• Tribology and Lubricants
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• v.31 no.1
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• pp.21-27
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• 2015

We carry out experiments to characterize textured bearing steel with varying hole density and depth. Textured surface is believed to reduce the friction coefficient, and improve performance and wearing caused by third-body contact. We employ three lubrication regime conditions based on the Stribeck curve: boundary lubrication, mixed lubrication, and hydrodynamic lubrication. Ultrasonic machining is an untraditional machining method wherein abrasive grit particles are used. The hammering process on the work piece surface by abrasive provides the desired form. In this study, we create multi-holes on the bearing steel surface for texturing purposes. Holes are formed by an ultrasonic machine with a diameter of 0.534 mm and a depth of about 2-4 mm, and they are distributed on the contact surface with a density between 1.37-2.23%. The hole density over the surface area is an important factor affecting the friction. We test nine types of textured specimens using four times replication and compare them with the untextured specimen using graphs, as well as photographs taken using a scanning electron microscope. We use Analyzes variant in this experiment to find the correlation between each pair of treatments. Finally, we report the effect of hole density and depth on the friction coefficient.

• Journal of Biomedical Engineering Research
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• v.29 no.6
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• pp.436-442
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• 2008

Magnetic resonance electrical impedance tomography(MREIT) has been suggested to produce cross-sectional conductivity images of an electrically conducting object such as the human body. In most previous studies, recessed electrodes have been used to inject imaging currents into the object. An MRI scanner was used to capture induced magnetic flux density data inside the object and a conductivity image reconstruction algorithm was applied to the data. This paper reports the performance of a thin and flexible carbon-hydrogel electrode that replaces the bulky and rigid recessed electrode in previous studies. The new carbon-hydrogel electrode produces a negligible amount of artifacts in MR and conductivity images and significantly simplifies the experimental procedure. We can fabricate the electrode in different shapes and sizes. Adding a layer of conductive adhesive, we can easily attach the electrode on an irregular surface with an excellent contact. Using a pair of carbon-hydrogel electrodes with a large contact area, we may inject an imaging current with increased amplitude primarily due to a reduced average current density underneath the electrodes. Before we apply the new electrode to a human subject, we evaluated its performance by conducting MREIT imaging experiments of five swine legs. Reconstructed conductivity images of the swine legs show a good contrast among different muscles and bones. We suggest a future study of human experiments using the carbon-hydrogel electrode following the guideline proposed in this paper.

• Korean Journal of Agricultural Science
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• v.46 no.4
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• pp.723-735
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• 2019

The power-train is the most important component of an agricultural tractor. In this study, the strength of the driving gear transmission of an 82 kW-class tractor was analyzed using equivalent torque during plow tillage. The load measurement system consisted of an engine revolution speed sensor, torque-meters, revolution speed sensors for four axles, and pressure sensors for two hydraulic pumps. The load data were measured during plow tillage for four speed stages: F2 (2.78 km/h), F5 (5.35 km/h), F7 (7.98 km/h), and F8 (9.75 km/h). Aspects of the gear-strength such as bending stress, contact stress, and safety factors were analyzed under two torque conditions: the equivalent torque at the highest plow load for the F8 speed stage and the maximum engine torque. The simulation results using KISSsoft showed that the maximum engine torque conditions had a lower safety factor than did the highest equivalent torque condition. The bending safety factors were > 1 at all gear stages, indicating that gear breakage did not occur under actual measured operating conditions, nor under the maximum torque conditions. However, the equivalent torque condition in the contact stress safety factor was > 1, and the maximum torque condition was < 1 at the first gear pair. The method of analysis using the equivalent torque showed lower stress and higher safety factor than did the method using maximum torque. Therefore, when designing a tractor by applying actual working torque, equivalent torque method would support more reliable product development.

• Macromolecular Research
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• v.11 no.5
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• pp.375-381
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• 2003

Silver salt complex membranes with glassy poly(methyl methacrylate) (PMMA) unexpectedly showed higher propylene permeance than those with rubbery poly(butyl methacrylate) (PBMA) where as neat PMMA is much less permeable to propylene than that of neat PBMA. Such unusual facilitated olefin transport has been systematically investigated by changing the side chain length of polymethacrylates (PMAs) from methyl, ethyl to butyl. The ab initio calculation showed almost the same electron densities of the carbonyl oxygens in the three PMAs, expecting very similar intensity of the interaction between carbonyl oxygen and silver ion. However, the interaction intensity decreases with the length of the alkyl side chain: PMMA > PEMA > PBMA according to wide angle X-ray scattering and FT-Raman spectroscopy. The difference in the interaction intensity may arise from the difference in the hydrophilicity of the three PMAs, as confirmed by the contact angle of water, which determines the concentrations of the ionic constituents of silver salts: free ion, contact ion pair and higher order ionic aggregate. However, propylene solubilities and facilitated propylene transport vary with the side chain length significantly even at the same concentration of the free ion, the most active olefin carrier, suggesting possible difference in the prohibition of the molecular access of propylene to silver ion by the side chains: the steric hindrance. Therefore, it may be concluded that both the hydrophilicity and the steric hindrance associated with the side chain length in the three PMAs are of pivotal importance in determining facilitated olefin transport through polymer/silver salt complex membranes.

