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Sökning: WFRF:(Zheng W.) > Teknik

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1.
  • Fenstermacher, M.E., et al. (författare)
  • DIII-D research advancing the physics basis for optimizing the tokamak approach to fusion energy
  • 2022
  • Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 62:4
  • 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.
  • Shimwell, T. W., et al. (författare)
  • The LOFAR Two-metre Sky Survey: V. Second data release
  • 2022
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 659
  • Tidskriftsartikel (refereegranskat)abstract
    • In this data release from the ongoing LOw-Frequency ARray (LOFAR) Two-metre Sky Survey we present 120a 168 MHz images covering 27% of the northern sky. Our coverage is split into two regions centred at approximately 12h45m +44 30a and 1h00m +28 00a and spanning 4178 and 1457 square degrees respectively. The images were derived from 3451 h (7.6 PB) of LOFAR High Band Antenna data which were corrected for the direction-independent instrumental properties as well as direction-dependent ionospheric distortions during extensive, but fully automated, data processing. A catalogue of 4 396 228 radio sources is derived from our total intensity (Stokes I) maps, where the majority of these have never been detected at radio wavelengths before. At 6a resolution, our full bandwidth Stokes I continuum maps with a central frequency of 144 MHz have: a median rms sensitivity of 83 μJy beama 1; a flux density scale accuracy of approximately 10%; an astrometric accuracy of 0.2a; and we estimate the point-source completeness to be 90% at a peak brightness of 0.8 mJy beama 1. By creating three 16 MHz bandwidth images across the band we are able to measure the in-band spectral index of many sources, albeit with an error on the derived spectral index of > a ±a 0.2 which is a consequence of our flux-density scale accuracy and small fractional bandwidth. Our circular polarisation (Stokes V) 20a resolution 120a168 MHz continuum images have a median rms sensitivity of 95 μJy beama 1, and we estimate a Stokes I to Stokes V leakage of 0.056%. Our linear polarisation (Stokes Q and Stokes U) image cubes consist of 480a A a 97.6 kHz wide planes and have a median rms sensitivity per plane of 10.8 mJy beama 1 at 4a and 2.2 mJy beama 1 at 20a; we estimate the Stokes I to Stokes Q/U leakage to be approximately 0.2%. Here we characterise and publicly release our Stokes I, Q, U and V images in addition to the calibrated uv-data to facilitate the thorough scientific exploitation of this unique dataset.
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3.
  • Fan, W., et al. (författare)
  • Function block-based closed-loop adaptive machining for assembly interfaces of large-scale aircraft components
  • 2020
  • Ingår i: Robotics and Computer-Integrated Manufacturing. - : Elsevier. - 0736-5845 .- 1879-2537. ; 66
  • Tidskriftsartikel (refereegranskat)abstract
    • To guarantee the docking accuracy of large-scale components, their assembly interfaces usually need to be finished before the final assembly. However, there are some crucial problems affecting finishing efficiency and quality, e.g. use of hard-to-machine material at the assembly interface, manual interventions and process diversity in finish machining, difficulties in the alignment of the large component, as well as errors between the as-built and as-designed status of the large component. These problems significantly enhance the uncertainty in finish machining on a shop floor. To solve these problems, this paper proposes an approach of adaptive process planning and execution, i.e., IEC 61499 Function Block (FB) based Closed-Loop Adaptive Machining (CLAM). Thus, the adaptive alignment of the large component is achieved, which can guarantee the correct location between the assembly interface and the cutting tool. As well as the on-line CLAM of the assembly interface is also realized to improve the machining efficiency and quality. As a result, a FB based CLAM system for the assembly interfaces is established, which contains a CAD system, a FB enabled High-Level Controller (HLC), and several Low-Level Controllers (LLCs), as well as a mechanical system. The most notable is that the related FBs are designed to plan and execute the finishing process. Finally, the proposed method and system are validated by a large component from a real aviation industry, i.e., a vertical tail of a passenger aircraft. The experimental results indicate that the proposed method and system are feasible and effective to address the above-mentioned problems.
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4.
