Time-resolved fluorescence spectra of europium methylbenzoates (MBA)with 1,10-phenanthroline(phen)have been measured at room temperature.For each of the europium chelates,where the ligand triple states lie above the ~...Time-resolved fluorescence spectra of europium methylbenzoates (MBA)with 1,10-phenanthroline(phen)have been measured at room temperature.For each of the europium chelates,where the ligand triple states lie above the ~5D_1 level of Eu^(3-),the spectra providc evidence that the Eu^(3-) ~5D_0 state is populated by nonradiative energy transfer from the higher-lying ~5D_1,state.The relaxation time for energy decay from ~5D_1 state is measured in the microcrystals to bc of the order of a few microseconds.It is suggested that the ligand C=0 and C=C stretching vibrations and Eu-O vibrations,chclate ring and benzene ring vibrations make important contributions to the relaxation process.The ~5D\-1—~5D\-0 relaxation time of Eu- (p-MBA)_3phen is shorter than those of Eu(m-MBA)_3phen and Eu(o-MBA)_3phen since nonradiative degradation to ~5D_0 from ~5D_1 appears to be more strongly influenced by the E_u^(3+)sites in the former.展开更多
The construction of a new beamline,BL10U1,was completed at the Shanghai synchrotron radiation facility in 2020.This multipurpose beamline was designed to provide X-ray scattering techniques such as ultra-small-angle X...The construction of a new beamline,BL10U1,was completed at the Shanghai synchrotron radiation facility in 2020.This multipurpose beamline was designed to provide X-ray scattering techniques such as ultra-small-angle X-ray scattering(USAXS),small-angle X-ray scattering(SAXS),wide-angle X-ray scattering,and microfocus SAXS(μSAXS)for a broad user community.To realize fast time-resolved USAXS experiments,the beamline adopted an in-vacuum undulator with a total length of 1.6 m as the photon source.An in-house cryogenic-cooled double multilayer monochromator was installed to deliver a photon flux of approximately 10^(13) photons/s at a photon energy of 10 keV.The three-year successful operation of this beamline demonstrated that the monochromator operated smoothly,as expected.BL10U1 has three end stations in succession:USAXS end station,μSAXS end station,and end station for industrial applications.The minimum scattering vector q~0.0042 nm^(-1) at 10 keV can be achieved at the USAXS end station equipped with a 28 m-long and 1.8 m-diameter vacuum flight tube.At theμSAXS end station,a beam spot of less than 10×8μm was achieved for micro-SAXS experiments.In contrast,in situ experimental instruments up to 5 m high and 8 m wide can be mounted at the industrial application end station,which offers industrial scientists the opportunity to use their large industrial equipment.BL10U1 opens up a new capability to investigate phenomena such as non-equilibrium and dynamic processes of materials with a wide length scale from angstroms to micrometers with millisecond time resolution.In this paper,we also report beamline design considerations and commissioning results.展开更多
A time resolved chemiluminescent analysis for simultaneous determination of trace Au(Ⅲ) and Os(Ⅳ) was proposed. The method is based on the kinetic distinction of Au(Ⅲ) and Os(Ⅳ) in Tween 80 KOH chemilumescent sy...A time resolved chemiluminescent analysis for simultaneous determination of trace Au(Ⅲ) and Os(Ⅳ) was proposed. The method is based on the kinetic distinction of Au(Ⅲ) and Os(Ⅳ) in Tween 80 KOH chemilumescent system. The detection limits were 1.1×10 -9 g/ml for Au(Ⅲ) and 1.0×10 -8 g/ml for Os(Ⅳ), with the linear ranges of 1.0×10 -8 ～1.0×10 -5 g/ml for Au(Ⅲ) and 1.0×10 -7 ～1.0×10 -6 g/ml for Os(Ⅳ). The method was applied to the determination of Au(Ⅲ) and Os(Ⅳ) in the sample of metallurgical materials of noble metals with satisfactory results.展开更多
Terahertz(THz)microscopy has attracted attention owing to distinctive characteristics of the THz frequency region,particularly non-ionizing photon energy,spectral fingerprint,and transparency to most nonpolar material...Terahertz(THz)microscopy has attracted attention owing to distinctive characteristics of the THz frequency region,particularly non-ionizing photon energy,spectral fingerprint,and transparency to most nonpolar materials.Nevertheless,the well-known Rayleigh diffraction limit imposed on THz waves commonly constrains the resultant imaging resolution to values beyond the millimeter scale,consequently limiting the applicability in numerous emerging applications for chemical sensing and complex media imaging.In this theoretical and numerical work,we address this challenge by introducing,to our knowledge,a new imaging approach based on acquiring high-spatial frequencies by adapting the Fourier synthetic aperture approach to the THz spectral range,thus surpassing the diffractionlimited resolution.Our methodology combines multi-angle THz pulsed illumination with time-resolved field measurements,as enabled by the state-of-the-art time-domain spectroscopy technique.We demonstrate the potential of the approach for hyperspectral THz imaging of semi-transparent samples and show that the technique can reconstruct spatial and temporal features of complex inhomogeneous samples with subwavelength resolution.展开更多
