Spatial Charge Separation in Asymmetric Structure of Au Nanoparticle on TiO₂ Nanotube by Light-Induced Surface Potential Imaging

Yoo, Hyunjun,Bae, Changdeuck,Yang, Yunjeong,Lee, Seonhee,Kim, Myungjun,Kim, Hyunchul,Kim, Yunseok,Shin, Hyunjung American Chemical Society 2014 NANO LETTERS Vol.14 No.8

<P>Both enhancing the excitons’ lifetime and ingeniously controlling the spatial charge transfer are the key to the realization of efficiently photocatalytic and artificially photosynthetic devices. Nanostructured metal/metal-oxide interfaces often exhibit improved energy conversion efficiency. Understanding the surface potential changes of nano-objects under light illumination is crucial in photoelectrochemical cells. Under ultraviolet (UV) illumination, here, we directly observed the charge separation phenomena at the Au-nanoparticle/TiO<SUB>2</SUB>-nanotube interfaces by using Kelvin probe force microscopy. The surface potential maps of TiO<SUB>2</SUB> nanotubes with and without Au nanoparticles were compared on the effect of different substrates. We observed that in a steady state, approximately 0.3 electron per Au particle of about 4 nm in diameter is effectively charged and consequently screens the surface potential of the underlying TiO<SUB>2</SUB> nanotubes. Our observations should help design improved photoelectrochemical devices for energy conversion applications.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-8/nl501381a/production/images/medium/nl-2014-01381a_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl501381a'>ACS Electronic Supporting Info</A></P>

The Development of Gamma Energy Identifying Algorithm for Compact Radiation Sensors Using Stepwise Refinement Technique

Yoo, Hyunjun,Kim, Yewon,Kim, Hyunduk,Yi, Yun,Cho, Gyuseong The Korean Association for Radiation Protection 2017 방사선방어학회지 Vol.42 No.2

Background: A gamma energy identifying algorithm using spectral decomposition combined with smoothing method was suggested to confirm the existence of the artificial radio isotopes. The algorithm is composed by original pattern recognition method and smoothing method to enhance the performance to identify gamma energy of radiation sensors that have low energy resolution. Materials and Methods: The gamma energy identifying algorithm for the compact radiation sensor is a three-step of refinement process. Firstly, the magnitude set is calculated by the original spectral decomposition. Secondly, the magnitude of modeling error in the magnitude set is reduced by the smoothing method. Thirdly, the expected gamma energy is finally decided based on the enhanced magnitude set as a result of the spectral decomposition with the smoothing method. The algorithm was optimized for the designed radiation sensor composed of a CsI (Tl) scintillator and a silicon pin diode. Results and Discussion: The two performance parameters used to estimate the algorithm are the accuracy of expected gamma energy and the number of repeated calculations. The original gamma energy was accurately identified with the single energy of gamma radiation by adapting this modeling error reduction method. Also the average error decreased by half with the multi energies of gamma radiation in comparison to the original spectral decomposition. In addition, the number of repeated calculations also decreased by half even in low fluence conditions under $10^4$ ($/0.09cm^2$ of the scintillator surface). Conclusion: Through the development of this algorithm, we have confirmed the possibility of developing a product that can identify artificial radionuclides nearby using inexpensive radiation sensors that are easy to use by the public. Therefore, it can contribute to reduce the anxiety of the public exposure by determining the presence of artificial radionuclides in the vicinity.

Understanding Photoluminescence of Monodispersed Crystalline Anatase TiO₂ Nanotube Arrays

Yoo, Hyunjun,Kim, Myungjun,Bae, Changdeuck,Lee, Seonhee,Kim, Hyunchul,Ahn, Tae Kyu,Shin, Hyunjung American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.18

<P>Despite huge potential of nanostructured TiO<SUB>2</SUB> in many applications, the concrete understanding of optical properties associated with their defect structures remains elusive to date. Here, we present a systematic study on the photoluminescence (PL) characteristics of anatase TiO<SUB>2</SUB> nanotube (TNT) arrays as a function of wall thicknesses (<I>t</I><SUB>wall</SUB>) and thereby grain sizes. Highly uniform anatase TNTs were prepared by template-directed atomic layer deposition techniques, followed by thermal annealing. The relative amounts of surface/grain boundary (GB) defects to the bulk oxygen vacancies were tailored in a controlled manner by utilizing the crystallization kinetics between thin and thick wall layers during amorphous to anatase transformation. PL spectra of anatase TNT arrays were attained at variable temperatures from 300 down to 20 K. By changing <I>t</I><SUB>wall</SUB>, remarkably, the predominant PL emissions were likely discernible from either self-trapped excitons, oxygen vacancies, or surface/GB defects. Our results indicate that the properties of TNTs are surface-dominated when <I>t</I><SUB>wall</SUB> < ∼3 nm and bulk-dominated when <I>t</I><SUB>wall</SUB> > ∼3 nm by detecting surface-dangling bonds of TNTs located as deep traps with decreasing <I>t</I><SUB>wall</SUB>. Moreover, our TNT arrays with <I>t</I><SUB>wall</SUB> = 20 nm and highly crystalline anatase domains emit resonant PL that may suggest STEs coupled with a specific phonon mode. The present work provides us an emergent understanding on the optical properties of one-dimensional, wide-gap oxide semiconductor photoelectrodes in extremely uniform dimensions.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-18/jp4125588/production/images/medium/jp-2013-125588_0006.gif'></P>

