Dihadron azimuthal correlations containing a high transverse momentum(pr)trigger particle are sensit-ive to the properties of the nuclear medium created at RHIC through the strong interactions occurring between the tr...Dihadron azimuthal correlations containing a high transverse momentum(pr)trigger particle are sensit-ive to the properties of the nuclear medium created at RHIC through the strong interactions occurring between the traversing parton and the medium,ie.jet-quenching.Previous measurements revealed a strong modification to di-hadron azimuthal correlations in Au+Au collisions with respect to ptp and d+Au collisions.The modification in-creases with the collision centrality,suggesting a path-length or energy density dependence to the je-quenching ef-fect.This paper reports STAR measurements of dihadron azimuthal correlations in mid-central(20%-60%)Au+Au collisions at√^(S)NN=200 GeV as a function of the trigger particle's azimuthal angle relative to the event plane,Ф_(s)=|Ф_(t)-ψ_(Ep)|.The azimuthal correlation is studied as a function of both the trigger and associated particle pr.The subtractions of the combinatorial background and anisotropic flow,assuming Zero Yield At Minimum(ZYAM),are described.The correlation results are first discussed with subtraction of the even harmonic(elliptic and quadrangu-lar)flow backgrounds.The away-side correlation is strongly modifed,and the modification varies withФ_(s),with a double-peak structure for out-of-plane trigger particles.The near-side ridge(long range pseudo-rapidity△_(η)correla-tion)appears to drop with increasingФ_(s)while the jet-like component remains approximately constant.The correla-tion functions are further studied with the subtraction of odd harmonic triangular flow background arising from fluc-tuations.It is found that the triangular flow,while responsible for the majority of the amplitudes,is not sufficient to explain theφs-dependence of the ridge or the away-side double-peak structure.The dropping ridge withФ_(s)could be attributed to aФ_(s)-dependent lliptie anisotropy;however,the physics mechanism of the ridge remains an open ques-tion.Even with aФ_(s)-dependent elliptic flow,the away-side correlation structure is robust.These results,with exte展开更多
Soil acid phosphomonoesterase activity (APA) plays a vital role in controlling phosphorus (P) cycling and reflecting the current degree of P limitation. Responses of soil APA to elevating nitrogen (N) deposition are i...Soil acid phosphomonoesterase activity (APA) plays a vital role in controlling phosphorus (P) cycling and reflecting the current degree of P limitation. Responses of soil APA to elevating nitrogen (N) deposition are important because of their potential applications in addressing the relationship between N and P in forest ecosystems. A study of responses of soil APA to simulated N deposition was conducted in three succession forests of subtropical China. The three forests include a Masson pine (Pinus massoniana) forest (MPF)-pioneer community, a coniferous and broad-leaved mixed forest (MF)-transition community and a monsoon evergreen broad-leaved forest (MEBF)-climax community. Four N treatments were designed for MEBF: control (without N added), low-N (50 kg N ha-1 year-1), and medium-N (100 kg N ha-1 year-1) and high-N (150 kg N ha-1 year-1), and only three N treatments (i.e., control, low-N, medium-N) were established for MPF and MF. Results showed that soil APA was highest in MEBF, followed by MPF and MF. Soil APAs in both MPF and MF were not influenced by low-N treatments but depressed in medium-N treatments. However, soil APA in MEBF exhibited negative responses to high N additions, indicating that the environment of enhanced N depositions would reduce P supply for the mature forest ecosystem. Soil APA and its responses to N additions in subtropical forests were closely related to the succession stages in the forests.展开更多
In 2018,the STAR collaboration collected data from^(96)_(44)Ru+^(96)_(44)Ru and^(96)_(40)Zr+^(96)_(40)Zr at√^(S)NN=200 Ge V to search for the presence of the chiral magnetic effect in collisions of nuclei.The isobar ...In 2018,the STAR collaboration collected data from^(96)_(44)Ru+^(96)_(44)Ru and^(96)_(40)Zr+^(96)_(40)Zr at√^(S)NN=200 Ge V to search for the presence of the chiral magnetic effect in collisions of nuclei.The isobar collision species alternated frequently between 9644 Ru+^(96)_(44)Ru and^(96)_(40)Zr+^(96)_(40)Zr.In order to conduct blind analyses of studies related to the chiral magnetic effect in these isobar data,STAR developed a three-step blind analysis procedure.Analysts are initially provided a"reference sample"of data,comprised of a mix of events from the two species,the order of which respects time-dependent changes in run conditions.After tuning analysis codes and performing time-dependent quality assurance on the reference sample,analysts are provided a species-blind sample suitable for calculating efficiencies and corrections for individual≈30-min data-taking runs.For this sample,species-specific information is disguised,but individual output files contain data from a single isobar species.Only run-by-run corrections and code alteration subsequent to these corrections are allowed at this stage.Following these modifications,the"frozen"code is passed over the fully un-blind data,completing the blind analysis.As a check of the feasibility of the blind analysis procedure,analysts completed a"mock data challenge,"analyzing data from Au+Au collisions at√^(S)NN=27 Ge V,collected in 2018.The Au+Au data were prepared in the same manner intended for the isobar blind data.The details of the blind analysis procedure and results from the mock data challenge are presented.展开更多
High transverse momentum(pT)particle production is suppressed owing to the parton(jet)energy loss in the hot dense medium created in relativistic heavy-ion collisions.Redistribution of energy at low-to-modest pT has b...High transverse momentum(pT)particle production is suppressed owing to the parton(jet)energy loss in the hot dense medium created in relativistic heavy-ion collisions.Redistribution of energy at low-to-modest pT has been difficult to measure,owing to large anisotropic backgrounds.We report a data-driven method for background evaluation and subtraction,exploiting the away-side pseudorapidity gaps,to measure the jetlike correlation shape in Au+Au collisions at √sNN=200 GeV in the STAR experiment.The correlation shapes,for trigger particles pT>3GeV/c and various associated particle pT ranges within 0.5<pT<10GeV/c,are consistent with Gaussians,and their widths increase with centrality.The results indicate jet broadening in the medium created in central heavy-ion collisions.展开更多
