| 1. |
- Zhao, Wenhao, et al.
(författare)
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Comparison and application of SOFM, fuzzy c-means and k-means clustering algorithms for natural soil environment regionalization in China
- 2023
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Ingår i: Environmental Research. - : Elsevier. - 0013-9351 .- 1096-0953. ; 216
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Tidskriftsartikel (refereegranskat)abstract
- Soil attributes and their environmental drivers exhibit different patterns in different geographical directions, along with distinct regional characteristics, which may have important effects on substance migration and transformation such as organic matter and soil elements or the environmental impacts of pollutants. Therefore, regional soil characteristics should be considered in the process of regionalization for environmental management. However, no comprehensive evaluation or systematic classification of the natural soil environment has been established for China. Here, we established an index system for natural soil environmental regionalization (NSER) by combining literature data obtained based on bibliometrics with the analytic hierarchy process (AHP). Based on the index system, we collected spatial distribution data for 14 indexes at the national scale. In addition, three clustering algorithms—self-organizing feature mapping (SOFM), fuzzy c-means (FCM) and k-means (KM)—were used to classify and define the natural soil environment. We imported four cluster validity indexes (CVI) to evaluate different models: Davies-Bouldin index (DB), Silhouette index (Sil) and Calinski-Harabasz index (CH) for FCM and KM, clustering quality index (CQI) for SOFM. Analysis and comparison of the results showed that when the number of clusters was 13, the FCM clustering algorithm achieved the optimal clustering results (DB = 1.16, Sil = 0.78, CH = 6.77 × 106), allowing the natural soil environment of China to be divided into 12 regions with distinct characteristics. Our study provides a set of comprehensive scientific research methods for regionalization research based on spatial data, it has important reference value for improving soil environmental management based on local conditions in China.
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| 2. |
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| 3. |
- Carlsson, Henning, et al.
(författare)
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Numerical and experimental study of flame propagation and quenching of lean premixed turbulent low swirl flames at different Reynolds numbers
- 2015
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Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 162:6, s. 2582-2591
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a joint experimental and large eddy simulation (LES) study of lean premixed low swirl stabilized methane/air flames at different Reynolds numbers (Re similar to 20,000-100,000). The aims are to investigate the sensitivity of the structures and dynamics of low swirl flames to the inflow boundary conditions and to evaluate the capability of an LES flamelet model in predicting the stabilization and local extinction of the flames. Chemiluminescence measurements are carried out for Re - 20,000-50,000 and further detailed oxygen concentration and temperature fields are measured using rotational coherent anti-Stokes Raman spectroscopy (RCARS) for Re - 20,000 and 30,000 along the centerline of the burner and at various radial positions at different heights above the burner. The data are used first for validation of the combustion LES model employed in the numerical simulations, and then the RCARS and LES results are used to delineate the effect of ambient air entrainment on the flame structure at various burner exit velocities. A three-scalar flamelet model based on a level-set G-equation shows excellent predictions of the lift-off positions and the structures of the flames, including quenching at the trailing edge of the flame. The results show that the flame lift-off height varies only slightly when the burner exit velocity is increased, which is consistent with a shear-layer flame stabilization mechanism reported previously. The volume of the flame decreases substantially with increasing burner exit velocity at relatively low Reynolds numbers, as a result of flame quenching at the trailing edge of the flame caused by entrainment of the ambient air into the fuel/air stream and the flame itself. At high Reynolds numbers the flame structures become fairly self-similar with the flame volume nearly independent of the Reynolds number. (C) 2015 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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| 4. |
- Meng, Qinglai, et al.
(författare)
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The NDM-1 biosensor rapidly and accurately detected antibiotic plasma concentrations in Cefuroxime-treated patients
- 2024
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Ingår i: International Journal of Antimicrobial Agents. - 1872-7913. ; 64:2
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Tidskriftsartikel (refereegranskat)abstract
- Therapeutic drug monitoring (TDM) of β-lactam antibiotics in critically ill patients may benefit dose optimization, thus improving therapeutic outcomes. However, rapidly and accurately detecting these antibiotics in blood remains a challenge. Our research group recently developed a thermometric biosensor called the New Delhi metallo-β-lactamase-1 (NDM-1) biosensor, which detected multiple classes of β-lactam antibiotics in spiked plasma samples. This study assesses the NDM-1 biosensor's effectiveness in detecting plasma concentrations of β-lactam antibiotic in treated patients. Seven patients receiving Cefuroxime were studied. Plasma samples collected pre- and post-antibiotic treatment were analyzed using the NDM-1 biosensor and compared with liquid chromatography coupled with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The biosensor detected plasma samples without dilution, and a brief pre-treatment using a PVDF filter significantly lowered matrix effects, reducing the running time to 5-8 minutes per sample. The assay's linear range for Cefuroxime (6.25 to 200 mg/L) covered target concentrations during the trough phase of pharmacokinetics in critically ill patients. The pharmacokinetic properties of Cefuroxime in treated patients determined by the NDM-1 biosensor and the UPLC-MS/MS were comparable, and the Cefuroxime plasma concentrations measured by the two methods showed a statistically good consistency. These data demonstrate that the NDM-1 biosensor assay is a fast, sensitive, and accurate method for detecting Cefuroximeplasma concentration in treated patients and highlights the NDM-1 biosensor as a promising tool for on-site TDM of β-lactam antibiotics in critically ill patients.
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| 5. |
- Wu, Yajing, et al.
