Quantum materials have attracted a great deal of attention because of their rich landscape of electronic structures,topological phases,strong correlation effects,and exotic orders.These systems provide a fertile platf...Quantum materials have attracted a great deal of attention because of their rich landscape of electronic structures,topological phases,strong correlation effects,and exotic orders.These systems provide a fertile platform for the exploration of novel quantum phenomena and materials applications.Particularly exciting is the exploration of nonequilibrium dynamics in quantum materials,which has significant research and potential application values.Pump-probe techniques play a key role in revealing the dynamics of quantum materials on remarkably short timescales,providing an attractive yet challenging avenue of research.In this context,time-resolved x-ray as an emerging probe exhibits high time resolution,momentum resolution,and substantial momentum coverage.It can reveal unprecedented transient states,distinguish between entangled ordered states,and has a compelling potential to probe ultrafast dynamics in a wide variety of quantum materials.Despite its unique advantages,time-resolved x-ray scattering still faces several technological and methodological challenges.In this review,we highlight recent advances focusing on the use of time-resolved x-ray scattering to probe dynamic processes in quantum materials.We discuss representative examples across structural,electronic,magnetic,and lattice degrees of freedom,and outline promising directions for future research in this rapidly evolving field.展开更多
Time-resolved flow cytometry(TRFC)was used to measure metabolic differences in estrogen receptor-positive breast cancer cells.This specialty cytometry technique measures fluorescence lifetimes as a single-cell paramet...Time-resolved flow cytometry(TRFC)was used to measure metabolic differences in estrogen receptor-positive breast cancer cells.This specialty cytometry technique measures fluorescence lifetimes as a single-cell parameter thereby providing a unique approach for high-throughput cell counting and screening.Differences in fluorescence lifetime were detected and this was associated with sensitivity to the commonly prescribed therapeutic tamoxifen.Differences in fluorescence lifetime are attributed to the binding states of the autofluorescent metabolite NAD(P)H.The function of NAD(P)H is well described and in general involves cycling from a reduced to oxidized state to facilitate electron transport for the conversion of pyruvate to lactate.NAD(P)H fluorescence lifetimes depend on the bound or unbound state of the metabolite,which also relates to metabolic transitions between oxidative phosphorylation and glycolysis.To determine if fundamental metabolic profiles differ for cells that are sensitive to tamoxifen compared to those that are resistant,large populations of MCF-7 breast cancer cells were screened and fluorescence lifetimes were quantified.Additionally,metabolic differences associated with tamoxifen sensitivity were measured with a Seahorse HS mini metabolic analyzer(Agilent Technologies Inc.Santa Clara,CA)and confocal imaging.Results show that tamoxifen-resistant breast cancer cells have increased utilization of glycolysis for energy production compared to tamoxifen-sensitive breast cancer cells.This work is impacting because it establishes an early step toward developing a reliable screening technology in which large cell censuses can be differentiated for drug sensitivity in a label-free fashion.展开更多
The ultrafast dynamics through conical intersections in 2,6-dimethylpyridine has been studied by femtosecond time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy. Upon absorption of 266 nm ...The ultrafast dynamics through conical intersections in 2,6-dimethylpyridine has been studied by femtosecond time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy. Upon absorption of 266 nm pump laser, 2,6-dimethylpyridine is excited to the S2 state with a ππ character from So state. The time evolution of the parent ion signals consists of two exponential decays. One is a fast component on a timescale of 635 fs and the other is a slow component with a timescale of 4.37 ps. Time-dependent photo- electron angular distributions and energy-resolved photoelectron spectroscopy are extracted from time-resolved photoelectron imaging and provide the evolutive information of S2 state. In brief, the ultrafast component is a population transfer from S2 to S1 through the S2/S1 conical intersections, the slow component is attributed to simultaneous IC from the S2 state and the higher vibrational levels of S1 state to So state, which involves the coupling of S2/S0 and S1/So conical intersections. Additionally, the observed ultrafast S2--＋S1 transition occurs only with an 18% branching ratio.展开更多