Hermetic packaging is often an essential requirement to enable proper functionality throughout the device＇s lifetime and ensure the optimal performance of a micro electronic mechanical system （MEMS） device. Solid-l...Hermetic packaging is often an essential requirement to enable proper functionality throughout the device＇s lifetime and ensure the optimal performance of a micro electronic mechanical system （MEMS） device. Solid-liquid interdiffusion （SLID） bonding is a novel and attractive way to encapsulate MEMS devices at a wafer level. SLID bonding utilizes a low-melting-point metal to reduce the bonding process temperature; and metallic seal rings take out less of the valuable surface area and have a lower gas permeability compared to polymer or glass- based sealing materials. In addition, ductile metals can adopt mechanical and thermo-mechanical stresses during their service lifetime, which improves their reliability. In this study, the principles of Au-Sn and Cu-Sn SLID bonding are presented, which are meant to be used for wafer-level hermetic sealing of MEMS resonators. Seal rings in 15.24 cm silicon wafers were bonded at a width of 60 gin, electroplated, and used with Au-Sn and Cu-Sn layer structures. The wafer bonding temperature varied between 300 ℃ and 350 ℃, and the bonding force was 3.5 kN under the ambient pressure, that is, it was less than 0.1 Pa. A shear test was used to compare the mechanical properties of the interconnections between both material systems, in addition, important factors pertaining to bond ring design are discussed according to their effects on the failure mechanisms. The results show that the design ofmetal structures can significantly affect the reliability of bond rings.展开更多
The localized and uniform corrosion resistances of bulk nanocrystalline 304 stainless steel（NC-304 SS）produced by severe rolling technique, and its conventional polycrystalline 304 stainless steel（CC-304 SS）counte...The localized and uniform corrosion resistances of bulk nanocrystalline 304 stainless steel（NC-304 SS）produced by severe rolling technique, and its conventional polycrystalline 304 stainless steel（CC-304 SS）counterpart, were investigated in high-concentration hydrochloric acid solutions at room temperature.NC-304 SS can scarcely suffer from localized corrosion in 4 mol/L and 5 mol/L HCl solutions during 5-day immersion tests, and in 1-3 mol/L HCl solutions during thirty-five-day immersion tests. The corrosion rate of NC-304 SS was also less than that of CC-304 SS during these immersion tests. The improved localized and uniform corrosion resistances of NC-304 SS were explained in terms of the adsorption and chemical activity of Cl;on NC-304 SS and CC-304 SS characterized by X-ray photoelectron spectroscopy,and the valence electron configurations of NC-304 SS and CC-304 SS were characterized by ultra-violet photoelectron spectroscopy rather than conventional electrochemical results.展开更多
Ultra-intense laser-driven fast electron beam propagation in a silicon target is studied by three-dimensional hybrid particle-in-cell–fluid simulations.It is found that the transverse spatial profile of the fast elec...Ultra-intense laser-driven fast electron beam propagation in a silicon target is studied by three-dimensional hybrid particle-in-cell–fluid simulations.It is found that the transverse spatial profile of the fast electron beam has a significant influence on the propagation of the fast electrons.In the case of a steep spatial profile(e.g.,a super-Gaussian profile),a tight fast electron beam is produced,and this excites more intense resistive magnetic fields,which pinch the electron beam strongly,leading to strong filamentation of the beam.By contrast,as the gradient of the spatial profile becomes more gentle(e.g.,in the case of a Lorentzian profile),the resistive magnetic field and filamentation become weaker.This indicates that fast electron propagation in a solid target can be controlled by modulating the spatial gradient of the laser pulse edge.展开更多
Pipes are often used to transport multiphase flows in many engineering applications.The total fluid flow density inside a pipe may vary with time and space.In this paper,a simply supported pipe conveying a variable de...Pipes are often used to transport multiphase flows in many engineering applications.The total fluid flow density inside a pipe may vary with time and space.In this paper,a simply supported pipe conveying a variable density flow is modeled theoretically,and its stability and nonlinear vibrations are investigated in detail.The variation of the flow density is simulated using a mathematical function.The equation governing the vibration of the pipe is derived according to Euler-Bernoulli beam theory.When the internal flow density varies with time,the pipe is excited parametrically.The stability of the pipe is determined by Floquet theory.Some simple parametric and combination resonances are determined.For a higher mass ratio(mean flow mass/pipe structural mass),higher flow velocity,or smaller end axial tension,the pipe becomes unstable more easily due to wider parametric resonance regions.In the subcritical flow velocity regime,the vibrations of the pipe are periodic and quasiperiodic for simple and combination resonances,respectively.However,in the supercritical regime,the vibrations of the pipe exhibit much richer dynamics including periodic,multiperiodic,quasiperiodic,and chaotic behaviors.展开更多
Structural materials usually suffer from several attacks during their service,such as tension,fatigue and corrosion.It is necessary to synchronously improve these properties for their lightweight and longlifetime,but ...Structural materials usually suffer from several attacks during their service,such as tension,fatigue and corrosion.It is necessary to synchronously improve these properties for their lightweight and longlifetime,but corrosion resistance and ductility are generally inverse correlation with strength,it is very difficult to simultaneously optimize all three properties.However,bulk nanocrystalline 304 stainless steel(BN-304SS)produced by severe rolling technology possessed the larger yield and ultimate tensile strengths with sufficient elongation(>40%)during tensile test,the larger saturation stress and longer lifetime during low-cycle fatigue,the enhanced uniform and pitting corrosion resistances during fiveday immersion test in 6 mol/L HCl,the lowered stress corrosion cracking(SCC)susceptibility with larger yield(~2.40 GPa)and ultimate tensile(~2.66 GPa)strengths,and enough elongation(>30%)during stress corrosion in comparison with conventional polycrystalline 304 stainless steel(CP-304 SS)counterpart.The uniform and pitting corrosion resistances of fractured BN-304SS were enhanced in comprsion with those of fractured CP-304 SS during seven-day immersion test in 1 mol/L HCl.These results demonstrated the strengths,ductility and corrosion resistances of BN-304SS can be simultaneously optimized by severe rolling technology.These improved results of BN-304SS in different disciplines were understood by its valence electron configurations rather than traditional microstructural parameters.展开更多
