Byungho Lee

A discrete-time sliding mode controller and observer with computation time delay

Abstract Based on discrete-time sliding mode, a robust controller and an observer that consider computation time delay are presented. The computation time delay is assumed to be constant and smaller than the sampling time. To cancel out the effects of perturbation, the proposed controller uses the concept of Time Delay Control (TDC). In the design of the observer, the concept of the discrete-time equivalent control approach is adopted. Furthermore, the combined controller–observer system is investigated. The usefulness of the proposed controller and the observer is demonstrated through experiments on a direct drive motor.

Graded bandgap structure for PbS/CdS/ZnS quantum-dot-sensitized solar cells with a PbxCd1−xS interlayer

To suppress the electron-hole recombination in the multishell sensitizer for quantum-dot-sensitized solar cells (QDSCs), the PbxCd1−xS interlayer is incorporated between the PbS core and CdS shell. The PbS/PbxCd1−xS/CdS structure enhances the cell efficiency by ∼60% compared to PbS/CdS QDSCs, and consequently shows a power-conversion efficiency of 1.37% with ZnS coating. Open-circuit voltage decay confirmed that the PbxCd1−xS interlayer effectively reduces the recombination at the PbS/CdS interface. Furthermore, with respect to the peak shift of incident photon-to-current conversion efficiency, the interlayer also increases the light-harvesting efficiency in the higher-wavelength region by reducing the exciton confinement within the PbS sensitizer.

Solvent and Intermediate Phase as Boosters for the Perovskite Transformation and Solar Cell Performance.

High power conversion efficiency and device stabilization are two major challenges for CH3NH3PbI3 (MAPbI3) perovskite solar cells to be commercialized. Herein, we demonstrate a diffusion-engineered perovskite synthesis method using MAI/ethanol dipping, and compared it to the conventional synthesis method from MAI/iso-propanol. Diffusion of MAI/C2H5OH into the PbCl2 film was observed to be more favorable than that of MAI/C3H7OH. Facile perovskite conversion from ethanol and highly-crystalline MAPbI3 with minimized impurities boosted the efficiency from 5.86% to 9.51%. Additionally, we further identified the intermediates and thereby the reaction mechanisms of PbCl2 converting into MAPbI3. Through straightforward engineering to enhance the surface morphology as well as the crystallinity of the perovskite with even faster conversion, an initial power conversion efficiency of 11.23% was obtained, in addition to superior stability after 30 days under an ambient condition.

An effective oxidation approach for luminescence enhancement in CdS quantum dots by H2O2

The effects of surface passivation on the photoluminescence (PL) properties of CdS nanoparticles oxidized by straightforward H2O2 injection were examined. Compared to pristine cadmium sulfide nanocrystals (quantum efficiency ≅ 0.1%), the surface-passivated CdS nanoparticles showed significantly enhanced luminescence properties (quantum efficiency ≅ 20%). The surface passivation by H2O2 injection was characterized using X-ray photoelectron spectroscopy, X-ray diffraction, and time-resolved PL. The photoluminescence enhancement is due to the two-order increase in the radiative recombination rate by the sulfate passivation layer.

Sub-optimal collision-free motion planning of a two-robot system using free arc

Abstract This paper presents a method for planning collision-free motion of a two-robot system. The concept of free arc is introduced for the purpose of developing the method in the C-space. Free arc is defined as a set composed of the configuration points of a robot manipulator satisfying its collision-free motion constraint at each sampling time, represented with respect to the coordinate frame having the origin at the goal configuration in the C-space. Thus, both the motion constraint and the collision constraint of a robot manipulator are represented in the form of free arc. Then, the free arc is used as a tool for collision-free motion planning, and optimality is considered when the collision-free path is determined from the free arcs. This concept enables us to transform the problem of collision-free motion planning into a Sub-Optimal Collision Avoidance Problem (SOCAP). The presented method is implemented in a real two-robot system which consists of two industrial SCARA type manipulators, and the experimental results are provided to show the validity of the method.

From Nanostructural Evolution to Dynamic Interplay of Constituents: Perspectives for Perovskite Solar Cells

Moving away from the high-performance achievements in organometal halide perovskite (OHP)-based optoelectronic and photovoltaic devices, intriguing features have been reported in that photocarriers and mobile ionic species within OHPs interact with light, electric fields, or a combination of both, which induces both spatial and temporal changes of optoelectronic properties in OHPs. Since it is revealed that the transport of photocarriers and the migration of ionic species are affected not only by each other but also by the inhomogeneous character, which is a consequence of the route selected to deposit OHPs, understanding the nanostructural evolution during OHP deposition, in terms of the resultant structural defects, electronic traps, and nanoscopic charge behaviors, will be valuable. Investigation of the film-growth mechanisms and strategies adopted to realize OHP films with less-defective large grains is of central importance, considering that single-crystalline OHPs have exhibited the most beneficial properties, including carrier lifetimes. Critical factors governing the behavior of photocarriers, mobile ionic species, and nanoscale optoelectronic properties resulting from either or all of them are further summarized, which may potentially limit or broaden the optoelectronic and photovoltaic applications of OHPs. Through inspection of the recent advances, a comprehensive picture and future perspective of OHPs are provided.

