• The Journal of Korean Academy of Prosthodontics
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• 제31권4호
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• pp.643-659
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• 1993

This study was performed for the purpose of evaluating the stress distributions around five different types of implants according to their structures. The stress distribution around the surrounding bone was analysed by two-dimensional photoelastic method. Five epoxy resin models were made, and vertical and lateral forces were applied to the models. A circular polariscope was used to record the isochromatic fringes. The results of this study were summerized as follows : 1. Threaded type implants showed more even stress distribution patterns than cylinderical type implants when vertical and lateral forces were applied. 2. The stress concentrated patterns were observed at the neck portion and middle portion of the cylindrical type implants comparing with threaded type implants when vertical force was applied. 3. Model 1 and model 4 which are tthreaded type implants showed similar stress distribution patterns at the middle and apical portions and more stress was concentrated at the neck porion of model 1 comparing with model 4 when vertical force was applied. The stresses around model 1 were more evenly distributed when lateral force was applied. 4. More stress was concentrated at the neck and middle portion of cylindrical type implants than threaded type implants when lateral force was applied. 5. Model 1 showed the most even stress distribution patterns when lateral force was applied and stress distribution did no occured at the apical portion of modedl 2 when lateral force was applied. 6. There were almost no differences in stress concentrated patterns with or without having hollow design. And the stress concentrated patterns were observed at the corner of apex in model 5 which has hollow design when vertical force was applied.

• The korean journal of orthodontics
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• 제19권2호
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• pp.57-73
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• 1989

The purpose of this study was to investigate the tissue response of the rat molar periodontium incident to intermittent orthodontic force. The author intended to observe the healing process of injured periodontium and the response of injured tissue to the resumed force. Oxytetracyclin 50mg/Kg was given to each rat intraperitonially. 5 days later, maxillary 1st molars were moved mesially from the incisors with closed coil spring of 100gram. 7 days later, the appliances were removed and 20mg/Kg of calcein were given intraperitonially to each rat. At the same time, maxillary left 1st molars of 15 rats were moved by the same method, but force was lowered to 20 gram. After 1 day, maxillary left 1st molars of another 15 rats were moved by the same method and 50mg/Kg of oxytetracycline was given intraperitonially. After 4 days, another 15 rats were treated as above. After 7 days, another 15 rats were treated as above. 1,4,7,10 and 14 days after change of force, 3 rats were sacrificed in each group respectively. 2 rats were decalcified, embedded in paraffin, and stained with hematoxylin-eosin stain and with Masson's trichrome stain. Another rat was embedded in polyester resin and undecalcified specimen were made. Microradiograms were taken with the undecalcified sections. Observations were made with light and fluorescence microscope. Following conclusions were made. 1. Connective tissue cells and vessels were infiltrated into the hyalinized tissue from the bony cleft and along the border of the hyalinized tissue with bone and root surface. At the same time, elimination of hyalinized tissue, bone and root resorption occurred. 2. Bone and root were resorbed directly and indirectly. 3. Hyalinized tissue was removed within 5 days after force removal. 4. Hyalinized zone was less extensive and easily removed as the rest period prolonged. 5. Hyalinized tissue developed more rapidly and extensively and lasted over 10 days as the force resumed on the already formed hyalinized tissue.

• Interaction and multiscale mechanics
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• 제5권1호
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• pp.75-90
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• 2012

This paper investigates the effects of sports ground materials on the transfer characteristics of the landing impact force using a coupled foot-shoe-ground interaction model. The impact force resulting from the collision between the sports shoe and the ground is partially dissipated, but the remaining portion transfers to the human body via the lower extremity. However, since the landing impact force is strongly influenced by the sports ground material we consider four different sports grounds, asphalt, urethane, clay and wood. We use a fully coupled 3-D foot-shoe-ground interaction model and we construct the multi-layered composite ground models. Through the numerical simulation, the landing impact characteristics such as the ground reaction force (GRF), the acceleration transfer and the frequency response characteristics are investigated for four different sports grounds. It was found that the risk of injury, associated with the landing impact, was reduced as the ground material changes from asphalt to wood, from the fact that both the peak vertical acceleration and the central frequency monotonically decrease from asphalt to wood. As well, it was found that most of the impact acceleration and frequency was dissipated at the heel, then not much changed from the ankle to the knee.

• Journal of the Korean Society for Precision Engineering
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• 제30권5호
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• pp.529-536
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• 2013

Most serious stroke patients have the paralysis on their wrists, and can't use their hands freely. But their wrists can be recovered by rehabilitation exercises. Recently, professional rehabilitation therapeutists help stroke patients exercise their wrists in hospital. But it is difficult for them to rehabilitate their wrists, because the therapeutists are much less than stroke patients in number. Therefore, the wrist twist-exercise rehabilitation robot that can measure the twist force of the patients' wrists is needed and developed. In this paper, the six-axis force/moment sensor was designed appropriately for the robot. As a test result, the interference error of the six-axis force/moment sensor was less than 0.85%. It is thought that the sensor can be used to measure the wrist twist force of the patient.