We investigate the spatial and temporal correlations of hot-electron generation in high-intensity laser interaction with massive and thin copper targets under conditions relevant to inertial confinement fusion.Using K...We investigate the spatial and temporal correlations of hot-electron generation in high-intensity laser interaction with massive and thin copper targets under conditions relevant to inertial confinement fusion.Using Ka time-resolved imaging,it is found that in the case of massive targets,the hot-electron generation follows the laser pulse intensity with a short delay needed for favorable plasma formation.Conversely,a significant delay in the x-ray emission compared with the laser pulse intensity profile is observed in the case of thin targets.Theoretical analysis and numerical simulations suggest that this is related to radiation preheating of the foil and the increase in hot-electron lifetime in a hot expanding plasma.展开更多
Ultrafast electron sources, which enable high spatiotemporal resolution in time-resolved electron microscopy and scanning probe microscopy, are receiving increased attention. The most widely used method for achieving ...Ultrafast electron sources, which enable high spatiotemporal resolution in time-resolved electron microscopy and scanning probe microscopy, are receiving increased attention. The most widely used method for achieving ultrafast electron sources involves irradiating metal tips by ultrashort laser pulses, causing electron beam emission via the photoelectric effect [including photon-driven(quantum) or field-driven(classical) emission]. However, the thermionic electrons emission process due to the heating effect of ultrashort lasers, particularly its dynamic aspects, has rarely been addressed in previous studies. In this paper, we improved the signal-to-noise ratio of a two-pulse correlation measurement on the tip electron emission by nearly two orders of magnitude using a delay time modulation method. This allowed us to obtain information on the temperature evolution of hot electrons and phonons in a non-equilibrium state, and to extract characteristic time scales for electron-phonon and phonon-phonon scattering. Our findings indicate that the thermionic electrons emission, unlike the instantaneous photoelectric effect, causes electron emission to lag behind the laser pulse by tens of picoseconds, thus significantly affecting the detection of ultrafast dynamics of samples. Furthermore, such a lagging effect was found to be sensitive to the local structure of the metal tip, offering new insights into the improved design of ultrafast electron sources.展开更多
Besides equilibrium behavior,exploring the spin–phonon coupling in multiferroic materials under non-equilibrium conditions is crucial for a deep understanding of the mechanisms as well as their high-frequency applica...Besides equilibrium behavior,exploring the spin–phonon coupling in multiferroic materials under non-equilibrium conditions is crucial for a deep understanding of the mechanisms as well as their high-frequency applications.Here,by utilizing time-resolved refectance spectroscopy,we demonstrate ultrafast spin–phonon coupling dynamics in multiferroic 0.58BiFeO_(3)-0.42Bi_(0.5)K_(0.5)TiO_(3)(BF-BKT)single crystals.With ultrafast laser pumping,coherent acoustic phonons with low damping are created in BF-BKT.Temperature-dependent results indicate that both the frequency and amplitude of laser-induced coherent phonons are sensitive to the emergence of antiferromagnetic order.Moreover,the spin state change driven by external magnetic felds can enhance the oscillation amplitude of the coherent acoustic phonons even above the magnetic Néel temperature.These fndings experimentally confrm that spin–phonon coupling in multiferroic materials exists not only in the spin-ordered state but also in the spin-disordered state,and not only in the equilibrium state but also in the non-equilibrium state excited by ultrafast lasers,suggesting their promising applications in high-frequency devices.展开更多
The advent of high-resolution black hole imaging—most notably by the Event Horizon Telescope(EHT)—has propelled black hole physics into a new observational regime[1].However,most theoretical interpretations remain a...The advent of high-resolution black hole imaging—most notably by the Event Horizon Telescope(EHT)—has propelled black hole physics into a new observational regime[1].However,most theoretical interpretations remain anchored in stationary,time-averaged general relativistic magnetohydrodynamic(GRMHD)simulations within the Kerr paradigm,often neglecting dynamic accretion structures and potential deviations from general relativity[2].展开更多
