• Title/Summary/Keyword: High impact

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Psychiatric Problems in the Student Victims of School Violence and Their Parents (학교폭력 피해학생과 부모의 정신의학적 문제)

  • Jang, Hyuk Jin;Kwack, Young Sook
    • Journal of the Korean Academy of Child and Adolescent Psychiatry
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    • v.25 no.4
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    • pp.224-229
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    • 2014
  • Objectives : This study was conducted in order to investigate the influences of school violence on the mental health of student victims and their parents. Methods : A total of 56 (aged 7-18) student victims and their parents were selected to participate in a survey. The students had experienced school violence from June 2012 to October 2013. They completed a set of self-report questionnaires, including socio-demographic characteristics, family relationship, Impact of Event Scale-Revised, Child Depression Inventory (CDI), Beck Depression Inventory, Revised Children's Manifest Anxiety Scale, and Parental Bonding Instrument to evaluate psychiatric complications and to understand the emotional bonding between them. Results : The student's level of impact of event was significantly related to the parent's level of impact of event (p<.001). The student's high CDI score showed positive correlation with high level of impact of event (p<.001). In addition, higher level of the student's perceived emotional support and understandability of family showed association with lower level of impact of event (p<.01, p<.05). Conclusion : The results of this study suggest that the psychiatric sequelae of school violence is seriously affected by family support and parent's level of impact of event. Therefore, more active intervention is needed for both students and their parents.

A Resistance Property Against High Velocity Impact on Oxynitride Glasses (질화유리의 고속충돌 저항물성)

  • Kim, Chang-Wook;Lee, Hyung-Bock
    • Journal of the Korean Ceramic Society
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    • v.43 no.10 s.293
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    • pp.646-652
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    • 2006
  • Several oxynitride glasses were fabricated by means of adding $Si_3N_4$ powders as nitrogen source to Ca-Al-Si-O-N (CAS) and Mg-Al-Si-O-N (MAS) glass powders, and heat-treated in graphite crucible at 1600$^{\circ}C$ for 1 h. The physical and mechanical properties as well as impact resistance were generally increased and compared with each other. The impact resistance properties of those manufactured glasses were evaluated by DOP (depth of penetration) method which is a way to analyze armor materials. There were two means to be used herein; the copper jet impacted at hyper velocity by exploding K2l5 warhead and tungsten heavy alloy (WHA) impact bar at high velocity by firing in 30 mm solid propellent gun. The impact resistance properties against copper jet were increased and then decreased with increasing nitrogen content, while those against WHA bar were not changed apparently with nitrogen content.

Impact Characteristics and Morphology of Nylon 6/Polypropylene Blends (Nylon 6/Polypropylene 블렌드의 충격특성 및 모폴로지)

  • Kim, Jong-Guk;Yun, Ju-Ho;Go, Jae-Song;Choe, Hyeong-Gi;Kim, Sang-Uk
    • Korean Journal of Materials Research
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    • v.12 no.1
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    • pp.10-15
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    • 2002
  • Melt blends of maleic anhydride grafted polypropylerle(PP-g-MA) and Nylon 6 were prepared to study the influence of chemical reaction between the two polymer components. By adding the MA grafted polystyrene pold (ethylene/butadiene) and polystyrene[SEBS-g-MA] as the compatible modifiers to reinforce the impact resistance, the Izod impact strength, high rate impact strength and morphology were studied. The notched Izod impact strength increased with the content of PP-g-MA and SEBS- g-MA. The energy of high rate impact strength increased as the thickness of specimen increased, while, it increased as the specimen displacement decreased. In the morphology observed by SEM, finally, we confirmed the improvement of the compatibilization and interfacial adhesion with the content of SEBS-g-MA. The continuous phase of PP-g-MA was the main cause of the modified properties.

