We present a minimal theoretical model for self-sustained oscillations of a thin elastic sheet on a hot plate,induced by thermomechanical coupling.As the plate temperature increases,the sheet’s static deflection beco...We present a minimal theoretical model for self-sustained oscillations of a thin elastic sheet on a hot plate,induced by thermomechanical coupling.As the plate temperature increases,the sheet’s static deflection becomes unstable via a Hopf bifurcation at a critical temperature TC,giving rise to spontaneous periodic motion.Linear stability analysis yields analytical expressions for the critical oscillation temperature TC and the oscillation period at onset.Numerical simulations of the nonlinear equations confirm the bifurcation and reveal how key parameters(stiffness,thermal softening,thermal coupling,etc.)govern the oscillation amplitude and waveform.Finally,we demonstrate that the self-oscillating sheet can perform mechanical work as a heat engine,and we compare its performance to the Carnot efficiency limit.This work provides design principles for thermally driven selfoscillators with potential applications in soft robotics,adaptive structures,and thermal energy harvesting.展开更多
Circularly polarized luminescence(CPL)and two-photon absorption(TPA)materials have garnered considerable attentions due to their minimal energy loss and superior optical penetration[1,2].However,the current challenge ...Circularly polarized luminescence(CPL)and two-photon absorption(TPA)materials have garnered considerable attentions due to their minimal energy loss and superior optical penetration[1,2].However,the current challenge lies in the absence of well-developed strategies for designing materials that combine these two exceptional optical properties.展开更多
Carbazole-core multi-branched chromophores 9-ethyl- 3, 6-bis （ 2- { 4- [ 5- （4-tert-butyl-phenyl） - [ 1, 3, 4 ] oxadiazol-2-yl ] - phenyl }-vinyl） -carbazole（3） and 9-ethyl-3-（ 2- {4-[ 5-（4-tert-butyl- phenyl...Carbazole-core multi-branched chromophores 9-ethyl- 3, 6-bis （ 2- { 4- [ 5- （4-tert-butyl-phenyl） - [ 1, 3, 4 ] oxadiazol-2-yl ] - phenyl }-vinyl） -carbazole（3） and 9-ethyl-3-（ 2- {4-[ 5-（4-tert-butyl- phenyl） -[ 1, 3, 4 ] oxadiazol-2-yl ] -phenyl }-vinyl ） -carbazole （ 2 ） are synthesized through Wittig reaction and characterized by nuclear magnetic resonance（NMR）and infrared（IR）. The two- photon absorption properties of chromophores are investigated. These chromophores exhibit large two-photon absorption crosssections and strong blue two-photon excited fluorescence. The cooperative enhancement of two-photon absorption（TPA） in the multi-branched structures is observed. This enhancement is partly attributed to the electronic coupling between the branches. The electronic push-pull structures in the arm and their cooperative effects help the extended charge transfer for TPA.展开更多
Vicinal diamines are key motifs widely-found in many pharmaceuticals and biologically active molecules.An appealing approach for synthesizing these molecules is the amination of enamines,but few examples have been exp...Vicinal diamines are key motifs widely-found in many pharmaceuticals and biologically active molecules.An appealing approach for synthesizing these molecules is the amination of enamines,but few examples have been explored.With the utilization of nitrogen-centered radicals(NCRs),here we present the development of a dual bio-/photo-catalytic system for achieving enantioselective hydroamination of enamides,which can give easy access to diverse enantioenriched vicinal diamines.These reactions progress efficiently under green light excitation and exhibit excellent enantioselectivities(up to>99%enantiomeric excess).Mechanistic studies uncovered the synergistic effect of the enzyme and the externally added organophotoredox catalyst Rhodamine B(RhB).This work demonstrates the effectiveness of photobiocatalysis to generate and control high-energy radical intermediates,addressing a long-standing challenge in chemical synthesis.展开更多
Exploring advanced techniques capable of probing nanometric acoustic waves in nanostructures is critically important for the development of miniaturized acoustic devices.In this study,we probe the optically-excited ac...Exploring advanced techniques capable of probing nanometric acoustic waves in nanostructures is critically important for the development of miniaturized acoustic devices.In this study,we probe the optically-excited acoustic waves in a single silicon nanowire(NW)using the time-resolved(tr-)high-order Laue-zone(HOLZ)lines under convergent-beam electron diffraction(CBED)conditions in an ultrafast transmission electron microscope(UTEM).We devise an experimental scheme to obtain tr-HOLZ lines under off-zone-axis CBED conditions.We also propose a geometric description of HOLZ line formation and use this alternative description to quantitatively evaluate the dynamics of optically-excited silicon NW.Using part of the deformation gradient tensor,our simulations of the dynamics of Si NW reproduce the experimental results.We further discuss the feasibility of a full retrieval of the deformation gradient tensor by using a set of HOLZ lines from three zone axes.Our findings illustrate a strategy for the quantitative access to dynamical acoustic waves optically excited in micro-and nano-structures using UTEM.展开更多
