Determining the Predictors of Postpartum Depression in Vietnamese Women: Mediating Effect of Maternal Role Strain

NGUYEN THI PHUONG THAO Garduate school, Inje university, Korea 2021 국내박사

Postpartum depression is a significant public health issue which has not only negative effects on maternal postpartum health but also on family relationship and infant growth and development. In Vietnam, postpartum depression is not usually cared in the community as well as in the health care system because it is insufficiently screened or diagnosed and followed up during the postpartum period. Moreover, there is very little research analyzing, predicting factors of postpartum depression. Especially there is less study of the mediating effects of maternal role strain among self-efficacy, social support, infant temperament, and postpartum depression in Vietnam. Moreover, the support of the theoretical model in which self-efficacy, social support, and infant temperament were linked to postpartum depression symptoms through their effects on maternal role strain is important both contribute to conceptual understanding of these processes and to seek effective interventions for postpartum depression in Vietnamese women. Thus, the purposes of this study are to identify the predictors for postpartum depression and determine the mediating effects of the maternal role strain on the relationship among the degree of self-efficacy, infant temperament, social support, and postpartum depression. Methods: The focus of correlational descriptive research design was performed on 190 mothers who were the first birth from four weeks to six months and be enrolled to give vaccination in 12 community health centers of Hue city in Vietnam. Data gathering tools included the “Perceived Self-Efficacy Scale”, “Maternal Social Support Scale”, “Difficult Infant Temperament Scale”, “Maternal Role Strain Scale”, and “Edinburgh Postnatal Depression Scale (EPDS)”. Data analysis was done by using the SPSS software, which was based on descriptive statistics and statistical independent t-test or one-way ANOVA test, mediation. These were tested by a series of multiple regressions by using Baron and Kenny methods. The Sobel test was used to test the significance of the mediating effects. Results: The prevalence of probable postpartum depression which had the EPDS score at or greater cut-off of 13 points was 18.9%. There were a significant differences between postpartum depression and mother’s occupation (t=-2.86, p=.005), relationship with her husband (F=5.91, p=.003), stressful life events (t=2.94, p=.004), paid maternity leave (F=6.83, p=.001), and gestational age (t=3.32, p=.001), history of mental health (t=3.86, p<.001), self-efficacy (r=-.15, p=.030), and social support (r=-.38, p<.001), infant temperament (r=.40, p<.001), and maternal role strain (r=.59, p<.001). Furthermore, there was identified paid maternity leave (β=-.16, p=.004), gestational age (β=.15, p=.005), history of mental health (β=-.19, p=.002), self-efficacy (β=.12, p=.031), and the maternal role strain (β=.47, p<.001) as the prediction of postpartum depression. The regression model with significant predictors explains 46% of the variance. As the mediating effects, maternal role strain had a full mediating effect on the relationship between self-efficacy and postpartum depression. Besides, maternal role strain was also a partial mediating effect on the relationship between maternal social support, infant temperament and postpartum depression among postpartum women. Conclusion: The findings of this study contribute to nursing science by identifying the mediating effects of maternal role strain on postpartum depression in Vietnam. Future research suggests solutions for professional experts of community mental health to develop effective intervention strategies which aims at the reduction of maternal role strain to decrease the impact of self-efficacy, social support, infant temperament on postpartum depression.

Development of SOI MEMS-based silicon strain gauges for fuel cell electric vehicle

