Silicotungstate, a Potential Electron Transporting Layer for Low-Temperature Perovskite Solar Cells

Choi, Yoon Ho,Kim, Hyun Bin,Yang, In Seok,Sung, Sang Do,Choi, Young Sik,Kim, Jeongho,Lee, Wan In American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.30

<P>Thin films of a heteropolytungstate, lithium silicotungstate (Li4SiW12O40, termed Li-ST), prepared by a solution process at low temperature, were successfully applied as electron transporting layer (ETL) of planar-type perovskite solar cells (PSCs). Dense and uniform Li-ST films were prepared on FTO glass by depositing a thin Li-ST buffer layer, followed by coating of a main Li-ST layer. The film thickness was controlled by varying the number of coating cycles, consisting of spin-coating and thermal treatment at 150 degrees C. In particular, by employing 60 nm-thick Li-ST layer obtained by two cycles of coating, the fabricated CH3NH3PbI3 PSC device demonstrates the photovoltaic conversion efficiency (PCE) of 14.26% with J(SC) of 22.16 mA cm(-2), V-OC of 0.993 mV and FF of 64.81%. The obtained PCE is significantly higher than that of the PSC employing a TiO2 layer processed at the same temperature (PCE = 12.27%). Spectroscopic analyses by time-resolved photoluminescence and pulsed light-induced transient measurement of photocurrent indicate that the Li-ST layer collects electrons from CH3NH3PbI3 more efficiently and also exhibits longer electron lifetime than the TiO2 layer thermally treated at 150 degrees C. Thus, Li-ST is considered to be a promising ETL material that can be applied for the fabrication of flexible PSC devices.</P>

The Legacy of Pro-Democracy Mass Protest and Democratic Survival: A Cross-National Survival Analysis from 1946 to 2016

( Jeongho Choi ),( Byung-deuk Woo ) 서강대학교 사회과학연구소 2021 社會科學硏究 Vol.29 No.2

Why do some democratic countries experience democratic breakdown, while others endure? Even though various potential factors behind democratic breakdown or survival have been widely examined, we still cannot fully explain the different fates of democratic regimes. This article sheds light on the role of the legacy of pro-democracy mass protest during the transition period in democratic survival of democratic regimes. Using cross-national time-series data on 135 democratic regimes in 103 democratic countries and the Cox Proportional Hazard model, we demonstrate that the legacy of prodemocracy mass protest decreases the hazard rate of democratic breakdown. This relationship is consistently robust in alternative model specifications. Moreover, our empirical results indicate that nonviolent pro-democracy mass protests compared to violent ones exert much more substantive deterrent impacts on democratic breakdown.

Theoretical Study of Various Unit Models for Biomedical Application

Choi, Jeongho The Korean Society of Industry Convergence 2019 한국산업융합학회 논문집 Vol.22 No.4

This paper presents an analytical study on the strength and stiffness of various types of truss structures. The applied models are triangular-like opened truss-wall triangular model (OTT), closed truss-wall triangular model (CTT), opened solid-wall triangular model (OST), and hypercube models defined as core-filled or core-spaced cube. The models are analyzed by numerical model analysis using DEFORM 2D/3D tool with AISI 304 stainless steel. Then, the ideal solutions for stiffness and strength are defined. Finally, the relative elastic modulus of the core-spaced model is obtained as 0.0009, which is correlated with the cancellous bone for the relative density range of 0.029-0.03, and the relative elastic modulus for the core-filled model is obtained as 0.0015, which is correlated with cancellous bone for the relative density range of 0.035-0.036. For the relative compressive yield strength, the OTT reasonably agrees with the cancellous bone for the relative density of 0.042 and the relative compressive strength of 0.05. The CTT and OST are in good agreement at the relative density of 0.013 and the relative compressive yield strength of 0.002. The hypercube models can be used for the cancellous bone for stiffness, and the triangular models can be used for the cancellous bone for strength. However, none of the models can be used to replace the compact bone because it requires much higher stiffness and strength. In the near future, compact bone replacement must be further studied. In addition, previously mentioned models should be developed further.

Theoretical Study of Various Unit Models for Biomedical Application

( Jeongho Choi ) 한국산업융합학회 2019 한국산업융합학회 논문집 Vol.22 No.4

This paper presents an analytical study on the strength and stiffness of various types of truss structures. The applied models are triangular-like opened truss-wall triangular model (OTT), closed truss-wall triangular model (CTT), opened solid-wall triangular model (OST), and hypercube models defined as core-filled or core-spaced cube. The models are analyzed by numerical model analysis using DEFORM 2D/3D tool with AISI 304 stainless steel. Then, the ideal solutions for stiffness and strength are defined. Finally, the relative elastic modulus of the core-spaced model is obtained as 0.0009, which is correlated with the cancellous bone for the relative density range of 0.029- 0.03, and the relative elastic modulus for the core-filled model is obtained as 0.0015, which is correlated with cancellous bone for the relative density range of 0.035-0.036. For the relative compressive yield strength, the OTT reasonably agrees with the cancellous bone for the relative density of 0.042 and the relative compressive strength of 0.05. The CTT and OST are in good agreement at the relative density of 0.013 and the relative compressive yield strength of 0.002. The hypercube models can be used for the cancellous bone for stiffness, and the triangular models can be used for the cancellous bone for strength. However, none of the models can be used to replace the compact bone because it requires much higher stiffness and strength. In the near future, compact bone replacement must be further studied. In addition, previously mentioned models should be developed further.

