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1

Reaction Kinetics and Morphological Study of TiNb2O7 Synthesized by Solid-State Reaction

Choi S. H., Ali B., Choi K. S., Hyun S. K., Sim J. J., Choi W. J., Joo W., Lim J. H., Lee T. H., Kim T. S., Park K. T.

Archives of Metallurgy and Materials

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2017

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Vol. 62, iss. 2B

1051--1056

EN

Although TiNb2O7 is regarded as a material with high application potential in lithium-ion batteries (LIBs) and solid-oxide fuel cells (SOFCs), it has been difficult to find suitable cost-effective conditions for synthesizing it on a commercial scale. In this study, TiNb2O7 compounds were synthesized by a solid state synthesis process. For stoichiometrically precise synthesis of the TiNb2O7 phase, the starting materials, TiO2 and Nb2O5 were taken in a 1:1 molar ratio. Activation energy and reaction kinetics of the system were investigated at various synthesis temperatures (800,1000,1200, and 1400°C) and for various holding durations (1,5,10, and 20 h). Furthermore, change in the product morphology and particle size distribution were also evaluated as a function of synthesis temperature and duration. Additionally, quantitative phase analysis was conducted using the Rietveld refinement method. It was found that increases in the synthesis temperature and holding time lead to increase in the mean particle size from 1 to 4.5 μm. The reaction rate constant for the synthesis reaction was also calculated.

2

Lifting strength in two-person teamwork

Lee T. H.

International Journal of Occupational Safety and Ergonomics

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2016

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Vol. 22, No. 2

179--185

EN

This study examined the effects of lifting range, hand-to-toe distance, and lifting direction on single-person lifting strengths and two-person teamwork lifting strengths. Six healthy males and seven healthy females participated in this study. Two-person teamwork lifting strengths were examined in both strength-matched and strength-unmatched groups. Our results showed that lifting strength significantly decreased with increasing lifting range or hand-to-toe distance. However, lifting strengths were not affected by lifting direction. Teamwork lifting strength did not conform to the law of additivity for both strength-matched and strength-unmatched groups. In general, teamwork lifting strength was dictated by the weaker of the two members, implying that weaker members might be exposed to a higher potential danger in teamwork exertions. To avoid such overexertion in teamwork, members with significantly different strength ability should not be assigned to the same team.

3

Endurance time, muscular activity and the hand/arm tremor for different exertion forces of holding

Lee T. H.

International Journal of Occupational Safety and Ergonomics

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2016

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Vol. 22, No. 1

71--76

EN

This study aimed to examine the effects of exertion force on endurance time, muscular activity and hand/arm tremor during holding. Fifteen healthy young males were recruited as participants. The independent variable was exertion force (20%, 40%, 60% and 80% maximum holding capacity). The dependent variables were endurance time, muscular activity and hand/arm tremor. The results showed that endurance time decreased with exertion force while muscular activity and hand/arm tremor increased with exertion force. Hand/arm tremor increased with holding time. Endurance time of 40%, 60% and 80% maximum holding capacity was approximately 22.7%, 12.0% and 5.6% of that of 20% maximum holding capacity, respectively. The rms (root mean square) acceleration of hand/arm tremor of the final phase of holding was 2.27-, 1.33-, 1.20- and 1.73-fold of that of the initial phase of holding for 20%, 40%, 60% and 80% maximum holding capacity, respectively.

4

The effects of load magnitude and lifting speed on the kinematic data of load and human posture

Lee T. H.

International Journal of Occupational Safety and Ergonomics

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2015

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Vol. 21, No. 1

55--61

EN

This study examined the effects of load magnitude and lifting speed on the kinematic data of load and human posture in a lifting task. Three load magnitudes (10, 20 and 30 kg) and three lifting speeds (fast, normal and slow) were examined in this study. This study showed that participants shortened the load acceleration period on lifting a lighter load than on lifting a heavier load. For normal and slow lifting speeds, participants moved and lifted the load closer to their body when lifting a heavy load. Participants tended to maintain their postures by using an ankle strategy when in heavier load or faster lifting conditions. The profiles of angle velocity of knee and ankle joints demonstrated the important role of the lower extremities in the acceleration of the load in the initial stage of fast lifting. In addition, participants could not easily control the momentum transmitted to the ankle joint for lifting the heavy load.

