| 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. |
- Algaba, Juan-Carlos, et al.
(författare)
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Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign
- 2021
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 911:1
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Forskningsöversikt (refereegranskat)abstract
- In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ∼6.5 × 109 M o˙. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87's spectrum. We can exclude that the simultaneous γ-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded.
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| 3. |
- Annadi, A., et al.
(författare)
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Anisotropic two-dimensional electron gas at the LaAlO3/SrTiO3 (110) interface
- 2013
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- The observation of a high-mobility two-dimensional electron gas between two insulating complex oxides, especially LaAlO3/SrTiO3, has enhanced the potential of oxides for electronics. The occurrence of this conductivity is believed to be driven by polarization discontinuity, leading to an electronic reconstruction. In this scenario, the crystal orientation has an important role and no conductivity would be expected, for example, for the interface between LaAlO3 and (110)-oriented SrTiO3, which should not have a polarization discontinuity. Here we report the observation of unexpected conductivity at the LaAlO3/SrTiO3 interface prepared on (110)-oriented SrTiO3, with a LaAlO3-layer thickness-dependent metal-insulator transition. Density functional theory calculation reveals that electronic reconstruction, and thus conductivity, is still possible at this (110) interface by considering the energetically favourable (110) interface structure, that is, buckled TiO2/LaO, in which the polarization discontinuity is still present. The conductivity was further found to be strongly anisotropic along the different crystallographic directions with potential for anisotropic superconductivity and magnetism, leading to possible new physics and applications.
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| 4. |
- Cheng, X-P, et al.
(författare)
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Compact Bright Radio-loud AGNs. III. A Large VLBA Survey at 43 GHz
- 2020
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Ingår i: Astrophysical Journal, Supplement Series. - : American Astronomical Society. - 1538-4365 .- 0067-0049. ; 247:2
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Tidskriftsartikel (refereegranskat)abstract
- We present the results from the 43 GHz Very Long Baseline Array (VLBA) observations of 124 compact radio-loud active galactic nuclei (AGNs) that were conducted between 2014 November and 2016 May. The typical dimensions of the restoring beam in each image are about 0.5 mas x 0.2 mas. The highest resolution of 0.2 mas corresponds to a physical size of 0.02 pc for the lowest redshift source in the sample. The 43 GHz very long baseline interferometry (VLBI) images of 97 AGNs are presented for the first time. We study the source compactness on milliarcsecond and submilliarcsecond scales, and suggest that 95 sources in our sample are suitable for future space VLBI observations. By analyzing our data supplemented with other VLBA AGN surveys from the literature, we find that the core brightness temperature increases with increasing frequency below a break frequency similar to 7 GHz, and decreases between similar to 7 and 240 GHz but increases again above 240 GHz in the rest frame of the sources. This indicates that the synchrotron opacity changes from optically thick to thin. We also find a strong statistical correlation between radio and gamma-ray flux densities. Our correlation is tighter than those in the literature derived from lower-frequency VLBI data, suggesting that the gamma-ray emission is produced more cospatially with the 43 GHz VLBA core emission. This correlation can also be extrapolated to the unbeamed AGN population, implying that a universal gamma-ray production mechanism might be at work for all types of AGNs.
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| 5. |
- L.Q.Zhang,, et al.
(författare)
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Fabrication of novel unipolar nanodiodes in InAs/AlSb for microwave detection
- 2011
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Ingår i: Infrared, Millimeter and Terahertz Waves (IRMMW-THz), 2011 36th International Conference on. - 2162-2027. - 9781457705083 ; :2-7 Oct. 2011, s. 1-2
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Konferensbidrag (refereegranskat)abstract
- Abstract—We report on the fabrication of unipolar nanodiodes into an InAs/AlxGa1-xSb quantum-well heterostructure for room temperature microwave detection up to 110 GHz. Electron-beam lithography was combined with both dry- and wet-etching, and we explored the differences in the electric and detection parameters with the two methods.
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| 6. |
- Pelliciari, Jonathan, et al.
(författare)
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Evolution of spin excitations from bulk to monolayer FeSe
- 2021
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- In ultrathin films of FeSe grown on SrTiO (FeSe/STO), the superconducting transition temperature T is increased by almost an order of magnitude, raising questions on the pairing mechanism. As in other superconductors, antiferromagnetic spin fluctuations have been proposed to mediate SC making it essential to study the evolution of the spin dynamics of FeSe from the bulk to the ultrathin limit. Here, we investigate the spin excitations in bulk and monolayer FeSe/STO using resonant inelastic x-ray scattering (RIXS) and quantum Monte Carlo (QMC) calculations. Despite the absence of long-range magnetic order, bulk FeSe displays dispersive magnetic excitations reminiscent of other Fe-pnictides. Conversely, the spin excitations in FeSe/STO are gapped, dispersionless, and significantly hardened relative to its bulk counterpart. By comparing our RIXS results with simulations of a bilayer Hubbard model, we connect the evolution of the spin excitations to the Fermiology of the two systems revealing a remarkable reconfiguration of spin excitations in FeSe/STO, essential to understand the role of spin fluctuations in the pairing mechanism.
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| 7. |
- Wang, Keqing, et al.