We conducted experiments in a wind tunnel with Mach number 2 to explore the evolution of a transverse plasma jet and its modification effect on a shock wave induced by a ramp with an angle of 24°. The transverse ...We conducted experiments in a wind tunnel with Mach number 2 to explore the evolution of a transverse plasma jet and its modification effect on a shock wave induced by a ramp with an angle of 24°. The transverse plasma jet was created by arc discharge in a small cylindrical cavity with a 2 mm diameter orifice. Three group tests with different actuator arrangements in the spanwise or streamwise direction upstream from the ramp were respectively studied to compare their disturbances to the shock wave. As shown by a time-resolved schlieren system, an unsteady motion of the shock wave by actuation was found： the shock wave was significantly modified by the plasma jet with an upstream motion and a reduced angle. Compared to spanwise actuation, a more intensive impact was obtained with two or three streamwise actuators working together. From shock wave structures, the control effect of the plasma jet on the shock motion based on a thermal effect, a potential cause of shock modification, was discussed. Furthermore, we performed a numerical simulation by using the Improved Delayed Detached Eddy Simulation（IDDES） method to simulate the evolution of the transverse plasma jet plume produced by two streamwise actuators. The results show that flow structures are similar to those identified in schlieren images. Two streamwise vortices were recognized, which indicates that the higher jet plume is the result of the overlap of two streamwise jets.展开更多
Limited particle transit time is one of several limiting factors which determine the maximum temporal resolution of a Langmuir probe.In this work,we have revisited the known fast sweep Langmuir probe techniques in a u...Limited particle transit time is one of several limiting factors which determine the maximum temporal resolution of a Langmuir probe.In this work,we have revisited the known fast sweep Langmuir probe techniques in a uniform,quiescent multi-dipole confined hot cathode discharge with two operation scenarios:one in which the probe sweeping frequency fsweepis much lower than the ion plasma frequency fpi,another one where fsweepis much greater than fpi,respectively.This allows investigation into the effect of limited ion-motion on I–V traces.Serious distortions of I–V traces at high frequencies,previously claimed to be an ion-motion limitation effect,were not found unless shunt resistance is sufficiently high,despite a f;/f;ratio of~3.On the other hand,evidences of sheath capacitance on the I–V traces have been observed.Distortions of I–V traces qualitatively agree with predictions of sheath capacitance response to the sweeping voltage.Additionally,techniques in fast sweep Langmuir probe are briefly discussed.The comparison between the high-speed dual Langmuir probe(HDLP)and the single probe setup shows that the capacitive response can be removed via subtracting a leakage current for the single probe setup almost as effectively as using the HDLP setup,but the HDLP setup does remain advantageous in its facilitation of better recovery of weak current signal commonly in low density plasma.展开更多
A very long lifetime exciton emission with non-single exponential decay characteristics has been reported for single InA-s/GaAs quantum dot(QD)samples,in which there exists a long-lived metastable state in the wetting...A very long lifetime exciton emission with non-single exponential decay characteristics has been reported for single InA-s/GaAs quantum dot(QD)samples,in which there exists a long-lived metastable state in the wetting layer(WL)through radiative field coupling between the exciton emissions in the WL and the dipole field of metal islands.In this article we have proposed a new three-level model to simulate the exciton emission decay curve.In this model,assuming that the excitons in a metastable state will diffuse and be trapped by QDs,and then emit fluorescence in QDs,a stretchedlike exponential decay formula is derived as I(t)=At^(β−1)e^(−(rt)^(β)),which can describe well the long lifetime decay curve with an analytical expression of average lifetime(τ)=1/rГ(1/β+1),where G is the Gamma function.Furthermore,based on the proposed three-level model,an expression of the second-order auto-correlation function g^(2)(t)which can fit the measured g^(2)(t)curve well,is also obtained.展开更多
The pharmaceuti-cally active com-pound atenolol,a kind of β-blockers,may result in ad-verse effects both for human health and ecosystems if it is excreted to the surface water resources.To e ectively remove atenolol ...The pharmaceuti-cally active com-pound atenolol,a kind of β-blockers,may result in ad-verse effects both for human health and ecosystems if it is excreted to the surface water resources.To e ectively remove atenolol in the environ-ment,both direct and indirect photodegradation,driven by sunlight play an important role.Among indirect photodegradation,singlet oxygen(^(1)O_(2)),as a pivotal reactive species,is likely to determine the fates of atenolol.Nevertheless,the kinetic information on the re-action of atenolol with singlet oxygen has not been well investigated and the reaction rate constant is still ambiguous.Herein,the reaction rate constant of atenolol with singlet oxy-gen is investigated directly through observing the decay of the^(1)O_(2)phosphorescence at 1270 nm.It is determined that the reaction rate constant between atenolol and^(1)O_(2)is 7.0×10^(5)(mol/L)^(-1)·s^(-1)in D2O,8.0×10^(6)(mol/L)^(-1)·s^(-1)in acetonitrile,and 8.4×10^(5)(mol/L)^(-1)·s^(-1)in EtOH,respectively.Furthermore,the solvent effects on the title reaction were also inves-tigated.It is revealed that the solvents with strong polarity and weak hydrogen donating ability are suitable to achieve high rate constant values.These kinetics information on the reaction of atenolol with singlet oxygen may provide fundamental knowledge to the indirect photodegradation of β-blockers.展开更多
