| 1. |
- Liu, Wei, et al.
(författare)
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Coherent dynamics of multi-spin V-B(-) center in hexagonal boron nitride
- 2022
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Ingår i: Nature Communications. - : Nature Portfolio. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Hexagonal boron nitride (hBN) has recently been demonstrated to contain optically polarized and detected electron spins that can be utilized for implementing qubits and quantum sensors in nanolayered-devices. Understanding the coherent dynamics ofmicrowave driven spins in hBN is of crucial importance for advancing these emerging new technologies. Here, we demonstrate and study the Rabi oscillation and related phenomena of a negatively charged boron vacancy (V-B(-)) spin ensemble in hBN. We report on different dynamics of the V-B(-) spins at weak and strong magnetic fields. In the former case the defect behaves like a single electron spin system, while in the latter case it behaves like a multi-spin system exhibiting multiple-frequency dynamical oscillation as beat in the Ramsey fringes. We also carry out theoretical simulations for the spin dynamics of V-B(-) and reveal that the nuclear spins can be driven via the strong electron nuclear coupling existing in V-B(-) center, which can be modulated by the magnetic field and microwave field.
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| 2. |
- Chen, Jun-Tong, et al.
(författare)
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Corydalis sunhangii (Papaveraceae) : A new species from Xizang, China, based on plastome and morphological data
- 2024
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Ingår i: Ecology and Evolution. - : John Wiley & Sons. - 2045-7758. ; 14:4
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Tidskriftsartikel (refereegranskat)abstract
- A new species of Papaveraceae, Corydalis sunhangii, in the section Trachycarpae, is described and illustrated from Nyingchi City, Xizang, China. The new species has some resemblance to Corydalis kingdonis, but differs by radical leaves prominent, usually several, blade tripinnate (vs. insignificant, few, blade bi- to triternate); cauline leaf usually one, much smaller than radical leaves, usually situated in lower half of stem (vs. usually two, larger than radical leaves, concentrated in upper third of stem); racemes densely 13-35-flowered (vs. rather lax, 4-11-flowered); claw of lower petal shallowly saccate (vs. very prominently and deeply saccate); capsule oblong, with raised lines of dense papillae (vs. broadly obovoid, smooth). Phylogenetic analysis, based on 68 protein-coding plastid genes of 49 samples, shows that C. sunhangii is not closely related to any hitherto described species, which is consistent with our morphological analysis.
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| 3. |
- Depalo, Francesco, et al.
(författare)
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Effects of dynamic axial stiffness of elastic moorings for a wave energy converter
- 2022
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 251
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Tidskriftsartikel (refereegranskat)abstract
- This work studies the effects of the dynamic axial stiffness of elastic moorings on the dynamic behaviour of a point absorber wave energy converter. Following two mooring analysis procedures, coupled dynamic analysis of a taut-moored WEC with three legs is performed using the FEM program DeepC in three irregular wave conditions. Two synthetic fibre rope materials are investigated, i.e. a normally stiff polyester and a wire-lay 3-strand nylon rope. The results of WEC motions and mooring tensions obtained from a quasi-static stiffness model and the dynamic stiffness model are compared and discussed. The former analysis applies the non-linear stiffness working curves of the ropes in the simulations, while the latter utilizes the dynamic stiffness expression with an iterative process following a practical mooring analysis procedure. For the nylon rope, the influence of the load amplitude on the dynamic stiffness and the WEC response is presented and analysed. It was found that the quasi-static stiffness model tends to underestimate the maximum mooring tensions, leading to 30%–40% lower results compared to the one accounting for the dynamic stiffness effects. For the studied WEC system, the nylon rope shows advantages over polyester, because of the lower mooring tensions and higher WEC motions.
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| 4. |
- Jiang, Mingkai, et al.
(författare)
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The fate of carbon in a mature forest under carbon dioxide enrichment
- 2020
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 580:7802, s. 227-231
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric carbon dioxide enrichment (eCO2) can enhance plant carbon uptake and growth1–5, thereby providing an important negative feedback to climate change by slowing the rate of increase of the atmospheric CO2 concentration6. Although evidence gathered from young aggrading forests has generally indicated a strong CO2 fertilization effect on biomass growth3–5, it is unclear whether mature forests respond to eCO2 in a similar way. In mature trees and forest stands7–10, photosynthetic uptake has been found to increase under eCO2 without any apparent accompanying growth response, leaving the fate of additional carbon fixed under eCO2 unclear4,5,7–11. Here using data from the first ecosystem-scale Free-Air CO2 Enrichment (FACE) experiment in a mature forest, we constructed a comprehensive ecosystem carbon budget to track the fate of carbon as the forest responded to four years of eCO2 exposure. We show that, although the eCO2 treatment of +150 parts per million (+38 per cent) above ambient levels induced a 12 per cent (+247 grams of carbon per square metre per year) increase in carbon uptake through gross primary production, this additional carbon uptake did not lead to increased carbon sequestration at the ecosystem level. Instead, the majority of the extra carbon was emitted back into the atmosphere via several respiratory fluxes, with increased soil respiration alone accounting for half of the total uptake surplus. Our results call into question the predominant thinking that the capacity of forests to act as carbon sinks will be generally enhanced under eCO2, and challenge the efficacy of climate mitigation strategies that rely on ubiquitous CO2 fertilization as a driver of increased carbon sinks in global forests.
