• Journal of Dental Rehabilitation and Applied Science
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• v.30 no.2
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• pp.102-111
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• 2014

Purpose: Surface damage and bonding strength difference after micromechanical treatment of zirconia surface are to be studied yet. The aim of this study was to evaluate the difference of fracture resistance and bonding strength between more surface-damaged group from higher air-blasting particle size and pressure, and less damaged group. Materials and Methods: Disk shape zirconia ($LAVA^{TM}$) was sintered and air-blasted with $30{\mu}m$ particle size (Cojet), under 2.8 bar for 15 seconds, $110{\mu}m$ particle size (Rocatec), under 2.8 bar for 15 seconds, and $110{\mu}m$ particle size (Rocatec), under 3.8 bar for 30 seconds respectively. Biaxial flexure test and bonding failure load test were performed serially (n = 10 per group). For bonding test, specimens were bonded on the base material having similar modulus of elasticity of dentin with $200{\mu}m$-thick resin cement for tension of surface damage. Failure load of bonding was detected with acoustic emission (AE) sensor. Results: There were no significant differences both in the biaxial flexure test and bonding failure load test between groups (P > 0.05). Sub-surface cracks were all radial cracks except for two specimens. Conclusion: Within the limitations of no aging under monotonic load test, surface damage from higher air-blasting particle size and pressure was not significant. Evaluations of failure load with bonded zirconia disks was clinically relevant modality for surface damage and bonding strength, simultaneously.

• Journal of the Korean Geotechnical Society
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• v.25 no.12
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• pp.5-12
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• 2009

As rock bolts become one of the main support systems in tunnels and underground structures, the integrity of the rock bolts affects the safety of these structures. The purpose of this study is the evaluation of rock bolt integrity using wavelet transforms of the guided ultrasonic waves by using transmission test in the field. After several rock bolts with various defect ratios are embedded into a large scale concrete block and rock mass, guided waves are generated by a piezo disk element and measured by an acoustic emission (AE) sensor. The captured signals are analyzed in the time-frequency domain using the wavelet transform based on a Gabor wavelet. Peak values in the time-frequency domain represent the interval of travel time of each echo. The energy velocities of the guided waves increase with an increase in the defect ratio. The suitable curing time for the evergy velocity analysis is proposed by the laboratory test, and in-situ tests are performed in two tunnelling sites to verify the applicability of rock bolt integrity tests performed after proposed curing time. This study proves that time-frequency domain analysis is an effective tool for the evaluation of the rock bolt integrity.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.4
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• pp.659-666
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• 2006

Servo-motors are used as key components of automated system by performing precise motion control as accurate positioning and accurate speed regulation in response to the commands from computers and sensors. Especially, the linear brushless servo-motors have numerous advantages over the rotary servo motors which have connection with the friction induced transfer mechanism such as ball screws, timing belts, rack/pinion. This paper proposes an estimation method of unknown motor system parameters using the informations from the sinusoidal driving type linear brushless DC motor dynamics and outputs. The estimated parameters can be used to tune the controller gain and a disturbance observer. In order to meet this purpose high performance Digital Signal Processor, TMS320F240, designed originally for implementation of a Field Oriented Control(FOC) technology is adopted as a controller of the liner BLDC servo motor. Having A/D converters, PWM generators, rich I/O port internally, this servo motor application specific DSP play an important role in servo motor controller. This linear BLDC servo motor system also contains IPM(Intelligent Power Module) driver and hail sensor type current sensor module, photocoupler module for isolation of gate signals and fault signals.

• Korean Journal of Remote Sensing
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• v.34 no.1
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• pp.1-15
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• 2018

Passive microwave sea surface temperatures (SST) were validated in the Northwest Pacific using a total of 102,294 collocated matchup data between Global Precipitation Measurement (GPM) / GPM Microwave Sensor(GMI) data and oceanic in-situ temperature measurements from March 2014 to December 2016. A root-mean-square (RMS) error and a bias error of the GMI SST measurements were evaluated to $0.93^{\circ}C$ and $0.05^{\circ}C$, respectively. The SST differences between GMI and in-situ measurements were caused by various factors such as wind speed, columnar atmospheric water vapor, land contamination near coastline or islands. The GMI SSTs were found to be higher than the in-situ temperature measurements at low wind speed (<6 m/s) during the daytime. As the wind speed increased at night, SST errors showed positive bias. In addition, other factors, coming from atmospheric water vapor, sensitivity degradation at a low temperature range, and land contamination, also contributed to the errors. One of remarkable characteristics of the errors was their latitudinal dependence with large errors at high latitudes above $30^{\circ}N$. Seasonal characteristics revealed that the errors were most frequently observed in winter with a significant positive deviation. This implies that SST errors tend to be large under conditions of high wind speeds and low SSTs. Understanding of microwave SST errors in this study is anticipated to compensate less temporal capability of Infrared SSTs and to contribute to increase a satellite observation rate with time, especially in SST composite process.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6B
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• pp.954-961
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• 2010

