In this work, the influences of alumina addition on cristobalite crystallization and properties of injec- tion molded silica-based ceramic cores were investigated. X-ray diffraction （XRD） was used to characterize ph...In this work, the influences of alumina addition on cristobalite crystallization and properties of injec- tion molded silica-based ceramic cores were investigated. X-ray diffraction （XRD） was used to characterize phase transformations in the samples, and the XRD result indicated that the addition of alumina pro- moted crystallization of fused silica during sintering at 1180-1220 ℃ and thus increases the amount of cristobalite. The increased amount of cristobalite as well as alumina addition led to much more thermal dilation due to their higher coefficients of thermal expansion than that of fused silica. The flexural strengths at room temperature and 1500 ~C were tested, and it was shown that alumina addition could not affect room temperature strength, but decreased the flexural strength at 1500 ℃. In addition, deflection resis- tance during heating to high temperatures was investigated, and the result indicated that alumina addition speeded up high temperature softening of the samples. XRD and scanning electron microscopy equipped with energy dispersive spectrometry （SEMJEDS） analysis suggested that this softening behavior was related with viscous flow sintering which could be accelerated by the reaction of alumina and silica with a product of mullite.展开更多
A series of Mge10(AlþY)alloys with various weight ratios of Al to Y were cast to investigate the role of Al_(2)Y in grain refinement in MgeAleY ternary system.Thermal analysis combined with microstructural and ED...A series of Mge10(AlþY)alloys with various weight ratios of Al to Y were cast to investigate the role of Al_(2)Y in grain refinement in MgeAleY ternary system.Thermal analysis combined with microstructural and EDX analysis was used to determine the phase transformation temperatures during solidification process.Experimental results show that when the Al content is below 4 wt%,a peritectic reaction,LþAl_(2)Y/a-Mg,occurs after the intermetallic Al_(2)Y forms directly from the melt as a pro-peritectic phase.Once the Al content is above 4 wt%,an eutectic reaction occurs at a lower temperature.The presence of the pro-peritectic phase can lead to nucleation of a-Mg directly through a peritectic reaction although grain refining efficiency is also closely related to the active particle size.In the case where solidification does not involve a peritectic reaction,the growth restriction factor,quantitatively the Q-value,governs the grain refining efficiency.Higher Q-value corresponds to finer grains.展开更多
Estimates of the surface heat budget over drifting ice and open water in the Arctic Ocean are made using eddy correlation and flux-profile methods using data obtained from drifting ice and from the R/V Xuelong in the ...Estimates of the surface heat budget over drifting ice and open water in the Arctic Ocean are made using eddy correlation and flux-profile methods using data obtained from drifting ice and from the R/V Xuelong in the Chinese National Arctic Research Expedition during August 19—24,1999. The results show that the net radiation received by the ice surface is mainly lost through the sensible heat flux and the heat flux due to melting ice, and the latent heat flux making small contribution to the heat balance. However, the heat balance of the open water surface was dominated by the radiative flux whereas the latent and sensible heat fluxes and the oceanic heat flux were greater than those on the sea-ice surface. These results emphasize that thermodynamic processes are quite different between air/open water and air/sea-ice over the Arctic Ocean which is important when considering the effect of sea-air-ice interaction on climate change process dur-ing the summer period.展开更多
The superτ-charm facility(STCF)is an electron–positron collider proposed by the Chinese particle physics community.It is designed to operate in a center-of-mass energy range from 2 to 7 GeV with a peak luminosity of...The superτ-charm facility(STCF)is an electron–positron collider proposed by the Chinese particle physics community.It is designed to operate in a center-of-mass energy range from 2 to 7 GeV with a peak luminosity of 0.5×10^(35) cm^(–2)·s^(–1) or higher.The STCF will produce a data sample about a factor of 100 larger than that of the presentτ-charm factory—the BEPCII,providing a unique platform for exploring the asymmetry of matter-antimatter(charge-parity violation),in-depth studies of the internal structure of hadrons and the nature of non-perturbative strong interactions,as well as searching for exotic hadrons and physics beyond the Standard Model.The STCF project in China is under development with an extensive R&D program.This document presents the physics opportunities at the STCF,describes conceptual designs of the STCF detector system,and discusses future plans for detector R&D and physics case studies.展开更多
In the present work,80 mm thick 6082Al alloy plates were successfully double-side welded by friction stir welding(FSW).The relationship between the microstructures and mechanical properties was built for the double-si...In the present work,80 mm thick 6082Al alloy plates were successfully double-side welded by friction stir welding(FSW).The relationship between the microstructures and mechanical properties was built for the double-side FSW butt joint with more attention paid to the local characteristic zones.It was shown that a phenomenon of microstructural inhomogeneity existed in the nugget zone(NZ)through the thickness direction.The grain size presented an obvious gradient distribution from the top to the bottom for each single-pass weld,and the microhardness values decreased from both surfaces to the middle of the NZ.The lowest hardness zone(LHZ)exhibited a"hyperbolical"-shaped distribution extending to the middle of the NZ.Similar tensile properties were obtained in the three sliced specimens of the FSW joint,and the joint coefficient reached about 70%which achieved the same level as the conventional FSW Al alloy joints.Finite element modeling proved that the"hyperbolical"-shaped heat affected zone(HAZ)was beneficial to resisting the strain concentration in the middle layer specimen which helped to increase the tensile strength.Based on the analysis of the hardness contour map,tensile property and microstructural evolution of the joints,an Isothermal Softening Layer(ISL)model was proposed and established,which may have a helpful guidance for the optimization on the FSW of ultra-thick Al alloy plates.展开更多
