• Steel and Composite Structures
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• v.2 no.6
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• pp.475-488
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• 2002

In steel bridges fatigue cracks are sometimes repaired by placing drilled holes at the crack tips. From the meaning that the drilled holes stop the propagation of cracks, they are called stop-holes. Since stop-holes are regarded as an emergency measure to delay crack propagation, usually some substantial repair follows. However, if the stress at the stop-holes is below their fatigue limit, fatigue cracks would not be expected to occur. The purpose of this study is to present the conditions under which stop-holes prevent the reinitiation of fatigue cracks. The fatigue limit of stop-holes and the equations necessary to estimate the maximum stress on the circumference of the stop-holes are provided.

• Journal of the Korean Society of Safety
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• v.7 no.2
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• pp.47-56
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• 1992

The retardation effect of fatigue crack propagation after cyclic overloading seems to be affected by strain hardening exponent. Namely, for the material with high values of n, the delay effect is found to be severe. We proposed a modified crack retardation equation which may apply the retardation of fatigue crack growth after a cyclic overloading, as (da/dN)'$_{cyc}$=($\mu$n＋λ)B $\Delta$ $K^{q}$ /[(1－ $R_{eff}$) $K_{cf}$ －$\Delta$K]. where, $R_{eff}$ is effective stress ratio [＝( $K_{min}$－K, os)/( $K_{max}$－ $K_{res}$)] The constants $\mu$＝－0.5 and λ＝0.6, and the values are found to be identical for materials such as aluminum (A 1060), steel (SS 34), brass ( $B_{s}$ SIB) and stainless steel (SUS 304) used in this investigation. (SUS 304) used in this investigation.ation.n.n.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.55 no.11
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• pp.491-494
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• 2006

In the adder design, reduction of the delay of the carry propagation or ripple is the most important consideration. Previously, it was introduced that, if a redundant number system is adopted, the carry propagation is completely eliminated, with which addition can be done in a constant time, without regarding to the count of the digits of numbers involved in addition. In this paper, a RBCD(Redundant Binary Coded Decimal) is adopted to code 0 to 11, and an efficient and economic carry-free BCD adder is designed.

• Journal of the Korean Society of Safety
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• v.8 no.4
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• pp.114-119
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• 1993

The explosion characteristics of nonhomogeneous LPG-Air mixtures was measured in a cylindrical vessel and a pipe. The maximum explosion pressure, the maximum rate of explosion pressure rise, and the flame propagation velocity were measured and compared with that of homogeneous explosion by changing the effective factors on the explosion of nonhomogeneous mixtures such as pressure difference, effusion time and delay time. Explosion was occured even in the lower concentration than the lean flammability limit of mixture. The maximum explosion pressure was increased with increase of LPG concentration, however, the maximum explosion pressure rise was not in the nonhomogeneous explosion. An d the flame propagation velocity was decreased with nonhomogeneity, however, the maximum explosion pressure was always above 0.7kg/$\textrm{cm}^2$.

• The Journal of Information Technology
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• v.9 no.4
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• pp.65-74
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• 2006

The back propagation of neural networks has the problems of falling into local minimum and delay of the speed by the iterative learning. An algorithm to solve the problem and improve the speed of the learning was already proposed in[8], which updates the learning parameter related with the connection weight. In this paper, we propose the algorithm generating initial weight to improve the efficiency of the algorithm by offering the difference between the input vector and the target signal to the generating function of initial weight. The algorithm proposed here can classify more than 98.75% of the handwritten digits and this rate shows 30% more effective than the other previous methods.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.1
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• pp.101-105
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• 2008

This paper proposes an analytical model to calculate VoIP (Voice of IP) capacity over wireless LANs with frequent bit errors. Since the traditional analytical models for VoIP capacity have not included the effect of bit errors, simulations ould only evaluate VoIP capacity over erroneous channels. For analytically accurate estimation of VoIP capacity over noisy channels, we extend the conventional model to include the effect of propagation errors, end-to-end delay, voice quality, the waiting time in AP(Access Point). The experiments show that our model predicts the VoIP capacity of a given network within the range from 3% to 9% difference comparing with the simulation results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.2
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• pp.199-207
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• 2001

In this paper, the technique of prediction and analysis on the characteristics of propagation in indoor environment is presented. This technique needs no reception sphere commonly used in 3D-ray tracing scheme, and thereby it lends us easy code realization. The validity of developed code is verified by comparing with the values of image methods and measurement. The developed technique applied to the structure of rectangular corridor with the iron door and we calculated the path loss for the variation of the iron door angle. The path loss decreased about 15 dB at the distance of30 m from the iron door and the delay spread increased approximately by four times. Based on the computation, we confirmed that indoor propagation in PCS is heavily affected by the iron door in corridor.

• The Journal of Information Technology
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• v.2 no.2
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• pp.145-161
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• 1999

This paper proposes a high speed back propagation neural networks which uses the residue number system. making the high speed operation possible without carry propagation Consisting of MAC(Multiplication and Accumulation) operator unit using Residue number system and sigmoid function operator unit using Mixed Residue Conversion is designed, The Designed circuits are descripted by VHDL and synthesized by Compass tools. Result of simulations shows that critical path delay time is about 19nsec and the size can be reduced to 40% compared to the neural networks implemented by the real number operation unit. The proposed design circuits can be implemented in parallel distributed processing system with desired real time processing.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.2
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• pp.389-396
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• 1994

It is very important to clarify the ignition and flame propagation processes of methanol fuel in the Spark-ignition engine. High speed Schlieren photography and pressure trace analyses were used to study on combustion characteristics of methanol fuel in a constant volume chamber. Methanol-air mixtures equivalence rations from lean limit to 1.4 were ignited at initial pressure (0.1, 0.3, 0.5 MPa), temperature (313 343, 373 K) and ignition energy (40, 180 mJ). As the result of this study, we verified the characteristics such as ignition delay, effective thermal efficiency, flame propagation velocity, lean limit, ignitability and combustion duration. Obatained results are as follows. (1) The time to 10% reach of maximum pressure was 40-50% of the total combustion duration for this experimental condition hardly affected by equivalence ratio. (2) The Effective thermal efficiency, as calculated from maximum pressure was the highest when the mixture was slightly lean $({\phi} 0.8-0.9)$ and maximum pressure was the highest when the mixiture was slightly rich $({\phi} 1.2-1.2).$

• ETRI Journal
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• v.43 no.3
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• pp.377-388
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• 2021

Owing to the difficulties associated with conducting millimeter-wave (mmWave) field measurements, especially in high-speed train (HST) environments, most propagation channels for mmWave HST have been studied using methods based on simulation rather than measurement. In this study, considering a linear cell layout in which base stations are installed along a railway, measurements were performed at 28 GHz with a speed up to 170 km/h in two prevalent HST scenarios: viaduct and tunnel scenarios. By observing the channel impulse responses, we could identify single- and double-bounced multipath components (MPCs) caused by railway static structures such as overhead line equipment. These MPCs affect the delay spread and Doppler characteristics significantly. Moreover, we observed distinct path loss behaviors for the two scenarios, although both are considered line-of-sight (LoS) scenarios. In the tunnel scenario, the path loss exponent (PLE) is 1.3 owing to the waveguide effect, which indicates that the path loss is almost constant with respect to distance. However, the LoS PLE in the viaduct scenario is 2.46, which is slightly higher than the free-space loss.