Correlation between surface tension and fatigue properties of Ti-6Al-4V alloy fabricated by EBM additive manufacturing

Choi, Youngsin,Lee, Dong-Geun Elsevier BV * North-Holland 2019 Applied Surface Science Vol.481 No.-

<P><B>Abstract</B></P> <P>The powder bed fusion method using a heat source for 3D printing can be applied to fabricate the geometrical shapes of some parts, and enables rapid melting and cooling. 3D EBM additive manufacturing can supply a near-net-shape or net-shape and precise parts better than micro scale casting and precision casting. Casting parts have residual stress in the matrix and their microstructure, which can affect the dynamic properties, but if they are heat-treated under the optimal conditions, the residual stress can be reduced to enhance the dynamic-mechanical properties of 3D printed parts. In this study, Ti-6Al-4V bulk bars were fabricated by EBM additive manufacturing, and the microstructures, residual stress, and various interior defects of the specimens were analyzed. The residual stress and surface tension were measured and calculated in different specimens heat-treated at 850–950 °C. The relationship between the residual stress and surface tension was explained using the related equations and the influence on the high cycle fatigue properties was evaluated.</P> <P><B>Highlights</B></P> <P> <UL> <LI> AM parts with residual stress and surface tension </LI> <LI> Influences of post treatment on residual stress and fatigue properties </LI> </UL> </P>

Characteristics of fabricated si PIN-type radiation detectors on cooling temperature

Kim, Han Soo,Jeong, Manhee,Kim, Young Soo,Lee, Dong Hun,Cho, Seung Yeon,Ha, Jang Ho Elsevier BV * North-Holland 2015 Nuclear Instruments & Methods in Physics Research. Vol. No.

<P><B>Abstract</B></P> <P>Si PIN photodiode radiation detectors with three different active areas (3×3mm<SUP>2</SUP>, 5×5mm<SUP>2</SUP>, and 10×10mm<SUP>2</SUP>) were designed and fabricated at the Korea Atomic Energy Research Institute (KAERI) for low energy X- and gamma-ray detection. In Si-based semiconductor radiation detectors, one of the noise sources is thermal noise, which degrades their energy resolution performance. In this study, the temperature effects on the energy resolution were investigated using a 3×3mm<SUP>2</SUP> active area PIN photodiode radiation detector using a Thermoelectric Module (TEM) from room temperature to −23°C. Energy resolutions from 25keV auger electrons to 81keV gamma-ray from a Ba-133 calibration source were measured and compared at every 10°C interval. At −23°C, energy resolutions were improved by 15.6% at 25keV, 4.0% at 31keV, and 1.2% at 81keV in comparison with resolutions at room temperature. CsI(Tl)/PIN photodiode radiation detectors were also fabricated for relatively high energy gamma-ray detection. Energy resolutions for Cs-137, Co-60, and Na-22 sources were measured and compared with the spectral responsivity.</P>

Improvement in interfacial characteristics of low-voltage carbon nanotube thin-film transistors with solution-processed boron nitride thin films

Jeon, Jun-Young,Ha, Tae-Jun Elsevier BV * North-Holland 2017 Applied Surface Science Vol.413 No.-

<P><B>Abstract</B></P> <P>In this article, we demonstrate the potential of solution-processed boron nitride (BN) thin films for high performance single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) with low-voltage operation. The use of BN thin films between solution-processed high-k dielectric layers improved the interfacial characteristics of metal-insulator-metal devices, thereby reducing the current density by three orders of magnitude. We also investigated the origin of improved device performance in SWCNT-TFTs by employing solution-processed BN thin films as an encapsulation layer. The BN encapsulation layer improves the electrical characteristics of SWCNT-TFTs, which includes the device key metrics of linear field-effect mobility, sub-threshold swing, and threshold voltage as well as the long-term stability against the aging effect in air. Such improvements can be achieved by reduced interaction of interfacial localized states with charge carriers. We believe that this work can open up a promising route to demonstrate the potential of solution-processed BN thin films on nanoelectronics.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We demonstrate the potential of solution-processed boron nitride (BN) thin films for nanoelectronics. </LI> <LI> Improved interfacial characteristics reduced the leakage current by three orders of magnitude. </LI> <LI> The BN encapsulation improves all the device key metrics of low-voltage SWCNT-TFTs. </LI> <LI> Such improvements were achieved by reduced interaction of interfacial localized states. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Flipped SU(5) from Z_12-I orbifold with Wilson line