We report the experimental results of the commissioning phase in the 10 PW laser beamline of the Shanghai Superintense Ultrafast Laser Facility(SULF).The peak power reaches 2.4 PW on target without the last amplifying...We report the experimental results of the commissioning phase in the 10 PW laser beamline of the Shanghai Superintense Ultrafast Laser Facility(SULF).The peak power reaches 2.4 PW on target without the last amplifying during the experiment.The laser energy of 72±9 J is directed to a focal spot of approximately 6μm diameter(full width at half maximum)in 30 fs pulse duration,yielding a focused peak intensity around 2.0×10^(21)W/cm^(2).The first laser-proton acceleration experiment is performed using plain copper and plastic targets.High-energy proton beams with maximum cut-off energy up to 62.5 MeV are achieved using copper foils at the optimum target thickness of 4μm via target normal sheath acceleration.For plastic targets of tens of nanometers thick,the proton cut-off energy is approximately 20 MeV,showing ring-like or flamented density distributions.These experimental results reflect the capabilities of the SULF-10 PW beamline,for example,both ultrahigh intensity and relatively good beam contrast.Further optimization for these key parameters is underway,where peak laser intensities of 10^(22)-10^(23)w/cm^(2)are anticipated to support various experiments on extreme field physics.展开更多
Theγ-ray emission from the W51 complex is widely acknowledged to be attributed to the interaction between the cosmic rays(CRs)accelerated by the shock of supernova remnant(SNR)W51C and the dense molecular clouds in t...Theγ-ray emission from the W51 complex is widely acknowledged to be attributed to the interaction between the cosmic rays(CRs)accelerated by the shock of supernova remnant(SNR)W51C and the dense molecular clouds in the adjacent star-forming region,W51B.However,the maximum acceleration capability of W51C for CRs remains elusive.Based on observations conducted with the Large High Altitude Air Shower Observatory(LHAASO),we report a significant detection ofγrays emanating from the W51 complex,with energies from 2 to 200 TeV.The LHAASO measurements,for the first time,extend theγ-ray emission from the W51 complex beyond 100 TeV and reveal a significant spectrum bending at tens of TeV.By combining the"π^(0)-decay bump"featured data from Fermi-LAT,the broadbandγ-ray spectrum of the W51 region can be well-characterized by a simple pp-collision model.The observed spectral bending feature suggests an exponential cutoff at~400 TeV or a power-law break at~200 TeV in the CR proton spectrum,most likely providing the first evidence of SNRs serving as CR accelerators approaching the PeV regime.Additionally,two young star clusters within W51B could also be theoretically viable to produce the most energeticγrays observed by LHAASO.Our findings strongly support the presence of extreme CR accelerators within the W51 complex and provide new insights into the origin of Galactic CRs.展开更多
The Water Cherenkov Detector Array(WCDA) is a major component of the Large High Altitude Air Shower Array Observatory(LHAASO), a new generation cosmic-ray experiment with unprecedented sensitivity, currently under con...The Water Cherenkov Detector Array(WCDA) is a major component of the Large High Altitude Air Shower Array Observatory(LHAASO), a new generation cosmic-ray experiment with unprecedented sensitivity, currently under construction. WCDA is aimed at the study of TeV γ-rays. In order to evaluate the prospects of searching for TeV γ-ray sources with WCDA, we present a projection of the one-year sensitivity of WCDA to TeV γ-ray sources from TeVCat using an all-sky approach. Out of 128 TeVCat sources observable by WCDA up to a zenith angle of 45°, we estimate that 42 would be detectable in one year of observations at a median energy of 1 TeV. Most of them are Galactic sources, and the extragalactic sources are Active Galactic Nuclei(AGN).展开更多
V-based kagome superconductors AV_(3)Sb_(5)(A=K,Rb,and Cs)host a charge density wave(CDW)and a topological nontrivial band structure,thereby providing a great platform to study the interplay of superconductivity(SC),C...V-based kagome superconductors AV_(3)Sb_(5)(A=K,Rb,and Cs)host a charge density wave(CDW)and a topological nontrivial band structure,thereby providing a great platform to study the interplay of superconductivity(SC),CDW,frustration,and topology.Here,we report ultralow-temperature thermal conductivity measurements of CsV_(3)Sb_(5 ) and Ta-doped Cs((V_(0.86)Ta_(0.14)))_(3)Sb_(5) and scanning tunneling microscopy(STM)measurements of CsV_(3)Sb_(5 ).The finite residual linear term of thermal conductivity at zero magnetic field suggests the existence of a residual density of states(DOS)in the superconducting state of CsV_(3)Sb_(5 ).This is supported by the observation of non-zero conductance at zero bias in STM spectrum at an electronic temperature of 90 mK.However,in Cs(V_(0.86)Ta_(0.14))_(3)Sb_(5),which does not have CDW order,there is no evidence for the residual DOS.These results show the importance of CDW order for the residual DOS,and that a nodal s-wave gap or residual Fermi arc may be the origin of the residual DOS in such an unusual multiband kagome superconductor,CsV_(3)Sb_(5 ).展开更多