THz time-domain spectroscopy(THz-TDS)is used to study the THz-optical properties of a single crystal bismuth ferrite BiFeO3(BFO).It can be found that the anisotropy of BiFeO3 is strongly dependent on the temperature.A...THz time-domain spectroscopy(THz-TDS)is used to study the THz-optical properties of a single crystal bismuth ferrite BiFeO3(BFO).It can be found that the anisotropy of BiFeO3 is strongly dependent on the temperature.A giant birefringence up to around 3.6 is observed at 1 THz.The presence of a spatially modulated cycloidal antiferromagnetic structure leads to spin cycloid resonances(SCR)ψandΦ,corresponding to the out-of-plane and in-plane modes of the spin cycloid,respectively.We distinguish the SCR with respect to their response to orthogonal polarizations of the electric fields of the incident THz beam.In addition,we observe a resonance appearing below 140 K,which might be interpreted as an electromagnon mode and related to a spin reorientation transition.Our present observations present that the temperature and polarization,as the external control parameters,can be used to modulate the THz optical properties of BFO single crystal.展开更多
A wide range of techniques has been developed to image biological samples at high spatial and temporal resolution.In this paper,we report recent results from deep-UV confocal fAuorescence microscopy to image inherent ...A wide range of techniques has been developed to image biological samples at high spatial and temporal resolution.In this paper,we report recent results from deep-UV confocal fAuorescence microscopy to image inherent emission from fuorophores such as tryptophan,and structured ilumination microscopy(SIM)of biological materials.One motivation for developing deep-UV fhuorescence imaging and SIM is to provide methods to complement our measurements in the emerging field of X-ray coherent diffractive imaging.展开更多
Time-resolved volumetric fluorescence imaging over an extended duration with high spatial/temporal resolution is a key driving force in biomedical research for investigating spatial-temporal dynamics at organism-level...Time-resolved volumetric fluorescence imaging over an extended duration with high spatial/temporal resolution is a key driving force in biomedical research for investigating spatial-temporal dynamics at organism-level systems,yet it remains a major challenge due to the trade-off among imaging speed,light exposure,illumination power,and image quality.Here,we present a deep-learning enhanced light sheet fluorescence microscopy(LSFM)approach that addresses the restoration of rapid volumetric time-lapse imaging with less than 0.03%light exposure and 3.3%acquisition time compared to a typical standard acquisition.We demonstrate that the convolutional neural network(CNN)-transformer network developed here,namely U-net integrated transformer(UI-Trans),successfully achieves the mitigation of complex noise-scattering-coupled degradation and outperforms state-of-the-art deep learning networks,due to its capability of faithfully learning fine details while comprehending complex global features.With the fast generation of appropriate training data via flexible switching between confocal line-scanning LSFM(LS-LSFM)and conventional LSFM,this method achieves a three-to five-fold signal-to-noise ratio(SNR)improvement and~1.8 times contrast improvement in ex vivo zebrafish heart imaging and long-term in vivo 4D(3D morphology+time)imaging of heartbeat dynamics at different developmental stages with ultra-economical acquisitions in terms of light dosage and acquisition time.展开更多
文摘Time-resolved fluorescence spectra of europium methylbenzoates (MBA)with 1,10-phenanthroline(phen)have been measured at room temperature.For each of the europium chelates,where the ligand triple states lie above the ~5D_1 level of Eu^(3-),the spectra providc evidence that the Eu^(3-) ~5D_0 state is populated by nonradiative energy transfer from the higher-lying ~5D_1,state.The relaxation time for energy decay from ~5D_1 state is measured in the microcrystals to bc of the order of a few microseconds.It is suggested that the ligand C=0 and C=C stretching vibrations and Eu-O vibrations,chclate ring and benzene ring vibrations make important contributions to the relaxation process.The ~5D\-1—~5D\-0 relaxation time of Eu- (p-MBA)_3phen is shorter than those of Eu(m-MBA)_3phen and Eu(o-MBA)_3phen since nonradiative degradation to ~5D_0 from ~5D_1 appears to be more strongly influenced by the E_u^(3+)sites in the former.
