• Tribology and Lubricants
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• v.30 no.2
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• pp.108-115
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• 2014

The friction behaviors of bulk amorphous thermal spray coating (BAC) and second phase-reinforced composite coatings using a high velocity oxy-fuel spraying process were investigated using a ball-on-disk test rig that slides against a ceramic ball in an atmospheric environment. The surface temperatures were measured using an infrared thermometer installed 50 mm from the contact surface. The crystallinities of the coating layers were determined using X-ray diffraction. The morphologies of the coating layers and worn surfaces were observed using a scanning electron microscope and energy-dispersive spectroscopy. The results show that the friction behavior of the monolithic amorphous coating was sensitive to the testing conditions. Under lower than normal loads, a low and stable friction coefficient of about 0.1 was observed, whereas under a higher relative load, a high and unstable friction coefficient of greater than 0.3 was obtained with an instant temperature increase. For the composite coatings, a sudden increase in friction coefficient did not occur, i.e., the transition region did not exist and during the friction test, a gradual increase occurred only after a significant delay. The BAC morphology observations indicate that viscous plastic flow was generated with low loads, but severe surface damage (i.e., tearing) occurred at high loads. For composite coatings, a relatively smooth surface was observed on the worn surface for all applied loads.

• Food Science of Animal Resources
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• v.38 no.3
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• pp.476-486
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• 2018

In this study, the droplet size distribution, rheological properties, and stability of dairy cream-based emulsions homogenized with different sucrose fatty acid ester (SFAE, a non-ionic small-molecule emulsifier) concentrations (0.08%, 0.16%, and 0.24% w/w) at different homogenization pressures (10 MPa and 20 MPa) were examined. Homogenization at a high pressure resulted in a smaller droplet size and narrower droplet size distribution. The D[4,3] (volume-weighted mean) and D[3,2] (surface-weighted mean) values of the emulsions decreased with an increase in the SFAE concentration. The flow properties of the emulsions homogenized with SFAE showed shear-thinning (n=0.21-0.46) behavior. The apparent viscosity (${\eta}_{a,10}$) and consistency index (K) of the homogenized emulsions were lower than those of the control sample that is non-homogenized and without SFAE, and decreased with an increase in SFAE concentration. The storage modulus (G') and loss modulus (G") of all emulsions homogenized with SFAE were also lower than those of the control sample. The stability of all emulsions with SFAE did not show any significant change for 30 d at $5^{\circ}C$. However, the emulsions stored at $40^{\circ}C$ were unstable over the storage period. Therefore, the addition of SFAE enhanced the stability of dairy cream emulsions during storage at refrigeration temperature ($5^{\circ}C$).

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.410-413
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• 2005

The results of an experimental and analytical study of composite pressure hull on buckling pressure are presented for LRN 300. Composite tensile test was done to know the composite material properties applied FE analysis for URN composite. We predicted the buckling and post buckling analysis of composite laminated cylindrical panels under external compression by using ABAQUS /Standard[Ver 6.4]. To obtain nonlinear static equilibrium solutions for unstable problems, where the load-displacement response can exhibit the type of nonlinear buckling behavior, during periods of the response, the load and/or the displacement may decrease as the solution evolves, used the modified Riks method. The modified Riks method is an algorithm that allows effective solution of such cases [7]. Experiments were conducted to verify the validation of present analysis for cross-ply laminated shells. The shells considered in the study have two different lamination patterns, $[{\pm}45/0/90]_{18s\;and}\;[/0/90]_{18s}$. Cylindrical panel of experiment and analysis have the radius of 200mm, length of 210mm and 60 degree of cutting angle. The critical load from experiment is $69\%$ of that of numerical analysis, because the fracture of matrix was generated before buckling. So URN 300 is not proper to use at the condition under high external pressue.

• Journal of Biosystems Engineering
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• v.30 no.6 s.113
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• pp.366-372
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• 2005

The objective of this study was to evaluate the bump crossing and loading stability of a proto-type mini-forwarder under development. The evaluation was performed by computer simulation using a multi-body dynamic analysis program, Recur- Dyn 5.21. The proto-type was modeled and its properties such as mass, mass center, and mass moment of inertia were determined using 3D CAD modeler, Solid Edge 8.0. The $\%$ errors of masses, mass center, mass moment of inertia, and vertical motion of the model were within less than $10\%$ and the model's behavior agreed relatively well with those of the proto-type when traversing over a rectangular bump. Using the validated model, bump crossing of the proto-type was simulated and the loading limit was determined. It was found that effects of the shapes of bump on the bump crossing performance was insignificant within the practical heights of bumps. Stability of bump crossing increased with loading. However, loading of longer logs than 2.7 m made the crossing unstable because the ends of logs contacted ground when traversing over the bump. The maximum loading capacity of the proto-type was estimated to be 7.8 kN of 2.7 m long logs.

• Nuclear Engineering and Technology
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• v.27 no.3
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• pp.358-373
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• 1995

The Heat Transport system loop stability of CANDU-6 reactor using the CANFLEX fuel bundle was studied. The Thermal-hydraulic behavior of CANFLEX fuel bundle is similar to the conventional 37-element fuel bundle since the reactor power and the frictional pressure drop through the fuel channel is almost the same each other, Mounter the CANFLEX fuel bundle gives higher critical channel power and more homogeneous enthalpy distributions in the subchannels than 37-element fuel bundle. The SOPHT modelling or the CANFLEX fuel bundle and the Reactor outlet Header(ROH) interconnection line was made and the stability analysis response of Wolsong-1 reactor with CANFLEX fuel bundle was obtained. Without the ROH interconnection line the Heat Transport system loop using 43-element fuel bundle is unstable like the current 37-element fuel bundle. With the ROH interconnection line, however, the Heat Transport system is stable within $\pm$1％ of nominal flow. In the Heat Transport system loop stability point of view for Wolsong-1 plant therefore, the CANFLEX fuel loading is considered to be acceptable.