Kim, J.E.,Kyae, B. Elsevier BV * North-Holland 2007 Nuclear Physics, Section B Vol.770 No.1-2

We construct a three family flipped SU(5) model from the heterotic string theory compactified on the Z<SUB>12-I</SUB> orbifold with one Wilson line. The gauge group is SU(5)xU(1)<SUB>X</SUB>xU(1)<SUP>3</SUP>x[SU(2)xSO(10)xU(1)<SUP>2</SUP>]<SUP>'</SUP>. This model does not derive any non-Abelian group except SU(5) from E<SUB>8</SUB>, which is possible only for two cases in case of one shift V, one in Z<SUB>12-I</SUB> and the other in Z<SUB>12-II</SUB>. We present all possible Yukawa couplings. We place the third quark family in the twisted sectors and two light quark families in the untwisted sector. From the Yukawa couplings, the model provides the R-parity, the doublet-triplet splitting, and one pair of Higgs doublets. It is also shown that quark and lepton mixings are possible. So far we have not encountered a serious phenomenological problem. There exist vector-like flavor SU(5) exotics (including Q<SUB>em</SUB>=+/-16 color exotics and Q<SUB>em</SUB>=+/-12 electromagnetic exotics) and SU(5) vector-like singlet exotics with Q<SUB>em</SUB>=+/-12 which can be removed near the GUT scale. In this model, sin<SUP>2</SUP>θ<SUB>W</SUB><SUP>0</SUP>=38 at the full unification scale.

Evaluation of high grid strip densities based on the moiré artifact analysis for quality assurance: Simulation and experiment

Je, U.K.,Park, C.K.,Lim, H.W.,Cho, H.S.,Lee, D.Y.,Lee, H.W.,Kim, K.S.,Park, S.Y.,Kim, G.A.,Kang, S.Y.,Park, J.E.,Kim, W.S.,Jeon, D.H.,Woo, T.H. Elsevier BV * North-Holland 2017 Nuclear Instruments & Methods in Physics Research. Vol. No.

<P><B>Abstract</B></P> <P>We have recently developed precise x-ray grids having strip densities in the range of 100 – 250 lines/inch by adopting the precision sawing process and carbon interspace material for the demands of specific x-ray imaging techniques. However, quality assurance in the grid manufacturing has not yet satisfactorily conducted because grid strips of a high strip density are often invisible through an x-ray nondestructive testing with a flat-panel detector of an ordinary pixel resolution (>100 μ m). In this work, we propose a useful method to evaluate actual grid strip densities over the Nyquist sampling rate based on the moiré artifact analysis. We performed a systematic simulation and experiment with several sample grids and a detector having a 143- μ m pixel resolution to verify the proposed quality assurance method. According to our results, the relative differences between the nominal and the evaluated grid strip densities were within 0.2% and 1.8% in the simulation and experiment, respectively, which demonstrates that the proposed method is viable with an ordinary detector having a moderate pixel resolution for quality assurance in grid manufacturing.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The precise carbon-interspaced antiscatter grids have been studied. </LI> <LI> It is proposed for a useful method to evaluate actual grid strip densities over the Nyquist sampling rate based on the moiré artifact analysis. </LI> <LI> The simulation and experimental results demonstrate that the proposed method is viable with an ordinary detector having a moderate pixel resolution (>100 μ m) for quality assurance in grid manufacturing. </LI> </UL> </P>

Several polynomials associated with the harmonic numbers

Cheon, G.-S.,Hwang, S.-G.,Lee, S.-G. Elsevier BV, North-Holland 2007 Discrete Applied Mathematics Vol.155 No.18

We develop polynomials in z@?C for which some generalized harmonic numbers are special cases at z=0. By using the Riordan array method, we explore interesting relationships between these polynomials, the generalized Stirling polynomials, the Bernoulli polynomials, the Cauchy polynomials and the Norlund polynomials.