Recently, the quantum description of electromagnetic waves in conducting media has been performed. It has been demonstrated that in particular case, the Hamiltonian of the corresponding field can be expressed by Caldi...Recently, the quantum description of electromagnetic waves in conducting media has been performed. It has been demonstrated that in particular case, the Hamiltonian of the corresponding field can be expressed by Caldirola–Kanai Hamiltonian. In this paper, using the associated annihilation and creation operators of the above-mentioned quantized field, the time-and conductivity-dependent squeezed vacuum and one-photon squeezed states as well as their superpositions, and also the time-and conductivity-dependent excited even and odd coherent states are produced. Also,using a few well-known nonclassicality criteria, the time evolution of nonclassicality features of the above classes of obtained states, in addition to the influence of medium conductivity on them are demonstrated, numerically. It has been shown that the nonclassicality indicators may be adjusted by tuning the conductivity of media.展开更多
The electronic structure of methanol/TiO2（ll0） interface has been studied by photoemis- sion spectroscopy. The pronounced resonance which appears at 5.5 eV above the Fermi level in two-photon photoemission spectrosc...The electronic structure of methanol/TiO2（ll0） interface has been studied by photoemis- sion spectroscopy. The pronounced resonance which appears at 5.5 eV above the Fermi level in two-photon photoemission spectroscopy （2PPE） is associated with the photocatalyzed dissociation of methanol at fivefold coordinated Ti sites （Ti5c） on TiO2 （110） surface [Chem- ical Science 1, 575 （2010）]. To check whether this resonance signal arises from initial or intermediate states, photon energy dependent 2PPE and comparison between one-photon photoemission spectroscopy and 2PPE have been performed. Both results consistently sug- gest the resonance signal originates from the initially unoccupied intermediate states, i.e., excited states. Dispersion measurements suggest the excited state is localized. Time-resolved studies show the lifetime of the excited state is 24 fs. This work presents comprehensive char- acterization of the excited states on methanol/TiO2（110） interface, and provides elaborate experimental data for the development of theoretical methods in reproducing the excited states on TiO2 surfaces and interfaces.展开更多
Objective To observe the clinical efficacy of excitement transfer therapy for insomnia. Methods According to the inclusion criteria, 32 patients, selected from Guoyitang, affiliated Zhongshan Hospital Yanwu Branch of ...Objective To observe the clinical efficacy of excitement transfer therapy for insomnia. Methods According to the inclusion criteria, 32 patients, selected from Guoyitang, affiliated Zhongshan Hospital Yanwu Branch of Xiamen University from May to October, 2016, were diagnosed with insomnia and included in this study. All the patients were treated by adopting the excitement transfer therapy, i.e. cluster needling was carried out at the acupoints of wrist and ankle in the manner of penetration needling, and combined with sliding- cupping at governor vessel and bladder meridian on the back. All the subjects were treated for 3 times per week, and treatment for 6 times was considered as I course of treatment. The curative effect was observed after treatment for 2 courses, and follow-up visit was performed for two months after treatment. Efficacy evaluation criteria were established by reference to Guidelines of Clinical Research on Chinese New Herbal Medicine （Trial） Results Cured： 11 cases （34%4 markedly effective： 16 cases （50%）, effective： 4 cases （13%4 ineffective： 1 case. The total effective rate was up to 97%. There was no relapse during two months after the treatment. Conclusion The efficacy of excitement transfer therapy for insomnia was significant, which was worthy of clinical promotion and application.展开更多
