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Phark, Chuntak,Kim, Whapeoung,Yoon, Yeo-Song,Shin, Gwyam,Jung, Seungho Elsevier 2018 Journal of loss prevention in the process industri Vol.56 No.-
<P><B>Abstract</B></P> <P>An emergency response to chemical accidents proceeds in the order of prevention, mitigation, preparedness, response, and recovery. One of the methods of response is emergency evacuation orders. To minimize the loss of life, it is important to issue prompt and precise evacuation orders when chemical accidents such as toxic gas emissions occur near populated areas.</P> <P>This paper presents a method and its results for predicting emergency evacuation orders using a naïve Bayes classifier and an artificial neural network. A study was conducted using ATSDR's National Toxic Substance Incidents Program (NTSIP) dataset and The Hazardous Substances Emergency Events Surveillance (HSEES) database by extracting 61,563 of 115,569 accidents that occurred between 1996 and 2014.</P> <P>According to the results of the study, for predicting emergency evacuation orders, Artificial Neural Network prediction had a high level of accuracy when compared to Naïve Bayes Classifier. Based on the Area Under the Curve (AUC) value of the predicted results, the discriminatory power of the model was reliable. These results suggest that using machine learning in the field of chemical process safety can yield meaningful results.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An emergency evacuation order can be predicted using machine learning. </LI> <LI> Machine learning can shorten incident response time. </LI> <LI> NFPA rating is useful for incident response. </LI> </UL> </P>
Spin-polarized scanning tunneling microscopy with quantitative insights into magnetic probes
Phark Soo-hyon,Sander Dirk 나노기술연구협의회 2017 Nano Convergence Vol.4 No.8
Spin-polarized scanning tunneling microscopy and spectroscopy (spin-STM/S) have been successfully applied to magnetic characterizations of individual nanostructures. Spin-STM/S is often performed in magnetic fields of up to some Tesla, which may strongly influence the tip state. In spite of the pivotal role of the tip in spin-STM/S, the contribution of the tip to the differential conductance dI/dV signal in an external field has rarely been investigated in detail. In this review, an advanced analysis of spin-STM/S data measured on magnetic nanoislands, which relies on a quantitative magnetic characterization of tips, is discussed. Taking advantage of the uniaxial out-of-plane magnetic anisotropy of Co bilayer nanoisland on Cu(111), in-field spin-STM on this system has enabled a quantitative determination, and thereby, a categorization of the magnetic states of the tips. The resulting in-depth and conclusive analysis of magnetic characterization of the tip opens new venues for a clear-cut sub-nanometer scale spin ordering and spin-dependent electronic structure of the non-collinear magnetic state in bilayer high Fe nanoislands on Cu(111).
Nucleation and growth of primary nanostructures in SrTiO <sub>3</sub> homoepitaxy
Phark, Soo-hyon,Chang, Young Jun Springer US 2015 Nanoscale research letters Vol.10 No.1
<P>SrTiO<SUB>3</SUB> nanoislands on SrTiO<SUB>3</SUB> (001) in a <I>diffusion-limited growth</I> regime were studied using <I>in situ</I> scanning tunneling microscopy (STM). The STM images revealed two characteristic features of nucleation stages. First, the minimum lateral size of the one-unit-cell (<I>uc</I>)-high SrTiO<SUB>3</SUB> islands was 4 × 4 <I>uc</I><SUP>2</SUP>. Second, one-dimensional SrTiO<SUB>3</SUB> islands of a 4 <I>uc</I> width grew along the crystal symmetry directions. These observations suggest that 4 × 4-<I>uc</I><SUP>2</SUP> islands act as a minimum nucleation seed, and the addition of SrTiO<SUB>3</SUB> molecular species of the same width is the primary and dominant growth process in SrTiO<SUB>3</SUB> homoepitaxy. A close inspection of the surface of the substrate during the deposition process revealed possible connections between surface reconstruction and energetically favorable nucleation of SrTiO<SUB>3</SUB> islands.</P>
On the determination of characters D_8 and Q_8
Phark, Joong-Soo 又石大學校 1988 論文集 Vol.10 No.-
거의 모든 기약의 표현들은 그들의 특성다항식에 의하여 구별된다. 그러나 일반적으로 두개의 기약의 표현들이 똑같은 특성다항식을 가지고 있다고 해서 그들이 같다고는 할 수 없다. 따라서, 기약의 표현들이 서로 다름을 나타내기 위한 어떠한 다른 도구가 필요하게 된다. 그 도구들 중의 하나로서 특성다항식의 determinant가 있다. 이 도구를 이용해서 똑같은 특성다항식을 가지고 있는 D_8 과 Q_8의 기약 표현들이 서로 다름을 보인다.
Current transport in Pt Schottky contacts to <i>a</i>-plane n-type GaN
Phark, Soo-Hyon,Kim, Hogyoung,Song, Keun Man,Kang, Phil Geun,Shin, Heung Soo,Kim, Dong-Wook Institute of Physics [etc.] 2010 Journal of physics. D, applied physics Vol.43 No.16
<P>The temperature-dependent electrical properties of Pt Schottky contacts to nonpolar <I>a</I>-plane n-type GaN were investigated. Barrier height and ideality factor, estimated from the conventional thermionic emission model, were highly temperature dependent. A notable deviation from the theoretical Richardson constant value was also observed in the conventional Richardson plot. Analyses using the thermionic field emission model showed that consideration of defect-assisted tunnelling was necessary to explain the observed electrical behaviours.</P>
Characterization of Pt/a-Plane GaN Schottky Contacts Using Conductive Atomic Force Microscopy
Phark, Soo-Hyon,Kim, Hogyoung,Song, Keun Man,Kang, Phil Geun,Shin, Heung Soo,Kim, Dong-Wook American Scientific Publishers 2011 Journal of Nanoscience and Nanotechnology Vol.11 No.2
<P>We investigated the local electrical properties of Pt Schottky contacts to a-plane n-type GaN using conductive atomic force microscopy (C-AFM). Current-voltage characteristics obtained by C-AFM showed rectifying properties, indicating nano-scale Schottky junction formation. Two-dimensional current maps revealed that the surface microstructures of GaN influenced transport properties of the junctions.</P>
Phark, S.H.,Khim, Z.G.,Yoon, S. Elsevier 2008 Current Applied Physics Vol.8 No.6
We have investigated the growth of nanometer-scale gold stripes on reconstructed Au(111) surface using scanning tunneling microscopy (STM). The experiment was carried out under the conditions of ultrahigh vacuum and room temperature. The stripes were grown by the scanning motion of the STM tip over the area containing more than one step edge with the tunnel resistance less than several tens of mega ohms (MΩs). Unlike the previous reports [J.C. Heyraud, J.J. Metoris, Surf. Sci. 100 (1989) 519; V.M. Hallmark, S. Chiang, J.F. Rabolt, J.D. Swalen, R.J. Wilson, Phys. Rev. Lett. 59 (1987) 2879], we found, by directly comparing the direction of the stripes and the orientation of the underlying lattice, that the gold stripes grow preferentially along [1,-1,0] direction and its threefold symmetric directions at (111) surface of fcc structure. We also found that the scanning direction of the STM tip does not affect the direction of the stripe growth although the growth rate is suppressed remarkably when the scanning direction is close to [1,1,-2] direction of Au(111) surface.