• International Journal of Air-Conditioning and Refrigeration
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• v.17 no.1
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• pp.1-6
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• 2009

The optimum design of back pressure chamber is one of the most important factors in designing scroll compressors because it has a great influence on the efficiency and other design parameters. The design process can be divided into 2 parts. One is obtaining the optimum pressure of the chamber and keeping it in constant value. The other is finding out the minimum inflow rate of medium with which back pressure chamber is filled. In this study we are focused on the first step. At first we added a simple structure that can change back pressure without reassembling compressor. It makes possible to obtaining optimum back pressure. Then we designed an equipment that the back pressure control valve assembly could be independently tested with. Spring was redesigned to decrease stiffness variation. Also sealing mechanism of back pressure control valve was improved to more effective way. As a result, it was verified that in a real mode test back pressure variation could be retained in 2.3% with discharge pressure and operating frequency varied. In addition the integrated structure of back pressure control valve is expected to contribute to effective manufacturing process.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.398-400
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• 2008

In this work, an air-bending test using magnesium alloy ZK60 sheet was carried out at the various temperatures from room temperature to $300^{\circ}C$ in order to investigate the effect of grain size on the spring-back characteristic. It was found out from experiments that the amount of spring-back was nearly zero at all temperature range when the specimens with grain sizes of 14.66 and $60.71{\mu}m$ were bent by $90^{\circ}$. On the other hand, the spring-back amount dramatically increased at room temperature and phenomenon of spring-go was observed at high temperature when the specimen with submicro grain size of $0.98{\mu}m$ was bent by $90^{\circ}$. From this kind of different spring-back characteristics according to the grain size, it was confirmed that the grain size of material is one of the important factors which have an effect on the spring-back.

• The Journal of Korean Academy of Orthopedic Manual Physical Therapy
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• v.12 no.2
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• pp.11-20
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• 2006

Low back pain is often experienced by many people who are in an activity flag. Their work and daily life are affected by low back pain. There are many causes of low back pain. Among those many causes, this study was focused on a relation between low back pain and the tightness of iliopsoas. The study was implemented by measuring the angles of the hip joints in subjects consisting of a 30 patients group, who had been selected from the outpatients at the Median Hospital, and a 30 people control group from the outpatients at the M Hospital and employee of M hospital. The patients group consists of the patients with low back pain who have intermittently or continuously experienced low back pain within the last 6 months. The group also had no symptom of spondylolysis or spondylolithesis and no muscular abnormality in terms of pathology without any experience of disc or spine fusion operation. The control group consisted out of persons who had never experienced lower back pain and had never been subjected to physical therapy due to lower back pain. The hip joint angles of the subjects of this study were measured by means of the modified Thomas test position. Data was analysed by independent sampling t-test using SPSS 11.0. The following results were obtained: 1. The measured angles of patient's both hip joints were significantly smaller than the control group's. 2. In the males group, The angles of patients' both hip joints were smaller than the controls'. In the females group, The angles of patients' both hip joints were smaller than the controls'. In conclusion, this study demonstrates that there is a significant difference in the tightness of the iliopsoas muscles when comparing the patient group with the control group. We should therefore pay more attention in releasing the muscle tightness of iliopsoas muscles when performing physical therapy with patients with lower back pain.

• Journal of Korean Physical Therapy Science
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• v.13 no.1
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• pp.39-52
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• 2006

The purpose of this study was to investigate the effects of lumbar stabilization exercise therapy on low back pain patients' lumbar spinal function. Identify the effect of stabilization exercise therapy, this study attempted to determine lumbar spinal functions, using spinoscopy, for 20 patients with low back pain This study applied lumbar stabilization exercise to 20 low back pain patients without a control group for 8 weeks and 4 times a week, and examined their spinal functions before and after the application. Data collected from the test were analyzed using Wilcoxon signed ranked test, a nonparametric test. Absolute index, functionality and performance increased significantly compared to them before treatment. FE loads and velocity control while conducting exercise tasks increased significantly compared to them before treatment. Test item ROL and ROM, which indicate the change of angle, both showed significant differences. Of stiff spine, stiff pelvic score and sprain score, which indicate the effects of the conduct of exercise tasks on the movement of the spine, stiff spine score and sprain score showed significant differences. According to the results as presented above, lumbar stabilization exercise may be greatly helpful in improving low back pain patients' lumbar spinal functions.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.410-415
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• 2007