The phase transformation behavior of an as-cast Ti-42Al-5 Mn(at.%)alloy after subsequent quenching from 1380℃to 1000℃was investigated based on the differential thermal analysis(DTA),electron probe micro analyzer-bac...The phase transformation behavior of an as-cast Ti-42Al-5 Mn(at.%)alloy after subsequent quenching from 1380℃to 1000℃was investigated based on the differential thermal analysis(DTA),electron probe micro analyzer-backscattered electrons(EPMA-BSE),transmission electron microscope(TEM)and X-ray diffraction(XRD).The results show that,the solidification path can be summarized as follows:Liquid→Liquid+β→β→β→α→β+α+γ→βo+α2+γ→βo+γ+α2/γ→βo+γ+α2/γ+βo,sec,with the phase transformationα→βtemperature(Tβ)=1311℃,phase transformationγ→βtemperature of(Tγsolv)=1231℃,phase transformationα2→αorβo→βtemperature(Tα2→α/Tβo→β)=1168 C,eutectoid temperature(Teut)=1132℃and T(α2/γ→βo,sec)≈1120℃.In comparison with Ti-42 Al alloy,the Teut and Tγsolv are slightly increased while both the Tp is decreased obviously by 5%Mn addition.When quenched from the temperature of 1380-1260℃,the martensitic transformationβ→α'could occur to form the needlelike martensite structure inβarea.This kind of martensitic structure is much obvious with the increase of temperature from 1260℃to 1380℃.When the temperature is below Tγsolv(1231℃),theγgrains would nucleate directly from theβphase.For the temperature slightly lower than T(eut)(1132℃),the dottedβ(o,sec)phases could nucleate in the lamellar colonies besides theγlamellae precipitated withinα2 phase.Finally,at room-temperature(RT),the alloy exhibits(po+α2+γ)triple phase with microstructure ofβo+lamellae+γ,of which the lamellar structure consists ofα2,γandβo,sec phases.The phase transformation mechanisms in this alloy,involvingβ→α',β→γ,α2→α2/γandα2→βo,sec were discussed.展开更多
We report the properties of more than 600 bursts(including cluster-bursts)detected from the repeating fast radio burst(FRB)source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio Telescope during an ...We report the properties of more than 600 bursts(including cluster-bursts)detected from the repeating fast radio burst(FRB)source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio Telescope during an extremely active episode on UTC 2021 September 25–28,in a series of four papers.The observations were carried out in the band of 1.0–1.5 GHz by using the center beam of the L-band 19-beam receiver.We monitored the source in sixteen1 hr sessions and one 3 hr session spanning 23 days.All the bursts were detected during the first four days.In this first paper of the series,we perform a detailed morphological study of 624 bursts using the two-dimensional frequencytime“waterfall”plots,with a burst(or cluster-burst)defined as an emission episode during which the adjacent emission peaks have a separation shorter than 400 ms.The duration of a burst is therefore always longer than 1 ms,with the longest up to more than 120 ms.The emission spectra of the sub-bursts are typically narrow within the observing band with a characteristic width of~277 MHz.The center frequency distribution has a dominant peak at about 1091.9 MHz and a secondary weak peak around 1327.9 MHz.Most bursts show a frequencydownwarddrifting pattern.Based on the drifting patterns,we classify the bursts into five main categories:downward drifting(263)bursts,upward drifting(3)bursts,complex(203),no drifting(35)bursts,and no evidence for drifting(121)bursts.Subtypes are introduced based on the emission frequency range in the band(low,middle,high and wide)as well as the number of components in one burst(1,2,or multiple).We measured a varying scintillation bandwidth from about 0.5 MHz at 1.0 GHz to 1.4 MHz at 1.5 GHz with a spectral index of 3.0.展开更多
Tendril-bearing climbing plants must recur to the tendril helices with chiral perversion or dual chirality for climbing and to obtain sun exposure. Despite researchers' prolonged fascination with climbing tendrils...Tendril-bearing climbing plants must recur to the tendril helices with chiral perversion or dual chirality for climbing and to obtain sun exposure. Despite researchers' prolonged fascination with climbing tendrils since Darwin's time and even earlier, why the soft and slender tendrils can bear heavy loads such as the self-weight of a plant or additional load caused by rain remains elusive. In this paper, we take towel gourd tendrils as an example and investigate the macroscopic and microscopic mechanical behaviors of tendrils through experiments and simulations. Our study indicates that the tendril filament exhibits rubber-like hyperelastic behaviors and can particularly endure large elongation, which is mainly attributed to the superelasticity of the cellulose fibril helix contained in the cell wall. Combination of the tendril helical structure with dual chirality or chiral perversion at a macroscale and a cellulose filament helix at a subcellular level creates superior elasticity for biological species relying on support and climbing. This study provides deep insight into the structure-property relationship of climbing tendrils, and the relationship is useful for the bioinspired design of composite systems with superior elasticity.展开更多
