Hyunsuk Lee

A novel approach to preparing nano-size Co3O4-coated Ni powder by the Pechini method for MCFC cathodes

The dissolution of nickel oxide cathodes in the electrolyte is one of the major technical obstacles to the commercialization of molten carbonate fuel cells (MCFC). A novel alternative cathode material for MCFC was synthesized, which was made of nano-size Co3O4 coated on the surface of Ni powder using a polymeric precursor based on the Pechini method. X-Ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDAX), electron microprobe analysis (EPMA), and Raman spectrometry were employed in characterization of the novel alternative cathode materials. The Co-coated Ni cathode prepared by the tape-casting technique has a lower solubility in the molten carbonate than in the NiO cathode under CO2 ∶ O2 (67 ∶ 33) atmosphere at 650 °C. The reason is that the nano-size Co3O4-coated Ni powder can significantly retard the dissolution of NiO in molten carbonate due to the formation of the stable LiCo1−yNiyO2 phase on the surface of NiO in molten carbonate. During 300 h cell operation, the closed-circuit voltage (CCV) of unit cells using NiO and Co-coated Ni cathodes were found to be 0.80 V and 0.82 V, respectively, at a current density of 150 mA cm−2. The results show that the Co-coated Ni cathode used as an alternative cathode could resolve the problems in scale-up of the electrode and lengthen the lifetime of MCFC.

Effect of molecular architecture on micellization, drug loading and releasing of multi-armed poly(ethylene glycol)-b-poly(ε-caprolactone) star polymers

This study investigated the effect of molecular architecture of amphiphilic star polymers on micelle formation and drug loading and releasing. For this, multi-armed star block copolymers having poly(ethylene glycol) as a hydrophilic block and poly(ε-caprolactone) as a hydrophobic block were synthesized by using a divergent synthetic method consisting of a coupling reaction and a ring opening polymerization. The molecular weight and molecular weight distribution of the block copolymers were characterized by 1H NMR and GPC measurements. Dynamic light scattering and fluorescence spectroscopic analysis were employed to observe micellization, drug loading, and drug release behaviors. We have figured out that the number of arms is a critical factor that changes critical micelle concentration as well as drug loading and releasing behaviors; increase in the number of arms not only led to lowering the critical micelle concentration and drug release rate but also increased the micelle size and drug loading efficiency.

Curb feature based localization of a mobile robot in urban road environments

Urban road environments that have pavement and curb are characterized as semi-structured road environments. In semi-structured road environments, the curb provides useful information for robot navigation. In this paper, we present a practical localization method for outdoor mobile robots using the curb features in semi-structured road environments. The curb features are especially useful in urban environment, where the GPS failures take place frequently. A curb extraction is conducted on the basis of the Kernel Fisher Discriminant Analysis (KFDA) to minimize false detection. We adopt the Extended Kalman Filter (EKF) to combine the curb information with odometry and Differential Global Positioning System (DGPS). The uncertainty models for the sensors are quantitatively analyzed to provide a practical solution.

Localization of Outdoor Mobile Robots Using Curb Features in Urban Road Environments

Urban road environments that have pavement and curb are characterized as semistructured road environments. In semistructured road environments, the curb provides useful information for robot navigation. In this paper, we present a practical localization method for outdoor mobile robots using the curb features in semistructured road environments. The curb features are especially useful in urban environment, where the GPS failures take place frequently. A curb extraction is conducted on the basis of the Kernel Fisher Discriminant Analysis (KFDA) to minimize false detection. We adopt the Extended Kalman Filter (EKF) to combine the curb information with odometry and Differential Global Positioning System (DGPS). The uncertainty models for the sensors are quantitatively analyzed to provide a practical solution.

Autonomous Navigation of a Surveillance Robot in Harsh Outdoor Road Environments

This paper deals with the autonomous navigation problem of a mobile robot in outdoor road environments. The target application is surveillance in petroleum storage bases. Although there have been remarkable technological achievements recently in the area of outdoor navigation, robotic systems are still expensive due to a large number of high cost sensors. This paper proposes the reliable extraction algorithm of traversable regions using a single onboard Laser Range Finder (LRF) in outdoor road environments. The traversable regions are derived from the classifications of the road surfaces, curbs, and obstacles. The proposed scheme was experimentally tested in success. Since there are many potential applications that require autonomous service robots to move in semistructured road environments, the proposed scheme can be widely used as a low-cost practical solution.

Global localization using distances between reflectors

This paper proposes a global localization method using reflectors for mobile robots. Where the natural feature is not clear, the localization using only natural features is difficult. Furthermore, where the surrounding environment is changed frequently, there is a problem needs to be updated the global map each time. For these, we propose a global localization using reflectors. Global localization is possible to perform the localization at random position without information on the previous state. In this paper, we use only distances between reflectors measured by laser range finder sensor. In experimental results, we verified that proposed method can estimate the global pose in a real environment.

Performance analysis of path planners for autonomous parking control

Path planning for autonomous parking control is difficult and complicated because of its non-holonomic constraints. We proposed the parking path planner KPP (Korea University Path Planner) in our prior work. The purpose of this paper is to prove the advantages of KPP through quantitative and qualitative analyses. Numerical simulations have been carried out for comparison. This paper shows that KPP exhibits outstanding performance from viewpoint of the travel time and the computational time compared with the conventional RRT (Rapidly Exploring Random Tree) method.

Localization of an outdoor mobile robot considering the uncertainty model of the road curb

As one of the dominant features in the road environment, the curbs provide useful information for navigation. However, when the uncertainty model does not defined correctly, the road curb does not contribute to the estimated robot pose. In order to solve this problem, we propose the integrated localization scheme using curb features on the basis of uncertainty model of road curb. The uncertainty model for the extracted curb is quantitatively determined from experiments. Extended Kalman Filter is exploited for the fusion of curbs and DGPS measurements.

Effect of plasticity hardening exponent and creep exponent on crack tip stress under elastic-plastic-creep conditions for SE(B) specimen

This paper investigates an effect of plasticity hardening exponent (m) and creep exponent (n) on crack tip stress under elastic-plastic-creep conditions for Single-Edge-Notched (SE(B)) specimen, via two-dimensional (2-D) finite element (FE) analyses. For analysis, finite element results compare with Riedel and Rice equation. In case of creep exponent (n) equal or bigger than plasticity hardening exponent (m), crack tip stress field under elastic-plastic-creep conditions is predicted by Riedel and Rice equation using creep exponent since crack tip stress field is affected by creep exponent than plasticity hardening exponent. On the other hand, in case of n less than m, crack tip stress field under elastic-plastic-creep conditions is predicted by Riedel and Rice equation using m since crack tip stress field is affected by m than n.

Localization of a patrol robot using curb feature in road environment

Patrol robots to perform specific service in environment travel the same path repeatedly based on map. For the safe navigation of patrol robots, environment recognition and precise localization should be necessary. In outdoor environment, it is generally using expensive equipment and many sensors for environmental recognition and localization. However, complex system configuration and increase in costs of robot are required. Furthermore, in urban road environment, the precision of GPS is reduced by high structures. In order to solve these problems, we propose localization algorithm using the curb feature. An onboard LRF is used to extract curb. The extracted curb is matched with line map and fused by Extend Kalman Filter with odometry and DGPS measurement. We verify the robustness of the proposed algorithm by experiment, although the large DGPS error occurs due to the buildings.