Freestanding porous sulfurized polyacrylonitrile fiber as a cathode material for advanced lithium sulfur batteries

Liu, Ying,Haridas, Anupriya K.,Lee, Younki,Cho, Kwon-Koo,Ahn, Jou-Hyeon Elsevier BV * North-Holland 2019 Applied Surface Science Vol.472 No.-

<P><B>Abstract</B></P> <P>A freestanding porous sulfurized polyacrylonitrile/vapor grown carbon fiber (SVF) composite was prepared as cathode material for high-performance lithium sulfur batteries by a facile electrospinning technique. The synthesized composite possessed high sulfur utilization, high Coulombic efficiency, and excellent cycling stability with the property of flexibility, essential to the development of flexible batteries. The capacity retentions of the SVF cell were 903 mAh g<SUP>−1</SUP> after 150 cycles at 1 C and 600 mAh g<SUP>−1</SUP> after 300 cycles at 2 C. At a high rate of 4 C, the SVF composite showed reasonable capacity retention. The superior performance of SVF composite was attributed to the highly porous structure, which effectively improved the wettability, accessibility, and absorption of electrolyte to facilitate rapid ion transfer in the cell. Vapor-grown carbon fibers embedded inside SVF as a carbon material notably enhanced the electrical conductivity of the cell, guaranteeing the electrochemical performance at high C-rates. The freestanding porous SVF fiber composite is a promising cathode material for advanced flexible lithium sulfur batteries.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Freestanding porous sulfurized polyacrylonitrile/VGCF composite was synthesized via a facile electrospinning. </LI> <LI> Highly porous structure can effectively improve ionic transfer. </LI> <LI> The high conductivity of VGCF can improve the electrical conductivity of the composite. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Freestanding porous sulfurized polyacrylonitrile/vapor grown carbon fiber (SVF) composite was prepared through a facile electrospinning process followed by sulfurization, as cathode material for high-performance flexible lithium sulfur batteries. The highly porous structure, high electrical conductivity and flexible property of the composite could greatly improve electrochemical performances.</P> <P>[DISPLAY OMISSION]</P>

ZnO supported Au/Pd bimetallic nanocomposites for plasmon improved photocatalytic activity for methylene blue degradation under visible light irradiation

Lee, Seung Jun,Jung, Hyeon Jin,Koutavarapu, Ravindranadh,Lee, Seung Heon,Arumugam, Malathi,Kim, Ju Hyun,Choi, Myong Yong Elsevier BV * North-Holland 2019 Applied Surface Science Vol.496 No.-

<P><B>Abstract</B></P> <P>Recently, photocatalysis has attracted great attention due to its potential applications in the environmental sector. Visible light driven metal–semiconductor photocatalysts with efficient light absorption, high charge separation, enhanced surface plasmon resonance, and utilized active sites have emerged as promising materials for the degradation of organic pollutants. Here, plasmonic ZnO/Au/Pd nanocomposites, with various concentrations of Au (5, 10, and 15 wt%) and 5 wt% of Pd nanoparticles (NPs) were prepared by a facile and eco–friendly three–step pulsed laser ablation in liquid and photodeposition technique without utilizing any surfactants or capping agents to enhance the photocatalytic performance under visible light illumination. The plasmonic properties of Au NPs and an excellent trapping of photogenerated electrons on the surface of Pd led to the improved photocatalytic activity (PCA). The as-prepared ZnO/Au/Pd nanocomposites were characterized by numerous spectroscopic and microscopic techniques, and the results confirmed the fabrication of Au and Pd NPs homogeneously decorated on the surface of ZnO nanospheres. The effect of plasmon improved photocatalytic activity of the ZnO/Au/Pd photocatalysts was investigated by the degradation of methylene blue dye under visible light illumination. The optimum ZnO/Au/Pd nanocomposite was ca. 5.4 times more efficient at degrading methylene blue than pure ZnO. This exceptional improvement of photocatalytic activity for the ZnO/Au/Pd catalysts was due to the enhanced surface plasmon resonance effect of the Au NPs under visible light illumination, and the deposited Pd NPs assisted as an electron storage chamber for the degradation of methylene blue, thus, enabling the separation of charge carriers. Based on the experimental results, a possible photocatalytic mechanism for the degradation of methylene blue catalyzed by the ZnO/Au/Pd nanocomposite was proposed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> ZnO/Au/Pd catalyst prepared by pulsed laser ablation and photodeposition technique. </LI> <LI> Facile and eco-friendly technique without utilizing surfactants or capping agents. </LI> <LI> Plasmon improved photocatalytic performance of the ZnO/Au/Pd photocatalysts. </LI> <LI> Photocatalytic degradation of methylene blue under visible light illumination. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

