• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.6
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• pp.87-94
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• 2002

As a section insulator dividing the electric railroad catenaries with different phases, the AC/DC section insulator which divides AC and DC railroad catenary have the complex structure, and suffer irregular abrasion on the surface or insulator rods when it is installed at the underground railroad. This paper intended as an investigation of the irregular abrasion of section insulators, provides the field measurements of abrasion level along insulator length and the abrasion patterns. The height variation of insulator parts and the balding length of insulators against pantograph's contact force are analysed experimentally, and the irregular abrasion mechanism is clarified with the help of theoretical analysis on the interaction between pantographs and section insulators. On the basis of experimental and theoretical analysis, the countermeasures to reduce the irregular abrasion are provided too.

• The Journal of Korean Physical Therapy
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• v.9 no.1
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• pp.127-145
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• 1997

The purpose of this study wa9 to analyse the gait patterns of two female children with hemiplegic cerebral palsy by using the three-dimensional video motion analysis technique. Case 1 has mild spastic hemiplegia on the right side while Case 3 has moderate spastic hemiplegia on the left side. A group of 10, normal female children of the same age(7-8 years old) were selected as the control group for comparison. Time and distance variables as well as the Center of Mass displacement, and the pelvic and joint motions in three anatomical planes were analysed for this purpose. The following observations were made through the analysis : Case 1 revealed an asymmetrical gait pattern in which the step length of the unaffected side was shorter than that of the affected side, which wan a result of the effort to minimize loading on the affected leg by shortening the swing phase of the unaffected leg. Case 1 scored similar phase ratios, cadence and walking velocity to the normal group. A slight posterior tilt of the pelvis was observed throughout the gait cycle. Less hip and knee flexion than the normal group was observed, and demonstrated hyperextension of the knee in the terminal stance phase. The main problem in case 1 originated from the insufficient dorsiflexion of the affected foot during the swing phase. Therefore, Case 1 has difficulty with foot clearance in the swing phase. Usually, this is compensated for by using exessive hip abduction and medial rotation in conjuction with trunk elevation as well as increased vortical displacement of the center of mass. Case 1 revealed a foot-flat initial contact pattern. Case 2 was characterized by a consistent retraction ef the affected aide of the body througout the gait cycle, As a result, an asymmetrical gait pattern with increased stance phase ratios of the unaffected side was observed. In spite of this the step lengths of both sieds were similar. Case 2 scored lower cadence and walking speed than the normal group with lower gait stability. The main problem in Case 2 originated from an excessive plantaflexion of the affected foot which, in turn, rebutted in high hip and knee flexion. Hyperextension of the knee was observed at mid-stance, and execessive anterior tilt of the pelvis throughout the gait cycle was noticed. A gait pattern with high hip abduction and medial circumduction was maintained for the stability in the stance phase and foot clearance in the swing phase. Case 2 revealed a forefoot-contact initial contact pattern.

• Journal of Periodontal and Implant Science
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• v.34 no.1
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• pp.177-193
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• 2004

Several experimental studies showed that the application of small amounts of electric current to bone stimulated osteogenesis at the site of the cathode and suggested that electrical currents promote osseointegration around dental implants. The purpose of this study was to determine the effect of direct microcurrent to endosseous titanium implants placed in bone defects. The right and left 2nd, 3rd and 4th mandibular premolars in ten mongrel dogs (15Kg of weight) were extracted. One monthe later, Ti-machined screw type implants(3.8 mm diameter x 8.5 mm length, $AVANA^{(R)}$, Ostem) were placed in surgically created circumferential defect area(width 5mm, depth 4mm). The implants were divided into three groups according to the treatment modalities: Control group- implants without electrical stimulation; Experimental group I- implants with allogenic demineralized freeze dried bone grafting; and Experimental group II-implants allogenic demineralized freeze dried bone grafting and electric stimulation. The animals were sacrificed in the 4th and 8th week after implant placement and un-decalcified specimens were prepared for histological and histometrical evaluation of bone-implant contact ratio (BIC) and bone formation area ratio (BFA) in defect area. Some specimens at 8 weeks after implantation were used for removal torque testing. Histologically, there was connective tissue infiltration in the coronal part of defect area in control and the experimental group I, whereas direct bone contact was found in the experimental group II without connective tissue invasion. Average BIC ratios at 4 weeks of healing were 60.1% in the experimental group II, 47.4% in the experimental group I and 42.7% in the control. Average BIC ratios at 8 weeks after implantation were 67.6% in the experimental group II, 55.9% in the experimental group I and 54.6% in the control. The average BFA ratio was 84.0% in the experimental group II, 71.8% in the experimental group I and 58.8% in the control at 4 weeks, and the BFA ratios were 89.6% in the experimental group II, 81.4% in the experimental group I and 70.5% in the control at 8 weeks after implantation. The experimental group II showed also significantly greater BIC and BFA ratios compared to the control and the experimental group I (p<0.05). The removal torque values at 8 weeks after implantation were 56 Ncm in the experimental group II, 49 Ncm in the experimental group I and 43 Ncm in the control. There was a statistically significant difference among 3 groups (p<0.05). These results suggest that electrical stimulation improve and accelerate bone healing around endosseous titanium implants in bone defect.

