Donghyung Kim

Effect of post treatments on the structure and thermal stability of titanate nanotubes

TiO2 sol was prepared hydrothermally in an autoclave from aqueous TiOCl2 solutions as a starting precursor. Titanate nanotubes were obtained when the sol?gel-derived TiO2 sol was treated chemically with a 10?M NaOH solution and subsequently heated in the autoclave at 150??C for 48?h. The samples were characterized using XRD, TEM, SEM, EDX, Raman spectroscopy, and a BET surface area analyser. The effect of post treatments, such as washing with and without hydrochloric acid and calcination, on the phase structure, shape and morphology, pore structures, and BET surface area of the titanate nanotubes was investigated. When a sample containing 7.08?wt% Na (after washing only with water) was calcined at different temperatures from 300 to 900??C, it showed the formation of a mixture of sodium trititanates and sodium hexatitanates and was found to preserve the tubular morphology at higher temperatures. However, a sample containing 0.06?wt% Na obtained after prolonged washing with hydrochloric acid followed by heat treatment showed the formation of TiO2 anatase involving TiO2 (B) as an intermediate at lower temperatures and anatase was further transformed to the rutile phase when the temperature was raised. On the basis of different observations, a general formula NaxH2?xTi3O7?nH2O has been proposed for the trititanate nanotubes.

Scalable 3-D Carbon Nitride Sponge as an Efficient Metal-Free Bifunctional Oxygen Electrocatalyst for Rechargeable Zn–Air Batteries

Rational design of efficient and durable bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts is critical for rechargeable metal-air batteries. Here, we developed a facile strategy for fabricating three-dimensional phosphorus and sulfur codoped carbon nitride sponges sandwiched with carbon nanocrystals (P,S-CNS). These materials exhibited high surface area and superior ORR and OER bifunctional catalytic activities than those of Pt/C and RuO2, respectively, concerning its limiting current density and onset potential. Further, we tested the suitability and durability of P,S-CNS as the oxygen cathode for primary and rechargeable Zn-air batteries. The resulting primary Zn-air battery exhibited a high open-circuit voltage of 1.51 V, a high discharge peak power density of 198 mW cm-2, a specific capacity of 830 mA h g-1, and better durability for 210 h after mechanical recharging. An extraordinary small charge-discharge voltage polarization (∼0.80 V at 25 mA cm-2), superior reversibility, and stability exceeding prolonged charge-discharge cycles have been attained in rechargeable Zn-air batteries with a three-electrode system. The origin of the electrocatalytic activity of P,S-CNS was elucidated by density functional theory analysis for both oxygen reactions. This work stimulates an innovative prospect for the enrichment of rechargeable Zn-air battery viable for commercial applications such as armamentaria, smart electronics, and electric vehicles.

Rough sets attributes reduction based expert system in interlaced video sequences

A deinterlacing algorithm that is based on rough sets theory is researched and applied in this paper. The fundamental concepts of rough sets, with upper and lower approximations, offer a powerful means of representing uncertain boundary regions in image processing. However, there are a few studies that discuss the effectiveness of the rough sets concept in the field of engineering. Moreover, the studies involving deinterlacing systems that are based on rough sets have not been proposed yet. Thus, this paper proposes a deinterlacing method that will reliably confirm that the method being tested is the most suitable for the sequence, with almost perfect reliability. This proposed deinterlacing approach employs a size reduction of the database system, keeping only the essential information for the process. Decision making and interpolation results are presented. The results of computer simulations show that the proposed method outperforms a number of methods presented in the literature

Fuzzy rough sets hybrid scheme for motion and scene complexity adaptive deinterlacing

Current research activities in the field of deinterlacing include the selection of suitable deinterlacing methods and the estimation of the exact value of a missing line. This paper proposes a spatio-temporal domain fuzzy rough sets rule for selecting a deinterlacing method that is suitable for regions with high motion or frequent scene changes. The proposed algorithm consists of two parts. The first part is fuzzy rule-based edge-direction detection with an edge preserving part that utilizes fuzzy theory to find the most accurate edge direction and interpolates the missing pixels. Using the introduced gradients in the interpolation, the vertical resolution in the deinterlaced image is subjectively concealed. The second part of the proposed algorithm is a rough sets-assisted optimization which selects the most suitable of five different deinterlacing methods and successively builds approximations of the deinterlaced sequence. Moreover, this approach employs a size reduction of the database system, keeping only the information essential for the process. The proposed algorithm is intended not only to be fast, but also to reduce deinterlacing artifacts.

A new temporal error concealment method for H.264 using adaptive block sizes

H.264 adopts new coding tools such as variable block size, quarter-pixel-accuracy motion estimation/compensation, multiple reference frames, loop filter, etc. The adoption of these tools enables a macroblock to have more information compared with previous standards. In H.264 each macroblock can have up to sixteen motion vectors, four reference frames, and a mode of the macroblock, all of which can be used for temporal error concealment. The H.264 error concealment in the informative part, however, uses a similar method to prior coding standards that consider only motion vectors of macroblocks adjacent to the lost macroblock. In this paper, we propose an effective temporal error concealment algorithm for H.264-coded video. It uses not only motion vectors and reference frames but the modes of macroblocks adjacent to the lost macroblock as well. Depending on the modes of neighboring macroblocks, each lost macroblock is concealed on the basis of different block sizes. Simulation results show the proposed method yields better video quality than conventional approaches.