  • Xia, Yuxin, et al. (författare)
  • Inverted all-polymer solar cells based on a quinoxaline-thiophene/naphthalene-diimide polymer blend improved by annealing
  • 2016
  • Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:10, s. 3835-3843
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated the effect of thermal annealing on the photovoltaic parameters of all-polymer solar cells based on a quinoxaline-thiophene donor polymer (TQ1) and a naphthalene diimide acceptor polymer (N2200). The annealed devices show a doubled power conversion efficiency compared to nonannealed devices, due to the higher short-circuit current (J(sc)) and fill factor (FF), but with a lower open circuit voltage (V-oc). On the basis of the morphology-mobility examination by several scanning force microscopy techniques, and by grazing-incidence wide-angle X-ray scattering, we conclude that better charge transport is achieved by higher order and better interconnected networks of the bulk heterojunction in the annealed active layers. The annealing improves charge transport and extends the conjugation length of the polymers, which do help in charge generation and meanwhile reduce recombination. Photoluminescence, electroluminescence, and light intensity dependence measurements reveal how this morphological change affects charge generation and recombination. As a result, the J(sc) and FF are significantly improved. However, the smaller band gap and the higher HOMO level of TQ1 upon annealing causes a lower V-oc. The blend of an amorphous polymer TQ1, and a semi-crystalline polymer N2200, can thus be modified by thermal annealing to double the power conversion efficiency.
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5.
  • Zhang, Yang, et al. (författare)
  • Planning and operation of an integrated energy system in a Swedish building
  • 2019
  • Ingår i: Energy Conversion and Management. - : Elsevier. - 0196-8904 .- 1879-2227. ; 199
  • Tidskriftsartikel (refereegranskat)abstract
    • More flexibility measures are required due to the increasing capacities of variable renewable energies (VRE). In buildings, the integration of energy supplies forms integrated energy systems (IES). IESs can provide flexibility and increase the VRE penetration level. To upgrade a current building energy system into an IES, several energy conversion and storage components are needed. How to decide the component capacities and operate the IES were investigated separately in studies on system planning and system operation. However, a research gap exists that the system configuration from system planning is not validated by actual operation conditions in system operation. Meanwhile, studies on system operation assume that IES configurations are predetermined. This work combines system planning and system operation. The IES configuration is determined by mixed integer linear programming in system planning. Actual operation conditions and forecast errors are considered in system operation. The actual operation profiles are obtained through year-round simulations of different energy management systems. The results indicate that the system configuration from system planning can meet energy demands in system operation. Among different energy management systems, the combination of robust optimization and receding horizon optimization achieves the lowest yearly operation cost. Meanwhile, two scenarios that represent high and low forecast accuracies are studied. Under the high and low forecast accuracy scenarios, the yearly operation costs are about 4% and 6% higher than that obtained from system planning.
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6.
  • Li, W., et al. (författare)
  • Probabilistic shaping-assisted bit-energy efficient THz photonic wireless transmission
  • 2019
  • Ingår i: IET Conference Publications. - : Institution of Engineering and Technology.
  • Konferensbidrag (refereegranskat)abstract
    • We experimentally demonstrate a transmission of beyond 60 Gbit/s probabilistically shaped 16-QAM signals over a 4.5 m 350 GHz photonic wireless link, achieving a reduced energy consumption per bit of 1.38e-17 J/bit/m compared to the uniform format. 
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7.
  • Liu, X., et al. (författare)
  • Effect of burner geometry on swirl stabilized methane/air flames : A joint LES/OH-PLIF/PIV study
  • 2017
  • Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 207, s. 533-546
  • Tidskriftsartikel (refereegranskat)abstract
    • Large eddy simulation (LES) using a transported PDF model and OH-PLIF/PIV experiments were carried out to investigate the quarl effects on the structures of swirl stabilized methane/air flames. Two different quarls were investigated, one straight cylindrical quarl and one diverging conical quarl. The experiments show that the flames are significantly different with the two quarls. With the straight cylindrical quarl a compact blue flame is observed while with the diverging conical quarl the flame appears to be long and yellow indicating a sooty flame structure. The PIV results show the formation of a stronger flow recirculation inside the diverging conical quarl than that in the straight quarl. LES results reveal further details of the flow and mixing process inside the quarl. The results show that with the diverging quarl vortex breakdown occurs much earlier towards the upstream of the quarl. As a result the fuel is convected into the air flow tube and a diffusion flame is stabilized inside the air flow tube upstream the quarl. With the straight quarl, vortex breakdown occurs at a downstream location in the quarl. The scalar dissipation rate in the shear layer of the fuel jet is high, which prevents the stabilization of a diffusion flame in the proximity of the fuel nozzle; instead, a compact partially premixed flame with two distinct heat release layers is stablized in a downstream region in the quarl, which allows for the fuel and air to mix in the quarl before combustion and a lower formation rate of soot. The results showed that the Eulerian Stochastic Fields transported PDF method can well predict the details of the swirl flame dynamics.
