• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1994년도 특별강연 및 추계학술발표 개요집
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• pp.93-95
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• 1994

• Journal of Welding and Joining
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• 제17권5호
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• pp.61-68
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• 1999

For the last two decades, waveform control techniques have been successively developed and applied for the inverter welding machines resulting in the substantial reduction of spatter generated in CO₂ welding. One of the constituents commonly involved in those techniques is to delay the instant of current increase to some extent after the initiation of short-circuiting. Although this technique has been known to be quite effective in reducing the spatter generation through the suppression of is instantaneous short circuiting, the delay time necessary for minimum spatter has not been clearly understood. In this study, the control system for varying the delay time was constructed so that the spatter generation rates could be measured over a wide range of delay time, 0.29-2.0 msec. As a result of this study, it was demonstrated that spatter generation rate(SGR) sharply decreased at delay time of 0.6 msec and longer accompanied with the change in characteristics of short circuit mode from the instantaneous short-circuiting(ISC) dominant to normal short-circuiting(NSC) dominant. Another feature that have been found in current waveform of over 0.6msec was the creation of current pulse right after the arc reignition stage. Because of this current pulses weld pool oscillated in wave-like fashion and it looks like to play an important role in developing short circuiting between electrode and weld pool.

• 한국ITS학회 논문지
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• 제8권1호
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• pp.30-36
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• 2009

도심지역에서 사용되는 DSRC 통신시스템은 노변기지국과 차량간 100미터의 통신거리를 갖고 있으며, 이 특성을 이용하여 DSRC시스템에서 RSE(Road Side Equipment)는 차량으로부터 교통정보를 수집하거나 차량에 교통정보를 제공한다. 그러나 고속도로상에서 100미터 통신범위를 갖는 RSE를 사용하는 것은 장비가격 및 설치비가 고가이어서 현실적으로 많은 어려움이 있다. 본 논문에서는 RSE의 표준 셀 범위를 100미터에서 300미터로 확장하고 차량단말기가 RSE와 통신할 수 없는 불감지역을 Cover 하기 위하여 Fixed Relay를 도입하였으며, 이로 인해 Fixed Relay를 사용하는 것이 RSE 만을 사용하는 것 보다 더 경제적인 것을 보인다.

• 융합신호처리학회논문지
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• 제23권2호
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• pp.50-61
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• 2022

This work demonstrates the design and evaluation of Aqua-Aware, a lightweight miniaturized light emitting diode (LED) based underwater compact sensor node which is used to obtain different characteristics of the underwater environment. Two optical sensor nodes have been designed, developed, and evaluated for a short and medium link range called as Aqua-Aware short range (AASR) and Aqua-Aware medium range (AAMR), respectively. The hardware and software implementation of proposed sensor node, algorithms, and trade-offs have been discussed in this paper. The underwater environment is emulated by introducing different turbulence effects such as air bubbles, waves and turbidity in a 4-m water tank. In clear water, the Aqua-Aware achieved a data rate of 0.2 Mbps at communication link up to 2-m. The Aqua-Aware was able to achieve 0.2 Mbps in a turbid water of 64 NTU in the presence of moderate water waves and air bubbles within the communication link range of 1.7-m. We have evaluated the luminous intensity, packet success rate and bit error rate performance of the proposed system obtained by varying the various medium characteristics.

• Journal of the Optical Society of Korea
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• 제16권4호
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• pp.331-335
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• 2012

A miniaturized laser beam transmitter, in which a visible laser module at ${\lambda}$=650 nm is precisely stacked upon an infrared (IR) module at ${\lambda}$=905 nm, has been proposed and constructed to provide an IR collimated beam in conjunction with a collinear monitoring visible beam. In particular, the IR beam is selectively dispersed through a perforated sheet diffuser, so as to create a rapidly diverging close-range beam in addition to a highly defined long-range beam simultaneously. The complementary close-range beam plays a role in mitigating the blind region in the vicinity of the transmitter, which is inevitably missed by the main long-range beam, thereby uniformly extending the transmitter's effective trajectory that is sensed by a receiver. The proposed transmitter was designed through numerical simulations and then fabricated by incorporating a diffuser sheet, perforated with an aperture of 2 mm. For the manufactured transmitter, the IR long-range beam was observed to have divergences of ~2.3 and 1.6 mrad in the fast and slow axes, respectively, while the short-range beam yielded a divergence of ~24 mrad. The angular alignment between the long-range IR and visible beams was as accurate as ~0.5 mrad. According to an outdoor feasibility test involving a receiver, the combination of the IR long- and short-range beams was proven to achieve a nearly uniform trajectory over a distance ranging up to ~600 m, with an average detectable cross-section of ${\sim}60{\times}80cm^2$.