Fine edge-preserving deinterlacing algorithm for progressive display

This paper proposes a fine edge-preserving deinterlacing algorithm that is based on local gradient features. The proposed algorithm uses horizontal and vertical gradient operators to find the various edges, and then determines the dominant edge using the surrounding edges of the interpolating pixel, to increase the edge direction accuracy. The proposed method uses different reference pixels and weighting factors depending on the dominant edge direction. Experimental results demonstrate that the proposed method outperforms the conventional deinterlacing methods.

A Fast Mode Selection Algorithm in H.264 Video Coding

For improvement of coding efficiency, the H.264 video coding standard uses new coding tools, such as variable block size, quarter-pixel-accuracy motion estimation, multiple reference frames, intra prediction, loop filter, etc. Using these coding tools, H.264 achieves significant improvement in coding efficiency compared with existing standards. However, encoder complexity increases tremendously. Among the tools, the macroblock mode selection and the motion estimation contribute most to total encoder complexity. This paper focuses on complexity reduction in macroblock mode selection. Of all macroblock modes which can be selected, inter8times8 and intra4times4 have the highest complexity. We propose two methods for complexity reduction of inter8times8 and intra4times4 by using the costs of the other macroblock modes. Simulation results show that the proposed methods save up to 57.7% of total encoding time compared with the H.264 reference implementation, whereas the average PSNR only decreases less than 0.05 dB

Highly active and durable carbon nitride fibers as metal-free bifunctional oxygen electrodes for flexible Zn–air batteries

The design of flexible, highly energetic, and durable bifunctional oxygen electrocatalysts is indispensable for rechargeable metal-air batteries. Herein we present a simple approach for the development of carbon nitride fibers co-doped with phosphorus and sulfur, grown in situ on carbon cloth (PS-CNFs) as a flexible electrode material, and demonstrate its outstanding bifunctional catalytic activities toward ORR and OER compared to those of precious metal-based Pt/C and IrO2 on account of the dual action of P and S, numerous active sites, high surface area, and enhanced charge transfer. Furthermore, we demonstrate the flexibility, suitability, and durability of PS-CNFs as air electrodes for primary and rechargeable Zn-air batteries. Primary Zn-air batteries using this electrode showed high peak power density (231 mW cm-2), specific capacity (698 mA h g-1; analogous energy density of 785 W h kg-1), open circuit potential (1.49 V), and outstanding durability of more than 240 h of operation followed by mechanical recharging. Significantly, three-electrode rechargeable Zn-air batteries revealed a superior charge-discharge voltage polarization of ∼0.82 V at 20 mA cm-2, exceptional reversibility, and continuous charge-discharge cycling stability during 600 cycles. This work provides a pioneering strategy for designing flexible and stretchable metal-free bifunctional catalysts as gas diffusion layers for future portable and wearable renewable energy conversion and storage devices.

A study on motion control of 6WD/6WS vehicle using optimum tire force distribution method

This paper presents a motion control method of 6WD/6WS (6-wheel-drive and 6-wheel-steering) vehicle using optimum tire force distribution method. When we make used of independent driving and steering system, the motion control performance of the 6WD/6WS vehicle can be improved. For example, vehicles maneuverability is more improved at low speed and vehicles stability is also improved at high speed. Therefore, it needs to find a control strategy using optimum tire forces. A control strategy must satisfy the drivers command and minimize the energy consumption. When the driver commands vehicle (input steering angle and acceleration/brake pedal stroke), we can obtain the desired yaw moment, the desired lateral force and the desired longitudinal force. Those values are used in the optimum tire force distribution method. The optimum tire force distribution method can find the longitudinal tire force and lateral tire force. That force minimizes the cost function. The cost function is the sum of normalized tire force. The longitudinal tire forces and lateral tire force of each wheel are converted to the reference torque inputs and steering wheel angle inputs. The method was tested on the simulation and effectiveness was verified.

Hierarchically Designed 3D Holey C2N Aerogels as Bifunctional Oxygen Electrodes for Flexible and Rechargeable Zn-Air Batteries

The future of electrochemical energy storage spotlights on the designed formation of highly efficient and robust bifunctional oxygen electrocatalysts that facilitate advanced rechargeable metal-air batteries. We introduce a scalable facile strategy for the construction of a hierarchical three-dimensional sulfur-modulated holey C2N aerogels (S-C2NA) as bifunctional catalysts for Zn-air and Li-O2 batteries. The S-C2NA exhibited ultrahigh surface area (∼1943 m2 g-1) and superb electrocatalytic activities with lowest reversible oxygen electrode index ∼0.65 V, outperforms the highly active bifunctional and commercial (Pt/C and RuO2) catalysts. Density functional theory and experimental results reveal that the favorable electronic structure and atomic coordination of holey C-N skeleton enable the reversible oxygen reactions. The resulting Zn-air batteries with liquid electrolytes and the solid-state batteries with S-C2NA air cathodes exhibit superb energy densities (958 and 862 Wh kg-1), low charge-discharge polarizations, excellent reversibility, and ultralong cycling lives (750 and 460 h) than the commercial Pt/C+RuO2 catalysts, respectively. Notably, Li-O2 batteries with S-C2NA demonstrated an outstanding specific capacity of ∼648.7 mA h g-1 and reversible charge-discharge potentials over 200 cycles, illustrating great potential for commercial next-generation rechargeable power sources of flexible electronics.