We report on experimental observation of non-laminar proton acceleration modulated by a strong magnetic field in laser irradiating micrometer aluminum targets.The results illustrate the coexistence of ring-like and fi...We report on experimental observation of non-laminar proton acceleration modulated by a strong magnetic field in laser irradiating micrometer aluminum targets.The results illustrate the coexistence of ring-like and filamentation structures.We implement the knife edge method into the radiochromic film detector to map the accelerated beams,measuring a source size of 30-110μm for protons of more than 5 MeV.The diagnosis reveals that the ring-like profile originates from low-energy protons far off the axis whereas the filamentation is from the near-axis high-energy protons,exhibiting non-laminar features.Particle-in-cell simulations reproduced the experimental results,showing that the short-term magnetic turbulence via Weibel instability and the long-term quasi-static annular magnetic field by the streaming electric current account for the measured beam profile.Our work provides direct mapping of laser-driven proton sources in the space-energy domain and reveals the non-laminar beam evolution at featured time scales.展开更多
A Cu-10wt%Fe composite was prepared through hot-pressed sintering,and the material was subsequently solution treated.The hot-pressed sintered and solution treated materials were rolled and aged.The precipitation behav...A Cu-10wt%Fe composite was prepared through hot-pressed sintering,and the material was subsequently solution treated.The hot-pressed sintered and solution treated materials were rolled and aged.The precipitation behavior and performance changes were systematically studied by using scanning electron microscopy and transmission electron microscopy.In contrast to the hot-pressed sintered specimen,the solution treatment significantly affects the thermal stability and properties of the Cu-10wt%Fe composite.The Cu-10wt%Fe composite was prepared after solid solution,cold rolling and aging at 773 K for 1 h,and it obtained excellent tensile strength of 494 MPa,uniform elongation of 16.3%,electrical conductivity of 51.1%IACS and softening temperature of 838 K.Mechanisms for the distinct difference in thermal stability and properties between hot-pressed sintered and solution treated specimens were analyzed.These findings provide a theoretical basis for designing high-performance Cu-based in-situ composites by post treatment.展开更多
Guided waves in the multilayered one-dimensional quasi-crystal plates are,respectively,investigated in the context of the Bak and elasto-hydrodynamic models.Dispersion curves and phonon and phason displacements are ca...Guided waves in the multilayered one-dimensional quasi-crystal plates are,respectively,investigated in the context of the Bak and elasto-hydrodynamic models.Dispersion curves and phonon and phason displacements are calculated using the Legendre polynomial method.Wave characteristics in the context of these two models are analyzed in detail.Results show that the phonon-phason coupling effects on the first two layers are the same at low frequencies;but,they are more significant on the first layer than those on the second layer at high frequencies.These obtained results lay the theoretical basis of guided-wave nondestructive test on multilayered quasi-crystal plates.展开更多
The effects of ion motion on the generation of short-cycle relativistic laser pulses during radiation pressure acceleration are investigated by analytical modeling and particle-in-cell simulations. Studies show that t...The effects of ion motion on the generation of short-cycle relativistic laser pulses during radiation pressure acceleration are investigated by analytical modeling and particle-in-cell simulations. Studies show that the rear part of the transmitted pulse modulated by ion motion is sharper compared with the case of the electron shutter only. In this study, the ions further modulate the short-cycle pulses transmitted. A 3.9 fs laser pulse with an intensity of 1.33×1021W cm-2is generated by properly controlling the motions of the electron and ion in the simulations. The short-cycle laser pulse source proposed can be applied in the generation of single attosecond pulses and electron acceleration in a small bubble regime.展开更多
The effect of different amounts of silicon on the microstructure of the yttrium modified Ni3Al base alloy IC6 was studied with transmission electron microscope (TEM). The chemical compositions of phases formed due to ...The effect of different amounts of silicon on the microstructure of the yttrium modified Ni3Al base alloy IC6 was studied with transmission electron microscope (TEM). The chemical compositions of phases formed due to the presence of silicon and yttrium were analyzed with energy dispersive spectrum(EDS) technique of electron probe microstructural analysis (EPMA). The results showed that a bulk shape phase rich in Mo and Si was formed in the alloys with addition of 0.10-0.20wt%Si and 0.12wt%Y, and that a needle like phase named Y-NiMo was precipitated in the interdendritic area in the alloy with addition of 0.30wt%Si and 0.12wt%Y besides the formation of the bulk shape phase mentioned above. The stress rupture properties under 1100℃/80MPa and the thermal fatigue properties at 1100℃ were improved by adding 0. 12wt%Y but decreased by adding 0.10-0.30wt%Si and 0.12wt%Y. The addition of 0. 10-0.20wt%Si and 0.12wt%Y has no obvious influence on the tensile properties of alloy IC6 at room temperature (R. T.), 760, and 900℃, respectively.展开更多
