• Journal of the Korean Society of Safety
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• v.32 no.1
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• pp.128-133
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• 2017

This study deals with the roundabout traffic accidents by traffic impeding factor. The purpose of this study is to comparatively analyze the characteristics of accidents and to develop the accident models. In pursuing the above, this study used a statistical program SPSS 20.0 to analyze 2,342 accidents occurred within 79 roundabouts in Korea. The main results are as follows. First, 4 accident models which were all statistically significant were developed. Second, the traffic volume and width of right-turn-only lane were analyzed to be common variable in the bus stop related models. The variables such as right-turn-only lane, street light, turning radius of entry lane were selected as specific variables. Especially street light and turning radius of entry lane were evaluated to have negative effects to the accidents. It is, therefore, essential to install the street light and place a sufficient turning radius in order to reduce the roundabout accidents. Finally, the traffic volume and number of entry lane were analyzed to be common variable in the on-street parking related models. Also, the width of right-turn-only lane and bus stop were evaluate to be specific variables in the model with on-street parking. This can be expected to give some implications to making the accident reduction guidelines.

• International Journal of Highway Engineering
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• v.17 no.4
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• pp.63-68
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• 2015

PURPOSES : A study on the efforts to minimize the road traffic noise has been underway. An attempt has been made to measure the noise level using a noise map; however, the attempt is limited to certain areas only. In general, a noise barrier is employed to prevent road traffic noise; however, unplanned noise barriers developed without considering the surrounding environment, including excessively high walls, cause problems such as infringement on prospect right. Noise ceiling at daytime in Korea is 68 dB(A), which is relatively higher than in other countries. METHODS: The noise barrier used mainly for road noise reduction was analyzed to estimate the optimal height. Related variables such as road width, the height of the upper part, distance to the building, and angle (for instance, $30^{\circ}$). RESULTS : A formula to calculate the optical height of the noise barrier, considering the road environment (i.e., parameters such as road width and distance to building), was developed in this study in an attempt to mitigate the noise generated from the road. CONCLUSIONS : The formula to calculate the noise barrier is expected to lead to cost saving, accurate installation of barriers, and protection of the right of prospect.

• Korean Journal of Optics and Photonics
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• v.13 no.4
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• pp.319-323
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• 2002

1.55 ${\mu}m$multi-quantum well (MQW) broad area laser diodes with different linewidth enhancement factors ($\alpha{-factor}$) of 2 and 4 were fabricated. The far-fields of the laser diodes were measured. It was observed that the full width at half maximum (FWHM) of the far-fields and the filamentations were reduced in the laser diodes for which the value of the $\alpha{-factor}$ was small. As injection current increased, the FWHM of the far-field also increased regardless of the a-factor. This phenomenon was explained by reduction of filament spacing as injection current increased.

• The Journal of the Korea institute of electronic communication sciences
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• v.7 no.4
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• pp.833-837
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• 2012

This paper proposes a DRAM data retention time enhancement method that minimizes silicon loss and undercut at STI sidewall by reducing the SC1 (Standard Cleaning) time. SC1 time optimization debilitates the parasitic electric field in STI's top corner, which reduces an inverse narrow width effect to result in reduction of channel doping density without increasing the subthreshold leakage of cell Tr. Moreover, it minimizes the electric field in depletion area from cell junction to P-well, increasing yield or data retention time.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.6 s.165
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• pp.1026-1038
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• 1999

Interlaminar fracture toughness of carbon/epoxy composite materials has been studied under tensile and flexural loading by the use of width tapered double cantilever beam(WTDCB) and end notched flexure(ENF) specimens. This study has significantly examined the effect of various interfacial ply orientation, ${\alpha}(0^{\circ},\;45^{\circ}\;and\;90^{\circ})$ and crack propagation direction, ${\theta}(0^{\circ},\;15^{\circ},\;30^{\circ}\;and\;45^{\circ})$ in terms of critical strain energy release rate through experiments. Twelve differently layered laminates were investigated. The data reduction for evaluating the fracture energy is based on compliance method and beam theory. Beam theory is used to analyze the effect of crack propagation direction. The geometry and lay-up sequence of specimens are considered various conditions such as skewness parameter, beam volume, and so on. The results show that the fiber bridging occurred due to the non-midplane crack propagation and causes the difference of fracture energy evaluated by both methods. For safer and more reliable composite structures, we obtain the optimal stacking sequence from initial fracture energy in each mode.