김진웅 Garduate School, Korea University 2019 국내박사

Hydrogen gas is attracting much attention as a next-generation fuel to replace fossil fuels that have a problem of resource depletion and environmental pollution. The reason is that when hydrogen gas is used in fuel cells, it is an environmentally friendly material that is more efficient than gasoline vehicles and can reduce carbon emissions. A hydrogen fuel cell vehicle with these advantages has a built-in fuel tank that stores hydrogen, and a stable pressure sensor is essential for this fuel tank. In other words, a high-sensitivity silicon strain gauge is indispensable to constitute a pressure sensor system capable of continuously monitoring the loading state of hydrogen gas in the fuel cell automobile sector, which mainly uses hydrogen gas. The recently commercialized hydrogen pressure sensor diaphragm is made of stainless steel 316L to prevent hydrogen embrittlement. This material has a larger coefficient of thermal expansion than any other material. Therefore, it is very difficult to completely attach the strain gage chip to this diaphragm without any post-misalignments such as break, rotation and movement. It is very important that the gauge is attached to the metal diaphragm because the output performance of the pressure sensor, such as durability and reliability, depends on the quality of the silicon strain gauge. Many post-misalignments occur due to the stress caused by the coefficient of thermal expansion (CTE) mis-match between the substrate and the diaphragm of the conventional gauge. Open-type silicon strain gages have been commercialized to address this problem, but it is much more difficult to automate the alignment and bonding processes because the gages are open and fragile, requiring more manufacturing cost and time. In this thesis, I present a new half-bridge silicon strain gauge fabricated on a silicon-on-insulator (SOI) substrate by MEMS bulk micromachining technology that can compromise the problems presented above. These gauges have holes etched through the wafer by deep reactive ion etching (DRIE) and a closed shape with four sides, unlike the current competitive devices with open structures. This unique design minimizes the shifting or gating position and enhances the bonding strength during glass-frit bonding, leading to improved sensor performance and yield, and thus a reduction in sensor cost. In addition, the ratio of the area of the through hole to the total area of the chip is optimized based on the results of the post-misalignments test using gauges having various through hole ratios, and an asymmetric gauge for improving the sensitivity is presented. In order to demonstrate the feasibility of using a hydrogen fuel cell pressure sensor, the prototype half-bridge gages were tested under pressure ranging from 0 bar to 900 bar and showed a linear output with a typical gage factor of about 112 and an average hysteresis of 0.0192 %FSO. In addition, the full bridge output for 0-900 bar shows a typical sensitivity of about 0.0086 mV/V/bar, a maximum thermal zero shift of -3.1 %FSO, and a thermal sensitivity shift of -15.12 %FSO.

(The) effect of an antigalvanic reduction of silver on gold for the stability of a self-assembled alkanethiol monolayer and chemical lift-off lithography

Nguyen Minh Hoang Garduate School, Korea University 2019 국내석사

The effects of silver anti-galvanic reduction (Ag AGR) on the structure of alkanethiol self-assembled monolayers (SAMs) on gold with regard to the ordered structure and surface coverage were studied using electrochemical methods. In this paper, we report the structure changes as well as the chemical lift-off lithography (CLL) performance of SAMs dependent on chain lengths, namely 1-butanethiol, 6-mercapto-1-hexanol and 11-mercapto-1-undecanol. Cyclic voltammetry of redox probe and linear sweep voltammetry of reductive desorption demonstrated that the structure of SAMs with Ag AGR pretreatment are more ordered resulted from higher surface coverage and stronger molecules interaction. Meanwhile, influence of Ag AGR on the CLL efficiency behaved differently depending on the SAM chain lengths in both electrochemistry and AFM imaging. Nevertheless, the formation of alkanethiol SAMs on Ag AGR/Au has enabled a facile method which possesses a great potential on the quality control of the SAMs system.

Study of optical, electrical and chemical phenomena on silicon nitride interface in liquid crystal display