Purpose: To examine the effect of an intravitreal injection of angiostatin on vascular leakage in retina and iris of the diabetes and study its possible mechanism. Methods: Experimental diabetes was induced in 24 rats...Purpose: To examine the effect of an intravitreal injection of angiostatin on vascular leakage in retina and iris of the diabetes and study its possible mechanism. Methods: Experimental diabetes was induced in 24 rats by an intravenous injection of streptozotocin (STZ) during 48 adult rats. Three groups were randomization distributed of them. There were 8 of both normal and diabetic rats in each group. STZ-diabetic rats and age-matched normal rats received an intravitreal injection of 5 μl of sterile PBS (Phosphate Buffered Saline) into the right eye, and the left eye was non-injected in the group A; Angiostatin was injected into the vitreous of the right eye (7.5 μg / 5 μl / eye), and the left eye received the same volume of sterile PBS as the control in the group B and C. The vascular permeability of retina and iris was measured using the Evans blue method at 2 days following the injection in the group A and B. Expression of VEGF in retina was evaluated using western blot analysis 24 hours following the injection in the group C. Results: Diabetic rats showed significant increases of vascular permeability in the retina ( P < 0.01) and iris ( P < 0.05). Angiostatin-injected eyes showed significant decreases in vascular permeability in the retina ( P < 0.01) and iris ( P < 0.05) comparing with the PBS-injected eyes in STZ-diabetic rats. In contrast, intravitreal injection of the same dose of angiostatin into the age-matched normal rats did not result in any significant reduction in vascular permeability in the retina and iris, when compared with the contralateral eye with PBS injection ( P > 0.05). Angiostatin injection significantly reduced VEGF level in the retinas of STZ-diabetic rats but did not affect retinal VEGF level in normal rats. Conclusions: Angiostatin significantly reduce pathological vascular permeability in the retina and iris of STZ-diabetic rats but not in normal rats. Angiostatin down-regulates VEGF expression and thus, blocks the major cause of vascular leakage in the diabetic retina. Theref展开更多
Due to the similarity in composition and crystal structure of some Ti Al Si ternary intermetallics,it is quite difficult to accurately confirm their physic characteristics,and thus,to tailor microstructure to improve ...Due to the similarity in composition and crystal structure of some Ti Al Si ternary intermetallics,it is quite difficult to accurately confirm their physic characteristics,and thus,to tailor microstructure to improve mechanical properties of metal materials related to the Ti Al Si intermetallics.Therefore,the formation process of Ti Al Si intermetallics was investigated during heating Ti-A356 mixed powder compact at a A356 alloy semisolid temperature of 595℃.The results indicated that two kinds of intermetallics ofτ1(tetragonal,I41/amd)andτ2(orthorhombic,Cmcm)generated,and both the concentration and supply direction of Ti atoms,which are related to local breakage of oxide films on neighboring Ti and A356 alloy powders,determined the phase and morphology of the intermetallics.τ1 andτ2 crystals all had an intrinsic plate morphology,butτ2 crystals were thinner due to more anisotropic growth resulted from their high density of stacking faults(SFs).τ1 lamellar domains generated during growth ofτ2 crystals,which were accompanied by decrease in density of SFs.The combined effect of size difference and internal energy difference betweenτ1 andτ2 crystals made largeτ1 crystals coarsen at the expense ofτ2 crystals in Ostwald ripening,leading them to finally evolve into an agglomerate of largeτ1 plates.展开更多
One of the key challenges in the total maximum daily load(TMDL)development process is how to define the critical condition for a receiving waterbody.The main concern in using a continuous simulation approach is the ab...One of the key challenges in the total maximum daily load(TMDL)development process is how to define the critical condition for a receiving waterbody.The main concern in using a continuous simulation approach is the absence of any guarantee that the most critical condition will be captured during the selected representative hydrologic period,given the scarcity of long-term continuous data.The objectives of this paper are to clearly address the critical condition in the TMDL development process and to compare continuous and event-based approaches in defining critical condition during TMDL development for a waterbody impacted by both point and nonpoint source pollution.A practical,event-based critical flow-storm(CFS)approach was developed to explicitly addresses the critical condition as a combination of a low stream flow and a storm event of a selected magnitude,both having certain frequencies of occurrence.This paper illustrated the CFS concept and provided its theoretical basis using a derived analytical conceptual model.The CFS approach clearly defined a critical condition,obtained reasonable results and could be considered as an alternative method in TMDL development.展开更多
文摘In this work, the influences of alumina addition on cristobalite crystallization and properties of injec- tion molded silica-based ceramic cores were investigated. X-ray diffraction （XRD） was used to characterize phase transformations in the samples, and the XRD result indicated that the addition of alumina pro- moted crystallization of fused silica during sintering at 1180-1220 ℃ and thus increases the amount of cristobalite. The increased amount of cristobalite as well as alumina addition led to much more thermal dilation due to their higher coefficients of thermal expansion than that of fused silica. The flexural strengths at room temperature and 1500 ~C were tested, and it was shown that alumina addition could not affect room temperature strength, but decreased the flexural strength at 1500 ℃. In addition, deflection resis- tance during heating to high temperatures was investigated, and the result indicated that alumina addition speeded up high temperature softening of the samples. XRD and scanning electron microscopy equipped with energy dispersive spectrometry （SEMJEDS） analysis suggested that this softening behavior was related with viscous flow sintering which could be accelerated by the reaction of alumina and silica with a product of mullite.
