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41.
Fornberg Bengt; Flyer Natasha; Hovde Susan; Piret Cecile 《IMA Journal of Numerical Analysis》2008,28(1):121-142
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Summary Some aspects on the situation of analytical chemistry as science are presented. Two examples can illustrate the influence of other sciences on the progress of analytical chemistry. 相似文献
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Abdullah S. AlRamadan Moez Ben Houidi Julien Sotton Marc Bellenoue Bengt Johansson S. Mani Sarathy 《Proceedings of the Combustion Institute》2021,38(4):5539-5548
One approach to enhancing the thermal efficiency of combustion systems is to burn fuels at ultra-lean conditions (equivalence ratio below 0.5). It has been recently reported that the auto-ignition of some hydrocarbon fuels, under specific temperature, pressure, and mixture conditions, releases heat in three distinctive stages. The three auto-ignition stages can be divided as a first low-temperature auto-ignition stage with conventional low temperature, and a high-temperature stage separated into two sub-stages. This study presents ignition delay time measurements of n-heptane and methyl-cyclohexane (MCH) mixtures in a flat piston rapid compression machine (RCM) under ultra-lean conditions. It provides experimental evidence of three-stage auto-ignition. This phenomenon of delayed high-temperature heat release is seldom reported in the literature and this is the first time to be reported for these types of fuels. The experiments cover two binary n-heptane/MCH mixtures of 15/85 and 70/30 by volume, pressures of 11 bar and 16 bar, temperature range of 700 to 900 K, and equivalence ratio of 0.4. The RCM optical access was utilized for high-speed chemiluminescence imaging. Detailed chemical kinetic simulations in a homogenous batch reactor with variable volume were conducted to further interrogate the three-stage auto-ignition phenomenon. Chemiluminescence shows that three-stage auto-ignition occurs in the adiabatically compressed end-gas, which indicates that this phenomenon is chemically-driven and is not induced by a thermal stratification in the RCM experiments. The model predicts the features of three-stage auto-ignition, which were experimentally observed at temperatures approximately below 750 K. As expected, significant discrepancies are observed in the ignition delays of experiment and simulation in the negative temperature coefficient (NTC) region. The simulation of the n-heptane/MCH 70/30 mixture shows better agreement with experiments in the Positive Temperature Coefficient (PTC) region compared to the 15/85 mixture. 相似文献
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B. Friman F. Karsch K. Redlich V. Skokov 《The European Physical Journal C - Particles and Fields》2011,71(7):1694
We discuss the relevance of higher order cumulants of net baryon number fluctuations for the analysis of freeze-out and critical
conditions in heavy ion collisions at LHC and RHIC. Using properties of O(4) scaling functions, we discuss the generic structure of these higher cumulants at vanishing baryon chemical potential and
apply chiral model calculations to explore their properties at non-zero baryon chemical potential. We show that the ratios
of the sixth to second and eighth to second order cumulants of the net baryon number fluctuations change rapidly in the transition
region of the QCD phase diagram. Already at vanishing baryon chemical potential they deviate considerably from the predictions
of the hadron resonance gas model which reproduce the second and fourth order cumulants of the net proton number fluctuations
at RHIC. We point out that the sixth order cumulants of baryon number and electric charge fluctuations remain negative at
the chiral transition temperature. Thus, they offer the possibility to probe the proximity of the chemical freeze-out to the
crossover line. 相似文献