Stream cipher was worse than block cipher in terms of security, but faster in execution speed as an advantage. However, since so far there have been many algorithm researches about the execution speed of block cipher, these days, there is almost no difference between them in the execution speed of AES. Therefore an secure and fast stream cipher development is urgently needed. In this paper, we propose a 32bit output fast stream cipher, AA32, which is composed of ASR(Arithmetic Shifter Register) and simple logical operation. Proposed algorithm is a cipher algorithm which has been designed to be implemented by software easily. AA32 supports 128bit key and executes operations by word and byte unit. As Linear Feedback Sequencer, ASR 151bit is applied to AA32 and the reduction function is a very simple structure stream cipher, which consists of two major parts, using simple logical operations, instead of S-Box for a non-linear operation. The proposed stream cipher AA32 shows the result that it is faster than SSC2 and Salsa20 and satisfied with the security required for these days. Proposed cipher algorithm is a fast stream cipher algorithm which can be used in the field which requires wireless internet environment such as mobile phone system and real-time processing such as DRM(Digital Right Management) and limited computational environments such as WSN(Wireless Sensor Network).

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.2
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• pp.257-264
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• 2007

In order to obtain a fine picture, a camera has many convenient functions. Its representative functions are Auto Focus(AF), Auto White Balance(AWB) and Auto Exposure(AE). In this paper, we present the new algorithm of Auto Exposure control system, one of its useful functions The proposed algorithm of Auto Exposure control system is based on IIR Filter with Variable Time Constant. First, in order to establish the standards of exposure control, we compare change of the picture luminance with luminance of an object in the Zone system. Second, we make an ideal characteristic graph of luminance by using the results. Finally, we can find the value of the right exposure by comparing an ideal characteristic graph of the luminance with the value of the current expose of a scene. We can find an appropriate exposure as comparing the ideal characteristic graph of the luminance with current exposure of a scene. In order to find a suitable exposure state, we make use of IIR Filter instead of a conventional method using micro-controller. In this paper, the proposed system has therefore simple structure, we use it for compact image sensor module used in the handheld device.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.1
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• pp.25-30
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• 2007

In this paper, lead-free [$Li_{0.04}(Na_{y}K_{1-y})_{0.96}](Nb_{0.86}Ta_{0.1}Sb_{0.04})O_{3}$ (y=0.4 - 0.58) ceramics were manufactured using conventional miked oxide method for acoustic emission(AE) sensor application and their dielectric and piezoelectric properties were investigated with the variations of Na/K ratio. The samples in the composition Na/K=54/46 exhibited excellent electrical properties of $d_{33}=300$ PC/N and kp=0.49. Taking into consideration above piezoelectric properties, it can be concluded that the [$Li_{0.04}(Na_{y}K_{1-y})_{0.96}](Nb_{0.86}Ta_{0.1}Sb_{0.04})O_{3}$ system ceramics are the promising lead-free materials capable of substituting PZT system ceramics.

• Journal of Sensor Science and Technology
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• v.15 no.5
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• pp.323-327
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• 2006

Manganese, copper and chlorine-doped ZnS phosphors (ZnS:Mn,Cu,Cl) were synthesized through solid-state reaction. Manganese was added in the range of amount $1.4{\sim}5.3$ mol % to ZnS phosphors containing 0.2 or 1.0 mol % of copper and a small amount of chlorine. As-synthesized phosphors showed a spherical morphology with a mean size of ${\sim}20\;{\mu}m$ and structural properties of Wurtzite, which were identified by SEM and XRD, respectively. Optical properties of ZnS:Mn,Cu,Cl synthesized with various concentrations of activators were analysed by both of PL and EL spectra. Samples mainly showing only 580 nm-orange emission by 380 nm-UV excitation gave different EL spectra of blue, green, and orange emissions at 450, 480 and 580 nm, respectively, depending on concentrations of $Cu^{2+}$ and $Mn^{2+}$.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.7B
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• pp.619-631
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• 2006

With the advent of ubiquitous computing environments, it has become increasingly important for applications to take full advantage of context information, such as the user's location, to offer greater services to the user without any explicit request. In this paper, we propose context-aware active services on the basis of CAMUS (Context-Aware Middleware for URC Systems). CAMUS is a middleware for providing context-aware applications with development and execution methodology. Accordingly, the applications developed by CAMUS respond in a timely fashion to contexts. To evaluate, we apply proposed active services to TV application domain. Therefore, we implement and experiment the TV contents recommendation service agent, control service agent and TV task based on CAMUS. The context-aware TV task is to recommend programs and control of TV according to user preference, location and voice commands.

• Journal of Sensor Science and Technology
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• v.6 no.2
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• pp.155-162
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• 1997

Zinc oxide(ZnO) thin films were deposited on r-plane sapphires from a solution containing zinc acetate. The films were obtained in a hot wall reactor by the pyrolysis of an aerosol produced by an ultrasonic generator. The crystallinity, surface morphology and composition of the films have been studied using the x-ray diffraction method(XRD) scanning electron microscopy(SEM) and Auger electron spectroscopy (AES) respectively. The influences of the substrate temperature on the crystallinity of the films were studied. Strongly (110) oriented ZnO films were obtained at a substrate temperature of $350^{\circ}C$. The resistivity was increased to above $3{\times}10^{6}{\Omega}{\cdot}cm$ with copper doping and vapor oxidation.