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A vital objective in the wetting of Au deposited on chemically heterogeneous oxides is to synthesize a completely continuous, highly crystalline, ultrathin-layered geometry with minimized electrical and optical losses. However, no effective solution has been proposed for synthesizing an ideal Au-layered structure. This study presents evidence for the effectiveness of atomic oxygen-mediated growth of such an ideal Au layer by improving Au wetting on ZnO substrates with a substantial reduction in free energy. The unexpected outcome of the atomic oxygen-mediated Au growth can be attributed to the unconventional segregation and incorporation of atomic oxygen along the outermost boundaries of Au nanostructures evolving in the clustering and layering stages. Moreover, the experimental and numerical investigations revealed the spontaneous migration of atomic oxygen from an interstitial oxygen surplus ZnO bulk to the Au-ZnO interface, as well as the segregation (float-out) of the atomic oxygen toward the top Au surfaces. Thus, the implementation of a 4-nm-thick, two-dimensional, quasi-single-crystalline Au layer with a nearly complete crystalline realignment at a mild temperature (570 K) enabled exceptional optoelectrical performance with record-low resistivity (7.5 × 10

Oxyapatite[Ca2Nd8(SiO4)6O2] glass-ceramics have been suggested as wasteforms for the immobilisation of rare-earth radioactive nuclides because of their high waste-loading capability and good chemical durability. In particular, a partitioning effect is predicted to contribute to an enhancement of corrosion resistance in glass-ceramics compared with that of conjugate glasses of the same composition. Because rare-earths are inherently insoluble nuclides, detection of changes in corrosion behavior between glass-ceramics and conjugate glasses under normal conditions is not easy. In this study, therefore, we revealed the partitioning effect by exposing glass-ceramics and glasses to solution of pH 2, 7 and 10 at 90 °C for 20 d. In addition, we proposed the corrosion mechanism for oxyapatite glass-ceramics under various corrosion conditions. Especially, the glassy phase dissolved first, followed by the oxyapatite phase during pH 7 corrosion.

Background/aims For the management of hilar malignant biliary obstruction (HMBO), endoscopic biliary drainage (EBD) is preferred over percutaneous transhepatic biliary drainage (PTBD) because of its convenience. However, there is no established guideline for malignant hilar obstruction that requires multiple stenting. In this study, we compared the efficacy of bilateral metal stents (BMS) versus multiple plastic stents (MPS). Methods In this retrospective study, we analyzed 102 patients who underwent EBD with either BMS or MPS due to HMBO caused by hilar cholangiocarcinoma between 1996 and 2018 at Samsung Medical Center. We compared the successful drainage rates, cholangitis events, overall complications, mortality, and conversion rates to PTBD between the two groups. Results The successful drainage rates in the BMS group and the MPS group were 71.4% (25/35) and 65.6% (44/67), respectively, with no significant difference. The MPS group had a higher cholangitis risk (hazard ratio [HR], 2.08; 95% confidence interval [CI], 1.21 to 3.58) and higher 6-month mortality (HR, 2.91; 95% CI, 1.26 to 6.71) than the BMS group. There were no significant differences in overall complications or the conversion rate to PTBD between the groups. Conclusions In patients with malignant HMBO, the BMS group showed better outcomes in terms of the cholangitis rate and 6-month mortality than the MPS group. Therefore, if possible, bilateral metal stenting is recommended for HMBO caused by hilar cholangiocarcinoma.

This article proposes a novel adaptive backstepping hierarchical sliding mode control with balance and transfer for a ridable ballbot. The algorithm is applied to the dynamics of coupling two vertical planes. The dynamic model is a multiple-input–multiple-output underactuated system. Based on the backstepping and hierarchical sliding mode schemes, a robust nonlinear control law is obtained to govern the balance and transfer of the ridable ballbot; this scheme considers input constraints as well as matched and mismatched uncertainties. The influence of actuator saturation is examined by proposing an auxiliary system. The stability of the whole system is guaranteed via Lyapunov theory and Barbalat’s lemma, which shows that the switching gains are limited by the upper bound of the matched uncertainty. An adaptive law is proposed to estimate the matched uncertainty using radial bias function networks. As a result, the robustness is enhanced, and the constraints of the switching gains on the matched uncertainty can be relaxed. The stabilizing and tracking problems of the ridable ballbot are investigated through comparative simulations. The results demonstrate the effectiveness and robustness of the proposed control algorithm in the presence of parameter variations, external disturbances, and input saturation.

