• Journal of Korean Society for Quality Management
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• v.24 no.2
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• pp.25-43
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• 1996

This paper presents the optimal and practical constant-stress accelerated life test plans for the lognormal lifetime distribution tinder assumptions of intermittent inspection and Type-I censoring. In an optimal plan, the low stress level and the proportions of test units allocated at each stress are determined under given inspection scheme and number of inspections such that the asymptotic variance of the maximum likelihood estimator of a certain quantile at use condition is minimized. Although the practical plan adopts the same design criterion, it involves three rather than two overstress levels in order to compromise the practical deficiencies of the optimal plan. Computational experiments are conducted to choose an allocation plan and a inspection scheme of the practical plan and to compare with test plans over a range of parameter values.

• Bulletin of the Korean Chemical Society
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• v.20 no.7
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• pp.796-800
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• 1999

Three anthrylazacrown ethers in which the anthracene fluorophore π system is separated from the electron donor atoms by one methylene group were synthesized, and their photophysical study was accomplished. These fluorescent compounds showed a maximum fluorescence intensity at pH=5 in aqueous solutions and a decrease in fluorescence intensity upon binding of paramagnetic metal cations (Mn 2+ (d 5 ), Co 2+ (d 7 ), Cu 2+ (d 9 )). The decrease in fluorescence intensity may be attributed to the paramagnetic effect of metal cations to deactivate the excited state by the nonradiative quenching process. The benzylic nitrogen was found to play an important role in changing fluorescence intensity. From the observed linear Stern-Volmer plot and the fluorescence lifetime independence of the presence of metal ions, it was inferred that the chelation enhanced fluorescence quenching (CHEQ) mechanism in the system is a ground state static quenching process. Enhanced fluorescence was also observed when an excess Na + ion was added to the quenched aqueous solution, and it was attributed to cation displacement of a complexed fluorescence quencher.

• International journal of advanced smart convergence
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• v.7 no.4
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• pp.19-26
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• 2018

One of the distinct features of Wireless Sensor Networks (WSNs) is duty cycling mechanism, which is used to conserve energy and extend the network lifetime. Large duty cycle interval introduces lower energy consumption, meanwhile longer end-to-end (E2E) delay. In this paper, we introduce an energy consumption minimization problem for duty-cycled WSNs. We have applied Q-learning algorithm to obtain the maximum duty cycle interval which supports various delay requirements and given Delay Success ratio (DSR) i.e. the required probability of packets arriving at the sink before given delay bound. Our approach only requires sink to compute Q-leaning which makes it practical to implement. Nodes in the different group have the different duty cycle interval in our proposed method and nodes don't need to know the information of the neighboring node. Performance metrics show that our proposed scheme outperforms existing algorithms in terms of energy efficiency while assuring the required delay bound and DSR.

• Bulletin of the Korean Chemical Society
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• v.5 no.6
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• pp.219-223
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• 1984

The 8-methoxypsoralen$<^{4',5'}_{5',6}>$ thymidine monoadducts are isolated from the irradiation mixture of 8-methoxypsoralen and thymidine in a dry film state by a flash column followed by lobar column chromatography. Some physical properties of the adducts were determined. The fluorescence maximum and quantum yield of the monoadduct are dependent on the solvent polarity and the phosphorescence to fluorescence quantum yield ratio was 2.10 which was significantly increased by external heavy atoms. The phosphorescence lifetime was 1.2s which is relatively large compared to other coumarin derivatives. Accurate spectral data of the monoadducts are presented.

• Journal of Industrial and Engineering Chemistry
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• v.67
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• pp.236-243
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• 2018

A series of $Er^{3+}/Yb^{3+}$ co-doped fluorophosphate glasses with varying $YbF_3$ concentration were prepared by a high temperature melt quenching technique. Absorption and emission cross-sections were determined by using the McCumber theory. The larger emission cross-section ($9.86{\times}10^{-21}cm^2$) and longer fluorescence lifetime (12.37 ms) were obtained for the $^4I_{13/2}{\rightarrow}^4I_{15/2}$ transition of ABS3Er4Yb glass. The sensitivity and temperature of the maximum sensitivity were evaluated by the fluorescence intensity ratio method from the measured upconversion spectra. The results were discussed and compared to the other reported glasses.

• Journal of the Semiconductor & Display Technology
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• v.21 no.4
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• pp.86-91
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• 2022

Cache bypassing is a scheme to prevent unnecessary cache blocks from occupying the capacity of the cache for avoiding cache contamination. This method is introduced to alleviate the problems of non-volatile memories (NVMs)-based memory system. However, the prior works have been studied without considering wear-out attack. Malicious writing to a small area in NVMs leads to the failure of the system due to the limited write endurance of NVMs. This paper proposes a novel scheme to prolong the lifetime with higher resistance for the wear-out attack. First, the memory reference pattern is found by modified reuse distance calculation for each cache block. If a cache block is determined as the target of the attack, it is forwarded to higher level cache or main memory without updating the NVM-based cache. The experimental results show that the write endurance is improved by 14% on average and 36% on maximum.

