• Journal of Power Electronics
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• 제10권1호
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• pp.27-33
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• 2010

This paper presents a bidirectional DC-DC converter suitable for low-voltage super capacitor-based electric energy storage systems. The DC-DC converter presented here consists of a full-bridge circuit and a current-fed push-pull circuit with a high frequency (HF) transformer-link. In order to reduce the device-conduction losses due to the large current of the super capacitor as well as unnecessary ringing, synchronous rectification is employed in the super capacitor-charging mode. A wide range of voltage regulation between the battery and the super capacitor can be realized by employing a Phase-Shifting (PS) Pulse Width Modulation (PWM) scheme in the full-bridge circuit for the super capacitor charging mode as well as the overlapping PWM scheme of the gate signals to the active power devices in the push-pull circuit for the super capacitor discharging mode. Essential performance of the bidirectional DC-DC converter is demonstrated with simulation and experiment results, and the practical effectiveness of the DC-DC converter is discussed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1989년도 하계종합학술대회 논문집
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• pp.571-575
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• 1989

A position control system of D.C. Servo motor based on discrete variable structure system with sliding mode is presented. The sliding mode has been designed for a continuous system, but it is often realized in digital fashion because the complex switching logic can be easily carried out. In digital control system, the ideal sliding mode does not occur since the structure can't be switched during sampling interval. However, there can be exist a motion which is confined to a regoin including the sliding surface and proceeds to the origin along the surface. This notion is called quasisliding mode. In this paper, we introduce this control scheme to the D.C. Servo motor position control in order to reduce the chattering phenonenon.

• 부모자녀건강학회지
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• 제13권2호
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• pp.95-101
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• 2010

Purpose: This study is intended to identify difference postpartum depression according to delivery mode in the postpartum women. Methods: The subjects were 239 postpartum women in D and A city. Data collected from June 9, 2006 to August 6, 2007 using structured questionnaire surveys and convenience sampling. Measuring instrument was BDI (Beck Depression Inventory) translated By Lee and Song (1991). Collected data was analyzed by $x^2$-test, ANCOVA, Stepwise Multiple Regression with SPSS/PC 14.0. Results: There were significant differences in postpartum period ($x^2$=12.40, p = .002) and sleeping hours ($x^2$=9.09, p = .011) as analysed distribution of the subjects according to delivery mode. As result of analyzing the difference of postpartum depression according to delivery mode using ANCOVA, C-sec women's postpartum depression was higher than vaginal delivery women statistically (F=6.32, p = .013). As a result of Multiple Regression, income was a influencing factor of postpartum depression in vaginal delivery women and support of spouse and sleeping hours were influencing factors in C-sec women. Conclusion: There were differences in postpartum depression and their influencing factors according to delivery mode. Therefore it is necessary to develop and study a concrete nursing intervention and strategies for reducing the postpartum depression according to delivery mode.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 하계학술대회 논문집 C
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• pp.1171-1173
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• 1995

Polyimide thin films were fabricated through the vapor deposition polymerization method, and the structure and capacitance characteristics of them were investigated in detail. It was found that the chemical structure and uniformity of the film could be stabilized with curing. The peaks of $720cm^{-l},\;1380cm^{-1}\;and\;1780cm^{-1}$ show C=O stretch mode, C-N stretch mode and carbonyl stretch mode, and those of polyimide which cured over $300^{\circ}C$ were fixed. It was found that capacitance was changed in proportion to temperature.

• Structural Engineering and Mechanics
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• 제63권1호
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• pp.11-21
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• 2017

In this paper, the efficiency and the accuracy of classical (CE) and high order (HE) beam element are improved by introducing two novel techniques. The first proposed element (FPE) provides an alternative for (HE) by taking the mode shapes of the clamped-clamped (C-C) beam into account. The second proposed element (SPE) which could be utilized instead of (CE) and (HE) considers not only the mode shapes of the (C-C) beam but also some virtual nodes. It is numerically proven that the eigenvalue problem and the frequency response function for Euler-Bernoulli beam are obtained more accurate and efficient in contrast to the traditional ones.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.206-211
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• 2000

Fatigue test was conducted on a S45C steel using hour-glass shaped smooth tubular specimen under biaxial loading in order to investigate the crack formation and growth at room temperature. Three types of loading system, i.e fully reserved cyclic torsion without a superimposed static tension or compression, fully reserved cyclic torsion with a superimposed static tension and fully reserved cyclic torsion with a superimposed static compression were employed. The test results show that a superimposed static tensile mean stress reduced fatigue lifetime. however a superimposed static compressive mean stress increased fatigue lifetime. Experimental results indicated that cracks were initiated on planes of maximum shear strain with either a superimposed mean stresses or not. A biaxial mean stress had an effect on the direction which cracks nucleated and propagated at stage I (mode II).