2D Ballbot is an actual under-actuated system with second-order nonholonomic velocity constraints and input coupling case where only control input is employed to control two outputs of the system. Controlling such a system is not easy because it faces many changelings including nonlinearities, external disturbances, and uncertainties. This study proposed a robust control system for a Ballbot mobile robot. The proposed control scheme is constructed using the hierarchical sliding mode control technique. The kinematics and dynamics of the Ballbot are derived. A Lyapunov function is used to prove the stability of the closed-loop control system. The stabilizing and transferring problems are investigated through several simulations and experiments by using the actual Ballbot platform.

The desire to enhance the efficiency of organic light-emitting devices (OLEDs) has driven to the investigation of advanced materials with fascinating properties. In this work, the efficiency of top-emission OLEDs (TEOLEDs) is enhanced by introducing ampicillin microstructures (Amp-MSs) with dual phases (α-/β-phase) that induce photoluminescence (PL) and electroluminescence (EL). Moreover, Amp-MSs can adjust the charge balance by Fermi level (E

Structure engineering is essential for manipulating the chemical, electrical, and optical properties of Au. However, it is challenging to design nanoscopic structures because no effective method is available to deviate from the intrinsic evolution behavior during and after synthesis via vapor deposition. Here, we propose an approach that utilizes the oxidation-induced clustering and layering of Au due to the strong O interference at the outmost surfaces of nanoscopic Au geometries. This promotes the evolution of Au clusters and layers that are highly wetted on their oxide supports. A 4-nm-thick epitaxial Au layer eventually evolved from the proposed growth mode, simultaneously exhibiting higher optical transparency than Ag, a near-bulk resistivity of 8 × 10−8 Ω m, and extreme resilience to chemical corrosion and mechanical deformation. This result provides a definite solution to transparent metal electrodes that are highly vulnerable to degradation in ambient and working environments.

The effect of ultraviolet-ozone (UVO) irradiation on amorphous (am) SnO2 and its impact on the photoconversion efficiency of MAPbI3-based perovskite solar cells were investigated in detail. UVO treatment was found to increase the amount of chemisorbed oxygen on the am-SnO2 surface, reducing the surface energy and contact angle. Physicochemical changes in the am-SnO2 surface lowered the Gibbs free energy for the densification of perovskite films and facilitated the formation of homogeneous perovskite grains. In addition, the Fermi energy of the UVO-treated am-SnO2 shifted upwards to achieve an ideal band offset for MAPbI3, which was verified by theoretical calculations based on the density functional theory. We achieved a champion efficiency of 19.01 % with a statistical reproducibility of 17.01 ± 1.34 % owing to improved perovskite film densification and enhanced charge transport/extraction, which is considerably higher than the 13.78 ± 2.15 % of the counterpart. Furthermore, UVO-treated, am-SnO2-based devices showed improved stability and less hysteresis, which is encouraging for the future application of up-scaled perovskite solar cells.

Crawler excavators are important, utilitarian machines in construction industries. Special features of the chain and chassis allow them to operate and move on unstable ground. The shock motions of the links, which coincide with the changes of the forces impacting the foundation, create vibrations within the entire system. The highest level of vibrations appears when the boom moves, as it holds the robotic excavator's entire actuator with large mass and moment of inertia. These undesired fluctuations cause system instability, driver discomfort, reduced operating efficiency, and increased energy consumption. In this study, a hierarchical sliding mode control focusing on boom movement is designed based on the system dynamic model. This controller allows the boom to move precisely with a slight fluctuation angle of the main body, even while the other links are moving using a parameter estimator. Maintaining stable boom movements significantly simplifies arm and bucket control. The effectiveness of the entire work is investigated by numerical simulation and implementation results on a small-scale hydraulic excavator.