On CCE graphs of doubly partial orders

Kim, Seog-Jin,Kim, Suh-Ryung,Rho, Yoomi Elsevier BV, North-Holland 2007 Discrete Applied Mathematics Vol.155 No.8

<P><B>Abstract</B></P><P>Let <I>D</I> be a digraph. The competition-common enemy graph (CCE graph) of <I>D</I> has the same set of vertices as <I>D</I> and an edge between vertices <I>u</I> and v if and only if there are vertices w and <I>x</I> in <I>D</I> such that (w,u), (w,v), (u,x), and (v,x) are arcs of <I>D</I>. We call a graph a CCE graph if it is the CCE graph of some digraph. In this paper, we show that if the CCE graph of a doubly partial order does not contain <SUB>C4</SUB> as an induced subgraph, it is an interval graph. We also show that any interval graph together with enough isolated vertices is the CCE graph of some doubly partial order.</P>

Power-law analysis of nonlinear active-pixel detector responses as a function of mammographic energy

Kam, Soohwa,Kim, Dong Woon,Yun, Seungman,Kim, Ho Kyung Elsevier BV * North-Holland 2019 Nuclear Instruments & Methods in Physics Research. Vol. No.

<P><B>Abstract</B></P> <P>This study investigates the imaging performance of a complementary metal-oxide-semiconductor (CMOS) active pixel sensor (APS) array coupled with a gadolinium oxysulfide phosphor. A wide range of mammographic energy was considered, which corresponds to an aluminum-equivalent thickness in the range of 0.515 to 0.689 mm in terms of half-value layers. The performance metrics include the modulation-transfer function (MTF), Wiener noise-power spectrum (NPS), and detective quantum efficiency (DQE). The detector showed a nonlinear response at low exposure ranges, so it was described using a power-law model to linearize image data before evaluating the MTF, NPS, and DQE. We show that the NPS, which is measured from images without linearization but corrected by the exponent of the power function (viz., nonlinearity correction), can be consistent with that obtained using the linearization procedure. Negligible difference in MTFs measured with and without linearization showed good agreement between the nonlinearity-corrected and linearized DQEs. The DQE performance of the detector was comparable to published data for conventional digital mammography detectors. However, the detector design with a CMOS APS array in conjunction with a thin phosphor was energy-sensitive. The overall spatial-resolution performance (the size of effective aperture) improved by about 13%, the noise performance was degraded by about 22%, and the zero-frequency DQE was reduced by about 26% when measured with a Mo-target beam quality of 25 kV to 31 kV and a similar exposure of about 6 mR. The detector design may be appropriate for operation in a narrow range of energy. Further design considerations of the phosphor with output that tolerates variations in energy could lead to applications in convertible mammography and tomosynthesis.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Power model for nonlinear detector responses describes NPS without linearization. </LI> <LI> Detector design with CMOS APS/thin gadolinium oxysulfide phosphor is energy-sensitive. </LI> <LI> Lower optical Swank factor limits the performance of gadolinium oxysulfide phosphors. </LI> </UL> </P>