• Journal of the Korean Mathematical Society
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• v.61 no.2
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• pp.377-393
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• 2024

In this paper, we study the positive solutions to a discrete harmonic function for a random walk satisfying finite range and ellipticity conditions, killed at the boundary of an unbounded cylinder in ℤ^d. We first prove the existence and uniqueness of positive solutions, and then establish that all the positive solutions are generated by two special solutions, which are exponential growth at one end and exponential decay at the other. Our method is based on maximum principle and a Harnack type inequality.

• Journal of Korean Society for Atmospheric Environment
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• v.32 no.3
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• pp.320-328
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• 2016

Among biogenic volatile organic compounds (BVOCs) in the natural ecosystem, monoterpenes, along with isoprene, play important roles in atmospheric chemistry and make significant impacts on air pollution and climate change, especially due to their contribution to secondary organic aerosol production and photochemical ozone formation. It is essential to measure monoterpene concentrations accurately for understanding their oxidation processes, emission processes and estimation, and interactions between biosphere and atmosphere. Thus, traceable calibration standards are crucial for the accurate measurement of monoterpenes at ambient levels. However, there are limited information about developing calibrations standards for monoterpenes in pressured cylinders. This study describes about developing primary standard gas mixtures (PSMs) for monoterpenes at about 2 nmol/mol, near ambient levels. The micro-gravimetric method was applied to prepare monoterpene (${\alpha}$-pinene, 3-carene, R-(+)-limonene, 1,8-cineole) PSMs at $10{\mu}mol/mol$ and then the PSMs were further diluted to 2 nmol/mol level. To select an optimal cylinder for the development of monoterpene PSMs, three different kinds of cylinders were used for the preparation and were evaluated for uncertainty sources including long-term stability. Results showed that aluminum cylinders with a special internal surface treatment (Experis) had little adsorption loss on the cylinder internal surface and good long-term stability compared to two other cylinder types with no treatment and a special treatment (Aculife). Results from uncertainty estimation suggested that monoterpene PSMs can be prepared in pressured cylinders with a special treatment (Experis) at 2 nmol/mol level with an uncertainty of less than 4%.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.1
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• pp.9-18
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• 2013

Two-phase vapor-liquid flows exist in many shell and tube heat exchangers such as condensers, evaporators, and nuclear steam generators. To understand the fluid dynamic forces acting on a structure subjected to a two-phase flow, it is essential to obtain detailed information about the characteristics of a two-phase flow. The characteristics of a two-phase flow and the flow parameters were introduced, and then, an experiment was performed to evaluate the pressure loss in the tube bundles and the fluid-dynamic force acting on the cylinder owing to the pressure distribution. A two-phase flow was pre-mixed at the entrance of the test section, and the experiments were undertaken using a normal triangular array of cylinders subjected to a two-phase cross-flow. The pressure loss along the flow direction in the tube bundles was measured to calculate the two-phase friction multiplier, and the multiplier was compared with the analytical value. Furthermore, the circular distributions of the pressure on the cylinders were measured. Based on the distribution and the fundamental theory of two-phase flow, the effects of the void fraction and mass flux per unit area on the pressure coefficient and the drag coefficient were evaluated. The drag coefficient was calculated by integrating the measured pressure on the tube by a numerical method. It was found that for low mass fluxes, the measured two-phase friction multipliers agree well with the analytical results, and good agreement for the effect of the void fraction on the drag coefficients, as calculated by the measured pressure distributions, is shown qualitatively, as compared to the existing experimental results.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2885-2889
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• 2007

In this study, the effect of particle aggregation on dynamic response time of Electrorheological (ER) fluid is investigated. The particle aggregation time is defined as the time interval between the application of the field and the formation of the first chain bridging the two electrodes. The dynamic response times of an ER fluid sheared between two concentric cylinders have been obtained under two different experimental conditions: the one is that the electric field is induced before shearing, and the other is that the electric field is induced after shearing. From the difference between two response times, the particle aggregation times are determined under various electric fields and shear rates. The experimental results show that the aggregation rate is decreased with an increase of shear rate, while electric field has little effect on it. Therefore, it is verified that the hydrodynamic force hinders the formation of chain-like structures.

