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Wu H.,Jiangsu Key Laboratory of New Energy Generation and Power Conversion | Wan C.,Beijing Spacecrafts | Sun K.,Tsinghua University | Xing Y.,Jiangsu Key Laboratory of New Energy Generation and Power Conversion
IEEE Transactions on Power Electronics | Year: 2015

In this letter, a quasi two-stage architecture is proposed for wide input voltage range (voltage ranges ≈ 1:2) and high step-down multiple output conversion. A dc-DCX, which operates as a dc-dc converter with regulated output when the input voltage is low and as a dc-dc transformer with unregulated output when the input voltage is high, is adopted in the first stage to provide optimized intermediate dc-bus voltages for the second-stage point-of-load converters. The input and output of the dc-DCX are in series and connected to the total input voltage. Hence, part of the input power is directly transferred to the intermediate bus without conversion. The devices' voltage stresses and the transformer turns ratio of the dc-DCX are reduced by using the proposed quasi two-stage architecture. Thus, the conversion efficiency is improved significantly. Furthermore, a dual-output LLC resonant converter with hybrid center-tapped and full-bridge rectifier is proposed for the dc-DCX to achieve high efficiency and high power density. A 100-W prototype with three outputs is built and tested to verify the analysis. © 2014 IEEE.


Zhang Y.,Taiyuan University of Technology | Zhang B.,Beijing Spacecrafts
Journal of Materials Science: Materials in Electronics | Year: 2014

The effect of grain size on the dielectric properties of MgO-TiO 2-ZnO-CaO ceramics is investigated. Attrition milling is chosen to obtain nanometre particle size from micrometre particle size powders. Additionally, the present study is focused on the effect of the nature of milling balls on εr, tanδ, and the temperature coefficient of capacitance (abbreviated as TCC). For that, three kinds of balls are tested: A1, A2 or A5 mm stabilised zirconia balls. For the samples milled by A2 mm balls for 10 h, the ceramics sintered at 1,270 °C showed favorable dielectric properties with εr = 22.6, tanδ = 1.3 × 10-5, and TCC = 19.1 ppm/°C. © 2014 Springer Science+Business Media New York.


Chen X.,University of Electronic Science and Technology of China | Jia C.,University of Electronic Science and Technology of China | Wan Z.,University of Electronic Science and Technology of China | Zhang J.,Beijing Spacecrafts | Yao X.,Lanzhou University
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2014

Three phenothiazine-triphenylamine-based organic dyes (CD-1, CD-2 and CD-3) are designed based on the dye WD-8. The geometries, electronic structures, and electronic absorption spectra of these dyes before and after binding to TiO 2 are studied by density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The calculated geometries indicate that these dyes show good steric hindrance effect which is advantage to inhibit the close intermolecular π-π aggregation effectively. The lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels of these dyes could ensure positive effect on the process of electron injection and dye regeneration. The simulated spectra of CD-1∼3 show better absorption than that of WD-8 in the low energy zone. All the calculated results demonstrate that these dyes could be used as potential sensitizers for DSSCs and show better performances than WD-8. © 2013 Elsevier B.V. All rights reserved.


Jia C.,University of Electronic Science and Technology of China | Zhang J.,University of Electronic Science and Technology of China | Zhang L.,Beijing Spacecrafts | Yao X.,Lanzhou University
New Journal of Chemistry | Year: 2011

The properties of two donor-acceptor compounds tetrathiafulvalene- acenaphtho[1,2-b] quinoxaline (1) and tetrathiafulvalene-3-nitro-acenaphtho[1,2- b]quinoxaline (2) have been investigated by solution-state studies (electrochemistry, absorption, self-assembly) and theoretical calculations (DFT, TD-DFT). The electrochemical studies indicate the nitro-substituted effect on their redox properties is negligible. Both compounds show effective intramolecular charge transfer (ICT) transitions in the UV-Visible range in solution. Compared with compound 1, compound 2 has a bathochromic shift in the absorption spectra, the λ max-ICT has been extended from 20800 cm -1 to 19700 cm -1 (480 nm to 507 nm). In addition, when the nitro group is employed, the self-assembly characteristics of the two compounds are substantially changed from ribbon-like nanostructures to root-like nanostructures. Density functional theory (DFT) calculations provide insights into their molecular geometries, electronic structures, and physico-chemical properties. © 2011 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.


Zhang Y.,Taiyuan University of Technology | Wu S.,Tianjin University | Zhang B.,Beijing Spacecrafts | Wu X.,Taiyuan University of Technology
Journal of Materials Science: Materials in Electronics | Year: 2014

The effect of Li2O3-B2O 3-SiO2 (LBS) liquid-phase additives on the sintering, microstructures, and dielectric properties of MgO-TiO2-ZnO-CaO (MTZC) ceramics was investigated. It was found that the sintering temperature could be lowered easily, and the dielectric properties of MTZC ceramics could be greatly improved by adding a small amount of LBS solution additives. With the addition of 10 wt% LBS, the ceramics sintered at 900 °C showed favorable dielectric properties with εr = 21.7, Qf = 5.0 × 104 GHz, and TCF = -21.6 ppm/ °C. The distructive physical analysis showed an excellent co-firing interfacial behavior between the MTZC ceramic and the Ag electrode. It indicated that MTZC ceramics with LBS solution additives have a number of potential applications on passive integrated devices based on the low-temperature co-fired ceramics technology. © 2014 Springer Science+Business Media New York.