• Journal of Power Electronics
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• v.11 no.2
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• pp.132-139
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• 2011

The selective harmonic elimination pulse width modulation (SHEPWM) switching strategy has been applied to multilevel inverters to remove low harmonics. Naturally, the related equations do not have feasible solutions for some operating points associated with the modulation index (M). However, with these infeasible points, minimizing instead of eliminating harmonics is performed. Thus, harmful harmonics such as the $5^{th}$ harmonic still remains in the output waveform. Therefore, it is proposed in this paper to ignore solving the equation associated with the highest order harmonics. A reduction in the eliminated harmonics results in an increase in the degrees of freedom. As a result, the lower order harmonics are eliminated in more operating points. A 9-level inverter is chosen as a case study. The genetic algorithm (GA) for optimization purposes is used. Simulation results verify the proposed method.

• Journal of the Korean Society of Safety
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• v.32 no.3
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• pp.123-129
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• 2017

This study deals with the traffic accident of truck at circular intersection. The purpose of this study is to develop the truck accident models based on type of accident and conflict. In pursuing the above, the study gives particular attentions to selecting the appropriate models among Poisson and Negative binomial models using statistical program LIMDEP 8.0. The traffic accident data from 2007 to 2014 are collected from TAAS data set of Road Traffic Authority. Such the dependent variable as number of truck accidents and the 24 independent variables as geometry, traffic volume and others are used. The main results are as follows. First, 5 Poisson models (${\rho}^2$ of 0.164~0.351) which are all statistically significant are selected. Second, the common variable based on type of accident and conflict is analyzed to be truck apron width. The specific variables are, however, evaluated to splitter island, area of splitter island, speed limit sign, truck apron, number approach road, circular intersection sign, speed hump and traffic volume. Finally, widening the truck apron width and improving the above specific variables are analyzed to be important for truck accident reduction at circular intersections.

• Wind and Structures
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• v.26 no.5
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• pp.317-329
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• 2018

Wake characteristics of the flow over a finite square prism at different incidence angles were experimentally investigated using an open-loop wind tunnel. A finite square prism with a width D = 15 mm and a height H = 7D was vertically mounted on a horizontal flat plate. The Reynolds number was varied from $6.5{\times}10^3$ to $28.5{\times}10^3$ and the incidence angle ${\alpha}$ was changed from $0^{\circ}$ to $45^{\circ}$. The ratio of boundary layer thickness to the prism height was about ${\delta}/H=7%$. The time-averaged velocity, turbulence intensity and the vortex shedding frequency were obtained through a single-component hotwire probe. Power spectrum of the streamwise velocity fluctuations revealed that the tip and base vortices shed at the same frequency as that ofspanwise vortices. Furthermore, the results showed that the critical incidence angle corresponding to the maximum Strouhal number and minimum wake width occurs at ${\alpha}_{cr}=15^{\circ}$ which is equal to that reported for an infinite prism. There is a reduction in the size of the wake region along the height of the prism when moving away from the ground plane towards the free end.

• Journal of Power Electronics
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• v.15 no.6
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• pp.1524-1532
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• 2015

Conventional space vector pulse width modulation based asymmetrical dual inverter configuration produces high common mode voltage (CMV) variations. This CMV causes the flow of common mode current, which adversely affects the motor bearings and electromagnetic interference of nearby electronic systems. In this study, a simple and generalized carrier based pulse width modulation (PWM) technique is proposed for dual inverter configuration. This simple approach generates various continuous and discontinuous modulating signals based PWM algorithms. With the application of the discontinuous modulating signal based PWM algorithm to the asymmetrical dual inverter configuration, the CMV can be reduced with a slightly improved quality of output voltage. The performance of the continuous and discontinuous modulating signals based PWM algorithms is explored through both theoretical and experimental studies. Results show that the discontinuous modulating signal based PWM algorithm efficiently reduces the CMV and switching losses.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.2
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• pp.253-258
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• 2012

A computationally efficient interpolation filter with a low-distortion performance is a key component to utilize the naturally-sampled pulse width modulation (NPWM) in a digital domain. To realize the efficient interpolation filter, we propose a novel design based on the recently-proposed modified Farrow filter. The proposed filter shows a better pass-band distortion performance maintaining similar degree of complexity compared with the conventional Lagrange interpolation filter. We achieve the maximum distortion deviation of 10-3 dB to 20-kHz audible frequency range and distortion reduction of 1/6 times compared with the Lagrange interpolation filter.