The function of protein in long-range biological electron transfer is a question of debate. We report some preliminary results in femtosecond spectroscopic study of photosynthetic bacterial light-harvesting antenna co...The function of protein in long-range biological electron transfer is a question of debate. We report some preliminary results in femtosecond spectroscopic study of photosynthetic bacterial light-harvesting antenna complex assembled onto TiO2 nanoparticle with an average size of 8 nm in diameter. Crystal structure shows that photosynthetic bacterial antenna complex LH2 has a ring-like structure composed by alpha- and beta-apoprotein helices. The alpha- and beta-transmembrance helices construct two concentric cylinders with pigments bacteriochlorophyll a (Bchl a) and carotenoid (Car) buried inside the protein. We attempt to insert TiO2 nanoparticle into the cavity of the inner cylindrical hollow of LH2 to investigate the nature of the electron transfer between the excited-state Bchl a and the TiO2 nanoparticle. A significant decrease in the ground state bleaching recovery time constant for Bchl a at 850 run (B850) in respect to that of the Bchl a in free LH2 has been observed. By using the relation of distance-dependent long-range electron transfer rate in protein, the distance between the donor B850 and the acceptor TiO2 nanoparticle has been estimated, which is about 0.6 nm. The proposed method of assembling proteins onto wide-gap semiconductor nanoparticle can be a promising way to determine the role of the protein playing in biological electron transfer processes.展开更多
The benzoin group caged compound has received strong interests due to its excellent photo- deprotection properties and wide use in chemical and biological studies. We used timeresolved infrared spectroscopy to investi...The benzoin group caged compound has received strong interests due to its excellent photo- deprotection properties and wide use in chemical and biological studies. We used timeresolved infrared spectroscopy to investigate the photochemical reaction of the benzoin caged compound, o-（2-methylbenzoyl）-DL-benzoin under 266 nm laser irradiation. Taking advantage of the specific vibrational marker bands and the IR discerning capability, we have detected and identified the uncaging product 2-methylbenzoic acid, and two intermediate radicals of benzoyl and 2-methylbenzoate benzyl in the transient infrared spectra. Our results provide spectral evidence to support the homolytic cleavage reaction of C-C=O bond in competition with the deprotection reaction. Moreover, the product yields of 2-methylbenzoic acid and benzoyl radical were observed to be affected by solvents and a largely water contalning solvent can be in favor of the deprotection reaction.展开更多
We experimentally investigated the forward 353.8 nm radiation from plasma filaments in pure nitrogen gas pumped by intense circularly polarized 800 nm femtosecond laser pulses.This emission line corresponds to the B^2...We experimentally investigated the forward 353.8 nm radiation from plasma filaments in pure nitrogen gas pumped by intense circularly polarized 800 nm femtosecond laser pulses.This emission line corresponds to the B^2Σu^+(u'=4)-X^2Σg^+(u=3)transition of nitrogen ions.In the presence of an external seeding pulse,the 353.8 nm signal was amplified by 3 orders of magnitude.Thanks to the much enhanced intensity,we performed time-resolved measurement of the amplified 353.8 nm emission based on the sum-frequency generation technique.It was revealed that the built-up time and duration of these emissions are both inversely proportional to the gas pressure,while the radiation peak power grows up nearly quadratically with pressure,indicating that the 353.8 nm radiation is of the nature of superradiance.展开更多
The properties of norfloxacin(NFX)and its 4?-N-acetyl derivative(ANFX)are investigated in different pH aqueous solutions and H2O-CH3CN mixed solutions,to determine the effects of pH and polarity on their ground and ex...The properties of norfloxacin(NFX)and its 4?-N-acetyl derivative(ANFX)are investigated in different pH aqueous solutions and H2O-CH3CN mixed solutions,to determine the effects of pH and polarity on their ground and excited states.The triplet states of NFX and ANFX are affected more by pH than by polarity.The pH dependence of the NFX and ANFX triplet states is likely due to the different quantum yields of different protonated forms.Steady-state fluorescence,time-resolved fluorescence,and laser flash photolysis experiments at different pH values provide clear evidence of the involvement of different intramolecular charge-transfer pathways in the singlet states of NFX and ANFX.The different electron-donating capacities of 1-N,1?-N,and 4?-N under different conditions determine the major pathway.展开更多
The relationship between the in the logarithmic law （log-law） region of bursting event and the low/high-speed streak a turbulent boundary layer is investigated. A tomographic time-resolved particle image velocimetry...The relationship between the in the logarithmic law （log-law） region of bursting event and the low/high-speed streak a turbulent boundary layer is investigated. A tomographic time-resolved particle image velocimetry （TRPIV） system is used to measure the instantaneous three-dimensional-three-component （3D-3C） velocity field. The momentum thickness based Reynolds number is about 2 460. The topological information in the log-law region is obtained experimentally. It is found that the existence of the quadrupole topological structure implies a three-pair hairpin-like vortex packet, which is in connection with the low/high-speed streak. An idealized 3D topological model is then proposed to characterize the observed hairpin vortex packet and low/high-speed streak.展开更多