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| 5. |
- Johannesson, Pär, et al.
(författare)
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Mechanical reliability of flexible power cables for marine energy
- 2021
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Ingår i: Proceedings of the European Wave and Tidal Energy Conference. - : European Wave and Tidal Energy Conference Series. - 2706-6932 .- 2706-6940. ; , s. 2146-1-2146-10, s. 2146-1-2146-10
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Konferensbidrag (refereegranskat)abstract
- Marine power cables play a crucial role to utilize energy in marine areas, such as offshore wind, wave energy and tidal energy. Marine energy devices are typically grouped into arrays to increase the economic viability, and power cables transfer the energy from the devices to a central hub which is then transmitted ashore. Cables connected to moving devices may experience millions of load cycles per year, and thus they need to be flexible and designed for mechanical loads due to the movements of the cable. In this study, the focus is on the mechanical life of flexible cables connecting devices to hubs, and thus lowand medium voltage power cables is the focus. The reliability design method Variational Mode and Effect Analysis (VMEA) is applied that is based on identifying and quantifying different types of uncertainty sources, such as scatter, model uncertainties and statistical uncertainties. It implements a load-strength-approach that combines numerical simulations to assess the loads on the cable and experimental tests to assess the strength of the cable. The VMEA method is demonstrated for an evaluation of bending fatigue, and it has been found to be a useful tool to evaluate uncertainties in fatigue life for cables in WEC (Wave Energy Converter) systems during the design phase. The results give a firm foundation for evaluation of safety against fatigue and are also helpful for identifying weak spots in the reliability assessment that can motivate actions in the improvement process. Uncertainties in terms of scatter, statistical uncertainty and model uncertainty have been evaluated with respect to the WaveEL 3.0, a WEC designed by the company Waves4Power, and deployed in Runde, Norway. A major contribution to the overall uncertainty is found to originate from the fatigue life model, both in terms of scatter and model uncertainty.
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| 6. |
- Ringsberg, Jonas, 1971, et al.
(författare)
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Design of mooring solutions and array systems for point absorbing wave energy devices - Methodology and application
- 2020
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Ingår i: Journal of Offshore Mechanics and Arctic Engineering-Transactions of The Asme. - : American Society of Mechanical Engineers (ASME). - 0892-7219 .- 1528-896X. ; 142:3
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Tidskriftsartikel (refereegranskat)abstract
- Most of the ocean energy technologies are considered to be in a pre-commercial phase and need technical development. This study focuses on the design of mooring solutions and compares array systems of a specific floating point-absorbing wave energy converter (WEC) developed by the company Waves4Power. A full-scale prototype of the WEC is installed in Runde (Norway) where it is moored with three polyester mooring lines, each having one floater and one gravity anchor. Based on this reference installation, the method of systems engineering was used to propose 22 conceptual mooring solutions for different array systems. They were compared and reduced to four top concepts in a systematic elimination procedure using Pugh and Kesselring matrices. The top concepts were assessed in detail by means of levelized cost of energy (LCOE), life cycle analysis (LCA), and risk analyses. The fatigue life of the mooring lines and the energy capture were calculated using results obtained from coupled hydrodynamic and structure response analyses in the dnv-gl deepc software. Two final concepts were proposed for the water depths 75 and 200 m.
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| 7. |
- Ringsberg, Jonas, 1971, et al.
(författare)
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Mooring forces in a floating point-absorbing WEC system–a comparison between full-scale measurements and numerical simulations
- 2021
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Ingår i: Ships and Offshore Structures. - : Taylor and Francis Ltd.. - 1744-5302 .- 1754-212X. ; 15:S1, s. S70-S81
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Tidskriftsartikel (refereegranskat)abstract
- The study presents an investigation of Waves4Power’s WaveEL 3.0 wave energy converter (WEC). It was used as a reference for full-scale measurements of the mooring forces and buoy motions in a measurement campaign 2017 at an installation location off the coast of Runde in Norway. A numerical simulation model of the installation was developed in the DNV GL software SESAM. Unfortunately, the sea state conditions were not measured during the measurement campaign. Hence, a methodology was developed that used the recorded motion data to compute the sea state conditions at the test site. The simulated WEC motions based on the computed sea states agreed very well with the measured WEC motions. The measured and simulated mooring forces were compared under various environmental conditions. 3-hour sea state realizations are typically preferred in numerical simulations. However, influences from the tide at the test site showed that sea states were normally stationary for only 1–2 h. The measured and simulated average mooring forces agreed very well during 1-hour periods, whereas the simulations overestimated the mooring forces in 3-hour periods because of the tide. © 2020 The Author(s).