基金This work was supported by the National Key R&D Program of China(No.2020YFA0405802)the Shanghai Large Scientific Facilities Center.
文摘The construction of a new beamline,BL10U1,was completed at the Shanghai synchrotron radiation facility in 2020.This multipurpose beamline was designed to provide X-ray scattering techniques such as ultra-small-angle X-ray scattering(USAXS),small-angle X-ray scattering(SAXS),wide-angle X-ray scattering,and microfocus SAXS(μSAXS)for a broad user community.To realize fast time-resolved USAXS experiments,the beamline adopted an in-vacuum undulator with a total length of 1.6 m as the photon source.An in-house cryogenic-cooled double multilayer monochromator was installed to deliver a photon flux of approximately 10^(13) photons/s at a photon energy of 10 keV.The three-year successful operation of this beamline demonstrated that the monochromator operated smoothly,as expected.BL10U1 has three end stations in succession:USAXS end station,μSAXS end station,and end station for industrial applications.The minimum scattering vector q~0.0042 nm^(-1) at 10 keV can be achieved at the USAXS end station equipped with a 28 m-long and 1.8 m-diameter vacuum flight tube.At theμSAXS end station,a beam spot of less than 10×8μm was achieved for micro-SAXS experiments.In contrast,in situ experimental instruments up to 5 m high and 8 m wide can be mounted at the industrial application end station,which offers industrial scientists the opportunity to use their large industrial equipment.BL10U1 opens up a new capability to investigate phenomena such as non-equilibrium and dynamic processes of materials with a wide length scale from angstroms to micrometers with millisecond time resolution.In this paper,we also report beamline design considerations and commissioning results.
文摘A time resolved chemiluminescent analysis for simultaneous determination of trace Au(Ⅲ) and Os(Ⅳ) was proposed. The method is based on the kinetic distinction of Au(Ⅲ) and Os(Ⅳ) in Tween 80 KOH chemilumescent system. The detection limits were 1.1×10 -9 g/ml for Au(Ⅲ) and 1.0×10 -8 g/ml for Os(Ⅳ), with the linear ranges of 1.0×10 -8 ～1.0×10 -5 g/ml for Au(Ⅲ) and 1.0×10 -7 ～1.0×10 -6 g/ml for Os(Ⅳ). The method was applied to the determination of Au(Ⅲ) and Os(Ⅳ) in the sample of metallurgical materials of noble metals with satisfactory results.
基金Agence Nationale de la Recherche(ANR-22-CE42-0005-HYPSTER,ANR 22-PEEL-0003-Comptera)。
文摘Terahertz(THz)microscopy has attracted attention owing to distinctive characteristics of the THz frequency region,particularly non-ionizing photon energy,spectral fingerprint,and transparency to most nonpolar materials.Nevertheless,the well-known Rayleigh diffraction limit imposed on THz waves commonly constrains the resultant imaging resolution to values beyond the millimeter scale,consequently limiting the applicability in numerous emerging applications for chemical sensing and complex media imaging.In this theoretical and numerical work,we address this challenge by introducing,to our knowledge,a new imaging approach based on acquiring high-spatial frequencies by adapting the Fourier synthetic aperture approach to the THz spectral range,thus surpassing the diffractionlimited resolution.Our methodology combines multi-angle THz pulsed illumination with time-resolved field measurements,as enabled by the state-of-the-art time-domain spectroscopy technique.We demonstrate the potential of the approach for hyperspectral THz imaging of semi-transparent samples and show that the technique can reconstruct spatial and temporal features of complex inhomogeneous samples with subwavelength resolution.
