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Xiuting Sun,Feng Wang,Jian Xu 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.6 No.4
In order to realize the energy harvesting structure working for an external perturbation or ultralow-frequency excitation, a continuous structure with adjustable nonlinearity is proposed and analyzed. The novel energy harvesting structure is consisted of a piezoelectric elastic beam and two pairs of magnets. Different from normal assembly of magnets in the same direction of the vibration motion, two pairs of magnets are assembled vertically to the vibration direction to induce adjustable nonlinear restoring force similar as the pre-deformed elastic components in so-called quasi-zero-stiffness system. With the model of magnets, the interaction energy and interaction force are obtained. Considering the the piezoelectric cantilever beam, it can realize a multi-stable vibration structure. The zero equilibrium is stable and the interaction energy there is very high, while there are two symmetry stable equilibriums with very low interaction energy. Thus, for small-amplitude and ultralow-frequency excitations from natural phenomenon such as dropping raining, the structure can have large-amplitude vibration with adjustable output frequency. At last, we realize the proposed vibration energy harvester by designing the structural according to the theoretical analysis. The structure of this study has potentially remarkable applications in intelligent and sustainable power generation.
Xiuting Luo(나수정),Soohyung Kim(김수형) 한국신재생에너지학회 2021 한국신재생에너지학회 학술대회논문집 Vol.2021 No.7
Dye materials in dye-sensitized solar cells (DSSCs) can only absorb light within visible range (400 nm to 700nm). To improve the light harvesting of DSSCs, up-conversion phosphor (UCP) material composed of rare-earth Er<sup>3+</sup> and Yb<sup>3+</sup> co-doped TiO<sub>2</sub> and down-conversion phosphor (DCP) material composed of Eu<sup>2+</sup>, Nd<sup>3+</sup> co-doped CaAl<sub>2</sub>O<sub>4</sub> materials are synthesized by spray pyrolysis method, respectively, in this study. The UCP, DCP, and UCP/DCP composites are then introduced into photoanodes of DSSCs by mixing them with TiO<sub>2</sub> nanoparticles. By combining the UCP and DCP (ratio in 1:1, totally 5 wt% in TiO<sub>2</sub> matrix) into DSSCs, the resulting power conversion efficiency of DSSCs is observed to be 41.4% increment compared with reference DSSCs, and has the highest value of 8.19%, which is also higher than DSSCs based on single UCP of 7.55 % or single DCP 6.68%. This suggests that both the light converting and scattering effects of UCP and DCP fabricated in this study can extend the spectral absorption of DSSCs from UV and IR, which enabled us to minimize the solar photons loss and maximize the light harvesting efficiency.
On classical solutions and the classical limit of the Vlasov-Darwin system
Xiuting Li,Jiamu Sun 대한수학회 2018 대한수학회보 Vol.55 No.5
In this paper we study the initial value problem of the non-relativistic Vlasov-Darwin system with generalized variables (VDG). We first prove local existence and uniqueness of a nonnegative classical solution to VDG in three space variables, and establish the blow-up criterion. Then we show that it converges to the well-known Vlasov-Poisson system when the light velocity $c$ tends to infinity in a pointwise sense.
ON CLASSICAL SOLUTIONS AND THE CLASSICAL LIMIT OF THE VLASOV-DARWIN SYSTEM
Li, Xiuting,Sun, Jiamu Korean Mathematical Society 2018 대한수학회보 Vol.55 No.5
In this paper we study the initial value problem of the non-relativistic Vlasov-Darwin system with generalized variables (VDG). We first prove local existence and uniqueness of a nonnegative classical solution to VDG in three space variables, and establish the blow-up criterion. Then we show that it converges to the well-known Vlasov-Poisson system when the light velocity c tends to infinity in a pointwise sense.
Luo, Xiuting,Ahn, Ji Young,Park, Young Su,Kim, Jong Man,Lee, Hyung Woo,Kim, Soo Hyung Elsevier 2017 SOLAR ENERGY -PHOENIX ARIZONA THEN NEW YORK- Vol.150 No.-
<P><B>Abstract</B></P> <P>We fabricated uniform multiwalled carbon nanotube (MWCNT) thin films on fluorine-doped tin oxide (FTO) glass substrates with controlled thickness by an easy and versatile spin-coating process (SCP). Aqueous dispersions of MWCNTs were dropped on the FTO glass substrates and spin-coated to form uniform MWCNT thin films, which were then used as the catalytic medium on the counter electrodes (CEs) of dye-sensitized solar cells (DSCs). For the DSC with an optimized MWCNT-thin-film thickness coated on the CE, the short circuit current density (<I>J<SUB>sc</SUB> </I>) was more than that of the conventional Pt-based DSC (10.97±0.13mAcm<SUP>−2</SUP> vs 9.58±0.17mAcm<SUP>−2</SUP>), while its power conversion efficiency (<I>PCE</I>) was comparable to that of conventional DSC (∼4.41±0.14% and ∼4.69±0.22%, respectively). This suggests that the accumulation of MWCNTs on the CE increases the interfacial contact area between the MWCNTs and liquid electrolyte in the DSC, allowing the rapid reduction of I<SUB>3</SUB> <SUP>−</SUP>. Simultaneously, it decreases the charge transfer resistance owing to rapid electron transport through the MWCNT medium with its relatively high electrical conductivity. Thus, the precisely controlled rapid accumulation of MWCNT thin films by the SCP on the CEs of DSCs is a very promising approach for replacing the expensive Pt metal that is currently used in DSC applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Uniform MWCNT films on fluorine-doped indium tin oxide substrates were formed. </LI> <LI> They acted as counter electrodes in dye-sensitized solar cells. </LI> <LI> The resulting DSCs showed enhanced <I>J</I> <SUB>sc</SUB> but similar PCE to conventional Pt-based DSCs. </LI> <LI> It is a practical, inexpensive alternative to Pt-based counter electrodes of DSCs. </LI> </UL> </P>