| 1. |
- Beal, Jacob, et al.
(författare)
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Robust estimation of bacterial cell count from optical density
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
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| 2. |
- Cai, Zun, et al.
(författare)
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Effect of cavity geometry on fuel transport and mixing processes in a scramjet combustor
- 2018
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Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638. ; 80, s. 309-314
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports a numerical investigation on the effect of cavity geometry on fuel transport and mixing processes in a scramjet combustor with a single rear-wall-expansion cavity. The numerical solver and the LES methods were validated against available experimental data and the numerical results were shown in good agreement with the experiments. Effect of the cavity rear wall height on the non-reacting flow fields was then investigated. It was found that the vertical flow velocity of the region located right after the expansion wave starting from the cavity leading edge was increased significantly towards the cavity when lowering the rear wall height, leading to an enhanced fuel entrainment into the cavity. Subsequently, at a larger cavity expansion ratio, the mixture inside the cavity became more fuel-rich, giving rise to a deteriorated mixing environment. In addition, the cavity recirculation zone was further compressed and the turbulent flow and scalar dissipation inside the cavity would be enhanced, which were likely the reason causing the ignition failures and poor flame stabilizations. An optimal cavity expansion ratio for the maximum fuel entrainment was found in the present rig.
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| 3. |
- Cai, Zun, et al.
(författare)
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Effect of combustor geometry and fuel injection scheme on the combustion process in a supersonic flow
- 2016
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Ingår i: Acta Astronautica. - : Elsevier BV. - 0094-5765. ; 129, s. 44-51
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Tidskriftsartikel (refereegranskat)abstract
- The combustion process in a hydrogen fueled scramjet combustor with a rearwall-expansion cavity was investigated numerically under inflow conditions of Ma=2.52 with stagnation pressure P0=1.6 Mpa and stagnation temperature T0=1486 K. The numerical solver was first evaluated for supersonic reactive flows in a similar combustor configuration where experimental data is available. Wall-pressure distribution was compared with the experiments, and grid independency analysis and chemical mechanism comparison were conducted. The numerical results showed fairly good agreements with the available experimental data under supersonic combustion conditions. Then the numerical solver was used to study the effects of combustor geometry, fuel injection scheme and injection equivalence ratio on the combustion process. It was found that under the same fuel injection condition, the combustor configuration with a rearwall-expansion cavity is in favor of the supersonic combustion mode and present better ability of thermal choking prevention than the other combustor configurations. For the rearwall-expansion cavity combustor, the supersonic flow field was found to be sensitive to the injector position and injection scheme, but not highly sensitive to the injection pressure. Besides, rearwall-expansion cavity with the combined fuel injection scheme (with an injection upstream the cavity and a direct injection on the rear wall) is an optimized injection scheme during the flame stabilization process.
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| 4. |
- Cai, Zun, et al.
(författare)
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Ignition processes and modes excited by laser-induced plasma in a cavity-based supersonic combustor
- 2018
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619. ; 228, s. 1777-1782
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Tidskriftsartikel (refereegranskat)abstract
- The ignition processes in an ethylene-fueled supersonic combustor excited by laser-induced plasma (LIP) were investigated experimentally under the condition of inflow Ma number of 2.92. The LIP excitation was implemented near the center floor of a flameholding cavity. Optical measurements, including simultaneous CH∗/OH∗ chemiluminescence imaging and Schlieren photography, were used to investigate the ignition processes. It is found that the CH∗ and OH∗ initiated by the LIP are mainly in the region between the cavity front wall and the LIP excitation site. The CH∗ and OH∗ are quenched rapidly, in particular at a low fueling rate. After a short delay, the distribution of CH∗ and OH∗ appears in the region between the rear wall of the cavity and the LIP excitation site, showing the onset of ignition therein. A stable flame was established in the shear layer between the downstream part of the cavity and the outer supersonic flow. It is concluded that the ignition processes excited by the LIP can be divided into a LIP initiation regime and a transient ignition reaction regime. Both the fueling rate and the LIP energy significantly affect the cavity ignition processes. Increasing the fueling rate or the laser energy can shorten the ignition processes in the cavity. A weak ignition mode and an intense ignition mode are postulated to explain the combustion behavior of the ignition processes in the cavity-based supersonic combustor.
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| 5. |
- Cai, Zun, et al.
(författare)
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Large Eddy Simulation of the flame propagation process in an ethylene fueled scramjet combustor in a supersonic flow
- 2017
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Ingår i: 21st AIAA International Space Planes and Hypersonics Technologies Conference, Hypersonics 2017. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624104633
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Konferensbidrag (refereegranskat)abstract
- Large Eddy Simulation (LES) was employed to investigate the flow field characteristics in an ethylene fueled scramjet combustor with a rearwall-expansion cavity in both non-reaction and reacting flows. The numerical solver was first validated against experiments and the numerical results were shown in reasonably good agreement with the available experimental data. Characteristics of the flow field under different combined fuel injection schemes were then studied. It was found thatfor the flame stabilizationprocess, applying the cavity direct injection on the cavity leading edge could improve the combustion process outside the cavity effectively witha fast combustion rate achieved in the region downstream the cavity. In contrast, applying the cavity direct injection on the cavity rear wall is more suitable for improving the combustion process inside the cavity and a more evenly distributed flame would be stabilized in the entire combustor. However, the combustion rate downstream the cavity will be slower. For the rearwall-expansion cavity, both the non-reaction and reacting processes could be improved by applying the combined fuel injection scheme.