• Journal of the Korea Society for Simulation
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• v.20 no.1
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• pp.51-59
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• 2011

This paper is concerned with locomotion of dog-like quadruped robots that can adapt to various terrains, mainly dealing with implementation methods and characteristics of static and dynamic gaits. To this end, a 12-DOF robot is built in house, motional trajectories of its body and feet are generated mimicking biological life, and the corresponding leg joint angles are analytically obtained by inverse kinematics. Such joint angle data are then applied to the robot's ADAMS model for computer simulations so that the planned walk and trot gaits are both confirmed dynamically stable. However, contrary to the simulation results, previous trot patterns showed unstable behavior during experiments. This problem led us to analyze the reason, and in the course we discovered the importance of maximally utilizing the concept of WSM rather than ZMP and therefore reducing the gait period to secure the stability of dynamic gaits such as trot.

• ETRI Journal
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• v.31 no.6
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• pp.660-666
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• 2009

We investigate the effects of interfacial dielectric layers (IDLs) on the electrical properties of top-gate In-Ga-Zn-oxide (IGZO) thin film transistors (TFTs) fabricated at low temperatures below $200^{\circ}C$, using a target composition of In:Ga:Zn = 2:1:2 (atomic ratio). Using four types of TFT structures combined with such dielectric materials as $Si_3N_4$ and $Al_2O_3$, the electrical properties are analyzed. After post-annealing at $200^{\circ}C$ for 1 hour in an $O_2$ ambient, the sub-threshold swing is improved in all TFT types, which indicates a reduction of the interfacial trap sites. During negative-bias stress tests on TFTs with a $Si_3N_4$ IDL, the degradation sources are closely related to unstable bond states, such as Si-based broken bonds and hydrogen-based bonds. From constant-current stress tests of $I_d$ = 3 ${\mu}A$, an IGZO-TFT with heat-treated $Si_3N_4$ IDL shows a good stability performance, which is attributed to the compensation effect of the original charge-injection and electron-trapping behavior.

• Journal of the Korean Institute of Intelligent Systems
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• v.18 no.6
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• pp.746-753
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• 2008

In this paper, we introduce the improved control method are communicated between a master and a slave robot in the teleoperation systems. When the master and slave robots are located in different places, time delay is unavoidable under the network environment and it is well known that the system can become unstable when even a small time delay exists in the communication channel. The time delay may cause instability in teleoperation systems especially if those systems include haptic feedback. This paper presents a control scheme based on the estimator with virtual master model in teleoperation systems over the network. As the behavior of virtual model is tracking the one of master model, the operator can control real master robot by manipulating the virtual robot. And LQG/LTR scheme was adopted for the compensation of un-modeled dynamics. The approach is based on virtual master model, which has been implemented on a robot over the network. Its performance is verified by the computer simulation and the experiment.

• Structural Engineering and Mechanics
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• v.25 no.4
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• pp.481-500
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• 2007

The dynamic instability of doubly curved panels, subjected to non-uniform tensile in-plane harmonic edge loading $P(t)=P_s+P_d\;{\cos}{\Omega}t$ is investigated. The present work deals with the problem of the occurrence of combination resonances in contrast to simple resonances in parametrically excited doubly curved panels. Analytical expressions for the instability regions are obtained at ${\Omega}={\omega}_m+{\omega}_n$, (${\Omega}$ is the excitation frequency and ${\omega}_m$ and ${\omega}_n$ are the natural frequencies of the system) by using the method of multiple scales. It is shown that, besides the principal instability region at ${\Omega}=2{\omega}_1$, where ${\omega}_1$ is the fundamental frequency, other cases of ${\Omega}={\omega}_m+{\omega}_n$, related to other modes, can be of major importance and yield a significantly enlarged instability region. The effects of edge loading, curvature, damping and the static load factor on dynamic instability behavior of simply supported doubly curved panels are studied. The results show that under localized edge loading, combination resonance zones are as important as simple resonance zones. The effects of damping show that there is a finite critical value of the dynamic load factor for each instability region below which the curved panels cannot become dynamically unstable. This example of simultaneous excitation of two modes, each oscillating steadily at its own natural frequency, may be of considerable interest in vibration testing of actual structures.

• Geomechanics and Engineering
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• v.11 no.5
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• pp.657-670
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• 2016

The energy dissipation of coal under dynamic loads is a major issue in geomechanics and arising extensive concerns recently. In this study, dynamic loading tests of coal were conducted using a split Hopkinson pressure bar (SHPB) system, the characteristics of dynamic behavior and energy dissipation of coal were analyzed, and the mechanism of energy dissipation was discussed based on the fracture processes of coal under dynamic loads. Experimental results indicate that the energy dissipation of coal under dynamic loads has a positive linear correlation with both incident energy and dynamic compressive strength, and the correlation coefficients between incident energy, dynamic compressive strength and the energy dissipation rate are 0.74 and 0.98, respectively. Theoretical analysis demonstrates that higher level of stress leads to greater energy released during unstable crack propagation, thus resulting in larger energy dissipation rate of coal under dynamic loads. At last, a semi-empirical energy dissipation model is proposed for describing the positive relationship between dissipated energy and stress.