(författare)
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Ultrasonic-Aided Fabrication of Nanostructured Au-Ring Microelectrodes for Monitoring Transmitters Released from Single Cells
- 2017
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 89:17, s. 8683-8688
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Tidskriftsartikel (refereegranskat)abstract
- We report a novel ultrasonic-aided fast and straightforward approach to fabricate Au microelectrodes by electroless deposition of nanostructured gold films on the rigid outer surface of pulled glass capillaries. Microelectrodes with tip diameters ranging from several hundred nanometers to several micrometers were fabricated within 20 min via three sequential ultrasonication steps. The ultrasonication technique has been validated to be a very effective route in engineering the morphology of Au film surfaces and improves the fabrication efficiency of Au microelectrodes. The nanostructured surfaces of the Au microelectrodes demonstrate excellent sensing activity and antifouling for dopamine oxidation. The microelectrodes were applied for measurement of catecholamines released from exocytosis events from single chromaffin cells and exhibited faster dynamic peak parameters, compared with carbon fiber microelectrodes. This report provides a generally accessible and complementary platform for analyzing catecholamines release events, which should be useful for new electrode designs and neurochemical sensing.
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| 8. |
- Wang, Q., et al.
(författare)
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Uniaxial pressure induced stripe order rotation in La 1.88 Sr 0.12 CuO 4
- 2022
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Static stripe order is detrimental to superconductivity. Yet, it has been proposed that transverse stripe fluctuations may enhance the inter-stripe Josephson coupling and thus promote superconductivity. Direct experimental studies of stripe dynamics, however, remain difficult. From a strong-coupling perspective, transverse stripe fluctuations are realized in the form of dynamic “kinks”—sideways shifting stripe sections. Here, we show how modest uniaxial pressure tuning reorganizes directional kink alignment. Our starting point is La1.88Sr0.12CuO4 where transverse kink ordering results in a rotation of stripe order away from the crystal axis. Application of mild uniaxial pressure changes the ordering pattern and pins the stripe order to the crystal axis. This reordering occurs at a much weaker pressure than that to detwin the stripe domains and suggests a rather weak transverse stripe stiffness. Weak spatial stiffness and transverse quantum fluctuations are likely key prerequisites for stripes to coexist with superconductivity.
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| 9. |
- Willander, Magnus, 1948-, et al.
(författare)
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Excitonic effects in ZnO nanowires and hollow nanotubes
- 2007
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Ingår i: Proceedings of SPIE, the International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 6486:648614
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Tidskriftsartikel (refereegranskat)abstract
- Energy levels and wave functions of ground and excited states of an exciton are calculated by the method of imaginary time. Energy levels as functions of radius of single and double wall nanotube are studied. Asymptotic behavior of energy levels at large and small values of the radius using perturbation theory and adiabatic approximation is considered. Spatially indirect exciton in semiconductor nanowire is also investigated. Experimental result from high quality reproducible ZnO nanowires grown by low temperature chemical engineering is presented. State of the art high brightness white light emitting diodes (HB-LEDs) are demonstrated from the grown ZnO nano-wires. The color temperature and color rendering index (CRI) of the HB-LEDs values was found to be (3250 K, 82), and (14000 K, 93), for the best LEDs, which means that the quality of light is superior to one obtained from GaN LEDs available on the market today. The role of VZn and Vo on the emission responsible for the white light band as well as the peak position of this important wide band is thoroughly investigated in a systematic way.
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| 10. |
- Zhang, M., et al.
(författare)
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Identification of geranylgeranyl diphosphate synthase genes from Tripterygium wilfordii
- 2015
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Ingår i: Plant Cell Reports. - : Springer Science and Business Media LLC. - 0721-7714 .- 1432-203X. ; 34:12, s. 2179-2188
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Tidskriftsartikel (refereegranskat)abstract
- We found triptolide synthesis is correlated with the expressions of TwGGPPS1 and TwGGPPS4 . This lays the foundation for future studies of biosynthetic pathways for triptolide and other diterpenoids in T. wilfordii. Tripterygium wilfordii is a traditional Chinese medical plant commonly used to treat rheumatoid arthritis. One of its main bioactive compounds is triptolide, which is identified as an abietane-type diterpenoid natural product. Geranylgeranyl diphosphate synthase (GGPPS) catalyses the synthesis of GGPP (geranylgeranyl diphosphate), the common precursor of diterpenes, and is therefore a crucial enzyme in diterpene biosynthesis. A previous study showed that GGPP could be catalyzed by copalyl diphosphate synthase and kaurene synthase like of Salvia miltiorrhiza (SmCPS, SmKSL) to miltiradiene, a key intermediate in tanshinone biosynthesis. In this paper, five new full-length cDNAs (TwGGPPS) encoding GGPP synthases were cloned from T. wilfordii. Sequence comparisons revealed that all six TwGGPPSs (including TwGGPPS2 cloned previously) exhibit similarities to GGPPSs of other plants. Subsequent functional complement assays demonstrated that TwGGPPS1, TwGGPPS4 and TwGGPPS5 can participate in miltiradiene biosynthesis in the recombinant E. coli. Correlation analysis of gene expressions and secondary metabolite accumulation indicated that TwGGPPS1 and TwGGPPS4 are likely involved in the biosynthesis of triptolide. These findings lay the foundation for future studies of the biosynthetic pathways for triptolide and other diterpenoids in T. wilfordii.
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