The optimization of back pressure chamber is one of the most important factors in designing scroll compressors, because it has a great influence on the efficiencies and other design parameters. The design process can be divided into 2 parts. One is obtaining the optimum pressure of the chamber and keeping it in constant value. And the other is finding out the minimum inflow rate of medium with which back pressure chamber is filled. In this study we are focused on the first step. At first we added a simple structure that could change back pressure without reassembling compressor. It makes the optimum back pressure be obtained. And then we devised an equipment that the back pressure control valve assembly could be independently tested with. A spring was redesigned to decrease stiffness variation. And sealing mechanism of back pressure control valve was improved to more effective way. As a result it was verified in a real mode test that back pressure variation could be stabilized within 2.3% when discharge pressure and operating frequency varied. And the integrated structure of back pressure control valve is expected to contribute to an effective manufacturing process.

• Steel and Composite Structures
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• v.42 no.1
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• pp.1-22
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• 2022

In cold-formed steel (CFS) structures, such as trusses, transmission towers and portal frames, the use of back-to-back built-up CFS unequal angle sections are becoming increasingly popular. In such an arrangement, intermediate welds or screw fasteners are required at discrete points along the length, preventing the angle sections from buckling independently. Limited research is available in the literature on axial strength of back-to-back built-up CFS unequal angle sections. The issue is addressed herein. This paper presents an experimental investigation reported by the authors on back-to-back built-up CFS unequal angle sections with intermediate stiffeners under axial compression. The load-axial shortening behaviour along with the deformed shapes at failure are reported. A nonlinear finite element (FE) model was then developed, which includes material non-linearity, geometric imperfections and modelling of intermediate fasteners. The FE model was validated against the experimental test results, which showed good agreement, both in terms of failure loads and deformed shapes at failure. The validated finite element model was then used for the purpose of a parametric study comprising 96 models to investigate the effect of longer to shorter leg ratios, stiffener provided in the longer leg, thicknesses and lengths on axial strength of back-to-back built-up CFS unequal angle sections. Four different thicknesses and seven different lengths (stub to slender columns) with three overall widths to the overall depth (B/D) ratios were investigated in the parametric study. Axial strengths obtained from the experimental tests and FE analyses were used to assess the performance of the current design guidelines as per the Direct Strength Method (DSM); obtained comparisons show that the current DSM is conservative by only 7% and 5% on average, while predicting the axial strengths of back-to-back built-up CFS unequal angle sections with and without the stiffener, respectively.

• Korean Journal of Adult Nursing
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• v.20 no.2
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• pp.269-279
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• 2008

Purpose: The study was to examine the effect of lumbar stabilization exercise on back pain, physical fitness, sleep, and depression in middle-aged women who have chronic back pain. Methods: With one group pre-post test design, 18 subjects who have had more than 6 months of back pain were recruited by convenience sampling in D metropolitan area. Lumbar stabilization exercise was based on Tai Chi for back pain program developed by Lam(2003). This program was mainly focusing on strengthening lumbar stabilizing muscle for one hour per session, twice a week for 20 weeks. Degree of back pain, back pain disability, sleep, and depression were measured at three time points(pretest, 12 weeks, and 20 weeks) by a structured study questionnaire. Physical fitness variables including waist flexibility, mobility, and back muscle strength were measured three times at health promotion center located in the university hospital. Data were analyzed by frequency, descriptive statistics, and repeated measures of ANOVA. Results: Mean age of subjects was 52 years(SD = 6.4). Most of them(90%) had suffered from back pain more than one year and 67% was taking medicine to relieve their back pain. Results showed that back pain score and disability score were not significantly decreased after the exercise. On physical fitness variables, however, waist flexibility(F = 3.50, p = .04) and mobility(F = 3.31, p = .04) were improved after the exercise. Quality of sleep(F = 4.48, p = .03) was improved gradually and depression scores were also decreased(F = 3.12, p = .05) after the exercise. Conclusion: This lumbar stabilization exercise was not able to reduce chronic back pain, but could improve physical fitness and psycho-social variables for community dwelling women who have chronic back pain. Further study is needed to replicate this exercise with control group to confirm the positive effect.