• 한국전자파학회논문지
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• 제29권11호
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• pp.834-841
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• 2018

본 논문은 $0.18{\mu}m$ CMOS 공정을 이용한 Sub-GHz 근거리 무선통신을 위한 전력증폭기 설계에 관한 내용이다. 가상접지 노드를 용이하게 형성하며, 출력전력을 키울 수 있는 차동구조로 설계하였으며, breakdown으로 인한 문제를 최소화하기 위하여 cascode 구조로 설계하였다. 또한 출력전력과 Power Added Efficiency(PAE)가 최대가 되도록 트랜지스터 게이트 폭을 결정하고, matching network으로 인한 손실이 최소화하기 위해 EM simulation을 통하여 balun을 최적화하였다. 제작된 전력증폭기는 크기가 $2.14mm^2$이며, 860~960 MHz의 주파수 범위에서 49.5 dB 이상의 이득과 26.7 dBm의 최대출력을 가지며, 최대효율은 20.7 %이다.

• Current Applied Physics
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• 제18권11호
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• pp.1248-1254
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• 2018

Magnetization versus temperature and magnetic-field measurements, M(T, $H_a$), have been carried out to study the magnetic and critical properties of polycrystalline $La_{1-x}Ba_xCoO_3$ (x = 0.3 and 0.5) cobaltites. These compounds with the density of ${\sim}6.2g/cm^3$ crystallized in the $R{\bar{3}}c$ rhombohedral and $Pm{\bar{3}}m$ cubic structures, respectively. With an applied field $H_a=200Oe$, M(T) data have revealed that the samples with x = 0.3 and 0.5 exhibit the ferromagnetic-paramagnetic (FM-PM) phase transition at the Curie temperature points $T_C=202$ and 157 K, respectively. At 4.2 K, the saturation magnetization ($M_{sat}$) decreases from 35.9 emu/g for x = 0.3-26.1 emu/g for x = 0.5. Particularly, the critical-behavior analyses in the vicinity of $T_C$ reveal all samples undergoing a second-order phase transition, with critical exponent values (${\beta}=0.328$ and ${\gamma}=1.251$ for x = 0.3, and ${\beta}=0.331$ and ${\gamma}=1.246$ for x = 0.5) close to those expected for the 3D Ising model. This proves short-range magnetic order existing in $La_{1-x}Ba_xCoO_3$. We believe that magnetic inhomogeneities due to the mixture of hole-rich FM regions (confined in the trivalent-cobalt hole-poor anti-FM matrix) and uniaxial anisotropy prevent long-range order in $La_{1-x}Ba_xCoO_3$.

• Advances in materials Research
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• 제4권2호
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• pp.97-111
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• 2015

Polypropylene short fiber (PP)-clay particulate-epoxy ternary composites were prepared by reinforcing PP short fiber and clay particles in the range of 0.1 phr to 0.7 phr into epoxy resin. Prepared hybrid composites were characterized for their mechanical, thermal and flame retardant properties. The obtained results indicated an increase in impact resistance, tensile strength, flexural strength and Young's modulus to an extent (up to 0.5 phr clay and 0.5 phr PP short fiber) and then decreases as the reinforcing phases are further increased. The thermal stability of these materials are found to increase up to 0.2 phr clay and 0.2 phr PP addition, beyond which it is decreased. Addition of clay is found to have the negative effect on epoxy-PP short fiber composites, which is evident from the comparison of mechanical and thermal properties of epoxy-0.5 phr PP short fiber composite and epoxy-0.5 phr PP short fiber-0.5 phr clay composite hybrid. UL-94 tests conducted on the composite hybrids have showed a reduction in the burning rate. Morphological observations indicated a greater fiber pull with the addition of clay. The performed tests in the present study indicated that materials under investigation have promising applications in construction, agriculture and decorative purposes.

• Journal of Communications and Networks
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• 제15권1호
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• pp.54-60
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• 2013

In this paper, a novel method called location-based delivery (LBD), which combines the short message service (SMS) and global position system (GPS), is proposed, and further, a realistic system for tracking a target's movement is developed. LBD reduces the number of short message transmissions while maintaining the location tracking accuracy within the acceptable range. The proposed approach, LBD, consists of three primary features: Short message format, location prediction, and dynamic threshold. The defined short message format is proprietary. Location prediction is performed by using the current location, moving speed, and bearing of the target to predict its next location. When the distance between the predicted location and the actual location exceeds a certain threshold, the target transmits a short message to the tracker to update its current location. The threshold is dynamically adjusted to maintain the location tracking accuracy and the number of short messages on the basis of the moving speed of the target. The experimental results show that LBD, indeed, outperforms other methods because it satisfactorily maintains the location tracking accuracy with relatively fewer messages.

• 한국정보통신학회논문지
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• 제17권9호
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• pp.2174-2182
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• 2013

본 논문에서는 LED 기반 VLC 통신시스템의 기술동향 및 국제표준인 IEEE 802.15.7의 PHY 기술을 분석하였다. 또한, PHY I mode의 세부기술을 분석하고 RS 부호 및 블록 인터리버를 설계함으로써 시스템의 복잡도 분석 및 가시광 무선채널 환경에서의 수신 성능을 분석하였다. 결과에 의하면, Single mode로 운영되는 PHY I의 경우, 짧은 메시지 전송이라는 환경에 비해 시스템 설계의 복잡도가 크다는 것을 확인할 수 있었고, 다중경로 가시광 채널환경에서는 1.5dB의 수신 SNR이 추가적으로 요구됨을 확인할 수 있었다.