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- 实验方案
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Electro-Thermal Formation of Uniform Lying Helix Alignment in a Cholesteric Liquid Crystal Cell
摘要： We demonstrated previously that the temperature of a sandwich-type liquid crystal cell with unignorable electrode resistivity could be electrically increased as a result of dielectric heating. In this study, we take advantage of such an electro-thermal effect and report on a unique electric-field approach to the formation of uniform lying helix (ULH) texture in a cholesteric liquid crystal (CLC) cell. The technique entails a hybrid voltage pulse at frequencies f1 and, subsequently, f2, which are higher and lower than the onset frequency for the induction of dielectric heating, respectively. When the cell is electrically sustained in the isotropic phase by the voltage pulse of V = 35 Vrms at f1 = 55 kHz or in the homeotropic state with the enhanced ionic effect at V = 30 Vrms and f1 = 55 kHz, our results indicate that switching of the voltage frequency from f1 to f2 enables the succeeding formation of well-aligned ULH during either the isotropic-to-CLC phase transition at f2 = 1 kHz or by the electrohydrodynamic effect at f2 = 30 Hz. For practical use, the aligning technique proposed for the first time in this study is more applicable than existing alternatives in that the obtained ULH is adoptable to CLCs with positive dielectric anisotropy in a simple cell geometry where complicated surface pretreatment is not required. Moreover, it is electrically switchable to other CLC textures such as Grandjean planar and focal conic states without the need of a temperature controller for the phase transition, the use of ion-rich LC materials, or mechanical shearing for textural transition.
关键词： cholesteric liquid crystals,uniform lying helix,dielectric heating
更新于2025-11-14 17:28:48
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Preparation of high quality perovskite thin film in ambient air using ethylacetate as anti-solvent
摘要： Methylamine lead iodide (CH3NH3PbI3) perovskite thin film solar cell has attracted much attention due to its low cost and high photoelectric conversion efficiency. Preparation of high quality perovskite thin film is the key to obtain high conversion efficiency of solar cells. Here, the pinhole-free CH3NH3PbI3 layer with high coverage and smooth surface is prepared by the one-step solution method in air with ethylacetate as anti-solvent on an electron transport hybrid layer of TiO2 nanoparticles coated porous carbon. The effect of ethylacetate as anti-solvent on the quality of perovskite thin film is studied in detail by comparing with chlorobenzene and ethylether. The high saturation and humidity resistance of ethylacetate in air control the nucleation and growing kinetics of perovskite crystals during the spin coating process, which facilitates the formation of uniform pinhole-free perovskite thin films. The perovskite solar cell based on the prepared high quality thin film achieves the highest conversion efficiency of 17.41% in ambient air with a relative humidity of 35%, which is superior to the perovskite thin films prepared with chlorobenzene and ethylether (conversion efficiency of 10.80% and 10.20%). The higher light-to-electric conversion efficiency is due to high coverage of the pinhole-free perovskite thin film and good contact with the electron transport layer and the hole transport layer.
关键词： Anti-solvent,Perovskite solar cell,Uniform perovskite thin film,Ethylacetate
更新于2025-11-14 17:03:37
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One-step fabrication of effective mesoporous layer consisted of self-assembled MgO/TiO<sub>2</sub> core/shell nanoparticles for mesostructured perovskite solar cells
摘要： perovskite directly, which can not only passivate surface defects and reduce charge-suppressed J-V hysteresis. Meanwhile, the photovoltaic characteristics and the well-power conversion efficiency (PCE) was increased from 13.13% to 16.30% with well-interface and electrons transfer in PSCs. Based on the mesoporous layer consisting of nanoparticles instead of adding an additional surface modified layer for mesostructured recombination, but also facilitate charge-extraction at the mesoporous layer/perovskite perovskite solar cells (PSCs). An amorphous ultrathin outer nanolayer of MgO was Such self-assembled MgO/TiO2 core/shell nanostructures would retain the mesoporous of PSCs was 1.00 V, 4.2% higher than the uncoated TiO2 based PSCs, and the obtained structure feature, supply more contact interface of MgO/TiO2 and separate the TiO2 and conformally coated onto TiO2 core nanoparticles in a one-step bottom-up approach. proposed an efficient nanoparticulate mesoporous layer consisted of coated TiO2 optimized MgO-coated TiO2 nanoparticles, the corresponding open circuit voltage (VOC) Considering the intrinsic rich defect, poor H2O or UV light stability of TiO2, we resistance is obtained for the cell based on m-TiO2 with MgO coating. In addition, we behaved junction property were further clarified by the ideal model, a much lower series provided an easy regulated uniform coating route to fabricate well-defined core-shell nanoparticles with modified properties.
