| 1. |
- Han, Xinlu, et al.
(author)
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A projection procedure to obtain adiabatic flames from non-adiabatic flames using heat flux method
- 2021
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In: Proceedings of the Combustion Institute. - : Elsevier BV. - 1540-7489. ; 38:2, s. 2143-2151
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Journal article (peer-reviewed)abstract
- Laminar burning velocity S L at elevated temperature T u and its temperature dependence coefficient α in SL/S0L = (Tu T0u)α are important parameters for industrial applications. However, experimental systems with high unburned gas temperatures may encounter pre-dissociation, leading to significant data scattering in the measurements. To negate this, the present work proposes a projection procedure to obtain adiabatic flame parameters at various unburned gas temperatures using non-adiabatic flames on a heat flux burner, by which the preheating can be achieved within much shorter time scale than, e.g., in conventional spherical flame methods, and the advantage of good data consistency in the heat flux method is kept. Burning velocity experiments were carried out with CH 4 + air atmospheric flames covering T u = 298-473 K, and the results show good agreement with the proposed projection equations. OH * spontaneous emission profiles were measured, indicating that the projection may extend to other flame characteristics. Uncertainty of the projection process was evaluated and comparisons were made with six popular kinetic mechanisms: GRI-Mech, FFCM-1 mech, Konnov mechanism, Glarborg mechanism, San Diego mechanism and Aramco mechanism. It is found that the simulated coefficients α are higher than experimental data especially at rich conditions; this is also found for literature values of high unburned gas temperature experiments. Possible reasons for this divergence are discussed.
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| 2. |
- Han, Xinlu, et al.
(author)
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Over-rich combustion of CH4, C2H6, and C3H8 +air premixed flames investigated by the heat flux method and kinetic modeling
- 2019
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In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 210, s. 339-349
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Journal article (peer-reviewed)abstract
- An uncommon non-monotonic behavior of the temperature dependence of adiabatic laminar burning velocity has been found in over-rich methane+air flames at equivalence ratio, ϕ = 1.4. To find out the universality and reasons of this turning point, methane, ethane and propane + air flames are studied both experimentally by the heat flux method and numerically using GRI-mech, USC-mech, UCSD-mech, FFCM mech, and Aramco mech over ϕ = 0.6–1.8, at unburned temperatures up to 368 K, and atmospheric pressure. Results show that the over-rich phenomena stem from a unique flame structure, where, after the flame front, H2O is reduced to H2 and C2Hx (x>1) is oxidized to CO, causing the temperature overtone (super adiabatic flame temperature), while some key reactions important for flame propagation changing their sensitivity signs. Inside the flame front, the importance of CH3 overwhelms other radicals like OH and H. By these distinguishing features, a method using temperature overtone to identify accurate turning points of over-rich regime is demonstrated.
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| 3. |
- Han, Xinlu, et al.
(author)
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Parametrization of the temperature dependence of laminar burning velocity for methane and ethane flames
- 2019
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In: Fuel. - : Elsevier BV. - 0016-2361. ; 239, s. 1028-1037
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Journal article (peer-reviewed)abstract
- The power exponent α in the temperature dependence of laminar burning velocity [Formula presented]=[Formula presented]α is usually considered an empirical parameter extracted from measurements performed at different temperatures. In this paper an analytical derivation of α is proposed, calculating the power exponent from the overall activation energy as: αTu 0→Tu =[Formula presented]·X+x. This relation is verified against experimental burning velocity data measured with the heat flux method and chemical kinetic models for flames with equivalence ratios, Φ, from 0.6 to 1.6 at up to 368 K unburned gas temperature and 1atm. Both methane and ethane were used as fuel. Laminar burning velocity predictions at elevated temperatures are made using proposed relation and the resulting values are in good agreement with existing data for methane flames up to 500 K. This indicates that the proposed mathematical derivation of α is accurate. In addition to providing a reliable extrapolation of the burning velocity at varying temperatures, isolating the temperature dependence of the power exponent α enables more accurate quantification of other factors, e.g., Φ, the unburned gas temperature and pressure, that influence laminar burning velocity. Additionally, it provides a simple means to evaluate the overall activation energy, Ea.
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| 4. |
- Han, Xinlu, et al.
(author)
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Temperature dependence of the laminar burning velocity for n-heptane and iso-octane/air flames
- 2020
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In: Fuel. - : Elsevier BV. - 0016-2361. ; 276
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Journal article (peer-reviewed)abstract
- The heat flux method is advantageous for obtaining adiabatic stretch-less flame and measuring laminar burning velocity, SL, with low uncertainty. However, its implementation is sometimes hampered by the instability, manifested as cellularity of the flame stabilized over a flat perforated burner. This paper summarizes the approaches of flame cellularity abatement on the heat flux burner, which are implemented in the present study for measuring burning velocities of n-heptane and iso-octane/air flames. The combination of approaches helped to effectively overcome the cellularity at the fuel-rich side of the tested flames, and the SL was measured at unburnt temperatures Tu=298K-358K and equivalence ratios ϕ=0.7-1.6, at atmospheric pressure, with the SL uncertainty being evaluated. Numerical simulations were carried out using LLNL mechanism, Chaos mechanism and Luong171 mechanism, and the results agree well with the experimental data. From the obtained experimental and numerical SL data, the temperature coefficients α in [Formula presented] as well as the overall activation energy, Ea, were derived. It was noted that for n-heptane and iso-octane/air flames, the tendencies of the α and Ea against ϕ resemble those for methane, ethane, and propane/air flames. Distinct over-rich flame structures were observed and discussed for n-heptane and iso-octane/air flames around ϕ≥1.5. Moreover, extrapolation proced/ure of the SLmeasurements was validated using analytical presentation of the heat flux method sensitivity, s vs. [Formula presented], and other parameters involved in the data processing, which may help to improve the accuracy of future experiments.