基金The authors would like to thank the CSIRO Flagship in Light Metals and the CAST Cooperative Research Centre(CAST CRC)for financial support.
文摘A series of Mge10(AlþY)alloys with various weight ratios of Al to Y were cast to investigate the role of Al_(2)Y in grain refinement in MgeAleY ternary system.Thermal analysis combined with microstructural and EDX analysis was used to determine the phase transformation temperatures during solidification process.Experimental results show that when the Al content is below 4 wt%,a peritectic reaction,LþAl_(2)Y/a-Mg,occurs after the intermetallic Al_(2)Y forms directly from the melt as a pro-peritectic phase.Once the Al content is above 4 wt%,an eutectic reaction occurs at a lower temperature.The presence of the pro-peritectic phase can lead to nucleation of a-Mg directly through a peritectic reaction although grain refining efficiency is also closely related to the active particle size.In the case where solidification does not involve a peritectic reaction,the growth restriction factor,quantitatively the Q-value,governs the grain refining efficiency.Higher Q-value corresponds to finer grains.
基金This study was supported primarily by grants of Chinese National Arctic Scientific Program and IARC/Frontier Fairbanks +1 种基金USA and the National Natural Science Foundation of China (Grant No. 49975006)
文摘Estimates of the surface heat budget over drifting ice and open water in the Arctic Ocean are made using eddy correlation and flux-profile methods using data obtained from drifting ice and from the R/V Xuelong in the Chinese National Arctic Research Expedition during August 19—24,1999. The results show that the net radiation received by the ice surface is mainly lost through the sensible heat flux and the heat flux due to melting ice, and the latent heat flux making small contribution to the heat balance. However, the heat balance of the open water surface was dominated by the radiative flux whereas the latent and sensible heat fluxes and the oceanic heat flux were greater than those on the sea-ice surface. These results emphasize that thermodynamic processes are quite different between air/open water and air/sea-ice over the Arctic Ocean which is important when considering the effect of sea-air-ice interaction on climate change process dur-ing the summer period.
基金supported by the National Key R&D Program of China under Contract No.2022YFA1602200the International Partnership Program of the Chineses Academy of Sciences under Grant No.211134KYSB20200057the STCF Key Technology Research and Development Project.
文摘The superτ-charm facility(STCF)is an electron–positron collider proposed by the Chinese particle physics community.It is designed to operate in a center-of-mass energy range from 2 to 7 GeV with a peak luminosity of 0.5×10^(35) cm^(–2)·s^(–1) or higher.The STCF will produce a data sample about a factor of 100 larger than that of the presentτ-charm factory—the BEPCII,providing a unique platform for exploring the asymmetry of matter-antimatter(charge-parity violation),in-depth studies of the internal structure of hadrons and the nature of non-perturbative strong interactions,as well as searching for exotic hadrons and physics beyond the Standard Model.The STCF project in China is under development with an extensive R&D program.This document presents the physics opportunities at the STCF,describes conceptual designs of the STCF detector system,and discusses future plans for detector R&D and physics case studies.
基金supported by the Youth Innovation Promotion Association of the Chinese Academy of Sciences(2017236)National Natural Science Foundation of China under grant No.U1760201.
文摘In the present work,80 mm thick 6082Al alloy plates were successfully double-side welded by friction stir welding(FSW).The relationship between the microstructures and mechanical properties was built for the double-side FSW butt joint with more attention paid to the local characteristic zones.It was shown that a phenomenon of microstructural inhomogeneity existed in the nugget zone(NZ)through the thickness direction.The grain size presented an obvious gradient distribution from the top to the bottom for each single-pass weld,and the microhardness values decreased from both surfaces to the middle of the NZ.The lowest hardness zone(LHZ)exhibited a"hyperbolical"-shaped distribution extending to the middle of the NZ.Similar tensile properties were obtained in the three sliced specimens of the FSW joint,and the joint coefficient reached about 70%which achieved the same level as the conventional FSW Al alloy joints.Finite element modeling proved that the"hyperbolical"-shaped heat affected zone(HAZ)was beneficial to resisting the strain concentration in the middle layer specimen which helped to increase the tensile strength.Based on the analysis of the hardness contour map,tensile property and microstructural evolution of the joints,an Isothermal Softening Layer(ISL)model was proposed and established,which may have a helpful guidance for the optimization on the FSW of ultra-thick Al alloy plates.
