• Honam Mathematical Journal
• /
• v.41 no.1
• /
• pp.185-195
• /
• 2019

In this work, we study the conditions between null geodesic curves and timelike ruled surfaces in dual Lorentzian space. For this study, we establish a system of differential equations characterizing timelike ruled surfaces in dual Lorentzian space by using the invariant quantities of null geodesic curves on the given ruled surfaces. We obtain the solutions of these systems for special cases. Regarding to these special solutions, we give some results of the relations between null geodesic curves and timelike ruled surfaces in dual Lorentzian space.

• Kyungpook Mathematical Journal
• /
• v.62 no.3
• /
• pp.497-507
• /
• 2022

In this study, we define tubular surfaces in Pseudo Galilean 3-space as type-1 or type-2. Using the X(s, t) position vectors of the surfaces and G(s, t) Gaussian transformations, we obtain equations for the two types of tubular surfaces that satisfy the conditions ∆X(s, t) = 0, ∆X(s, t) = AX(s, t), ∆X(s, t) = λX(s, t), ∆X(s, t) = ∆G(s, t), ∆G(s, t) = 0, ∆G(s, t) = AG(s, t) and ∆G(s, t) = λG(s, t).

• Honam Mathematical Journal
• /
• v.45 no.3
• /
• pp.380-396
• /
• 2023

In this study, we introduce the adjoint curves of framed curves. We examine some characterizations of adjoint curve of a framed curve. In addition, we give the conditions for framed curves and adjoint curves to be Bertrand and Mannheim curves. Then, we introduce adjoint curves of Frenet-type framed curves and give ruled surfaces related to adjoint curves. Finally, we create normal and binormal surfaces of the framed adjoint curves and obtain some characterizations of these surfaces and we support by the results with figures.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2002.10b
• /
• pp.227-228
• /
• 2002

One of the serious challenges in developing rotary compressor with HFC refrigerant is the prediction of scuffing times and wear amounts between vane and roller surface. In this study, the tribological characteristics of sliding surfaces using roller-vane geometry of rotary compressor were investigated. The sliding tests were carried out under various sliding speeds, normal loads and surface roughness. During the tests, friction force, wear scar width, time to failure, surface temperature, and surface roughness were monitored. Because severe wear was occurred on vane surface, TiN coating was applied on sliding surfaces to prolong the wear-life of vane-roller interfaces. From the sliding tests, it was found that there was the optimum initial surface roughness to break in and to prolong the wear life of sliding surfaces. Depending on load and speed, the protective layers, which were composed of metallic oxide and organic compound, were formed on sliding surfaces. Those would play an important role in the amount of friction and wear between roller and vane surfaces.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.122-122
• /
• 2012

The exterior structures of natural organisms have continuously evolved by controlling wettability, such as the Namib Desert beetle, whose back has hydrophilic/hydrophobic contrast for water harvesting by mist condensation in dry desert environments, and some plant leaves that have hierarchical micro/nanostructures to collect or repel liquid water. In this work, we have provided a method for wettability contrast on metals by both nano-flake or needle patterns and tuning of the surface energy. Metals including steel alloys and aluminum were provided with hierarchical micro/nanostructures of metaloxides induced by fluorination and a subsequent catalytic reaction of fluorine ions on metal surfaces in water with various ranges from room to boiling temperature of water. Then, a hydrophobic material was deposited on the structured surfaces, rendering superhydrophobicity. Plasma oxidization induces the formation of superhydrophilic surfaces on selective regions surrounded by superhydrophobic surfaces. We show that wettability contrast surfaces align liquid water within patterned hydrophilic regions during the condensation process. Furthermore, this method could have a greater potential to align other liquids or living cells.

• Journal of the Korean Electrochemical Society
• /
• v.13 no.1
• /
• pp.70-74
• /
• 2010

The immobilization of proteins on silicon surfaces using electrochemical reaction has been studied. Chemical deposition of nitrobenzendiazonium (NiBD) cations is employed to modify silicon surfaces. Electrochemical reduction of nitro-group to primary amine-group have been conducted on the modified surfaces to activate silicon surfaces for the protein immobilization. Attachment of gold nanoparticles was used to prove the reduction. The current method was applied to selective activation of a silicon nanowire and immobilize proteins on the selected nanowire. It has been demonstrated that the use of chemical and electrochemical reaction NiBD is efficient for the selective immobilization of proteins on silicon nanowire surfaces.