基金funding via EUROfusion Enabling research Project No.AWP21-ENR-01-CEA-02“Advancing Shock Ignition for Direct-Drive Inertial Fusion,”the framework of the EUROfusion Consortium,funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No.101052200-EUROfusion)+2 种基金the Czech Ministry of Education,Youth and Sports (CMEYS) for funding the operation of the PALS facility (Grant No.LM2023068)the EuroHPC Joint Undertaking for awarding access to Karolina at IT4Innovations (VSB-TU),Czechia under Project No.EHPC-REG-2023R02-006(DD-23-157)the Ministry of Education,Youth and Sports of the Czech Republic through e-INFRA CZ (Grant No.ID:90140)
文摘We investigate the spatial and temporal correlations of hot-electron generation in high-intensity laser interaction with massive and thin copper targets under conditions relevant to inertial confinement fusion.Using Ka time-resolved imaging,it is found that in the case of massive targets,the hot-electron generation follows the laser pulse intensity with a short delay needed for favorable plasma formation.Conversely,a significant delay in the x-ray emission compared with the laser pulse intensity profile is observed in the case of thin targets.Theoretical analysis and numerical simulations suggest that this is related to radiation preheating of the foil and the increase in hot-electron lifetime in a hot expanding plasma.
基金supported by the National Key R&D Program under Grant No.2021YFA1400500the National Natural Science Foundation of China under Grant No.22273029+1 种基金the New Cornerstone Science Foundation through the New Cornerstone Investigator Program under Grant No.NCI202303 and the XPLORER PRIZEthe Beijing Outstanding Young Scientist Program under Grant No.JWZQ20240101002。
文摘Ultrafast electron sources, which enable high spatiotemporal resolution in time-resolved electron microscopy and scanning probe microscopy, are receiving increased attention. The most widely used method for achieving ultrafast electron sources involves irradiating metal tips by ultrashort laser pulses, causing electron beam emission via the photoelectric effect [including photon-driven(quantum) or field-driven(classical) emission]. However, the thermionic electrons emission process due to the heating effect of ultrashort lasers, particularly its dynamic aspects, has rarely been addressed in previous studies. In this paper, we improved the signal-to-noise ratio of a two-pulse correlation measurement on the tip electron emission by nearly two orders of magnitude using a delay time modulation method. This allowed us to obtain information on the temperature evolution of hot electrons and phonons in a non-equilibrium state, and to extract characteristic time scales for electron-phonon and phonon-phonon scattering. Our findings indicate that the thermionic electrons emission, unlike the instantaneous photoelectric effect, causes electron emission to lag behind the laser pulse by tens of picoseconds, thus significantly affecting the detection of ultrafast dynamics of samples. Furthermore, such a lagging effect was found to be sensitive to the local structure of the metal tip, offering new insights into the improved design of ultrafast electron sources.
基金supported by the National Key R&D Program of China(Grant No.2021YFA1600200)the National Natural Science Foundation of China(Grant Nos.U2032218 and 12111530283)。
文摘Besides equilibrium behavior,exploring the spin–phonon coupling in multiferroic materials under non-equilibrium conditions is crucial for a deep understanding of the mechanisms as well as their high-frequency applications.Here,by utilizing time-resolved refectance spectroscopy,we demonstrate ultrafast spin–phonon coupling dynamics in multiferroic 0.58BiFeO_(3)-0.42Bi_(0.5)K_(0.5)TiO_(3)(BF-BKT)single crystals.With ultrafast laser pumping,coherent acoustic phonons with low damping are created in BF-BKT.Temperature-dependent results indicate that both the frequency and amplitude of laser-induced coherent phonons are sensitive to the emergence of antiferromagnetic order.Moreover,the spin state change driven by external magnetic felds can enhance the oscillation amplitude of the coherent acoustic phonons even above the magnetic Néel temperature.These fndings experimentally confrm that spin–phonon coupling in multiferroic materials exists not only in the spin-ordered state but also in the spin-disordered state,and not only in the equilibrium state but also in the non-equilibrium state excited by ultrafast lasers,suggesting their promising applications in high-frequency devices.
文摘The advent of high-resolution black hole imaging—most notably by the Event Horizon Telescope(EHT)—has propelled black hole physics into a new observational regime[1].However,most theoretical interpretations remain anchored in stationary,time-averaged general relativistic magnetohydrodynamic(GRMHD)simulations within the Kerr paradigm,often neglecting dynamic accretion structures and potential deviations from general relativity[2].
