Eutectic solidification in near-eutectic Al-13 wt pct Si casting alloys and the effect of trace addition of boron or strontium on it have been investigated using thermal analysis and microstructural characterization. ...Eutectic solidification in near-eutectic Al-13 wt pct Si casting alloys and the effect of trace addition of boron or strontium on it have been investigated using thermal analysis and microstructural characterization. In unmodified alloy, dual eutectic structure has been observed. The coarse eutectic （dendrite-like Al＋ coarse Si flakes） is formed above the equilibrium temperature of eutectic （Al＋Si） reaction （577℃）. The coarse eutectic （CE） grains nucleate from the primary silicon particles formed earlier due to local enrichment of silicon solute and grow in a divorced mode between the dendritic Al phase and large silicon flakes. The fine eutectic （FE） grains nucleate later on other potential sites activated by melt undercooling and grow in coupled-growing mode with the silicon crystals as fine flakes. The formation of the FE grains is favored in the alloys containing boron because of a great number of potential nucleation sites being added from boron-containing particles. Addition of strontium to the alloys restrains completely the formation of primary silicon particles and hence limits the nucleation of the CE. This is because the eutectic point has moved far enough to make the alloy, at this composition （Al-13 wt pct Si）, hypo-eutectic. Local cooling rate during solidification has an important influence on competition formation of these two eutectics.展开更多
Miniaturization has been an everlasting theme in the development of semiconductor lasers.One important breakthrough in this process in recent years is the use of metal-dielectric composite structures that made truly s...Miniaturization has been an everlasting theme in the development of semiconductor lasers.One important breakthrough in this process in recent years is the use of metal-dielectric composite structures that made truly subwavelength lasers possible.Many different designs of metallic cavity semiconductor nanolasers have been proposed and demonstrated.In this article,we will review some of the most exciting progresses in this newly emerging field.In particular,we will focus on metallic-cavity nanolasers with volume smaller than wavelength cubed under electrical injection with emphasis on high-temperature operation.Such devices will serve as an important component in the future integrated nanophotonic systems due to its ultra-small size.展开更多
The physics of laser-plasma interaction is studied on the Shenguang III prototype laser facility under conditions relevant to inertial confinement fusion designs.A sub-millimeter-size underdense hot plasma is created ...The physics of laser-plasma interaction is studied on the Shenguang III prototype laser facility under conditions relevant to inertial confinement fusion designs.A sub-millimeter-size underdense hot plasma is created by ionization of a low-density plastic foam by four high-energy(3.2 kJ)laser beams.An interaction beam is fired with a delay permitting evaluation of the excitation of parametric instabilities at different stages of plasma evolution.Multiple diagnostics are used for plasma characterization,scattered radiation,and accelerated electrons.The experimental results are analyzed with radiation hydrodynamic simulations that take account of foam ionization and homogenization.The measured level of stimulated Raman scattering is almost one order of magnitude larger than that measured in experiments with gasbags and hohlraums on the same installation,possibly because of a greater plasma density.Notable amplification is achieved in high-intensity speckles,indicating the importance of implementing laser temporal smoothing techniques with a large bandwidth for controlling laser propagation and absorption.展开更多
Data from the Tibet air shower array were used to examine the cosmic ray shadows of the Moon and the Sun at energies around 10Tev.The shadowing effect was clearly observed at the 5.8level for the Moon,while the shadow...Data from the Tibet air shower array were used to examine the cosmic ray shadows of the Moon and the Sun at energies around 10Tev.The shadowing effect was clearly observed at the 5.8level for the Moon,while the shadow of the Sun was found in the direction away from the sun by 0.86°tothe west and 0.43°to the south.The effect of the geomagnetic field has also been observed in the shadow of cosmic rays by the Moon.The observed deflection of the sun’s shadow is briefly discussed in connection with the effect of the magnetic fields between the sun and the Earth.This is the first observation of the effects of such magnetic fields on the cosmic ray shadow.The maximum-likelihood analysis of the Moon data set shows that the angular resolutions of the array for showers with its mode energies 7TeVand 35TeV are 0.87°-0.13°+0.10°and 0.54°-0.08°+0.11°,respectively.展开更多
基金supported by the National Natural Science Foundation of China under Grant No. 50771031the Research Foundation of Southeast University under Grant No. XJ0612238
文摘Eutectic solidification in near-eutectic Al-13 wt pct Si casting alloys and the effect of trace addition of boron or strontium on it have been investigated using thermal analysis and microstructural characterization. In unmodified alloy, dual eutectic structure has been observed. The coarse eutectic （dendrite-like Al＋ coarse Si flakes） is formed above the equilibrium temperature of eutectic （Al＋Si） reaction （577℃）. The coarse eutectic （CE） grains nucleate from the primary silicon particles formed earlier due to local enrichment of silicon solute and grow in a divorced mode between the dendritic Al phase and large silicon flakes. The fine eutectic （FE） grains nucleate later on other potential sites activated by melt undercooling and grow in coupled-growing mode with the silicon crystals as fine flakes. The formation of the FE grains is favored in the alloys containing boron because of a great number of potential nucleation sites being added from boron-containing particles. Addition of strontium to the alloys restrains completely the formation of primary silicon particles and hence limits the nucleation of the CE. This is because the eutectic point has moved far enough to make the alloy, at this composition （Al-13 wt pct Si）, hypo-eutectic. Local cooling rate during solidification has an important influence on competition formation of these two eutectics.