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8.
  • Chen, H., et al. (författare)
  • Unprecedented non-hysteretic superelasticity of [001]-oriented NiCoFeGa single crystals
  • 2020
  • Ingår i: Nature Materials. - : Nature Research. - 1476-1122 .- 1476-4660.
  • Tidskriftsartikel (refereegranskat)abstract
    • Superelasticity associated with the martensitic transformation has found a broad range of engineering applications1,2. However, the intrinsic hysteresis3 and temperature sensitivity4 of the first-order phase transformation significantly hinder the usage of smart metallic components in many critical areas. Here, we report a large superelasticity up to 15.2% strain in [001]-oriented NiCoFeGa single crystals, exhibiting non-hysteretic mechanical responses, a small temperature dependence and high-energy-storage capability and cyclic stability over a wide temperature and composition range. In situ synchrotron X-ray diffraction measurements show that the superelasticity is correlated with a stress-induced continuous variation of lattice parameter accompanied by structural fluctuation. Neutron diffraction and electron microscopy observations reveal an unprecedented microstructure consisting of atomic-level entanglement of ordered and disordered crystal structures, which can be manipulated to tune the superelasticity. The discovery of the large elasticity related to the entangled structure paves the way for exploiting elastic strain engineering and development of related functional materials. 
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9.
  • Du, A., et al. (författare)
  • On the hardness and elastic modulus of phases in SiC-reinforced Al composite : Role of La and Ce addition
  • 2021
  • Ingår i: Materials. - : MDPI. - 1996-1944 .- 1996-1944. ; 14:21
  • Tidskriftsartikel (refereegranskat)abstract
    • The use of silicon carbide particles (SiCp) as reinforcement in aluminium (Al)-based composites (Al/SiCp) can offer high hardness and high stiffness. The rare-earth elements like lanthanum (La) and cerium (Ce) and transition metals like nickel (Ni) and copper (Cu) were added into the matrix to form intermetallic phases; this is one way to improve the mechanical property of the composite at elevated temperatures. The α-Al15 (Fe,Mn)3 Si2, Al20 (La,Ce)Ti2, and Al11 (La,Ce)3, π-Al8 FeMg3 Si6 phases are formed. Nanoindentation was employed to measure the hardness and elastic modulus of the phases formed in the composite alloys. The rule of mixture was used to predict the modulus of the matrix alloys. The Halpin–Tsai model was applied to calculate the elastic modulus of the particle-reinforced composites. The transition metals (Ni and Cu) and rare-earth elements (La and Ce) determined a 5–15% increase of the elastic modulus of the matrix alloy. The SiC particles increased the elastic modulus of the matrix alloy by 10–15% in composite materials.
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10.
  • Du, A., et al. (författare)
  • Role of matrix alloy, reinforcement size and fraction in the sliding wear behaviour of Al-SiCp MMCs against brake pad material
  • 2023
  • Ingår i: Wear. - : Elsevier. - 0043-1648 .- 1873-2577. ; 530-531
  • Tidskriftsartikel (refereegranskat)abstract
    • Aluminium metal matrix composites were produced by a newly developed stirring device for stir casting with different matrix alloys, SiC particle fractions and sizes to investigate these parameters' influence on the materials' wear performance. The wear performance of the composites was evaluated with dry sliding pin-on-plate tests against a high-speed train brake pad, and the study of wear surfaces was completed by electron microscopy. The formation of an iron-based tribolayer during wear protected the metal matrix composite from further wear damage. The composite reinforced with 19% SiC particles sized 32 μm showed an increasing coefficient of friction during wear, and the wear surface showed traces of third body wear. The rare earth and transition metal added to the matrix alloy increased the hardness of the composite, and the intermetallic phases reduced the development of the Fe-based tribolayer. The composites with small SiC particles presented the Fe transfer on the exposed aluminium surface, with a lower wear rate and friction coefficient than other composites. The direct comparison of composites produced with different sizes of SiC particles highlighted that the relationship between the wear rate and the coefficient of friction of the composites and the brake pad showed a linear trend.
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  • Resultat 1-10 av 26

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