| 1. |
- Fenstermacher, M.E., et al.
(författare)
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DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy
- 2022
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 62:4
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Tidskriftsartikel (refereegranskat)abstract
- DIII-D physics research addresses critical challenges for the operation of ITER and the next generation of fusion energy devices. This is done through a focus on innovations to provide solutions for high performance long pulse operation, coupled with fundamental plasma physics understanding and model validation, to drive scenario development by integrating high performance core and boundary plasmas. Substantial increases in off-axis current drive efficiency from an innovative top launch system for EC power, and in pressure broadening for Alfven eigenmode control from a co-/counter-I p steerable off-axis neutral beam, all improve the prospects for optimization of future long pulse/steady state high performance tokamak operation. Fundamental studies into the modes that drive the evolution of the pedestal pressure profile and electron vs ion heat flux validate predictive models of pedestal recovery after ELMs. Understanding the physics mechanisms of ELM control and density pumpout by 3D magnetic perturbation fields leads to confident predictions for ITER and future devices. Validated modeling of high-Z shattered pellet injection for disruption mitigation, runaway electron dissipation, and techniques for disruption prediction and avoidance including machine learning, give confidence in handling disruptivity for future devices. For the non-nuclear phase of ITER, two actuators are identified to lower the L-H threshold power in hydrogen plasmas. With this physics understanding and suite of capabilities, a high poloidal beta optimized-core scenario with an internal transport barrier that projects nearly to Q = 10 in ITER at ∼8 MA was coupled to a detached divertor, and a near super H-mode optimized-pedestal scenario with co-I p beam injection was coupled to a radiative divertor. The hybrid core scenario was achieved directly, without the need for anomalous current diffusion, using off-axis current drive actuators. Also, a controller to assess proximity to stability limits and regulate β N in the ITER baseline scenario, based on plasma response to probing 3D fields, was demonstrated. Finally, innovative tokamak operation using a negative triangularity shape showed many attractive features for future pilot plant operation.
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| 2. |
- Liao, Zhong-Wei, et al.
(författare)
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Robust Low Voltage Program-Erasable Cobalt-Nanocrystal Memory Capacitors with Multistacked Al2O3/HfO2/Al2O3 Tunnel Barrier
- 2009
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Ingår i: Chinese Physics Letters. - 0256-307X .- 1741-3540. ; 26:8, s. 087303-
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Tidskriftsartikel (refereegranskat)abstract
- An atomic-layer-deposited Al2O3/HfO2/Al2O3 (A/H/A) tunnel barrier is investigated for Co nanocrystal memory capacitors. Compared to a single Al2O3 tunnel barrier, the A/H/A barrier can significantly increase the hysteresis window, i. e., an increase by 9V for +/- 12V sweep range. This is attributed to a marked decrease in the energy barriers of charge injections for the A/H/A tunnel barrier. Further, the Co-nanocrystal memory capacitor with the A/H/A tunnel barrier exhibits a memory window as large as 4.1V for 100 mu s program/erase at a low voltage of +/- 7V, which is due to fast charge injection rates, i. e., about 2.4 x 10(16) cm(-2) s(-1) for electrons and 1.9 x 10(16) cm(-2) s(-1) for holes.
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| 3. |
- Zhang, Wei-Wei, et al.
(författare)
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Phase equilibria of the Fe-Ni-Si system at 850 degrees C
- 2009
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 481:1-2, s. 509-514
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Tidskriftsartikel (refereegranskat)abstract
- By means of X-ray diffraction, metallography, scanning electron microscopy with energy dispersive Xray analysis, and electron probe microanalysis, the constitution of the ternary Fe-Ni-Si system at 850 degrees C over the entire composition range was established with 24 alloys. Ten of the three-phase equilibria were well determined at 850 degrees C. The existence of the ternary compound Fe5Ni3Si2 (tau(1)) with a cubic crystal structure at 850 degrees C is confirmed. The homogeneity ranges were measured and the lattice parameters were determined for most observed phases.
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| 4. |
- You, Xiaohu, et al.
