• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 추계학술발표회논문집(1)
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• pp.309-314
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• 1996

Feasibility study has been accomplished to evaluate the effectiveness of the in-vessel core debris cooling through lower cavity flooding using two dimensional finite difference scheme. The volume of cerium pool and decay power rate generated in corium pool were evaluated as important parameters to the temperature distribution on the reactor vessel lower head through previous works. In this study, the corium volume based on the System 80＋ core structure and time dependent decay power rate are considered for feasibility evaluation. In addition, preliminary plans for the in-vessel core debris cooling through lower cavity flooding as severe accident management strategy, i.e. flooding timing, method and capacity, are suggested based on the result of the numerical study, international tendency related to in-vessel core debris cooling through lower cavity flooding.

• 한국환경과학회지
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• 제9권1호
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• pp.75-80
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• 2000

Kinetic data for the acid phase anaerobic digestion were presented in this study and the constants were determined with acid production rate and gas production rate. Process models based on continuous culture theory were used to describe the characteristics of the acid forming microorganisms and to enable further development toward utilization of the process in a more rational manner. Acid phase digestion can be separated with appropriate manipulation of hydraulic retention time in anaerobic digestion. Kinetic analysis of data from the various hydraulic retention times using a phase specific model obtained form the acid phase indicated maximum specific growth rate of 0.40/h, saturation constant of 2,000mgCOD.$\ell$, yield coefficient of 0.35 mgVSS/msCOD utilized and decay constant of 0.04/h for the acid production rate. Similar analysis of data for the gas production rate indicated maximum specific growth rate of 0.003/h, saturation constant of 2,200mgCOD/$\ell$, yield coefficient of 0.035 mgVSS/mgCOD utilized and decay constant of 0.06/h.

• East Asian mathematical journal
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• 제32권5호
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• pp.659-675
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• 2016

In this paper, we study the generalized Kirchhoff type equation in the presence of past and finite history $$\large u_{tt}-M(x,t,{\tau},\;{\parallel}{\nabla}u(t){\parallel}^2){\Delta}u+{\normalsize\displaystyle\smashmargin{2}{\int\nolimits_0}^t}\;h(t-{\tau})div[a(x){\nabla}u({\tau})]d{\tau}\\\hspace{25}-{\normalsize\displaystyle\smashmargin{2}{\int\nolimits_{-{\infty}}}^t}\;k(t-{\tau}){\Delta}u(x,t)d{\tau}+{\mid}u{\mid}^{\gamma}u+{\mu}_1u_t(x,t)+{\mu}_2u_t(x,t-s(t))=0.$$ Under the smallness condition with respect to Kirchhoff coefficient and the relaxation function and other assumptions, we prove the expoential decay rate of the Kirchhoff type energy.

• 센서학회지
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• 제18권6호
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• pp.449-455
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• 2009

In this paper, we developed a digital gait analyzer using the triaxial accelerometer(TA). An approach for normal gait detection employing decay slope peak detection(DSPD) algorithm was presented. The TA was attached to the center of the waist of a subject. The subject walked a bare floor at 60, 92 and 120 steps/minute. We analyzed vertical axis acceleration signal for gait detection. At 60, 92, 120 steps/minute walking, detection accuracy of gait events were over 99 % accuracy.

• The Korean Journal of Ecology
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• 제21권5_1호
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• pp.427-433
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• 1998

The standing crop and net production were estimated in Moojaechi on Mt. Jungjok. By using the decay model of organic carbon, absolute year of bog peat was calculated. Pollen analysis to bog peat revealed vegetational history and climate change around Moojaechi. The time required for amount of the accumulated peat in the bog was estimated in terms of the balance of the accumulation and decay of organic carbon of the deposit peat. Absolute year of the peat surveyed in this study was about 314 years. Pollen of Pinus was predominant in all the pollen zone, Geamineae and Cyperaceae increased in lower pollen zone while Pinus in upper pollen zone. This showes that climate of the past was probably more humid than that of present. In addition, middle pollen zone showed warming trend which is suggested by high pollen concentration of Quercus, Juglans, Carpinus and Corylus. It suggests that overall environment and vegetation were changed from warmer and more humid to dry condition in Moojaechi and it is considered as the course of boggy ground formation by retrogressive successions.

• Journal of Electrical Engineering and information Science
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• 제2권6호
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• pp.90-94
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• 1997

The joints between the superconducting wires are inevitably needed from the requirement of a high magnetic stability with respect to time in the superconducting MRI magnet. In this study, a new superconducting joint using Cu/Nb-Ti sleeve has been tried on the MRI type Nb-Ti superconducting wires. The transformer induction type apparatus was made and applied to measure the joint resistance. A very low joint resistance of 10\ulcorner $\Omega$ could be successfully obtained from this joint method. It was confirmed that the initial rapid current decay occurs before the very stable current decay due to only superconducting joint. Some unstable part in the joint like exposed filaments causes the initial induced current to lower and influence on the increase of the joint resistance.