Safety Assessment of a Metal Cask under Aircraft Engine Crash

  • Lee, Sanghoon;Choi, Woo-Seok;Seo, Ki-Seog
    • Nuclear Engineering and Technology
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    • v.48 no.2
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    • pp.505-517
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    • 2016
  • The structural integrity of a dual-purpose metal cask currently under development by the Korea Radioactive Waste Agency (KORAD) was evaluated, through numerical simulations and a model test, under high-speed missile impact reflecting targeted aircraft crash conditions. The impact conditions were carefully chosen through a survey on accident cases and recommendations from literature. In the impact scenario, a missile flying horizontally hits the top side of the cask, which is freestanding on a concrete pad, with a velocity of 150 m/s. A simplified missile simulating a commercial aircraft engine was designed from an impact loade-time function available in literature. In the analyses, the dynamic behavior of the metal cask and the integrity of the containment boundary were assessed. The simulation results were compared with the test results for a 1:3 scale model. Although the dynamic behavior of the cask in the model test did not match exactly with the prediction from the numerical simulation, other structural responses, such as the acceleration and strain history during the impact, showed very good agreement. Moreover, the containment function of the cask survived the missile impact as expected from the numerical simulation. Thus, the procedure and methodology adopted in the structural numerical analyses were successfully validated.

Method of Setting Nozzle Intervals at the Finishing Scale Breaker

  • Park, Jong-Wook;Kim, Sung-Cho;Park, Jin-Won
    • Journal of Mechanical Science and Technology
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    • v.17 no.6
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    • pp.870-878
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    • 2003
  • The scale is removed from the strip by high pressure hydraulic descaling at the FSB (Finishing Scale Breaker). Recently, the spray height of nozzle has a trend to be shorter for the purpose of increasing the impact pressure by the high pressure water jet. Here, the nozzle intervals should be decided after considering the impact pressure and the temperature distribution on the strip. In other words, the minimum of impact pressure at the overlap of spray influences the surface grade of the strip due to scale and the overlap distance of the spray affects the temperature variation in the direction of the width of strip. In the present study, the impact pressure of the high pressure water jet is measured by the hydraulic descaling system and calculated with regard to the lead angle of 15$^{\circ}$ and the offset angle of 15$^{\circ}$, and then the temperature distribution and the temperature variation are calculated at the overlap distances of 0 mm, 10 mm, 20 mm, and 30 mm, respectively. The method of setting nozzle intervals is shown by utilizing these results.

The Impact of COVID-19, Day-of-the-Week Effect, and Information Flows on Bitcoin's Return and Volatility

  • LIU, Ying Sing;LEE, Liza
    • The Journal of Asian Finance, Economics and Business
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    • v.7 no.11
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    • pp.45-53
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    • 2020
  • Past literatures have not studied the impact of real-world events or information on the return and volatility of virtual currencies, particularly on the COVID-19 event, day-of-the-week effect, daily high-low price spreads and information flow rate. The study uses the ARMA-GARCH model to capture Bitcoin's return and conditional volatility, and explores the impact of information flow rate on conditional volatility in the Bitcoin market based on the Mixture Distribution Hypothesis (Clark, 1973). There were 3,064 samples collected during the period from 1st of January 2012 to 20th April, 2020. Empirical results show that in the Bitcoin market, a daily high-low price spread has a significant inverse relationship for daily return, and information flow rate has a significant positive relationship for condition volatility. The study supports a significant negative relationship between information asymmetry and daily return, and there is a significant positive relationship between daily trading volume and condition volatility. When Bitcoin trades on Saturday & Sunday, there is a significant reverse relationship for conditional volatility and there exists a day-of-the-week volatility effect. Under the impact of COVID-19 event, Bitcoin's condition volatility has increased significantly, indicating the risk of price changes. Finally, the Bitcoin's return has no impact on COVID-19 events and holidays (Saturday & Sunday).

Performance and modeling of high-performance steel fiber reinforced concrete under impact loads

  • Perumal, Ramadoss
    • Computers and Concrete
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    • v.13 no.2
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    • pp.255-270
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    • 2014
  • Impact performance of high-performance concrete (HPC) and SFRC at 28-day and 56-day under the action of repeated dynamic loading was studied. Silica fume replacement at 10% and 15% by mass and crimped steel fiber ($V_f$ = 0.5%- 1.5%) with aspect ratios of 80 and 53 were used in the concrete mixes. Results indicated that addition of fibers in HPC can effectively restrain the initiation and propagation of cracks under stress, and enhance the impact strengths and toughness of HPC. Variation of fiber aspect ratio has minor effect on improvement in impact strength. Based on the experimental data, failure resistance prediction models were developed with correlation coefficient (R) = 0.96 and the estimated absolute variation is 1.82% and on validation, the integral absolute error (IAE) determined is 10.49%. On analyzing the data collected, linear relationship for the prediction of failure resistance with R= 0.99 was obtained. IAE value of 10.26% for the model indicates better the reliability of model. Multiple linear regression model was developed to predict the ultimate failure resistance with multiple R= 0.96 and absolute variation obtained is 4.9%.