• The Journal of Korean Academy of Prosthodontics
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• v.42 no.5
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• pp.556-571
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• 2004

Statement of problem: Surface texture of the implant is one of the important factors of the implant success, especially in the immediate implant loading. Many methods of the surface treatment of implant have developed and introduced. Purpose : This study was to evaluate the effects of the Ca-P coating implant crystallized the hydroxyapatite on the surface by the removal torque test and the histomorphometric analysis in vivo. Material and methods: 135 screw type implants, 4.0mm in length and 3.75mm in diameter were used in this study. Implants were divided into 3 groups and treated in the different mothods. Group I was not treated, Group II was treated in the SLA method, and Group III was treated in the Ca-P coating with the anodizing method and the hydroxyapatite was crystallized on the surface with the hydrothermal treatment. Firstly, the surface roughness of each group was measured, 45 rabbits were used in this experiment. Two implants were inserted on right tibial metaphysis and one implant was inserted on left side with the alternating order. After the healing periods of 3, 5, and 12 weeks, the rabbits were sacrificed to evaluate the osseointergration by the removal torque test and the histomorphometric analysis. Results : 1. In the analysis for the surface roughness, Group II showed the highest roughness. And Group III showed higher secondly. There was a significant difference one another statistically 2. In the removal torque test, Group III and II were significantly higher than Group I. There was no statistical difference between Group III and Group II. 3. For all Groups, the removal torque values at 12th week were significantly higher than at 3rd and 5th week. 4. In histomorphometric analysis, the bone implant contact rates of Group III and II were higher than that of Group I at 3rd and 5th week. There was a significant difference at 5th week. 5. In histomorphometric analysis, the bone implant contact rate of Group III and II increased from 3rd week to 5th week, but decreased at 12th week. In Group I, the contact rate at 12th week was significantly higher than at 3rd week and 5th week.

• Journal of the Korean institute of surface engineering
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• v.46 no.4
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• pp.145-152
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• 2013

The growth behavior of nanocrystalline diamond (NCD) film has been studied for three different substrates, i.e. bare Si wafer, 1 ${\mu}m$ thick W and Ti films deposited on Si wafer by DC sputter. The surface roughness values of the substrates measured by AFM were Si < W < Ti. After ultrasonic seeding treatment using nanometer sized diamond powder, surface roughness remained as Si < W < Ti. The contact angles of the substrates were Si ($56^{\circ}$) > W ($31^{\circ}$) > Ti ($0^{\circ}$). During deposition in the microwave plasma CVD system, NCD particles were formed and evolved to film. For the first 0.5h, the values of NCD particle density were measured as Si < W < Ti. Since the energy barrier for heterogeneous nucleation is proportional to the contact angle of the substrate, the initial nucleus or particle densities are believed to be Si < W < Ti. Meanwhile, the NCD growth rate up to 2 h was W > Si > Ti. In the case of W substrate, NCD particles were coalesced and evolved to the film in the short time of 0.5 h, which could be attributed to the fact that the diffusion of carbon species on W substrate was fast. The slower diffusion of carbon on Si substrate is believed to be the reason for slower film growth than on W substrate. The surface of Ti substrate was observed as a vertically aligned needle shape. The NCD particle formed on the top of a Ti needle should be coalesced with the particle on the nearby needle by carbon diffusion. In this case, the diffusion length is longer than that of Si or W substrate which shows a relatively flat surface. This results in a slow growth rate of NCD on Ti substrate. As deposition time is prolonged, NCD particles grow with carbon species attached from the plasma and coalesce with nearby particles, leaving many voids in NCD/Ti interface. The low adhesion of NCD films on Ti substrate is related to the void structure of NCD/Ti interface.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.3
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• pp.362-374
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• 2007

