• Title/Summary/Keyword: Behavior state

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Effect of Temperature on the Micro-scale Adhesion Behavior of Thermoplastic Polymer Film (열가소성 폴리머 필름의 마이크로 점착 거동에 대한 온도의 영향)

  • Kim, Kwang-Seop;Heo, Jung-Chul;Kim, Kyung-Woong
    • Tribology and Lubricants
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    • v.25 no.2
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    • pp.86-95
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    • 2009
  • Adhesion tests were carried out in order to investigate the effect of temperature on the adhesion behavior between a PMMA film and a fused silica lens in the micro scale. For the tests, a microtribometer system was specially designed and constructed. The pull-off forces on the PMMA film were measured under atmospheric condition as the temperature of the PMMA film was increased from 300 K to 443 K and decreased to 300 K. The contact area between the PMMA film and the lens was observed during the test. The adhesion behavior was changed with the change of the PMMA surface state as the temperature increased. In glassy state below 363 K, the pull-off force did not change with the increase of temperature. In rubbery state from 383 K to 413 K, the pull-off force increased greatly as the temperature increased. In addition, the area of contact was enlarged. In viscous state above 423 K, the fingering instability was observed in the area of contact when the PMMA film contacted with the lens. It was also found that the adhesion behavior can be varied with the thermal history of the PMMA film. The residual solvent in the PMMA film could emerge to the PMMA surface due to the heating and reduced the pull-off force.

Modeling of rheological behavior of nanocomposites by Brownian dynamics simulation

  • Song Young Seok;Youn Jae Ryoun
    • Korea-Australia Rheology Journal
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    • v.16 no.4
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    • pp.201-212
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    • 2004
  • Properties of polymer based nanocomposites depend on dispersion state of embedded fillers. In order to examine the effect of dispersion state on rheological properties, a new bi-mode FENE dumbbell model was proposed. The FENE dumbbell model includes two separate ensemble sets of dumbbells with different fric­tion coefficients, which simulate behavior of well dispersed and aggregated carbon nanotubes (CNTs). A new parameter indicating dispersion state of the CNT was proposed to account for degree of dispersion quantitatively as well as qualitatively. Rheological material functions in elongational, steady shear, and oscillatory shear flows were obtained numerically. The CNT/epoxy nanocomposites with different dis­persion state were prepared depending on whether a solvent is used for the dispersion of CNTs or not. Dis­persion state of the CNT in the epoxy nanocomposites was morphologically characterized by the field emission scanning electronic microscope and the transmission electron microscope images. It was found that the numerical prediction was in a good agreement with experimental results especially for steady state shear flow.

Switching Characteristics of Amorphous GeSe TFT for Switching Device Application

  • Nam, Gi-Hyeon;Kim, Jang-Han;Jo, Won-Ju;Jeong, Hong-Bae
    • Proceedings of the Korean Vacuum Society Conference
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    • 2012.02a
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    • pp.403-404
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    • 2012
  • We fabricated TFT devices with the GeSe channel. A single device consists of a Pt source and drain, a Ti glue layer and a GeSe chalcogenide channel layer on SiO2/Si substrate which worked as the gate. We confirmed the drain current with variations of gate bias and channel size. The I-V curves of the switching device are shown in Fig. 1. The channel of the device always contains amorphous state, but can be programmed into two states with different threshold voltages (Vth). In each state, the device shows a normal Ovonic switching behavior. Below Vth (OFF state), the current is low, but once the biasing voltage is greater than Vth (ON state), the current increases dramatically and the ON-OFF ratio is high. Based on the experiments, we draw the conclusion that the gate voltage can enhance the drain current, and the electric field by the drain voltage affects the amorphous-amorphous transition. The switching device always contains the amorphous state and never exhibits the Ohmic behavior of the crystalline state.

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Electrical Switching Characteristics of Thin Film Transistor with Amorphous Chalcogenide Channel

  • Nam, Gi-Hyeon;Kim, Jang-Han;Jeong, Hong-Bae
    • Proceedings of the Korean Vacuum Society Conference
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    • 2011.08a
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    • pp.280-281
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    • 2011
  • We fabricated the devices of TFT type with the amorphous chalcogenide channel. A single device consists of a Pt source and drain, a Ti glue layer and a GeSe chalcogenide channel layer on SiO2/Si substrate which worked as the gate. We confirmed the drain current with variations of gate bias and channel size. The I-V curves of the switching device are shown in Fig. 1. The channel of the device always contains amorphous state, but can be programmed into two states with different threshold voltages (Vth). In each state, the device shows a normal Ovonic switching behavior. Below Vth (OFF state), the current is low, but once the biasing voltage is greater than Vth (ON state), the current increases dramatically and the ON-OFF ratio is about 4 order. Based on the experiments, we contained the conclusion that the gate voltage can enhance the drain current, and the electric field by the drain voltage affects the amorphous-amorphous transition. The switching device always contains the amorphous state and never exhibits the Ohmic behavior of the crystalline state.