Cable-driven parallel robots (CDPRs) are vulnerable to vibration due to the inevitable flexible properties of the cables. Thus, vibration analysis is critical for CDPR’s operation in which highly accurate motion is required. However, most of the current methods related to vibration analysis of CDPRs rely on simple spring models which have limitations in their performance and complexity that are not general to analyze the vibration of various CDPRs. Hence, accurate, simple and general approaches for vibration analysis in CDPRs are need. To solve this problem, this paper presents the finite element method (FEM) and the modified analytical method to analyze the vibration of CDPRs. To validate these methods, free vibration analysis was conducted using the proposed methods for the planar and spatial cable-driven parallel robots. The natural frequencies of these two CDPRs were computed by the proposed two methods and compared with those of the commercial software, SAP2000. The solutions obtained by the FEM and the modified analytical models turned out to be close to SAP2000’s results, thereby verifying the validity of the proposed methods.

Modern buildings are designed with wheelchair accessibility, giving an opportunity for wheeled robots to navigate through sloped areas while avoiding staircases. Nonetheless, working safely and autonomously in uneven or unstructured environments is still challenging for mobile robots. Herein, we propose the use of a point cloud treatment and Monte Carlo localization in an algorithm for 3D localization of a mobile robot in uneven and unstructured environments. The point cloud treatment consists of projecting the acquired 3D point cloud and generated 2D features. These features are used to recreate an occupancy map. To perform localization in real-time, the robot systems use the occupancy map and 2D features as input in conjunction with the Monte Carlo algorithm.

Hydraulic crawler excavators have been widely used for construction in industry, mining, and agriculture because of their special ability to work on weak soil support. However, the elastic properties of the ground increase the undesired vibrations of the entire operating machine. These oscillations significantly influence the working productivity, the level of fuel expenditure, and the comfort of the driver. There have been many works addressing this problem, although they mainly focus on mechanical dampers. Considering the system from robotic and control aspects, this study presents a new approach to deal with the abovementioned problem. A controller design, which uses a combination of feedback linearization and sliding mode control, is proposed based on a dynamic model. This control law reduces the vibrations of the system working on an elastic foundation, while also allowing for accurate tracking performance of the links. This control law is applied to a small-scale platform to investigate its feasibility for practical applications.

A ridable ballbot has unstable underactuated dynamics with nonholonomic velocity constraints and input coupling case. Such a robot can carry people and move in any direction on the floor. In this study, a pseudo-2D dynamic model of the ridable ballbot is derived. An improved nonlinear double-loop control system combined with the partial feedback linearization (PFL) technique is proposed for the ridable ballbot, which allows it to balance and transfer. Feedforward compensation is added to the controller to consider uncertainties, friction, and disturbances. Numerical simulations and experiments show the validity of the PFL double-loop control based on the pseudo-2D dynamic model.

A ridable ballbot, a personal robot, is an underactuated system. The four state variables of the ball motion and body motion are controlled by two input signals acting on the ball. Euler–Lagrange equation is applied to obtain the dynamic model of the ridable ballbot. On the basis of this dynamic model, a nonlinear controller is analyzed and designed to control balancing and transferring of the robot. The nonlinear control scheme is proposed based on the combination of two control design techniques: (i) partial feedback linearization, which is designed to maintain the body in the upright position; and (ii) sliding mode control, which provides robust control in ball motion on the floor against model imprecision, uncertainty of system parameters and friction, and external disturbances. These two control mechanisms are successfully merged into a combined controller. Numerical and experimental results indicate the effectiveness of the combined controller and proposed a dynamic model. The control algorithm asymptotically stabilizes all system responses.