(författare)
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Effect of geometrical contraction on vortex breakdown of swirling turbulent flow in a model combustor
- 2016
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Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 170, s. 210-225
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Tidskriftsartikel (refereegranskat)abstract
- Large Eddy Simulation (LES) studies of isothermal and incompressible turbulent swirling flows in a model gas turbine combustion chamber geometry have been carried out. The focus is on the effect of outlet geometry contraction on the vortex breakdown structure and the precessing vortex core in the chamber. Nine different outlet geometries with different contraction ratio C-r are considered. The results from a baseline case are compared with experimental data in the literature. The swirling flow is generated using a swirler with fifteen guide vanes similar to an existing industrial gas turbine burner. In all cases the swirler and the main chamber geometry are kept the same. The detailed swirler geometry is considered in the simulation using unstructured grids. Sensitivity tests on the influence of the grid resolution and the sub grid scale models are carried out. The mean flow field shows different vortex breakdown structures when the contraction ratio changes from 0325 to 1.0. In particular, along the axis of the chamber the flow is shown to switch its direction when the contraction increases as a result of the change of the structure of the center recirculation zone. The underlying flow physics is analyzed by comparing the budget terms in the momentum equations, and by performing a global instability analysis. (C) 2015 Elsevier Ltd. All rights reserved.
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| 6. |
- Wu, Yajing
(författare)
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Large Eddy Simulation of Turbulent Swirling Flows in Combustor Related Geometries
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the physics of turbulent swirling flows. Large eddy simulation (LES) method is used to investigate the vortex breakdown process, the precessing vortex core (PVC), and the effect of swirl number and flow field configuration on swirling flows. The study is based on an open source CFD code, \textit{OpenFoam}. Turbulent swirling flows are widely used in combustion devices such as internal combustion engines and gas turbine combustors to promote fuel/air/hot gas mixing so that a compact combustor can be designed and to provide combustion stabilization. The aims of the thesis work are to gain deeper understanding on the structures of the vortex breakdown and PVC and to develop and to evaluate simulation methods for predicting turbulent swirling flows. The work is focused on isothermal turbulent swirling flows in gas turbine related geometries. The LES approach is first applied to simulate turbulent swirling flows in several experimental rigs where laser doppler velocimeter (LDV) and particle imaging velocimeter (PIV) data are available. The experimental data are used to evaluate the performance of LES models and the requirement of grid resolution and then they are used as baseline cases for further exploration of the flow physics with respect to variations in the flow conditions and geometrical configurations. In all cases it is found that the LES results are comparable to the experimental results and the sensitivity of LES results to the sub-grid models is not high provided that a sufficient grid resolution is used. Several criteria for the assessment of LES accuracy are examined. It is found that the vortex breakdown structure in a combustor is sensitive to the swirl number in the inflow. In a given combustor geometry when swirl number increases above a critical level vortex breakdown is shown to occur. Further increase the swirl number leads to the onset of PVC and the drastic change in the structures of the recirculation zones. The coherent structures associated with vortex breakdown becomes unsteady. The onset of vortex breakdown and the unsteady mode are analysed using dynamic mode analysis (DMD) method. For a given swirl number it is found that when the combustor outlet geometry is changed the vortex breakdown structures can be significant affected. When the outlet area is gradually decreased a center bubble type vortex breakdown is replaced by an annular recirculation zone, and the center vortex core becomes more dynamic. This is expected to have a significant influence on the way the flame is stabilized in the combustor. Examination of the LES results indicates that the transition from the center bubble recirculation to the annular recirculation structures is a manifestation of the coupling of the tangential momentum and the pressure gradient.
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| 7. |
- Yan, Beibei, et al.
(författare)
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Experimental and modeling study of laminar burning velocity of biomass derived gases/air mixtures
- 2011
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Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 1879-3487 .- 0360-3199. ; 36:5, s. 3769-3777
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Tidskriftsartikel (refereegranskat)abstract
- Laminar burning velocities of four biomass derived gases have been measured at atmospheric pressure over a range of equivalence ratios and hydrogen contents, using the heat flux method on a perforated flat flame burner. The studied gas mixtures include an air-blown gasification gas from an industrial gasification plant, a model gasification gas studied in the literature, and an upgraded landfill gas (bio-methane). In addition, co-firing of the industrial gasification gas (80% on volume basis) with methane (20% on volume basis) is studied. Model simulations using GRI mechanisms and detailed transport properties are carried out to compare with the measured laminar burning velocities. The results of the bio-methane flame are generally in good agreement with data in the literature and the prediction using GRI-Mech 3.0. The measured laminar burning velocity of the industrial gasification gas is generally higher than the predictions from GRI-Mech 3.0 mechanism but agree rather well with the predictions from GRI-Mech 2.11 for lean and moderate rich mixtures. For rich mixtures, the GRI mechanisms under-predict the laminar burning velocities. For the model gasification gas, the measured laminar burning velocity is higher than the data reported in the literature. The peak burning velocities of the gasification gases/air and the co-firing gases/air mixtures are in richer mixtures than the bio-methane/air mixtures due to the presence of hydrogen and CO in the gasification gases. The GRI mechanisms could well predict the rich shift of the peak burning velocity for the gasification gases but yield large discrepancy for the very rich gasification gas mixtures. The laminar burning velocities for the bio-methane/air mixtures at elevated initial temperatures are measured and compared with the literature data. Copyright (C) 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
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