We performed femtosecond time-resolved coherent anti-Stokes Raman scattering （fs-CARS） measurements on liquid toluene and PVK film. For both samples, we selectively excited the CH stretching vibrational modes and ob...We performed femtosecond time-resolved coherent anti-Stokes Raman scattering （fs-CARS） measurements on liquid toluene and PVK film. For both samples, we selectively excited the CH stretching vibrational modes and observed the expected quantum beat signals. The frequency of the well-defined beats is in good agreement with the energy difference between the two simultaneously excited modes, which demonstrates that a coherent coupling between the vibrational modes of the C H chemical bonds exists at the different positions of the molecules. The dephasing times of the excited modes are obtained simultaneously.展开更多
Time-resolved IR absorption spectroscopy has been used to atudy the photochemistry of W(CO)_6 in cyclohexane, carbon tetrachloride, and the mixture of carbon tetrachloride and cyelohexane. The reastion of photolytical...Time-resolved IR absorption spectroscopy has been used to atudy the photochemistry of W(CO)_6 in cyclohexane, carbon tetrachloride, and the mixture of carbon tetrachloride and cyelohexane. The reastion of photolytically generated W(CO)_5. C_6H_(12) with CCl_4 was investigated. An intermediate with a lifetime of about 0.5ms, presumably attributed as W(GO)_5.CCl_4, was first observed.展开更多
A silicon nanoporous pillar array （Si-NPA） is thought to be a promising functional substrate for constructing a variety of Si-based optoelectronic nanodevices, due to its unique hierarchical structure and enhanced p...A silicon nanoporous pillar array （Si-NPA） is thought to be a promising functional substrate for constructing a variety of Si-based optoelectronic nanodevices, due to its unique hierarchical structure and enhanced physical properties. This makes the in-depth understanding of the photoluminescence （PL） of Si-NPA crucial for both scientific research and practical applications. In this work, the PL properties of Si-NPA are studied by measuring both the steady-state and time-resolved PL spectrum. Based on the experimental data, the three PL bands of Si-NPA, i.e., the ultraviolet band, the purple-blue plateau and the red band are assigned to the oxygen-excess defects in Si oxide or silanol groups at the surface of Si nanocrystallites （nc-Si）, oxygen deficiency defects in Si oxide, and band-to-band transition of nc-Si under the frame of quantum confinement combining with the surface states like Si=O and Si-O^i bonds at the surface of nc-Si, respectively. These results may provide some novel insight into the PL process of Si-NPA and may be helpful for clarifying the PL mechanism.展开更多
In-situ time-resolved Raman spectroscopy(TRRS)has been applied on studies of electrochemical adsorption of thiocyanate at silver electrode during potential cycles and potential step.It is shown that some dynamic infor...In-situ time-resolved Raman spectroscopy(TRRS)has been applied on studies of electrochemical adsorption of thiocyanate at silver electrode during potential cycles and potential step.It is shown that some dynamic information about the adsorption and desorption processes can be obtained.展开更多
We performed a quantitative analysis of time-resolved laser-induced breakdown air plasma spectra to obtain the evolution of temperatures and species relative fractions.The air plasma was generated by focusing a 100 mJ...We performed a quantitative analysis of time-resolved laser-induced breakdown air plasma spectra to obtain the evolution of temperatures and species relative fractions.The air plasma was generated by focusing a 100 mJ Nd:YAG laser pulse,and the time-resolved spectra were recorded by an intensified charge-coupled device camera with incremental delay.The attention was mainly focused on the emission spectra of the first negative system of nitrogen(N_(2)^(+),B^(2)Σ-(u)^(-)-X^(2)Σ^(+)g)and the violet system of carbon nitride(CN,B^(2)Σ^(+)-X^(2)Σ^(+))located at 383-396 nm.A custom-built model was developed to perform the simulation and fitting of the N_(2)^(+)and the CN spectra from the air plasma.The model was verified by comparing to a published model with a 0.9860 Spearman correlation coefficient.With this model,the time-resolved non-equilibrium temperatures and relative fractions of N_(2)^(+)and CN were obtained with a fitting correlation coefficient higher than 0.9108.展开更多
Photoswitchable fluorescent polymeric nanoparticles were widely concerned because of their excellent features including the flexible design,easy preparation and functionalization,and thus exhibited great application p...Photoswitchable fluorescent polymeric nanoparticles were widely concerned because of their excellent features including the flexible design,easy preparation and functionalization,and thus exhibited great application potential in information encryption,anti-counterfeiting,but remained challenging in improving the security.Herein,we described a self-erased time-resolved information encryption via using photoswitchable dual-color fluorescent polymeric nanoparticles(PDFPNs)containing two fluorescence dyes(blue and red)and photochromic spiroxazine derivatives.In view of the different thermo-induced isomerization rates of photochromic spiroxazine derivatives in different flexible substrates,the decoloration rate of PDFPNs can be programmatically tuned by regulating ratio between rigid polymer and flexible polymer.Therefore,after ultraviolet light(UV)irradiation,correct information could only be recognized in preestablished time during the self-erased process.Our results indicated that PDFPNs exhibited fast photo-responsibility(2 min),high fluorescence contrast,well-pleasing photo-reversibility(>20 times),and programmable thermo-responsiveness(24 s-6 h).We thus demonstrated their application in the selferased time-resolved information encryption and anti-counterfeiting with high security.展开更多