Ultraintense laser-driven relativistic electrons provide a way of heating matter to high energy density states related to many applications. However, the transport of relativistic electrons in solid targets has not be...Ultraintense laser-driven relativistic electrons provide a way of heating matter to high energy density states related to many applications. However, the transport of relativistic electrons in solid targets has not been understood well yet,especially in dielectric targets. We present the first detailed two-dimensional particle-in-cell simulations of relativistic electron transport in a silicon target by including the field ionization and collisional ionization processes. An ionization wave is found propagating in the insulator, with a velocity dependent on laser intensity and slower than the relativistic electron velocity. Widely spread electric fields in front of the sheath fields are observed due to the collective effect of free electrons and ions. The electric fields are much weaker than the threshold electric field of field ionization. Two-stream instability behind the ionization front arises for the cases with laser intensity greater than 5 × 1019W/cm^2 that produce high relativistic electron current densities.展开更多
We report systematic studies of laser-driven proton beams produced with micrometer-thick solid targets made of aluminum and plastic,respectively.Distinct effects of the target materials are found on the total charge,c...We report systematic studies of laser-driven proton beams produced with micrometer-thick solid targets made of aluminum and plastic,respectively.Distinct effects of the target materials are found on the total charge,cutoff energy,and beam spot of protons in the experiments,and these are described well by two-dimensional particle-in-cell simulations incorporating intrinsic material properties.It is found that with a laser intensity of 8×10^(19) W/cm^(2),target normal sheath acceleration is the dominant mechanism for both types of target.For a plastic target,the higher charge and cutoff energy of the protons are due to the greater energy coupling efficiencies from the intense laser beams,and the larger divergence angle of the protons is due to the deflection of hot electrons during transport in the targets.We also find that the energy loss of hot electrons in targets of different thickness has a significant effect on the proton cutoff energy.The consistent results obtained here further narrow the gap between simulations and experiments.展开更多
The Lobster Eye Imager for Astronomy(LEIA),a pathfinder of the Wide-field X-ray Telescope of the Einstein Probe mission,was successfully launched onboard the SATech-01 satellite of the Chinese Academy of Sciences on20...The Lobster Eye Imager for Astronomy(LEIA),a pathfinder of the Wide-field X-ray Telescope of the Einstein Probe mission,was successfully launched onboard the SATech-01 satellite of the Chinese Academy of Sciences on2022 July 27.In this paper,we introduce the design and on-ground test results of the LEIA instrument.Using stateof-the-art Micro-Pore Optics(MPO),a wide field of view of 346 square degrees(18.6°×18.6°)of the X-ray imager is realized.An optical assembly composed of 36 MPO chips is used to focus incident X-ray photons,and four large-format complementary metal-oxide semiconductor(CMOS)sensors,each of size 6 cm×6 cm,are used as the focal plane detectors.The instrument has an angular resolution of 4’-8’(in terms of FWHM)for the central focal spot of the point-spread function,and an effective area of 2-3 cm^(2) at 1 keV in essentially all the directions within the field of view.The detection passband is 0.5-4 keV in soft X-rays and the sensitivity is2-3×10^(-11) erg s^(-1) cm^(-2)(about 1 milliCrab)with a 1000 s observation.The total weight of LEIA is 56 kg and the power is 85 W.The satellite,with a design lifetime of 2 yr,operates in a Sun-synchronous orbit of 500 km with an orbital period of 95 minutes.LEIA is paving the way for future missions by verifying in flight the technologies of both novel focusing imaging optics and CMOS sensors for X-ray observation,and by optimizing the working setups of the instrumental parameters.In addition,LEIA is able to carry out scientific observations to find new transients and to monitor known sources in the soft X-ray band,albeit with limited useful observing time available.展开更多
The ground-state mass excess of the T_(z)=−2 drip-line nucleus ^(22)Al is measured for the first time as 18103(10)keV using the newly-developed Bρ-defined isochronous mass spectrometry method at the cooler storage ri...The ground-state mass excess of the T_(z)=−2 drip-line nucleus ^(22)Al is measured for the first time as 18103(10)keV using the newly-developed Bρ-defined isochronous mass spectrometry method at the cooler storage ring in Lanzhou.The new mass excess value allowed us to determine the excitation energies of the two low-lying 1+states in ^(22)Al with significantly reduced uncertainties of 51 keV.When compared to the analogue states in its mirror nucleus ^(22)F,the mirror energy differences of the two 1^(+)states in the ^(22)Al-^(22)F mirror pair are determined to be−625(51)keV and−330(51)keV.The excitation energies and mirror energy differences are used to test the state-of-the-art ab initio valence-space in-medium similarity renormalization group calculations with four sets of interactions derived from the chiral effective field theory.The mechanism leading to the large mirror energy differences is investigated and attributed to the occupation of theπs_(1/2) orbital.展开更多
A nanofabricated superconducting quantum interference device(nano-SQUID)is a direct and sensitive flux probe used for magnetic imaging of quantum materials and mesoscopic devices.Due to the functionalities of supercon...A nanofabricated superconducting quantum interference device(nano-SQUID)is a direct and sensitive flux probe used for magnetic imaging of quantum materials and mesoscopic devices.Due to the functionalities of superconductive integrated circuits,nano-SQUIDs fabricated on chips are particularly versatile,but their spatial resolution has been limited by their planar geometries.Here,we use femtosecond laser 3-dimensional(3D)lithography to print a needle onto a nano-SQUID susceptometer to overcome the limits of the planar structure.The nanoneedle coated with a superconducting shell focused the flux from both the field coil and the sample.We performed scanning imaging with such a needle-on-SQUID(NoS)device on superconducting test patterns with topographic feedback.The NoS showed improved spatial resolution in both magnetometry and susceptometry relative to the planarized counterpart.This work serves as a proof-of-principle for integration and inductive coupling between superconducting 3D nanostructures and on-chip Josephson nanodevices.展开更多
