• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.1
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• pp.49-55
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• 2017

Welding deformation is a permanent deformation that is caused in structures by welding heat. Welding distortion is the primary cause of reduced productivity, due to welded structural strength degradation, low dimensional accuracy, and appearance. As a result, research and numerous experiments are being carried out to control welding deformation. The aim of this study is to analyze the mechanism of longitudinal bending deformation due to welding. Welding experiments and numerical analyses were performed for this study. The welding experiments were performed on 4 mm and 8.5 mm thickness steel plates, and the numerical analysis was conducted on the welding deformation using the FE software MSC.marc.

• Journal of Microbiology and Biotechnology
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• v.9 no.2
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• pp.168-172
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• 1999

The antifungal mechanism of the antifungal peptide against Aspergillus fumigatus, $K^{18,19}$-CA(l-8)-ME(l-12), derived from cecropin A(l-8)-melittin(l-12) was investigated by confocal laser scanning microscopy, cell wall regeneration, ATPase activity inhibition, and released potassium ion. By confocal laser scanning microscopy, $K^{18,19}$-CA(l-8)-ME(l-12) was detected on the surface of A. fumigatus, while cecropin A used as a negative control peptide was not detected. The protoplast of A. fumigatus treated with$K^{18,19}$-CA(1-8)-ME(1-12) failed to regenerate the fungal cell walls. Compared with cecropin A, the amount of potassium ion released by $K^{18,19}$-CA(l-8)-ME(l-12) was increased. Furthermore, $K^{18,19}$-CA(l-8)-ME(l-12) inhibited the ATPase activity on the plasma membrane. These results suggested that $K^{18,19}$-CA(l-8)-ME(1-12) acts on the plasma membrane of A. fumigatus and its antifungal action is due to the ion channel or pore formation on the plasma membrane.

• Bulletin of the Korean Chemical Society
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• v.34 no.12
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• pp.3690-3694
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• 2013

The $H_2Ge=Ge:$ and its derivatives ($X_2Ge=Ge:$, X = H, Me, F, Cl, Br, Ph, Ar${\ldots}{\ldots}$) is a new species. Its cycloaddition reactions is a new area for the study of germylene chemistry. The mechanism of the cycloaddition reaction between singlet state Cl2Ge=Ge: and formaldehyde has been investigated with CCSD(T)//MP2/$6-31G^*$ method. From the potential energy profile, it could be predicted that the reaction has only one dominant reaction pathway. The reaction rule presented is that the two reactants first form a fourmembered Ge-heterocyclic ring germylene through the [2+2] cycloaddition reaction. Because of the 4p unoccupied orbital of Ge: atom in the four-membered Ge-heterocyclic ring germylene and the ${\pi}$ orbital of formaldehyde forming a ${\pi}{\rightarrow}p$ donor-acceptor bond, the four-membered Ge-heterocyclic ring germylene further combines with formaldehyde to form an intermediate. Because the Ge: atom in intermediate hybridizes to an $sp^3$ hybrid orbital after transition state, then, intermediate isomerizes to a spiro-Ge-heterocyclic ring compound via a transition state. The research result indicates the laws of cycloaddition reaction between $H_2Ge=Ge:$ and formaldehyde, and laid the theory foundation of the cycloaddition reaction between $H_2Ge=Ge:$ and its derivatives ($X_2Ge=Ge:$, X = H, Me, F, Cl, Br, Ph, Ar${\ldots}{\ldots}$) and asymmetric ${\pi}$-bonded compounds, which is significant for the synthesis of small-ring and spiro-Ge-heterocyclic compounds. The study extends research area and enriches the research content of germylene chemistry.

• Journal of Communications and Networks
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• v.11 no.6
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• pp.574-588
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• 2009

