Electron-positron pair production in spatial inhomogeneous electric fields with sinusoidal phase modulation is studied within the Dirac-Heisenberg-Wigner formalism.The focus is on discussing the effects of the modulation parameters on the momentum spectrum and the reduced particle number at various spatial scales.For the momentum spectrum,the interference effect becomes more and more remarkable with the increase of modulated amplitude or frequency,while the symmetry is severely destroyed with modulated amplitude.For the reduced particle number,it is greatly enhanced by about a few times and evenly one order of magnitude when modulation parameters are applied.Moreover,the effect of spatial scales on the reduced particle number is carefully examined,and it is found that it increases rapidly at small spatial scales,while it tends to be a constant at large spatial scales.We also obtain the optimal pair production that can be achieved through different modulations.These results can provide a possibility for realizing the optimal pair production by combining the advantages of field spatial inhomogeneity with different choices of phase modulation.
Li-Na HuOrkash AmatLie-Juan LiMelike MohamedsedikB S Xie
As the fifth-generation(5G)mobile communication network may not meet the requirements of emerging technologies and applications,including ubiquitous coverage,industrial internet of things(IIoT),ubiquitous artificial intelligence(AI),digital twins(DT),etc.,this paper aims to explore a novel space-air-ground integrated network(SAGIN)architecture to support these new requirements for the sixth-generation(6G)mobile communication network in a flexible,low-latency and efficient manner.Specifically,we first review the evolution of the mobile communication network,followed by the application and technology requirements of 6G.Then the current 5G non-terrestrial network(NTN)architecture in supporting the new requirements is deeply analyzed.After that,we proposes a new flexible,low-latency and flat SAGIN architecture,and presents corresponding use cases.Finally,the future research directions are discussed.
Huanxi CuiJun ZhangYuhui GengZhenyu XiaoTao SunNing ZhangJiajia LiuQihui WuXianbin Cao
Using the firm-level panel datasets and hand-collected data on county level minimum wage,this paper estimates the effect of minimum wage on firm profitability.As firms may take time to adjust in response to changes in minimum wage,this paper estimates a dynamic panel model with lagged minimum wage.To capture the heterogeneous effect of minimum wage on profitability,this paper further estimates quantile regression dynamic panel model.The estimation results suggest that the effect on firm profitability of minimum wage in the current year is negative across the whole conditional distribution of profitability and it exhibits an inverted-U shape across conditional quantiles.The effect on profitability of lagged minimum wage is positive at the 5th,10th,15th quantiles,negative at the 90th and 95th quantiles,and not significant at other quantiles.Turning to the overall effect on profitability of minimum wage,we find that minimum wage exerts significantly negative effect on profitability at the 5th quantile and quantiles higher than 40th and the absolute value of the effect of minimum wage increases with these quantiles.For other quantiles,the overall effect of minimum wage on profitability is negligible.
Nutriology relies on advanced analytical tools to study the molecular compositions of food and provide key information on sample quality/safety. Small nutrients detection is challenging due to the high diversity and broad dynamic range of molecules in food samples, and a further issue is to track low abundance toxins. Herein, we developed a novel plasmonic matrix-assisted laser desorption/ionization mass spectrometry(MALDI MS)approach to detect small nutrients and toxins in complex biological emulsion samples. Silver nanoshells(SiO_2@-Ag) with optimized structures were used as matrices andachieved direct analysis of ~ 6 n L of human breast milk without any enrichment or separation. We performed identification and quantitation of small nutrients and toxins with limit-of-detection down to 0.4 pmol(for melamine) and reaction time shortened to minutes, which is superior to the conventional biochemical method currently in use. The developed approach contributes to the near-future application of MALDI MS in a broad field and personalized design of plasmonic materials for real-case bio-analysis.
Shu WuLinxi QianLin HuangXuming SunHaiyang SuDeepanjali D.GuravMawei JiangWei CaiKun Qian
Traffic incidents result in remarkable congestion and delays.In order to help reduce the influence of incident...
Binghao Lu is with Dept of Automation,Tsinghua University,Beijing,100084,China.Runmin Xu is with Dept of Automation,Tsinghua University,Beijing,100084,China Lin Hou is with Dept of Automation,Tsinghua University,Beijing,100084,China.Zuo Zhang is with Dept of Automation,Tsinghua University,Tsinghua National Laboratory of Information Science and Technology,Beijing,100084,China
Assembled protein-based substances are emerging and promising classes of materials that provide unique properties for various applications in biotechnology and nanotechnolegy. Self-assembly is an effective way to immobilize protein. In this study, DNAs-conjugated bovine serum albumin （BSA） assembled into fibers via DNA hybridization is demonstrated. The morphology of fibers was observed by optical microscopy, scanning electron microscopy （SEM）, and atomic force microscopy （AFM）, and the assembly mechanism was then analysed and discussed. BSA molecules were first linked by DNA molecule and formed linear chains. These chains then were parallelly linked through additional DNA hybridization. Finally, several BSA chains further assembled into fibers by layering lamellae in a parallel manner. This work perhaps will provide a guide to the immobilization of enzyme, which could be applied to increase its catalytic efficiency in biomedicine and nanotechnology.
The nonlinear space charge effect of bunched beam in linac is one of theimportant factors that induces the emittance growth due to the conversion of thefield energy to kinetic energy. Using a cylinder model of space charge in a linac,we derive the internal energy for a bunched beam with some nonuniform spacecharge distributions, such as Gaussian, waterbag and parabolic distributions inboth the longitudinal and transverse directions. And the emittance growth causedby these nonuniformities is worked out.
The porosity and mechanical properties of GH4169(a precipitation strengthened nickel-base superalloy)specimens fabricated using the laser melting deposition technique at different laser powers were investigated.The results showed that the dendritic structure with the Laves phase and carbides embedded in the Ni-γ matrix formed in the as-fabricated GH4169 due to the strong temperature gradient and the high cooling rates.Porosity remarkably decreased first and slightly increased subsequently as the laser power increased from 300 to 800 W.The lowest porosity of the specimens characterized by 3D X-ray tomography is 0.28%.The specimens fabricated at 600 W tensiled along the direction perpendicular to the building direction exhibit the average yield strength of 587 MPa,the ultimate tensile strength of 903 MPa,and the elongation at fracture of 13.6%.Furthermore,the fatigue limit of the 600 W fabricated specimens is 173.7 MPa corresponding to the fatigue ratio of 0.1.And the relationship among the porosity,laser power and mechanical properties is discussed.
