• Composites Research
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• v.22 no.5
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• pp.15-23
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• 2009

The lubricant tribological characteristics of $Al_2O_3$ fiber and SiC particle hybrid metal matrix composites (MMCs) fabricated by squeeze casting method was investigated using a pin-on-disk wear tester. The wear tests of the MMCs were performed according to fiber/particle hybrid ratio in the planar-random (PR) and normal (N) orientations sliding against a counter steel disk at a fixed speed and $25\;kg_f$ loading under different sliding distances and temperatures. The test results showed that the wear behavior of MMCs varied with fiber orientation and hybrid ratio. At room temperature, the lubricant wear behavior of F20P0 unhybrid PR-MMCs was superior to that of N-MMCs while the hybrid composites exhibited the reverse lubricant wear behavior. It was also revealed that the wear resistance of PR-MMCs was superior to that of the N-MMCs due to the joint action of reinforcements and lubricant film between the friction surfaces at an elevated temperature of $100^{\circ}C$ for both fiber only and hybrid cases. In case of $150^{\circ}C$, although the trend of weight loss was similar to that of others, the wear resistance of PR-MMCs was better than that of N-MMCs for hybrid MMCs.

• The Journal of the Petrological Society of Korea
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• v.3 no.2
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• pp.138-155
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• 1994

Granitic gneiss containing biotite banded gneiss relict around the Daeheung talc deposit are widely distributed which were formed by regional metamorphism of both epidote-amphibolite and iater greenschist facies and granitization. They were derived from same silico-aluminous rocks of sedimentary origin. The mineral assemblages, which are common in the biotite banded gneiss, formed during regional metamorphisms, are survived in the granitic gneiss. The mineral assemblages of the latter greenschist facies may be formed retrogressively from the first epidote-amphibolite facies. The chemical compositions of biotite, muscovite, and chlorite, the important constituents of the gneisses, were controlled by the bulk composition, the chemical composition of the original mineral, and environment of the regional metamorphisms and granitization. The chemical equilibrium between coexisting'minerals, especially biotite and muscovite, is relatively well established, which was controlled mainly by tschermakitic and phengitic substitutions. Cholrite was formed mainly from either biotite or muscovite by retrogressive alteration or granitization, and have nearly similar chemical compositions regardless of the occurrences. The orientation trend of the foliation, joint and quartz vein developed in the gneisses was analyzed by equal area projection which the latter two show nearly identical trend in the strike and dip. This may suggest that the hydrothermal solution was introduced along joint during wet granitization.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.1
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• pp.21-29
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• 2003

It is very important to reduce the computational time in estimating the parameters of vision control algorithm for robot's position control in real time. Unfortunately, the batch estimation commonly used requires too murk computational time because it is iteration method. So, the batch estimation has difficulty for robot's position control in real time. On the other hand, the Extended Kalman Filtering(EKF) has many advantages to calculate the parameters of vision system in that it is a simple and efficient recursive procedures. Thus, this study is to develop the EKF algorithm for the robot's vision control in real time. The vision system model used in this study involves six parameters to account for the inner(orientation, focal length etc) and outer (the relative location between robot and camera) parameters of camera. Then, EKF has been first applied to estimate these parameters, and then with these estimated parameters, also to estimate the robot's joint angles used for robot's operation. finally, the practicality of vision control scheme based on the EKF has been experimentally verified by performing the robot's position control.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.3
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• pp.127-133
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• 2012

To achieve low-cost and high-efficiency of thin-film solar cells applications, the sol-gel method that can be coated on a large area substrate, obtain homogeneous thin films of high purity was used. We studied structural and optical characteristics versus annealing temperature of $Cu_2ZnSnS_4$ which has kesterite structure by substitution low-cost sulfur (S) instead of high-cost selenium (Se). By analyzing XRD patterns, main peak was observed at $2{\theta}=28.5^{\circ}$ when Zn/Sn ratio is 0.8/1.2. And when we observed kesterite structure which has orientation of (112) direction, the more annealing temperature increase the bigger strength of (112) direction is. $Cu_2ZnSnS_4$ thin film showed characteristics of kesterite structure at $550^{\circ}C$. And when we calculated lattice constant, a = 5.5047 and $c=11.014{\AA}$ as same JCPDS (Joint Committee on Powder Standards) data measured. We measured optical transmittance to analyze optical characteristics. Optical transmittance was lower than 65 % at visible ray (${\lambda}=380{\sim}770nm$).

• Journal of rehabilitation welfare engineering & assistive technology
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• v.9 no.2
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• pp.137-144
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• 2015

In this paper, we present an inertial sensor-based gait analysis system to measure and analyze lower-limb movements. We developed an integral AHRS(Attitude Heading Reference System) using a combination of rate gyroscope, accelerometer and magnetometer sensor signals. Several AHRS modules mounted on segments of the patient's body provide the quaternions representing the patient segments's orientation in space. And a method is also proposed for calculating three-dimensional inter-segment joint angle which is an important bio-mechanical measure for a variety of applications related to rehabilitation. To evaluate the performance of our AHRS module, the Vicon motion capture system, which offers millimeter resolution of 3D spatial displacements and orientations, is used as a reference. The evaluation resulted in a RMSE(Root Mean Square Error) of 1.08 and 1.72 degree in yaw and pitch angle. In order to evaluate the performance of our the gait analysis system, we compared the joint angle for the hip, knee and ankle with those provided by Vicon system. The result shows that our system will provide an in-depth insight into the effectiveness, appropriate level of care, and feedback of the rehabilitation process by performing real-time limb or gait analysis during the post-stroke recovery.

