| 451. |
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| 452. |
- Xiaoming, Chen, 1983, et al.
(författare)
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Comparison of Ergodic Capacities From Wideband MIMO Antenna Measurements in Reverberation Chamber and Anechoic Chamber
- 2011
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Ingår i: IEEE Antennas and Wireless Propagation Letters. - 1548-5757 .- 1536-1225. ; 10, s. 446-449
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Tidskriftsartikel (refereegranskat)abstract
- It has previously been shown that ergodic multiple-input-multiple-output (MIMO) capacity of a multiport antenna system can be conveniently determined from channel measurements in a reverberation chamber. In this letter, we compare such MIMO capacity results to results based on measurements in an anechoic chamber of the embedded far-field functions and efficiencies at all antenna ports. The comparison is performed over two-octaves bandwidth by using the decade bandwidth eleven antenna, a log-periodic dual-dipole array. The agreement between the reverberation chamber results and the anechoic chamber results is good over the entire frequency band 2-8 GHz.
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| 453. |
- Xiaoming, Chen, 1983, et al.
(författare)
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Investigation of the Effect of Noise Correlations on Diversity Gains and Capacities of Multiport Antennas Using Reverberation Chamber
- 2012
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Ingår i: International Journal of Antennas and Propagation. - : Hindawi Limited. - 1687-5869 .- 1687-5877. ; 2012, s. Art. no. 486730-
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Tidskriftsartikel (refereegranskat)abstract
- Most of previous studies on diversity gains and capacities of multiantenna systems assumed independent and identically distributed (i.i.d.) Gaussian noises. There are a few studies about the noise correlation effects on diversity gains or MIMO capacities, however, by simulations only. In this paper, the maximum ratio combining (MRC) diversity gain and multiple-input multiple-output (MIMO) capacity including correlated noises are presented. Based on the derived formulas, measurements in a reverberation chamber are performed for the first time to observe the effect of noise correlations on diversity gains and MIMO capacities.
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| 454. |
- Xiaoming, Chen, 1983, et al.
(författare)
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MRC Diversity and MIMO Capacity Evaluations of Multi-Port Antennas Using Reverberation Chamber and Anechoic Chamber
- 2013
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Ingår i: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 61:2, s. 917-926
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Tidskriftsartikel (refereegranskat)abstract
- It has been shown that diversity gains and MIMO capacity of multi-port antennas can be conveniently determined from reverberation chamber measurements. In this paper, we first present the covariance eigenvalue approach and the embedded far field function method to determine diversity gain and MIMO capacity, respectively, for arbitrary multi-port antennas. Then, we discuss the convergence of the covariance eigenvalue approach. In the end, we apply both methods to compare MRC diversity gains and MIMO capacity measured in a reverberation chamber (based on direct channel measurements) and an anechoic chamber (based on measurements of the embedded far field functions and efficiencies at all antenna ports). The comparison is performed over 2-8 GHz using a wideband multi-port antenna in two configurations. There are in general good agreements between the reverberation and anechoic chamber measurement results.
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| 455. |
- Xie, C., et al.
(författare)
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An Ultrawideband Dipole With a Director as a Feed for Reflector Antennas
- 2017
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Ingår i: IEEE Antennas and Wireless Propagation Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1548-5757 .- 1536-1225. ; 16, s. 1341-1344
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Tidskriftsartikel (refereegranskat)abstract
- A novel ultrawideband directional flat dipole capped by a planar director is proposed in this letter. The novelty of the antenna is the great improvement of the bandwidth of a flat dipole above an ordinary finite ground plane by using a simple parasitic top patch, referred to as the "director." A linearly polarized prototype has been designed and manufactured, and achieved a nearly 3:1 operating bandwidth (2.2-6.5 GHz) with a return loss higher than 10 dB, nearly constant radiation patterns, and high aperture efficiency over the entire operating band.
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| 456. |
- Xie, C., et al.
(författare)
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Low-Profile Ultra-Wideband Directional Dipole Antenna as a Feed for Reflectors in Radio Telescopes
- 2016
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Ingår i: 9th International Conference on Microwave and Millimeter Wave Technology Proceedings, Vol. 1, (ICMMT 2016). ; 1, s. 495-497
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Konferensbidrag (refereegranskat)abstract
- In this paper, a small top plate is found useful to improve the impedance bandwidth of an ultra-wideband dipole antenna horizontally above a ground plane. A linearly-polarized prototype based on this new and simple design methodology can operate over nearly 3.5:1 bandwidth with return losses better than 10 dB, and with nearly stable radiation patterns, high BOR1 efficiency and aperture efficiency over the entire operating band.
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| 457. |
- Xie, Hujun, et al.