5

Effects of carrying handles, postures, materials and distances on carrying capability

Lee T. H., Yeh Y.-C.

International Journal of Occupational Safety and Ergonomics

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2015

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Vol. 21, No. 3

250--255

EN

This study recruited 14 industrial workers to examine the effects of carrying handles, postures, materials and distances on maximum acceptable weights of carrying (MAWC), and resulting heart rate and body rating of perceived exertion (RPE) for a 20 min intensive carrying task. This study showed that MAWC of carrying with bar handles, carrying with hands-and-body posture, solid materials and 4 m distance were significantly higher than that of carrying with groove handles, carrying with hands posture, liquid materials and 8 m distance, respectively. The resulting heart rates while carrying MAWCs of groove handles, hands-and-body carrying posture, solid materials and 4 m distance were lower than the resulting heart rates while carrying MAWCs of bar handles, hands carrying posture, liquid materials and 8 m distance, respectively. Most pair levels of independent variables resulted in similar body's RPEs except for the pair levels of carrying distance.

6

Effect Of Different Mechanical Milling Processes On Morphology And Microstructural Changes Of Nano And Micron Al-Powders

Kim H.-S., Madavali B., Eom T.-J., Kim C.- M., Koo J.-M., Lee T. H., Hong S.-J.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2B

1235--1239

EN

In this research, effect of the various mechanical milling process on morphology and microstructural changes of nano and micron Al-powders was studied. The milling of Al-powders was performed by both high energy and low energy ball milling process. The influence of milling (pulverizing) energy on the structural changes of Al-powders was studied. Al-nanoparticles were agglomerated during the MA and its size was increased with increasing milling while micron Al-powder gets flattened shape during high energy ball milling due to severe plastic deformation. Meanwhile, structural evolution during high energy ball milling of the nano powder occurred faster than that of the micron powder. A slight shift in the position of X-ray diffraction peaks was observed in nano Al-powders but it was un-altered in macro Al-powders. The variation in lattice parameters was observed only for nano Al powders during the high energy ball milling due to lattice distortion.

7

Subjective Perception of Load Heaviness

Lee T. H.

International Journal of Occupational Safety and Ergonomics

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2014

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Vol. 20, No. 3

421--427

EN

This study examined human subjective perception of load heaviness. Forty-two (3 boxes × 14 weights) and 27 (3 boxes × 9 weights) experimental conditions were randomly presented to male and female participants, respectively. The results showed that the participants were not able to discriminate the effect of the box on perceived weight. The participants underestimated the weight for low weights and overestimated it for high weights. The females perceived a greater increase in weight than the males for the same increase in weight. The participants’ linguistic term for perceived weight was positively correlated to the magnitude of weight. Approximately 50% of the males perceived a weight of 20 kg or over as risky, while ~60% of the females perceived a weight of 14 kg or over as risky. This study supposes that the gender difference in muscular capability is responsible for the effect of gender on the risk perception of weight.

8

Grip Force and Heart Rate Responses to Manual Carrying Tasks: Effects of Material, Weight, and Base Area of the Container

Lee T. H., Tseng C. Y.

International Journal of Occupational Safety and Ergonomics

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2014

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Vol. 20, No. 3

377--383

EN

This study recruited 16 industrial workers to examine the effects of material, weight, and base area of container on reduction of grip force (ΔGF) and heart rate for a 100-m manual carrying task. This study examined 2 carrying materials (iron and water), 4 carrying weights (4.4, 8.9, 13.3, 17.8 kg), and 2 base areas of container (24 ´ 24 cm, 35 ´ 24 cm). This study showed that carrying water significantly increased ΔGF and heart rate as compared with carrying iron. Also, ΔGF and heart rate significantly increased with carrying weight and base area of container. The effects of base area of container on ΔGF and heart rate were greater in carrying water condition than in carrying iron condition. The maximum dynamic effect of water on ΔGF and heart rate occurred when water occupied ~60%–80% of full volume of the container.