关键词： Uniform coating,mesoporous layer,Core-shell nanostructure,Perovskite solar cells
更新于2025-11-14 15:27:09
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Preparation of Monodispersed Nanoparticles of Transparent Conductive Oxides
摘要： Generally, indium-tin-oxides (ITO) thin film is prepared by the sputtering process with ITO target, but only 20 % of ITO yielded from the target is deposited on the substrate. Namely, about 80 % ITO is exhausted by the deposition elsewhere far from the substrate. The recycling process of indium is limited so that ca. 20 % ITO of the starting material is lost without any recovery. Even if the recycling of ITO has been carried out in this process, we should prepare ITO target of 5 times more than apparent use of ITO on film. If we change it to printing process from the sputtering, the reduction in ITO use is expected as ca. 50 %, considering the increase in film thickness by printing. Our target technology also includes ITO nanoink for the project. As a result, monodispersed ITO nanoparticles (NPs) with a cubic shape were fabricated by using quaternary ammonium hydroxide-assisted metal hydroxide organogels. These NPs have perfect uniformity in size with beautiful shape, and perfect single crystalline structure including Sn. As we were attempted to make thin film with ITO nanoink, it was successfully fabricated below 200 nm in thickness and the resistivity was drastically decreased below 1.0 × 10–3 Ω cm after heat treatments. GZO nanoink as substitute of ITO has also been developed.
关键词： indium tin oxide,transparent conductive oxides,uniform nanoparticles,shape control
更新于2025-09-23 15:23:52
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Uniform-in-time bounds for approximate solutions of the drift–diffusion system
摘要： In this paper, we consider a numerical approximation of the Van Roosbroeck’s drift–diffusion system given by a backward Euler in time and finite volume in space discretization, with Scharfetter–Gummel fluxes. We first propose a proof of existence of a solution to the scheme which does not require any assumption on the time step. The result relies on the application of a topological degree argument which is based on the positivity and on uniform-in-time upper bounds of the approximate densities. Secondly, we establish uniform-in-time lower bounds satisfied by the approximate densities. These uniform-in-time upper and lower bounds ensure the exponential decay of the scheme towards the thermal equilibrium as shown in Bessemoulin-Chatard (Numer Math 25(3):147–168, 2016).
关键词： Finite volume method,Uniform-in-time bounds,Scharfetter–Gummel scheme,Drift–diffusion system,Numerical analysis
更新于2025-09-23 15:23:52
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Non-Uniform Quantization Codebook Based Hybrid Precoding to Reduce Feedback Overhead in Millimeter Wave MIMO Systems
摘要： In this paper, we propose two non-uniform quantization (NUQ) codebook based hybrid precoding schemes for two main hybrid precoding implementations, i.e., the full-connected structure and the sub-connected structure, to reduce the feedback overhead in millimeter wave single user multiple-input multiple-output (SU-MIMO) systems. Specifically, we firstly group the angles of the arrive/departure (AOAs/AODs) of the scattering paths into several spatial lobes by exploiting the sparseness property of the millimeter wave in the angular domain, which divides the total angular domain into effective spatial lobes' coverage angles and ineffective coverage angles. Then, we map the quantization bits non-uniformly to different coverage angles and construct NUQ codebooks, where high numbers of quantization bits are employed for the effective coverage angles to quantize AoAs/AoDs and zero quantization bit is employed for ineffective coverage angles. Finally, two low-complexity hybrid analog/digital precoding schemes are proposed that utilize the NUQ codebooks. Simulation results demonstrate that, the proposed two NUQ codebook based hybrid precoding schemes achieve near-optimal spectral efficiencies and show the superiority in reducing the feedback overhead compared with the uniform quantization codebook based works.