基金Supported in part by the Offices of NP and HEP within the U.S.DOE Office of Sciencethe U.S.NSF+18 种基金the Sloan Foundationthe DFG cluster of excellence‘Origin and Structure of the Universe’of Germany,CNRS/IN2P3STFC and EPSRC of the United KingdomFAPESP CNPq of Brazil,Ministry of Ed.Sci.of the Russian FederationNNSFCCASMoSTMoE of ChinaGA and MSMT of the Czech RepublicFOM and NWO of the NetherlandsDAEDSTCSIR of IndiaPolish Ministry of Sci.Higher Ed.,Korea Research Foundation,Ministry of Sci.,Ed.Sports of the Rep.Of CroatiaRussian Ministry of Sci.and TechRos-Atom of Russia。
文摘Dihadron azimuthal correlations containing a high transverse momentum(pr)trigger particle are sensit-ive to the properties of the nuclear medium created at RHIC through the strong interactions occurring between the traversing parton and the medium,ie.jet-quenching.Previous measurements revealed a strong modification to di-hadron azimuthal correlations in Au+Au collisions with respect to ptp and d+Au collisions.The modification in-creases with the collision centrality,suggesting a path-length or energy density dependence to the je-quenching ef-fect.This paper reports STAR measurements of dihadron azimuthal correlations in mid-central(20%-60%)Au+Au collisions at√^(S)NN=200 GeV as a function of the trigger particle's azimuthal angle relative to the event plane,Ф_(s)=|Ф_(t)-ψ_(Ep)|.The azimuthal correlation is studied as a function of both the trigger and associated particle pr.The subtractions of the combinatorial background and anisotropic flow,assuming Zero Yield At Minimum(ZYAM),are described.The correlation results are first discussed with subtraction of the even harmonic(elliptic and quadrangu-lar)flow backgrounds.The away-side correlation is strongly modifed,and the modification varies withФ_(s),with a double-peak structure for out-of-plane trigger particles.The near-side ridge(long range pseudo-rapidity△_(η)correla-tion)appears to drop with increasingФ_(s)while the jet-like component remains approximately constant.The correla-tion functions are further studied with the subtraction of odd harmonic triangular flow background arising from fluc-tuations.It is found that the triangular flow,while responsible for the majority of the amplitudes,is not sufficient to explain theφs-dependence of the ridge or the away-side double-peak structure.The dropping ridge withФ_(s)could be attributed to aФ_(s)-dependent lliptie anisotropy;however,the physics mechanism of the ridge remains an open ques-tion.Even with aФ_(s)-dependent elliptic flow,the away-side correlation structure is robust.These results,with exte
基金the "Strategic Priority Research Program" of the Chinese Academy of Sciences (No.XDA05050208)the National Natural Science Foundation of China (Nos.31070439 and 40730102)the Knowledge Innovation Program of the Chinese Academy of Sciences (Nos.KSCX2-EW-Q-8 and KSCX2-EW-J-28)
文摘Soil acid phosphomonoesterase activity (APA) plays a vital role in controlling phosphorus (P) cycling and reflecting the current degree of P limitation. Responses of soil APA to elevating nitrogen (N) deposition are important because of their potential applications in addressing the relationship between N and P in forest ecosystems. A study of responses of soil APA to simulated N deposition was conducted in three succession forests of subtropical China. The three forests include a Masson pine (Pinus massoniana) forest (MPF)-pioneer community, a coniferous and broad-leaved mixed forest (MF)-transition community and a monsoon evergreen broad-leaved forest (MEBF)-climax community. Four N treatments were designed for MEBF: control (without N added), low-N (50 kg N ha-1 year-1), and medium-N (100 kg N ha-1 year-1) and high-N (150 kg N ha-1 year-1), and only three N treatments (i.e., control, low-N, medium-N) were established for MPF and MF. Results showed that soil APA was highest in MEBF, followed by MPF and MF. Soil APAs in both MPF and MF were not influenced by low-N treatments but depressed in medium-N treatments. However, soil APA in MEBF exhibited negative responses to high N additions, indicating that the environment of enhanced N depositions would reduce P supply for the mature forest ecosystem. Soil APA and its responses to N additions in subtropical forests were closely related to the succession stages in the forests.
文摘In 2018,the STAR collaboration collected data from^(96)_(44)Ru+^(96)_(44)Ru and^(96)_(40)Zr+^(96)_(40)Zr at√^(S)NN=200 Ge V to search for the presence of the chiral magnetic effect in collisions of nuclei.The isobar collision species alternated frequently between 9644 Ru+^(96)_(44)Ru and^(96)_(40)Zr+^(96)_(40)Zr.In order to conduct blind analyses of studies related to the chiral magnetic effect in these isobar data,STAR developed a three-step blind analysis procedure.Analysts are initially provided a"reference sample"of data,comprised of a mix of events from the two species,the order of which respects time-dependent changes in run conditions.After tuning analysis codes and performing time-dependent quality assurance on the reference sample,analysts are provided a species-blind sample suitable for calculating efficiencies and corrections for individual≈30-min data-taking runs.For this sample,species-specific information is disguised,but individual output files contain data from a single isobar species.Only run-by-run corrections and code alteration subsequent to these corrections are allowed at this stage.Following these modifications,the"frozen"code is passed over the fully un-blind data,completing the blind analysis.As a check of the feasibility of the blind analysis procedure,analysts completed a"mock data challenge,"analyzing data from Au+Au collisions at√^(S)NN=27 Ge V,collected in 2018.The Au+Au data were prepared in the same manner intended for the isobar blind data.The details of the blind analysis procedure and results from the mock data challenge are presented.
文摘High transverse momentum(pT)particle production is suppressed owing to the parton(jet)energy loss in the hot dense medium created in relativistic heavy-ion collisions.Redistribution of energy at low-to-modest pT has been difficult to measure,owing to large anisotropic backgrounds.We report a data-driven method for background evaluation and subtraction,exploiting the away-side pseudorapidity gaps,to measure the jetlike correlation shape in Au+Au collisions at √sNN=200 GeV in the STAR experiment.The correlation shapes,for trigger particles pT>3GeV/c and various associated particle pT ranges within 0.5<pT<10GeV/c,are consistent with Gaussians,and their widths increase with centrality.The results indicate jet broadening in the medium created in central heavy-ion collisions.
