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Implementation of Time-Scale Transformation Based on Continuous Wavelet Theory

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Journal of Systems Engineering and Electronics 2000年第1期11卷 32-37页

作者： zhu, xiaoguang Hong, Bingrong Wang, Dongmu Harbin Inst of Technology Harbin China

The basic objective of time-scale transformation is to compress or expand the signal in time field while keeping the same spectral properties. This paper presents two methods to derive time-scale transformation formula based on continuous wavelet transform. For an arbitrary given square-integrable function f(t),g(t) = f(t/λ) is derived by continuous wavelet transform and its inverse transform. The result shows that time-scale transformation may be obtained through the modification of the time-scale of wavelet function filter using equivalent substitution. The paper demonstrates the result by theoretic derivations and experimental simulation.

关键词： Frequency domain analysis Integral equations Signal processing Spectrum analysis Time domain analysis Time series analysis Wave filters

Applications of Wavelets in 3-D Audio Simulation

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Journal of Systems Engineering and Electronics 2000年第3期11卷 74-81页

作者： zhu, xiaoguang Hong, Bingrong Wang, Dongmu Harbin Inst of Technology Harbin China

Wavelet has been used as a powerful tool in the signal processing and function approximation recently. This paper presents the application of wavelets for solving two key problems in 3-D audio simulation. First, we employ discrete wavelet transform (DWT) combined with vector quantization (VQ) to compress audio data in order to reduce tremendous redundant data storage and transmission times. Secondly, we use wavelets as the activation functions in neural networks called feed-forward wavelet networks to approach auditory localization information cues (head-related transfer functions (HRTFs) are used here). The experimental results demonstrate that the application of wavelets is more efficient and useful in 3-D audio simulation.

关键词： Approximation theory Computer simulation Data structures Feedforward neural networks Wavelet transforms

Hydrogel-derived nitrogen-doped porous carbon framework with vanadium nitride decoration for supercapacitors with superior cycling performance

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Journal of Materials Science & Technology 2023年第24期155卷 167-174页

作者： Ziqiang Wu Qian Chen Changdian Li Lili zhu Yanan Huang xiaoguang zhu Xuebin zhu Yuping Sun Key Laboratory of Materials Physics Institute of Solid State Physics HFIPS Chinese Academy of Sciences Hefei 230031 China University of Science and Technology of China Hefei 230026 China High Magnetic Field Laboratory HFIPS Chinese Academy of Sciences Hefei 230031 China Collaborative Innovation Center of Advanced Microstructures Nanjing University Nanjing 210093 China

Transition metal nitrides(TMNs)and their composites with carbon materials hold tremendous potential for supercapacitor(SC)electrodes because of their excellent electronic conductivity and electrochemical ***,realizing cycling stable TMN/carbon-based supercapacitors with economically viable and environmentally-friendly approaches remains a significant ***,polyacrylamide(PAM)hydrogel,as a water-soluble linear polymer electrolyte,is expected to be a remarkable candidate precursor for preparing N-doped porous carbon(NPC)due to the high contents of carbon and nitrogen *** this study,vanadium nitride(VN)embedded in PAM hydrogel-derived NPC was fabricated successfully via an ammonia-free *** VN/NPC delivers a high specific capacitance of 198.3 F g^(−1)at a current density of 1 A g^(−1),with a remarkable cycling stability of 107%after 16,000 *** electrochemical performances of VN/NPC compared to bare VN nanoparticles are strongly improved due to the composite ***,the VN/NPC-based solid-state symmetric device delivers an excellent energy density of 21.97µWh cm^(−2)at a power density of 0.5 mW cm^(−2),and an outstanding cycling durability of 90.9%after 18,000 *** work paves the way to design metal nitride/porous carbon materials,which also opens up unique horizons for the recovery of hydrogel electrolyte.

