• Korean Journal of Materials Research
• /
• v.12 no.7
• /
• pp.580-586
• /
• 2002

The effect of processing and designing variables such as pouring temperature(1400 or $1500^{\circ}C$), inoculation and risering design(T and H type) on the formation of defects such as external depression, primary and secondary shrinkage cavities in GC150 gray cast iron was investigated. In T type risering design, external depression or primary shrinkage cavity due to liquid contraction was formed in all of the eight cases. Regardless of its modulus value, the riser could not function properly in T type risering design because directional solidification was not promoted toward the riser. On the other hand, the four cases of H type risering design in which thermal sleeves were set onto the risers produced defect-free castings. In both types of the risering designs, secondary shrinkage cavity caused by solidification contraction was not observed in the casting because of the expansion pressure due to graphite precipitation and the application of rigid pep-set mold. The degree of external depression or primary shrinkage cavity was reduced with lowered pouring temperature. The effect of inoculation was diminished because of the high carbon equivalent of GC 150 gray cast iron.

• Korean Journal of Applied Biomechanics
• /
• v.30 no.1
• /
• pp.111-119
• /
• 2020

Objective: The purpose of this study is to apply exercise learning effect to various subjects through training effect and information accumulation based on verification of the effect on dumbbell curl exercises applied with virtual reality. Method: To analyze the effect on the dumbbell curl exercise in the virtual environment, a total of 20 persons with 10 males and 10 females who does not have orthopedics diseases were selected. The dumbbell weight of the subjects was set to a weight of 70% strength of 1RM. At this time, the virtual environment situation was set to four types; presence/absence of virtual environment, preferred colors, and unfavorable colors to perform dumbbell curl exercise. The anaysis of muscle activity was conducted by adhering four surface electrodes (Biceps Brachii, Triceps Brachii, Brachioradialis Muscle, Extensor Carpi Radialis Longus Muscle) on the right upper limbs. Independent sample t-test using SPSS (24.0) program was carried out to analyze average values and standard deviations for each variable depending on the presence/absence of virtual environments and changes in color (preferred colors, unfavorable colors) and the level of significance was set to a=.05. Results: In the eccentric contraction, males showed high muscle activity in the Biceps Brachii under virtual reality. On the other hand, females had high muscle activity in the Biceps Brachii in the absence of virtual reality. Also, in case of a change of colors in the virtual environment, females had the high muscle activity in the unfavorable color in the eccentric contraction. Conclusion: During the dumbbell curl exercise, results of different exercises present depending on gender. When males put VR on and performs a basic dumbbell curl exercise, the effect of Biceps presents Brachii for them while exercising in unfavorable colors. However, since it is the basic research data of muscle exercise using virtual reality, it is necessary to verify whether or not it is effective for myopachynsis through long-term training rather than unity.

• Journal of the Ergonomics Society of Korea
• /
• v.30 no.6
• /
• pp.689-694
• /
• 2011

Objective: The aim of this study is to evaluate the fluctuation of signal amplitude during repetitive dynamic contraction based on surface electromyography(EMG). Background: The most previous studies were considered isometric muscle contraction and they were difference to smoothing window length by moving average filter. In practical, the human movement is dynamic state. Dynamic EMG signal which indicated as the nonstationary pattern should be analyzed differently compared with the static EMG signal. Method: Ten male subjects participated in this experiment, and EMG signal was recorded by biceps brachii, anterior/posterior deltoid, and upper/lower trapezius muscles. The subject was performed to repetitive right horizontal lifting task during ten cycles. This study was considered three independent variables(muscle, amplitude processing technique, and smoothing window length) as the within-subject experimental design. This study was estimated muscular activation by means of the linear envelope technique(LE). The dependent variable was set coefficient of variation(CV) of LE for each cycle. Results: The ANOVA results showed that the main and interaction effects between the amplitude processing technique and smoothing window length were significant difference. The CV value of peak LE was higher than mean LE. According to increase the smoothing window length, this study shows that the CV trend of peak LE was decreased. However, the CV of mean LE was analyzed constant fluctuation trend regardless of the smoothing window length. Conclusion: Based on these results, we expected that using the mean LE and 300ms window length increased reproducibility and signal noise ratio during repetitive dynamic muscle contraction. Application: These results can be used to provide fundamental information for repetitive dynamic EMG signal processing.

• PNF and Movement
• /
• v.17 no.3
• /
• pp.451-461
• /
• 2019

Purpose: This study identified the effect of abdominal muscle contraction using changes in waist circumference for healthcare workers with back pain due to inadequate posture during working hours. Methods: In this study, we provided educational training focused on posture alignment and utilized waist circumference change sensors to induce the contraction of abdominal muscles as a method to address low back pain in healthcare workers. All 32 participants received the same training and then were assigned to two groups: wearing the keeping core band (CB) and not wearing the keeping core band (NCB). For the CB group, the waist circumference change sensor was applied for 6 weeks during working hours. Wilcoxon's signed-ranks test and paired t-tests were used to compare the differences between the groups. All statistical significance levels were set to α=0.05. Results: Trunk muscle endurance increased significantly in the CB group. There was no significant difference in stability index to evaluate static postural control, but active hip abduction tests, which evaluate dynamic postural control, showed significant decrease in the CB group. Conclusion: These results suggest that the induction of abdominal contraction using the waist circumference change sensor may improve the trunk muscle endurance and the postural control ability of the hip and pelvis of healthcare workers.