• KIPS Transactions on Software and Data Engineering
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• v.2 no.10
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• pp.723-730
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• 2013

This paper presents the design of an arm gesture recognition system using Kinect sensor. A variety of methods have been proposed for gesture recognition, ranging from the use of Dynamic Time Warping(DTW) to Hidden Markov Models(HMM). Our system learns a unique HMM corresponding to each arm gesture from a set of sequential skeleton data. Whenever the same gesture is performed, the trajectory of each joint captured by Kinect sensor may much differ from the previous, depending on the length and/or the orientation of the subject's arm. In order to obtain the robust performance independent of these conditions, the proposed system executes the feature transformation, in which the feature vectors of joint positions are transformed into those of angles between joints. To improve the computational efficiency for learning and using HMMs, our system also performs the k-means clustering to get one-dimensional integer sequences as inputs for discrete HMMs from high-dimensional real-number observation vectors. The dimension reduction and discretization can help our system use HMMs efficiently to recognize gestures in real-time environments. Finally, we demonstrate the recognition performance of our system through some experiments using two different datasets.

• International Journal of Computer Science & Network Security
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• v.22 no.12
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• pp.63-70
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• 2022

The essence of the definition of "tolerance" is analyzed. Motivational, knowledge and behavioral criteria for tolerance of future teachers are highlighted. Indicators of the motivational criterion are the formation of value orientations, motivational orientation, and the development of empathy. Originality and productivity of thoughts and judgments, tact of dialogue, pedagogical ethics and tact are confirmed as indicators of the knowledge criterion. The behavioral criterion includes social activity as a life position, emotional and volitional endurance, and self-control of one's own position. The formation of tolerance is influenced by a number of factors: the social environment, the information society, existing stereotypes and ideas in society, the system of education and relationships between people, and the system of values. The main factors that contribute to the education of tolerance in future teachers are highlighted. Analyzing the structure of tolerance, it is necessary to distinguish the following functions of tolerance: - motivational (determines the composition and strength of motivation for social activity and behavior, promotes the development of life experience, because it allows the individual to accept other points of view and vision of the solution; - informational (understanding the situation, the personality of another person); - regulatory (tolerance has a close connection with the strong - willed qualities of a person: endurance, selfcontrol, self-regulation, which were formed in the process of Education); - adaptive (allows the individual to develop in the process of joint activity a positive, emotional, stable attitude to the activity itself, which the individual carries out, to the object and subject of joint relations). The implementation of pedagogical functions in the information society: educational, organizational, predictive, informational, communicative, controlling, etc. provides grounds to consider pedagogical tolerance as an integrative personal quality of a representative of any profession in the field of "person-person". The positions that should become conditions for the formation of tolerance of the future teacher in the information society are listed.

• Journal of rehabilitation welfare engineering & assistive technology
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• v.7 no.2
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• pp.47-54
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• 2013

In this paper, we present an inertial sensor-based motion capturing system to measure and analyze whole body movements. This system implements a wireless AHRS(attitude heading reference system) we developed using a combination of rate gyroscope, accelerometer and magnetometer sensor signals. Several AHRS modules mounted on segments of the patient's body provide the quaternions representing the patient segments's orientation in space. We performed 3D motion capture using the quaternion data calculated. And a method is also proposed for calculating three-dimensional inter-segment joint angle which is an important bio-mechanical measure for a variety of applications related to rehabilitation. To evaluate the performance of our AHRS module, the Vicon motion capture system, which offers millimeter resolution of 3D spatial displacements and orientations, is used as a reference. The evaluation resulted in a RMSE of 2.56 degree. The results suggest that our system will provide an in-depth insight into the effectiveness, appropriate level of care, and feedback of the rehabilitation process by performing real-time limbs or gait analysis during the post-stroke recovery process.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.4
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• pp.11-17
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• 2010

The electromigration phenomenon in lead-free flip-chip solder joint has been one of the serious problems. To understand the mechanism of this phenomenon, the crystallographic orientation of Sn grain in the Sn-Ag-Cu solder bump has been analyzed. Different time to failure and different microstructural changes were observed in the all test vehicle and bumps, respectively. Fast failure and serious dissolution of Cu electrode was observed when the c-axis of Sn grain parallel to electron flow. On the contrary of this, slight microstructural changes were observed when the c-axis of Sn perpendicular to electron flow. In addition, underfill could enhance the electromigration reliability to prevent the deformation of solder bump during EM test.

• Journal of Welding and Joining
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• v.33 no.2
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• pp.8-13
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• 2015

This study was carried out to evaluate mechanical properties of the jointed Al6061/HT590 alloys by friction stir welding (FSW). FSW was conducted under the conditions with tool rotating speed of 500 RPM and traveling speed of 300 mm/min., where Ar gas was introduced to prevent the materials from corrosion during the welding process. Electron back-scattering diffraction (EBSD) was used to characterize microstructures such as grain size, misorientation angle and crystal orientation. Evolution of intermetallic compounds in Al6061 during the process were examined in terms of morphology, size and aspect ratio at three distinct zones Al base material, heat affected zone and stir zone, where transmission electron microscope (TEM) was used. It was revealed that FSW gave rise to refinement of grains as well as growth of intermetallic compounds in Al6061. The morphological changes of intermetallic compounds exerted an influence on mechanical properties, resulting in occurrence of fracture in the part of the base material instead of the jointed parts (heat affected zone and stir zone). This study systematically evaluated the microstructural evolutions during the FSW for joining Al6061 with HT590 and their effect on mechanical properties.