최낙초 Garduate School, Korea University 2019 국내박사

LCD 디스플레이를 만드는데 사용하고 있는 Silicon Nitride 막 계면에서 일어나는 광학적, 전기적 그리고 화학적 현상에 대한 연구이다. 특히 현재 LCD TV의 Main stream으로 높은 대비비를 가지는 Polymer Stabilized Vertical Alignment(PS-VA) Mode에서 액정 및 픽셀 전극 하부에 SiNx가 존재하는데, 전극층과 SiNx 사이에서 생기는 Stress miss matching에 의한 Patterned-induced Retardation을 처음으로 관찰하고 정량화하여 그 원인을 찾아내 Black 휘도를 낮출 수 있었다. 또한 PS-VA mode에서 액정내 미량 존재하는 Monomer를 UV 전계 노광 공정을 통해 Pretilt 형성을 하여 높은 투과율과 빠른 응답시간을 구현하는데 있어서 정교한 Fringe field 통제가 필요한데, SiNx 하부에 mobile ion이 존재할 경우, 전계 노광 공정 시 Fringe filed 를 왜곡시켜 액정 Texture발생시켜 투과율 저하를 일으키는 것을 화학 분석과 3차원 시뮬레이션을 통해 밝혔으며, 이를 극복하는 방안을 제시하여 검증하였다. 마지막으로 소비자들의 높은 해상도를 가지는 TV를 요구함에 따라 고해상도 TV PIXEL 구조에서 개구비를 낮추지 않으면서도 우수한 측면 시인성을 만들 수 있는 Coupled Capacitance(CC) Mode를 이중 투명 전극을 사용하여 구현하였으며, 이때 상온, 고온 잔상의 문제를 액정과 SiNx사이의 RC miss matching 에 의한 AC전압에서의 전기적 현상 때문임을 수식으로 밝혔다. 이 후 SiNx의 RC 값 즉, retention time을 액정의 값과 맞추기 위하여 SiNx막의 비저항을 조절하기 위하여 Si과 N의 비율을 변화시켜 액정의 RC와 맞출 수 있었다. 이를 통해 CC mode에서 잔상을 근본적으로 해결하여 향후 QUHD (8k) TV에 사용할 수 있는 Pixel 구조와 PA를 제시하였다.

D-π-A structural porphyrins with various π-extended donor units for highly efficient dye-sensitized solar cells

김수현 Garduate School, Korea University 2019 국내석사

Due to intense absorption bands in the visible region, porphyrin sensitizers have been considered as promising sensitizers for dye-sensitized solar cells. However, the lack of light-harvesting ability at around 500 nm and beyond 600 nm and aggregation tendency on TiO2 have remained to be some challenges for porphyrin sensitizers. Thus, the development of novel porphyrin-based sensitizers is essential to resolve these issues. In this regard, we designed and synthesized D-π-A porphyrin dyes (SGT-030 and SGT-031) with asymmetric thieno[3,2-b]benzothiophene (TBT) and alkylated thieno[3,2-b]indole (TI) moiety, respectively. The extended π-spacer units (TBT and TI) are promising candidates for effective moiety to get narrow band gap and to improve the light harvesting ability. The absorption spectra of these dyes were red-shifted with the further increased π-bridges with compared to SGT-053 reference dye. By introducing a various π-extended donor unit in the porphyrin dyes, the power conversion efficiency (PCE) was improved with the increased short-circuit current (Jsc) and open-circuit voltage (Voc), because of the change of electron donating ability. Consequently, we obtained a maximum PCE of 10.69% for SGT-030 and 10.80% for SGT-031. Especially, by replacing the benzene with the TBT and alkylated TI, SGT-030 and SGT-031 showed more red-shifted absorption maxima than that of SGT-053. And then, when the alkylated TI moiety is introduced as π-extended donor unit instead of the TBT unit, it caused to red-shift the ICT absorption band and enhance the LHE. As a result, D-π-A porphyrin with π-extended donor unit exhibited better efficiency than SGT-053. But DSSCs employing the cobalt(II/III) redox shuttle with SGT-030 and SGT-031 exhibited similar efficiency. It indicates that π-extended donor ability in D-π-A porphyrin with π-extended donor units has strong influence on cell performance.

Effects of bulky substituent on the phosphorescence properties of homoleptic Iridium(III) complexes

박재현 Garduate School, Korea University 2019 국내석사

Comparison of the results with those of the reference Ir(ppy)3 reveal that the emission color and photophysical properties of the other Ir complexes are influenced by the electron-donating groups (-CH3 and phenyl derivatives) attached to the ppy ligand. In particular, systematic red-shifts are observed by increasing the electron-donating ability. The emission spectrum of Ir(Me-ppy)3, hav-ing small electron-donating -CH3 group, is red-shifted; however, the emission quantum yield is low and the nonradiative decay constant is large. On the other hand, although bulky phenyl de-rivative-adducts (Ir(Ph-ppy)3, Ir(MePh-ppy)3, and Ir(diMePh-ppy)3) also exhibit red-shifted emission, but their kinetic and photophysical behaviors are more optimal than those of Ir(Me-ppy)3, whose behavior does not follow the energy gap law.

