• Geomechanics and Engineering
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• v.16 no.2
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• pp.195-204
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• 2018

Based on theories of rock mechanics, rock fragmentation, mechanics of elasto-plasticity, and energy dissipation etc., a method is presented for evaluating the rock fragmentation efficiency by using plastic energy dissipation ratio as an index. Using the presented method, the fragmentation efficiency of rocks with different strengths (corresponding to soft, intermediately hard and hard ones) under indentation is analyzed and compared. The theoretical and numerical simulation analyses are then combined with experimental results to systematically reveal the fragmentation mechanism of rocks under indentation of indenter. The results indicate that the fragmentation efficiency of rocks is higher when the plastic energy dissipation ratio is lower, and hence the drilling efficiency is higher. For the rocks with higher hardness and brittleness, the plastic energy dissipation ratio of the rocks at crush is lower. For rocks with lower hardness and brittleness (such as sandstone), most of the work done by the indenter to the rocks is transferred to the elastic and plastic energy of the rocks. However, most of such work is transferred to the elastic energy when the hardness and the brittleness of the rocks are higher. The plastic deformation is small and little energy is dissipated for brittle crush, and the elastic energy is mainly transferred to the kinetic energy of the rock fragment. The plastic energy ratio is proved to produce more accurate assessment on the fragmentation efficiency of rocks, and the presented method can provide a theoretical basis for the optimization of drill bit and selection of well drilling as well as for the selection of the rock fragmentation ways.

• Microbiology and Biotechnology Letters
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• v.14 no.5
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• pp.407-413
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• 1986

In an agitated bead reaction system, the enzymatic saccharification of uncooked starch was substantially enhanced. The enhancement mechanism was investigated front the view of the structural aspect of starch. The mechanical impact caused by the movement of the attrition-milling media resulted neither the destruction of microcrystalline structure nor the fragmentation of starch granule. instead, the most distinct phenomenon was the swelling of starch granule up to about 2.5 times, and the swelling mechanism was not similar with that caused by cooking. However, in the case of the enzyme addition in the attrition coupled reaction system, the swollen starch was easily fragmented into the large number of small particles by the synergistic action of the enzyme and milling-media. The exposed surface area of the fragmented particles plays the major role in enhancing the saccharification. The saccharification rate was quite different depending on the source of starch, the reason was discussed in terms of the granular structure of uncooked starches.

• 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.

• 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.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.46.4-47
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• 2016

About 50% of stars reside in binary or multiple systems. However, the formation mechanism of the multiplicity is poorly understood. Theoretical studies suggest two main mechanisms for the multiplicity: turbulent fragmentation and disk fragmentation. We can testify which mechanism is more plausible by measuring the separation between companions or the alignment of stellar spins. Here we present our ALMA Cycle 2 observational results of a proto-binary system, IRAS 04191+1523, which consists of two Class I sources. We detected disks around both Class I sources, which are located in a common dense filamentary structure traced by $C^{18}O$ J=2-1. Two protostellar disks are separated by ~900 AU and their rotational axes are almost perpendicular, which strongly support that this binary system formed by the turbulent fragmentation.

• Journal of the Korea Society of Computer and Information
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• v.14 no.10
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• pp.101-110
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• 2009

The 6LoWPAN(IPv6 Low-power Wireless Personal Area Network) performs IPv6 header compression, TCP/UDP/IGMP header compression, packet fragmentation and re-assemble to transmit IPv6 packet over IEEE 802,15.4 MAC/PHY. However, from the point of view of security. It has the existing security threats issued by IP packet fragmenting and reassembling, and new security threats issued by 6LoWPAN packet fragmenting and reassembling would be introduced additionally. If fragmented packets are retransmitted by replay attacks frequently, sensor nodes will be confronted with the communication disruption. This paper analysis security threats introduced by 6LoWPAN fragmenting and reassembling, and proposes a re-transmission mechanism that could minimize re-transmission to be issued by replay attacks. Re-transmission procedure and fragmented packet structure based on the 6LoWPAN standard(RFC4944) are designed. We estimate also re-transmission delay of the proposed mechanism. The mechanism utilizes timestamp, nonce, and checksum to protect replay attacks. It could minimize reassemble buffer overflow, waste of computing resource, node rebooting etc., by removing packet fragmentation and reassemble unnecessary.

• Journal of the Korea Society for Simulation
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• v.11 no.1
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• pp.31-44
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• 2002

VPN which cuts down on expense and assures security and reliance, has increased its market shares quickly because the requirement of enterprise on security has increased. But Fragmentation may raise communication failure when VPN has been implemented using IPSec. In our paper, we have given careful consideration to various reasons Preventing us from communicating stable and have presented the existing solutions about them. Also we hate provided adaptive PMTU discovery mechanism to improve: the solutions. We have proven a prowess of this mechanism through simulation

• The KIPS Transactions:PartA
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• v.8A no.4
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• pp.331-338
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• 2001

With the general use of network, cyber terror rages throughout the world. However, IP Fragmentation isn\`t free from its security problem yet, even though it guarantees effective transmission of the IP package in its network environment. Illegal invasion could happen or disturb operation of the system by using attack mechanism such as IP Spoofing, Ping of Death, or ICMP taking advantage of defectiveness, if any, which IP Fragmentation needs improving. Recently, apart from service refusal attack using IP Fragmentation, there arises a problem that it is possible to detour packet filtering equipment or network-based attack detection system using IP Fragmentation. In the paper, we generate the real time access log file to make the system manager help decision support and to make the system manage itself in case that some routers or network-based attack detection systems without packet reassembling function could not detect or suspend illegal invasion with divided datagrams of the packet. Through the implementation of the self-managing system we verify its validity and show its future effect.

• Bulletin of the Korean Chemical Society
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• v.19 no.7
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• pp.792-794
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• 1998

• Bulletin of the Korean Chemical Society
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• v.17 no.10
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• pp.969-971
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• 1996