Statement of problem. The intial stability for osseointegration of implant has been an interesting factor. Especially, in the case of poor bone quality or immediately loaded implant, various strategies have been developed focusing on the surface of materials to improve implant fixation to bone. The microscopic properties of implant surfaces play a major role in the osseous healing of dental implants. Purpose. The aims of this study are to perform a histologic and histomorphometric comparison of the healing characteristics of three different surfaces and the comparison of resonance frequency analysis (RFA) values measured by $Osstell^{TM}$ and perio-test values (PTV) measured by Periotest. Material and methods. A total of 24 screw titanium implants (Dentium Co., Seoul, Korea) with 6mm in length and 3.4mm in diameter, were placed in the mandible of 4 beagle dogs. Implants were divided into three groups following the surface treatment methods: Group I is machined(control group). Group II is anodically oxidized. Group III is coated 500nm in thickness with hydroxyapatite(HA) by ion beam assisted deposition(IBAD) on the anodized oxidization. Bone blocks from 2 dogs were caught after 3 weeks of covered healing and another blocks from 2 dogs after 6 weeks. RFA values and PTV were measured right after insertion and at 3 and 6weeks. Histomorphometric analysis was made with Kappa Image Base System to calculate bone-to-implant contact (BIC) and bone area inside the threads. Pearson's correlation analyses were performed to evaluate the correlation between RFA and PTV, BIC and bone area ratio of three different surfaces at 3 and 6 weeks. Results. 1) In all surface treatment methods, the RFA values decreased and the PTV values increased until 6 weeks in comparison to initial values. 2) At 3 weeks, no significant difference was found from bone-to-implant contact ratio and bone area ratio of three different surface treatment methods(P>0.05). However, at 6 weeks, different surface treatment methods showed significantly different bone-toimplant contact ratio and bone area ratio(P<0.05). 3) In the implants with the IBAD on the anodic oxidization, significant difference was found between the 3 weeks and the 6 weeks bone area ratio(P<0.05). 4) Correlation was found between the RFA values and the bone area ratio at 3 and 6 weeks with significant difference(P<0.05). Conclusions. These results indicate that the implants with the IBAD on the anodic oxidization may have a high influence on the initial stability of implant.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.22 no.3
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• pp.274-287
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• 2000

The use of dental implants has increased tremendously in recent years and is expected to increase even more in the future. The successful outcome of any implant procedure is surely dependent on interrelationship of the various components of an equation that includes biocompatibility of implant material, macroscopic and microscopic nature of the implant surface, the status of implant bed, surgical technique, undisturbed healing phase and subsequent prosthetic design and long-term loading phase. The purpose of this study was to clarify the effects of adrenalectomy on the osseointegration of pure titanium implants. Seventy rats, 11 weeks of age, were divided into two groups : an adrenalectomized group and a control group. Titanium screw implant(diameter, 2.0mm; length, 3.5mm) was placed into left tibia of 70 rats, 35 in control group and 35 in the experimental group. The rats were sacrificed at different time interval (1, 2, 3, 4, 6, 8, and 12 weeks after implantation) for histopathologic observation, histomorphometric analysis and immunohistochemistry with fibronectin and CD44 antibody. The results obtained from this study were as follows: 1. Histopathogically, findings, newly formed bone was seen at 3 weeks control group and became lamellar bone at 12 weeks. At 6 weeks, lipocytes were observed in bone marrow space. Thickness of regenerated trabecular bone increased till 6 weeks after then, that decreased gradually. 2. By histomorphometric analysis, marrow bone density and contact ratio of marrow bone to implant decreased significantly from 8 to 12 weeks in experimental group compared to control group and also total bone to implant contact ratio decreased significantly from 4 to 12 weeks in experimental group compared to control group. 3. Fibronectin immunoreactivity was very strong at 3 and 4 weeks control group. And after that reduced gradually. But it was continuously strong from 1 to 12 weeks experimental group. 4. CD44 immunoreactivity was very strong in the newly formed osteoblasts at 3 and 4 weeks control group. But it reacted minimally later. However, it reacted continuously strong from 3 to 12 weeks experimental group. From these results, bone to implant contact ratio decreased gradually from 4 weeks in adrenalectomized group compared to control group. CD44 and fibronectin immunoreactivities were strong at all times in adrenalectomized rats. Therefore, it could be stated that immature bone remained continuously for a long time and not readily proceeded into mature status.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.226-228
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• 2007