关键词： Vanadium nitride Nitrogen-doped porous carbon Polyacrylamide Hydrogel Supercapacitor

Synthesis of Vertically Oriented GaN Nanowires on a LiAlO_(2) Substrate via Chemical Vapor Deposition

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Nano Research 2009年第4期2卷 321-326页

作者： Xiaoli He Guowen Meng xiaoguang zhu Mingguang Kong Key Laboratory of Materials Physics and Anhui Key Laboratory of Nanomaterials and NanostructuresInstitute of Solid State PhysicsChinese Academy of SciencesHefei 230031China

Vertically oriented nanowires(NWs)of single-crystalline wurtzite GaN have been fabricated on a-LiAlO_(2)(100)substrate coated with a Au layer,via a chemical vapor deposition process at 1000℃ using gallium and ammonia as source *** GaN NWs grow along the nonpolar[10]direction with steeply tapering tips,and have triangular cross-sections with widths of 50100 nm and lengths of up to several *** GaN NWs are formed by a vapor liquid solid growth mechanism and the tapering tips are attributed to the temperature decrease in the final stage of the synthesis *** aligned GaN NWs show blue-yellow emission originating from defect levels,residual impurities or surface states of the GaN NWs,and have potential applications in nanotechnology.

关键词： GaN LiAlO_(2) chemical vapor deposition triangular cross-section vapor liquid solid photoluminescence

Effective fabrication of porous Au-Ag alloy nanorods for in situ Raman monitoring catalytic oxidation and reduction reactions

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Journal of Materials Science & Technology 2021年第32期91卷 262-269页

作者： Shanlin Ke Caixia Kan Xingzhong zhu Changshun Wang Weijian Gao Zhaosheng Li xiaoguang zhu Daning Shi College of Science Nanjing University of Aeronautics and AstronauticsNanjing 210016China Key Laboratory of Aerospace Information Materials and Physics Ministry of Industry and Information TechnologyNanjing 210016China National Laboratory of Solid State Microstructures Nanjing UniversityNanjing 210093China Institute of Solid State Physics Chinese Academy of SciencesHefei 230031China Key Laboratory for Intelligent Nano Materials and Devices of the Ministry of Education Nanjing 210016China

Porous metal nanostructures exhibit excellent catalytic properties due to their high surface-to-volume ratios and abundant catalytic active sites. However, it is still challenging to control nanopores density and structural features in a facile route and the preparation of porous alloy nanorods for catalytic application has not been well explored. In this work, we demonstrate a synthetic strategy to fabricate highly porous Au–Ag alloy nanorods(P-Au Ag NRs) by critically dealloying Ag atoms from homogeneous solid Au–Ag alloy nanorods(Au Ag NRs). Combining the merits of the tunable plasmonic properties of noble metal nanorods, excellent stabilities of alloys, and superior catalytic activities of porous structures, we use the P-Au Ag NRs as a Raman probe for the in situ monitoring of the catalytic oxidation of 3,3',5,5' tetramethylbenzidine(TMB) and reduction of 4-nitrothiophenol(4-NTP). We also compare their compositiondependent catalytic activities. The results show that P-Au Ag NRs possess superior chemical stability and higher catalytic activity than those of core-shell structures due to synergistic structural and chemical mechanisms. This strategy provides a predictive design approach for the next-generation alloy catalysts with high-performance.

关键词： Catalysis Porous Au-Ag alloy nanorod High-index facets Raman monitoring Oxidation and reduction

Vapor-phase hydrothermal growth of single crystalline NiS2 nanostructure film on carbon fiber cloth for electrocatalytic oxidation of alcohols to ketones and simultaneous H2 evolution

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Nano Research 2018年第2期11卷 1004-1017页

作者： Tianxing Wu xiaoguang zhu Guozhong Wang Yunxia Zhang Haimin Zhang Huijun Zhao Key Laboratory of Materials Physics Centre for Environmental and Energy Nanomaterials Anhui Key Laboratory of Nanomaterials and Nanotechnology CAS Center for Excellence in Nanoscience Institute of Solid State Physics Chinese Academy of Sciences Hefei China Centre for Clean Environment and Energy Griffith University Gold Coast Campus Nathan Australia

