Formation mechanism of bright and dark concentric-ring pattern in dielectric barrier discharge

In this work,a bright and dark concentric-ring pattern is reported in a dielectric barrier discharge for the first time.The spatiotemporal dynamics of the bright and dark concentric-ring pattern are investigated with an intensified charge-coupled device and photomultiplier tubes.The results indicate that the bright and dark concentric-ring pattern is composed of three concentric-ring sublattices.These are bright concentric-ring structures,dark concentric-ring structures and wider concentric-ring structures,respectively.The bright concentric-ring structures and dark concentricring structures are alternately distributed.The bright concentric-ring structures are located at the centre of the wider concentric-ring structures.The wider concentric-ring structures first form from the outer edge and gradually develop to the centre.The essence of all three concentric-ring structures is the individual discharge filaments.The optical emission spectra of different sublattices are acquired and analysed.It is found that the plasma parameters of the three concentricring sublattices are different.Finally,the formation mechanism of the bright and dark concentricring pattern is discussed.

Controllable and tunable plasma photonic crystals through a combination of photonic crystal and dielectric barrier discharge patterns

We report five types of patterns with square symmetry,including three novel types obtained by inserting a specially designed grid photonic crystal(PC)into a dielectric barrier discharge system.They are studied using an intensified charge-coupled device camera and photomultiplier tubes.The three novel types of patterns are a square pattern with one structure,a square superlattice pattern with four sublattices and a(1/4)K_(grid)(K_(grid)is the basic wave vector of the grid),and another square pattern with a complex inversion discharge sequence.From the application viewpoint,the five types of patterns can be used as plasma photonic crystals(PPCs).Their band diagrams under a transverse-magnetic wave simulated by the finite element method show that there are a large number of band gaps.Compared with the original PC with only a unidirectional band gap,the five types of PPCs have tunable and omnidirectional band gaps,which is very important in controlling the propagation of electromagnetic waves in the mm-wave region.The experimental results enrich the pattern types in the dielectric barrier discharge system and provide a method for obtaining PPCs with symmetry controllability and bandgap tunability.

Square grid pattern with direction-selective surface discharges in dielectric barrier discharge

A new phenomenon that a filament discharged only once instead of twice in a cycle of the applied voltage is observed in a square grid pattern in a dielectric barrier discharge(DBD)with a larger gas gap,which is named intermittent discharge.Its spatiotemporal dynamics and the formation mechanism are studied by the multiple photomultiplier tubes and an intensified charge-coupled device.Corresponding to the positions of spots in the picture with an exposure time of 40 ms,there are some bright spots(discharge spots)and black spots(non-discharged spots)in the instantaneous image with an exposure time of 10μs(a half cycle of the applied voltage).There are at least two bright spots around one black spot and vice versa.The surface discharges(SDS)can be observed between any two adjacent spots.The intensity of the SDSbetween the bright spot and the black spot is 2.5 times greater than that between two adjacent bright spots,which indicates that the SDSare directional-selective.The intermittent discharge with positive(negative)current polarity changes to that with negative(positive)current polarity,after it sustains up to 14 voltage cycles at the longest.The spatial distribution of the electric field component is calculated through COMSOL software to solve the Poisson equation numerically.It is found that the inhomogeneous distribution of surface electric field is caused by the inhomogeneous distribution of wall charges,which leads to direction-selective SDS.The intermittent discharge is formed by the competition between the direction-selective SDSand volume discharges(VDS)in DBD.This is the reason why the intermittent discharge is generated.

Formation of honeycomb-Kagome hexagonal superlattice pattern with dark discharges in dielectric barrier discharge

A honeycomb-Kagome hexagonal superlattice pattern with dark discharges is observed in a dielectric barrier discharge system for the first time.The spatiotemporal structure of the honeycomb-Kagome hexagonal superlattice pattern with dark discharges is investigated by an intensified charge-coupled device and the photomultipliers show that it is an interleaving of three different sub-lattices,which are bright-spot,invisible honeycomb lattice,and Kagome lattice with invisible frameworks and dim-spots,respectively.The invisible honeycomb lattices and Kagome lattices are actually composed of dark discharges.By using the optical emission spectra method,it is found that the plasma parameters of the three different sub-lattices are different.The influence of the dark discharges on pattern formation is discussed.The results may have significance for the investigation of the dark discharges and will accelerate the development of self-organized pattern dynamics.

Efficient photoelectrochemical conversion of CO_(2)to syngas by photocathode engineering

The synthesis of renewable chemical fuels from CO_(2) and H_(2)O via photoelectrochemical(PEC)route reprensents a promising room-temperature approach for transforming greenhouse gas into value-added chemicals(e.g.,syngas),but to date it has been hampered by the lack of efficient photocathode for CO_(2) reduction.Herein,we report efficient PEC CO_(2) reduction into syngas by photocathode engineering.The photocathode is consisting of a planar p-n Si junction for strong light harvesting,GaN nanowires for efficient electron extraction and transfer,and Au/TiO_(2)for rapid electrocatalytic syngas production.The photocathode yields a record-high solar energy conversion efficiency of 2.3%.Furthermore,desirable syngas compositions with CO/H_(2)ratios such as 1:2 and 1:1 can be produced by simply varying the size of Au nanoparticle.Theoretical calculations reveal that the active sites for CO and H_(2)generation are the facet and undercoordinated sites of Au particles,respectively.

Advances in the dynamic control of metabolic pathways in Saccharomyces cerevisiae

The metabolic engineering of Saccharomyces cerevisiae has great potential for enhancing the production of high-value chemicals and recombinant proteins.Recent studies have demonstrated the effectiveness of dynamic regu-lation as a strategy for optimizing metabolic flux and improving production efficiency.In this review,we provide an overview of recent advancements in the dynamic regulation of S.cerevisiae metabolism.Here,we focused on the successful utilization of transcription factor(TF)-based biosensors within the dynamic regulatory network of S.cerevisiae.These biosensors are responsive to a wide range of endogenous and exogenous signals,including chemical inducers,light,temperature,cell density,intracellular metabolites,and stress.Additionally,we ex-plored the potential of omics tools for the discovery of novel responsive promoters and their roles in fine-tuning metabolic networks.We also provide an outlook on the development trends in this field.