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| 6. |
- Cai, Zun, et al.
(författare)
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Large Eddy Simulation of the fuel transport and mixing process in a scramjet combustor with rearwall-expansion cavity
- 2016
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Ingår i: Acta Astronautica. - : Elsevier BV. - 0094-5765. ; 126, s. 375-381
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Tidskriftsartikel (refereegranskat)abstract
- Large Eddy Simulation (LES) was employed to investigate the fuel/oxidizer mixing process in an ethylene fueled scramjet combustor with a rearwall-expansion cavity. The numerical solver was first validated for an experimental flow, the DLR strut-based scramjet combustor case. Shock wave structures and wall-pressure distribution from the numerical simulations were compared with experimental data and the numerical results were shown in good agreement with the available experimental data. Effects of the injection location on the flow and mixing process were then studied. It was found that with a long injection distance upstream the cavity, the fuel is transported much further into the main flow and a smaller subsonic zone is formed inside the cavity. Conversely, with a short injection distance, the fuel is entrained more into the cavity and a larger subsonic zone is formed inside the cavity, which is favorable for ignition in the cavity. For the rearwall-expansion cavity, it is suggested that the optimized ignition location with a long upstream injection distance should be in the bottom wall in the middle part of the cavity, while the optimized ignition location with a short upstream injection distance should be in the bottom wall in the front side of the cavity. By employing a cavity direct injection on the rear wall, the fuel mass fraction inside the cavity and the local turbulent intensity will both be increased due to this fueling, and it will also enhance the mixing process which will also lead to increased mixing efficiency. For the rearwall-expansion cavity, the combined injection scheme is expected to be an optimized injection scheme.
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| 7. |
- Klechikov, Alexey, et al.
(författare)
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Graphene decorated with metal nanoparticles : Hydrogen sorption and related artefacts
- 2017
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 250, s. 27-34
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen sorption by reduced graphene oxides (r-GO) is not found to increase after decoration with Pd and Pt nanoparticles. Treatments of metal decorated samples using annealing under hydrogen or air were tested as a method to create additional pores by effects of r-GO etching around nanoparticles. Increase of Specific Surface Area (SSA) was observed for some air annealed r-GO samples. However, the same treatments applied to activated r-GO samples with microporous nature and higher surface area result in breakup of structure and dramatic decrease of SSA. Our experiments have not revealed effects which could be attributed to spillover in hydrogen sorption on Pd or Pt decorated graphene. However, we report irreversible chemisorption of hydrogen for some samples which can be mistakenly assigned to spillover if the experiments are incomplete.
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| 8. |
- Li, Peibo, et al.
(författare)
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Three-dimensional flow structures and droplet-gas mixing process of a liquid jet in supersonic crossflow
- 2019
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Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638. ; 90, s. 140-156
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Tidskriftsartikel (refereegranskat)abstract
- The mixing process of a liquid jet in supersonic crossflow with a Mach number of 2.1 was investigated numerically using large eddy simulation (LES) based on the Eulerian-Lagrangian method. The gas phase was described using the Navier-Stokes equations and the liquid phase was represented using discrete droplets, which were injected and tracked in the computational domain individually according to Newton's second law of motion. The KH (Kelvin-Helmholtz) breakup model was used to calculate the droplet stripping process, and the secondary breakup process was simulated by coupling the RT (Rayleigh-Taylor) breakup model and the TAB (Taylor Analogy Breakup) model. Two-way coupling was enforced to consider the momentum and energy exchange between the gas and the droplets. It was found that the LES predicted spray characteristics, including spray penetration and cross-sectional distribution, agree reasonably well with the experiment. The major gas flow structures such as the bow shock, the large-scale vortices, and the recirculation zones were replicated successfully in the simulations. It was found that the gas flow structures have a significant effect on the mixing process of the droplets. The simulation results revealed that two sets of counter-rotating vortex pair (CVP) exist in the gas-liquid mixing region. Under the influence of CVP, part droplets were transported to the near wall region and subsequently to both sides of the core spray region. The formation mechanism of the CVP was analyzed by comparing the pressure gradient and the source term of droplets in the Navier-Stokes equations. Differences of the mixing process of liquid jet in supersonic crossflow, gas jet in supersonic crossflow and liquid jet in incompressible crossflow were identified.
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| 9. |
- Mingbo, Sun, et al.
(författare)
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A Modified Sub-Cell-Fix Method for Re-Initialization of Level-Set Distance Function and Its Dependence Tests on Grid Stretching
- 2010
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Ingår i: Modern Physics Letters B. - 0217-9849. ; 24:15, s. 1615-1629
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Tidskriftsartikel (refereegranskat)abstract
- The sub-cell-fix (SCF) method proposed by Russo and Smereka(3) computes the distance function of the cells adjacent to the zero level-set without disturbing the original zero level-set. A modified sub-cell-fix scheme independent of local curvature is developed in this paper, which makes use of a combination of the points adjacent to zero level-set surfaces and preserves the interface in a second-order accuracy. The new sub-cell-fix scheme is capable of handling large local curvature, and as a result it demonstrates satisfactory performance on several challenging test cases. The limitations of the modified scheme on stretched grids are tested and it is found that the highly stretched grid causes large numerical errors, and needs further assessment and modification.
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| 10. |
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