DFT Investigation of Nuclear ¹⁴N Quadrupole Coupling Constants for Four HMX Polymorphs

Abstract

Density functional theory investigation of 14 N nuclear quadrupole coupling constants (NQCC) for HMX polymorphs was performed. During the calculation of NQCC and asymmetry parameter (η) of β-HMX, single molecule model is found to be worse than cluster model. The calculated results are more sensitive to the proper model than to the basis set. The calculation for β-HMX using cluster model at B3LYP/6-311＋＋G(d,p) level gives better agreement with experiment. This approach was subsequently applied to α, γ, and δ-HMXs. The difference of simulated 14 N NQR frequency was found. The NQR spectrum is useful for the study of explosive or propellant on their detection, phase transition, and aging process.

Investigation of Denitrifying Phosphorus Removal Organisms in a Two-Sludge Denitrifying Phosphorus Removal Process

“…FISH image [ Fig.2 (b)] shows Accumulibacter, shown in yellow, was a considerable proportion in anoxic tank. This find is well consistent with the good phosphorus removal performance observed in this system in our previous experiments 19 . The results of elements analysis by EDS that the content of phosphorus contained in anoxic sludge was significantly higher than in traditional activated sludge, as discussed in the energy dispersive spectrometry for DPB in this paper.…”

“…The excited atoms counts of phosphorus element in the anaerobic sludge were 0.55 k, while were 1.18 k in the anoxic sludge, suggesting that the difference of phosphorus content in the denitrifying phosphorus removal sludge between anaerobic and anoxic should be due to the different performances of DPB in different conditions, including that phosphorus was released anaerobically and taken up anoxically. The phosphorus content of excess sludge in this study, namely anoxic sludge, was 12.3 % of dry weight significantly higher than in traditional biological phosphorus removal process (3 %) 22 , suggesting that two independent sludge cultivation systems proposed here, separating the nitrifying sludge from denitrifying phosphorus removal sludge, could effectively enhance the phosphorus removal efficiency, which are consistent with the results of chemical analysis 19 . Further research is needed to determine the relative distributions of phosphorus contained in and intracellular structures and extracellular polysaccharides.…”