IDH2 deficiency accelerates skin pigmentation in mice via enhancing melanogenesis

박정현 Garduate School, Korea University 2019 국내박사

Melanogenesis is a complex biosynthetic pathway regulated by multiple agents, which are involved in the production, transport, and release of melanin. Melanin has diverse roles, including determination of visible skin color and photoprotection. Studies indicate that melanin synthesis is tightly linked to the interaction between melanocytes and keratinocytes. α-melanocyte-stimulating hormone (α-MSH) is known as a trigger that enhances melanin biosynthesis in melanocytes through paracrine effects. Accumulated reactive oxygen species (ROS) in skin affects both keratinocytes and melanocytes by causing DNA damage, which eventually leads to the stimulation of α-MSH production. Mitochondria are one of the main sources of ROS in the skin and play a central role in modulating redox-dependent cellular processes such as metabolism and apoptosis. Therefore, mitochondrial dysfunction may serve as a key for the pathogenesis of skin melanogenesis. Mitochondrial NADP+-dependent isocitrate dehydrogenase (IDH2) is a key enzyme that regulates mitochondrial redox balance and reduces oxidative stress-induced cell injury through the generation of NADPH. Downregulation of IDH2 expression resulted in an increase in oxidative DNA damage in mice skin through ROS-dependent ATM-mediated p53 signaling. IDH2 deficiency also promoted pigmentation on the dorsal skin of mice, as evident from the elevated levels of melanin synthesis markers. Furthermore, pretreatment of mitochondria-targeted antioxidant mito-TEMPO alleviated oxidative DNA damage and melanogenesis induced by IDH2 deficiency both in vitro and in vivo. Together, our findings highlight the role of IDH2 in skin melanogenesis in association with mitochondrial ROS and suggest unique therapeutic strategies for the prevention of skin pigmentation.

Integrator-augmented terminal sliding mode control for second order system

진병연 Garduate School, Korea University 2019 국내석사

Robust Control is a design method of a controller that deals with uncertainties. Sliding Mode Control (SMC), one of robust control, is a control method by designing input signal to be switched on the sliding surface set in the state space. So, robustness and stability are ensured through a sliding mode in which the state trajectory of the system to be controlled moves along the plane. SMC is robust to uncertainties in the control model and has the advantage of being unaffected by disturbances. Based on this, the Terminal Sliding Mode Control (TSMC) is designed to ensure that the error converges to 0 within a finite time to be applied to the actual systems. However, TSMC may cause chattering phenomenon in the input signal as in the SMC, which may damage the actuators or cause incorrect control. In this paper, I propose extended-order terminal sliding surface for the control input with the elimination of the chattering by arranging the integrator in front of the control target. Also, the proposed method is verified for chattering reduction by MATLAB simulation and experiment on DC motor system. 강인제어는 불확실성을 다루는 제어기의 설계 기법이다. 이 중 슬라이딩 모드 제어 (SMC, Sliding Mode Control)는 상태 공간 내에 설정한 슬라이딩 평면 (sliding surface)을 기준으로 스위칭 되도록 입력 신호를 설계하여 제어 대상이 되는 시스템의 상태 궤적이 이 평면을 따라 이동하는 슬라이딩 모드에 있게 함으로써 안정시키는 제어 기법이다. 슬라이딩 모드 제어는 제어 모델에 대한 불확실성에 강인하고 외란에 영향을 받지 않는 장점을 가진다. 이를 토대로 실제 시스템에 적용하기 위해 유한한 시간 내에 오차가 0으로 수렴할 수 있게 보장되도록 설계한 것이 터미널 슬라이딩 모드 제어 (TSMC, Terminal Sliding Mode Control)이다. 하지만 터미널 슬라이딩 모드 제어도 슬라이딩 모드 제어와 마찬가지로 입력 신호에 고주파 형태의 떨림 현상 (chattering phenomenon)이 발생하여 액츄에이터를 손상시키거나 부정확한 제어를 초래할 수 있다. 앞선 연구에서 터미널 슬라이딩 모드 제어의 수렴 시간을 결정하는 멱함수 (power function)의 지수 범위를 실수로 넓히는 확장된 터미널 슬라이딩 모드 제어 (ETSMC, Extended Terminal Sliding Mode Control)가 제안되었다. 본 논문에서는 확장된 터미널 슬라이딩 모드 제어에서 제어 대상 (plant)의 앞에 적분기를 배치하여 떨림 현상이 제거된 제어 입력이 만들어지도록 하고 이를 위해 차수가 확장된 슬라이딩 평면을 제안한다. 또한 떨림 현상이 제거되지 않은 기존의 ETSMC와 SMC의 떨림 현상을 감소시키기 위해 보편적으로 사용되었던 포화함수를 이용한 ETSMC, 그리고 제안된 방법으로 떨림을 제거한 ETSMC의 이 3가지에 대한 시뮬레이션과 DC모터에 적용한 실험 결과를 비교하고 제안된 방법의 효과를 검증하였다.