基金supported by the National Natural Science Foundation of China(Nos.51522606,51507187,51276197,51407197,and 11472306)
文摘We conducted experiments in a wind tunnel with Mach number 2 to explore the evolution of a transverse plasma jet and its modification effect on a shock wave induced by a ramp with an angle of 24°. The transverse plasma jet was created by arc discharge in a small cylindrical cavity with a 2 mm diameter orifice. Three group tests with different actuator arrangements in the spanwise or streamwise direction upstream from the ramp were respectively studied to compare their disturbances to the shock wave. As shown by a time-resolved schlieren system, an unsteady motion of the shock wave by actuation was found： the shock wave was significantly modified by the plasma jet with an upstream motion and a reduced angle. Compared to spanwise actuation, a more intensive impact was obtained with two or three streamwise actuators working together. From shock wave structures, the control effect of the plasma jet on the shock motion based on a thermal effect, a potential cause of shock modification, was discussed. Furthermore, we performed a numerical simulation by using the Improved Delayed Detached Eddy Simulation（IDDES） method to simulate the evolution of the transverse plasma jet plume produced by two streamwise actuators. The results show that flow structures are similar to those identified in schlieren images. Two streamwise vortices were recognized, which indicates that the higher jet plume is the result of the overlap of two streamwise jets.
基金supported by the Inner Mongolia Autonomous Region Open Major Basic Research Project(Grant No.20120905)the National Natural Science Foundation of China(Grant No.51666014)
文摘Wind tunnel experiments of the wake characteristics of a two-blade wind turbine, in the downstream region of 0
基金supported by National Natural Science Foundation of China(No.11875285)the CAS Key Research Program of Frontier Sciences(No.QYZDB-SSWSLH001)the Chinese Academy of Science Hundred Youth Talent Program。
文摘Limited particle transit time is one of several limiting factors which determine the maximum temporal resolution of a Langmuir probe.In this work,we have revisited the known fast sweep Langmuir probe techniques in a uniform,quiescent multi-dipole confined hot cathode discharge with two operation scenarios:one in which the probe sweeping frequency fsweepis much lower than the ion plasma frequency fpi,another one where fsweepis much greater than fpi,respectively.This allows investigation into the effect of limited ion-motion on I–V traces.Serious distortions of I–V traces at high frequencies,previously claimed to be an ion-motion limitation effect,were not found unless shunt resistance is sufficiently high,despite a f;/f;ratio of~3.On the other hand,evidences of sheath capacitance on the I–V traces have been observed.Distortions of I–V traces qualitatively agree with predictions of sheath capacitance response to the sweeping voltage.Additionally,techniques in fast sweep Langmuir probe are briefly discussed.The comparison between the high-speed dual Langmuir probe(HDLP)and the single probe setup shows that the capacitive response can be removed via subtracting a leakage current for the single probe setup almost as effectively as using the HDLP setup,but the HDLP setup does remain advantageous in its facilitation of better recovery of weak current signal commonly in low density plasma.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFA0301202)the National Natural Science Foundation of China(Grant Nos.61827823 and 11974342).
文摘A very long lifetime exciton emission with non-single exponential decay characteristics has been reported for single InA-s/GaAs quantum dot(QD)samples,in which there exists a long-lived metastable state in the wetting layer(WL)through radiative field coupling between the exciton emissions in the WL and the dipole field of metal islands.In this article we have proposed a new three-level model to simulate the exciton emission decay curve.In this model,assuming that the excitons in a metastable state will diffuse and be trapped by QDs,and then emit fluorescence in QDs,a stretchedlike exponential decay formula is derived as I(t)=At^(β−1)e^(−(rt)^(β)),which can describe well the long lifetime decay curve with an analytical expression of average lifetime(τ)=1/rГ(1/β+1),where G is the Gamma function.Furthermore,based on the proposed three-level model,an expression of the second-order auto-correlation function g^(2)(t)which can fit the measured g^(2)(t)curve well,is also obtained.
基金This work was supported by the National Natural Science Foundation of China(No.21773013).
