| 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. |
- Zhu, Z, et al.
(författare)
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Vapor-solid-solid grown Ge nanowires at integrated circuit compatible temperature by molecular beam epitaxy
- 2017
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 122:9, s. 94304-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate Au-assisted vapor-solid-solid (VSS) growth of Ge nanowires (NWs) by molecular beam epitaxy at the substrate temperature of similar to 180 degrees C, which is compatible with the temperature window for Si-based integrated circuit. Low temperature grown Ge NWs hold a smaller size, similar uniformity, and better fit with Au tips in diameter, in contrast to Ge NWs grown at around or above the eutectic temperature of Au-Ge alloy in the vapor-liquid-solid (VLS) growth. Six growth orientations were observed on Ge (110) by the VSS growth at similar to 180 degrees C, differing from only one vertical growth direction of Ge NWs by the VLS growth at a high temperature. The evolution of NWs dimension and morphology from the VLS growth to the VSS growth is qualitatively explained by analyzing the mechanism of the two growth modes.
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| 3. |
- Zhong, T., et al.
(författare)
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Assessment of solar photovoltaic potentials on urban noise barriers using street-view imagery
- 2021
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Ingår i: Renewable energy. - : Elsevier Ltd. - 0960-1481 .- 1879-0682. ; 168, s. 181-194
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Tidskriftsartikel (refereegranskat)abstract
- Solar energy captured by solar photovoltaic (PV) systems has great potential to meet the high demand for renewable energy sources in urban areas. A photovoltaic noise barrier (PVNB) system, which integrates a PV system with a noise barrier, is a promising source for harvesting solar energy to overcome the problem of having limited land available for solar panel installations. When estimating the solar PV potential at the city scale, it is difficult to identify sites for installing solar panels. A computational framework is proposed for estimating the solar PV potential of PVNB systems based on both existing and planned noise barrier sites. The proposed computational framework can identify suitable sites for installing photovoltaic panels. A deep learning-based method is used to detect existing noise barrier sites from massive street-view images. The planned noise barrier sites are identified with urban policies. Based on the existing and planned sites of noise barriers in Nanjing, the annual solar PV potentials in 2019 are 29,137 MW h and 113,052 MW h, respectively. The estimation results show that the potential PVNB systems based on the existing and planned noise barrier in 2019 have the potential installed capacity of 14.26 MW and 57.24 MW, with corresponding potential annual power generation of 4662 MW h and 18,088 MW h, respectively.
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| 4. |
- Han, Y., et al.
(författare)
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A comparative study of selective dry and wet etching of germanium-tin (Ge1-xSnx) on germanium
- 2018
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 33:8
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Tidskriftsartikel (refereegranskat)abstract
- A comparative study of selective dry and wet etching methods for germanium-tin (Ge1-xSnx) alloys (3.5% < x < 7.7%) and germanium (Ge) is carried out. Both etching methods are optimized from the perspectives of selectivity and morphology, and then compared. A special behavior of the selective dry etching process is discovered and explained, whereby the selectivity has a dramatic increase to as high as 336 when the Sn concentration is above 6%. Different morphologies of suspended microstructures fabricated by different etching methods are investigated. Comparative study shows that the selective dry etching is a better choice for high Sn concentration GeSn (above 7%) against Ge to have better morphology, selectivity and verticality. While for low Sn concentration GeSn (below 6%), wet etching is a better way to fabricate a suspended GeSn microstructure on Ge. This work provides a comparative understanding of both methods of selective etching for GeSn. This comparative understanding is expected to be applied in the processing of next generation electronic and photonic devices.
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| 5. |
- Bao, J., et al.
(författare)
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Performance analysis of uplink sparse code multiple access with iterative multiuser receiver
- 2017
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Ingår i: 2017 IEEE International Conference on Communications, ICC 2017. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781467389990
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Konferensbidrag (refereegranskat)abstract
- This paper investigates the asymptotic performance of bit-interleaved coded modulation (BICM) with iterative multiuser detection and decoding in uplink sparse code multiple access (SCMA) systems. The extrinsic information transfer (EXIT) characteristics analysis of the joint multiuser detector for SCMA is provided, and shows that the average detection reliability for multiple users converges to the single-user case, if ideal feedback from the decoder is available to the detector. We develop a tight analytical bound on the convolutionally encoded bit-error rate (BER) for independent Rayleigh fadings, based on the single-user bound with arbitrary multidimensional constellations. Moreover, we analyze the achievable coding and diversity gains of the SCMA-BICM system with iterative receiver. Simulations are carried out to verify the effectiveness of the analysis.
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| 6. |
- Han, Delong, et al.
