29 research outputs found
Enhancing Indoor Positioning with GNSS-Aided In-Building Wireless Systems
No full textWireless indoor positioning systems are challenged by the reliance on densely deployed hardware and exhaustive site surveys, leading to elevated deployment and maintenance costs that limit scalability. This paper introduces a novel positioning framework that enhances the existing In-Building Wireless (IBW) infrastructure by retransmitting Global Navigation Satellite System (GNSS) signals. Pseudorange residuals extracted from raw GNSS measurements, when mapped against known cable lengths, facilitate anchor identification and precise ranging. In parallel, directional and inertial measurements are derived from the channel state information (CSI) of cellular reference signals. Building upon these observations, we develop a Hybrid Adaptive Filter-Graph Fusion (HAF-GF) algorithm for high-precision positioning, wherein the adaptive filter modulates observation noise based on Line-of-Sight (LoS) conditions, while a factor graph optimization over multiple positional constraints ensures global consistency and accelerates convergence. Ray tracing-based simulations in a complex office environment validate the efficacy of the proposed approach, demonstrating a 30% improvement in positioning accuracy and at least a threefold increase in deployment efficiency compared to conventional methods
Jacketed homopolymer with bipolar dendritic side groups and its applications in electroluminescent devices
No full textA dendritic monomer with bipolar side groups containing dendritic carbazole and oxadiazole structures was synthesized by a convergent strategy. The homopolymer was synthesized through a conventional radical polymerization. The number-average molecular weight determined by gel permeation chromatography was 40,000 g/mol. Its 5% weight loss temperature was 358 degrees C. Its photophysical properties were studied in solution and in film. The photoluminescent emission peak of the film was at 408 nm, which had a blue shift of 9 nm compared with that of the tetrahydrofuran solution. And there was an energy transfer from oxadiazole to carbazole. The highest occupied molecular orbital (HOMO) and lower unoccupied molecular orbital (LUMO) levels calculated from cyclic voltammetry data were -5.55 and -2.52 eV, respectively, and the band gap was 3.03 eV, which suggested that the polymer had both hole- and electron-transporting capabilities. The efficiencies of the single-layer device based on this homopolymer were much higher than those of the same-generation homopolymer without the oxadiazole moiety. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 581-589, 2012Polymer ScienceSCI(E)EI4ARTICLE3581-5895
Mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals
No full textFor the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson's ratios of the two GaN polycrystals were calculated using Voigt and Hill approximations, and the results show wurtzite GaN has larger shear and elastic moduli and exhibits more obvious brittleness. Moreover, both wurtzite and zinc-blende GaN monocrystals present obvious mechanical anisotropic behavior. For wurtzite GaN monocrystal, the maximum and minimum elastic moduli are located at orientations [001] and < 111 >, respectively, while they are in the orientations < 111 > and < 100 > for zinc-blende GaN monocrystal, respectively. Compared to the elastic modulus, the shear moduli of the two GaN monocrystals have completely opposite direction dependences. However, different from elastic and shear moduli, the bulk moduli of the two monocrystals are nearly isotropic, especially for the zinc-blende GaN. Besides, in the wurtzite GaN, Poisson's ratios at the planes containing [001] axis are anisotropic, and the maximum value is 0.31 which is located at the directions vertical to [001] axis. For zinc-blende GaN, Poisson's ratios at planes (100) and (111) are isotropic, while the Poisson's ratio at plane (110) exhibits dramatically anisotropic phenomenon. Additionally, the calculated Debye temperatures of wurtzite and zinc-blende GaN are 641.8 and 620.2 K, respectively. At 300 K, the calculated heat capacities of wurtzite and zinc-blende are 33.6 and 33.5 J mol-1 K-1, respectively. Finally, the band gap is located at the G point for the two crystals, and the band gaps of wurtzite and zinc-blende GaN are 3.62 eV and 3.06 eV, respectively. At the G point, the lowest energy of conduction band in the wurtzite GaN is larger, resulting in a wider band gap. Densities of states in the orbital hybridization between Ga and N atoms of wurtzite GaN are much higher, indicating more electrons participate in forming Ga-N ionic bonds in the wurtzite GaN.Electronic Components, Technology and Material
Influence of Pressure on the Mechanical and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals
No full textThe mechanical and electronic properties of two GaN crystals, wurtzite and zinc-blende GaN, under various hydrostatic pressures were investigated using first principles calculations. The results show that the lattice constants of the two GaN crystals calculated in this study are close to previous experimental results, and the two GaN crystals are stable under hydrostatic pressures up to 40 GPa. The pressure presents extremely similar trend effect on the volumes of unit cells and average Ga-N bond lengths of the two GaN crystals. The bulk modulus increases while the shear modulus decreases with the increase in pressure, resulting in the significant increase of the ratios of bulk moduli to shear moduli for the two GaN polycrystals. Different with the monotonic changes of bulk and shear moduli, the elastic moduli of the two GaN polycrystals may increase at first and then decrease with increasing pressure. The two GaN crystals are brittle materials at zero pressure, while they may exhibit ductile behaviour under high pressures. Moreover, the increase in pressure raises the elastic anisotropy of GaN crystals, and the anisotropy factors of the two GaN single crystals are quite different. Different with the obvious directional dependences of elastic modulus, shear modulus and Poisson’s ratio of the two GaN single crystals, there is no anisotropy for bulk modulus, especially for that of zinc-blende GaN. Furthermore, the band gaps of GaN crystals increase with increasing pressure, and zinc-blende GaN has a larger pressure coefficient. To further understand the pressure effect on the band gap, the band structure and density of states (DOSs) of GaN crystals were also analysed in this study
Dendron-Jacketed Electrophosphorescent Copolymers: Improved Efficiency and Tunable Emission Color by Partial Energy Transfer
No full textA styrene-based phosphorescent monomer VC3DbmIr(ppy)(2) with cyclometalated iridium complex was synthesized. It was then copolymerized with the first-generation dendritic carbazole monomer VC3CbzG1 through the conventional free radical polymerization to obtain a series of electrophosphorescent random copolymers. Characteristic vibrational bands in the FT-IR spectra were utilized to determine the compositions of the copolymers. The glass transition temperatures of the copolymers were about 90 degrees C, and the 5% weight loss temperatures were all above 346 degrees C. All the copolymers exhibited similar absorbing bands of the carbazole units in the UV-vis absorption spectra. In the photoluminescent spectra of the copolymer films, energy transfer was found from the carbazole units to iridium phosphors. No obvious energy transfer was found in the copolymer solutions. Light-emitting diodes were fabricated with two configurations. With increasing iridium content, the electroluminescence of the copolymers shifted from blue to orange and passed through a near-white emission region. After the optimization of the device structure, the device containing the copolymer PCbzG1Ir3 had the best performance with a maximum luminescence of 2441 cd/m(2) and a maximum external quantum efficiency of 0.520%.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000298198600010&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Polymer ScienceSCI(E)EI9ARTICLE249556-95644
Synthesis and properties of silicon-containing bismaleimide resins
No full textTwo novel bismaleimide (BMI) monomers containing silicon atom in the structure, i.e., bis[4-(4-maleimidophenylcarbonyloxy)phenyl]dimethylsilane (BMI-SiE1) and bis [4-(4-maleimidophenyloxycarbonyl)phenyl]dimethylsilane (BMI-SiE2), were designed, synthesized, and polymerized with and without the use of diamine as comonomers to yield novel silicon-containing BMI resins. Both monomers obtained are readily soluble in organic solvents, such as chloroform and N, N-dimethylformamide. Differential scanning calorimetry and thermogravimetric analysis investigation of these two monomers indicated a high polymerization temperature (T-p > 240 degrees C) and a good thermal and thermo-oxidative stability of cured BMI resins. The onset temperature for 5% weight loss was found to be above 450 degrees C in nitrogen and above 400 degrees C in the air. Polymerization of BMI-SiE1 and BMI-SiE2 with 4,4'-diaminodiphenylether (DPE) yielded a series of polyaspartimides that had good solubility and could be thermally cured at 250 degrees C. TGA investigations of the cured diamine-modified BMI resins showed onset of degradation temperatures (T(d)s) in the range of 344-360 degrees C in nitrogen and 332-360 degrees C in the air. Composites based on the cured diamine-modified BMI resins and glass cloth were prepared and characterized for their dynamic mechanical properties. All the composites showed high glass transition temperatures (e.g., >190 degrees C) and high bending modulus in the range of 1000-2700 MPa. (C) 2008 Wiley Periodicals, Inc.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000255626700025&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Polymer ScienceSCI(E)EI18ARTICLE1190-19910