Evaluation of the Joint Strength of Lead-free Solder Ball Joints at High Strain Rates (고속 변형률 속도에서의 무연 솔더 볼 연결부의 강도 평가)

  • Joo, Se-Min;Kim, Taek-Young;Lim, Woong;Kim, Ho-Kyung
    • Journal of the Korean Society of Safety
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    • v.27 no.6
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    • pp.7-13
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    • 2012
  • A lack of study on the dynamic tensile strengths of Sn-based solder joints at high strain rates was the motivation for the present study. A modified miniature Charpy impact testing machine instrumented with an impact sensor was built to quantitatively evaluate the dynamic impact strength of a solder joint under tensile impact loading. This study evaluated the tensile strength of lead-free solder ball joints at strain rates from $1.8{\times}10^3s^{-1}$ and $8.5{\times}10^3s^{-1}$. The maximum tensile strength of the solder ball joint decreases as the load speed increases in the testing range. This tensile strength represented that of the interface because of the interfacial fracture site. The tensile strengths of solder joints between Sn-3.0Ag-0.5Cu and copper substrate were between 21.7 MPa and 8.6 MPa in the high strain range.

The impacts of teacher education on students' academic achievement and satisfaction in mathematics lessons

  • Suh, Heejoo;Bae, Yunhee;Lee, Ji Su;Han, Sunyoung
    • The Mathematical Education
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    • v.57 no.4
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    • pp.393-412
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    • 2018
  • Teacher quality is a key factor that determines quality of education. Being aware of this, the Korean government and teachers have been striving to improve teachers' professionalism. Research about the impacts of efforts to enhance teacher professionalism on students' academic achievement and course satisfaction, however, is extremely limited. This study sought to advance our understanding of the relationship between these factors by analyzing what teacher characteristics impact students' achievement and satisfaction. To this end, the study drew on the middle and high school data from 3rd to 6th year survey of the Seoul Educational Longitudinal Study. Structural equational modeling were used as the main approach. Latent profile analysis, a kind of mixture modeling analysis, were used as needed. This study found that teachers' participation in instruction enhancement activity and professional development impact students' attitude toward mathematics lessons and their perception on class atmosphere, and ultimately impact their academic achievement as well as their overall satisfaction in the course. In addition, teachers' use of EBS textbooks and videos impact 3rd grade high schoolers' academic achievement. These findings suggest that effort to improve teacher professionalism positively impact students' academic achievement and course satisfaction, although there is a difference according to the year grade. This study provides implications for education policy makers and teacher educators.

A non-dimensional theoretical approach to model high-velocity impact on thick woven plates

  • Alonso, L.;Garcia-Gonzalez, D.;Navarro, C.;Garcia-Castillo, S.K.
    • Steel and Composite Structures
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    • v.38 no.6
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    • pp.717-737
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    • 2021
  • A theoretical energy-based model to capture the mechanical response of thick woven composite laminates, which are used in such applications as maritime or aerospace, to high-velocity impact was developed. The dependences of the impact phenomenon on material and geometrical parameters were analysed making use of the Vaschy-Buckingham Theorem to provide a non-dimensional framework. The model was divided in three different stages splitting the physical interpretation of the perforation process: a first where different dissipative mechanisms such as compression or shear plugging were considered, a second where a transference of linear momentum was assumed and a third where only friction took place. The model was validated against experimental data along with a 3D finite element model. The numerical simulations were used to validate some of the new hypotheses assumed in the theoretical model to provide a more accurate explanation of the phenomena taking place during a high-velocity impact.