Synergetic effect of double-step blocking layer for the perovskite solar cell

In an organometallic CH3NH3PbI3 (MAPbI3) perovskite solar cell, we have demonstrated a vastly compact TiO2 layer synthesized by double-step deposition, through a combination of sputter and solution deposition to minimize the electron-hole recombination and boost the power conversion efficiency. As a result, the double-step strategy allowed outstanding transmittance of blocking layer. Additionally, crystallinity and morphology of the perovskite film were significantly modified, provoking enhanced photon absorption and solar cell performance with the reduced recombination rate. Thereby, this straightforward double-step strategy for the blocking layer exhibited 12.31% conversion efficiency through morphological improvements of each layer.

Route to Improving Photovoltaics Based on CdSe/CdSexTe1–x Type-II Heterojunction Nanorods: The Effect of Morphology and Cosensitization on Carrier Recombination and Transport

One-dimensionally elongated nanoparticles with type-II staggered band offset are of potential use as light-harvesting materials for photovoltaics, but only a limited attention has been given to elucidate the factors governing the cell performance obtainable from such materials. Herein, we describe a combined strategy to enhance charge collection from CdSe/CdSexTe1-x type-II heterojunction nanorods (HNRs) utilized as light harvesters for sensitized solar cells. By integrating morphology- and composition-tuned type-II HNRs into solar cells, factors that yield interfaces favorable both for the electron injection into TiO2 and hole transfer to electrolyte are examined. Furthermore, it is shown that a more efficient photovoltaic system results from cosensitization with CdS quantum dots (QDs) predeposited on a TiO2 scaffold, which improves charge collection from HNRs. Electrochemical impedance spectroscopy (EIS) analysis suggests that such a synergistically enhanced system benefits from the decreased recombination within HNRs and facilitated charge transport through the cosensitized TiO2 electrode, even with the activation of a recombination path presumably related to the photogenerated holes in CdS QDs.

Potential Survival and Pathogenesis of a Novel Strain, Vibrio parahaemolyticus FORC_022, Isolated From a Soy Sauce Marinated Crab by Genome and Transcriptome Analyses

Vibrio parahaemolyticus can cause gastrointestinal illness through consumption of seafood. Despite frequent food-borne outbreaks of V. parahaemolyticus, only 19 strains have subjected to complete whole-genome analysis. In this study, a novel strain of V. parahaemolyticus, designated FORC_022 (Food-borne pathogen Omics Research Center_022), was isolated from soy sauce marinated crabs, and its genome and transcriptome were analyzed to elucidate the pathogenic mechanisms. FORC_022 did not include major virulence factors of thermostable direct hemolysin (tdh) and TDH-related hemolysin (trh). However, FORC_022 showed high cytotoxicity and had several V. parahaemolyticus islands (VPaIs) and other virulence factors, such as various secretion systems (types I, II, III, IV, and VI), in comparative genome analysis with CDC_K4557 (the most similar strain) and RIMD2210633 (genome island marker strain). FORC_022 harbored additional virulence genes, including accessory cholera enterotoxin, zona occludens toxin, and tight adhesion (tad) locus, compared with CDC_K4557. In addition, O3 serotype specific gene and the marker gene of pandemic O3:K6 serotype (toxRS) were detected in FORC_022. The expressions levels of genes involved in adherence and carbohydrate transporter were high, whereas those of genes involved in motility, arginine biosynthesis, and proline metabolism were low after exposure to crabs. Moreover, the virulence factors of the type III secretion system, tad locus, and thermolabile hemolysin were overexpressed. Therefore, the risk of foodborne-illness may be high following consumption of FORC_022 contaminated crab. These results provided molecular information regarding the survival and pathogenesis of V. parahaemolyticus FORC_022 strain in contaminated crab and may have applications in food safety.

Mechanism design and autonomous movement and jump control for a jumping robot

This work introduces an autonomous jumping robot, capable of moving over the ground, and identifying obstacles as well as jumping over stairs. The robot could be employed to patrol in a building subject to stairs. The robot requires fast autonomous motion and makes use of novel jumping mechanisms to be fit into small-packed volume, reducing the weight enough to be held on humans hand. Several sensors are located on the robot including: a camera for monitoring and tracking a target, PSD (Position Sensitive Device) for distance measurements and ultrasonic sensors for alignment. Jumping is achieved using a four-bar link mechanism that pushes against the ground with the help of the compressed spring. The jumping height can be controlled by changing the tilt angle of the robot body, which allows the robot to adapt the obstacle size.