Ballbot is a robot that can transfer to a given position while maintaining a self-balanced upright posture on a spherical ball. This paper proposes a nonlinear control of a ballbot using three omnidirectional wheels in the driving mechanism. Assuming a small swing angle for balance, the full dynamics of the ballbot can be decomposed into three, which are two underactuated dynamics for two orthogonal vertical planes and the fully actuated dynamics for one horizontal plane. The passivity of closed-loop systems of vertical planes is derived from the modified potential energy function. The proposed controller is designed to control the balancing and transferring of the system based on Lyapunov theory and the passivity of the system. A proportional-derivative feedforward controller is applied to regulate the heading motion in the horizontal plane. Experiments are performed with a real ballbot system to validate the effectiveness of system modeling and to show the controllability of the proposed algorithm.

In this study, we propose a nonlinear double-loop control system for a ridable ballbot. An improved nonlinear double-loop control technique based on double-loop control scheme and sliding mode technology is used, and the inner-loop consists of proportional–integral feedback plus feedforward control. A sliding mode control enables the ridable ballbot to balance and transfer on the floor. Feedforward compensation has been added for the stability of the ballbot. As a result, the control system can stabilize all state variables of the ballbot system despite the uncertainties of the system parameters such as model, friction, and external disturbances, and relatively large body inertia. Experiments demonstrate the effectiveness of the proposed control system and the performance validation of the nonlinear double-loop control.

Different WO3 facets have different surface energies and electronic structures, and exhibit different water oxidation abilities and photocatalytic performance as a result. Because of the material’s limited photoresponse region, loading a narrow bandgap material on WO3 is a generally known method for improving photo-harvesting. In this paper, we have synthesized WO3 films with different crystal facet ratios. After loading BiVO4 on these WO3 films, we measured the photoelectrochemical (PEC) performance to investigate the effects of WO3 facet choice on the heterojunction film electrode’s performance. We found that a high-intensity ratio of the (002) WO3 facet in X-ray diffraction (XRD) leads to a more negative onset potential and higher photocurrents in a lower potential region. The ultraviolet photoelectron spectra show a lower work function for the 002-dominant WO3 film compared to other WO3 films, which may result in a higher quasi-fermi level for the heterojunction electrode. Based on the XRD results, the high-intensity ratio of the (002) WO3 facet preferentially exposes the (020) BiVO4 facet, which may be a reason for the better charge extraction observed at low applied potential and high faradic efficiency on PEC water splitting. Together, this results in a high hole injection efficiency for 002-dominant WO3/BiVO4 films compared with WO3/BiVO4 films favoring other WO3 facet ratios.

Autonomous vessels have been given interesting research topics in both the maritime area and the control engineering field with increasingly numerous applications. The practical system is impacted by a vast range of uncertainties, including the high nonlinearities of the dynamic model, the variable working environments, and the influences of ocean currents, waves, and wind. These factors give the big challenges for control, especially precise trajectory tracking control. In this research, a new stage adaptive neural network back-stepping control based on sliding-mode control for the Fossen’s ship model is proposed. By using the artificial neural network to approximate the composite time-varying disturbance function, the controller can solve the problems of accurate control tracking the displacement of the surface vessel following the convergence of the Lyapunov function. The numerical simulation results illustrate the effectiveness of the designed control law.

Spherical robots are the mobile robots with the locomoting by displacing its centre of gravity to generate torque and rotate itself. Therefore, the angle of the main body inside the robot determines the position and posture of the robot. There is only one contact point between the robot and the ground, and the inappropriate control strategy can generate the sizeable angular amplitude of the main body. As a result, the stable movement of the robot cannot be satisfied along with the appeared vibrations. This problem significantly impacts the tracking control quality and creates the clumsy gestures of the robot. In this research, an under-actuated dynamic model-based back-stepping control focusing on the rolling motion is developed and applied for a designed two-wheel spherical robot. With the provided closed-loop control law, both the precision and stability of the robot’s movement are guaranteed. The entire work’s efficiency is investigated by the experimental results.

