| 1. |
- Bielecki, Johan, 1982, et al.
(författare)
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Electrospray sample injection for single-particle imaging with x-ray lasers
- 2019
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Ingår i: Science advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 5:5
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of imaging single proteins constitutes an exciting challenge for x-ray lasers. Despite encouraging results on large particles, imaging small particles has proven to be difficult for two reasons: not quite high enough pulse intensity from currently available x-ray lasers and, as we demonstrate here, contamination of the aerosolized molecules by nonvolatile contaminants in the solution. The amount of contamination on the sample depends on the initial droplet size during aerosolization. Here, we show that, with our electrospray injector, we can decrease the size of aerosol droplets and demonstrate virtually contaminant-free sample delivery of organelles, small virions, and proteins. The results presented here, together with the increased performance of next-generation x-ray lasers, constitute an important stepping stone toward the ultimate goal of protein structure determination from imaging at room temperature and high temporal resolution.
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| 2. |
- Canton, Jacopo, et al.
(författare)
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Linear global stability of two incompressible coaxial jets
- 2017
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Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press. - 0022-1120 .- 1469-7645. ; 824, s. 886-911
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Tidskriftsartikel (refereegranskat)abstract
- The linear stability of two incompressible coaxial jets, separated by a thick duct wall, is investigated by means of both a modal and a non-modal approach within a global framework. The attention is focused on the range of unitary velocity ratios for which an alternate vortex shedding from the duct wall is known to dominate the flow. In spite of the inherent convective nature of jet flow instabilities, such behaviour is shown to originate from an unstable global mode of the dynamics linearised around the axisymmetric base flow. The corresponding wavemaker is located in the recirculating-flow region formed behind the duct wall. At the same time, the transient-growth analysis reveals that huge amplifications (up to 20 orders of magnitude) of small flow perturbations at the nozzle exit can occur in the subcritical regime, especially for high ratios between the outer and the inner velocities.
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| 3. |
- Marini, E., et al.
(författare)
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The intense production of silicates during the final AGB phases of intermediate mass stars
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 670
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Tidskriftsartikel (refereegranskat)abstract
- Context. The formation of silicates in circumstellar envelopes of stars evolving through the asymptotic giant branch (AGB) is still highly debated given the uncertainties affecting stellar evolution modelling, the description of the dust formation process, and the capability of silicate grains to accelerate stellar outflows via radiation pressure.Aims. We study the formation of dust in the winds of intermediate mass (M ≥ 4 M⊙) stars of solar metallicity while evolving through the AGB phase. We tested the different treatments of the mass-loss mechanism by this class of stars, with the aim of assessing their contribution to the general enrichment of silicates of the interstellar medium of galaxies and, on more general grounds, to the silicates budget of the Universe.Methods. We consider a sub-sample of AGB stars, whose spectral energy distribution (SED) is characterised by deep absorption features at 10 μm and 18 μm, which can be regarded as the class of stars providing the most relevant contribution to the silicates’ production across the Universe. Results from stellar evolution and dust formation modelling were used to fit the observed SED and to reproduce, at the same time, the detected pulsation periods and the derived surface chemical composition. This analysis leads to the derivation of tight constraints on the silicates’ production rates experienced by these sources during the final AGB stages.Results. Two out of the four sources investigated are interpreted as stars currently undergoing hot bottom burning (HBB), evolving through phases close to the stage when the mass-loss rate is largest. The remaining two stars are likely evolving through the very final AGB phases, after HBB was turned off by the gradual consumption of the convective mantle. Mass-loss rates of the order of 1 × 10−4 M⊙ yr−1 to 2 × 10−4 M⊙ yr−1 are required when looking for consistency with the observational evidence. These results indicate the need for a revision of the silicate yields by intermediate mass stars, which are found to be ∼3 times higher than previously determined.
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