Electrocatalytic synthesis of value-added chemicals is attracting significant research attention owing to its mild reaction conditions, environmental benignity, and potentially scalable application to organic synthetic chemistry. Herein, we report the preparation of a single-crystalline NiS2 nanostructure film of N 50 nm thickness grown directly on a carbon fiber doth （NiSJCFC） by a facile vapor-phase hydrothermal （VPH） method. NiSJCFC as an electrocatalyst exhibits activity for both the oxygen evolution reaction （OER） and the hydrogen evolution reaction （HER） in alkaline media. Furthermore, a series of alcohols （2-propanol, 2-butanol, 2-pentanol, and cyclohexanol） were electrocatalytically converted to the corresponding ketones with high selectivity, efficienc and durability using the NiSJCFC electrode in alkaline media. In the presence of 0.45 M alcohol, a remarkably decreased overpotential （- 150 mV, vs. RHE） at the NiS2/CFC anode compared with that for water oxidation to generate O2, i.e., the OER, in alkaline media leads to significantly improved H2 generation. For instance, the H2 generation rate in the presence of 0.45 M 2-propanol is almost 1.2-times of that obtained for pure water splitting, but in a system that employs an applied voltage at least 280 mV lower than that required for water splitting to achieve the same current density （20 mA-crn-2）. Thus, our results demonstrate the applicability of our bifunctional non-precious-metal electrocatalyst for organic synthesis and simultaneous H2 production.

关键词： vapor-phase hydrothermal single-crystalline NiS2 film carbon fiber cloth electrocatalytic oxidationof alcohols to ketones H2 generation

Highly ordered Nb_(2)O_(5)nanochannel film with rich oxygen vacancies for electrocatalytic N2 reduction:Inactivation and regeneration of electrode

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Chinese Chemical Letters 2021年第9期32卷 2833-2836页

作者： Jialu Wang Shenghong Kang xiaoguang zhu Guozhong Wang Haimin Zhang Key Laboratory of Materials Physics Centre for Environmental and Energy NanomaterialsAnhui Key Laboratory of Nanomaterials and NanotechnologyInstitute of Solid State PhysicsChinese Academy of SciencesHefei 230031China University of Science and Technology of China Hefei 230026China

We report the fabrication of highly ordered Nb_(2)O_(5)nanochannel film(Nb_(2)O_(5)-NCF)onto niobium foil by an anodization *** thermal treatment,the obtained Nb_(2)O_(5)-NCF with rich oxygen vacancies exhibits electrochemical N_(2)reduction reaction(NRR)activity with an NH3 yield rate of 2.52×10^(-10)mol cm^(-2)s^(-1)and a faradaic efficiency of 9.81%at-0.4 V(***)in 0.1 mol/L Na2SO4 electrolyte(pH 3.2).During electrocatalytic NRR,the Nb_(2)O_(5)-NCF takes place electrochromism(EC),along with a crystalline phase transformation from pseudo hexagonal phase to hexagonal phase owing to H+*** results in the reduced NRR activity due to the decrease of oxygen vacancies of hexagonal phase Nb_(2)O_(5),which can be readily regenerated by low-temperature thermal treatment or applying an anodic potential,showing superior recycling reproducibility.