(författare)
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N-Insertion reaction mechanisms of phenyl azides with a hafnium hydride complex : a quantum chemistry calculation
- 2017
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Ingår i: New Journal of Chemistry. - : ROYAL SOC CHEMISTRY. - 1144-0546 .- 1369-9261. ; 41:12, s. 5007-5011
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory (DFT) calculations were performed to investigate the detailed mechanisms for the N-insertion reaction of phenyl azides with a hafnium hydride complex. This reaction involves an intermolecular hydride transfer from the hafnium center of complex 1 (Cp2HfH2)-Hf-star to the terminal nitrogen atom of a phenyl azide. Subsequently, a 1,3 hydrogen shift from the N1 atom to the N3 atom takes place, accompanied by cleavage of the N2-N3 bond to provide amido complex 3 (Cp2HfH)-Hf-star(NHPh) and dinitrogen. A further reaction is related to the intermolecular hydride transfer from the hafnium center to the N1' atom of a second phenyl azide, followed by the formation of the final product, bis(amido) complex 9 (Cp2HfH)-Hf-star(NHPh)(2) via the liberation of the second dinitrogen, which is the rate-determining step with an overall barrier of 29.8 kcal mol(-1). Frontier molecular orbital theory analysis shows that phenyl azides are activated by nucleophilic attack by the hydride ligand, which is consistent with our previous studies of N2O activation by other transition-metal hydride complexes.
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| 458. |
- Xie, Jian, et al.
(författare)
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On the Impact Analysis of Emergency Vehicles Preemption on Signalized Intersections with Connected Vehicles
- 2022
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Ingår i: Smart Innovation, Systems and Technologies. - Singapore : Springer Nature Singapore. - 2190-3026 .- 2190-3018. ; 304 SIST, s. 151-160
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Konferensbidrag (refereegranskat)abstract
- In recent years, vehicle-to-infrastructure (V2I) and vehicle-to-vehicle (V2V) communication are the leading technologies in intelligent transportation systems. With V2I and V2V, new strategies are enabled to better facilitate emergency rescue and traffic emergency management. Since signalized intersection is the major source of delay and congestion, how to prioritize emergency vehicles (EVs) at intersections becomes an indispensable research topic and has drawn extensive studies. Albeit that emergency vehicles should be granted absolute priority, the influence of EVs on the intersection was rarely studied, especially when aggressive preemption strategies are adopted. To this end, this paper is devoted to evaluating the impacts of EVs on the control of signalized intersections, as an effort to better emergency management. Mixed-integer linear programming models are developed to optimize the intersection control before and after the pass of EVs, respectively. Case studies indicate that, by assuming the EV will take exclusively one lane at the intersection, the average delay could increase by 11.28% along with a capacity decrease of 6.63%.
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| 459. |
- Xie, Liang, et al.
(författare)
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Low-bandgap nonfullerene acceptor based on thieno[3,2-b]indole core for highly efficient binary and ternary organic solar cells
- 2022
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 427
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Tidskriftsartikel (refereegranskat)abstract
- A low-bandgap nonfullerene acceptor (NFA) TIT-2FIC based on thieno[3,2-b]indole-thiophenes core has been developed. Compared with the analogue NFAs DTC(4Ph)-4FIC and IT-4F, TIT-2FIC exhibited remarkably red-shifted absorption, and up-shifted HOMO energy level. In addition, TIT-2FIC showed interesting universal miscibility with the donors nonfluorinated PBDB-T and fluorinated PM6, therefore the corresponding organic solar cells achieved promising power conversion efficiencies (PCEs) of 11.80% and 13.00%, respectively, which are higher compared to the counterpart IT-4F based cells. Furthermore, the ternary PM6:TIT-2FIC:Y6 cell pronounced a high PCE of 17.22%, being significantly improved from that of 16.04% for the binary PM6:Y6 cell. Similar improvement in PCEs from 13.41% to 14.46% was also observed in the ternary PM6:TIT-2FIC:IT-4F cell with TIT-2FIC as the third component. These results indicated that TIT-2FIC is universally applicable as an acceptor with nonfluorinated or fluorinated polymer donor materials in both binary and ternary cells.
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| 460. |
- Xie, Yang, et al.
(författare)
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Tuning the Topology of Three-Dimensional Covalent Organic Frameworks via Steric Control : From pts to Unprecedented Ijh
- 2021
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 143:19, s. 7279-7284
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Tidskriftsartikel (refereegranskat)abstract
- Whether or not the topology of three-dimensional covalent organic frameworks (3D COFs) can be tuned via steric control remains a big question and has never been reported. Herein, we describe the designed synthesis of two highly crystalline 3D COFs (3D-TPB-COF-OMe and 3D-TPB-COF-Ph), through the polycondensation of tetra(p-aminophenyl)methane and methoxy-or phenyl- substituted 1,2,4,5-tetralcis(4-formylphenyobenzene on the 3- and 6-positions. Amazingly, by using the continuous rotation electron diffraction technique, 3D-TPB-COF-OMe is determined to have a 5-fold interpenetrated structure with a reported pts net, while 3D-TPB-COF-Ph adopts an unprecedented self-penetrated Ijh topology (Ijh = Luojia Hill) that does not exist in the database of ToposPro. Therefore, by altering the substituents from methoxy to phenyl groups, the topology of designed 3D COFs changes accordingly, and a rare net is now available. This result clearly demonstrates that such COF structures need to be carefully determined due to its complexity, and moreover, it is promising to design 3D COFs with new topology for interesting application by increasing the steric hindrance of molecular building blocks.
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