(författare)
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Analysis of Raman scattering from inclined GeSn/Ge dual-nanowire heterostructure on Ge(1 1 1) substrate
- 2019
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332. ; 463, s. 581-586
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the Raman spectra of GeSn/Ge dual-nanowire heterostructure grown on Ge(1 1 1) substrate are systematically analyzed within the framework of anisotropic elasticity and lattice dynamical theory. Based on the experimental samples grown by molecular beam epitaxy, the partially covered dual nanowires standing along 〈1 1 0〉 direction are modeled and the heterostructure presents effective elastic strain relaxation due to the free surfaces. The simulations show that the Raman shift of GeSn nanowire is mainly affected by the Sn content while the influences of strain become less important with the increase of thickness ratio. For Ge nanowire, the peak of Raman spectrum merely moves with Sn content, but the spectrum possesses asymmetric broadening induced by the non-uniform strain distribution. The red-shift and intensity reduction of the total Raman spectrum of dual nanowires are observed when the Sn content increases. Moreover, an analytic fitting expression for Raman peak position is obtained based on the numerical results and is expected to serve as a reference to estimate the Sn content in GeSn/Ge dual-nanowire heterostructure.
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| 7. |
- Bao, J., et al.
(författare)
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Joint Multiuser Detection of Multidimensional Constellations over Fading Channels
- 2017
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Ingår i: IEEE Transactions on Communications. - : IEEE Press. - 0090-6778 .- 1558-0857. ; 65:1, s. 161-172
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the error performance of multidimensional constellations in the multiple access and broadcast channels. More specifically, we provide closed-form expressions for the pairwise error probability (PEP) of the joint maximum likelihood detection, for multiuser signaling in the presence of additive white Gaussian noise and Rayleigh fading. Arbitrary numbers of users and multidimensional signal sets are assumed, while the provided formula for the PEP is a function of the dimension-wise distances of the multidimensional constellation. Furthermore, a useful upper bound on the average symbol error probability is also obtained through the union bound. The analysis is applied to the sparse code multiple access systems. The analytical results are validated successfully through simulations, and show their importance in the multidimensional constellation design.
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| 8. |
- Han, Y., et al.
(författare)
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Suspended GeSn microstructure for light source on Si
- 2017
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Ingår i: 2017 IEEE Photonics Society Summer Topicals Meeting Series, SUM 2017, San Juan, Puerto Rico, 10-12 July 2017. - 9781509065707 ; , s. 69-70
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Konferensbidrag (refereegranskat)abstract
- A novel suspended GeSn microstructure is demonstrated by selective etching of GeSn thin film on Ge. XRD and ?-Raman measurements show that the compressive strain in the GeSn thin film is effectively relaxed, and furthermore, unexpected tensile strain was introduced in the suspended GeSn.
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| 9. |
- Huang, Y. Z., et al.
(författare)
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Nanowire-supported plasmonic waveguide for remote excitation of surface-enhanced Raman scattering
- 2014
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Ingår i: Light: Science and Applications. - : Springer Science and Business Media LLC. - 2047-7538 .- 2095-5545. ; 3, s. Art. no. e199-
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Forskningsöversikt (refereegranskat)abstract
- Due to its amazing ability to manipulate light at the nanoscale, plasmonics has become one of the most interesting topics in the field of light-matter interaction. As a promising application of plasmonics, surface-enhanced Raman scattering (SERS) has been widely used in scientific investigations and material analysis. The large enhanced Raman signals are mainly caused by the extremely enhanced electromagnetic field that results from localized surface plasmon polaritons. Recently, a novel SERS technology called remote SERS has been reported, combining both localized surface plasmon polaritons and propagating surface plasmon polaritons (PSPPs, or called plasmonic waveguide), which may be found in prominent applications in special circumstances compared to traditional local SERS. In this article, we review the mechanism of remote SERS and its development since it was first reported in 2009. Various remote metal systems based on plasmonic waveguides, such as nanoparticle-nanowire systems, single nanowire systems, crossed nanowire systems and nanowire dimer systems, are introduced, and recent novel applications, such as sensors, plasmon-driven surface-catalyzed reactions and Raman optical activity, are also presented. Furthermore, studies of remote SERS in dielectric and organic systems based on dielectric waveguides remind us that this useful technology has additional, tremendous application prospects that have not been realized in metal systems.
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| 10. |
- Li, Y., et al.
(författare)
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Novel group IV nano- and micro-structures for light sources on silicon
- 2017
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Ingår i: 2017 IEEE Photonics Society Summer Topicals Meeting Series, SUM 2017; San Juan Marriott ResortSan Juan; Puerto Rico; 10 July 2017 through 12 July 2017. - 9781509065707 ; , s. 43-44
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Konferensbidrag (refereegranskat)abstract
- We present our recent researches on novel group IV nano- and micro-structures for potential light sources on Si, including the tensile strained Ge quantum dots (QDs), GeSn thin films and microstructures, and Ge(Sn) nanowires. Tensile-strained Ge QDs were grown by SS-MBE, and photoluminescence was achieved. The GeSn thin films were demonstrated with Sn concentration above the bandgap transition critical point, and partially suspended GeSn microstructures were fabricated for relaxing the compressive strain.
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