• Title/Summary/Keyword: Bullet

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Computational Analysis of Heracron Fabric at High-velocity Impact (Heracron 직물의 고속 충돌 해석)

  • Kim, YunHo;Choi, Chunghyeon;Kumar, Sarath Kumar Sathish;Cha, JiHun;Kim, Chun-Gon
    • Composites Research
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    • v.32 no.2
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    • pp.120-126
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    • 2019
  • Advanced fiber fabrics have been utilized in not only anti-stabbing and bullet-proofing for body armor but also various industrial fields including vehicular armor and spacecraft structure. Furthermore, there have been a number of research to improve the ballistic performance of advanced fabrics introducing many computational approaches. In our research, an advanced fabric, Heracron manufactured in South Korea was modelled firstly using Autodyn, a commercial software specializing in impact and explosion phenomenon. The sensitivity of the input parameters was also confirmed by conducting simulations. To verify the numerical modelling, we measured and compared the simulation results with velocity decrements after impact involving one, three, and five layers of Heracron under 200-500 m/s impacts by an aluminum spherical projectile. The Heracron fabric was successfully modelled using Autodyn.

Few-Layered MoS2 Nanoparticles Loaded TiO2 Nanosheets with Exposed {001} Facets for Enhanced Photocatalytic Activity

  • Chen, Chujun;Xin, Xia;Zhang, Jinniu;Li, Gang;Zhang, Yafeng;Lu, Hongbing;Gao, Jianzhi;Yang, Zhibo;Wang, Chunlan;He, Ze
    • Nano
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    • v.13 no.11
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    • pp.1850129.1-1850129.10
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    • 2018
  • To improve the high charge carrier recombination rate and low visible light absorption of {001} facets exposed $TiO_2$ [$TiO_2(001)$] nanosheets, few-layered $MoS_2$ nanoparticles were loaded on the surfaces of $TiO_2(001)$ nanosheets by a simple photodeposition method. The photocatalytic activities towards Rhodamine B (RhB) were investigated. The results showed that the $MoS_2-TiO_2(001)$ nanocomposites exhibited much enhanced photocatalytic activities compared with the pure $TiO_2(001)$ nanosheets. At an optimal Mo/Ti molar ratio of 25%, the $MoS_2-TiO_2(001)$ nanocomposites displayed the highest photocatalytic activity, which took only 30 min to degrade 50 mL of RhB (50 mg/L). The active species in the degradation reaction were determined to be $h^+$ and $^{\bullet}OH$ according to the free radical trapping experiments. The reduced charge carrier recombination rate, enhanced visible light utilization and increased surface areas contributed to the enhanced photocatalytic performances of the 25% $MoS_2-TiO_2(001)$ nanocomposites.

Pre- and Postsynaptic Actions of Reactive Oxygen Species and Nitrogen Species in Spinal Substantia Gelatinosa Neurons

  • Park, Areum;Chun, Sang Woo
    • International Journal of Oral Biology
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    • v.43 no.4
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    • pp.209-216
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    • 2018
  • Reactive oxygen species (ROS) and nitrogen species (RNS) are involved in cellular signaling processes as a cause of oxidative stress. According to recent studies, ROS and RNS are important signaling molecules involved in pain transmission through spinal mechanisms. In this study, a patch clamp recording was used in spinal slices of rats to investigate the action mechanisms of $O_2{^{{\bullet}_-}}$ and NO on the excitability of substantia gelatinosa (SG) neuron. The application of xanthine and xanthine oxidase (X/XO) compound, a ROS donor, induced inward currents and increased the frequency of spontaneous excitatory postsynaptic currents (sEPSC) in slice preparation. The application of S-nitroso-N-acetyl-DL-penicillamine (SNAP), a RNS donor, also induced inward currents and increased the frequency of sEPSC. In a single cell preparation, X/XO and SNAP had no effect on the inward currents, revealing the involvement of presynaptic action. X/XO and SNAP induced a membrane depolarization in current clamp conditions which was significantly decreased by the addition of thapsigargin to an external calcium free solution for blocking synaptic transmission. Furthermore, X/XO and SNAP increased the frequency of action potentials evoked by depolarizing current pulses, suggesting the involvement of postsynaptic action. According to these results, it was estblished that elevated ROS and RNS in the spinal cord can sensitize the dorsal horn neurons via pre- and postsynaptic mechanisms. Therefore, ROS and RNS play similar roles in the regulation of the membrane excitability of SG neurons.