Although much research has been conducted in the area of authentication in wireless networks, vehicular ad-hoc networks (VANETs) pose unique challenges, such as real-time constraints, processing limitations, memory constraints, frequently changing senders, requirements for interoperability with existing standards, extensibility and flexibility for future requirements, etc. No currently proposed technique addresses all of the requirements for message and entity authentication in VANETs. After analyzing the requirements for viable VANET message authentication, we propose a modified version of TESLA, TESLA++, which provides the same computationally efficient broadcast authentication as TESLA with reduced memory requirements. To address the range of needs within VANETs we propose a new hybrid authentication mechanism, VANET authentication using signatures and TESLA++ (VAST), that combines the advantages of ECDSA signatures and TESLA++. Elliptic curve digital signature algorithm (ECDSA) signatures provide fast authentication and non-repudiation, but are computationally expensive. TESLA++ prevents memory and computation-based denial of service attacks. We analyze the security of our mechanism and simulate VAST in realistic highway conditions under varying network and vehicular traffic scenarios. Simulation results show that VAST outperforms either signatures or TESLA on its own. Even under heavy loads VAST is able to authenticate 100% of the received messages within 107ms. VANETs use certificates to achieve entity authentication (i.e., validate senders). To reduce certificate bandwidth usage, we use Hu et al.'s strategy of broadcasting certificates at fixed intervals, independent of the arrival of new entities. We propose a new certificate verification strategy that prevents denial of service attacks while requiring zero additional sender overhead. Our analysis shows that these solutions introduce a small delay, but still allow drivers in a worst case scenario over 3 seconds to respond to a dangerous situation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.246-250
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• 2003

In this study, two new types of micro-grippers in which micro-fingers are actuated by piezoelectric multi-layer benders and stacks are introduced for the manipulation of micrometer-sized objects. First, we constructed a 3-chopstick-mechanism tungsten gripper, which is composed of three chopsticks: two are designed to grip micro-objects, and tile third is used to help grasp and release the objects through overcoming especially electrostatic force among some surface effects including electrostatic, van der Waals forces and surface tension. Second, a 2-chopstick-mechanism silicon micro-gripper that uses an integrated force sensor to control the gripping force was developed. The micro-gripper is composed of a piezoelectric multilayer bender for actuating the gripper fingers, silicon fingertips fabricated by use of silicon-based micromachining, and supplementary supports. The micro-gripper is referred to as a hybrid-type micro-gripper because it is composed of two main components; micro-fingertips fabricated using micromachining technology to integrate a very sensitive force sensor for measuring the gripping force, and piezoelectric gripper finger actuators that are capable of large gripping forces and moving strokes. The gripping force signal was found to have a sensitivity of 667 N/V. To the design of each of components of both of the grippers. a systematic design approach was applied, which made it possible to establish the functional requirements and design parameters of the micro-grippers. The micro-grippers were installed on a manual manipulator to assess its performance in tasks such as moving micro-objects from one position to a desired position. The experiment showed that the micro-grippers function effectively.

• Journal of the Ergonomics Society of Korea
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• v.31 no.6
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• pp.785-791
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• 2012

Objective: The aim of this study was to investigate the correlation between 3D visual fatigue and physiological measures by canonical correlation analysis enabling to categorical correlation. Background: Few studies have been conducted to investigate the physiological mechanism underlying the visual fatigue caused by processing 3D information which may make the cognitive mechanism overloaded. However, even the previous studies lack validation in terms of the correlation between physiological variables and the visual fatigue. Method: 9 Female and 6 male subjects with a mean age of $22.53{\pm}2.55$ voluntarily participated in this experiment. All participants were asked to report how they felt about their health sate at after viewing 3D. In addition, Low & Hybrid measurement test(Event Related Potential, Steady-state Visual Evoked Potential) and for evaluating cognitive fatigue before and after viewing 3D were performed. The physiological signal were measured with subjective fatigue evaluation before and after in watching the 3D content. For this study suggesting categorical correlation, all measures were categorized into three sets such as included Visual Fatigue set(response time, subjective evaluation), Autonomic Nervous System set(PPG frequency, PPG amplitude, HF/LF ratio), Central Nervous System set(ERP amplitude P4, O1, O2, ERP latency P4, O1, O2, SSVEP S/N ratio P4, O1, O2). Then the correlation of three variables sets, canonical correlation analysis was conducted. Results: The results showed a significant correlation between visual fatigue and physiological measures. However, different variables of visual fatigue were highly correlated to respective HF/LF ratio and to ERP latency(O2). Conclusion: Response time was highly correlated to ERP latency(O2) while the subjective evaluation was to HF/LF ratio. Application: This study may provide the most significant variables for the quantitative evaluation of visual fatigue using HF/LF ratio and ERP latency based human performance and subjective fatigue.