基金This work has been carried out as part of a Tekes Project:Real_metal(Grants Nos.40009/12,40010/12)the Finnish Funding Agency for Technology and Innovation(Tekes),Okmetic Oyj,and Murata Electronics for funding
文摘Hermetic packaging is often an essential requirement to enable proper functionality throughout the device＇s lifetime and ensure the optimal performance of a micro electronic mechanical system （MEMS） device. Solid-liquid interdiffusion （SLID） bonding is a novel and attractive way to encapsulate MEMS devices at a wafer level. SLID bonding utilizes a low-melting-point metal to reduce the bonding process temperature; and metallic seal rings take out less of the valuable surface area and have a lower gas permeability compared to polymer or glass- based sealing materials. In addition, ductile metals can adopt mechanical and thermo-mechanical stresses during their service lifetime, which improves their reliability. In this study, the principles of Au-Sn and Cu-Sn SLID bonding are presented, which are meant to be used for wafer-level hermetic sealing of MEMS resonators. Seal rings in 15.24 cm silicon wafers were bonded at a width of 60 gin, electroplated, and used with Au-Sn and Cu-Sn layer structures. The wafer bonding temperature varied between 300 ℃ and 350 ℃, and the bonding force was 3.5 kN under the ambient pressure, that is, it was less than 0.1 Pa. A shear test was used to compare the mechanical properties of the interconnections between both material systems, in addition, important factors pertaining to bond ring design are discussed according to their effects on the failure mechanisms. The results show that the design ofmetal structures can significantly affect the reliability of bond rings.
基金financially supported by the National Natural Sciences Foundation of China(No.51171199)the State key Project of Research and Development of China(No.2017YFA0206302)
文摘The localized and uniform corrosion resistances of bulk nanocrystalline 304 stainless steel（NC-304 SS）produced by severe rolling technique, and its conventional polycrystalline 304 stainless steel（CC-304 SS）counterpart, were investigated in high-concentration hydrochloric acid solutions at room temperature.NC-304 SS can scarcely suffer from localized corrosion in 4 mol/L and 5 mol/L HCl solutions during 5-day immersion tests, and in 1-3 mol/L HCl solutions during thirty-five-day immersion tests. The corrosion rate of NC-304 SS was also less than that of CC-304 SS during these immersion tests. The improved localized and uniform corrosion resistances of NC-304 SS were explained in terms of the adsorption and chemical activity of Cl;on NC-304 SS and CC-304 SS characterized by X-ray photoelectron spectroscopy,and the valence electron configurations of NC-304 SS and CC-304 SS were characterized by ultra-violet photoelectron spectroscopy rather than conventional electrochemical results.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.12175309,11975308,12005297,and 12275356)the Strategic Priority Research Program of the Chinese Academy of Science(Grant No.XDA25050200)the Fund for NUDT Young Innovator Awards(No.20180104).
文摘Ultra-intense laser-driven fast electron beam propagation in a silicon target is studied by three-dimensional hybrid particle-in-cell–fluid simulations.It is found that the transverse spatial profile of the fast electron beam has a significant influence on the propagation of the fast electrons.In the case of a steep spatial profile(e.g.,a super-Gaussian profile),a tight fast electron beam is produced,and this excites more intense resistive magnetic fields,which pinch the electron beam strongly,leading to strong filamentation of the beam.By contrast,as the gradient of the spatial profile becomes more gentle(e.g.,in the case of a Lorentzian profile),the resistive magnetic field and filamentation become weaker.This indicates that fast electron propagation in a solid target can be controlled by modulating the spatial gradient of the laser pulse edge.
基金The authors are grateful to the National Natural Science Foundation of China(Grants 51679167,51979193,and 51608059)for financial support.
文摘Pipes are often used to transport multiphase flows in many engineering applications.The total fluid flow density inside a pipe may vary with time and space.In this paper,a simply supported pipe conveying a variable density flow is modeled theoretically,and its stability and nonlinear vibrations are investigated in detail.The variation of the flow density is simulated using a mathematical function.The equation governing the vibration of the pipe is derived according to Euler-Bernoulli beam theory.When the internal flow density varies with time,the pipe is excited parametrically.The stability of the pipe is determined by Floquet theory.Some simple parametric and combination resonances are determined.For a higher mass ratio(mean flow mass/pipe structural mass),higher flow velocity,or smaller end axial tension,the pipe becomes unstable more easily due to wider parametric resonance regions.In the subcritical flow velocity regime,the vibrations of the pipe are periodic and quasiperiodic for simple and combination resonances,respectively.However,in the supercritical regime,the vibrations of the pipe exhibit much richer dynamics including periodic,multiperiodic,quasiperiodic,and chaotic behaviors.
基金the financial support of National Natural Sciences of Foundation of China(Contract No.51171199)the cooperation project from Pujiang,Chengdu,Sichuan Province,China,No.Y5N4811181.
文摘Structural materials usually suffer from several attacks during their service,such as tension,fatigue and corrosion.It is necessary to synchronously improve these properties for their lightweight and longlifetime,but corrosion resistance and ductility are generally inverse correlation with strength,it is very difficult to simultaneously optimize all three properties.However,bulk nanocrystalline 304 stainless steel(BN-304SS)produced by severe rolling technology possessed the larger yield and ultimate tensile strengths with sufficient elongation(>40%)during tensile test,the larger saturation stress and longer lifetime during low-cycle fatigue,the enhanced uniform and pitting corrosion resistances during fiveday immersion test in 6 mol/L HCl,the lowered stress corrosion cracking(SCC)susceptibility with larger yield(~2.40 GPa)and ultimate tensile(~2.66 GPa)strengths,and enough elongation(>30%)during stress corrosion in comparison with conventional polycrystalline 304 stainless steel(CP-304 SS)counterpart.The uniform and pitting corrosion resistances of fractured BN-304SS were enhanced in comprsion with those of fractured CP-304 SS during seven-day immersion test in 1 mol/L HCl.These results demonstrated the strengths,ductility and corrosion resistances of BN-304SS can be simultaneously optimized by severe rolling technology.These improved results of BN-304SS in different disciplines were understood by its valence electron configurations rather than traditional microstructural parameters.
