• Nuclear Engineering and Technology
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• v.56 no.1
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• pp.283-291
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• 2024

Sodium cooled Fast Reactors (SFR) are built with several engineered safety features and hence a severe accident such as a core melt accident is hypothetical with a probability of <10^-6/ry. However, in case of such accidents, the mixture of the molten fuel and structural materials interacts with sodium. This phenomenon is known as Molten Fuel Coolant Interaction (MFCI) and results in fragmentation of the melt due to various instabilities. The fragmented particles settle as a debris bed on the core catcher at the bottom of the reactor vessel, and continue to generate decay heat. Characteristics of the debris particles play a vital role in heat transfer from the bed and need thorough investigation. The size, shape, and physical state of the debris depend on the associated fragmentation mechanism, superheating of the melt, and sodium temperature. Experiments have been conducted by releasing simulated corium, a molten mixture of alumina and iron generated by the aluminothermy process at ~2400 ℃ into liquid sodium, to study the fragmentation phenomena. After the experiment, the fragmented debris was retrieved and the particle size distribution was determined by sieve analysis. The debris was subjected to microscopic investigation for obtaining morphological characteristics. Based on the characteristics of debris, an attempt has been made to assess of fragmentation mechanism of simulated corium in sodium.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.2
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• pp.215-224
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• 1997

This paper addresses the vertical class fragmentation in distributed object-oriented databases. In the proposed vertical fragmentation, after producing the attribute fragment by partitioning attributes, then the method fragment is produced by gathering methods referring the attribute in each fragment. For partitioning attributes, we define query access matrix(QAM) and method access matrix(MAM) to express attributes that method refers, and extend QAM, MAM and attribute usage matrix(AUM) to universal class environment for representing relationship among other classes through class hierarchy and class composite hierarchy.

• Rapid Communication in Photoscience
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• v.2 no.1
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• pp.31-33
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• 2013

The irradiation of electron-beam onto bis-(diphenylphosphino)methane, ethane, propane and butane initiated phenyl-shift from a phosphine to another phosphine atom and subsequent fragmentation resulted in the formation of triphenylphosphine derivative as key intermediate. The mechanism of those processes is speculated.

• Rapid Communication in Photoscience
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• v.5 no.2
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• pp.16-17
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• 2016

Arylalkyne cobalt complexes 5, 6 were prepared and irradiated with e-beam to study their fragmentation focused in alkyne formation. Thioaryl complex 6 showed facile CO ligand release and generated parent alkyne in 89% relative intensity. Meanwhile, hydroxyaryl complex 5 gave alkyne in 6% relative intensity.

• Journal of Photoscience
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• v.10 no.1
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• pp.89-96
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• 2003

Two important types of $\alpha$-heterolytic fragmentation reactions of aminium radicals are discussed. In these fragmentation processes, transfer of electrofugal groups from the aminium radicals to either Lowry-Bronsted or Lewis bases produces $\alpha$-amino radicals. The results of recent studies that provided key information about the dynamics of the important aminium radical fragmentation reactions, deprotonation, desilylation, are summarized. Finally, selected examples, which demonstrate how knowledge of the relative rates of aminium radical cleavage can be used to design synthetically relevant SET-promoted photocyclization reactions, are presented.

• Bulletin of the Korean Mathematical Society
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• v.42 no.4
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• pp.855-867
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• 2005

Shattering or disintegration of mass is a well known phenomenon in fragmentation processes first introduced by Kol­mogorov and Filippop and extensively studied by many physicists. Though the mass is conserved in each break-up, the total mass decreases in finite time. We investigate this phenomenon in the n particle system. In this system, shattering can be interpreted such that, in uniformly bounded time on n, order n of mass is located in order o(n) of clusters. It turns out that the tagged particle processes associated with the systems are useful tools to analyze the phenomenon. For the newly defined stochastic shattering based on the above ideas, we derive far sharper conditions of fragmentation kernels which guarantee the occurrence of such a phenomenon than our previous work [9].

• YAKHAK HOEJI
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• v.43 no.3
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• pp.385-390
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• 1999

Camptothecin (CPT) has been known to induce apoptosis in various cancer cell lines. To examine the intracellular apoptotic death signal initiated by CPT, we investigated the possible connection between caspase-3 activation and GSH depletion during CPT-induced apoptosis in HL-60 cells. Treatment of cells with $1{\;}{\mu}M$ CPT induced PARP cleavage accompanied by DNA fragmentation. z-VAD-fmk, a caspase-3 inhibitor, blocked the CPT-induced DNA fragmentation. Pretreatment of cells with N-acetylcysteine, a precursor of GSH biosynthesis, failed to inhibit CPT-induced PARP celavage and DNA gragmenatation. No significant changes in GSH depletion is not essential for caspase activation during CPT-induced apoptosis. We also investigated whether CPT-induced apoptosis is associated with changes of the levels of Bax and Bcl-2, two proteins involved in the control of apoptosis. Bcl-2 levels exhibited a late decrease compared with the kinetics of DNA fragmentation, whereas Bax levels increased more rapidly after CPT treatment. These results suggest that Bax plays more important role than Bcl-2 in inducing DNA fragmentation and may function upsteam of proteolytic activation of caspase-3 pathway in CPT-induced apoptosis.

• ETRI Journal
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• v.33 no.2
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• pp.230-239
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• 2011

Dynamic memory allocators for real-time embedded systems need to fulfill three fundamental requirements: bounded worst-case execution time, fast average execution time, and minimal fragmentation. Since embedded systems generally run continuously during their whole lifetime, fragmentation is one of the most important factors in designing the memory allocator. This paper focuses on minimizing fragmentation while other requirements are still satisfied. To minimize fragmentation, a part of a memory region is segregated by the proposed budgeting method that exploits the memory profile of the given application. The budgeting method can be applied for any existing memory allocators. Experimental results show that the memory efficiency of allocators can be improved by up to 18.85% by using the budgeting method. Its worst-case execution time is analyzed to be bounded.

• Journal of Korean Institute of Industrial Engineers
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• v.33 no.3
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• pp.381-392
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• 2007

In this paper, we present an analytical method for estimating the saturation throughput of an 802.11 ad hoc LAN in the presence of noise distorting transmitted frames. This is the first method that allows studying analytically the 802.11 network performance with consideration of correlated channel failures usually inherent to realistic wireless channels. With the study, we consider the possible packet fragmentation that can be adopted to reduce the performance degradation caused by noise-induced distortions. In addition to the throughput, our method allows estimating the probability of a packet rejection occurring when the number of packet transmission retries attains its limit. The obtained numerical results of investigating 802.11 LANs by the developed method are validated by simulation and show high estimation accuracy as well as the method efficiency in determining the optimal fragmentation threshold.

• Bulletin of the Korean Chemical Society
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• v.14 no.1
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• pp.107-109
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• 1993

Non-enzymatic glycosylation and fragmentation of collagen molecule were investigated by irradiating Ultraviolet A(UV-A) with or without scavengers of reactive oxygen species (ROS) in the presence of glucose. Non-enzymatic glycosylation was increased by UV-A at high concentration of glucose. It was reduced in the presence of the scavengers of superoxide radical and singlet oxygen, but not reduced in the presence of hydroxy radical scavenger. Fragmentation of collagen was increased by UV-A, but it was decreased in the presence of all ROS scavengers tested. Superoxide radical and singlet oxygen produced by autoxidation of glucose without UV-A may encounter the initial phase of glycosylation. Data presented here suggest that UV-A affects only on the fragmentation process, but all ROS except hydroxy radical act on both processes. It appears that hydroxy radical does not act on the glycosylation process.