Jia C.,University of Electronic Science and Technology of China | Zhang J.,University of Electronic Science and Technology of China | Zhang L.,Beijing Spacecrafts | Yao X.,Lanzhou University
Heterocycles | Year: 2011

A novel conjugated donor-acceptor compound (1) based on tetrathiafulvalene has been synthesized and fully characterized. Intramolecular charge transfer (ICT) in compound 1, arising from HOMO-LUMO singlet transitions, has been experimentally evidenced through absorption/fluorescence spectra and theoretical calculations. © The Japan Institute of Heterocyclic Chemistry.


Wan Z.,University of Electronic Science and Technology of China | Jia C.,University of Electronic Science and Technology of China | Zhang J.,Beijing Spacecrafts | Yao X.,Lanzhou University | Shi Y.,University of Electronic Science and Technology of China
Dyes and Pigments | Year: 2012

A novel and highly conjugated donor-acceptor dyad consisting of tetrathiafulvalene unit covalently attached to a porphyrin unit has been synthesized and characterized. As compared to tetraphenylporphyrin, the fluorescence intensity and lifetime of the dyad was decreased owing to photoinduced electron transfer between the tetrathiafulvalene and porphyrin units in the excited state. The fluorescence intensity of the dyad was recovered dramatically upon the addition of Fe(ClO 4) 3· 6H 2O to a solution of the dyad, and the fluorescence intensity grows with an increasing amount of Fe(ClO 4) 3·6H 2O. More importantly, the fluorescence intensity of the dyad can be reversibly modulated by the sequential electrochemical oxidation and reduction of the tetrathiafulvalene unit, thus a new redox fluorescence switch based on this dyad has been constructed. © 2011 Elsevier Ltd. All rights reserved.


Guo Y.,Taiyuan Normal University | Wang Y.,Taiyuan University of Technology | Zhang B.,Beijing Spacecrafts
Journal of Materials Science: Materials in Electronics | Year: 2015

ZnO–MgO–TiO2–CaO (ZMTC) ceramics were prepared by a conventional solid-state method and sintered at 1150 °C for various soaking times. The density, particle sizes and dielectric constant simultaneously increase with the soaking time. On the contrary, the dielectric loss of ZMTC ceramics declines with the soaking time. The XRD analysis revealed that CaTiO3 phase nearly appears with prolonging the sintering time. With increasing soaking time, the density and εr values increased, saturating at 1150 °C for 7 h with excellent dielectric properties of εr = 22.4, tanδ = 0.6 × 10−4, and TCF = 24.8 ppm/°C. © 2015, Springer Science+Business Media New York.


Zhang L.,Central South University | Gong W.,Beijing Spacecrafts | Chen J.,Central South University | Du Y.,Central South University
Calphad: Computer Coupling of Phase Diagrams and Thermochemistry | Year: 2014

Based on the first-principles computed activation energy, the frequency prefactor for impurity diffusivity of Pt in fcc Al was calculated by means of the Swalin correlation. The Vignes-Birchenall correlation originally developed for binary solutions with unlimited solubility was simplified to evaluate the interdiffusivities in binary terminal solutions with limited solubility. The simplified correlation was validated in fcc Ni-Al alloys, and then applied to evaluate interdiffusivities in fcc Pt-Al alloys, showing a reasonable agreement with the limited experimental data. On the basis of the limited experimental diffusivities in the literature and the presently evaluated interdiffusivities, a set of reasonable atomic mobilities in fcc Pt-Al alloys was established. This combinational approach by utilizing the limited experimental data, first-principles results, semi-empirical/empirical correlations and DIffusion Controlled TRAnsformation (DICTRA) software package is of general validity and applicable in other binary alloys with limited diffusivity information. © 2014 Elsevier Ltd. All rights reserved.


Zhang L.G.,Beijing Spacecrafts | Zhao G.M.,Beijing Spacecrafts | Lai X.M.,Beijing Spacecrafts
Advanced Materials Research | Year: 2011

In this paper, Aluminum trioxide ceramic coatings were grown on surfaces of 2024 Aluminum alloys by micro-plasma oxidation in an aluminate electrolytic solution. In order to decrease the density of the pores and increase the anti-wear property of the ceramic coatings, Titania were added into the aluminate electrolytic solution. The struture and anti-wear property of the produced ceramic coatings were measured by X-ray diffraction, scanning electron microscope, hardness tester and frictionometer. The results show that the thickness of the ceramic coating is about 24±1 μm, surfaces of the ceramic coatings are very uniform. The hardness of the doped coating is up to 930 HV, and the wear property of the coating is the more excellent than that of undoped coating. © (2011) Trans Tech Publications.

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