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Location-Based TDMA MAC for Reliable Aeronautical Communications
Hyungjun Jang,Eunkyung Kim,Jae-Joon Lee,Jaesung Lim IEEE 2012 IEEE transactions on aerospace and electronic syst Vol.48 No.2
<P>The growth of data traffic as air traffic increases is leading to bottlenecks. We propose a new time division multiple access (TDMA) protocol termed location-based TDMA (LBTM) to accommodate increasing data traffic and air-to-air communications. LBTM provides all three modes of communication: unicast, multicast, and broadcast. ACK needs a long guard time for reliable multicast in the aeronautical environment, because it is a long distance communication system. LBTM uses location information to overcome this problem. We can reduce the guard time of ACK and prevent collisions. In our scheme, multicast aircraft calculate ACK arrival time to ensure that ACKs arrive at the sender at different times. Therefore, LBTM reduces the amount of guard time of ACK and the total average time to complete a reliable multicast MAC request. This results in a significant increase in network utilization and throughput.</P>
Wafer-scale, conformal and direct growth of MoS<sub>2</sub> thin films by atomic layer deposition
Jang, Yujin,Yeo, Seungmin,Lee, Han-Bo-Ram,Kim, Hyungjun,Kim, Soo-Hyun Elsevier 2016 APPLIED SURFACE SCIENCE - Vol.365 No.-
<P><B>Abstract</B></P> <P>Molybdenum disulfide (MoS<SUB>2</SUB>) thin films were grown directly on SiO<SUB>2</SUB> covered wafers by atomic layer deposition (ALD) at the deposition temperatures ranging from 175 to 225°C using molybdenum hexacarbonyl [Mo(CO)<SUB>6</SUB>] and H<SUB>2</SUB>S plasma as the precursor and reactant, respectively. Self-limited film growth on the thermally-grown SiO<SUB>2</SUB> substrate was observed with both the precursor and reactant pulsing time. The growth rate was ∼0.05nm/cycle and a short incubation cycle of around 13 was observed at a deposition temperature of 175°C. The MoS<SUB>2</SUB> films formed nanocrystalline microstructure with a hexagonal crystal system (2H-MoS<SUB>2</SUB>), which was confirmed by X-ray diffraction and transmission electron microscopy. Single crystal MoS<SUB>2</SUB> nanosheets, ∼20nm in size, were fabricated by controlling the number of ALD cycles. The ALD-MoS<SUB>2</SUB> thin films exhibited good stoichiometry with negligible C impurities, approximately 0.1at.% from Rutherford backscattering spectrometry (RBS). X-ray photoelectron spectroscopy confirmed the formation of chemical bonding from MoS<SUB>2</SUB>. The step coverage of ALD-MoS<SUB>2</SUB> was approximately 75% at a 100nm sized trench. Overall, the ALD-MoS<SUB>2</SUB> process made uniform deposition possible on the wafer-scale (4in. in diameter).</P> <P><B>Highlights</B></P> <P> <UL> <LI> The formation of pure and stoichiometric MoS<SUB>2</SUB> thin film by atomic layer deposition (ALD). </LI> <LI> ALD of MoS<SUB>2</SUB> using Mo(CO)<SUB>6</SUB> and H<SUB>2</SUB>S plasma. </LI> <LI> Large-area (4in. in diameter) and direct growth of MoS<SUB>2</SUB> thin films and nanosheets by ALD. </LI> <LI> Remarkable step coverage at 100nm trench. </LI> </UL> </P>
Jang, Inyoung,Kim, Sungmin,Kim, Chanho,Lee, Hyungjun,Yoon, Heesung,Song, Taeseup,Paik, Ungyu Elsevier 2019 Journal of Power Sources Vol.435 No.-
<P><B>Abstract</B></P> <P>La<SUB>0.6</SUB>Sr<SUB>0.4</SUB>Co<SUB>0.2</SUB>Fe<SUB>0.8</SUB>O<SUB>3-δ</SUB> (LSCF) is a promising cathode material for solid oxide fuel cells due to its high oxygen reduction reaction (ORR) activity. A gadolinium-doped ceria (GDC) barrier layer is essential to preventing side reactions between LSCF and an yttrium-stabilized zirconia (YSZ) electrolyte. However, several challenges are associated with the coating of GDC barrier layer on the YSZ electrolyte, including delamination of the GDC layer due to sinterability differences and formation of an insulating layer at a high annealing temperature. In this study, we describe a structure for a newly designed interfacial layer consisting of a GDC barrier layer and a nano-web–structured LSCF thin-film layer (NW-LSCF) through a facile spin-coating method. A dense GDC barrier layer with a thickness of approximately 400 nm was successfully applied to the surface of a YSZ electrolyte without delamination at a low annealing temperature. The high surface area of the NW-LSCF enhanced ORR due to an increased triple-phase boundary length. Cells employing a GDC barrier layer and NW-LSCF interlayer exhibited improved electrochemical performance. Peak power density reached 1.29 W/cm<SUP>2</SUP> at an operating temperature of 550 °C and 2.14 W/cm<SUP>2</SUP> at 650 °C.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Newly designed interfacial layer structure is developed for interfacial engineering. </LI> <LI> Combined structure of GDC barrier layer/NW-LSCF improves electrochemical properties. </LI> <LI> The NW-LSCF enables higher oxygen reduction reaction at lower temperature. </LI> <LI> Results show the possibility of lowering SOFCs operating temperature. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Twin-Image Elimination in an In-Line Digital Holographic Microscope
Hyungjun Cho,Younghun Yu,Doocheol Kim,Jung-Young Son,Sanghoon Shin,Wongun Jang 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.4
A novel method is employed to eliminate the twin images in the so-called ``in-line" digital holographic microscope. We could develop a digital holographic microscope that can solve the problems of overlapping of real and imaginary images and eliminate one of them by padding and removing the DC term by using an averaging method. The entire process requires only one digital hologram. A novel method is employed to eliminate the twin images in the so-called ``in-line" digital holographic microscope. We could develop a digital holographic microscope that can solve the problems of overlapping of real and imaginary images and eliminate one of them by padding and removing the DC term by using an averaging method. The entire process requires only one digital hologram.
Jang Taehwan,Paik Dooam,Shin Seung‐Jae,Kim Hyungjun 대한화학회 2022 Bulletin of the Korean Chemical Society Vol.43 No.4
Solid–liquid interfaces are ubiquitous in scientifically and technologically important systems, and they govern complex chemophysical processes such as those in electrochemistry and heterogeneous catalysis. Atomic-level elucidation of interfacial structures has been extensively pursued; however, related research is still limited. A major obstacle lies in the intrinsic character of interfaces: they are located between two bulk phases that make the application of spectroscopic or surface-science techniques be difficult. Although this suggests the possibility of employing computational approaches to explore interfacial structures, modern molecular simulation methods suffer from an inability to simulate large interfacial systems in a sufficient time scale at the allatom resolution. To develop a method capable of simulating solid–liquid interfaces, we have been developing a mean-field quantum mechanics/molecular mechanics (QM/MM) method. This Review briefly summarizes the theoretical background of mean-field QM/MM, as well as recent efforts to advance it. Furthermore, we summarize several studies performed based on this method.