• Tribology and Lubricants
• /
• v.24 no.3
• /
• pp.122-128
• /
• 2008

To reduce the friction losses and the wear amounts in the piston assembly two methods were proposed. One is the modification of surface profile of the skirt part. The surface coating is another method to protect the sliding surfaces. To modify the profile of the skirt surfaces the surfaces were ground to have three different shapes of profiles. Also, several coatings, such as graphite, TiN, and $MoS_2$, and DLC, were used to protect the surfaces of the piston skirts. The specimens of the skirt and the cylinder bores were tested with the reciprocating wear tester. SAE 5W40 engine oil was used in boundary lubrication regime. Among several coatings the graphite and DLC coatings were very effective to reduce the friction forces. Especially, DLC film represented much better tribological performances than the others. The friction coefficient of the graphite coating was the lowest, but the graphite coating was not effective to protect the surfaces.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.7 no.5
• /
• pp.1133-1138
• /
• 2012

In the paper, design of nonlinear sliding surfaces which are based on optimal control is studied, The state trajectory by the input of optimal control was obtained by Frobenius theorem and matrix decomposition method, was set the nonlinear sliding surfaces of the system. The states is maintained to sliding surfaces from initial states. As the result, robustness of the system can be guaranteed throughout an entire response of the system starting form the initial time instance, the uncertainty and external disturbance that can occur during the reaching time is removed, the problem of large control input was solved, and setting the sliding surfaces optimal path was able to reduce the tracking time. The validity of the proposed control scheme is shown in computer simulation for inverted pendulum.

• Journal of Biosystems Engineering
• /
• v.1 no.1
• /
• pp.49-54
• /
• 1976

No reliable basic data were available on the kinetic friction coefficients between grains and frictional surfaces being used in grain handling equipments in Korea. In order to determine appropriate kinetic friction coefficient between three grains (Tongil, Jinheung, barley) and two surfaces at four levels of moisture content of grain, the laboratory tests using the newly designed experimental apparatus and strain gage measuring system were carried out, and the relationship among factors that affect kinetic friction coefficients of grains were analyzed. The results of this study are summarized as follows ; 1. Kinetic friction coefficient of samples being tested was dependent on surfaces and moisture content of grains . The ranges of them were 0.369-0.512 for Tongil variety , 0.347-0.469 for Jinheung variety, and 0.360-0.502 for barley, respectively. 2. There was a little difference of kinetic friction coefficients between two varieties of rice at the same testing conditions. Because the interaction had been large among treatments , each value of kinetic friction coefficient determined in this study should be used only for the corresponding conditions in this study . 3. Kinetic friction coefficients in creased linearly with increase in moisture content of grains and their regression equations were shown in Table.4. 4. Kinetic friction coefficients on a PVC surfaces was shown a little lower values than on the steel surfaces at various moisture levels, but especially in Jinheung and barley, a big difference was shown.

• PNF and Movement
• /
• v.16 no.1
• /
• pp.125-132
• /
• 2018

Purpose: The aim of this study was to investigate the isolated activation ratio of the quadriceps femoris muscle on different support surfaces during squat exercise. Methods: Twenty participants (10 males and 10 females) voluntarily agreed to participate in the research after receiving an explanation about the purpose and process of the study. Each participant performed squat exercises on three different support surfaces (a flat surface, a form roller, and an unstable surface). Muscle activities of the rectus femoris (RF), vastus medialis (VM), and vastus lateralis (VL) were measured by electromyography. The isolated activation ratio of the quadriceps femoris muscle was calculated using the %isolation formula. Results: For the squat exercise, the %isolation value of the VM was significantly higher on the unstable surface than on the flat surface and form roller. In contrast, the %isolation values for the RF for the squat exercise were significantly higher on the flat surface and form roller than on the unstable surface. There was no significant differences in the %isolation values of the VL on the three different surfaces. Conclusion: The findings indicate that squat exercise on different surfaces results in differential activation of the quadriceps femoris muscle, which suggests that squat exercise on a multi-directional unstable surface could increase the isolated activation ratio of the VM.