关键词： Niobium oxide(Nb_(2)O_(5)) Nitrogen(N_(2))reduction reaction(NRR) Electrochromism Oxygen vacancies Phase transformation

Metal/antiperovskite metal nitride composites Ag/AgNNi_(3)as novel efficient electrocatalysts for hydrogen evolution reaction in alkaline media

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Journal of Materials Science & Technology 2022年第17期112卷 222-229页

作者： Lili zhu Bingbing Yang Ziqiang Wu Changdian Li Han Li Hui Li Yanan Huang xiaoguang zhu Xuebin zhu Yuping Sun Key Laboratory of Materials Physics Institute of Solid State PhysicsHFIPSChinese Academy of SciencesHefei 230031China University of Science and Technology of China Hefei 230026China High Magnetic Field Laboratory HFIPSChinese Academy of SciencesHefei 230031China Collaborative Innovation Center of Advanced Microstructures Nanjing UniversityNanjing 210093China

Searching for effective hydrogen evolution reaction(HER)electrocatalysts is crucial for water *** metal nitrides(TMNs)are very attractive potential candidates since of high electrical conductivity,robust stability,element rich and high *** metal nitrides provide chemical flexibility since two different types of transition metal elements are contained,allowing partial substitution both for A-and ***,we report a novel antiperovskite metal nitride Ag_(x)Ni_(1-x)NNi_(3)(0≤x≤0.80)thin film used as highly effective HER *** phase antiperovskite nitride can be successfully obtained for Ag_(x)Ni_(1-x)NNi_(3)with x less than *** Ag_(0.76)Ni_(0.24)NNi_(3) towards HER shows an overpotential of 122 mV at 10 mA cm^(-2)in alkaline ***,considering the role of Ag for adsorbing hydroxyl groups,chemical engineering has been carried out for designing metal/antiperovskite nitride Ag/Ag_(x)Ni_(1-x)NNi_(3)composite *** 0.18 Ag/Ag_(0.80)Ni_(0.20)NNi_(3)electrocatalyst shows a mere 13 and 81 mV of overpotential to reach 1 and 10 mA cm^(-2),respectively,showing high durability in alkaline *** results will provide a novel type of HER catalysts based on antiperovskite metal nitrides and a strategic design for metal/antiperovskite metal nitride composite electrocatalysts for HER in alkaline media.

关键词： Hydrogen evolution reaction Antiperovskite Metal nitride Composite catalyst

Preparation and Characterization of Exfoliated Poly（ethyleneterephthalate）/Montmorillonite Nanocomposites Using Modified MMTs with Variable Content of Antimony Acetate

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Chinese Journal of Chemistry 2011年第6期29卷 1278-1284页

作者： Wang, xiaoqun Wang, Yaqing Zhao, Zhenlu zhu, xiaoguang Nie, Cong Du, Shanyi School of Material Science and Engineering Beihang University Beijing 100191 China

Poly（ethylene terephthalate）（PET）/montmorillonite （MMT） nanocomposite was prepared by the direct polymerization with MMTs modified with variable content of antimony acetate （Sb（OAc）3）, which was also used as catalyst polymerization. The modified MMTs （AS-Sb-MMT） were prepared by intercalating both Sb（OAc）3 and amphoteric surfactant （AS） into MMT layers. Nine kinds of Sb-MMTs [MMT treated with Sb（OAc）3] with different Sb content were obtained, but only six kinds of PET/MMT nanocomposites could be prepared. ICPAES was used to characterize Sb content of modified MMT, XRD was used to characterize interlayer spacing, IR spectroscopy was used to characterize composition change of Sb catalyst in modified MMT and TEM was used to investigate micromorphology of PET/MMT nanocomposites. Several results are obtained, i.e., （a） Sb content of Sb-MMT is affected by both drying temperature and washing-drying sequence, （b） compared with Na-MMT （unmodified MMT）, the change in the interlayer spacing of Sb-MMT is attributed to the solvent ethylene glycol （EG） rather than the intercalated or absorbed Sb（OAc）3, （c） based on this, a model is developed to describe the swelling of Na-MMT and modified MMT by EG and the effect of drying temperature on the interlayer spacing, （d） exfoliation state of MMT in PET matrix of nanocomposites is controlled not only by Sb content and interlayer spacing, but also by the composition of Sb catalyst in modified MMT.

关键词： organic-inorganic hybrid composites clay polyethylene terephthalate (PET) exfoliated interlayer spacing