For vibration attenuation of excavators, this study proposed two controllers: Feedback linearization controller [FLC], and Sliding mode controller [SMC]. The three actuators, consisting of boom, arm and bucket force, simultaneously actuate fine output consisting of boom angle, arm angle and one payload bucket angle. With dynamic modeling using the Lagrange equation, the mathematical analysis of boom, cancer, bucket and terminal was performed, and experimented with a scale of 1/14 excavator to investigate the quality of the two controllers. The performance comparison of the two proposed controllers through system modeling demonstrated the FLC improved the nonlinear system to the linear system, and the performance of the SMC controller improved the vulnerability to non-linearization of the FLC. In addition, in order to overcome the uncertainty structural instability factor using the reduced model, the parameters of the control algorithm were studied in the neural network learning to overcome structural suggestion elements.

The spherical rolling robot (SRR) is an underactuated system with nonholonomic constraints. The proposed drive mechanism for the mobile robot is comprised of three omnidirectional wheels to make the omnidirectional movement of the robot on the floor. The kinematic model of the SRR is derived via nonholonomic constraints. Numerical simulation is analyzed. Results indicate that the robot can track the desired trajectory and maintain its balance stably at the same time.

Nowadays, multi-sensor fusion is a popular tool for feature recognition and object detection. Integrating various sensors allows us to obtain reliable information about the environment. This article proposes a 3D robot trajectory estimation based on a multimodal fusion of 2D features extracted from color images and 3D features from 3D point clouds. First, a set of images was collected using a monocular camera, and we trained a Faster Region Convolutional Neural Network. Using the Faster Region Convolutional Neural Network, the robot detects 2D features from camera input and 3D features using the point’s normal distribution on the 3D point cloud. Then, by matching 2D image features to a 3D point cloud, the robot estimates its position. To validate our results, we compared the trained neural network with similar convolutional neural networks. Then, we evaluated their response for the mobile robot trajectory estimation.

최근 한국사회에서 청소년의 도박행동이 증가하면서, 도박을 즐기기 위한 재산범죄가 발생하는 등 사회적 부작용이 심각하다. 인터넷게임은 정보기술의 발전과 함께 청소년의 주요한 문화여가 활동으로 자리 잡았으나, 청소년의 비행행동과 유의미한 상관성이 있다는 연구결과가 빈번하게 보고되고 있다. 하지만 청소년의 도박행동과 인터넷게임의 관계를 분석한 연구는 상대적으로 찾아보기 어렵다. 따라서 본 연구는 청소년의 인터넷게임 사용이 도박행동에 미치는 영향을 분석하고자 하였다. 이를 위하여 한국 아동⋅청소년 패널조사의 중1패널 4차 년도 횡단면 자료를 활용한 이항 로지스틱 회귀분석을 실시하였다. 그 결과 성별, 약물사용, 도박행동 친구 수 및 인터넷게임 이용 등이 청소년의 도박행동을 통계적으로 유의미하게 예측하는 것으로 나타났다. 이를 바탕으로 청소년의 도박행동을 감소시키기 위한 연구의 시사점을 제시하였다.

A new hybrid electro‐hydraulic and pneumatic actuator system and its dynamic model for high‐performance control are presented. This work focuses on tracking control of rapidly changing acc...

This paper examines the changing nature of volatility spillovers among the U.S. and eight East Asian stock markets between two financial crises: the Asian currency crisis and the U.S. subprime credit crisis. Our empirical results suggest that volatility is not always spilled over from the directly affected markets to surrounding markets in crisis periods. The East Asian markets who directly suffered from the Asian currency crisis are the ones to which volatility is spilled over from other markets during the Asian currency crisis period, whereas uni-directional volatility spillovers from the U.S. market to other markets are observed during both crisis periods. This difference can be explained by a pre-determined hierarchy in which volatility spillovers tend to start from the U.S. market regardless of the geographical origin of the crisis. Furthermore, our results reveal that the markets in three major Asian financial hubs, i.e., Japan, Hong Kong and Singapore, are the markets to which volatility is spilled over uni-directionally from several other countries during the subprime credit crisis period, but not during the Asian currency crisis period. We attribute this difference to crisis-specific (currency or credit crisis), market-specific (credit derivatives market participation and foreign currency reserves), and time-specific (more integrated global market) factors.