N-ethylpyrrole is one of ethylsubstituted derivatives of pyrrole and its excited-state decay dynamics has never been explored.In this work,we investigate ultrafast decay dynamics of N-ethylpyrrole excited to the S_(1)...N-ethylpyrrole is one of ethylsubstituted derivatives of pyrrole and its excited-state decay dynamics has never been explored.In this work,we investigate ultrafast decay dynamics of N-ethylpyrrole excited to the S_(1)electronic state using a femtosecond time-resolved photoelectron imaging method.Two pump wavelengths of 241.9 and 237.7 nm are employed.At 241.9 nm,three time constants,5.0±0.7 ps,66.4±15.6 ps and 1.3±0.1 ns,are derived.For 237.7 nm,two time constants of 2.1±0.1 ps and 13.1±1.2 ps are derived.We assign all these time constants to be associated with different vibrational states in the S_(1)state.The possible decay mechanisms of different S_(1)vibrational states are briefly discussed.展开更多
The ultrafast dynamics of water molecules excited to the two F states is studied by combining two-photon excitation and time-resolved photoelectron imaging techniques. The lifetimes of the F1A1 and F1B1 states of H2O ...The ultrafast dynamics of water molecules excited to the two F states is studied by combining two-photon excitation and time-resolved photoelectron imaging techniques. The lifetimes of the F1A1 and F1B1 states of H2O (D2O) were derived to be 1.0±0.3 (1.9±0.4) and 10±3 (30±10) ps, respectively. We propose that the F1A1 state mainly decays through the D state, due to the nonadiabatic coupling between them, while the F1B1 state decays through the F1A1 state via Coriolis interaction.展开更多
Objective Observational studies have found associations between inflammatory bowel disease(IBD)and the risk of dementia,including Alzheimer’s dementia(AD)and vascular dementia(VD);however,these findings are inconsist...Objective Observational studies have found associations between inflammatory bowel disease(IBD)and the risk of dementia,including Alzheimer’s dementia(AD)and vascular dementia(VD);however,these findings are inconsistent.It remains unclear whether these associations are causal.Methods We conducted a meta-analysis by systematically searching for observational studies on the association between IBD and dementia.Mendelian randomization(MR)analysis based on summary genome-wide association studies(GWASs)was performed.Genetic correlation and Bayesian colocalization analyses were used to provide robust genetic evidence.Results Ten observational studies involving 80,565,688 participants were included in this metaanalysis.IBD was significantly associated with dementia(risk ratio[RR]=1.36,95%CI=1.04-1.78;I2=84.8%)and VD(RR=2.60,95%CI=1.18-5.70;only one study),but not with AD(RR=2.00,95%CI=0.96-4.13;I^(2)=99.8%).MR analyses did not supported significant causal associations of IBD with dementia(dementia:odds ratio[OR]=1.01,95%CI=0.98-1.03;AD:OR=0.98,95%CI=0.95-1.01;VD:OR=1.02,95%CI=0.97-1.07).In addition,genetic correlation and co-localization analyses did not reveal any genetic associations between IBD and dementia.Conclusion Our study did not provide genetic evidence for a causal association between IBD and dementia risk.The increased risk of dementia observed in observational studies may be attributed to unobserved confounding factors or detection bias.展开更多
This paper proposes an interdisciplinary talent training model that combines foreign language education with area studies.The model aims to cultivate international ocean affairs professionals with cross-cultural commu...This paper proposes an interdisciplinary talent training model that combines foreign language education with area studies.The model aims to cultivate international ocean affairs professionals with cross-cultural communication skills,in-depth regional and country knowledge,and practical expertise in ocean affairs.Additionally,the paper presents specific training pathways and policy recommendations for implementing this model.展开更多
Effect of Ti(iso-C3H7O)4 treatment on the photoinduced charge carrier kinetics of nanocrystalline porous TiO2 films is studied by time-resolved microwave conductivity measurements. Analysis of the transient photocond...Effect of Ti(iso-C3H7O)4 treatment on the photoinduced charge carrier kinetics of nanocrystalline porous TiO2 films is studied by time-resolved microwave conductivity measurements. Analysis of the transient photoconductivity decays indicates that Ti(iso-C3H7O)4 treatment leads to an increased concentration of photogenerated charge carriers and a fast interfacial transfer rate of holes via the surface modification of the freshly growing TiO2 nanocrystallites.展开更多
