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Abstract: The results of an experimental study of micro-jets produced with a gas dynamic virtual nozzle (GDVN) under the influence of an electric field are provided and discussed for the first time. The experimental study is performed with a 50% volume mixture of water and ethanol, and nitrogen focusing gas. The liquid sample and gas Reynolds numbers range from 0.09–5.4 and 0–190, respectively. The external electrode was positioned 400–500 μm downstream of the nozzle tip and an effect of electric potential between the electrode and the sample liquid from 0–7 kV was investigated. The jetting parametric space is examined as a function of operating gas and liquid flow rates, outlet chamber pressure, and an external electric field. The experimentally observed jet diameter, length and velocity ranged from 1–25 μm, 50–500 μm and 0.5–10 m/s, respectively. The jetting shape snapshots were processed automatically using purposely developed computer vision software. The velocity of the jet was calculated from the measured jet diameter and the sample flow rate. It is found that micro-jets accelerate in the direction of the applied electric field in the downstream direction at a constant acceleration as opposed to the standard GDVNs. New jetting modes were observed, where either the focusing gas or the electric forces dominate, encouraging further theoretical and numerical studies towards optimized system design. The study shows the potential to unlock a new generation of low background sample delivery for serial diffraction measurements of weakly scattering objects.
Keywords: micro jet, electric field, experimental study, flow focusing, Taylor cone, gas dynamic virtual nozzles
Published in DiRROS: 07.02.2024; Views: 379; Downloads: 134
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Published in DiRROS: 07.02.2024; Views: 190; Downloads: 58
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Abstract: Verticillium dahliae Kleb., the causal agent of Verticillium wilts, is a devastating plant disease affecting many plant species. Fungus V. dahliae was detected in a partially artificially established Acer pseudoplatanus L. forest stand in central Slovenia. This finding incited further study about the risk of different sources of V. dahliae isolates for maples in forests and the pathogenicity of three V. dahliae isolates of different origins was tested on saplings of A. pseudoplatanus, A. platanoides L., and A. campestre L. The inoculated saplings exhibited disease symptoms, i.e., leaf necrosis and wilting. At the end of the pathogenicity test, typical xylem browning was visible on the cross-sections, and the pathogen was successfully re-isolated. The isolates showed significant differences in their pathogenicity to specific maple hosts, with the agricultural isolate (originated from bell pepper) being the most aggressive on all three maple species. The disease severity index (DSI) and relative area under the disease progress curve (rAUDPC), as well as the success of re-isolation, indicate that A. platanoides is the most susceptible to inoculation with V. dahliae. In addition, significant differences in sapling biomass were observed between treated and control plants. These results suggest that maples in forest stands are threatened by V. dahliae, and biosecurity measures should be considered and implemented in forest management to reduce the transmission and potential spread of the pathogen.
Keywords: Verticillium wilt, Acer spp., pathogenicity test, Disease severity index, DSI, Area under the disease progress curve, AUDPC, biosecurity
Published in DiRROS: 07.02.2024; Views: 381; Downloads: 333
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Abstract: Purpose - This study aims to simulate the dendritic growth in Stokes flow by iteratively coupling a domain and boundary type meshless method. Design/methodology/approach - A preconditioned phase-field model for dendritic solidification of a pure supercooled melt is solved by the strong-form space-time adaptive approach based on dynamic quadtree domain decomposition. The domain-type space discretisation relies on monomial augmented polyharmonic splines interpolation. The forward Euler scheme is used for time evolution. The boundary-type meshless method solves the Stokes flow around the dendrite based on the collocation of the moving and fixed flow boundaries with the regularised Stokes flow fundamental solution. Both approaches are iteratively coupled at the moving solid–liquid interface. The solution procedure ensures computationally efficient and accurate calculations. The novel approach is numerically implemented for a 2D case. Findings - The solution procedure reflects the advantages of both meshless methods. Domain one is not sensitive to the dendrite orientation and boundary one reduces the dimensionality of the flow field solution. The procedure results agree well with the reference results obtained by the classical numerical methods. Directions for selecting the appropriate free parameters which yield the highest accuracy and computational efficiency are presented. Originality/value - A combination of boundary- and domain-type meshless methods is used to simulate dendritic solidification with the influence of fluid flow efficiently.
Keywords: dendritic solidification, Stokes flow, phase-field method, space-time adaptivity, meshless methods, RBF-FD, modified method of regularised sources
Published in DiRROS: 07.02.2024; Views: 266; Downloads: 107
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Keywords: tungsten, tungsten carbide, interface, microstructure, fusion energy
Published in DiRROS: 07.02.2024; Views: 241; Downloads: 123
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