3-D Shock Structure of Orion KL Outflow with IGRINS

  • Oh, Heeyoung;Pyo, Tae-Soo;Kaplan, Kyle F.;Koo, Bon-Chul;Yuk, In-Soo;Lee, Jae-Joon;Mace, Gregory N.;Sokal, Kimberly R.;Hwang, Narae;Park, Chan;Park, Byeong-Gon;Jaffe, Daniel T.
    • The Bulletin of The Korean Astronomical Society
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    • v.43 no.2
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    • pp.38.3-38.3
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    • 2018
  • We present the results of high-resolution near-IR spectral mapping toward the Orion KL outflow. In this study, we used the Immersion Grating Infrared Spectrometer (IGRINS) on the 2.7 m Harlan J. Smith Telescope at McDonald Observatory. IGRINS's large wavelength coverage over the H & K bands and high spectral resolving power (R ~ 45,000) allowed us to detect over 35 shock-excited ro-vibrational H2 transitions and to measure directly the gas temperature and velocity of the dense outflows. In our previous study toward the H2 peak 1 region in the Orion KL outflow, we identified 31 outflow fingers from a datacube of the H2 1-0 S(1) $2.122{\mu}m$ line and constructed a three-dimensional map of the fingers. The internal extinction (${\Delta}AV$ > 10 mag) and overall angular spread of the flow argue for an ambient medium with a high density (105 cm-3). In this presentation, we show preliminary results of additional mapping toward a remarkable chain of bows (HH 205 - HH 207) farther from the ejection center, and obtain a more clear view of the shock physics of a single isolated bullet that improves on the knowledge gained from observations of the more complex peak 1 region in our earlier study.

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Effect of Grain Refiner and Eutectic Si Modifier on Casting Properties of Al-Si-Cu Alloy System Containing Recycled Scrap (재활용 스크랩 함유 Al-Si-Cu계 합금의 주조특성에 미치는 결정립 미세화제와 공정 Si 개량화제의 영향)

  • Sung, Dong-Hyun;Kim, Heon-Joo
    • Journal of Korea Foundry Society
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    • v.38 no.6
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    • pp.121-131
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    • 2018
  • The effect of additives on the castability of the AC2BS aluminum alloy, which contains 35% recycled scrap, was investigated. For the wide utilization of the recycled scrap AC2BS aluminum alloy, the research results were compared to those with the AC2B virgin alloy, which is typical Al-Si-Cu alloy system. It was confirmed that the addition of Al-5%Ti-1%B increased the ${\alpha}$-Al nucleation temperature during solidification and decreased the grain size through cooling curve and microstructural observations of the recycled alloy. It was also found that an addition of Al-10%Sr decreased the eutectic Si growth temperature during the solidification process and modified the shape of the eutectic Si of the recycled alloy. The characteristics of fluidity, shrinkage and solidification crack strength were evaluated. For the AC2BS aluminum alloy containing 35% recycled scrap, both ${\alpha}$-Al grain refinement due to Ti-B and eutectic Si modifications due to Sr contributed to the improvement of the fluidity. The macro- shrinkage ratio increased with additions of both Al-10%Sr and Al-5%Ti-1%B and the micro-shrinkage ratio increased with the addition of Al-10%Sr but decreased with the addition of Al-5%Ti-1%B. The casting characteristics of TiB and Sr-treated AC2BS aluminum alloy containing 35% recycled scrap are similar to those of AC2B virgin alloy. The improvement of the solidification crack strength of the AC2BS aluminum alloy was possible by the reduction of the grain boundary the stress concentration through the enhancement by both ${\bullet}{\cdot}$-Al refinement and eutectic Si modification. More extensive use of the AC2BS aluminum alloy containing 35% recycled scrap can be expected in the future.

Remediation of Heavy Metal-Contaminated Soil Within a Military Shooting Range through Physicochemical Treatment (물리화학적 처리를 이용한 군부대 사격장 내 중금속 오염 토양의 정화)

  • Lee, Sang-Woo;Lee, Woo-Chun;Lee, Sang-Hwan;Kim, Soon-Oh
    • Journal of Soil and Groundwater Environment
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    • v.26 no.5
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    • pp.9-19
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    • 2021
  • This study evaluated the feasibility of combined use of physical separation and soil washing to remediate heavy metals (Pb and Cu) contaminated soil in a military shooting range. The soils were classified into two types based on the level of heavy metal concentrations: a higher contaminated soil (HCS) with Pb and Cu concentrations of 6,243 mg/kg and 407 mg/kg, respectively, and a lower contaminated soil (LCS) with their concentrations of 1,658 mg/kg and 232 mg/kg. Pb level in both soils exceeded the regulatory limit (700 mg/kg), and its concentration generally increased with decreasing soil particle size. However, in some cases, Pb concentrations increased with increasing soil particle size, presumably due to the presence of residues of bullets in the soil matrix. As a pretreatment step, a shaking table was used for physical separation of soil to remove bullet residues while fractionating the contaminated soils into different sizes. The most effective separation and fractionation were achieved at vibration velocity of 296 rpm/min, the table slope of 7.0°, and the separating water flow rate of 23 L/min. The efficiency of ensuing soil washing process for LCS was maximized by using 0.5% HCl with the soil:washing solution mixing ratio of 1:3 for 1 hr treatment. On the contrary, HCS was most effectively remediated by using 1.0% HCl with the same soil:solution mixing ratio for 3 hr. This work demonstrated that the combined use of physical separation and soil washing could be a viable option to remediate soils highly contaminated with heavy metals.