In modern society,the globalization of literary works is evident,with exceptional literary pieces from various countries spreading worldwide.Among these,children’s literature,due to the specificity of its target audi...In modern society,the globalization of literary works is evident,with exceptional literary pieces from various countries spreading worldwide.Among these,children’s literature,due to the specificity of its target audience,imposes distinct requirements on children’s books,compelling translators to approach the text from a child’s perspective.“The Little Prince”has renowned both within and outside of China,and a careful reading of this work can provide us with much inspiration.To this end,the present study adopts the perspective of Gideon Toury’s Descriptive Translation Studies to conduct an in-depth analysis of the different English and Chinese translations in conjunction with the original French novel.This approach aims to better guide literary research and explores translation methods for children’s literature through the analysis of translation norms and rules.展开更多
基金the National Key R&D Program of China(Grants Nos.2024YFA1408702 and 2021YFA1401903)Beijing Natural Science Foundation(Grant No.JQ24001)the National Natural Science Foundation of China(Grant No.12374143)。
文摘Quantum materials have attracted a great deal of attention because of their rich landscape of electronic structures,topological phases,strong correlation effects,and exotic orders.These systems provide a fertile platform for the exploration of novel quantum phenomena and materials applications.Particularly exciting is the exploration of nonequilibrium dynamics in quantum materials,which has significant research and potential application values.Pump-probe techniques play a key role in revealing the dynamics of quantum materials on remarkably short timescales,providing an attractive yet challenging avenue of research.In this context,time-resolved x-ray as an emerging probe exhibits high time resolution,momentum resolution,and substantial momentum coverage.It can reveal unprecedented transient states,distinguish between entangled ordered states,and has a compelling potential to probe ultrafast dynamics in a wide variety of quantum materials.Despite its unique advantages,time-resolved x-ray scattering still faces several technological and methodological challenges.In this review,we highlight recent advances focusing on the use of time-resolved x-ray scattering to probe dynamic processes in quantum materials.We discuss representative examples across structural,electronic,magnetic,and lattice degrees of freedom,and outline promising directions for future research in this rapidly evolving field.
基金the National Institute of Health for supporting this research under grants NIH R35GM152076,NIH 1SC1GM127175-01,NIH T32GM148394.
文摘Time-resolved flow cytometry(TRFC)was used to measure metabolic differences in estrogen receptor-positive breast cancer cells.This specialty cytometry technique measures fluorescence lifetimes as a single-cell parameter thereby providing a unique approach for high-throughput cell counting and screening.Differences in fluorescence lifetime were detected and this was associated with sensitivity to the commonly prescribed therapeutic tamoxifen.Differences in fluorescence lifetime are attributed to the binding states of the autofluorescent metabolite NAD(P)H.The function of NAD(P)H is well described and in general involves cycling from a reduced to oxidized state to facilitate electron transport for the conversion of pyruvate to lactate.NAD(P)H fluorescence lifetimes depend on the bound or unbound state of the metabolite,which also relates to metabolic transitions between oxidative phosphorylation and glycolysis.To determine if fundamental metabolic profiles differ for cells that are sensitive to tamoxifen compared to those that are resistant,large populations of MCF-7 breast cancer cells were screened and fluorescence lifetimes were quantified.Additionally,metabolic differences associated with tamoxifen sensitivity were measured with a Seahorse HS mini metabolic analyzer(Agilent Technologies Inc.Santa Clara,CA)and confocal imaging.Results show that tamoxifen-resistant breast cancer cells have increased utilization of glycolysis for energy production compared to tamoxifen-sensitive breast cancer cells.This work is impacting because it establishes an early step toward developing a reliable screening technology in which large cell censuses can be differentiated for drug sensitivity in a label-free fashion.
基金This work was supported by the National Natural Science Foundation of China （No.10704083）,the Innovation Foundation of Chinese Academyof Sciences （No.KJCX1-YW-N30）, and the Public Science and Technology Program of Shenzhen （No.SY200806260026A）.
文摘The ultrafast dynamics through conical intersections in 2,6-dimethylpyridine has been studied by femtosecond time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy. Upon absorption of 266 nm pump laser, 2,6-dimethylpyridine is excited to the S2 state with a ππ character from So state. The time evolution of the parent ion signals consists of two exponential decays. One is a fast component on a timescale of 635 fs and the other is a slow component with a timescale of 4.37 ps. Time-dependent photo- electron angular distributions and energy-resolved photoelectron spectroscopy are extracted from time-resolved photoelectron imaging and provide the evolutive information of S2 state. In brief, the ultrafast component is a population transfer from S2 to S1 through the S2/S1 conical intersections, the slow component is attributed to simultaneous IC from the S2 state and the higher vibrational levels of S1 state to So state, which involves the coupling of S2/S0 and S1/So conical intersections. Additionally, the observed ultrafast S2--＋S1 transition occurs only with an 18% branching ratio.