基金the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB16)the National Natural Science Foundation of China(Nos.11875307,11935008,11804348,11705260,11905278 and 11975302)the Youth Innovation Promotion Association of Chinese Academy of Sciences(No.2021242).
文摘We report the experimental results of the commissioning phase in the 10 PW laser beamline of the Shanghai Superintense Ultrafast Laser Facility(SULF).The peak power reaches 2.4 PW on target without the last amplifying during the experiment.The laser energy of 72±9 J is directed to a focal spot of approximately 6μm diameter(full width at half maximum)in 30 fs pulse duration,yielding a focused peak intensity around 2.0×10^(21)W/cm^(2).The first laser-proton acceleration experiment is performed using plain copper and plastic targets.High-energy proton beams with maximum cut-off energy up to 62.5 MeV are achieved using copper foils at the optimum target thickness of 4μm via target normal sheath acceleration.For plastic targets of tens of nanometers thick,the proton cut-off energy is approximately 20 MeV,showing ring-like or flamented density distributions.These experimental results reflect the capabilities of the SULF-10 PW beamline,for example,both ultrahigh intensity and relatively good beam contrast.Further optimization for these key parameters is underway,where peak laser intensities of 10^(22)-10^(23)w/cm^(2)are anticipated to support various experiments on extreme field physics.
基金supported by the National Natural Science Foundation of China(12393851,12261160362,12393852,12393853,12393854,12022502,2205314,12105301,12105292,12105294,12005246,and 12173039)Department of Science and Technology of Sichuan Province(24NSFJQ0060 and 2024NSFSC0449)+5 种基金Project for Young Scientists in Basic Research of Chinese Academy of Sciences(YSBR-061,2022010)Thailand by the National Science and Technology Development Agency(NSTDA)National Research Council of Thailand(NRCT):High-Potential Research Team Grant Program(N42A650868)the Chengdu Management Committee of Tianfu New Area for constant financial support to research with LHAASO datathe Milky Way Imaging Scroll Painting(MWISP)project,sponsored by the National Key R&D Program of China(2023YFA1608000 and 2017YFA0402701)the CAS Key Research Program of Frontier Sciences(QYZDJ-SSW-SLH047)。
文摘Theγ-ray emission from the W51 complex is widely acknowledged to be attributed to the interaction between the cosmic rays(CRs)accelerated by the shock of supernova remnant(SNR)W51C and the dense molecular clouds in the adjacent star-forming region,W51B.However,the maximum acceleration capability of W51C for CRs remains elusive.Based on observations conducted with the Large High Altitude Air Shower Observatory(LHAASO),we report a significant detection ofγrays emanating from the W51 complex,with energies from 2 to 200 TeV.The LHAASO measurements,for the first time,extend theγ-ray emission from the W51 complex beyond 100 TeV and reveal a significant spectrum bending at tens of TeV.By combining the"π^(0)-decay bump"featured data from Fermi-LAT,the broadbandγ-ray spectrum of the W51 region can be well-characterized by a simple pp-collision model.The observed spectral bending feature suggests an exponential cutoff at~400 TeV or a power-law break at~200 TeV in the CR proton spectrum,most likely providing the first evidence of SNRs serving as CR accelerators approaching the PeV regime.Additionally,two young star clusters within W51B could also be theoretically viable to produce the most energeticγrays observed by LHAASO.Our findings strongly support the presence of extreme CR accelerators within the W51 complex and provide new insights into the origin of Galactic CRs.
基金Supported by National Natural Science Foundation of China(11761141001,11635011,11873005)The LHAASO project is supported by the National Key R&D Program of China(2018YFA0404200),the Chinese Academy of Sciences,the Key Laboratory of Particle Astrophysics,IHEP,CAS。
文摘The Water Cherenkov Detector Array(WCDA) is a major component of the Large High Altitude Air Shower Array Observatory(LHAASO), a new generation cosmic-ray experiment with unprecedented sensitivity, currently under construction. WCDA is aimed at the study of TeV γ-rays. In order to evaluate the prospects of searching for TeV γ-ray sources with WCDA, we present a projection of the one-year sensitivity of WCDA to TeV γ-ray sources from TeVCat using an all-sky approach. Out of 128 TeVCat sources observable by WCDA up to a zenith angle of 45°, we estimate that 42 would be detectable in one year of observations at a median energy of 1 TeV. Most of them are Galactic sources, and the extragalactic sources are Active Galactic Nuclei(AGN).
