University of Electro-Communications

About: University of Electro-Communications is a education organization based out in Tokyo, Japan. It is known for research contribution in the topics: Laser & Robot. The organization has 8041 authors who have published 16950 publications receiving 235832 citations. The organization is also known as: UEC & Denki-Tsūshin Daigaku.

Elegant Construction of ZnIn2S4/BiVO4 Hierarchical Heterostructures as Direct Z-Scheme Photocatalysts for Efficient CO2 Photoreduction.

Abstract: The ZnIn2S4/BiVO4 heterostructures were elegantly designed through assembling ZnIn2S4 nanosheets onto the surface of BiVO4 decahedrons. This composite photocatalyst exhibits efficient photocatalytic conversion of CO2 into CO with a detectable amount of CH4 in the presence of water vapor. An electron spin-resonance spectroscopy (ESR) technique and density function theory (DFT) calculation affirm the direct Z-scheme structure in ZnIn2S4/BiVO4. The larger surface photovoltage (SPV) change and the longer liquid photoluminescence (PL) lifetime of the heterostructure, compared to the individual ZnIn2S4 and BiVO4 components, demonstrate that the Z-scheme structure can effectively promote the recombination of the photogenerated holes in the valence band (VB) of the ZnIn2S4 nanosheet with the electrons in the conduction band (CB) of the decahedral BiVO4 and lead to the abundant electrons surviving in the CB of ZnIn2S4 and holes in the VB of BiVO4, thus enhancing photocatalytic CO2 reduction performance. This study may make a potential contribution to the rational construction and deep understanding of the underlying mechanism of direct Z-schemes for advanced photocatalytic activity.

Cavity-enhanced channeling of emission from an atom into a nanofiber

Abstract: We study spontaneous emission of an atom near a nanofiber with two fiber-Bragg-grating (FBG) mirrors. We show that the coupling between the atom and the guided modes of the nanofiber can be significantly enhanced by the FBG cavity even when the cavity finesse is moderate. We find that, when the fiber radius is 200 nm and the cavity finesse is about 30, up to 94% of spontaneous emission from the atom can be channeled into the guided modes in the overdamped-cavity regime. We show numerically and analytically that vacuum Rabi oscillations and strong coupling can occur in the FBG cavity even when the cavity finesse is moderate (about 30) and the cavity length is large (on the order of 10 cm to 1 m), unlike the case of planar and curved Fabry-Perot cavities.

Suppressed Triplet Exciton Diffusion Due to Small Orbital Overlap as a Key Design Factor for Ultralong-Lived Room-Temperature Phosphorescence in Molecular Crystals.

Abstract: Persistent room-temperature phosphorescence (RTP) under ambient conditions is attracting attention due to its strong potential for applications in bioimaging, sensing, or optical recording. Molecular packing leading to a rigid crystalline structure that minimizes nonradiative pathways from triplet state is often investigated for efficient RTP. However, for complex conjugated systems a key strategy to suppress the nonradiative deactivation is not found yet. Here, the origin of small rates of a nonradiative decay process from triplet states of conjugated molecular crystals showing RTP is reported. Optical microscopy analysis showed that, despite a favorable molecular stacking, an aromatic crystal with strong RTP is characterized by small diffusion length and small values of the diffusion coefficient of triplet excitons. Quantum chemical calculations reveal a large overlap between the lowest unoccupied molecular orbitals but very small overlap between the highest occupied molecular orbitals (HOMOs). Inefficient electron exchange caused by the small overlap of HOMOs prevents triplet excitons from diffusing over long distances and consequently from quenching at defect sites inside the crystal or at the crystal surface. These results will allow design of comprehensive molecular structures to obtain molecular solids with more efficient RTP.

A practical design approach to stabilization of a 3-DOF RC helicopter

Abstract: This paper presents a practical design approach to the stabilization of a three degrees of freedom (3-DOF) RC helicopter. First, the nonlinear model of the RC helicopter is constructed. To facilitate control design, a simplified version of the nonlinear model is derived. A Takagi-Sugeno fuzzy model is then constructed to represent the simplified nonlinear model. The control purpose is to stabilize the RC helicopter while taking into account practical performance considerations in terms of good speed of response and small control effort. To achieve the control objective, we impose a decay rate condition to ensure a good speed of response and an input constraint condition to avoid actuator saturations in the control design. Both conditions are represented in terms of linear matrix inequalities (LMIs). By simultaneously solving them, we render a stabilizing fuzzy controller that achieves good speed of response with small control effort. However, the controller designed for the simplified model can not always stabilize the original nonlinear model due to discrepancies introduced via the simplification process. To overcome this limitation, we design a robust fuzzy controller to compensate for the modeling discrepancies. The resulting robust stability condition with good speed of response is represented in terms of LMIs. By simultaneously solving this condition together with an input constraint condition, we arrive at a robust stabilizing fuzzy controller that achieves good speed of response without actuator saturations. Both simulation and experimental results are included to demonstrate the viability and applicability of the approach.