9

Postural and Muscular Responses While Viewing Different Heights of Screen

Lee T. H., Liu T. Y.

International Journal of Occupational Safety and Ergonomics

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2013

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Vol. 19, No. 2

251--258

EN

This study aimed to examine the effects of visual display terminal (VDT) viewing angle on human postural angle and muscular activity. The participants’ neck, thoracic bending, and trunk inclination angles; and the activity of sternocleidomastoid, trapezius, splenius capitis, and erector spinae at 5 viewing angles (+400, +200, 00, –200, and –400) of a VDT screen were collected for 1 min. This study showed that neck and thoracic bending angles increased with viewing angle, while viewing angle did not significantly affect trunk inclination angle. In addition, the activity of trapezius and erector spinae increased when viewing a higher or lower VDT screen height compared with viewing a horizontal VDT screen height; however, the activity of splenius capitis decreased with viewing angle.

10

Analysis of Working Postures at a Construction Site Using the OWAS Method

Lee T. H., Han C. S.

International Journal of Occupational Safety and Ergonomics

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2013

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Vol. 19, No. 2

245--250

EN

This study used OWAS to analyze the working postures of construction workers on building the foundations of a log cabin. Three construction workers, with an average work experience of 40 years, participated in this study. Eight elementary jobs of building the foundations of a log cabin were videotaped at a construction site and analyzed later in the laboratory. For an overall distribution of trunk postures, OWAS identified that a bent and twisted trunk posture (34%), which fell into action category 3, was the major poor posture for construction workers. This study also identified that tying beams with steel bars, assembling column templates, and cement grouting of the ground were the 3 principal jobs in which workers building the foundations exhibited poor working posture. This article suggests ways to reduce and evaluate poor posture in a dynamic construction site.

11

Effects of Range and Mode on Lifting Capability and Lifting Time

Lee T. H.

International Journal of Occupational Safety and Ergonomics

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2012

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Vol. 18, No. 3

387--391

EN

This study examined the effects of 3 lifting ranges and 3 lifting modes on maximum lifting capability and total lifting time. The results demonstrated that the maximum lifting capability for FK (from floor to knuckle height)was greater than that for KS (from knuckle height to shoulder height) or FS (from floor to shoulder height. Additionally, asymmetric lifting with initial trunk rotation decreased maximum lifting capability compared with symmetric lifting or asymmetric lifting with final trunk rotation. The difference in total lifting time between KS and FS was not significant, while FK increased total lifting time by ~20% compared with FS even though the travel distance was 50% shorter.

12

Effects of Hand Posture, Breathing Type, Arm Posture and Body Posture on Hand Errors

Lee T. H., Cheng T. S.

International Journal of Occupational Safety and Ergonomics

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2012

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Vol. 18, No. 3

393--398

EN

This study consisted of 2 experiments. Experiment 1 examined the effects of hand posture, arm posture and body posture on hand error, while experiment 2 examined the effects of hand posture, breathing type and body posture on hand error. This study showed that more hand errors occurred in the nondominant hand, extended arm, normal breathing and standing compared with errors in the dominant hand, flexed arm, inspire–hold and sitting, respectively. This study advised people to use their dominant hand, flex their arm, inspire and hold the breath and support their body while performing fine manipulation tasks. Finally, hand error varied dramatically across the participants, indicating the need to screen individuals for fine manual manipulation tasks.

13

Asymmetric Lifting Capabilities for Different Container Dimensions

Lee T. H., Cheng T. S.

International Journal of Occupational Safety and Ergonomics

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2011

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Vol. 17, No. 2

187--193

EN

This study recruited 14 young male participants to examine human 4-h maximum acceptable weight of lifting (MAWL) and maximum weight of lifting (MWL) for different modes of asymmetric lifting and containers. The results showed that asymmetric lifting with trunk rotation decreased MAWL and MWL by 9.1 and 17.3%, respectively, and asymmetric lifting with body turn decreased MAWL and MWL by 6.1%, when compared with the symmetric lifting. The decreasing effects of container width and MAWL and MWL were greater than those of container length. Participants selected MAWL of ~33–37% of their MWL capability.