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| 8. |
- Ringsberg, Jonas, 1971, et al.
(författare)
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Opportunities with renewable wave energy and challenges in the design of floating wave energy converter systems
- 2021
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Ingår i: Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE. ; 9
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Konferensbidrag (refereegranskat)abstract
- Wave energy is one among several resources of renewable energy which needs to be utilized in the future to solve human’s energy demand. Several technologies have been proposed but yet there are few commercial concepts that have been connected to the grid. The floating wave energy converters (WECs) will have an important role in the supply of electricity in the future. But there are several challenges in their designs on systems and component levels that need to be overcome and solved. There are also challenges related to installation and maintenance. The current paper presents and discusses examples of challenges on component and systems level, with reference to floating WECs. One specific concept is studied in detail with an emphasis on mooring design, fatigue life of elastic mooring systems and umbilical cables, power performance of individual WECs vs WECs installed in wave parks. The levelized cost of electricity method is used to compare some configurations that have been studied in more detail. Examples of results from numerical simulations and full-scale measurements on a floating heave point-absorber are presented.
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| 9. |
- Wu, Kuan-Hsun, et al.
(författare)
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Considerations of SiP based Antenna in Package/Module (AiP/AiM) Design at Sub-Terahertz Frequencies for Potential B5G/6G Applications
- 2021
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Ingår i: Proceedings - Electronic Components and Technology Conference. - 0569-5503. ; , s. 1162-1168
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Konferensbidrag (refereegranskat)abstract
- Antenna-in-Package/Module (AiP/AiM) are the primary technologies to realize the RF subsystems for frequencies beyond millimeter-wave (mmW) bands, including sub-terahertz for potential B5G/6G applications. Due to the small wavelength, the mechanical process of the current system-in-package (SiP) results in limitations to realize antenna arrays at sub-terahertz. In this paper, the mechanical limits to cause radiation discrepancy is investigated by designing an AiP/AiM at 110 GHz band. Through the parametric studies based on the currently available cheap SiP process, one may summarize the considerations of AiP/AiM design for beyond sub-terahertz frequencies. The examination will consider the design of an 8x8 antenna array to provide a radiation gain of 20 dBi. Numerical full-wave simulations by HFSS were performed to obtain reliable behaviors of AiP/AiM radiations.
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| 10. |
- Yang, Shun-Han, 1987, et al.
(författare)
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Experimental and numerical investigation of a taut-moored wave energy converter : a validation of simulated mooring line forces
- 2021
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Ingår i: Ships and Offshore Structures. - : Taylor and Francis Ltd.. - 1744-5302 .- 1754-212X. ; 15:suppl 1
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Tidskriftsartikel (refereegranskat)abstract
- A reliable simulation model to calculate the motion and force responses of wave energy converters (WECs) is imperative to ensure the reliability and long-term performance of WEC systems; these aspects are fundamental to achieving full commercialisation of wave energy. A simulation model was developed and validated concerning the simulated WEC buoy motions in a previous study; this study validated the mooring force calculations for the same model. The example WEC system comprises a buoy, a power take-off (PTO) system, and a three-leg mooring system wherein each leg is divided into two taut segments joined by a submerged float. A 1:20 physical model was built and tested in the Deepwater Offshore Basin at Shanghai Jiao Tong University. Numerical models were developed to simulate the coupled hydrodynamic and structural responses of the WEC system, primarily using potential flow theory, the boundary element method, the finite element method, and the Morison equation. The simulated and measured axial force results at the top ends of the six mooring segments were compared; the results agreed best in the lower segments of each mooring leg and in the moorings on the downwind side because of the PTO system uncertainties and the uncalibrated damping in the numerical model. Nonetheless, the numerical model reasonably predicted the moorings’ accumulated fatigue damage, demonstrating that the model can be reliably used for mooring structural analyses. The study also used the validated numerical model to simulate a full-scale WEC system installed in Runde, Norway. A comparison of the results from the full-scale measurements and simulations shows that the numerical simulation model exhibited a good predictive capability for the mooring forces of the full-scale WEC system. © 2020, © 2020 The Author(s).
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