55권5호
• /
• pp.1821-1829
• /
• 2023

The temperature distribution of the reactor pool under natural circulation induced by the RVACS operation was experimentally studied. According to the Bo' based similarity law, which could reproduce the temperature distribution of the working fluid under natural circulation, SINCRO-2D facility was designed based on the PGSFR. It was reduced to 1 : 25 in length scale, having water as a simulant of the sodium, which is the original working fluid. In general, temperature was stratified, however, effect of the natural circulation flow could be observed by the entrainment of the stratified temperature. Relative cooling contribution of the upper plenum (narrow gap) and lower plenum was approximately 0.2 and 0.8, respectively. In the range of decay heat from 0.2% to 1.0%, only the magnitude of the temperature was changed, while the normalized temperature maintained. Boundary temperature distribution change made a global temperature offset of the pool, without a significant local change. Therefore, the decay heat and cooling boundary condition had no significant effect on temperature distribution characteristics of the pool within the given range of the decay heat and boundary temperature distribution.

• 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.

• 천문학회지
• /
• 제53권2호
• /
• pp.49-57
• /
• 2020

We present numerical simulations of decaying hydrodynamic turbulence initially driven by solenoidal (divergence-free) and compressive (curl-free) drivings. Most previous numerical studies for decaying turbulence assume an isothermal equation of state (EOS). Here we use a polytropic EOS, P ∝ ρ^γ, with polytropic exponent γ ranging from 0.7 to 5/3. We mainly aim at determining the effects of γ and driving schemes on the decay law of turbulence energy, E ∝ t^-α. We additionally study probability density function (PDF) of gas density and skewness of the distribution in polytropic turbulence driven by compressive driving. Our findings are as follows. First of all, we find that even if γ does not strongly change the decay law, the driving schemes weakly change the relation; in our all simulations, turbulence decays with α ≈ 1, but compressive driving yields smaller α than solenoidal driving at the same sonic Mach number. Second, we calculate compressive and solenoidal velocity components separately and compare their decay rates in turbulence initially driven by compressive driving. We find that the former decays much faster so that it ends up having a smaller fraction than the latter. Third, the density PDF of compressively driven turbulence with γ > 1 deviates from log-normal distribution: it has a power-law tail at low density as in the case of solenoidally driven turbulence. However, as it decays, the density PDF becomes approximately log-normal. We discuss why decay rates of compressive and solenoidal velocity components are different in compressively driven turbulence and astrophysical implication of our findings.

• 대한환경공학회지
• /
• 제35권4호
• /
• pp.276-282
• /
• 2013

하수재이용수는 부족한 수자원 문제를 해결할 수 있는 대표적인 대안으로 주목받고 있다. 본 연구에서는 하수재이용수의 공급시 유리잔류염소의 수체감소 특성을 온도별(5, 15, $25^{\circ}C$), 초기 주입농도별(1, 2, 4, 6 mg/L)로 살펴보았고 그 결과를 이용하여 최적 염소주입량을 산정하는 방법에 대하여 연구하였다. 하수재이용수는 정수와 비교하여 염소주입시 반응속도가 초기에 매우 빠르게 나타나 기존의 general first-order decay model ($C_t=C_o(e^{-k_bt})$)을 사용하기에 부적합하여 exponential firstorder decay model ($C_t=a+b(e^{-k_bt})$)을 적용한 결과 유리잔류염소의 감소를 더욱 정확하게 예측할 수 있었다($r^2$=0.872~0.988). 수체감소계수를 산출한 결과 초기주입량 1 mg/L, $25^{\circ}C$의 조건에서 653 $day^{-1}$로 가장 크게 나타났고, $5^{\circ}C$, 초기주입량 6 mg/L의 조건에서 3.42 $day^{-1}$로 가장 낮았다. 수체감소계수는 온도가 증가함에 따라 수체감소계수는 증가하는 경향을 나타내었고, 초기 주입농도가 증가함에 따라 수체감소계수는 감소하는 경향을 나타내었다. 적정 초기 염소요구량을 산정하기 위해서 전체 반응기간을 0~30분, 30~5,040분으로 구분한 후, 30~5,040분의 실험결과를 사용한 예측식을 사용함으로써 더욱 정확한 염소주입량 산정을 할 수 있었다. 또한, 온도별로 최적 염소주입량을 산정한 결과 염소주입 후 4시간이 경과한 시점에서 유리잔류염소 0.2 mg/L를 유지하기 위해서는 온도(x)별 초기 염소요구량(y)의 관계를 y = 1.409 + 0.450x와 같이 얻을 수 있었다.

• 한국치위생학회지
• /
• 제21권2호
• /
• pp.151-158
• /
• 2021

Objectives: The purpose of this study was to identify the effects of general and oral health status on dementia. Methods: Questionnaires were used for the KDSQ-C (Korean Dementia Screening Questionnaires-Cognition) and to investigate the oral health status of the participants. An independent t-test was conducted to analyze the differences between general health and oral health status depending on the normal and suspected dementia groups. Logistic regression analysis was performed to assess the effects of general and oral health status on dementia. Results: Regarding the health status of the subjects assessed by the KDSQ-C, the higher the current health status and the higher the exercise status, the lower was the dementia level (p<0.05). During the assessment of oral health conditions in KDSQ-C subjects, dementia was more suspected in subjects with dental decay and periodontal disease than in those without dental decay (p<0.05). Conclusions: Dementia has been confirmed to be closely related to general and oral health conditions. Therefore, oral health-related programs are essential for dementia prevention programs. Since dental hygienists are best suited for providing oral care to older adults with dementia, it is considered essential to reflect their occupation in future national policies.

• 대한수학회논문집
• /
• 제35권1호
• /
• pp.321-338
• /
• 2020

In this paper, we investigate the viscoelastic plate equation with a constant delay term and logarithmic nonlinearities. Under some conditions, we will prove the global existence. Furthermore, we use weighted spaces to establish a general decay rate of solution.

• KIEAE Journal
• /
• 제1권2호
• /
• pp.21-28
• /
• 2001

Naturally-ocurring short-lived decay products of radon gas in indoor air are the dominant source of ionizing radiation exposure to the general public. It is written in BEIR VI Report(l999l the radon progeny were identified as the second cause of lung cancer next to cigarette or 10 % to 14 %(15,400 to 21,800 persons p.a.) of all lung cancer deaths in USA. Indoor radon concentrations in houses typically result from radon gaining access to houses mainly from the underlying soil. In the States, they have "Indoor Radon Abatement Act" which was converted from "Toxic Substance Control Act" in 1988 to establish the national long-term goal that indoor air should be as free of radon as the ambient air outside of buildings. To review and study techniques for controlling radon, two test cells were constructed for a series of tests and are under measuring indoor and soil gas (underneath of floor slab)radon concentrations according to EPA's measurement protocol. In this paper, important theoretical studies are previewed and the following paper will explain the test results and confirm the theories reviewed to find out suitable coefficients. On the basis of test analysis, it will be described and evaluated various techniques that can be used to mitigate elevated indoor concentration of radon including the control of radon and its decay products.