• Journal of Biomedical Engineering Research
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• v.45 no.2
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• pp.66-74
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• 2024

This study analyzed the occurrence of abnormal muscle coactivations based on the assistance of upper limb weight during reaching task in stroke patients. Nine chronic stroke survivors with hemiplegia performed reaching tasks using a programmable haptic robot. Electromyography (EMG) coactivation levels in the upper limb muscles were analyzed using a linear model describing the activation levels of two muscles when the patient's upper limb weight was assisted at 0%, 25%, and 50%. As the upper limb weight assistance of the haptic robot decreased, the magnitude of the EMG signal in both the deltoid and biceps muscles increased simultaneously on both the paretic and non-paretic sides. However, no difference was found between the paretic and non-paretic sides when comparing the slope of the linear model describing the activation relationship between the deltoid and biceps. The aforementioned results suggest that in some stroke survivors, the deltoids, triceps, and biceps on the paretic side may not be abnormally coupled when supporting the upper limbs against gravity. Furthermore, these results suggest that the combination of haptic robots and EMG analysis might be utilized for evaluating abnormal coactivations in stroke patients.

• Journal of the Korean Wood Science and Technology
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• v.35 no.2
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• pp.29-38
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• 2007

This study was undertaken to investigate the variation of equilibrium moisture content (EMC) in transverse direction and three different directional (longitudinal, radial, and tangential) linear movements, and diffusion coefficients within a tree disc of Korean red pine (pinus densiflora). The EMC gradually increased in heartwood from pith. Therefore, the chemical components might differ even in heartwood and the radial variation in EMC might have a close relationship with the cellulose content within a cross section. The specific gravity increases gradually from pith and the porosity has not direct influence on the variation of EMC within a tree disk. Both the radial and tangential diffusion coefficients exhibited clear trend of increase from pith. The EMC change (${\Delta}EMC$) and tangential diffusion coefficient were close to be axisymmetrical but others were deviated from axisymmetry. The diffusion coefficient decreases with decreasing an activation energy and specific gravity, The diffusion coefficient increased with increasing ${\Delta}EMC$ and hygroscopicity of wood might be inversely proportional to the activation energy, The fJEMC may depend on the chemical constituents of cellulose, hemicellulose and lignin. As the number of sorption sites and sorption capacity of wood increase, therefore, it might be assumed that the hygroscopicity of wood increases while activation energy decreases. Modeling physico-mechanical behavior of wood, the variations should be considered to improve the accuracy.

• The Korean Journal of Pain
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• v.22 no.3
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• pp.210-215
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• 2009

Background: Several studies have indicated that a nerve injury enhances the expression of the voltage-gated calcium channel ${\alpha}2{\delta}1$ subunit (Cav ${\alpha}2{\delta}1$) in sensory neurons and the dorsal spinal cord. This study examined whether NMDA receptor activation is essential for Cav ${\alpha}2{\delta}1$-mediated tactile allodynia in Cav ${\alpha}2{\delta}1$ overexpressing transgenic mice and L5/6 spinal nerve ligated rats (SNL). These two models show similar Cav ${\alpha}2{\delta}1$ upregulation and behavioral hypersensitivity, without and with the presence of other injury factors, respectively. Methods: The transgenic (TG) mice were generated as described elsewhere (Feng et al., 2000). The left L5/6 spinal nerves in the Harlan Sprague Dawley rats were ligated tightly (SNL) to induce neuropathic pain, as described by Kim et al. (1992). Memantine 2 mg/kg (10 ul) was injected directly into the L5/6 spinal region followed by $10{\mu}l$ saline. Tactile allodynia was tested for any mechanical hypersensitivity. Results: The tactile allodynia in the SNL rats could be reversed by an intrathecal injection of memantine 2 mg/kg at 1.5 hours. The tactile allodynia in the Cav ${\alpha}2{\delta}1$ over-expressing TG mice could be reversed by an intrathecal injection of memantine 2 mg/kg at 1.5, 2.0 and 2.5 hours. Conclusions: The behavioral hypersensitivity was similar in the TG mice and nerve injury pain model, supporting the hypothesis that elevated Cav ${\alpha}2{\delta}1$ mediates similar pathways that underlie the pain states in both models. The selective activation of spinal NMDA receptors plays a key role in mediating the pain states in both the nerve-injury rats and TG mice.