• Journal of the Korean Institute of Gas
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• v.10 no.2 s.31
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• pp.27-32
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• 2006

In this paper, the contact stress and friction force between multi-balls and rolling friction contact surfaces of two cylinders have been presented using a finite element analysis. The multi-balls for a rolling friction motion may be contacted with a reciprocating mechanism of a parallel cylinder and a misaligned cylinder in a LPG filling unit. The FEM computed results indicate that SiC ceramic and SUS 304 balls show a high contact stress and friction force on the contact spot of rolling balls. But the PEEK balls show a low contact stress and friction loss due to a high flexibility of a PEEK polymer. In this study, we may recommend SiC and SUS 304 balls for high compressive loadings between a multi-ball and a cylinder contact mechanisms and PEEK balls for a low compressive force. And the misalignment between two cylinders should be restricted for a low contact stress and friction loss, especially.

• Journal of Technologic Dentistry
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• v.38 no.3
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• pp.135-142
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• 2016

Purpose: The aim of this research was to evaluate the influence of different surface treatments on the shear bond strength of zirconia ceramic to composite resin. Methods: Seventy two cylinder-shape (diameter: 5 mm; height: 12 mm) blocks of experimental industrially manufactured Y-TZP ceramic were abraded with $125{\mu}m\;Al_2O_3$ particles and randomly divided into 4 groups. All the materials were categorized as group Gc(control group - composite resin veneering on zirconia surface), Gr - composite resin veneering after surface treatment of Rocatec system (3M ESPE, Seefeld, Germany) group; Gz - composite resin veneering after surface treatment of Zirconia primer (Z-primer, Bisco, U.S.A) group; Gm - composite resin veneering after surface treatment of zirconia primer (Monobond plus, ivoclar vivadent AG, Liechtenstein) group. Two different zirconia primers and Rocatec system were used to zirconia cylinders (n=16) onto the zirconia surface. Zirconia specimens, polished and roughened, were pretreated and composite bilayer cylinders bonded using conventional adhesive techniques. Results: Shear bond strengths were analyzed using single-factor ANOVA(p<0.05). Bond strength values achieved after airbone particle abrasion and zirconia surface pre-treatments(p<0.05). Conclusion: Shear bond strength tests denmonstrated that zirconia primer is a viable method to improved bond strength between zirconia ceramic core and veneering composites.

• Journal of Forest and Environmental Science
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• v.38 no.4
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• pp.239-248
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• 2022

Forestry crane work in a forest harvester or forwarder is regarded as one of most hard work requiring a very high level of operation skill. The operator must handle two or more multi-axes joysticks simultaneously to control the multiple manipulators for maneuvering the crane-tip to its intended location. This study has been carried out to develop a crane-tip controller which can intuitively maneuver the crane-tip, resulting in improving the productivity by decreasing the technical difficulty of control as well as reducing the workload. The crane-tip controller consists of a single 2-axis joystick and a control algorithm run on microcontroller. Lab-scale forestry crane was constructed using electric cylinders. The crane-tip control algorithm has the crane-tip follow the waypoints generated on the given path considering the dead band region using LBO (Lateral Boundary Offset). A speed control gain to change the speed of relevant cylinders relatively is applied as well. By the P (Proportional) control within the control interval of 20 msec, the average error of crane-tip control on the predefined straight path turned out to be 14.5 mm in all directions. When the joystick is used the waypoints are generated in real time by the direction signal from the joystick. In this case, the average error of path control was 12.4 mm for straight up, straight forward and straight down movements successively at a certain constant speed setting. In the slant movement of crane-tip by controlling two axes of joystick simultaneously, the movement of crane-tip was controlled in the average error of 15.9 mm when the crane-tip is moved up and down while moving toward forward direction. It concluded that the crane-tip control was possible using the control algorithm developed in this study.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.3
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• pp.259-268
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• 2012