文摘The function of protein in long-range biological electron transfer is a question of debate. We report some preliminary results in femtosecond spectroscopic study of photosynthetic bacterial light-harvesting antenna complex assembled onto TiO2 nanoparticle with an average size of 8 nm in diameter. Crystal structure shows that photosynthetic bacterial antenna complex LH2 has a ring-like structure composed by alpha- and beta-apoprotein helices. The alpha- and beta-transmembrance helices construct two concentric cylinders with pigments bacteriochlorophyll a (Bchl a) and carotenoid (Car) buried inside the protein. We attempt to insert TiO2 nanoparticle into the cavity of the inner cylindrical hollow of LH2 to investigate the nature of the electron transfer between the excited-state Bchl a and the TiO2 nanoparticle. A significant decrease in the ground state bleaching recovery time constant for Bchl a at 850 run (B850) in respect to that of the Bchl a in free LH2 has been observed. By using the relation of distance-dependent long-range electron transfer rate in protein, the distance between the donor B850 and the acceptor TiO2 nanoparticle has been estimated, which is about 0.6 nm. The proposed method of assembling proteins onto wide-gap semiconductor nanoparticle can be a promising way to determine the role of the protein playing in biological electron transfer processes.
基金This work was supported by the National Natural Science Foundation of China （No.21333012 and No.21425313） and the National Basic Research Program of China （No.2013CB834602）.
文摘The benzoin group caged compound has received strong interests due to its excellent photo- deprotection properties and wide use in chemical and biological studies. We used timeresolved infrared spectroscopy to investigate the photochemical reaction of the benzoin caged compound, o-（2-methylbenzoyl）-DL-benzoin under 266 nm laser irradiation. Taking advantage of the specific vibrational marker bands and the IR discerning capability, we have detected and identified the uncaging product 2-methylbenzoic acid, and two intermediate radicals of benzoyl and 2-methylbenzoate benzyl in the transient infrared spectra. Our results provide spectral evidence to support the homolytic cleavage reaction of C-C=O bond in competition with the deprotection reaction. Moreover, the product yields of 2-methylbenzoic acid and benzoyl radical were observed to be affected by solvents and a largely water contalning solvent can be in favor of the deprotection reaction.
基金supported in part by the National Natural Science Foundation of China(Nos.11574213 and 11904232)Innovation Program of Shanghai Municipal Education Commission(No.2017-01-07-00-07-E00007)+1 种基金the Shanghai Municipal Science and Technology Commission(No.17060502500)the support of the Program for Professor of Special Appointment(Eastern Scholar)at the Shanghai Institutions of Higher Learning(No.TP2014046).
文摘We experimentally investigated the forward 353.8 nm radiation from plasma filaments in pure nitrogen gas pumped by intense circularly polarized 800 nm femtosecond laser pulses.This emission line corresponds to the B^2Σu^+(u'=4)-X^2Σg^+(u=3)transition of nitrogen ions.In the presence of an external seeding pulse,the 353.8 nm signal was amplified by 3 orders of magnitude.Thanks to the much enhanced intensity,we performed time-resolved measurement of the amplified 353.8 nm emission based on the sum-frequency generation technique.It was revealed that the built-up time and duration of these emissions are both inversely proportional to the gas pressure,while the radiation peak power grows up nearly quadratically with pressure,indicating that the 353.8 nm radiation is of the nature of superradiance.
基金supported by the National Natural Science Foundation of China(10675158)
文摘The properties of norfloxacin(NFX)and its 4?-N-acetyl derivative(ANFX)are investigated in different pH aqueous solutions and H2O-CH3CN mixed solutions,to determine the effects of pH and polarity on their ground and excited states.The triplet states of NFX and ANFX are affected more by pH than by polarity.The pH dependence of the NFX and ANFX triplet states is likely due to the different quantum yields of different protonated forms.Steady-state fluorescence,time-resolved fluorescence,and laser flash photolysis experiments at different pH values provide clear evidence of the involvement of different intramolecular charge-transfer pathways in the singlet states of NFX and ANFX.The different electron-donating capacities of 1-N,1?-N,and 4?-N under different conditions determine the major pathway.
基金Project supported by the National Natural Science Foundation of China(Nos.1332006,11272233,11202122,and 11411130150)the National Fundamental Research Program of China(973 Program)(No.2012CB720101)
文摘The relationship between the in the logarithmic law （log-law） region of bursting event and the low/high-speed streak a turbulent boundary layer is investigated. A tomographic time-resolved particle image velocimetry （TRPIV） system is used to measure the instantaneous three-dimensional-three-component （3D-3C） velocity field. The momentum thickness based Reynolds number is about 2 460. The topological information in the log-law region is obtained experimentally. It is found that the existence of the quadrupole topological structure implies a three-pair hairpin-like vortex packet, which is in connection with the low/high-speed streak. An idealized 3D topological model is then proposed to characterize the observed hairpin vortex packet and low/high-speed streak.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 20573028 and 20973050)
文摘We performed femtosecond time-resolved coherent anti-Stokes Raman scattering （fs-CARS） measurements on liquid toluene and PVK film. For both samples, we selectively excited the CH stretching vibrational modes and observed the expected quantum beat signals. The frequency of the well-defined beats is in good agreement with the energy difference between the two simultaneously excited modes, which demonstrates that a coherent coupling between the vibrational modes of the C H chemical bonds exists at the different positions of the molecules. The dephasing times of the excited modes are obtained simultaneously.
