Sangheon Lee

Modeling and analysis on the internal impact of a Stewart platform utilized for spacecraft docking

In this paper, impacts at the joints of a closed-chain mechanism are modeled and analyzed. It is assumed that a Stewart platform is attached to one end of a spacecraft to be utilized as a docking platform and the spacecraft docks with another spacecraft. When the spacecrafts dock with each other, impact will rise at the docking point and the impact is absorbed by the docking platform. Although the impact at the contact point is very large, most of the impact is absorbed by the docking platform and negligible impact is transmitted to the spacecraft. The docking platform can absorb the shock by inertial effect, not by damping or friction. To show this, modeling of the internal impulses at the joints of a multi-body system is introduced and the internal impulses of the docking platform are analyzed by the modeling method.

Effective wrapping of graphene on individual Li4Ti5O12 grains for high-rate Li-ion batteries

An effective way of synthesizing graphene-wrapped Li4Ti5O12 particles was developed by solid-state reaction between graphene oxide-wrapped P25 (TiO2) and Li2CO3. Compared to the previously reported graphene/Li4Ti5O12 composites, prior wrapping of TiO2 with subsequent chemical lithiation led to more effectively confined Li4Ti5O12. The Li4Ti5O12 tightly bound by graphene exhibited a remarkable specific capacity of 147 mA h g−1 at a rate of 10 C (1 C = 175 mA g−1) after 100 cycles. This rate capability is one of the highest values among reported Li4Ti5O12 with 150 ± 50 nm grains. The improved rate capability was attributed to the enhanced electronic conductivity of each Li4Ti5O12 grain via uniform graphene wrapping, with single-grain growth during annealing from the initial ∼25 nm TiO2 nanoparticles enclosed by outer graphene sheets. Graphene-eliminated Li4Ti5O12 by thermal decomposition was also directly compared to the graphene-coated sample, to clarify the role of graphene with nearly equivalent particle size/morphology distributions.

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.

Integration of CdSe/CdSexTe1−x Type-II Heterojunction Nanorods into Hierarchically Porous TiO2 Electrode for Efficient Solar Energy Conversion

Semiconductor sensitized solar cells, a promising candidate for next-generation photovoltaics, have seen notable progress using 0-D quantum dots as light harvesting materials. Integration of higher-dimensional nanostructures and their multi-composition variants into sensitized solar cells is, however, still not fully investigated despite their unique features potentially beneficial for improving performance. Herein, CdSe/CdSexTe1−x type-II heterojunction nanorods are utilized as novel light harvesters for sensitized solar cells for the first time. The CdSe/CdSexTe1−x heterojunction-nanorod sensitized solar cell exhibits ~33% improvement in the power conversion efficiency compared to its single-component counterpart, resulting from superior optoelectronic properties of the type-II heterostructure and 1-octanethiol ligands aiding facile electron extraction at the heterojunction nanorod-TiO2 interface. Additional ~32% enhancement in power conversion efficiency is achieved by introducing percolation channels of large pores in the mesoporous TiO2 electrode, which allow 1-D sensitizers to infiltrate the entire depth of electrode. These strategies combined together lead to 3.02% power conversion efficiency, which is one of the highest values among sensitized solar cells utilizing 1-D nanostructures as sensitizer materials.

Reduced graphene oxide/carbon double-coated 3-D porous ZnO aggregates as high-performance Li-ion anode materials

The reduced graphene oxide (RGO)/carbon double-coated 3-D porous ZnO aggregates (RGO/C/ZnO) have been successfully synthesized as anode materials for Li-ion batteries with excellent cyclability and rate capability. The mesoporous ZnO aggregates prepared by a simple solvothermal method are sequentially modified through distinct carbon-based double coating. These novel architectures take unique advantages of mesopores acting as space to accommodate volume expansion during cycling, while the conformal carbon layer on each nanoparticle buffering volume changes, and conductive RGO sheets connect the aggregates to each other. Consequently, the RGO/C/ZnO exhibits superior electrochemical performance, including remarkably prolonged cycle life and excellent rate capability. Such improved performance of RGO/C/ZnO may be attributed to synergistic effects of both the 3-D porous nanostructures and RGO/C double coating.

Effect of fibromyalgia syndrome on the health-related quality of life and economic burden in Korea

OBJECTIVE To investigate the health-related quality of life (HRQOL) and economic burden of patients with FM syndrome (FMS) and compare the changes in these parameters 3 months before and after FMS diagnosis. METHODS A total of 2098 patients with FMS (1818 previously diagnosed with FMS and 280 newly diagnosed with FMS) were enrolled in this study. The newly diagnosed patients with FMS participated in a 3-month prospective observational study to assess HRQOL and economic burden in terms of direct health-care costs, direct non-health-care costs and indirect costs. HRQOL was estimated using the Short Form 36 Health Survey. RESULTS Mean (S.D.) scores obtained on the physical component summary (PCS) and mental component summary (MCS) scales by patients with FMS were 34.01 (7.28) and 37.29 (11.17), respectively. The total expenditure for the 3 months before enrolment was

Torque distribution using a weighted pseudoinverse in a redundantly actuated mechanism

1481 (S.D.

Foliar application of the leaf-colonizing yeast Pseudozyma churashimaensis elicits systemic defense of pepper against bacterial and viral pathogens

2206). Indirect costs [

Evaluation of graphene-wrapped LiFePO4 as novel cathode materials for Li-ion batteries

1126 (S.D.

Improving scattering layer through mixture of nanoporous spheres and nanoparticles in ZnO-based dye-sensitized solar cells

2016)] were about three times higher than direct costs [