文摘V-based kagome superconductors AV_(3)Sb_(5)(A=K,Rb,and Cs)host a charge density wave(CDW)and a topological nontrivial band structure,thereby providing a great platform to study the interplay of superconductivity(SC),CDW,frustration,and topology.Here,we report ultralow-temperature thermal conductivity measurements of CsV_(3)Sb_(5 ) and Ta-doped Cs((V_(0.86)Ta_(0.14)))_(3)Sb_(5) and scanning tunneling microscopy(STM)measurements of CsV_(3)Sb_(5 ).The finite residual linear term of thermal conductivity at zero magnetic field suggests the existence of a residual density of states(DOS)in the superconducting state of CsV_(3)Sb_(5 ).This is supported by the observation of non-zero conductance at zero bias in STM spectrum at an electronic temperature of 90 mK.However,in Cs(V_(0.86)Ta_(0.14))_(3)Sb_(5),which does not have CDW order,there is no evidence for the residual DOS.These results show the importance of CDW order for the residual DOS,and that a nodal s-wave gap or residual Fermi arc may be the origin of the residual DOS in such an unusual multiband kagome superconductor,CsV_(3)Sb_(5 ).
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB16)National Natural Science Foundation of China(Nos.11875307,11935008,11804348,11705260,11905278,and 11975302)Youth Innovation Promotion Association of the Chinese Academy of Sciences.
文摘We report on experimental observation of non-laminar proton acceleration modulated by a strong magnetic field in laser irradiating micrometer aluminum targets.The results illustrate the coexistence of ring-like and filamentation structures.We implement the knife edge method into the radiochromic film detector to map the accelerated beams,measuring a source size of 30-110μm for protons of more than 5 MeV.The diagnosis reveals that the ring-like profile originates from low-energy protons far off the axis whereas the filamentation is from the near-axis high-energy protons,exhibiting non-laminar features.Particle-in-cell simulations reproduced the experimental results,showing that the short-term magnetic turbulence via Weibel instability and the long-term quasi-static annular magnetic field by the streaming electric current account for the measured beam profile.Our work provides direct mapping of laser-driven proton sources in the space-energy domain and reveals the non-laminar beam evolution at featured time scales.
基金This work was supported by the National Natural Science Foundation of China(Grant No.52101181).
文摘A Cu-10wt%Fe composite was prepared through hot-pressed sintering,and the material was subsequently solution treated.The hot-pressed sintered and solution treated materials were rolled and aged.The precipitation behavior and performance changes were systematically studied by using scanning electron microscopy and transmission electron microscopy.In contrast to the hot-pressed sintered specimen,the solution treatment significantly affects the thermal stability and properties of the Cu-10wt%Fe composite.The Cu-10wt%Fe composite was prepared after solid solution,cold rolling and aging at 773 K for 1 h,and it obtained excellent tensile strength of 494 MPa,uniform elongation of 16.3%,electrical conductivity of 51.1%IACS and softening temperature of 838 K.Mechanisms for the distinct difference in thermal stability and properties between hot-pressed sintered and solution treated specimens were analyzed.These findings provide a theoretical basis for designing high-performance Cu-based in-situ composites by post treatment.
基金The authors gratefully acknowledge the support by the National Natural Science Foundation of China(No.U1804134 and No.51975189)the Program for Innovative Research Team of Henan Polytechnic University(No.T2017-3)the Key Scientific and Technological Project of Henan Province(Nos.192102210189 and 182102210314).
文摘Guided waves in the multilayered one-dimensional quasi-crystal plates are,respectively,investigated in the context of the Bak and elasto-hydrodynamic models.Dispersion curves and phonon and phason displacements are calculated using the Legendre polynomial method.Wave characteristics in the context of these two models are analyzed in detail.Results show that the phonon-phason coupling effects on the first two layers are the same at low frequencies;but,they are more significant on the first layer than those on the second layer at high frequencies.These obtained results lay the theoretical basis of guided-wave nondestructive test on multilayered quasi-crystal plates.
基金supported by the 973 Program (No. 2011CB808104)the National Natural Science Foundation of China (Nos. 11335013, 10834008, 11125526, 60921004, and 11305236)+1 种基金the International S&T Cooperation Program of China (No. 2011DFA11300)Shanghai Natural Science Foundation (No. 13ZR1463300)
文摘The effects of ion motion on the generation of short-cycle relativistic laser pulses during radiation pressure acceleration are investigated by analytical modeling and particle-in-cell simulations. Studies show that the rear part of the transmitted pulse modulated by ion motion is sharper compared with the case of the electron shutter only. In this study, the ions further modulate the short-cycle pulses transmitted. A 3.9 fs laser pulse with an intensity of 1.33×1021W cm-2is generated by properly controlling the motions of the electron and ion in the simulations. The short-cycle laser pulse source proposed can be applied in the generation of single attosecond pulses and electron acceleration in a small bubble regime.