关键词： feedback overhead,non-uniform quantization,spatial lobe,Millimeter wave communication,hybrid precoding
更新于2025-09-23 15:23:52
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Hybrid Method for the Synthesis of Isophoric Phase-Shaped Beams
摘要： A novel hybrid approach to the power synthesis of mask-constrained shaped beams by means of concentric-ring isophoric arrays is presented. The basis of this procedure is to use the complex aperture distribution obtained by Elliott–Stern method as a starting point of an innovative algorithm that combines a classical density tapering method with a simulated annealing one. The proposed technique allows to outperform the previous procedures.
关键词： uniform distribution,shaped beams,Density tapering,sparse arrays
更新于2025-09-23 15:23:52
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Beam steering characteristics of highly directive photoconductive dipole phased array antenna for terahertz imaging application
摘要： In this paper, the beam-steering characteristics of photoconductive dipole phased array antenna configuration at 1.95 THz is presented. The proposed array antenna configuration with frequency selective surface favourably improves its gain and directivity which is useful to upsurge the imaging capabilities to address the deliberations such as limited depth-of-field (DoF) and size-weight-and-power of the THz source for imaging applications. These are important considerations for applications like stand-off imaging and surveillance of moving targets where the high angular resolution as well as extended DoF are the important parameters for successful detection of concealed explosives. The projected planar profile and compact highly directive (2 × 2) small-gap photoconductive dipole phased array antenna can be castoff for the exposure of concealed explosives such as RDX, TNT, and HMX which illustrate their substantial spectral absorption fingerprints in terahertz (1.4–2.2 THz) regime of the spectrum. A simple method of beam-steering has been explored based on phase controlled optical excitation of highly directive small-gap photoconductive dipole array antenna. Further, the effects of uniform progressive phase shift on the beam-steering of uniform linear array (along x-axis) as well as planar array (x-axis and y-axis) is investigated.
关键词： Terahertz frequency,Uniform current distribution,Photoconductive dipole antenna,Phased array,Frequency selective surface
更新于2025-09-23 15:23:52
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[IEEE 2018 18th International Symposium on Antenna Technology and Applied Electromagnetics (ANTEM) - Waterloo, ON (2018.8.19-2018.8.22)] 2018 18th International Symposium on Antenna Technology and Applied Electromagnetics (ANTEM) - A Log-Periodic Monopole Array with Uniform Spacing
摘要： This paper presents a log-periodic monopole array antenna with end-fire radiation and vertical polarization. It consists of 13 monopole elements and a meandering microstrip line on the bottom as the feeding line. The adjacent monopoles are of uniform spacing instead of conventional logarithmic spacing. A prototype is fabricated and tested. Measured results show that an impedance bandwidth from 2 to 6 GHz (3:1) for VSWR < 2 and a realized gain better than 7.6 dBi over the same operating frequency band are obtained.
关键词： log-periodic antenna,End-fire radiation,monopole array,uniform spacing
更新于2025-09-23 15:23:52
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[IEEE 2018 International Conference on Microwave and Millimeter Wave Technology (ICMMT) - Chengdu, China (2018.5.7-2018.5.11)] 2018 International Conference on Microwave and Millimeter Wave Technology (ICMMT) - An Ultra Wide-Stopband Lowpass Filter Using Smooth Transmission Line
摘要： A novel 6GHz ultra Wide Stopband lowpass filter using smooth transmission line is presented in this paper. The filter has the advantages of easy fabrication, sharp cutoff frequency response and wide stopband. Its spurious response is at about 35GHz, while the stopband of the most general filters typically extend to 3 times of the band edge frequency. Then the procedure of designing such non-uniform microstrip lowpass filters is introduced, and the measured results show good agreement with simulation results.
关键词： non-uniform microstrip line,wide stopband,Lowpass
更新于2025-09-23 15:22:29