Algorithm for Deadlock Prevention of Generalized Philosophers' Dining Problem (일반화된 철학자 만찬 문제의 교착상태 예방 알고리즘)

  • Sang-Un Lee
    • The Journal of the Institute of Internet, Broadcasting and Communication
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    • v.23 no.2
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    • pp.73-78
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    • 2023
  • The dining philosophers problem(DPP) is that five philosophers sit around a round table and eat spaghetti(or noodles) together, where they must have a pair of chopsticks(two) on both sides of them to eat, and if all philosophers have one chopstick on the right, no one can eat because the deadlock occurs. Deadlocks are a problem that frequently occur in parallel systems, and most current operating systems(OS) cannot prevent it. This paper proposes a silver bullet that causes no deadlock in an OS where all processors of 2≤n≤∞ have multiple parallel processing capabilities. The proposed method is a group round-robin method in which ⌊n/2⌋ odd processors form a group and perform simultaneously, and shift right to the next processor when execution ends. The proposed method is to perform two times for even processors, three times for odd processors per one round-robin. If the proposed method is performed n times, even-numbered processors perform n/2 times and odd-numbered processors perform (n-1)/2-times.

Development of Parent Guidelines for Parent-Performed Developmental Screening Tests

  • Sung Sil Rah;Soon-Beom Hong;Ju Young Yoon
    • Journal of the Korean Academy of Child and Adolescent Psychiatry
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    • v.34 no.2
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    • pp.141-149
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    • 2023
  • Objectives: Most developmental screening tests have been built as parent-performed questionnaires. However, they often do not guide parents on how to answer the questionnaire. This study aimed to develop easily applicable parent guidelines. Methods: We implemented the Delphi procedure with 20 panelists. The development of the initial questionnaire was based on the results of two surveys of parents and experts provided by a policy research report that investigated the item adequacy of the Korean Developmental Screening Test. Round one included 33 items comprising all possible measurements in six categories that were identified as difficult to understand or confusing. Round two merged and modified some items and included 32 items. We defined consensus as a median agreement value of one or less and convergence and stability values of 0.5 or less. The subjective usefulness of the parent guidelines was examined based on their previous test experiences. Results: Consensus was reached after the second round, reflecting the items with the highest level of accuracy in each category. Of the 167 parents who participated in the survey, 113 (67.7%) affirmed the usefulness of the guidelines, while 10 (6.0%) answered that they were not useful. Items that recommended a different scoring strategy in answering the questionnaire from their previous measurements were found to be more useful by the parents. Conclusion: The parent guidelines, composed of five bullet points, drew on the consensus of the experts. Further studies are required to assess whether these guidelines improve the accuracy of screening tests in clinical settings.

A Study on the Failure Modes of Neat Kevlar Fabric and Kevlar Liquid Armor Impregnated with Shear Thickening Fluid (케블라 직물과 전단농화유체로 함침된 케블라 액체 방탄재의 파단모드 연구)

  • Yoon, Byung-Il;Song, Heung-Sub;Paik, Jong-Gyu
    • Composites Research
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    • v.20 no.3
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    • pp.17-24
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    • 2007
  • In this study, the failure modes by ballistic impacts were studied both for a neat Kevlar woven fabric and a Kevlar liquid armor impregnated with shear thickening fluid (STF) containing silica particles. These two materials showed quite different failure modes macroscopically in ballistic impacts tests used by Cal.22 FSP and 9mm FMJ bullet. Yarn pull-out for the neat Kevlar woven fabric and yarn fracture occurred partially through all plies from 1st ply to last one for the STF-Kevlar are an important energy absorption mechanisms. The results observed by S.E.M showed commonly fiber damage which are torn skin in the longitudinal fiber direction, fiber split axially and fiber fracture for two materials. The reasons why STF-kevlar liquid armor material exhibits excellent ballistic performance are as follow: firstly the increased friction forces between yarn-yarn and fabric-fabric covered with silica particles and secondary the evolution of shear thickening phenomenmon resulting in suppression of yarn mobility.

Ballistic Analysis and Stacking Sequence of Laminate Plate for Enhancing Bulletproof Performance (방탄 성능 향상을 위한 적층 평판의 피탄 해석 및 적층 배열 연구)

  • Ki Hyun Kim;Min Kyu Kim;Min Je Kim;Myung Shin
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.36 no.5
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    • pp.331-338
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    • 2023
  • Modern bulletproof armor must be light and have excellent penetration resistance to ensure the mobility and safety of soldiers and military vehicles. The ballistic performance of heterogeneous structures of laminated flat plates as bulletproof armor depends on the arrangement of constituent materials for the same weight. In this study, we analyze bulletproof performance according to the stacking sequence of laminated bulletproof armor composed of Kevlar, ultra-high molecular weight polyethylene, and ethylene-vinyl-acetate foam. A ballistic analysis was performed by colliding a 7.62 × 51 mm NATO cartridge's M80 bullet at a speed of 856 m/s with six lamination arrangements with constituent materials thicknesses of 5 mm and 6.5 mm. To evaluate the bulletproof performance, the residual speed and residual energy of the projectile that penetrated the heterogeneous laminated flat plates were measured. Simulation results confirmed that the laminated structure with a stacking sequence of Kevlar, ultra-high molecular weight polyethylene, and ethylene-vinyl-acetate foam had the best bulletproof performance for the same weight.