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  • Resultat 913051-913060 av 1637242
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913051.
  • Nguyen, Tan N., et al. (författare)
  • Throughput Enhancement in FD-and SWIPT-enabled IoT Networks over Non-Identical Rayleigh Fading Channels
  • 2021
  • Ingår i: IEEE Internet of Things Journal. - : Institute of Electrical and Electronics Engineers (IEEE). - 2327-4662. ; , s. 1-1
  • Tidskriftsartikel (refereegranskat)abstract
    • Simultaneous wireless information and power transfer (SWIPT) and full-duplex (FD) communications have emerged as prominent technologies in overcoming the limited energy resources in Internet-of-Things (IoT) networks and improving their spectral efficiency (SE). The article investigates the outage and throughput performance for a decode-and-forward (DF) relay SWIPT system, which consists of one source, multiple relays, and one destination. The relay nodes in this system can harvest energy from the source’s signal and operate in FD mode. A suboptimal, low-complexity, yet efficient relay selection scheme is also proposed. Specifically, a single relay is selected to convey information from a source to a destination so that it achieves the best channel from the source to the relays. An analysis of outage probability (OP) and throughput performed on two relaying strategies, termed static power splitting-based relaying (SPSR) and optimal dynamic power splitting-based relaying (ODPSR), is presented. Notably, we considered independent and non-identically distributed (i.n.i.d.) Rayleigh fading channels, which pose new challenges in obtaining analytical expressions. In this context, we derived exact closed-form expressions of the OP and throughput of both SPSR and ODPSR schemes. We also obtained the optimal power splitting ratio of ODPSR for maximizing the achievable capacity at the destination. Finally, we present extensive numerical and simulation results to confirm our analytical findings. Both simulation and analytical results show the superiority of ODPSR over SPSR.
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913052.
  • Nguyen, Thi Quynh Hoa, et al. (författare)
  • Numerical study of a broadband metamaterial absorber using a single split circle ring and lumped resistors for X-band applications
  • 2020
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 10:3
  • Tidskriftsartikel (refereegranskat)abstract
    • We report a numerical study on the design of a broadband metamaterial absorber (MMA) with a single layer of metal-dielectric-metal based on an FR-4 substrate for X-band applications. The MMA structure consists of a periodic array of a split circle ring and lumped resistors coupled within split segments. The MMA structure achieves a broadband absorption response in the frequency range of 7.8-12.6 GHz with an absorptivity of above 90% under normal incidence for all polarization angles. The absorptivity remains above 70% in the frequency range of 6.8-11.8 GHz at wide incident angles from 0 degrees to 30 degrees for both transverse electric and transverse magnetic polarizations. The physical mechanism of the absorber is explained by the electric and the surface current distributions that, in turn, are significantly affected by magnetic resonance.
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913053.
  • Nguyen, Thi Quynh Hoa, et al. (författare)
  • Numerical study of a wide incident angle- and polarisation-insensitive microwave metamaterial absorber based on a symmetric flower structure
  • 2019
  • Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 9:6
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, we propose a wide incident angle- and polarisation-insensitive metamaterial absorber covered with structures comprising a metallic flower shape layer, a dielectric layer and a metallic ground plane. The influences of the structural parameters on the absorptivity are investigated numerically. The proposed absorber exhibits polarisation insensitivity as the number of symmetric petals of a flower shape reaches as high as 4, 6 and 8. Particularly, the absorber based on 8 petals shows an absorptivity of above 90% for wide incident angles up to 70° under transverse electric and transverse magnetic polarisations. The physical mechanism of these observations is clarified by investigating the electric, power loss density and induced current distributions, which is also supported by the retrieved constitutive electromagnetic parameters. That is, the absorption phenomenon is considerably affected by magnetic resonance. By modifying the petals into hollow shapes, the absorber becomes effective in confining the magnetic resonance and can thus minimise the resonant frequency variation to 0.22% without affecting the absorption performance. In comparison with other reported metamaterial absorbers, our design shows considerable practical feasibility in terms of resonant frequency stability, wide incident angle and polarisation insensitivity, thereby making it suitable for various applications in microwave frequency region.
