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DOA Estimation for Noncircular Signals under Strong Impulsive Noise
No full textDirection of arrival (DOA) estimation under impulsive noise has been an important research area. Most present methods are based on the fractional lower order statistics, while the computation load is heavy, and the estimation property degrades when the noise impact is strong. To get around this conundrum, a novel solution is presented, where the noncircular signals are introduced for modelling, a filtering preprocessing method is introduced to eliminate the impulsive noise, and a matrix reconstruction method is presented to smooth the residual noise. Firstly, the filtering preprocessing method is implemented to cut out the impulsive noise. Secondly, the characteristic of the noncircular signal is utilized to extend the array aperture. Thirdly, a new matrix reconstruction method is proposed to smooth the residual noise. Finally, the classical ESPRIT algorithm is adopted to estimate the DOAs. Simulations under different comparison of dimensions are conducted, and the mainstream methods are selected as comparison. The simulation results illustrate the outstanding performance of the proposed method in a strong impulsive noise environment
Influence of Several Phosphate-Containing Additives on the Stability and Electrochemical Behavior of Positive Electrolytes for Vanadium Redox Flow Battery
No full textThe poor operational stability of electrolytes is a persistent impediment in building redox flow battery technology; choosing suitable stability additives is usually the research direction to solve this problem. The effects of five phosphate containing additives (including 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), hexamethylene diamine tetramethylene phosphonic acid (HDTMPA), amino trimethylene phosphonic acid (ATMPA), sodium ethylenediamine tetramethylene phosphonate (EDTMPS), and diethyl triamine pentamethylene phosphonic acid (DTPMP)) on the thermal stability and electrochemical performance of the positive electrolyte of vanadium redox flow battery were investigated. With 0.5 wt% addition, most of the selected additives were able to improve the thermal stability of the electrolyte. HEDP and HDTMPA extended the stability time of the pentavalent vanadium electrolyte at 50 degrees C from 5 days (blank sample) to 30 days and 15 days, respectively. The electrochemical performance of the electrolyte was further investigated by cyclic voltammetry, steady state polarization, and electrochemical impedance spectroscopy tests. It was found that most of the additives enhanced the electrochemical activity of the positive electrolyte, and the diffusion coefficients, exchange current densities, and reaction rate constants of V(IV) species became larger with the addition of these additives. It is verified that the thermal stability and electrochemical stability of the electrolyte are significantly improved by the combination of ATMPA + HEDP or ATMPA + HDTMPA. This study provides a new approach to improve the stability of the positive electrolyte for vanadium redox flow battery
Ultrahigh Mass Activity for the Hydrogen Evolution Reaction by Anchoring Platinum Single Atoms on Active {100} Facets of TiC via Cation Defect Engineering
No full textImproving the platinum (Pt) mass activity for low-cost electrochemical hydrogen evolution is an important and arduous task. Here, a selective etching-reducing fluidized bed reactor technique is reported to create Ti vacancies and firmly anchor single Pt atoms on the active {100} facets of titanium carbide (TiC) to increase the Pt utilization efficiency and improve catalytic activity significantly by a synergistic effect between Ti vacancies and Pt atoms. The generated Ti vacancies are negatively charged and stabilize Pt atoms by forming covalent Pt-C bonds, showing excellent long-term durability. Pt single atoms (ultralow load of 1.2 mu g cm(-2)) on the defective TiC {100} show remarkable activity (24.9 mV at 10 mA cm(-2)) and a mass activity (49.69 A mg(-1)) approximate to 190 times that of the state-of-the-art Pt-C catalyst and nearly double the previously reported best values. The developed cation defect engineering exhibits excellent potential for fabricating next-generation advanced single-atom catalysts for large-scale hydrogen evolution at a low cost
Strategic Project of Science and Technology of the Chinese Academy of Sciences[XDB05050000]
No full textIntegrated microsphere-packed bed enzymatic membrane reactor for enhanced bioconversion efficiency and stability: A proof-of-concept study