文摘Time-resolved IR absorption spectroscopy has been used to atudy the photochemistry of W(CO)_6 in cyclohexane, carbon tetrachloride, and the mixture of carbon tetrachloride and cyelohexane. The reastion of photolytically generated W(CO)_5. C_6H_(12) with CCl_4 was investigated. An intermediate with a lifetime of about 0.5ms, presumably attributed as W(GO)_5.CCl_4, was first observed.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61176044 and 11074224
文摘A silicon nanoporous pillar array （Si-NPA） is thought to be a promising functional substrate for constructing a variety of Si-based optoelectronic nanodevices, due to its unique hierarchical structure and enhanced physical properties. This makes the in-depth understanding of the photoluminescence （PL） of Si-NPA crucial for both scientific research and practical applications. In this work, the PL properties of Si-NPA are studied by measuring both the steady-state and time-resolved PL spectrum. Based on the experimental data, the three PL bands of Si-NPA, i.e., the ultraviolet band, the purple-blue plateau and the red band are assigned to the oxygen-excess defects in Si oxide or silanol groups at the surface of Si nanocrystallites （nc-Si）, oxygen deficiency defects in Si oxide, and band-to-band transition of nc-Si under the frame of quantum confinement combining with the surface states like Si=O and Si-O^i bonds at the surface of nc-Si, respectively. These results may provide some novel insight into the PL process of Si-NPA and may be helpful for clarifying the PL mechanism.
文摘In-situ time-resolved Raman spectroscopy(TRRS)has been applied on studies of electrochemical adsorption of thiocyanate at silver electrode during potential cycles and potential step.It is shown that some dynamic information about the adsorption and desorption processes can be obtained.
基金Project supported by the National Natural Science Foundation of China(Grant No.62305087)。
文摘We performed a quantitative analysis of time-resolved laser-induced breakdown air plasma spectra to obtain the evolution of temperatures and species relative fractions.The air plasma was generated by focusing a 100 mJ Nd:YAG laser pulse,and the time-resolved spectra were recorded by an intensified charge-coupled device camera with incremental delay.The attention was mainly focused on the emission spectra of the first negative system of nitrogen(N_(2)^(+),B^(2)Σ-(u)^(-)-X^(2)Σ^(+)g)and the violet system of carbon nitride(CN,B^(2)Σ^(+)-X^(2)Σ^(+))located at 383-396 nm.A custom-built model was developed to perform the simulation and fitting of the N_(2)^(+)and the CN spectra from the air plasma.The model was verified by comparing to a published model with a 0.9860 Spearman correlation coefficient.With this model,the time-resolved non-equilibrium temperatures and relative fractions of N_(2)^(+)and CN were obtained with a fitting correlation coefficient higher than 0.9108.
基金financially supported by the National Key R&D Program of China(Nos.2023YFB3812400,2023YFB3812403)National Natural Foundation of China(Nos.52273206,52350233)+1 种基金Hunan Provincial Natural Science Foundation(No.2021JJ10029)Huxiang High-level Talent Gathering Project(No.2022RC4039).
文摘Photoswitchable fluorescent polymeric nanoparticles were widely concerned because of their excellent features including the flexible design,easy preparation and functionalization,and thus exhibited great application potential in information encryption,anti-counterfeiting,but remained challenging in improving the security.Herein,we described a self-erased time-resolved information encryption via using photoswitchable dual-color fluorescent polymeric nanoparticles(PDFPNs)containing two fluorescence dyes(blue and red)and photochromic spiroxazine derivatives.In view of the different thermo-induced isomerization rates of photochromic spiroxazine derivatives in different flexible substrates,the decoloration rate of PDFPNs can be programmatically tuned by regulating ratio between rigid polymer and flexible polymer.Therefore,after ultraviolet light(UV)irradiation,correct information could only be recognized in preestablished time during the self-erased process.Our results indicated that PDFPNs exhibited fast photo-responsibility(2 min),high fluorescence contrast,well-pleasing photo-reversibility(>20 times),and programmable thermo-responsiveness(24 s-6 h).We thus demonstrated their application in the selferased time-resolved information encryption and anti-counterfeiting with high security.
基金This work was supported by the National Natural Science Foundation of China(No.21833003 and No.21773213)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB17000000)Chinese Academy of Sciences(GJJSTD20190002).