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913054.
  • Nguyen, Thanh Son, et al. (författare)
  • A case study on the influence of THM coupling on the near field safety of a spent fuel repository in sparsely fractured granite
  • 2009
  • Ingår i: Environmental Geology. - : Springer Science and Business Media LLC. - 0943-0105 .- 1432-0495. ; 57:6, s. 1239-1254
  • Tidskriftsartikel (refereegranskat)abstract
    • In order to demonstrate the feasibility of geological disposal of spent CANDU fuel in Canada, a safety assessment was performed for a hypothetical repository in the Canadian Shield. The assessment shows that the maximum long term radionuclide release from such repository would meet international criteria for dose rate; however, uncertainties in the assumed evolution of the repository were identified. Such uncertainties could be resolved by the consideration of coupled Thermal-Hydro-Mechanical-Chemical (THMC) processes. In Task A of the DECOVALEX-THMC project, THM models were developed within the framework of the theory of poroelasticity. Such model development was performed in an iterative manner, using experimental data from laboratory and field tests. The models were used to perform near-field simulations of the evolution of the repository in order to address the above-mentioned uncertainties. This paper presents the definition and rationale of task A and the results of the simulations. From a repository safety point of view, the simulations predict that the maximum temperature would be well below the design target of 100A degrees C; however, the stress on the container can marginally exceed the design value of 15 MPa. However, the most important finding from the simulations is that a rock damage zone could form around the emplacement borehole. Such damage zone can extend a few metres from the walls of the emplacement holes, with permeability values that are orders of magnitude higher than the initial values. The damage zone has the potential to increase the radionuclide transport flux from the geosphere; the effect of such an increase should be taken into account in the safety assessment and mitigated if necessary by the provision of sealing systems.
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913055.
  • Nguyen, Tien Son, et al. (författare)
  • Carbon vacancy-related defect in 4H and 6H SiC
  • 2001
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:20
  • Tidskriftsartikel (refereegranskat)abstract
    • An electron paramagnetic resonance (EPR) spectrum was observed at temperatures above 25 K in p-type 4H and 6H SiC irradiated with electrons. The center has C-3V symmetry with an electron spin S= 1/2. Using high frequency (similar to 95 GHz) EPR it was possible to obtain the derailed hyperfine structure due to the interaction with the four nearest silicon neighbors, and to identify the defect as the carbon vacancy in the positive-charge state (VC+). The g values and hyper fine tensor of the center in both polytypes are almost the same and no dependence on the inequivalent lattice sites has been detected.
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913056.
  • Nguyen, Tien Son, et al. (författare)
  • Defects in semi-insulating SiC substrates
  • 2003
  • Ingår i: Materials Science Forum, Vols. 433-436. ; , s. 45-50
  • Konferensbidrag (refereegranskat)abstract
    • Electron paramagnetic resonance (EPR) was used to study defects in semi-insulating (SI) SiC substrates grown by high-temperature chemical vapour deposition (HTCVD) and physical vapour transport (PVT). The C vacancy, Si antisite and several other EPR centers, labelled SI-I to SI-8, were observed in the HTCVD and/or PVT 4H-SiC substrates. Photo-EPR has revealed several deep levels responsible for the SI properties in different types of SI 4H-SiC. Annealing behaviour of the defects and the stability of the SI properties with high temperature annealing were also studied.
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913057.