Controlling the shape and crystallography of nanocrystals during the early growth stages of a noble metal layer is important because of its correlation with the final layer morphology and optoelectrical features, but this task is unattainable in vapor deposition processes dominated by artificially uncontrollable thermodynamic free energies. We report on experimental evidence for the controllable evolution of Ag nanocrystals as induced by the addition of nitrogen, presumed to be nonresidual in the Ag lattice given its strong float-out behavior. This atypical formation of energetically stable Ag nanocrystals with significantly improved wetting abilities on a chemically heterogeneous substrate promotes the development of an atomically flat, ultrathin, high-purity Ag layer with a thickness of only 5 nm. This facilitates the fabrication of Ag thin-film electrodes exhibiting highly enhanced optical transparency over a broad spectral range in the visible and near-infrared spectral range. An Ag thin-film electrode with a ZnO/Ag/ZnO configuration exhibits an average transmittance of about 95% in the spectral range of 400-800 nm with a maximum transmittance of over 98% at 580 nm, which is comparable with the best transparency values so far reported for transparent electrodes. This degree of optical transparency provides an excellent chance to improve the photon absorption of photovoltaic devices employing an Ag thin film as their window electrode. This is clearly confirmed by the superior performance of a flexible organic solar cell with a power conversion efficiency of 8.0%, which is far superior to that of the same solar cell using a conventional amorphous indium tin oxide electrode (6.4%).

This study investigates stock price movements in response to macroeconomic shocks, allowing for asymmetry in this relationship. Given Ferson’s (1989) finding that large and small stocks can exhibit different risk behaviors, we examine the behaviors of the KOSPI and KOSDAQ stock markets in response to changes in the price level, real interest rate, and real USD/KRW exchange rate using simple and nonlinear autoregressive-distributed lag (ARDL) models. We find that the long-run effects of macroeconomic shocks are relatively insignificant under the simple ARDL model, whereas a significant and negative long-run effect is found for almost every explanatory variable–market pair under the nonlinear model. In addition, we find that the long-run effects of stock price shocks on macroeconomic variables are more significant under the nonlinear model. Overall, the results imply that it is difficult to identify the relationship between macroeconomic variables and stock price dynamics without considering asymmetry.

In this study, the dynamical model of a ridable ballbot system is investigated to derive a nonlinear model that can describe the spatial dynamics of the mechatronic system by use of a set of differential equations. An aggregated hierarchical sliding mode control is proposed for a spatial ridable ballbot which is a class of multiple-input and multiple-output underactuated systems funder input coupling case and nonholonomic velocity constraints. The spatial ridable ballbot system is divided into ball and body subsystems. The hierarchical structure of the sliding mode surfaces (SMSs) is designed on the basis of the two subsystems as follows. First, the SMS of every subsystem is defined. Then the SMS of each subsystem is defined as the first layer SMS. The first layer SMS is used to construct the second layer SMS with the SMS of the other subsystem. This process continues until the SMS of all subsystems is included. The total control law is deduced from the hierarchical structure. Asymptotic stability of the control system is theoretically proven by Barbalat’s lemma in the ideal of Lyapunov theory. Simulation and experimental results indicate the validity of the proposed controller.

Improving the wetting ability of Ag on chemically heterogeneous oxides is technically important to fabricate ultrathin, continuous films that would facilitate the minimization of optical and electrical losses to develop qualified transparent Ag film electrodes in the state-of-the-art optoelectronic devices. This goal has yet to be attained, however, because conventional techniques to improve wetting of Ag based on heterogeneous metallic wetting layers are restricted by serious optical losses from wetting layers. Herein, we report on a simple and effective technique based on the partial oxidation of Ag nanoclusters in the early stages of Ag growth. This promotes the rapid evolution of the subsequently deposited pure Ag into a completely continuous layer on the ZnO substrate, as verified by experimental and numerical evidence. The improvement in the Ag wetting ability allows the development of a highly transparent, ultrathin (6 nm) Ag continuous film, exhibiting an average optical transmittance of 94% in the spectral range 400-800 nm and a sheet resistance of 12.5 Ω sq-1, which would be well-suited for application to an efficient front window electrode for flexible solar cell devices fabricated on polymer substrates.