• Tribology and Lubricants
• /
• v.16 no.6
• /
• pp.477-483
• /
• 2000

Rolling contact fatigue (RCF) tests were performed for two kinds of commercial silicon nitride balls using 4-Ball rolling contact fatigue life tester under EHL condition (Λ=8.9) and boundary lubrication condition (Λ=0.2). All the test balls were finished up to the dimensional accuracy of Grade 5 defined in KS B 2001 (Steel Balls for Ball Bearings) with a size of 8.731 mm. RCF tests were then conducted under the initial theoretical maximum contact stress 6.63 GPa and the spindle speed 10,000 rpm. All the test balls were not failed until 3.75 $\times$ 107 contact cycles and wear tracks of test balls were not conspicuous under EHL condition (Λ= 8.9). In the operations of low lambda regime (Λ= 0.2), all the test balls were surface damaged and high rolling wear resistance was achievable in fully densified using MgO 1 wt% and HIPed balls. Rolling wear of silicon nitride balls under boundary lubrication condition depend mainly on grain size and intergranular phase content of silicon nitride balls.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 1998.04a
• /
• pp.300-306
• /
• 1998

A high precision angular contact ball bearing is developed by Hanwha Machinery Co. The developed bearing is 7004C with P4 class. The performance test was succeful until 60,000 rpm.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.8 no.4
• /
• pp.450-457
• /
• 2020

In this study, engineering characteristics such as flowability, segregation and compressive strength by age to derive fast hardening material mixing proportion using excavated soil. And based on optimal mixing proportion, field simulation experiment conducted in laboratory to examine the effectiveness of the method such as kelly ball drop test and soil penetration test for reviewing the following process. As as a result of evaluation, in case of kelly ball drop test and soil penetration test were securing the following process initiation time 3 hours after place CLSM. As results of these assessments, kelly ball drop test and soil penetration test were applicable for revewing following process in construction field besides unconfined compressive strength method.

• Transactions of the Korean hydrogen and new energy society
• /
• v.26 no.4
• /
• pp.386-392
• /
• 2015

Flow characteristics inside a 10 inch ball valve have been analyzed using three-dimensional numerical analysis and experiments. Continuity and three-dimensional Reynolds-averaged Navier-Stokes equations have been used as governing equations for the numerical analysis. The numerical model has been constructed through the grid dependency test and validation with the results of experiments to ensure reliability and numerical effectiveness. The shear stress transport (SST) model has been used as the turbulence closure. The experimental test-rig has been constructed to measure pressure, temperature and flow rate along the pipeline. Some valve opening angles have been tested to evaluate the flow characteristics inside the ball valve and pipeline. The results show that the rapid pressure variations is observed while the valve opening angle decreases, which caused by flow separation at the downstream of the ball valve.

• Current Photovoltaic Research
• /
• v.4 no.4
• /
• pp.140-144
• /
• 2016

In this paper, core-shell structure of nickel/gold (Ni/Au) conductive layer on poly-methyl-methacrylate (PMMA) micro-ball was fabricated and its conduction property was investigated. Firstly, PMMA micro-ball was synthesized by using dispersion polymerization method. Size of the ball was $2.8{\mu}m$ within ${\pm}7%$ deviation, and appropriate elastic deformation of the PMMA micro-ball ranging from 31 to 39% was achieved under 3 kg pressure. Also, 200 nm thick Ni/Au conductive layer was fabricated on the PMMA micro-ball by uniformly depositing with electroless-plating. Adhesion of the conductive layer was optimized with help of surface pre-treatment, and the layer adhered without peeling-off despite of thermal expansion by collision with accelerated electrons. Composite paste containing core-shell structured particles well cured at low temperature of $130^{\circ}C$ while pressing the test chip onto the substrate to make electrical contact, and electrical resistance of the conductive layer showed stable behavior of about $6.0{\Omega}$. Thus, it was known that core-shell structured particle of the Ni/Au conductive layer on PMMA micro-ball was feasible to flexible electronics.

• Tribology and Lubricants
• /
• v.11 no.5
• /
• pp.184-189
• /
• 1995

The antiwear performance of dialkyl 3, 5-di-t-butyl 4-hydroxy benzyl phosphonates was investigated using a four ball wear test machine. Diethyl 3, 5-di-t-butyl 4-hydroxy benzyl phosphonate (DEP) and dibutyl 3,5-di-t-butyl 4-hydroxy benzyl phosponate (DBP) among them showed excellent antiwear performances compared with conventional additives, ZDDP and TCP as the bulk oil temperature and the sliding velocity increased. The surface analysis through an optical microscopy was conducted for tribological studies.