During asymmetrical cold rolling in AA 5052 sheet a reduction per a rolling pass was varied to investigate the effect of the ratio of the contact length between the roll and sample ($l_c$) to the sheet thickness (d) on the formation of shear textures. In order to intensify the shear deformation during asymmetrical rolling, AA 5052 sheet was asymmetrically cold rolled without lubrication by using different roll velocities of upper and lower rolls. Asymmetrical rolling with $l_c$/d=1.8 led to the formation of texture gradients throughout the sheet thickness in which the outer thickness layers depicted shear textures and the center thickness layers displayed a rolling texture. Asymmetrical rolling with $l_c$/d=3.1 gave rise to the formation of shear textures in the whole through-thickness layer. The strain states associated with asymmetrical rolling were investigated by the finite element method (FEM) simulation. FEM results indicated that the evolution of deformation texture in a thickness layer is strongly governed by integrated values of strain rates and along the streamline in the roll gap.

• Physical Therapy Rehabilitation Science
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• v.1 no.1
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• pp.22-27
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• 2012

Objective: Falls are defined as contact of the body with the floor after losing balance during activities of daily living. Falls commonly occur among the elderly, and stroke patients in particular are at a high risk of falling. The purpose of this study was to investigate the changes of temporal and spatial gait parameters and gait symmetry according to experience falls in post-stroke patients. Design: Cross-sectional study. Methods: Fifty three patients with stroke were recruited on a voluntary basis from the rehabilitation unit, who currently undergoing physical therapy. All participants were asked to answer questions regarding the frequency of falls in the past 1 year. Fifty-three patients with stroke were allocated 2 groups according to experienced falls: stroke with falls (n=26) during past 1 year and stroke without falls (n=27). The spatial and temporal gait parameters and gait symmetry ratio were measured using GAITRite system. Results: The spatial gait parameters and the temporal gait parameters were significantly different between the stroke with falls group and the stroke without falls group (p<0.05). Furthermore, step length was the only significantly different among symmetry ratio (p<0.05). Conclusions: Experience of falls can lead to impairment of gait ability in stroke patients. This result is expected to be used as a basic data for rehabilitation program development to prevent a fall of post-stroke patients.

• Journal of the Korean Ceramic Society
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• v.49 no.5
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• pp.417-422
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• 2012

Copper nano particles have been considered as the materials for conductive ink due to its good thermal, electrical conductivity and low cost. However, copper nanoparticles oxidize easily, decreasing dispersion stability and electrical conductivity. Therefore, it is important to develop a method to minimize oxidation of copper nano particles to improve its dispersion stability property in copper nano ink. In this study, copper nano particles were coated with 1-Octanethiol VSAM(Vaporized Self Assembled Multilayers) to prevent oxidation and coated copper powders were dispersed in conductive ink successfully by studying its relationship of different chain length of solvents to 1-Octanethiol coating layer to fabricate nano ink. Various alcohol solvents, such as 1-Hexanol, 1-Octanol, and 1-Decanol were used. The coating layer was observed using FESEM and TEM. Furthermore, dispersion of copper nano particles in nano inks, was characterized using Turbiscan analyzer, viscometer, and contact angle measurement tool.