  • Nguyen, Tien Son, et al. (författare)
  • Hole and electron effective masses in 6H-SiC studied by optically detected cyclotron resonance
  • 2002
  • Ingår i: Materials Science Forum(ISSN 0255-5476), Vols. 389-393. - : Trans Tech Publications. ; , s. 525-528
  • Konferensbidrag (refereegranskat)abstract
    • We used optically detected cyclotron resonance (ODCR) at X-band frequency (similar to9.23 GHz) to study the hole effective masses in 6H-SiC. In high-purity 6H-SiC layers, two well-resolved cyclotron resonance (CR) peaks have been observed and attributed to the CR of electrons and holes. In 6H-SiC, the uppermost valence band near its maximum is found to be parabolic with the hole transverse effective mass m(hperpendicular to)=(0.66 +/- 0.02) m(0) and the longitudinal effective mass component M-hparallel to =(1.85 +/- 0.03) m(0). The average of the electron effective mass components in the basal plane-the transversal mass-is determined as m(eperpendicular to)=(0.48 0.02) m(0). With the obtained OJDCR data we can estimate the longitudinal electron effective mass to be in the range 3-6 m(0) depending on the anisotropy of the effective mass in the basal plane.
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913058.
  • Nguyen, Tien Son, et al. (författare)
  • Hole effective masses in 6H-SiC from optically detected cyclotron resonance
  • 2002
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:4
  • Tidskriftsartikel (refereegranskat)abstract
    • We used optically detected cyclotron resonance (ODCR) at X-band frequency (similar to9.23 GHz) to study the hole effective masses in 6H-SiC. In high-purity 6H-SiC layers, two well-resolved cyclotron resonance (CR) peaks have been observed and attributed to the CR of electrons and holes. Similar to 4H-SiC, the hole effective mass in 6H polytype is also found to be isotropic in the basal plane with the transverse mass m(hperpendicular to)=(0.66+/-0.02) m(0). The hole effective mass component along the c-axis is determined as m(hparallel to)=(1.85+/-0.03) m(0). From the obtained data we can estimate the electron effective mass component along the c-axis to be in the range 3-6 m(0) depending on the anisotropy of the electron effective mass in the basal plane.
  •  
913059.
  • Nguyen, T. S., et al. (författare)
  • Hydro-mechanical response of a fractured granitic rock mass to excavation of a test pit - the Kamaishi Mine experiment in Japan
  • 2001
  • Ingår i: International Journal of Rock Mechanics And Mining Sciences. - 1365-1609 .- 1873-4545. ; 38:1, s. 79-94
  • Tidskriftsartikel (refereegranskat)abstract
    • A thermo-hydro-mechanical experiment was conducted in a fractured granitic ruck mass at the Kamaishi Mine in Japan. The experiment consists of the excavation of a cylindrical test pit on the floor of an experimental drift. The test pit was then lilted with bentonite with an embedded heater. During the excavation of the test pit, the hydromechanical response of the surrounding rock was monitored. This paper presents the efforts of four research teams to numerically simulate the hydro-mechanical response of the rock mass during excavation. While the total inflow rate to the test pit, the flow distribution on the pit walls and the displacements in the rock mass away From the pit could be reasonably predicted, the pore pressure in individual boreholes, and the expansion behaviour of the pit were less successfully simulated. The reasons for these discrepancies are discussed in the paper.
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913060.
  • Nguyen, Tien Son, et al. (författare)
  • Identification of divacancies in 4H-SiC
  • 2006
  • Ingår i: Physica B: Condensed Matter, Vols. 376-377. - : Elsevier BV. ; , s. 334-337
  • Konferensbidrag (refereegranskat)abstract
    • The P6/P7 centers in 4H-SiC were studied by electron paramagnetic resonance (EPR) and ab initio supercell calculations. The hyperfine coupling constants of C and Si neighbors obtained by EPR are in good agreement with the calculated values for the neutral divacancy, VCVsi0. Our results suggest that the P6/P7 centers, which were previously assigned to the photo-excited triplet states of the carbon vacancy-carbon antisite pairs in the double positive charge state (VCCsi2+), are related to the triplet ground states of the C-3v/C-1h si configurations of VCVsi0 (c) 2006 Elsevier B.V. All rights reserved.
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