文摘The phase transformation behavior of an as-cast Ti-42Al-5 Mn(at.%)alloy after subsequent quenching from 1380℃to 1000℃was investigated based on the differential thermal analysis(DTA),electron probe micro analyzer-backscattered electrons(EPMA-BSE),transmission electron microscope(TEM)and X-ray diffraction(XRD).The results show that,the solidification path can be summarized as follows:Liquid→Liquid+β→β→β→α→β+α+γ→βo+α2+γ→βo+γ+α2/γ→βo+γ+α2/γ+βo,sec,with the phase transformationα→βtemperature(Tβ)=1311℃,phase transformationγ→βtemperature of(Tγsolv)=1231℃,phase transformationα2→αorβo→βtemperature(Tα2→α/Tβo→β)=1168 C,eutectoid temperature(Teut)=1132℃and T(α2/γ→βo,sec)≈1120℃.In comparison with Ti-42 Al alloy,the Teut and Tγsolv are slightly increased while both the Tp is decreased obviously by 5%Mn addition.When quenched from the temperature of 1380-1260℃,the martensitic transformationβ→α'could occur to form the needlelike martensite structure inβarea.This kind of martensitic structure is much obvious with the increase of temperature from 1260℃to 1380℃.When the temperature is below Tγsolv(1231℃),theγgrains would nucleate directly from theβphase.For the temperature slightly lower than T(eut)(1132℃),the dottedβ(o,sec)phases could nucleate in the lamellar colonies besides theγlamellae precipitated withinα2 phase.Finally,at room-temperature(RT),the alloy exhibits(po+α2+γ)triple phase with microstructure ofβo+lamellae+γ,of which the lamellar structure consists ofα2,γandβo,sec phases.The phase transformation mechanisms in this alloy,involvingβ→α',β→γ,α2→α2/γandα2→βo,sec were discussed.
基金supported by the National Natural Science Foundation of China(NSFC,Nos.11988101 and 11833009)the Key Research Program of the Chinese Academy of Sciences(Grant No.QYZDJ-SSWSLH021)+6 种基金supported by the Cultivation Project for the FAST scientific Payoff and Research Achievement of CAMS-CASsupported by the Key Research Project of Zhejiang Lab no.2021PE0AC0supported by the National SKA Program of China(2020SKA0120100)the National Key R&D Program of China(2017YFA0402602)the National Natural Science Foundation of China(No.12041303)the CAS-MPG LEGACY projectfunding from the MaxPlanck Partner Group。
文摘We report the properties of more than 600 bursts(including cluster-bursts)detected from the repeating fast radio burst(FRB)source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio Telescope during an extremely active episode on UTC 2021 September 25–28,in a series of four papers.The observations were carried out in the band of 1.0–1.5 GHz by using the center beam of the L-band 19-beam receiver.We monitored the source in sixteen1 hr sessions and one 3 hr session spanning 23 days.All the bursts were detected during the first four days.In this first paper of the series,we perform a detailed morphological study of 624 bursts using the two-dimensional frequencytime“waterfall”plots,with a burst(or cluster-burst)defined as an emission episode during which the adjacent emission peaks have a separation shorter than 400 ms.The duration of a burst is therefore always longer than 1 ms,with the longest up to more than 120 ms.The emission spectra of the sub-bursts are typically narrow within the observing band with a characteristic width of~277 MHz.The center frequency distribution has a dominant peak at about 1091.9 MHz and a secondary weak peak around 1327.9 MHz.Most bursts show a frequencydownwarddrifting pattern.Based on the drifting patterns,we classify the bursts into five main categories:downward drifting(263)bursts,upward drifting(3)bursts,complex(203),no drifting(35)bursts,and no evidence for drifting(121)bursts.Subtypes are introduced based on the emission frequency range in the band(low,middle,high and wide)as well as the number of components in one burst(1,2,or multiple).We measured a varying scintillation bandwidth from about 0.5 MHz at 1.0 GHz to 1.4 MHz at 1.5 GHz with a spectral index of 3.0.
基金the National Natural Science Foundation of China (Grants 11872273, 11472191, 11602163, and 11672297)the Major Program of the National Science Foundation of China (Grant 11890683)+1 种基金the Opening Fund of State Key Laboratory of Nonlinear Mechanicsthe Australian Endeavour Research Fellowship.
文摘Tendril-bearing climbing plants must recur to the tendril helices with chiral perversion or dual chirality for climbing and to obtain sun exposure. Despite researchers' prolonged fascination with climbing tendrils since Darwin's time and even earlier, why the soft and slender tendrils can bear heavy loads such as the self-weight of a plant or additional load caused by rain remains elusive. In this paper, we take towel gourd tendrils as an example and investigate the macroscopic and microscopic mechanical behaviors of tendrils through experiments and simulations. Our study indicates that the tendril filament exhibits rubber-like hyperelastic behaviors and can particularly endure large elongation, which is mainly attributed to the superelasticity of the cellulose fibril helix contained in the cell wall. Combination of the tendril helical structure with dual chirality or chiral perversion at a macroscale and a cellulose filament helix at a subcellular level creates superior elasticity for biological species relying on support and climbing. This study provides deep insight into the structure-property relationship of climbing tendrils, and the relationship is useful for the bioinspired design of composite systems with superior elasticity.
基金supported by the National Natural Science Foundation of China (Nos. 11775305, 11675264 and 11705282)Science Challenge Project (No. TZ2018001)+1 种基金Open Fund of the State Key Laboratory of High Field Laser Physics (SIOM)the support from the China Scholarship Council。
文摘Ultraintense laser-driven relativistic electrons provide a way of heating matter to high energy density states related to many applications. However, the transport of relativistic electrons in solid targets has not been understood well yet,especially in dielectric targets. We present the first detailed two-dimensional particle-in-cell simulations of relativistic electron transport in a silicon target by including the field ionization and collisional ionization processes. An ionization wave is found propagating in the insulator, with a velocity dependent on laser intensity and slower than the relativistic electron velocity. Widely spread electric fields in front of the sheath fields are observed due to the collective effect of free electrons and ions. The electric fields are much weaker than the threshold electric field of field ionization. Two-stream instability behind the ionization front arises for the cases with laser intensity greater than 5 × 1019W/cm^2 that produce high relativistic electron current densities.
