“Slow” active control of combustion instabilities by modification of liquid fuel spray properties

This paper describes an experimental investigation of the feasibility of using “slow” active control approaches, which “instantaneously” change liquid fuel spray properties, to suppress combustion instabilities. The objective of this control approach was to break up the feedback between the combustion process heat release and combustor pressure oscillations that drive the instability by changing the characteristics of the combustion process (e.g., the characteristic combustion time). To demonstrate the feasibility of such control, this study used a proprietary fuel injector (Nanomiser^TM), which can vary its fuel spray properties, to investigate the dependence of acoustics–combustion process coupling, i.e., the driving of combustion instabilities, upon the fuel spray properties. This study showed that by changing the spray characteristics it is possible to significantly damp combustion instabilities. Furthermore, using combustion zone chemiluminescence distributions, which were obtained by Abel’s deconvolution synchronized with measured acoustic data, it has been shown that the instabilities were mostly driven midway between the combustor centerline and wall, a short distance downstream from the flame holder, where the mean axial flow velocity is approximately zero in the vortex near the flame holder. The results of this study strongly suggest that a “slow” active control system that employs controllable fuel injectors could be effectively used to prevent the onset of detrimental combustion instabilities.     

The circular chemistry conceptual framework: A way forward to sustainability in industry 4.0

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时间序列的变化点检测和趋势分析

趋势分析和变化点检测是时间序列分析中常用的工具. 变化点检测是识别过程行为的自然或人为的突然的变化,而趋势可以定义为对逐渐偏离过去的规范的估计. 本文使用了Cox-Stuart方法和变化点算法分析时间序列数据趋势的存在,并以澳大利亚的近地表风速时间序列为例. 澳大利亚的近地表风速趋势是根据研究出的新开发的风速数据集,通过使用局部表面粗糙度信息,以及不同高度收集的混合观测数据构建. 10 m处的风的速度趋势通常会增加,而2 m处则趋于减小. 假设检验测试,变化点分析和人工检查记录表明有几个因素可能是导致差异的原因,例如伴随仪器变化的系统性偏差,随机数据错误(例如累积日错误)和数据采样问题. 均质化以及基于变化点检测的技术和多期趋势分析阐明了风速趋势不一致的根源.     

Comment on: “Entanglement in three coupled oscillators” [Phys. Lett. A 384 (2020) 126134]

In this comment we analyze a method for the solution of the eigenvalue equation for three coupled harmonic oscillators proposed recently. We argue that the authors did not obtain the frequencies and coordinates of the normal modes that make the Hamiltonian operator diagonal but merely six transcendental equations for the relevant parameters that they did not attempt to solve. We derive the conditions for the existence of bound states that the authors did not appear to be able to obtain probably because of the complexity exhibited by those equations.     

监测L\'{e}vy稳定过程均值变点的平均运行时间估计

平均运行长度(时间) (ARL)是判断一控制图监测变点效果好坏的一个重要工具\bd 本文主要研究L\'{e}vy 稳定过程的均值变点监测问题\bd 我们给出了三个控制图, 即EWMA, GEWMA和GLR的ARL 估计, 并通过数值模拟比较了4个控制图监测均值变点的效果和差异.     

Relaxation Dynamics In Photo-Excited Halogen-Bridged Pt-Complexes Studied By Femtosecond Luminescence Spectroscopy

The ultrafast dynamics of excited electronic states in a series of quasi-one-dimensional halogen-bridged platinum-complexes was investigated by using femtosecond luminescence spectroscopy. In Pt-Br system, the wave-packet oscillation of the local vibration of self-trapped excitons (STEs) was observed. The time evolutions of luminescence intensity in Pt-Br and Pt-Cl were successfully described by using a model based on a wave-packet motion on the interaction mode coordinate. In Pt-I, very fast decay was observed, suggesting the existence of efficient non-radiative decay channel directing to structural change.     

Evolutionary Pareto distributions

We consider here i.i.d. variables which are distributed according to a Pareto up to some point x₁ and a Pareto (with a different parameter) after this point. This model constitutes an approximation for estimating extreme tail probabilities, especially for financial or insurance data. We estimate the parameters by maximizing the likelihood of the sample, and investigate the rates of convergence and the asymptotic laws. We find here a problem which is very close to the change point question from the point of view of limits of experiments. Especially, the rates of convergence and the limiting law obtained here are the same as in a change point framework. Simulations are giving an illustration of the quality of the procedure.     

Interaction between anionic polyelectrolytes and anion exchange membranes and change in membrane properties

Electrodialytic transport properties of anion exchange membranes were measured after formation of anionic polyelectrolyte layers on the membrane surfaces: relative transport number of various anions to chloride ions, current efficiency and apparent diffusion coefficients of neutral molecules. The anionic polyelectrolyte layers were formed by immersing the membrane into an aqueous solution of polycondensation product of sodium naphthalene sulfonate and formaldehyde or polystyrene sulfonic acid.

The change in the relative transport number between anions was remarkable in the anion exchange membrane with high ion exchange capacity by forming the layer. Results were: the relative transport number of sulfate ions to chloride ions decreased and those of nitrate ions to chloride ions, fluoride ions to chloride ions and bromide ions to chloride ions increased compared with the corresponding membrane. Although the apparent diffusion coefficient of neutral molecules suggested clogging of the membrane pores by the polyelectrolyte, anions with higher hydrated ionic diameter were able to permeate through the membrane easily. This means that difference of electrostatic repulsion force against two anions is effective on the change in the relative transport number of anions.     

Temperature-dependent structural changes of[Bmim]FeCl4 magnetic ionic liquid characterized by an in-situ X-ray absorption fine structure

The temperature-dependent structural changes in 1-butyl-3-methylimidazolium tetrafluoride([Bmim]FeCl4)magnetic ionic liquid(MIL)were investigated by using in-situ X-ray absorption fine structure(XAFS)combined with Raman spectroscopy and DFT calculations.XAFS re sults revealed that the coordination number and bond length of Fe-Cl in the anion of[Bmim]FeCl4 MIL decreased with increments in temperature.These results directly reflected the dissociation of tetrahedral structure[FeCl4]^-,and the formation of bridge-chain[Fe2 Cl5]^+,and[FeCl2]^+species in the anion of[Bmim]FeCl4 MIL.These behaviors indicated that[FeCl4]^-dissociation was endothermic,and was promoted by increased temperature.The results obtained through XAFS were in agreement with those obtained through Raman spectroscopy and DFT calculations.     

Measuring the subprime crisis contagion: Evidence of change point analysis of copula functions

In this paper, we first determine the existence of structural changes in the dependence between time series of equity index returns of two markets using the change point testing method. The method is based on Archimedean copula functions, which are able to comprehensively describe dependence characteristics of random variables. The degree of financial contagion between markets is subsequently estimated using the tail dependence coefficient of copula functions before and after the change point. We empirically test our method by investigating financial contagion during the subprime crisis between the US S&P 500 index and five Asian markets, namely China, Japan, Korea, Hong Kong and Taiwan. Our results show that a statistically significant change point exists in the dependence between the US market and all Asian stock markets except Taiwan. The upper tail dependence is larger after the time of change, implying the existence of contagion during the banking crisis between the US and the Asian economies. The degree of financial contagion is also estimated and found to be consistent with market events and media reports during that period.