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Microwave Heating and Pre-sintering of Copper Powder Metal Compacts in Separated Electric and Magnetic Fields

  • Zimmerman, Darin T.;Johnson, Earnie J.;Ma, JunKun;Miskovsky, Nicholas M.;Weisel, Gary J.;Weiss, Brock L.
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09a
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    • pp.266-267
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    • 2006
  • We present a systematic study of the heating and pre-sintering behavior of porous copper powder metal compacts. We employ a TE102 single mode microwave system to position the samples in the separated electric field (E) or magnetic field (H) anti-node of the cavity. We observe significant differences in the heating, pre-sintering, and microstructure evolution of the samples due to the individual fields. We note that sample history (whether heated first in the E-field or H-field) greatly effects a difference in heating trends and subsequent heating behavior and does not appear to be solely a thermal process.

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Numerical analysis of melt migration and solidification behavior in LBR severe accident with MPS method

  • Wang, Jinshun;Cai, Qinghang;Chen, Ronghua;Xiao, Xinkun;Li, Yonglin;Tian, Wenxi;Qiu, Suizheng;Su, G.H.
    • Nuclear Engineering and Technology
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    • v.54 no.1
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    • pp.162-176
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    • 2022
  • In Lead-based reactor (LBR) severe accident, the meltdown and migration inside the reactor core will lead to fuel fragment concentration, which may further cause re-criticality and even core disintegration. Accurately predicting the migration and solidification behavior of melt in LBR severe accidents is of prime importance for safety analysis of LBR. In this study, the Moving Particle Semi-implicit (MPS) method is validated and used to simulate the migration and solidification behavior. Two main surface tension models are validated and compared. Meanwhile, the MPS method is validated by the L-plate solidification test. Based on the improved MPS method, the migration and solidification behavior of melt in LBR severe accident was studied furthermore. In the Pb-Bi coolant, the melt flows upward due to density difference. The migration and solidification behavior are greatly affected by the surface tension and viscous resistance varying with enthalpy. The whole movement process can be divided into three stages depending on the change in velocity. The heat transfer of core melt is determined jointly by two heat transfer modes: flow heat transfer and solid conductivity. Generally, the research results indicate that the MPS method has unique advantage in studying the migration and solidification behavior in LBR severe accident.

The Effectiveness of Assertive Training on the State Anxiety and Assertive Behavior of Nursing Students Experiencing Clinical Practice Training (주장훈련이 임상실습시 간호학생이 느끼는 불안과 주장행동에 미치는 효과)

  • Yang, Jin-Ju
    • The Journal of Korean Academic Society of Nursing Education
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    • v.7 no.1
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    • pp.54-67
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    • 2001
  • This study was tried to investigate the effectiveness of assertive training on the state anxiety and assertive behavior which nursing students had experienced during clinical practice training from April 29, to June 5, 2000. Subjects for this study were thirty-six nursing students of practicing in a general hospital. Eighteen nursing students were assigned for the experimental group and trained by assertive training program during 4 weeks and eighteen nursing students were assigned for the control group. The assertive training program was composed of cognitive, behavioral and emotional assertive training. Post- test assessment was administrated to all subjects on a week later after the last session. The data were analyzed with SPSS PC programs. The results of this study were summarized as follows: 1) There were no significant differences between the experimental group and the control group on post- intervention comparisons of the state anxiety score (p=0.230), but in the experimental group, the anxiety score more decreased after the assertive training than that in the control group with significant differences(p=0.019). 2) There were no significant differences between the experimental group and the control group on post- intervention comparisons of assertive behavior (p=0.530). However, after the assertive training, the experimental group became more assertive than the control group with no significant differences(p=0.721). 3) The hypothesis that the more the assertive behavior, the less the state anxiety experienced by nursing students of clinical practice training was supported(r=-0.397, p=0.017). On the basis of this study results, the assertive training is effective for the reduction of the state anxiety experienced by nursing students of clinical practice training.