This study measured the natural-convection heat transfer of two vertically staggered cylinders with varying vertical pitch-to-diameter ($P_v$/D) and horizontal pitch-to-diameter ($P_h$/D) ratios. The measured heat-transfer rates for the lower cylinder agreed well with the existing heat-transfer correlations for a single cylinder. At the smallest $P_v$/D, the rising plume from the lower cylinder provides the upper cylinder with a preheated flow, and the heat-transfer rates of the upper cylinder decrease, but increase very sensitively with $P_h$/D. However, at the largest $P_v$/D, the velocity effect dominates, and the heat-transfer rates of the upper cylinder are larger than that of a single cylinder, and decrease less sensitively with $P_h$/D. Even if $P_h$/D is increased, the heat-transfer rate of the upper cylinder is higher than that of the lower cylinder because of the chimney and side flow effects. This work expanded the flow ranges to turbulent flows. The cupric acid-copper sulfate ($H_2SO_4-CuSO_4$) electroplating system was adopted for the measurements of the mass-transfer rates instead of the heat-transfer experiments based on the analogy concept. The measurements were made by varying $P_v$/D (1.02-5) and $P_h$/D (0-2) in both laminar and turbulent flows. The Rayleigh number ranged from $1.5{\times}10^8$ to $2.5{\times}10^{10}$, and the Prandtl number was 2,014.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.4
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• pp.417-424
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• 2011

Natural convection heat transfer experiments from two parallel horizontal cylinders were performed varying the Pitch-to-Diameter ratio (P/D) of 1.02-9 at Sc of 2,014 to 8,334 and $Ra_D$ of $1.5{\times}10^8$ to $4.5{\times}10^{10}$. Mass transfer experiments that are analogous to the heat transfer experiments were performed using copper electroplating system. In all cases, the measured heat transfer rates for the lower cylinder agreed well with the existing heat transfer correlations developed from a single cylinder. For laminar flows, the measured heat transfer rates of the upper cylinder were less than those of the lower cylinder at P/D less than about 1.5. However, as the P/D increased, the heat transfer rates of the upper cylinder increased. For turbulent flows, the heat transfer rates of the upper cylinder were considerably similar to those of the lower cylinder when the P/D is approximately unity. In contrast, as the P/D increased, the heat transfer rates of the upper cylinder were always higher than those of the lower cylinder.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.2 s.54
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• pp.215-222
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• 2009

In this study, steel and FRP jackets are used to confine concrete cylinders. The FRP jacket behaviors compositely with concrete since there is bonding between them. However, the used steel jacket in this study do not behavior compositely with concrete since there is not an adhesive between them. The steel jackets are attached by external forces and the welding. This study suggests the measuring method of the axial strain for the confined concrete cylinders showing noncomposite behavior with the jackets and the correcting method of the measured strain for the composite-behavior jackets. For the noncomposite-behavior steel jacket, the axial strain of the steel surface does not represent the axial strain of the concrete inside. Also, a compressormeter can not be used. Thus, the two rigid plates at the top and bottom of a cylinder are placed and the distance of the two plates are measured and used for estimating the axial strain of the concrete. For the composite-behavior FRP jacket, the vertical strain measured on the FRP surface can be used for estimating the axial strain of the concrete. However, the vertical strain on the FRP surface contains the tensile strain due to the bulge of the concrete and, thus, the tensile strain should be corrected from the vertical strain. The corrected verticals strains compared with the measured strain or a existing constitute model; the result is satisfactory. The uncorrected stress-strain curves have the potential to under estimate the ductile behavior and the energy-dissipation-capacity of the composite-behavior FRP jackets.