• Journal of Astronomy and Space Sciences
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• v.16 no.1
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• pp.21-30
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• 1999

We perform CCD observations in VRI filters for AK Her during 3 nights in Feb 1997 and Mar 1998 at Mt. Sobaek National Observatory, and obtained 236 images in V, 198 in R, and 197 in I filter. From the data, we construct light curves which contain a pair primary and secondary minima and (O-C) diagram. We analyzed the obtained light curves of AK Her using the Wilson-Devinney code. From the analyses, we find that AK Her is more likely detached or semi-detached than contact system. From the (O-C) diagram, we find that the (O-C) residuals increases out of accordance with the expectation of Borkovits & Hegedus since 1990. However, we cannot identify cause of the periodic variation of the (O-C) residuals.

• Journal of Institute of Control, Robotics and Systems
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• v.11 no.7
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• pp.602-608
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• 2005

In the virtual environment, force feedback to the human operator makes virtual experiences more realistic. To ensure the safe operation and enhance the haptic feeling, stability should be guaranteed. Both motors and brakes are commonly used for haptic devices. Motors can generate a torque in any direction, but they can make the system active during operation, thus leading to instability. Brakes can generate a torque only against their rotation, but they dissipate energy during operation, which makes the system intrinsically stable. Consequently, motors and brakes are complementing each other. In this research, a two degree-of-freedom (DOF) haptic device equipped with motors and brakes has been developed to provide better haptic effects. Each DOF is actuated by a pair of motor and brake. Modeling of the environment and the control method are needed to utilize both actuators. Among various haptic effects, contact with the virtual wall, representation of friction and representation of plastic deformation have been investigated extensively in this paper. It is shown that the hybrid haptic device is more suited to some applications than the motor-based haptic device.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1071-1075
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• 2003

In a closed square cavity filled with a liquid, a cooled the upper horizontal wail and a heated the lower horizontal wall, the flow isn't generated under the ground-based condition when Rayleigh number is lower than 1700. In such case the flow phenomena near an air bubble under a cooled horizontal wall were investigated. The temperature and the flow fields were studied by using the Thermo-sensitive Liquid-Crystal and the image processing. The qualitative analysis for the temperature and the flow fields were carried out by applying the image processing technique to the original data. Injecting bubble at the center point of upper cooled wall, the symmetry shape of two vortexes near an air bubble was observed. The bubble size increased, the size of velocity and the magnitude of velocity increased. In spite of elapsed time, a pair of two vortexes was the unique and steady-state flow in a square cavity and wasn't induce to the other flow in the surround region.

• Animal cells and systems
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• v.13 no.2
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• pp.161-167
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• 2009

The cuticle of spider's exoskeleton is a hydrophobic and non-adhesive material, but the jumping spiders have the distinctive attachment apparatus for adhesion on smooth dry surface without sticky fluids. We have examined the whole tarsal appendages of the jumping spider, Plexippus setipes with using scanning electron microscope to reveal the fine structural characteristics of the dry adhesion system. All eight legs have the scopulae with a pair of claws on the tip of feet. Each scopula is composed of two groups of setae that are capable of dry adhesion on smooth surface, and the hook structure of the claw is advanced to move on the rough surface. The setae toward the bottom of the tarsal segment are densely covered by numerous setules on the underside which broadened from middle to distal portion. It has been revealed by this research that the contact area of the setule is always a triangular shape, and these cuticular surfaces are connected by the elongated stalks from the underlying setae. It is likely that the nano-scale structures including a triangular depression and a longitudinal groove on each setule could functionate when the spider detach its feet from the substrate.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.1
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• pp.15-20
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• 2002

An electro-hydraulic manipulator using hydraulic actuators has many nonlinear elements, and its parameter fluctuations are greater than those of an electrically driven manipulator. So it is relatively difficult to realize not only stable contact work but also accurate force control for the automatic assembly tasks using hydraulic manipulators. In this manuscript, we applied a compliance control, which is based on the position control by a disturbance observer for our manipulator system. A reference trajectory modification method is proposed in order to achieve accurate force control even though the stiffness and the position of the environment change. Experimental results show that highly robust force tracking by a 6-link electro-hydraulic manipulator could be achieved under various environment conditions. The proposed force control algorithm is applied to the approaching of bolt and the wrenching of nut tasks as one typical task in the maintenance work of live power electric line and is experimentally confirmed very effective for the task.

• Proceedings of the KAIS Fall Conference
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• 2006.05a
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• pp.203-206
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• 2006

The sensor consists of a heater, an insulating layer, a pair of contact electrodes, and CNT-sensing film on a micromachined diaphragm. The heater plays a role in the temperature change to modify sensor operation. Gas sensor responses of CNT-film to $NO_2$ at room temperature are reported. The sensor exhibits a reversible response with a time constant of a few minutes at thermal treatment temperature of $130^{\circ}C$.