• Journal of Internet Computing and Services
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• v.13 no.5
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• pp.1-8
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• 2012

In this paper, we propose a new clustering combination based on numerical data driven for rule generation mechanism. In large and complicated space, a clustering method can obtain limited performance results. To overcome the single clustering method problem, hybrid combined methods can solve problem to divided simple cluster estimation. Fundamental structure of the proposed method is combined by mountain clustering and modified Chen clustering to extract detail cluster information in complicated data distribution of non-parametric space. It has automatic rule generation ability with advanced density based operation when intelligent systems including neural networks and fuzzy inference systems can be generated by clustering results. Also, results of the mechanism will be served to information of decision support system to infer the useful knowledge. It can extend to healthcare and medical decision support system to help experts or specialists. We show and explain the usefulness of the proposed method using simulation and results.

• Annals of Clinical Neurophysiology
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• v.8 no.1
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• pp.63-70
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• 2006

Background: Testosterone is reported to have neuroprotective effect in various neurological diseases. Recently, the mechanism involved in nitric oxide (NO)-mediated motor neuron death is under extensive investigation. The Cu/Zn-superoxide dismutase (SOD1) mutations has been implicated in selective motor neuron death of amyotrophic lateral sclerosis (ALS) and it is said to play an important role in NO-mediated motor neuron death. However, neuroprotective effect of testosterone on motor neuron exposed to NO has rarely been studied. Methods: Motor neuron-neuroblastoma hybrid cells expressing wild-type or mutant (G93A or A4V) SOD gene were treated with $200{\mu}M$ S-nitrosoglutathione. After 24 hr, cell viability was measured by MTT assay. To see the neuroprotective effect of testosterone, pretreatment with 1 nM testosterone was done 1 hr before S-nitroglutathione treatment. To study the mechanism of protective effect, $20{\mu}M$ flutamide (androgen receptor antagonist) was also pretreated with testosterone 1 hr before S-nitroglutathione treatment. Results: S-nitrosoglutathione showed significant neurotoxic effect in all three cell lines. Percentage of cell death was somewhat different in each cell line. 1 nM testosterone showed neuroprotective effect in G93A and wild-type cell line. In A4V cell line, testosterone did not showed neuroprotective effect. The neuroprotective effect of testosterone was reversed by $20{\mu}M$ flutamide. Conclusions: These results indicate that testosterone induces neuroprotection in NO-mediated motor neuron death directly through the androgen receptor. This neuroprotective effect of testosterone varies according to the types of SOD1 gene mutation. These data suggest that testosterone may be of therapeutic value against ALS.

• Bulletin of the Korean Chemical Society
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• v.29 no.7
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• pp.1335-1343
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• 2008

Theoretical studies on the un-catalyzed and catalyzed aminations of ketene with $NH_3$ and $(NH_3)_2$, respectively, were studied using MP2 and hybrid density functional theory of B3LYP at the 6-31+G(d,p) and 6- 311+G(3df,2p) basis sets in the gas phase and in benzene and acetonitrile solvents. In the gas phase reaction, the un-catalyzed mechanism was the same as those previously reported by others. The catalyzed mechanism, however, was more complicated than expected requiring three transition states for the complete description of the C=O addition pathways. In the un-catalyzed amination, rate determining step was the breakdown of enol amide but in the catalyzed reaction, it was changed to the formation of enol amide, which was contradictory to the previous findings. Starting from the gas-phase structures, all structures were re-optimized using the CPCM method in solvent medium. In a high dielectric medium, acetonitrile, a zwitterions formed from the reaction of $CH_2$=C=O with $(NH_3)_2$, I(d), exists as a genuine minimum but other zwitterions, I(m) in acetonitrile and I(d) in benzene become unstable when ZPE corrected energies are used. Structural and energetic changes induced by solvation were considered in detail. Lowering of the activation energy by introducing additional $NH_3$ molecule amounted to ca. −20 $\sim$ −25 kcal/mol, which made catalyzed reaction more facile than un-catalyzed one.

• Journal of the Korea Society of Computer and Information
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• v.15 no.3
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• pp.81-89
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• 2010

The research on peer-to-peer streaming schemes has largely focused on tree-push and mesh-pull structures. However, the tree-push structure has a defect that the tree restructuring time is long, and the mesh-pull structure has long startup delay and lag time from source servers. In this paper, we propose a new peer-to-peer live streaming scheme based on a push-mesh structure that takes advantages of tree-push and mesh-pull structure simultaneously. This structure basically provides the mesh-pull mechanism for data transmission and utilizes peers with high network upload capacity. It also supports the push mechanism along with paths from a source server, super peers, and selected general peers. By NS-2 simulation experiments, we finally show that our proposed scheme can achieve shorter startup delay than the mesh-pull structure, similar lag time to tree-push structure and best playback continuity among the three schemes.