No full textFabricating high-performance enzyme reactors is requested for achieving efficient and stable bioconversions, but remains challenging, because few of them can possess high enzyme loading, sufficient mixing, and efficient mass transfer at the same time. Herein, we propose to develop a novel enzymatic packed bed membrane reactor (EPBMR) by integrating the advantages of both packed bed reactor (PBR) and enzymatic membrane reactor (EMR). A prototype study is conducted with the simplified enzyme-loaded microsphere-ultrafiltration EMR model (Mic-UF EMR). Invertase and dextranase are used in this work to produce glucose and oligodextran by hydrolysis of sucrose and dextran, respectively. Specifically, the use of microspheres can enlarge the contact area between enzymes and substrates and mitigate membrane fouling induced by free enzymes. Thus, Free&Mic-UF EMR (with both free and immobilized enzymes) exhibits a higher sucrose conversion rate (84%) than the EMR with free invertase (34%) and a negligible decline in sucrose conversion for 36 h continuous operation. Membrane fouling is ameliorated by alkaline cleaning and implementation of covalent bonding strategy. In addition, commercial resins with larger sizes are employed to replace konjac glucomannan microspheres (KGM) which reduce the pressure drop of EMR. Finally, by selecting the OF membrane with proper molecular weight cut-off (MWCO), the dextranase-based Mic-UF EMR system successfully produces oligodextran with desired molecular weight (Mw) and narrow Mw distribution. The outcome of this work not only offers a novel enzyme reactor construction strategy but also provides guidance for regulating the performance of EMR
Solvent effects on the interaction between alkali metal cations and 1,3-Diisopropoxycalix [4] arenecrown-6: Nuclear magnetic resonance spectroscopy and Independent Gradient Model Non-Covalent interactions analysis
No full textThe combination of 1,3-Diisopropoxycalix [4] arenecrown-6 (BPC6) and alkali metal ions were studied in different solvents by 1H and 133Cs Nuclear magnetic resonance (NMR) spectra, gmx_MMPBSA, and Independent Gradient Model (IGM) non-covalent interactions analysis based on Molecular Dynamics (MD) Simulations. The binding energy of BPC6 center dot M+ complex follows the order: BPC6 center dot Cs+ > BPC6 center dot Rb+ > BPC6 center dot K+ in CHCl3 , which is completely reverse to that in vacuum. In addition, the coordination properties depend on solvent polarity: In the low polarity solvent such as CHCl3 , all the oxygens in crown ether chain of BPC6 are involved in the coordination with Cs+ ions. By comparison, in the high polarity solvents such as CH3CN and CH3OH, the number of oxygens participates in the complexation decreases, and the cation -it interaction areas of complexes are also reduced. That is because the contribution of electrostatic interactions in complexation is weakened by solvent effect. The cation -it interaction plays a very impor-tant role in selectivity among alkali metal cations and coordination stability of BPC6 center dot M+ complex in dif-ferent solvents. (c) 2022 Elsevier B.V. All rights reserved
Solvent effects on the interaction between alkali metal cations and 1,3-Diisopropoxycalix [4] arenecrown-6: Nuclear magnetic resonance spectroscopy and Independent Gradient Model Non-Covalent interactions analysis
No full textThe combination of 1,3-Diisopropoxycalix [4] arenecrown-6 (BPC6) and alkali metal ions were studied in different solvents by 1H and 133Cs Nuclear magnetic resonance (NMR) spectra, gmx_MMPBSA, and Independent Gradient Model (IGM) non-covalent interactions analysis based on Molecular Dynamics (MD) Simulations. The binding energy of BPC6 center dot M+ complex follows the order: BPC6 center dot Cs+ > BPC6 center dot Rb+ > BPC6 center dot K+ in CHCl3 , which is completely reverse to that in vacuum. In addition, the coordination properties depend on solvent polarity: In the low polarity solvent such as CHCl3 , all the oxygens in crown ether chain of BPC6 are involved in the coordination with Cs+ ions. By comparison, in the high polarity solvents such as CH3CN and CH3OH, the number of oxygens participates in the complexation decreases, and the cation -it interaction areas of complexes are also reduced. That is because the contribution of electrostatic interactions in complexation is weakened by solvent effect. The cation -it interaction plays a very impor-tant role in selectivity among alkali metal cations and coordination stability of BPC6 center dot M+ complex in dif-ferent solvents. (c) 2022 Elsevier B.V. All rights reserved