基金The simulations were performed on the Qilin-2 supercomputer at Zhejiang University.This work was supported by the Science Challenge Project(No.TZ2016005)the National Natural Science Foundation of China(Grant Nos.119210067,11605269,11721091,11775144)the National Grand Instrument Project(Nos.2019YFF01014400,2019YFF01014404).
文摘We report systematic studies of laser-driven proton beams produced with micrometer-thick solid targets made of aluminum and plastic,respectively.Distinct effects of the target materials are found on the total charge,cutoff energy,and beam spot of protons in the experiments,and these are described well by two-dimensional particle-in-cell simulations incorporating intrinsic material properties.It is found that with a laser intensity of 8×10^(19) W/cm^(2),target normal sheath acceleration is the dominant mechanism for both types of target.For a plastic target,the higher charge and cutoff energy of the protons are due to the greater energy coupling efficiencies from the intense laser beams,and the larger divergence angle of the protons is due to the deflection of hot electrons during transport in the targets.We also find that the energy loss of hot electrons in targets of different thickness has a significant effect on the proton cutoff energy.The consistent results obtained here further narrow the gap between simulations and experiments.
基金supported by the Einstein Probe project,a mission in the Strategic Priority Program on Space Science of CAS(grant Nos.XDA15310000,XDA15052100)in part been supported by the European Union’s Horizon 2020 Program under the AHEAD2020 project(grant No.871158).
文摘The Lobster Eye Imager for Astronomy(LEIA),a pathfinder of the Wide-field X-ray Telescope of the Einstein Probe mission,was successfully launched onboard the SATech-01 satellite of the Chinese Academy of Sciences on2022 July 27.In this paper,we introduce the design and on-ground test results of the LEIA instrument.Using stateof-the-art Micro-Pore Optics(MPO),a wide field of view of 346 square degrees(18.6°×18.6°)of the X-ray imager is realized.An optical assembly composed of 36 MPO chips is used to focus incident X-ray photons,and four large-format complementary metal-oxide semiconductor(CMOS)sensors,each of size 6 cm×6 cm,are used as the focal plane detectors.The instrument has an angular resolution of 4’-8’(in terms of FWHM)for the central focal spot of the point-spread function,and an effective area of 2-3 cm^(2) at 1 keV in essentially all the directions within the field of view.The detection passband is 0.5-4 keV in soft X-rays and the sensitivity is2-3×10^(-11) erg s^(-1) cm^(-2)(about 1 milliCrab)with a 1000 s observation.The total weight of LEIA is 56 kg and the power is 85 W.The satellite,with a design lifetime of 2 yr,operates in a Sun-synchronous orbit of 500 km with an orbital period of 95 minutes.LEIA is paving the way for future missions by verifying in flight the technologies of both novel focusing imaging optics and CMOS sensors for X-ray observation,and by optimizing the working setups of the instrumental parameters.In addition,LEIA is able to carry out scientific observations to find new transients and to monitor known sources in the soft X-ray band,albeit with limited useful observing time available.
基金Supported in part by the Strategic Priority Research Program of Chinese Academy of Sciences (XDB34000000)the CAS Project for Young Scientists in Basic Research (YSBR-002)+4 种基金the National Nature Science Foundation of China (12135017,12121005,11975280,12105333,12205340,12322507,12305126,12305151)the Gansu Natural Science Foundation (22JR5RA123,23JRRA614)the National Key R&D Program of China (2021YFA1601500)Support from the Youth Innovation Promotion Association of Chinese Academy of Sciences (2021419,2022423)support from Young Scholar of Regional Development,CAS ([2023]15).
文摘The ground-state mass excess of the T_(z)=−2 drip-line nucleus ^(22)Al is measured for the first time as 18103(10)keV using the newly-developed Bρ-defined isochronous mass spectrometry method at the cooler storage ring in Lanzhou.The new mass excess value allowed us to determine the excitation energies of the two low-lying 1+states in ^(22)Al with significantly reduced uncertainties of 51 keV.When compared to the analogue states in its mirror nucleus ^(22)F,the mirror energy differences of the two 1^(+)states in the ^(22)Al-^(22)F mirror pair are determined to be−625(51)keV and−330(51)keV.The excitation energies and mirror energy differences are used to test the state-of-the-art ab initio valence-space in-medium similarity renormalization group calculations with four sets of interactions derived from the chiral effective field theory.The mechanism leading to the large mirror energy differences is investigated and attributed to the occupation of theπs_(1/2) orbital.
基金We would like to acknowledge support by the National Key R&D Program of China(Grant No.2021YFA1400100)National Natural Science Foundation of China(Grant Nos.11827805 and 12150003)Shanghai Municipal Science and Technology Major Project(Grant No.2019SHZDZX01).All of the authors are grateful for the experimental assistance of Y.P.Pan,Y.Feng,X.D.Zhou,and W.X.Tang.
文摘A nanofabricated superconducting quantum interference device(nano-SQUID)is a direct and sensitive flux probe used for magnetic imaging of quantum materials and mesoscopic devices.Due to the functionalities of superconductive integrated circuits,nano-SQUIDs fabricated on chips are particularly versatile,but their spatial resolution has been limited by their planar geometries.Here,we use femtosecond laser 3-dimensional(3D)lithography to print a needle onto a nano-SQUID susceptometer to overcome the limits of the planar structure.The nanoneedle coated with a superconducting shell focused the flux from both the field coil and the sample.We performed scanning imaging with such a needle-on-SQUID(NoS)device on superconducting test patterns with topographic feedback.The NoS showed improved spatial resolution in both magnetometry and susceptometry relative to the planarized counterpart.This work serves as a proof-of-principle for integration and inductive coupling between superconducting 3D nanostructures and on-chip Josephson nanodevices.
