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- 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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- Wang, S. T., et al.
(författare)
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A Fully Conjugated 3D Covalent Organic Framework Exhibiting Band-like Transport with Ultrahigh Electron Mobility
- 2021
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Ingår i: Angewandte Chemie-International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 133:17, s. 9407-9411
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Tidskriftsartikel (refereegranskat)abstract
- Although pi-conjugated two dimensional (2D) covalent organic frameworks (COFs) have been extensively reported, developing fully pi-conjugated 3D COFs is still an extremely difficult problem due to the lack of fully pi-conjugated 3D linkers. We synthesize a fully conjugated 3D COF (BUCT-COF-1) by designing a saddle-shaped building block of aldehyde-substituted cyclooctatetrathiophene (COThP)-CHO. As a consequence of the fully conjugated 3D network, BUCT-COF-1 demonstrates ultrahigh Hall electron mobility up to approximate to 3.0 cm(2) V-1 s(-1) at room temperature, which is one order of magnitude higher than the current pi-conjugated 2D COFs. Temperature-dependent conductivity measurements reveal that the charge carriers in BUCT- COF-1 exhibit the band-like transport mechanism, which is entirely different from the hopping transport phenomena observed in common organic materials. The findings indicate that fully conjugated 3D COFs can achieve electron delocalization and charge-transport pathways within the whole 3D skeleton, which may open up a new frontier in the design of organic semiconducting materials.
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- Yang, Y. -G, et al.
(författare)
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Effects of strain rate on austenite stability and mechanical properties in a 5Mn steel
- 2021
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Ingår i: Journal of Iron and Steel Research International. - : Springer Nature. - 1006-706X .- 2210-3988.
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Tidskriftsartikel (refereegranskat)abstract
- The austenite stability and the mechanical properties in a typical medium Mn grade steel, i.e., 5Mn steel, were investigated under a wide range of strain rates through the combination of experimental and theoretical methodologies. The obtained results indicate that austenite is more stable at a high strain rate, which is due to the suppression of the austenite to martensite transformation. This suppression is attributed to the increased stacking fault energy and the high deformation energy barrier. Moreover, the suppression of martensitic transformation also leads to the decrease in the ultimate tensile strength and the uniform elongation. Owing to the increase in an adiabatic heating temperature, an increase in the uniform elongation is acquired at a high strain rate. The obtained fundamental study results shed light on a wide application of the medium Mn steel under different strain rate conditions.
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- Zhao, G-H, et al.
(författare)
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Alloy design by tailoring phase stability in commercial Ti alloys
- 2021
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 815
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical characteristics and the operative deformation mechanisms of a metallic alloy can be optimised by explicitly controlling phase stability. Here an integrated thermoelastic and pseudoelastic model is presented to evaluate the beta stability in Ti alloys. The energy landscape of beta ->alpha ' /alpha '' martensitic transformation was expressed in terms of the dilatational and transformational strain energy, the Gibbs free energy change, the external mechanical work as well as the internal frictional resistance. To test the model, new alloys were developed by tailoring two base alloys, Ti-6Al-4V and Ti-6Al-7Nb, with the addition of beta-stabilising element Mo. The alloys exhibited versatile mechanical behaviours with enhanced plasticity. Martensitic nucleation and growth was fundamentally dominated by the competition between elastic strain energy and chemical driving force, where the latter term tends to lower the transformational energy barrier. The model incorporates thermodynamics and micromechanics to quantitatively investigate the threshold energy for operating transformation-induced plasticity and further guides alloy design.
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