• Journal of the Korean Society of Safety
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• 제27권5호
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• pp.1-8
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• 2012

The purpose of this study were to evaluate the dynamic characteristics of the portable slipmeters with respect to actual slipping and to compare their output with those of force platform. The selected slipmeters were commonly used devices for slipperiness measurement in situ floors. Their output quantity represented force (BOT-3000), loss of energy(British pendulum striker) and angle of inclination(English XL). The validity of these devices was studied with respect to actual slipping using a force platform. The precision of these devices was also evaluated with force platform. Based on dynamics of human subject behavior when slipping during normal walking, the all devices tested in this study showed poor performances: low built up ratio, low normal pressure, and long contact time prior to slip. Nevertheless, their results reasonably correlated with those calculated from the ground reaction forces generated by the operation of the selected slipmeters on the force platform although the absolute values of COF from these three devices could be quite different. Also the results showed good repeatability under the some test conditions.

• Journal of the Ergonomics Society of Korea
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• 제35권5호
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• pp.413-423
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• 2016

Objective:The aims of this study are to understand the effects of task (pushing, pulling, and clockwise and counter clockwise twisting) direction on the maximal output and their grip forces and to explore the relationship between the maximal output and the grip forces. Background: Knowing the normative maximal grip force is not enough to design a good hand tool. The industrial designers should understand the required grip forces in various motions toward a specific direction to make an effective and efficient hand tool. Method: Eighteen healthy volunteers participated in the series of isometric maximal output force tests. A custom-made force measuring equipment collected the output and the grip forces for three seconds. Force measurements along the vertical, coronal and sagittal axes were randomly repeated three times. Results: The pulling was strongest and the pushing was weakest in all directions. The effect of motion on the output forces varied in different directions. The corresponding grip force increased in the order of pushing, pulling, clockwise twisting, and counter clockwise twisting in all directions. The maximal output and their grip forces were highly correlated but the relationship was affected by motion and direction. The regression coefficient was greatest in pulling and smallest in clockwise twisting. Conclusion: The effect of motion on the output forces varied in different directions. The maximal output and their grip forces were correlated but the relationship was affected by motion and direction. Application: Findings of this study can be valuable information for industrial designers to develop more productive hand tools and work stations to help preventing the musculoskeletal disorders at work.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제24권5호
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• pp.1305-1313
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• 2000

In a co-rotating scroll compressor, both scrolls rotate on their fixed axes contrary to the conventional orbiting type scroll machine. This implies fixed locations and directions of the gas pressure force and sealing force. Because the tilting moment is mainly caused by interplay between the resultant force of above forces and bearing reaction force, the variation during one cycle is relatively small. Under real operation, this moment is balanced by the restoring moment created by the reaction between the baseplate and thrust bearing or between the scroll tip and baseplate. If these reactions become too large, greater torque is required due to increased friction in addition to the wear of mating parts. Consequently, appropriate study and minimization of tilting moment is important in the design of scroll machines. In this study, taking into account of the small variation of tilting moment during one cycle, we minimize the moment and thrust bearing reaction force by a properly designed back pressure chamber. As a result, for both the driving and driven scrolls, the tilting moment and the reaction force of thrust bearing can be minimized. And the stability is improved for all cases.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제41권5호
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• pp.415-420
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• 2017

Underactuated prosthetic hands are relatively light and economical. In this work, an economical grasping force control system is proposed for underactuated prosthetic hands with adaptive grasp capability. The prosthetic hand is driven by a main cable based on a set of electromyography sensors on the forearm of a user. Part of the main cable tension related to grasping force is fed back to the user by a skin-mounted vibrator. The proper relationship between the grasping force and the vibrator drive voltage was established and prototype tests were performed on a group of users. Relatively accurate grasping force control was achieved with minimal training of users.

• Computers and Concrete
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• 제20권5호
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• pp.617-625
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• 2017

Prestress force identification (PFI) is crucial to maintain the safety of prestressed concrete bridges. A synergic identification method has been proposed recently by the authors that can determine the prestress force (PF) and the excitation force simultaneously in prestressed concrete beams with good accuracy. In this paper, the ability of this method in the application with prestressed concrete box-girder bridges is demonstrated. A reasonable assumption is made to capture the similarity of the dynamic behavior of the prestressed concrete box-girder bridge and a beam under a certain loading scenario, and the feasibility of this method for application in a prestressed box-girder bridge is affirmed. A comprehensive laboratory test program is conducted, and the effects of PF, excitation, measuring time and uncertainties are studied. Results show that the proposed method can predict the PF and the excitation force in a prestressed concrete box-girder accurately and has a great robustness against uncertainties.

• Food Science of Animal Resources
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• 제32권5호
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• pp.578-583
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• 2012

The purpose of this study was to evaluate the ultrastructural and shear force changes of duck breast and leg meat during aging at $0^{\circ}C$. Pekin ducks (45 d old) purchased from Greemud Co. were used for this experiment, and were stored at $0^{\circ}C$ for 7 d in order to determine the changes of the meat structure using transmission electron microscopy (TEM) and shear force. At day 0, A-band, I-band, M-line and Z-line of sarcomeres were seen clearly, but sarcomeres started to lose structure and become extended in length from day 2. With extended aging periods, myofibrils were destroyed and symptoms of aging became more obvious. In the duck breast meat, some myofibrils were also destroyed at the Z-line, but were mainly destroyed at the M-line. The change in structure of duck leg meat over time was similar to that of breast meat. After five days and seven days of aging, mitochondria size and quantity were determined to be increased between the myofibrils. Shear force was decreased over time. From this study, aging at $0^{\circ}C$ was found to negatively influence the ultrastructure and shear force of duck meat.