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| 5. |
- Wang, Shixing, et al.
(author)
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Experimental study and kinetic analysis of the laminar burning velocity of NH3/syngas/air, NH3/CO/air and NH3/H2/air premixed flames at elevated pressures
- 2020
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In: Combustion and Flame. - : Elsevier BV. - 0010-2180. ; 221, s. 270-287
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Journal article (peer-reviewed)abstract
- Mixing ammonia with syngas can be a promising way to overcome the low reactivity of ammonia, allowing it to find usage in IGCC (Integrated Gasification Combined Cycle) systems and gas turbines for power generation. However, fundamental experimental data on laminar burning velocity of NH3/syngas/air are rather scarce, especially at elevated pressures. This information is critical for the development and validation of reaction mechanisms and advances in combustor design. In the present work, measurements of the laminar burning velocities (SL) of NH3/syngas/air, NH3/CO/air, and NH3/H2/air premixed flames were performed by the heat flux method at pressures up to 5 atm, equivalence ratios ranging from 0.7 to 1.6, ammonia mole fractions in the fuel mixture from 0.2 to 1.0 in the NH3/syngas/air mixtures and 0.03–1.0 in the NH3/CO/air mixtures. Several recently published ammonia oxidation mechanisms were tested against the present experimental data. The measurements and predictions of SL exhibit discrepancies especially for NH3/H2/air flames at elevated pressures. The pressure exponent factors, β, characterizing burning velocity at elevated pressure via empirical power-law correlation SL/SL0 = (P/P0)β are extracted from the measured SL and compared with the numerical results. The thermal, diffusion, and chemical effects of blending syngas with ammonia on SL of the mixtures are distinguished, and the dominant role of the adiabatic flame temperature on the variation of the pressure exponent β is discussed. Kinetic modeling and sensitivity analyses showed that reactions of NHi to N2Hi (i = 0–4) species affect the predicted SL under rich conditions. At elevated pressures, these reactions also affect the NO formation via third-body collision reactions and NHi + NO reactions. Even for rich flames, the ammonia consumption is favored with the addition of syngas which also promotes NO formation by enriching the H and OH radical pools and increasing the flame temperature. The addition of hydrogen or carbon monoxide has equally promoting effect on the ammonia decomposition and NOx formation although their flame speed differs a lot.
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| 6. |
- Yang, Shixing, et al.
(author)
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Weak Signal Detection With Low-Bit Quantization in Colocated MIMO Radar
- 2023
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In: IEEE Transactions on Signal Processing. - 1053-587X. ; 71, s. 447-460
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Journal article (peer-reviewed)abstract
- This paper addresses the weak signal detection problem in a massive colocated multiple-input multiple-output (MIMO) radar. To cope with the sheer amount of data produced by the large-scale antennas, a low-bit quantizer is introduced in the sampling process to enable both for hardware limitations and a high detection performance. The generalized likelihood ratio test (GLRT) detector is proposed for the quantized data, with the batch gradient descent algorithm being introduced to form an estimate of the unknown parameters. Furthermore, as a low-complexity alternative to the GLRT detector, we propose a multi-bit Rao detector, yielding a closed-form test statistic, whose theoretical distribution is also presented. Finally, we refine the design of the quantizer by optimizing the quantization thresholds, which are obtained using the particle swarm optimization algorithm. Results from simulation and experimental data demonstrate the performance of the detectors using both unquantized and quantized data. They corroborate the theoretical analyses and show that the performance with 3-bit quantization yields a performance that approaches the cases without quantization, while reducing the overall complexity of the system substantially.
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| 7. |
- Zheng, Shixing, et al.
(author)
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MTSS1 is downregulated in nasopharyngeal carcinoma (NPC) which disrupts adherens junctions leading to enhanced cell migration and invasion
- 2023
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In: Frontiers in Cell and Developmental Biology. - : Frontiers Media S.A.. - 2296-634X. ; 11
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Journal article (peer-reviewed)abstract
- Loss of cell-cell adhesions is the indispensable first step for cancer cells to depart from the primary tumor mass to metastasize. Metastasis suppressor 1 (MTSS1) is frequently lost in metastatic tissues, correlating to advanced tumor stages and poor prognosis across a variety of cancers. Here we explore the anti-metastatic mechanisms of MTSS1, which have not been well understood. We found that MTSS1 is downregulated in NPC tissues. Lower levels of MTSS1 expression correlate to worse prognosis. We show that MTSS1 suppresses NPC cell migration and invasion in vitro through cytoskeletal remodeling at cell-cell borders and assembly of E-cadherin/beta-catenin/F-actin in adherens junctions. The I-BAR domain of MTSS1 was both necessary and sufficient to restore this formation of E-cadherin/beta-catenin/F-actin-mediated cell adherens junctions.
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