Clarification of characteristic of bimetallic Ir(III)-Pt(II) complexes with alkyl bridging ligands

차현욱 Garduate School, Korea University 2019 국내석사

We investigated excited-state properties of 4′,7′-phenanthrolino-5′,6′:2,3-pyrazine (ppz)-bridged bimetallic complexes, (L)2Ir-ppz-PtCl2 (Ir-ppz-Pt) (L = 2-(4′,6′-difluorophenyl)pyridinato-N,C2 (dfppy)) and [(L)2Ir]2(ppz) (Ir-ppz-Ir). These properties were compared to those of reported dpp bridging complexes, 2,3-bis(2-pyridyl)pyrazine (dpp)-bridged bimetallic complexes, Ir-dpp-Pt and Ir-dpp-Ir. Excited state properties of hetero-bimetallic Ir-Pt systems were very different from those of related Ru-Pt systems with a dpp bridging ligand; while Ru-dpp-Pt displayed 3MLCT emission, Ir-dpp-Pt was relatively silent in emission. Steady-state photochemical studies and photodynamic studies were undertaken for each Ir or Pt center within peripheries of bridging ligands to confirm either energy or electron transfer and at the same time its direction. Thermodynamic driving force of the electron transfer (ET) process from Ir to Pt in the hetero-bimetallic Ir-Pt systems was predicted by the Rehm-Weller equation to be unfavorable for both Ir-ppz-Pt and Ir-dpp-Pt. However, when photo-induced electron transfer (PET) was considered, Ir-dpp-Pt could undergo a facile electron transfer process from Ir to Pt metal center. Such a prediction is well manifested from selective excitation on the bridging ligand.

(A) study of energy bigdata-based intelligent building energy management system

윤석호 Garduate School, Korea University 2019 국내박사

As the significance of power consumption in modern society is emphasized, the need for technology to raise energy efficiency is increasing. The power consumption of buildings comprises a large proportion of the total energy consumption and systematic methods are needed in order to manage it effectively. This paper proposes a multiple distributed power-based building energy management system(MDPBEMS) for efficient management of building energy. The analysis of the big data-based power usage measured in different types of buildings presents the power distribution method between distributed power sources. It also suggests and verifies an energy prediction model for efficient building energy management, which is called Adaptive Energy Consumption Prediction (AECP) algorithm. This paper proposes a building energy management method with the use of an energy prediction model and analyzes the efficiency by applying it to actual buildings. As a result of the efficiency analysis using the proposed system, the annual electricity rate reduction efficiency of 5% was shown.