• Journal of Korean Institute of Industrial Engineers
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• v.33 no.1
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• pp.76-85
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• 2007

A reliability acceptance sampling plan (RASP) consists of a set of life test procedures and rules for eitheraccepting or rejecting a collection of items based on the sampled lifetime data. Most of the existing RASPs areconcerned with the case where test items are available at the same time. However, as in the early stage ofproduct development, it may be difficult to secure test items at the same time. In such a case, it is inevitable toconduct a life test using sequentially supplied samples.In this paper, it is assumed that test items are sequentially supplied, the lifetimes of test items follow anexponential disthbution, failures are monitored continuously, arrival times of test items are known, and thenumber of test items at each arrival time is given. Under these assumptions, RASPs are developed by deter-mining the test completion time and the critical value for the maximum likelihood estimator of the mean lifetimesuch that the producer and consumer risks are satisfied. Then, the developed plans are compared to thetraditional Type-I censored RASPs in terms of the test completion time. Computational results indicate that thetest completion time of the developed RASP is shorter than that of the traditional Type-I censored plan in mostcases considered. It is also found that the superiority of the developed RASP becomes more prominent as theinter-arrival times of test items increase and/or the total number of test items gets larger.

• Journal of Industrial Convergence
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• v.18 no.3
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• pp.19-25
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• 2020

In the software development process, software reliability evaluation is a very important issue. In particular, finding the optimal development model that satisfies high reliability is the more important task for software developers. For this, in this study, Pareto and Erlang life distributions were applied to the finite failure NHPP model to evaluate the reliability attributes. For this purpose, parametric estimation is applied to the maximum likelihood estimation method, and nonlinear equations are calculated using the bisection method. As a result, the Erlang model showed better performance than the Pareto model in the evaluation of the strength function and the mean value function. Also, as a result of inputting future mission time and evaluating reliability, the Erlang model showed an effectively high trend together with the Pareto model, while the Goel-Okumoto basic model showed a decreasing trend. In conclusion, the Erlang model is the best model among the proposed models. Through this study, it is expected that software developers will be able to use it as a basic guideline for exploring and evaluating the optimal software reliability model.

• Journal of the Korean Ceramic Society
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• v.41 no.9
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• pp.696-702
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• 2004

Lifetime of excited electronic states inside the 4f configuration of rare-earth elements embedded in chalcogenide glasses is very sensitive to medium-range structural changes of the host glasses. We have measured lifetimes of the 1.6$\mu\textrm{m}$ emission originating from Pr$\^$3+/ : ($^3$F$_3$, $^3$F$_4$)\longrightarrow$^3$H$_4$ transition in amorphous chalcogenide samples consisting of Ge, Sb, and Se elements. The measured lifetimes fumed out to have their maximum at the mean coordination number of -2.67, which arises accordingly from structural changes of the host glasses from 2 dimensional layers to 3 dimensional networks. This new finding supports that the so-called topological structure model together with chemically ordered network model is adequate to explain relationship between the emission properties of rare-earth elements and the medium-range structures of amorphous chalcogenide hosts with a large covalent bond nature. Thus, it is validated to predict site distribution and lifetime of rare-earth elements doped in chalcogenide glasses simply based on their mean coordination number.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.36 no.4
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• pp.409-416
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• 2003

Marine populations are maintained through the processes of spawning, growth, recruitment, natural death and fishing in a marine ecosystem. Based upon each of these processes, a quantitative population dynamic model was developed to estimate damages in fishery production due to accidents in a fishing ground. This model was applied for the abalone culture grounds in Korean waters. Three components of damages were identified in the ecosystem of the abalone culture grounds, namely, physical damages in the substratum of the fishing ground, biological damages in the structure and function of the ecosystem, and damages in fishery production. Considering these three components the processes and durations of damages in fishery production were determined. Because the abalone population is composed of multiple year classes, damages influence all the year classes in the population, when they occur The model developed in this study is: $$y=(n_{\lambda}+1){\times}Y_E\;-\;\sum\limits^{n_\lambda-n_c}_{l=0}\;y_{n_c/i}$$ where, y is the expected damages in fishery production during the period of restoration of the damaged abalony population, $Y_E$ is the annual equilibrium yield, $n_{\lambda}$ is the maximum age in the population, $t_s$ is the year of damage occurrence, $n_c$ is the age at recruitment, and $\sum\limits^{n_\lambda-n_c}_{l=0}\;y\;_{n_c/i}$ is total expected lifetime catch of year classes which were recruited during the restoration period.