• Composites Research
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• v.15 no.6
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• pp.8-15
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• 2002

In this work, the effect of biodegradable poly(butylene succinate)(PBS) in difunctional epoxy(21:P) resin was investigated in terms of rheological properties, cure kinetics, thermal stabilities, and mechanical interfacial properties. Rheological properties of the blend system were measured under isothermal condition using a rheometer. Cross-linking activation energies($\textrm{E}_c$) were determined from the Arrhenius equation based on gel time and curing temperature. The $\textrm{E}_c$ was increased in the presence of 10 wt% PBS as compared with neat 2EP. From the DSC results of the blends, the cure activation energies($\textrm{E}_a$) showed a similar behavior with $\textrm{E}_c$ due to the increased intermolecular interaction between 2EP and PBS. The decomposed activation energies($\textrm{E}_t$) for the thermal stability derived from the integral method of Horowitz-Metzger equation, were also increased in 10 wt% PBS. In addition, 20 wt% PBS showed the highest critical stress intensity factor($\textrm{E}_{IC}$). which was explained by increasing the fracture toughness of the 2EP/PBS blend systems.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.181-186
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• 2001

JLF-1 steel (Fe-9Cr-2W-V-Ta), low activation ferritic steel, is one of the promising candidate materials fer fusion reactor applications. High temperature fatigue life and tensile strength of JLF-1 steel and its TIG welded joints were investigated at the room temperature and $400^{\circ}C$. The strength of base metal (JLF-1) is in between those of weld metal and the HAZ. When the test temperature was increased from room temperature to $400^{\circ}C$, both strength and ductility decreased for base metal, weld metal and the HAZ. The longitudinal specimens of base metal showed similar strength and ductility compared with those of the transverse specimens at room temperature and $400^{\circ}C$. Little anisotropy was observed in the JLF-1 steel base metal in terms of rolling direction. Fatigue limit of weld metal which was obtained from cross-weld specimen is 495MPa. Thus, the weld metal showed the higher fatigue limit than those of base metal at both room temperature and $400^{\circ}C$. Little anisotropy of fatigue properties was observed for JLF-1 base metal in terms of rolling direction. When the test temperature was increased from room temperature to $400^{\circ}C$, the fatigue limit of both base metal and weld metal decreased substantially.

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

• Physical Therapy Korea
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• v.16 no.2
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• pp.1-8
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• 2009

Anticipatory postural adjustments is an example of the ability of the central nervous system to predict the consequence of the mechanical effect of movement on posture and helps minimize a forth coming disturbance. The aim of this study was to evaluate the sequence of activation of the trunk muscles during the performance of hip and shoulder movement and to determine the relationship between anticipatory activity and subjects' motor and functional status in subjects with hemiplegia post stroke. Twenty-four poststroke hemiparetic patients enrolled in this study. Electromyographic activity of the lumbar erector spinae, latissimus dorsi, and of the obliquus internus muscles was recorded bilaterally during flexion of both arm and from the rectus abdominis, obliquus externus, and obliquus internus muscles during flexion of both hip. Onset latencies of trunk muscles were partially delayed in the subjects with hemiplegia post stroke (p<.05). With upper limb flexion, the onset of erector spinae muscle and latissimus dorsi muscle activity preceded the onset of deltoid on both side respectively (p<.05). A similar sequence of activation occurred with lower limb flexion. Also the onset of external oblique muscle and rectus abdominis muscle activity preceded the onset of rectus femoris muscle on both side (p<.05). Major impairments in the activity of trunk muscles in hemiparetic subjects were manifested in delayed onset between activation of pertinent muscular pairs. These problems were associated with motor and functional deficits and warrant specific consideration during physical rehabilitation of post stroke hemiparetic patients.