• 한국자동차공학회논문집
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• 제7권5호
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• pp.249-257
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• 1999

A three dimensional finite model of a human neck has been developed in an effort to study the mechanics of cervical spin while subjected to vertical impact. This model consisting of the vertebrae from C1 through C7 including posterior element and ligaments was constructed by 2mm thick transverse CT cross-sections and X-ray film taken at lateral side. Geometrical nonlinearity was also considered for the large deformation on the disc. ABAQUS package was used for calculation and its results were verified comparing with responses of a model under static loading condition with published in-vitro experimental data. There were more cervical fracture in the restrained (compression) mode than in the nonrestrained (flexion-compression and extension-compression) mode. Upper cervical(C1-C2) injuries were observed under compression-extension modes, while lower cervical injuries occurred undjer compression-flexion modes. Posterior ligament distraction without bony damage at the upper cervical spin(C1-C2) were observed secondary to C5-C7 trauma in compression-flexion modes.

• 한국세라믹학회지
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• 제35권12호
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• pp.1316-1322
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• 1998

The amount of VC and C/N ratio in Ti(CN) was varied to investigate the effect of VC addition on the mi-crostructural change in Ti(CN)-Ni system. As the amount of VC addition increases in Ti(C0.7N0.3)-20Ni sys-tem a complete solid solution was observed in Ti(C0.7N0.3)-20Ni-25VC system. It implies that the ratio of the dissolution rates of Ti(C0.7N0.3)to that of VC is nearly 2:1 at the sintering conditions used in this study. It was found from the experiments that the system composed of the Ti(C0.7N0.3) phase exhibits a rimless structure and relatively small amount of solid solution. That is among Ti(C0.7N0.3) phase exhibits a rimless structure and relatively small amount of solid solution. This is among Ti(C1-xNx) phases the dissolution rate of Ti(C0.3N0.7) is the lowest. Also fracture toughness(KIC) of the cermet was measured by indentation method. Attentions were paid to crack propagation path to look for a dominant fracture mode and to cor-relate it with fracture toughness values. The fracture toughness was relatively high with the addition of VC content. But the addition of a large VC content reduced the overall toughness of the cermet. This result is explained with the difference in fracture mode.

• 마이크로전자및패키징학회지
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• 제18권3호
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• pp.45-52
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• 2011

Flip Chip Ball Grid Array (FCBGA) 패키지의 솔더조인트 신뢰성을 평가하기 위한 방법으로는 다이 충격법, 다이 전단법, 3점 굽힘법, 열충격법 등이 활용된다. 본 연구에서는 솔더 접합부의 주요 고장메카니즘인 취성파괴를 확인하기 위한 방법으로 리플로우 상태, $85^{\circ}C$/85%RH 처리, $150^{\circ}C$/10hr 에이징의 처리한 후, 4가지 평가법으로 평가를 진행하여 파단모드를 분석하였다. 본 연구결과에서는 다이 충격법과 다이 전단법의 Good joint rate (GJR, %)는 리플로우 상태와 $85^{\circ}C$/85%RH처리에서 각각 89~91%와 100% 였으며, $150^{\circ}C$/10hr 에이징에서는 66%와 90%를 나타내었다. 3점 굽힘법과 열충격법의 GJR(%)는 3종류 샘플에서 모두 100%를 나타내어 변별력이 없었다. C4 솔더접합부의 신뢰성 평가법에 따른 GJR(%)의 변별력을 확인할 수 있는 방법은 die shock 과 die shear test였다.

• Bulletin of the Korean Chemical Society
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• 제31권12호
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• pp.3771-3776
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• 2010

The dynamics of the $CN^-$-ligated ferric cytochrome c (CytcCN) in $D_2O$ at 283 K following Q-band photoexcitation at 575 nm was observed using femtosecond time-resolved vibrational spectroscopy. The equilibrium vibrational spectrum of the CN stretching mode of CytcCN shows two overlapping bands: one main band (82%) at $2122\;cm^{-1}$ with $23\;cm^{-1}$ full width at half maximum (fwhm) and the other band (18%) at $2116\;cm^{-1}$ with $7\;cm^{-1}$ fwhm. The time-resolved spectra show bleaching of the CN fundamental mode of CytcCN and two absorption features at lower energies. The bleach signal and both absorption features are all formed within the time resolution of the experiment (< 200 fs) and decay with a life time of 1.9 ps. One transient absorption feature, appearing immediately red to the bleach signal, results from the thermal excitation of low-frequency modes of the heme that anharmonically couple to the CN fundamental mode, thereby shifting the CN mode to lower energies. The shift of the CN mode decays with a lifetime of 2 ps, equivalent to the time scale for vibrational cooling of the low-frequency heme modes. The other transient absorption feature, which is 3.3 times weaker than the bleach signal and shifted $27\;cm^{-1}$ toward lower energies, is attributed to the CN mode in an electronically excited state where the CN bond is weakened with a lowered extinction coefficient. These observations suggest that photoexcited CytcCN mainly undergoes ultrafast radiationless relaxation, causing photo-deligation of $CN^-$ from CytcCN highly inefficient. As also observed in $CN^-$-ligated myoglobin, inefficient ligand photodissociation might be a general property of $CN^-$-ligated ferric hemes.