• The Journal of Korean Physical Therapy
• /
• v.34 no.6
• /
• pp.292-297
• /
• 2022

Purpose: This study describes the effects of kicking a ball training on balance and upper limb function in chronic hemiplegia. Methods: Thirty chronic stroke patients were randomly selected; Kicking a ball (n=10), Treadmill gait (n=10), Stepping on the ground group (n=10). The Short Physical Performance Battery (SPPB) for balance and Foot Scan for weight distribution. Upper limb function was measured by the Manal Function Test (MFT). This treatment was performed five times a week for a total of 4 weeks. Results: Kicking group was significantly increased in SPPB (p<0.05) and MFT (p<0.05) between pretest vs post test and pretest vs follow-up. Conclusion: Kicking a ball was effective for improving weight acceptance on the paretic leg, balance and upper limb function. However, In terms of balance, the core stabilization that affected the upper extremity function was not evaluated. Thus, additional research may help determine correlation between core stability and upper limb function to improve balance.

• Physical Therapy Rehabilitation Science
• /
• v.5 no.4
• /
• pp.170-176
• /
• 2016

Objective: The purpose of this study was to compare the effect of ball kicking dual task gait training with the addition of a cognitive task with general treadmill gait training (TGT) on gait speed, gait endurance, functional gait, balance and balance confidence in patients with chronic hemiparetic stroke. Design: Randomized controlled trial. Methods: Fourteen stroke patients who volunteered to participate in this study were randomly divided into two groups with seven patients in each group: ball kicking dual task training (DTT) group and TGT group. The DTT group received ball kicking DTT with cognitive tasks consisted of three stages and the TGT group received TGT using normal walking speed, respectively, for 30 minutes per day 3 days per week for 4 weeks. Outcome assessments were made with the 10-meter walking test (10MWT), 6-minute walking test (6MWT), functional gait assessment (FGA), Berg balance scale (BBS), timed up and go test (TUG), and the activities-specific balance confidence (ABC) scale. Results: The DTT group showed more significant improvement in the 10MWT, 6MWT, FGA, BBS, TUG, and ABC than the TGT group (p<0.05). In addition, within groups comparison showed significant improvement in all variables (p<0.05). Conclusions: The findings suggest that both ball kicking dual task gait training and TGT improve gait performance and balance in patients with chronic hemiparetic stroke. However, ball kicking dual task gait training results showed more favorable outcomes than TGT for chronic hemiparetic stoke patients.

• Journal of the Korean Institute of Landscape Architecture
• /
• v.31 no.4
• /
• pp.82-89
• /
• 2003

This study was carried out to find the suitable root-ball size for the planting construction of landscape trees. Surveyed trees for this study were Cercidiphyllum japonicum and Prunus yedoensis, and the root-ball size was classified into 3D, 4D, 5D, and 6D(D meaning the diameter at the base of a tree). Visual ratings on a scale of 1 to 9 were used as a means for measuring the regrowth strength after planting tested trees. Test trees with 3, 4, 5 and 6D root-ball size were planted on March. 16, 2002 and visual ratings were measured up to April. 30, 2003. Cercidiphyllum japonicum and Prunus yedoensis started showing a difference in regrowth by each rootball size a month after planting. The regrowth quality of Cercidiphyllum japonicum was low at 3D, medium at 4∼5D and high at 6D root-ball size, while the regrowth quality of Prunus yedoensis was low at 3∼4D and medium-high at 5∼6D root-ball size. According to the above results, a root-ball size for good regrowth quality was a little bit different between Cercidiphyllum japonicum and Prunus yedoensis. 4D of Cercidiphyllum japonicum and 5D of Prunus yedoensis could be guidelines for root-ball diameters at the base of trees when planting. However, we concluded that 4D∼5D root-ball is the optimum guideline for regrowth when adapting this guideline to all landscape trees with 8∼l0cm diameter at the base.

• The Korean Journal of Rehabilitation Nursing
• /
• v.1 no.1
• /
• pp.15-25
• /
• 1998

The purposes of this study was to determine the effect of beach ball play in stroke patients, and to define the strategy to promote their depression, powerlessness, self-esteem, activity of daily living. The experimental design was designed non-equivalent control group, non-synchroniged design. The study method had been done by investigating the experimental group and control group through the questionnaire on 57 patients who had been in patient department in D University hospital in Pusan from January 5th 1998 to the end of February 28th, 1998. Beach ball play was carried out experimental group once per day for 10 minute's for two weeks period from Jan 1998 to Feb 1998. Data was collected before and after the experimenation. Collected data was analyzed by means of frequency, percentage, chi-square test, mean, S.D, t-test with SPSS/PC. The results were summarized as follows : 1. The 1st hypothesis : "The experimental group which received the beach ball play should be higher in depression than the control group" was supported(t=3.11, p=.003). 2. The 2nd hypothesis : "The experimental group which received the beach hall play should be higher in powerlessness than the control group" was supported(t=3.32, p=.002). 3. The 3rd hypothesis : "The experimental group which received the beach ball play should be higher in self-esteem than the control group" was not supported(t=-1.90, p=.064). 4. The 4th hypothesis : "The experimental group which received the beach ball play should be higher in activity of daily living than the control group" was not supported(t=-.47, p=.637). In conclusion, the patients who received beach ball play showed the increase in the degree of depression and powerlessness of stroke patients. So the beach ball play had been judged the nursing intervention to improve their emotional problem in stroke patients.