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Fracture properties and tensile strength of three typical sandstone materials under static and impact loads

  • Zhou, Lei;Niu, Caoyuan;Zhu, Zheming;Ying, Peng;Dong, Yuqing;Deng, Shuai
    • Geomechanics and Engineering
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    • v.23 no.5
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    • pp.467-480
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    • 2020
  • The failure behavior and tensile strength of sandstone materials under different strain rates are greatly different, especially under static loads and impact loads. In order to clearly investigate the failure mechanism of sandstone materials under static and impact loads, a series of Brazilian disc samples were used by employing green sandstone, red sandstone and black sandstone to carry out static and impact loading splitting tensile tests, and the failure properties subjected to two different loading conditions were analyzed and discussed. Subsequently, the failure behavior of sandstone materials also were simulated by finite element code. The good agreement between simulation results and experimental results can obtain the following significantly conclusions: (1) The relationship of the tensile strength among sandstone materials is that green sandstone < red sandstone < black sandstone, and the variation of the tensile sensitivity of sandstone materials is that green sandstone > red sandstone > black sandstone; (2) The mainly cause for the difference of dynamic tensile strength of sandstone materials is that the strength of crystal particles in sandstone material, and the tensile strength of sandstone is proportional to the fractal dimension; (3) The dynamic failure behavior of sandstone is greatly different from that of static failure behavior, and the dynamic tensile failure rate in dynamic failure behavior is about 54.92%.

Periparturient stocking density affects lying and ruminating behavior and one-week-calf performance of Holstein cows

  • Jiang, Mingming;Alugongo, Gibson Maswayi;Xiao, Jianxin;Li, Congcong;Ma, Yulin;Li, Tingting;Cao, Zhijun;Liu, Dasen
    • Animal Bioscience
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    • v.34 no.4
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    • pp.759-769
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    • 2021
  • Objective: This study aimed to investigate the effect of stocking density on the behavior, productivity, and metabolism of periparturient Holstein cows as well as calf performance. Methods: A total of 48 periparturient cows were randomly assigned into three groups at 28 days (±3 days) before their expected calving date. The stocking densities of the groups, relative to the standard cubicle and feed bunk number, were i) 80% (13 cows), ii) 100% (16 cows), and iii) 120% (19 cows). Lying and rumination behavior was recorded using electronic data loggers and HR-Tags from d -21 ("d-" means days before calving) until the calving date, d 0. Lying time was assessed to determine the diurnal total hours spent lying per day. Rumination time was averaged in 2 hours interval periods over 24 hours during the experimental period. Results: Cows in the 80% group spent more time lying and ruminating between d -21 and d -7 and tended to ruminate more between d -14 and d 0. Calcium levels tended to be higher for cows in the 80% group, no other observable differences were found in monitored blood parameters. Moreover, 3.5% fat corrected milk and energy corrected milk yields were higher in 80% group in the first month of lactation. No other observable differences were found in the yield and composition of colostrum and milk in the first 10 months of lactation. The growth and performance of calves in the first week of life was not affected by stocking density of the dams. Conclusion: We concluded that lower stocking density may increase lying and ruminating behavior of prepartum Holstein cows. However, this did not translate into improved productivity and metabolism.

A Constitutive Model for the Rate-dependent Deformation Behavior of a Solid Polymer (속도 의존적인 폴리머 거동에 대한 구성적 모델)

  • Ho, K.
    • Transactions of Materials Processing
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    • v.22 no.4
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    • pp.216-222
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    • 2013
  • Solid polymers exhibit rate-dependent deformation behavior such as nonlinear strain rate sensitivity and stress relaxation like metallic materials. Despite the different microstructures of polymeric and metallic materials, they have common properties with respect to inelastic deformation. Unlike most metallic materials, solid polymers and shape memory alloys (SMAs) exhibit highly nonlinear stress-strain behavior upon unloading. The present work employs the viscoplasticity theory [K. Ho, 2011, Trans. Mater. Process. 20, 350-356] developed for the pseudoelastic behavior of SMAs, which is based on unified state variable theory for the rate-dependent inelastic deformation behavior of typical metallic materials, to depict the curved unloading behavior of polyphenylene oxide (PPO). The constitutive equations are characterized by the evolution laws of two state variables that are related to the elastic modulus and the back stress. The simulation results are compared with the experimental data obtained by Krempl and Khan [2003, Int. J. Plasticity 19, 1069-1095].