• Journal of Radiation Protection and Research
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• 제22권2호
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• pp.111-117
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• 1997

최근 포괄적 핵실험금지조약 (Comprehensive Test Ban Traety : CTBT)의 체결은 전세계적으로 핵활동 감시 네트워크를 구축하는 것이다. 핵실험금지 위원회의 전문가들은 대기 방사성핵종의 측정을 핵실험 감시에 필수적인 요소로 제안하였으며, 이에 따른 기술적 요구사항을 제시하였다. 본 연구는 이를 근거로 핵활동으로부터 생성된 핵분열생성물을 검출하기 위하여 고성능 공기채집장치(High Volume Air Sampler: HVAS)와 여과지 압축기 그리고 고순도 게르마늄 반도체검출기(HPGe)로 대기 입자 방사성핵종 측정시스템을 구성하였다. 조속한 시일 내에 탐지와 최적의 측정 조건으로 본 시스템을 운영하기 위하여 CTBT 감시 전략에서 주요 핵종들에 대한 최소검출 방사능 농도(Minimum Detectable Concentration : MDC)를 decay time, counting time 그리고 sampler volumetric flow rate 등을 고려하여 결정하였다. 그 결과 각각 $10{\pm}$2h, $20{\pm}$2h, $850{\pm}50m^3$//h 정도로 선정하였다. 감마선 스펙트럼 분석에서 $^{212}Pb$ 방사능 농도의 변화는 Compton continuum의 baseline에 영향을 미치게 되므로 이에 기인한 MDC 관계식을 도출하였다. 이들 결과는 CTBT 감시 전략에 실제적인 도구로 사용될 수 있을 것으로 사료된다.

• Journal of Ecology and Environment
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• 제43권4호
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• pp.376-384
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• 2019

Background: Nutrient release during litter decomposition was investigated in Vitex doniana, Terminalia avecinioides, Sarcocephallus latifolius, and Parinari curatellifolius in Makurdi, Benue State Nigeria (January 10 to March 10 and from June 10 to August 10, 2016). Leaf decomposition was measured as loss in mass of litter over time using the decay model W_t/W₀ = e-^{kd t}, while $Kd=-{\frac{1}{t}}In({\frac{Wt}{W0}})$ was used to evaluate decomposition rate. Time taken for half of litter to decompose was measured using T₅₀ = ln ²/k; while nutrient accumulation index was evaluated as $NAI=(\frac{{\omega}t\;Xt}{{\omega}oXo})$. Results: Average mass of litter remaining after exposure ranged from 96.15 g, (V. doniana) to 78.11 g, (S. lafolius) in dry (November to March) and wet (April to October) seasons. Decomposition rate was averagely faster in the wet season (0.0030) than in the dry season (0.0022) with P. curatellifolius (0.0028) and T. avecinioides (0.0039) having the fastest decomposition rates in dry and wet seasons. Mean residence time (days) ranged from 929 to 356, while the time (days) for half the original mass to decompose ranged from 622 to 201 (dry and wet seasons). ANOVA revealed highly significant differences (p < 0.01) in decomposition rates and exposure time (days) and a significant interaction (p < 0.05) between species and exposure time in both seasons. Conclusion: Slow decomposition in the plant leaves implied carbon retention in the ecosystem and slow release of CO₂ back to the atmosphere, while nitrogen was mineralized in both seasons. The plants therefore showed effectiveness in nutrient cycling and support productivity in the ecosystem.

• 한국수소및신에너지학회논문집
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• 제26권6호
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• pp.581-589
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• 2015

In this study, the viscosity of a liquid carbon dioxide ($LCO_2$) that can potentially be used in a wet feed coal gasifier was evaluated. A pressurized capillary viscometer was employed to obtain the viscosity data of $LCO_2$ using two different methods. During the first method, the measurements were conducted under quasi-steady and high pressure flow conditions where two-phase flow was greatly minimized. The viscosity of $LCO_2$ was determined using turbulent friction relationship. At the second flow condition where unsteady flow is induced, the viscosity of $LCO_2$ was measured using the half-time pressure decay data and was further compared with values calculated by the first method.

• 센서학회지
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• 제17권3호
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• pp.217-222
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• 2008

$BaCl_2$ crystals were grown by using the Czochralski method, and their scintillation properties were measured. The emission spectrum was located in the range of $370{\sim}450$ nm, peaking at about 400 nm. The fluorescence decay time was approximately 75.9 ns for 662 keV ${\gamma}$-rays excitation. The energy resolution was about 24.4 % for $^{137}Cs$ 662 keV ${\gamma}$-rays, and the ${\alpha}/{\beta}$ ratio to $\alpha$ particles from a $^{210}Po$ 5.4 MeV was about 0.25.