文摘The pharmaceuti-cally active com-pound atenolol,a kind of β-blockers,may result in ad-verse effects both for human health and ecosystems if it is excreted to the surface water resources.To e ectively remove atenolol in the environ-ment,both direct and indirect photodegradation,driven by sunlight play an important role.Among indirect photodegradation,singlet oxygen(^(1)O_(2)),as a pivotal reactive species,is likely to determine the fates of atenolol.Nevertheless,the kinetic information on the re-action of atenolol with singlet oxygen has not been well investigated and the reaction rate constant is still ambiguous.Herein,the reaction rate constant of atenolol with singlet oxy-gen is investigated directly through observing the decay of the^(1)O_(2)phosphorescence at 1270 nm.It is determined that the reaction rate constant between atenolol and^(1)O_(2)is 7.0×10^(5)(mol/L)^(-1)·s^(-1)in D2O,8.0×10^(6)(mol/L)^(-1)·s^(-1)in acetonitrile,and 8.4×10^(5)(mol/L)^(-1)·s^(-1)in EtOH,respectively.Furthermore,the solvent effects on the title reaction were also inves-tigated.It is revealed that the solvents with strong polarity and weak hydrogen donating ability are suitable to achieve high rate constant values.These kinetics information on the reaction of atenolol with singlet oxygen may provide fundamental knowledge to the indirect photodegradation of β-blockers.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61975110,11674213,61735010,and 11604202)the 111 Project,China(Grant No.D18014)+3 种基金the International Joint Lab Program supported by Science and Technology Commission Shanghai Municipality,China(Grant No.17590750300)the Key Project supported by Science and Technology Commission Shanghai Municipality,China(Grant No.YDZX20193100004960)Science and Technology Commission of Shanghai Municipality,China(Shanghai Rising-Star Program 18QA1401700)Shanghai Educational Development Foundation,China(Chen Guang Project 16CG45).
文摘THz time-domain spectroscopy(THz-TDS)is used to study the THz-optical properties of a single crystal bismuth ferrite BiFeO3(BFO).It can be found that the anisotropy of BiFeO3 is strongly dependent on the temperature.A giant birefringence up to around 3.6 is observed at 1 THz.The presence of a spatially modulated cycloidal antiferromagnetic structure leads to spin cycloid resonances(SCR)ψandΦ,corresponding to the out-of-plane and in-plane modes of the spin cycloid,respectively.We distinguish the SCR with respect to their response to orthogonal polarizations of the electric fields of the incident THz beam.In addition,we observe a resonance appearing below 140 K,which might be interpreted as an electromagnon mode and related to a spin reorientation transition.Our present observations present that the temperature and polarization,as the external control parameters,can be used to modulate the THz optical properties of BFO single crystal.
基金We acknowledge the support of the Australian Research Council for the Center of Excellence for Coherent X-ray Science(CE0561787).
文摘A wide range of techniques has been developed to image biological samples at high spatial and temporal resolution.In this paper,we report recent results from deep-UV confocal fAuorescence microscopy to image inherent emission from fuorophores such as tryptophan,and structured ilumination microscopy(SIM)of biological materials.One motivation for developing deep-UV fhuorescence imaging and SIM is to provide methods to complement our measurements in the emerging field of X-ray coherent diffractive imaging.
基金supported by National Natural Science Foundation of China(52122008,52270008,52370003,62025502)Guangdong Introducing Innovative and Entrepreneurial Teams of“The Pearl River Talent Recruitment Program”(2021ZT09X044)Shenzhen Technology University under Grant JSZZ202301010.
文摘Time-resolved volumetric fluorescence imaging over an extended duration with high spatial/temporal resolution is a key driving force in biomedical research for investigating spatial-temporal dynamics at organism-level systems,yet it remains a major challenge due to the trade-off among imaging speed,light exposure,illumination power,and image quality.Here,we present a deep-learning enhanced light sheet fluorescence microscopy(LSFM)approach that addresses the restoration of rapid volumetric time-lapse imaging with less than 0.03%light exposure and 3.3%acquisition time compared to a typical standard acquisition.We demonstrate that the convolutional neural network(CNN)-transformer network developed here,namely U-net integrated transformer(UI-Trans),successfully achieves the mitigation of complex noise-scattering-coupled degradation and outperforms state-of-the-art deep learning networks,due to its capability of faithfully learning fine details while comprehending complex global features.With the fast generation of appropriate training data via flexible switching between confocal line-scanning LSFM(LS-LSFM)and conventional LSFM,this method achieves a three-to five-fold signal-to-noise ratio(SNR)improvement and~1.8 times contrast improvement in ex vivo zebrafish heart imaging and long-term in vivo 4D(3D morphology+time)imaging of heartbeat dynamics at different developmental stages with ultra-economical acquisitions in terms of light dosage and acquisition time.