文摘The effect of different amounts of silicon on the microstructure of the yttrium modified Ni3Al base alloy IC6 was studied with transmission electron microscope (TEM). The chemical compositions of phases formed due to the presence of silicon and yttrium were analyzed with energy dispersive spectrum(EDS) technique of electron probe microstructural analysis (EPMA). The results showed that a bulk shape phase rich in Mo and Si was formed in the alloys with addition of 0.10-0.20wt%Si and 0.12wt%Y, and that a needle like phase named Y-NiMo was precipitated in the interdendritic area in the alloy with addition of 0.30wt%Si and 0.12wt%Y besides the formation of the bulk shape phase mentioned above. The stress rupture properties under 1100℃/80MPa and the thermal fatigue properties at 1100℃ were improved by adding 0. 12wt%Y but decreased by adding 0.10-0.30wt%Si and 0.12wt%Y. The addition of 0. 10-0.20wt%Si and 0.12wt%Y has no obvious influence on the tensile properties of alloy IC6 at room temperature (R. T.), 760, and 900℃, respectively.
基金Supported by a grant from 2004 Shenzhen Technological Plan( code:200405097)
文摘Purpose: To examine the effect of an intravitreal injection of angiostatin on vascular leakage in retina and iris of the diabetes and study its possible mechanism. Methods: Experimental diabetes was induced in 24 rats by an intravenous injection of streptozotocin (STZ) during 48 adult rats. Three groups were randomization distributed of them. There were 8 of both normal and diabetic rats in each group. STZ-diabetic rats and age-matched normal rats received an intravitreal injection of 5 μl of sterile PBS (Phosphate Buffered Saline) into the right eye, and the left eye was non-injected in the group A; Angiostatin was injected into the vitreous of the right eye (7.5 μg / 5 μl / eye), and the left eye received the same volume of sterile PBS as the control in the group B and C. The vascular permeability of retina and iris was measured using the Evans blue method at 2 days following the injection in the group A and B. Expression of VEGF in retina was evaluated using western blot analysis 24 hours following the injection in the group C. Results: Diabetic rats showed significant increases of vascular permeability in the retina ( P < 0.01) and iris ( P < 0.05). Angiostatin-injected eyes showed significant decreases in vascular permeability in the retina ( P < 0.01) and iris ( P < 0.05) comparing with the PBS-injected eyes in STZ-diabetic rats. In contrast, intravitreal injection of the same dose of angiostatin into the age-matched normal rats did not result in any significant reduction in vascular permeability in the retina and iris, when compared with the contralateral eye with PBS injection ( P > 0.05). Angiostatin injection significantly reduced VEGF level in the retinas of STZ-diabetic rats but did not affect retinal VEGF level in normal rats. Conclusions: Angiostatin significantly reduce pathological vascular permeability in the retina and iris of STZ-diabetic rats but not in normal rats. Angiostatin down-regulates VEGF expression and thus, blocks the major cause of vascular leakage in the diabetic retina. Theref
基金supported by the National Key Research and Development Program(grant No.2018YFB2001800)the National Natural Science Foundation of China(grant No.51564035)。
文摘Due to the similarity in composition and crystal structure of some Ti Al Si ternary intermetallics,it is quite difficult to accurately confirm their physic characteristics,and thus,to tailor microstructure to improve mechanical properties of metal materials related to the Ti Al Si intermetallics.Therefore,the formation process of Ti Al Si intermetallics was investigated during heating Ti-A356 mixed powder compact at a A356 alloy semisolid temperature of 595℃.The results indicated that two kinds of intermetallics ofτ1(tetragonal,I41/amd)andτ2(orthorhombic,Cmcm)generated,and both the concentration and supply direction of Ti atoms,which are related to local breakage of oxide films on neighboring Ti and A356 alloy powders,determined the phase and morphology of the intermetallics.τ1 andτ2 crystals all had an intrinsic plate morphology,butτ2 crystals were thinner due to more anisotropic growth resulted from their high density of stacking faults(SFs).τ1 lamellar domains generated during growth ofτ2 crystals,which were accompanied by decrease in density of SFs.The combined effect of size difference and internal energy difference betweenτ1 andτ2 crystals made largeτ1 crystals coarsen at the expense ofτ2 crystals in Ostwald ripening,leading them to finally evolve into an agglomerate of largeτ1 plates.
基金This work was supported in part by the Virginia Department of Environmental Quality and the Virginia Environmental Endowment,Richmond,Virginia,USA.
文摘One of the key challenges in the total maximum daily load(TMDL)development process is how to define the critical condition for a receiving waterbody.The main concern in using a continuous simulation approach is the absence of any guarantee that the most critical condition will be captured during the selected representative hydrologic period,given the scarcity of long-term continuous data.The objectives of this paper are to clearly address the critical condition in the TMDL development process and to compare continuous and event-based approaches in defining critical condition during TMDL development for a waterbody impacted by both point and nonpoint source pollution.A practical,event-based critical flow-storm(CFS)approach was developed to explicitly addresses the critical condition as a combination of a low stream flow and a storm event of a selected magnitude,both having certain frequencies of occurrence.This paper illustrated the CFS concept and provided its theoretical basis using a derived analytical conceptual model.The CFS approach clearly defined a critical condition,obtained reasonable results and could be considered as an alternative method in TMDL development.