Differences among Credit Rating Agencies and the Information Environment

Hyunjun PARK,Youngtae YOO 한국유통과학회 2019 The Journal of Asian Finance, Economics and Busine Vol.6 No.2

In the Korean capital market, there are three credit rating agencies. Potential credit ratings based on credibility in the financial market are calculated independently for each rating agency. It often happens that despite the fact that the grades of the rating agencies are the same and have the same rating system, their actual ratings are different, even for the same firm. In such circumstances, investors may wonder why. In this study, we assume that the cause is the information environment in which the company operates. The credit ratings of rating agencies are mainly classified into bonds or commercial papers. The bonds are rated primarily for long-term of three years or more, and commercial papers specify ratings for less than one year. The information environment to be verified in this study was observed with a commercial paper. Under the assumption the larger the analyst following is, the more transparent is the information environment, we analyzed the influence of the number of analysts following on the degree to which ratings conflicted among credit rating agencies. The results of our analysis confirmed that opinion conflict among credit rating agencies is clearly reduced for companies with good information environments.

마이크로파 근접장 현미경을 이용한 λ-DNA의 비파괴 측정

유현준,유형근,양종일,김송희,이기진 한국비파괴검사학회 2004 학술대회 논문집 Vol.- No.-

We study the electrical properties of lambda DNA(λ-DNA) by using a near-field scanning microwave microscope (NSMM) at an operating frequency of f = 5 2 - 5.7 GHz. Distance between the probe tip and the sample was maintained the same distance in order to obtain a quantitative result using a tuning fork shear-force feedback system. The obtained NSMM images showed a topography with a dielectric constant image of h-DNA. We observed dielectric constant changes of λ-DNA due to a change by UV irradiation.

Exploring Knowledge Distribution in Neural Network Parameter

Hyunjun Jang,Minuk Ma,Chang D. Yoo 대한전자공학회 2019 대한전자공학회 학술대회 Vol.2019 No.6

Recently, convolutional neural networks have revealed remarkable classification performance on the ImageNet benchmark. Deep learning methods have successfully been applied to many fields including detection, reinforcement learning, natural language processing, etc. However, there is no clear understanding as to why deep learning methods perform well. In this paper, we investigate the knowledge distribution in neural network parameters specifically for policy networks. With both top-down and bottom-up investigation methods, we argue that the neurons in policy networks divide the labors in a modular way. We find that when there are too many neurons considering the complexity of the task, some neurons do not work at all, and can actually be removed for computational efficiency. Experiments on gym CartPole environment demonstrate our hypotheses.

SELF-POWERED HYBRID NANOGENERATOR FOR SIMULTANEOUSLY HARVESTING MECHANICAL AND SOLAR ENERGY

Hyunjun Kim,Moon-Hyun Chung,Seunghwan Yoo,Hakgeun Jeong 한국신재생에너지학회 2018 AFORE Vol.2018 No.8

반응표면과 실험계획을 이용한 브레이크 응력해석의 하중조건 개선

소현준(Hyunjun Soh),유정훈(Jeonghoon Yoo) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

In finite element analysis, it is difficult to get the analysis result of the single component analysis as precision as that of full system model analysis. However, it is used more popularly, since it need less time than full system model analysis. To obtain the precision analysis result, it is needed to apply more detailed boundary conditions. In this research, the establishment methodology of improved load boundary condition may be introduced. In order to get the approximate result with rig test result, strain values are compared. The each of partial load condition, as the equation form of the braking torque, is obtained using response surface method and design of experiments.

심전도를 이용한 통증자각 패턴분류기 설계

임현준(Hyunjun Lim),유선국(Sun Kook Yoo) 한국멀티미디어학회 2017 멀티미디어학회논문지 Vol.20 No.9

An Impact on the Hospitality Industry with Rare Resource and Sharing Economy Platform

Park Hyunjun(박현준),Yoo Youngtae(유영태) 한국산업정보학회 2018 한국산업정보학회논문지 Vol.23 No.3

An analysis of Airbnb and Kozaza will show how valuable and rare resource can have an impact on company performances. Airbnb applied the sharing economy platform, and this business model had disrupted the hospitality industry. Thus, this paper will investigate a Korean company called Kozaza which had benchmarked Airbnb. Furthermore, it will apply the theory of VRIO framework, which consists of how valuable, rare, costly to imitate (imitability), and organization (exploited by the organization) to find competitiveness of Kozaza in the hospitality industry. Thus, it will attempt to show that Kozaza’s business model of utilizing the unused resource of Hanok (traditional Korean house) and partnerships with Hanokstay, Seoul Metropolitan Government and Soul Tourism Organization and others have enhanced their resource and capability to strengthen their business model. Furthermore, this research will explore how Kozaza can competitively be successful in the future.