Faces of the Face

Choi, Jeongho Korean Society of Plastic and Reconstructive Surge 2017 Archives of Plastic Surgery Vol.44 No.3

The most important environment of human being is the human being itself. So we have been sensitive to the appearance of ours and others at the same time. This writing aims for locating origins of the face and discerning differences [1] between the face of humans and those of other animals [2]. The face assumes a substantial significance not merely as a body function, but, above all, a means of expressions and features being looked at. The face is an important means of communication to humans as social animals. Knowledges about the various faces of the face are useful to become a efficient specialist as an extensive generalist because the face is a regular patron to the plastic surgery. The face in Korean consists of two elements of eol (the soul or the mind) and gul a residing place). When Wittgenstein says "the face is the soul of the body," his semantics corresponds to the Korean meaning. The meaning of the face in Korean is summed up in five ways. (1) the head or the front of the face with the eye, the nose and the mouth, (2) reputation or honor, (3) the general description of the psychological state, such as "the face of sadness", (4) a figure person representing a particular area, such as "Sun Dong-yul is the face of the Korean baseball community," (5) the primary imagery of the things and the event, such as "He is the face of the 4.19 Revolution." As such, the word "face", referring to a body part, extends its usages in a wide variety of contexts. What image do you convoke when you think of a person? With rare exceptions, you are most likely to invoke the face of the person. The face has come to be a byword for one's reputation or honor, and a pronoun for an expression of the essence of the thing and the event. This is presumably true of other languages. That is because human beings are equipped with the universal rule of language. A comprehensive understanding of the face is a must for cosmetic surgeons whose main responsibility is to sculpt and repair the face (Fig. 1).

A Study of Soil Moisture Retention Relation using Weather Radar Image Data

Choi, Jeongho,Han, Myoungsun,Lim, Sanghun,Kim, Donggu,Jang, Bong-joo Korea Multimedia Society 2018 The journal of multimedia information system Vol.5 No.4

Potential maximum soil moisture retention (S) is a dominant parameter in the Soil Conservation Service (SCS; now called the USDA Natural Resources Conservation Service (NRCS)) runoff Curve Number (CN) method commonly used in hydrologic modeling for event-based flood forecasting (SCS, 1985). Physically, S represents the depth [L] soil could store water through infiltration. The depth of soil moisture retention will vary depending on infiltration from previous rainfall events; an adjustment is usually made using a factor for Antecedent Moisture Conditions (AMCs). Application of the method for continuous simulation of multiple storms has typically involved updating the AMC and S. However, these studies have focused on a time step where S is allowed to vary at daily or longer time scales. While useful for hydrologic events that span multiple days, this temporal resolution is too coarse for short-term applications such as flash flood events. In this study, an approach for deriving a time-variable potential maximum soil moisture retention curve (S-curve) at hourly time-scales is presented. The methodology is applied to the Napa River basin, California. Rainfall events from 2011 to 2012 are used for estimating the event-based S. As a result, we derive an S-curve which is classified into three sections depending on the recovery rate of S for soil moisture conditions ranging from 1) dry, 2) transitional from dry to wet, and 3) wet. The first section is described as gradually increasing recovering S (0.97 mm/hr or 23.28 mm/day), the second section is described as steeply recovering S (2.11 mm/hr or 50.64 mm/day) and the third section is described as gradually decreasing recovery (0.34 mm/hr or 8.16 mm/day). Using the S-curve, we can estimate the hourly change of soil moisture content according to the time duration after rainfall cessation, which is then used to estimate direct runoff for a continuous simulation for flood forecasting.

Preliminary Development of Pinwheel Model Created by Convergent Truss Structure with Biological DNA Structure

Jeongho Choi 한국융합학회 2016 한국융합학회논문지 Vol.7 No.4

The objective of this study is to find the effective stiffness and compressive strengths of a unit-cell pinwheel truss and double pinwheel truss model designed following a double helical geometry similar to that of the DNA (deoxyribonucleic acid) structure in biology. The ideal solution for their derived relative density is correlated with a ratio of the truss thickness and length. To validate the relative stiffness or relative strength, ABAQUS software is used for the computational model analysis on five models having a different size of truss diameter from 1mm to 5mm. Applied material properties are stainless steel type 304. The boundary conditions applied were fixed bottom and 5 mm downward displacement. It was assumed that the width, length, and height are all equal. Consequently, it is found that the truss model has a lower effective stiffness and a lower effective yielding strength.

An Evolutionary Understanding of Aging

Choi, Jeongho Korean Society of Plastic and Reconstructive Surge 2016 Archives of Plastic Surgery Vol.43 No.3

Quantitative Estimation of the Precipitation utilizing the Image Signal of Weather Radar

Choi, Jeongho,Lim, Sanghun,Han, Myoungsun,Kim, Hyunjung,Lee, Baekyu Korea Multimedia Society 2018 The journal of multimedia information system Vol.5 No.4

This study estimated rainfall information more effectively by image signals through the information system of weather radar. Based on this, we suggest the way to estimate quantitative precipitation utilizing overlapped observation area of radars. We used the overlapped observation range of ground hyetometer observation network and radar observation network which are dense in our country. We chose the southern coast where precipitation entered from seaside is quite frequent and used Sungsan radar installed in Jeju island and Gudoksan radar installed in the southern coast area. We used the rainy season data generated in 2010 as the precipitation data. As a result, we found a reflectivity bias between two radar located in different area and developed the new quantitative precipitation estimation method using the bias. Estimated radar rainfall from this method showed the apt radar rainfall estimate than the other results from conventional method at overall rainfall field.

Cosmetic Surgery: Is It Science or Art?

Choi, Jeongho Korean Society of Plastic and Reconstructive Surge 2015 Archives of Plastic Surgery Vol.42 No.5