• PNF and Movement
• /
• v.17 no.3
• /
• pp.471-480
• /
• 2019

Purpose: This study examined the correlations between a forward head posture and the endurance and maximal voluntary contraction of the deep neck flexor, neck pain, and the changed position of the mandible. Methods: The subjects of this study were 50 male and female adults who work at a desk for at least four hours a day. The head-spine angle was photographed with a camera, and the endurance and maximal voluntary contraction of the deep neck flexor and the changed position of the mandible were measured using pressure biofeedback. The Neck Disability Index was used to measure neck pain. To examine the correlations between a forward head posture and the endurance and maximal voluntary contraction of the deep neck flexor as well as the changed position of the mandible, a Spearman's correlation analysis was conducted. The statistical significance was set at 0.05. Results: A forward head posture and the endurance of the deep neck flexor showed a statistically significant positive correlation, and a forward head posture and neck pain showed a statistically significant negative correlation. In addition, the endurance of the deep neck flexor and neck pain showed a statistically significant negative correlation. Conclusion: The results of this study show that a forward head posture and the endurance of the deep neck flexor were correlated; in addition, a forward head posture and neck pain were correlated. Therefore, enhancing the endurance of the deep neck flexor can assist in correcting an imbalanced forward head posture, which can reduce neck pain.

• Journal of the Chungcheong Mathematical Society
• /
• v.3 no.1
• /
• pp.103-110
• /
• 1990

Let K be a nonempty weakly compact convex subset of a Banach space X and T : K ${\rightarrow}$ C(X) a nonexpansive mapping satisfying $P_T(x){\cap}clI_K(x){\neq}{\emptyset}$. We first show that if I - T is semiconvex type then T has a fixed point. Also we obtain the same result without the condition that I - T is semiconvex type in a Banach space satisfying Opial's condition. Lastly we extend the result of [5] to the case, that T is an 1-set contraction mapping.

• Korean Journal of Mathematics
• /
• v.24 no.3
• /
• pp.375-395
• /
• 2016

In this paper, we study the long-time dynamical behavior for the extensible suspension bridge equations with past history. We prove the existence of the global attractors by using the contraction function method. Furthermore, the regularity of global attractor is achieved.

• Communications of the Korean Mathematical Society
• /
• v.12 no.2
• /
• pp.275-285
• /
• 1997

Let E be a uniformly convex Banach space with a uniformly G$\hat{a}teaux differentiable norm, C a nonempty closed convex subset of $E, T : C \to E$ a nonexpansive mapping, and Q a sunny nonexpansive retraction of E onto C. For $u \in C$ and $t \in (0,1)$, let $x_t$ be a unique fixed point of a contraction $R_t : C \to C$, defined by $R_tx = Q(tTx + (1-t)u), x \in C$. It is proved that if ${x_t}$ is bounded, then the strong $lim_{t\to1}x_t$ exists and belongs to the fixed point set of T. Furthermore, the strong convergence of ${x_t}$ in a reflexive and strictly convex Banach space with a uniformly G$\hat{a}$teaux differentiable norm is also given in case that the fixed point set of T is nonempty.

• Physical Therapy Korea
• /
• v.16 no.4
• /
• pp.37-43
• /
• 2009

This study compared the electromyographic activities and input performance of computer operators using a computer mouse and a trackball. Muscle activities were assessed at the upper trapezius (UT), middle deltoid (MD), extensor digitorum (ED), and first dorsal interosseous muscle (FDI). Twenty-six healthy subjects were recruited, and the test order was selected randomly for each subject. The task set was to click moving targets on a Windows program. The EMG amplitude was normalized using the percentage of reference voluntary contraction for UT and MD and the percentage of maximal voluntary contraction for ED and FDI. To analyze the differences in EMG activity, a paired t-test was used. UT muscle activities were significantly greater when the computer mouse was used (p<.05). FDI muscle activities were significantly greater when the trackball was used (p<.05). Using a trackball can reduce the load on the UT during computer work and help to prevent and manage work-related musculoskeletal disorders.

• The Journal of Korean Physical Therapy
• /
• v.22 no.2
• /
• pp.25-30
• /
• 2010

Purpose: Behavior and movement are accomplished by voluntary contractions of skeletal muscles. There are three types of muscle contractions: concentric, isometric and eccentric. The aim of our study was to determine whether there is a difference in the cortical activation pattern between concentric contraction and eccentric contraction of the wrist extensor muscle. Methods: Four healthy right-handed volunteers without any previous history of physical or neurological illness were recruited. fMRI scanning was done during 4 repeated blocks of concentric and eccentric exercise of the wrist joint. Subjects exercised for 12 seconds and then rested for 12 seconds before beginning the second set of exercises. To determine the excitability of cortical neurons during exercise, voxel count and intensity index were analyzed. Results: For right hand movements, when concentric contractions of the right wrist were done, only the left primary motor area was activated. In contrast, during eccentric contraction, both the primary motor area and secondary motor area were activated. For left hand movements, both concentric and eccentric contractions induced only the supplementary motor cortex and the contralateral primary motor cortex. Conclusion: During eccentric contractions, both the primary motor area and secondary motor area are activated in ipsilateral and contralateral brain areas. Thus, eccentric contractions require more complex and difficult movements than concentric contractions do.