(författare)
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Towards 6G wireless communication networks: vision, enabling technologies, and new paradigm shifts
- 2021
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Ingår i: Science China Information Sciences. - : Science Press. - 1674-733X .- 1869-1919. ; 64:1
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Forskningsöversikt (refereegranskat)abstract
- The fifth generation (5G) wireless communication networks are being deployed worldwide from 2020 and more capabilities are in the process of being standardized, such as mass connectivity, ultra-reliability, and guaranteed low latency. However, 5G will not meet all requirements of the future in 2030 and beyond, and sixth generation (6G) wireless communication networks are expected to provide global coverage, enhanced spectral/energy/cost efficiency, better intelligence level and security, etc. To meet these requirements, 6G networks will rely on new enabling technologies, i.e., air interface and transmission technologies and novel network architecture, such as waveform design, multiple access, channel coding schemes, multi-antenna technologies, network slicing, cell-free architecture, and cloud/fog/edge computing. Our vision on 6G is that it will have four new paradigm shifts. First, to satisfy the requirement of global coverage, 6G will not be limited to terrestrial communication networks, which will need to be complemented with non-terrestrial networks such as satellite and unmanned aerial vehicle (UAV) communication networks, thus achieving a space-air-ground-sea integrated communication network. Second, all spectra will be fully explored to further increase data rates and connection density, including the sub-6 GHz, millimeter wave (mmWave), terahertz (THz), and optical frequency bands. Third, facing the big datasets generated by the use of extremely heterogeneous networks, diverse communication scenarios, large numbers of antennas, wide bandwidths, and new service requirements, 6G networks will enable a new range of smart applications with the aid of artificial intelligence (AI) and big data technologies. Fourth, network security will have to be strengthened when developing 6G networks. This article provides a comprehensive survey of recent advances and future trends in these four aspects. Clearly, 6G with additional technical requirements beyond those of 5G will enable faster and further communications to the extent that the boundary between physical and cyber worlds disappears.
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| 5. |
- Huo, Hong-wei, et al.
(författare)
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Coexistence of 2.4 GHz sensor networks in home environment
- 2010
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Ingår i: The Journal of China Universities of Posts and Telecommunications. - : Elsevier. - 1005-8885. ; 17:1, s. 9-18
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Tidskriftsartikel (refereegranskat)abstract
- The IEEE 802.15.4 is one of the low-layer communication standards for personal area networks (PANs) and wireless sensor networks (WSNs), which may be interfered by other wireless devices in the industrial, scientific and medical (ISM) frequency bands, especially in home environment, such as devices of IEEE 802.11b, Bluetooth, cordless telephone, and microwave oven radiation. This article examines the mutual interference effects of 2.4 GHz devices widely deployed at home, via both theoretical analysis and real-life experiment. An analytical model is proposed to estimate the packet error rate (PER) of radio frequency (RF) coexistent networks. The model is verified through a series of experiments. The experimental results also show that Bluetooth has little impact of interference on IEEE 802.15.4 sensor networks, and that the effect of microwave oven radiation on IEEE 802.15.4 sensor devices is tolerable if the device is a few meters away from the oven. Whereas, IEEE 802.11b wireless networks can cause problems to IEEE 802.15.4, however the effects can be significantly reduced by a proper channel selection. This article also proposes the interference duration model, which will be helpful in modeling of coexistence simulation. Simulation results show that the stationary scenario obeys the experiments result very well.
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| 6. |
- Liu, Tie, et al.
(författare)
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Effects of high magnetic fields on solidification microstructure of Al-Si alloys
- 2011
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 46:6, s. 1628-1634
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Tidskriftsartikel (refereegranskat)abstract
- The effects of high magnetic fields on the solidification microstructure of Al-Si alloys were investigated. Al-7.2 wt%Si and Al-11.8 wt%Si alloys were solidified in various high magnetic fields at different cooling rates. The secondary dendrite arm spacing (SDAS) of the primary Al dendrites and the lamellar spacing (LS) of the eutectics were measured. It was found that the application of a high magnetic field could decrease the SDAS of the primary Al dendrites in Al-7.2 wt% Si alloys and the LS of the eutectics in Al-11.8 wt% Si alloys. The effects of the high magnetic field on the SDAS decreased with increasing cooling rate. The decrease in the SDAS and LS can be attributed to the decrease of the solute diffusivity in the liquid ahead of the solid/liquid interface during the growth of the dendrite and eutectic. This decrease is caused by the high magnetic field which can damp the convection and avoid its contributions to the diffusion.
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| 7. |
- Zhang, Miao, et al.
(författare)
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From wood to thin porous carbon membrane : Ancient materials for modern ultrafast electrochemical capacitors in alternating current line filtering
- 2021
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Ingår i: Energy Storage Materials. - : Elsevier BV. - 2405-8289 .- 2405-8297. ; 35, s. 327-333
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Tidskriftsartikel (refereegranskat)abstract
- Ultrafast electrochemical capacitors with alternating current line filtering function have attracted growing attention owing to their potential to replace the state-of-the-art bulky aluminum electrolyte capacitors. In spite of rapid advance recently involving nanomaterials as electrode building units, it remains largely unexplored how to structurally and chemically engineer electrodes out of renewable resource with competitive or better rate performance. Herein, wood as a renewable resource was used to fabricate highly conductive, robust, porous thin carbon membranes as free-standing electrodes for ultrafast electrochemical capacitors. Transformation of wood slice to carbon membrane proceeds via wet-chemical treatment of wood slices and subsequent morphology maintaining carbonization by spark plasma sintering. Judiciously combining high conductivity, characteristic porous architecture with low tortuosity and high continuity, and the ultrathin thickness down to 20 ism, the carbon membrane-based electrochemical capacitor exhibits excellent frequency response with efficient 120 Hz filtering (phase angle = - 83.5 degrees). Compared to the latest electrodes for line filtering application that are fabricated from carbon nanotubes, graphene, and MXene, the wood-derived carbon membranes possess a competitive specific areal capacitance of up to 509.7 mu F cm(-2), and extremely low resistance-capacitance constant of 164.7 mu s, plus the inexpensive scalable fabrication strategy.