文摘N-ethylpyrrole is one of ethylsubstituted derivatives of pyrrole and its excited-state decay dynamics has never been explored.In this work,we investigate ultrafast decay dynamics of N-ethylpyrrole excited to the S_(1)electronic state using a femtosecond time-resolved photoelectron imaging method.Two pump wavelengths of 241.9 and 237.7 nm are employed.At 241.9 nm,three time constants,5.0±0.7 ps,66.4±15.6 ps and 1.3±0.1 ns,are derived.For 237.7 nm,two time constants of 2.1±0.1 ps and 13.1±1.2 ps are derived.We assign all these time constants to be associated with different vibrational states in the S_(1)state.The possible decay mechanisms of different S_(1)vibrational states are briefly discussed.
基金supported by the National Natural Science Foundation of China (No.21573228, No.21833003, No.21673232, and No.21773236)the Strategic Priority Research Program of the Chinese Academy of Sciences (No.XDB17000000)
文摘The ultrafast dynamics of water molecules excited to the two F states is studied by combining two-photon excitation and time-resolved photoelectron imaging techniques. The lifetimes of the F1A1 and F1B1 states of H2O (D2O) were derived to be 1.0±0.3 (1.9±0.4) and 10±3 (30±10) ps, respectively. We propose that the F1A1 state mainly decays through the D state, due to the nonadiabatic coupling between them, while the F1B1 state decays through the F1A1 state via Coriolis interaction.
基金supported by the China Postdoctoral Science Foundation(Grant No.2021M703366)Shenzhen Science and Technology Program(Grant No.KQTD20190929172835662).
文摘Objective Observational studies have found associations between inflammatory bowel disease(IBD)and the risk of dementia,including Alzheimer’s dementia(AD)and vascular dementia(VD);however,these findings are inconsistent.It remains unclear whether these associations are causal.Methods We conducted a meta-analysis by systematically searching for observational studies on the association between IBD and dementia.Mendelian randomization(MR)analysis based on summary genome-wide association studies(GWASs)was performed.Genetic correlation and Bayesian colocalization analyses were used to provide robust genetic evidence.Results Ten observational studies involving 80,565,688 participants were included in this metaanalysis.IBD was significantly associated with dementia(risk ratio[RR]=1.36,95%CI=1.04-1.78;I2=84.8%)and VD(RR=2.60,95%CI=1.18-5.70;only one study),but not with AD(RR=2.00,95%CI=0.96-4.13;I^(2)=99.8%).MR analyses did not supported significant causal associations of IBD with dementia(dementia:odds ratio[OR]=1.01,95%CI=0.98-1.03;AD:OR=0.98,95%CI=0.95-1.01;VD:OR=1.02,95%CI=0.97-1.07).In addition,genetic correlation and co-localization analyses did not reveal any genetic associations between IBD and dementia.Conclusion Our study did not provide genetic evidence for a causal association between IBD and dementia risk.The increased risk of dementia observed in observational studies may be attributed to unobserved confounding factors or detection bias.
基金supported by“Dalian Maritime University Teaching Reform Research Fund 2022 Annual Project”(Fund No.XJG2022-96).
文摘This paper proposes an interdisciplinary talent training model that combines foreign language education with area studies.The model aims to cultivate international ocean affairs professionals with cross-cultural communication skills,in-depth regional and country knowledge,and practical expertise in ocean affairs.Additionally,the paper presents specific training pathways and policy recommendations for implementing this model.
基金This work was supported by National Research Fund for Fundamental Key Project(G2000028205)Innovative Foundation of Chinese Academy of Sciences(KGCX2-303-02)the Project of the National Natural Science Foundation of China(29873057).
文摘Effect of Ti(iso-C3H7O)4 treatment on the photoinduced charge carrier kinetics of nanocrystalline porous TiO2 films is studied by time-resolved microwave conductivity measurements. Analysis of the transient photoconductivity decays indicates that Ti(iso-C3H7O)4 treatment leads to an increased concentration of photogenerated charge carriers and a fast interfacial transfer rate of holes via the surface modification of the freshly growing TiO2 nanocrystallites.
文摘In modern society,the globalization of literary works is evident,with exceptional literary pieces from various countries spreading worldwide.Among these,children’s literature,due to the specificity of its target audience,imposes distinct requirements on children’s books,compelling translators to approach the text from a child’s perspective.“The Little Prince”has renowned both within and outside of China,and a careful reading of this work can provide us with much inspiration.To this end,the present study adopts the perspective of Gideon Toury’s Descriptive Translation Studies to conduct an in-depth analysis of the different English and Chinese translations in conjunction with the original French novel.This approach aims to better guide literary research and explores translation methods for children’s literature through the analysis of translation norms and rules.
