Enhancing performance of GaN-based LDs by using GaN/InGaN asymmetric lower waveguide layers

The effects of Ga N/In Ga N asymmetric lower waveguide(LWG)layers on photoelectrical properties of In Ga N multiple quantum well laser diodes(LDs)with an emission wavelength of around 416 nm are theoretically investigated by tuning the thickness and the indium content of In Ga N insertion layer(In Ga N-IL)between the Ga N lower waveguide layer and the quantum wells,which is achieved with the Crosslight Device Simulation Software(PIC3D,Crosslight Software Inc.).The optimal thickness and the indium content of the In Ga N-IL in lower waveguide layers are found to be 300 nm and 4%,respectively.The thickness of In Ga N-IL predominantly affects the output power and the optical field distribution in comparison with the indium content,and the highest output power is achieved to be 1.25 times that of the reference structure(symmetric Ga N waveguide),which is attributed to the reduced optical absorption loss as well as the concentrated optical field nearby quantum wells.Furthermore,when the thickness and indium content of In Ga N-IL both reach a higher level,the performance of asymmetric quantum wells LDs will be weakened rapidly due to the obvious decrease of optical confinement factor(OCF)related to the concentrated optical field in the lower waveguide.

A novel 4D resolution imaging method for low and medium atomic number objects at the centimeter scale by coincidence detection technique of cosmic-ray muon and its secondary particles

The muon radiography imaging technique for high-atomic-number objects(Z)and large-volume objects via muon transmission imaging and muon multiple scattering imaging remains a popular topic in the field of radiation detection imaging.However,few imaging studies have been reported on low and medium Z objects at the centimeter scale.This paper presents an imaging system that consists of three layers of a position-sensitive detector and four plastic scintillation detectors.It acquires data by coincidence detection technique of cosmic-ray muon and its secondary particles.A 3D imaging algorithm based on the density of the coinciding muon trajectory was developed,and 4D imaging that takes the atomic number dimension into account by considering the secondary particle ratio information was achieved.The resultant reconstructed 3D images could distinguish between a series of cubes with 5-mm-side lengths and 2-mm-intervals.If the imaging time is more than 20 days,this method can distinguish intervals with a width of 1 mm.The 4D images can specify target objects with low,medium,and high Z values.

Hybrid model for muon tomography and quantitative analysis of image quality

Muon tomography is a novel method for the non-destructive imaging of materials based on muon rays,which are highly penetrating in natural background radiation.Currently,the most commonly used imaging methods include muon radiography and muon tomography.A previously studied method known as coinciding muon trajectory density tomography,which utilizes muonic secondary particles,is proposed to image low and medium atomic number(Z)materials.However,scattering tomography is mostly used to image high-Z materials,and coinciding muon trajectory density tomography exhibits a hollow phenomenon in the imaging results owing to the self-absorption effect.To address the shortcomings of the individual imaging methods,hybrid model tomography combining scattering tomography and coinciding muon trajectory density tomography is proposed and verified.In addition,the peak signal-to-noise ratio was introduced to quantitatively analyze the image quality.Different imaging models were simulated using the Geant4 toolkit to confirm the advantages of this innovative method.The simulation results showed that hybrid model tomography can image centimeter-scale materials with low,medium,and high Z simultaneously.For high-Z materials with similar atomic numbers,this method can clearly distinguish those with apparent differences in density.According to the peak signal-to-noise ratio of the analysis,the reconstructed image quality of the new method was significantly higher than that of the individual imaging methods.This study provides a reliable approach to the compatibility of scattering tomography and coinciding muon trajectory density tomography.

Mulberry Diels-Alder-type adducts:isolation,structure,bioactivity,and synthesis

Mulberry Diels-Alder-type adducts(MDAAs)are unique phenolic natural products biosynthetically derived from the intermolecular[4+2]-cycloaddition of dienophiles(mainly chalcones)and dehydroprenylphenol dienes,which are exclusively distributed in moraceous plants.A total of 166 MDAAs with diverse skeletons have been isolated and identified since 1980.Structurally,the classic MDAAs characterized by the chalcone-skeleton dienophiles can be divided into eight groups(Types A−H),while others with non-chalcone dienophiles or some variations of classic MDAAs are non-classic MDAAs(Type I).These compounds have attracted significant attention of natural products and synthetic chemists due to their complex architectures,remarkable biological activities,and synthetic challenges.The present review provides a comprehensive summary of the structural properties,bioactivities,and syntheses of MDAAs.Cited references were collected between 1980 and 2021 from the SciFinder,Web of Science,and China National Knowledge Internet(CNKI).