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| 8. |
- Fan, Jin, et al.
(författare)
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Development of wideband orthomode transducers for FAST cryogenic receiver system
- 2020
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Ingår i: Research in Astronomy and Astrophysics. - : IOP Publishing. - 1674-4527. ; 20:5
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes the design, construction, and performance of the wideband orthomode transducers (OMTs) for the L- (1.2-1.8 GHz), the S- (2-3 GHz) and the P- (0.56-1.12 GHz) band receiver systems of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). These OMTs operate at the cryogenic temperature of 70K to reduce their thermal noise contribution to the receiver chains. The development on the FAST L- and S-band quad-ridged waveguide (QRWG) OMTs is carried out based on the theoretical mode analysis. In view of the miniaturization of FAST cryogenic receiver system at P-band, a novel wideband compact bowtie dipole OMT is designed with an octave bandwidth as well as a length of only quarter wavelength. The proposed L-, S- and P-band OMTs are designed and optimized by using Ansys High Frequency Structure Simulator (HFSS), and then manufactured, tested at room temperature. Measurement of FAST cryogenic receiver system noise is also performed with the L-, S- and P-band OMTs installed. The measured results fully comply with the design specifications.
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| 9. |
- He, Wei, et al.
(författare)
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Operational performance of a novel heat pump assisted solar facade loop-heat-pipe water heating system
- 2015
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 146, s. 371-382
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Tidskriftsartikel (refereegranskat)abstract
- This paper aims to present an investigation into the operational performance of a novel heat pump assisted solar façade loop-heat-pipe (LHP) water heating system using both theoretical and experimental methods. This involved (1) development of a computer numerical model; (2) simulation of the operational performance of the system by using the model; (3) test rig construction; and (4) dedicated experiment for verification of the model. It was found that the established model is able to predict the operational performance of the system at a reasonable accuracy. Analyses of the research results indicated that under the selected testing conditions, the average thermal efficiency of the LHP module was around 71%, much higher than that of the loop heat pipe without heat pump assistance. The thermal efficiency of the LHP module grew when the heat pump was turned-on and fell when the heat pump was turned-off. The water temperature remained a steadily growing trend throughout the heat pump turned-on period. Neglecting the heat loss of the water tank, the highest coefficient of the performance could reach up to 6.14 and its average value was around 4.93. In overall, the system is a new façade integrated, highly efficient and aesthetically appealing solar water heating configuration; wide deployment of the system will help reduce fossil fuel consumption in the building sector and carbon emission to the environment.
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| 10. |
- He, Wei, et al.
(författare)
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Theoretical investigation of the thermal performance of a novel solar loop-heat-pipe facade-based heat pump water heating system
- 2014
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Ingår i: Energy and Buildings. - : Elsevier BV. - 0378-7788 .- 1872-6178. ; 77, s. 180-191
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the paper was to present a dedicated theoretical investigation into the thermal performance of a novel solar loop-heat-pipe façade based heat pump water heating system. This involved thermo-fluid analyses, computer numerical model development, the model running up, modelling result analyses and conclusion. An energy balance network was established on each part and the whole range of the system to address the associated energy conversion and transfer processes. On basis of this, a computer numerical model was developed and run up to predict the thermal performance of such a system at different system configurations, layouts and operational conditions. It was suggested that the loop heat pipes could be filled with either water, R134a, R22 or R600a; of which R600a is the favourite working fluid owing to its relatively larger heat transfer capacity and positive pressure in operation. Variations in the system configuration, i.e., glazing covers, heat exchangers, would lead to identifiable differences in the thermal performance of the system, represented by the thermal efficiency and COP. Furthermore, impact of the external operational parameters, i.e., solar radiation and ambient air temperature, to the system's thermal performance was also investigated. The research was based on an innovative loop-heat-pipe façade and came up with useful results reflecting the thermal performance of the combined system between the façade and heat pump. This would help promote development and market penetration of such an innovative solar heating technology, and thus contribute to achieving the global targets in energy saving and carbon emission reduction.
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