基金Research reported in this article in the authors group was supported by the Defense Advanced Research Project Agency program Nanoscale Architectures of Coherent Hyper-Optical Sources(grant no.W911-NF07-1-0314)by the Air Force Office of Scientific Research(grant no.FA9550-10-1-0444,Gernot Pomrenke)We thank Martin Hill for his collaboration over the last few years.
文摘Miniaturization has been an everlasting theme in the development of semiconductor lasers.One important breakthrough in this process in recent years is the use of metal-dielectric composite structures that made truly subwavelength lasers possible.Many different designs of metallic cavity semiconductor nanolasers have been proposed and demonstrated.In this article,we will review some of the most exciting progresses in this newly emerging field.In particular,we will focus on metallic-cavity nanolasers with volume smaller than wavelength cubed under electrical injection with emphasis on high-temperature operation.Such devices will serve as an important component in the future integrated nanophotonic systems due to its ultra-small size.
基金This project was partially supported by the Advanced Research Using High Intensity Laser Produced Photons and Particles(ADONIS)project(Grant No.CZ.02.1.01/0.0/0.0/16_019/0000789)the CAAS project(Grant No.CZ.02.1.01/0.0/0.0/16_019/0000778)+3 种基金both from the European Regional Development FundThe results of the LQ1606 project were partially obtained with the financial support from the Ministry of Education,Youth and Sports as part of targeted support from the National Programme of Sustainability IIThe authors acknowledge support from the National Natural Science Foundation of China(Grant Nos.11775033,11875241,11975215,11905204,12035002)the Laser Fusion Research Center Funds for Young Talents(Grant No.RCFPD3-2019-6).
文摘The physics of laser-plasma interaction is studied on the Shenguang III prototype laser facility under conditions relevant to inertial confinement fusion designs.A sub-millimeter-size underdense hot plasma is created by ionization of a low-density plastic foam by four high-energy(3.2 kJ)laser beams.An interaction beam is fired with a delay permitting evaluation of the excitation of parametric instabilities at different stages of plasma evolution.Multiple diagnostics are used for plasma characterization,scattered radiation,and accelerated electrons.The experimental results are analyzed with radiation hydrodynamic simulations that take account of foam ionization and homogenization.The measured level of stimulated Raman scattering is almost one order of magnitude larger than that measured in experiments with gasbags and hohlraums on the same installation,possibly because of a greater plasma density.Notable amplification is achieved in high-intensity speckles,indicating the importance of implementing laser temporal smoothing techniques with a large bandwidth for controlling laser propagation and absorption.
基金We are grateful to Prof.J.Arafune of ICRR,University of Tokyo and Prof.S.X.Fan of IHEP,Chinese Academy of Science for their support and encouragement.
文摘Data from the Tibet air shower array were used to examine the cosmic ray shadows of the Moon and the Sun at energies around 10Tev.The shadowing effect was clearly observed at the 5.8level for the Moon,while the shadow of the Sun was found in the direction away from the sun by 0.86°tothe west and 0.43°to the south.The effect of the geomagnetic field has also been observed in the shadow of cosmic rays by the Moon.The observed deflection of the sun’s shadow is briefly discussed in connection with the effect of the magnetic fields between the sun and the Earth.This is the first observation of the effects of such magnetic fields on the cosmic ray shadow.The maximum-likelihood analysis of the Moon data set shows that the angular resolutions of the array for showers with its mode energies 7TeVand 35TeV are 0.87°-0.13°+0.10°and 0.54°-0.08°+0.11°,respectively.