• Nuclear Engineering and Technology
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• v.43 no.3
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• pp.279-286
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• 2011

The aging degradation and lifetime assessment of a domestic class 1E Ethylene-Propylene-Diene-Monomer (EPDM), which is a popular insulating elastomer for electrical cables in the nuclear power plants, were studied for equipment qualification verification under the Loss of Coolant Accident (LOCA) conditions. The specimens were acceleratively aged, underwent a LOCA environment, as well as tested mechanically, thermo-gravimetrically, and spectroscopically according to the American Society of the Testing of Materials (ASTM) procedures. The tensile test results revealed that the elongation at break gradually decreased with an increasing aging temperature. The lifetime of EPDM aged isothermally at $140^{\circ}C$ was 1,316 hours and reduced to 1,120 hours after experiencing the severe accident test. The activation energies of the elongation reduction were $1.10{\pm}0.196$ eV and $0.93{\pm}0.191$ eV before and after the LOCA condition, respectively. The TGA test results also showed that the activation energy of the aging decomposition decreased from 1.35 eV to 1.02 eV after undergoing the LOCA environment. Although the mechanical property changes were discernibly observed during the aging process, along with the LOCA simulation, the FT-IR analysis showed that the spectroscopic peaks and their intensities did not alter significantly. Therefore, it can be concluded that the degradation of the domestic class 1E EPDM due to aging can be tolerable, even in severe accident conditions such as LOCA, and thus it qualifies as a suitable insulating material for electrical cables in the nuclear power plants.

• Corrosion Science and Technology
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• v.9 no.5
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• pp.223-232
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• 2010

NiTi alloy has been used for orthodontic wire due to good mechanical properties, such as elastic strength, friction resistance, and high corrosion resistance. Recently, these wire were coated by polymer and ceramic materials for aesthetics. The purpose of this study was to investigate electrochemical characteristics of tooth colored NiTi wire using various instruments. Wires (round type and rectangular type) were used, respectively, for experiment. Polymer coating was carried out for wire. Specimen was investigated with optical microscopy (OM), field emission scanning electron microscopy (FE-SEM) and energy dispersive x-ray spectroscopy (EDS). The corrosion properties of the specimens were examined using potentiodynamic tests (potential range of -1500 ~ 2000 mV) and electrochemical impedance spectroscopy (frequency range of 100 kHz ~ 10 mHz) in a 0.9 % NaCl solution by potentiostat. From the results of polarization behavior, the passive region of non-coated NiTi wire showed largely, whereas, the passive region of curved NiTi wire showed shortly in anodic polarization curve. In the case of coated NiTi wire, pitting and crevice corrosion occurred severely at interface between non-coated and coated region. From the results of EIS, polarization resistance(Rp) value of non-coated round and rectangular NiTi wire at curved part showed $5.10{\times}10^5{\Omega}cm^2$ and $4.43{\times}10^5{\Omega}cm^2$. lower than that of coated NiTi wire. $R_p$ of coated round and rectangular NiTi wire at curved part showed $1.31{\times}10^6{\Omega}cm^2$ and $1.19{\times}10^6{\Omega}cm^2$.

• Journal of Biomedical Engineering Research
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• v.39 no.4
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• pp.168-174
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• 2018

Adipocytes affect obesity through the regulation of lipid metabolism. Physical loading is an important regulator of fat tissue. There are ongoing in vitro studies inducing mechanotransduction on 3T3-L1 preadipocytes with mechanical stimulus in order to treat obesity by inhibiting adipogenesis and provoking cell death. In this study, our goal was to suggest a new therapy for obesity by investigating whether fluid shear stress (FSS) changes transcription factors on 3T3-L1 related with adipogenesis and cell death. FSS loading was applied to 3T3-L1 preadipocytes at 1Pa and 1Hz. After loading, bright field images were taken and an immunofluorescence assay was conducted to observe actin stress fiber formation. Western blot analysis was conducted to identify the activation of the ERK pathway as well as the adipogenic factors, which including C/EBPs and $PPAR{\gamma}$. The expression of osteopontin, a protein related to inflammation in adipose tissue, and cell death related factors, Bax, Bcl-2, and Beclin, were also measured. Results showed that FSS stimulated the formation of actin stress fibers in 3T3-L1 and also that the activation of C/EBPs decreased significantly when compared with the control group. $PPAR{\gamma}$ activation in the 2 hour FSS group was lower than the 1 hour FSS group, which implied that the results were time dependent. Additionally, there were no differences in the expression of cell death factors after FSS loading. In summary, similar to other fibroblasts, the formation of actin stress fibers induced by mechanotransduction may affect the differentiation of 3T3-L1, leading to inhibition of adipogenesis and inflammation.