• Steel and Composite Structures
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• v.33 no.4
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• pp.595-614
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• 2019

In cold-formed steel (CFS) structures, such as trusses, transmission towers and portal frames, the use of back-to-back built-up CFS unequal angle sections are becoming increasingly popular. In such an arrangement, intermediate welds or screw fasteners are required at discrete points along the length, preventing the angle sections from buckling independently. Limited research is available in the literature on axial strength of back-to-back built-up CFS unequal angle sections. The issue is addressed herein. This paper presents an experimental investigation on both the welded and screw fastened back-to-back built-up CFS unequal angle sections under axial compression. The load-axial shortening and the load verses lateral displacement behaviour along with the deformed shapes at failure are reported. A nonlinear finite element (FE) model was then developed, which includes material non-linearity, geometric imperfections and modelling of intermediate fasteners. The FE model was validated against the experimental test results, which showed good agreement, both in terms of failure loads and deformed shapes at failure. The validated FE model was then used for the purpose of a parametric study to investigate the effect of different thicknesses, lengths and, yield stresses of steel on axial strength of back-to-back built-up CFS unequal angle sections. Five different thicknesses and seven different lengths (stub to slender columns) with two different yield stresses were investigated in the parametric study. Axial strengths obtained from the experimental tests and FE analyses were used to assess the performance of the current design guidelines as per the Direct Strength Method (DSM); obtained comparisons show that the current DSM is conservative by only 7% on average, while predicting the axial strengths of back-to-back built-up CFS unequal angle sections.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.2
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• pp.327-333
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• 2003

Most of shape defects in steel strip are originated from the structure of rolling mill itself. For instance, strip crown occurs when the work roll is deformed by the bending moment induced on roll chocks. To get rids of the shape defects, it is necessary to increase the stiffness of rolling mill. The structure change of back-up roll is one of alternative ways to increase the mill stiffness without facility revamping from 4 high mill to 6 high mill. In this research work, the new back-up roll was developed and can be used in any type of 4 high mill to reduce the strip shape defects. The developed back-up roll consists of sleeve, arbor and phase angle adjusting system for arbor. The circumference of arbor is specially machined to adapt the strip width change during rolling. The experimental cold rolling test was done to prove the effectiveness of newly developed back-up roll. The experimental rolling results show that the new back-up roll has more powerful performance in reducing the shape defects than conventional back-up roll. It was also found that the new back-up roll has higher stability for shape control. In addition to, the only sleeve surface needs to be reground and changed in most cases, so that the maintenance cost can be greatly reduced.

• Journal of International Academy of Physical Therapy Research
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• v.2 no.2
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• pp.318-323
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• 2011

The purpose of this study identify that spinal decompression therapy effect on and pain, length Of leg distance(LLD), and muscle power and flexibility in patient with low back pain. The participants is 20 female and male with low back pain, and participant assign to decompression therapy group and control group at random. The decompression therapy apply to 20 minute 3 time for a week during 4 weeks. The Measurement items is pain, LLD, and muscle power, flexibility. The comparison between the before and after was Wilcoxon's U test, and 2 group after spinal decompression therapy application compared Mann-Whithney U test. Spinal decompression therapy reduced statistically significance the pain, LLD, and increased statistically significance the muscle power and flexibility increased the muscle power(p<.05). This study showed that spinal decompression therapy does affect pain, LLD, and muscle power and flexibility in patient with low back pain.