Vibration control is an efficient way to minimize a rotating machine’s vibration level so that its vibration fault-free can be realized.While,several factors,such as unbalance,misalignment and instability,contribute ...Vibration control is an efficient way to minimize a rotating machine’s vibration level so that its vibration fault-free can be realized.While,several factors,such as unbalance,misalignment and instability,contribute to the serious vibration of rotating machines.It is necessary that one apparatus can depress vibration caused by two or more reasons.The fault self-recovery(FSR) mechanism is introduced and investigated.Strategies of vibration control are investigated theoretically using numerical method firstly.Active magneticelectric exciter(AME) are selected as the actuator of a FSR device because it can provide suitable force by varying the control current in the exciters depending upon a proportional and derivative control law.By numerical study,it is indicate that only a small control force is needed to improve stability margins of the compressor and prevent subsynchronous vibration fault efficiently.About synchronous vibration,three control strategies,searching in whole circle,fast optimizing control(FOC),and none mistaking control,are investigated to show which of the control strategy can realize the fault self-recovery in the shortest time.Experimental study is conducted on a test rig with variable rotating speed.Results of the test indicate that the non-mistake control strategy can minimize synchronous vibration in less than three seconds.The proposed research can provide a new insight for subsynchronous and synchronous vibration restraining about centrifugal compressor.展开更多
A surface femtosecond two-photon photoemission （2PPE） spectrometer devoted to the study of ultrafast excited electron dynamics and photochemical kinetics on metal and metal oxide surfaces has been constructed. Low e...A surface femtosecond two-photon photoemission （2PPE） spectrometer devoted to the study of ultrafast excited electron dynamics and photochemical kinetics on metal and metal oxide surfaces has been constructed. Low energy photoelectrons are measured using a hemispherical electron energy analyzer with an imaging detector that allows us to detect the energy and the angular distributions of the photoelectrons simultaneously. A Mach-Zehnder interferom- eter was built for the time-resolved 2PPE （TR-2PPE） measurement to study ultrafast surface excited electron dynamics, which was demonstrated on the Cu（111） surface. A scheme for measuring time-dependent 2PPE （TD-2PPE） spectra has also been developed for studies of surface photochemistry. This technique has been applied to a preliminary study on the photochemical kinetics on ethanol/TiO2（110）. We have also shown that the ultrafast dynamics of photoinduced surface excited resonances can be investigated in a reliable way by combining the TR-2PPE and TD-2PPE techniques.展开更多
The excited state intramolecular proton transfer （ESIPT） coupled charge transfer of baicalein has been investigated using steady-state spectroscopic experiment and quantum chemistry calculations. The absence of the ...The excited state intramolecular proton transfer （ESIPT） coupled charge transfer of baicalein has been investigated using steady-state spectroscopic experiment and quantum chemistry calculations. The absence of the absorption peak from S1 excited state both in the experi-mental and calculated absorption spectra indicates that S1 is a dark state. The dark excited state S1 results in the very weak fluorescence of solid baicalein in the experiment. The fron- tier molecular orbital and the charge difference densities of baicalein show clearly that the S1 state is a charge-transfer state whereas the S2 state is a locally excited state. The only one stationary point on the potential energy profile of excited state suggests that the ESIPT reaction of baicalein is a barrierless process.展开更多
Herein we have employed high-level multi-reference CASSCF and MS-CASPT2 electronic structure methods to systematically study the photochemical mechanism of intramolecularly hydrogen-bonded 2-（2＇-hydroxyphenyl）-4-me...Herein we have employed high-level multi-reference CASSCF and MS-CASPT2 electronic structure methods to systematically study the photochemical mechanism of intramolecularly hydrogen-bonded 2-（2＇-hydroxyphenyl）-4-methyloxazole. At the CASSCF level, we have optimized minima, conical intersections, minimum-energy reaction paths relevant to the excited-state intramolecular proton transfer （ESIPT）, rotation, photoisomerization, and the excited-state deactivation pathways. The energies of all structures and paths are refined by the MS-CASPT2 method. On the basis of the present results, we found that the ESIPT process in a conformer with the OH... N hydrogen bond is essentially barrierless process; whereas, the ESIPT process is inhibited in the other conformer with the OH... O hydrogen bond. The central single-bond rotation of the S1 enol species is energetically unfavorable due to a large barrier. In addition, the excited-state deactivation of the S1 keto species, as a result of the ultrafast ESIPT, is very efficient because of the existence of two easily-approached keto S1/S0 conical intersections. In stark contrast to the S1 keto species, the decay of the S1 enol species is almostly blocked. The present theoretical study contributes valuable knowledge to the understanding of photochemistry of similar intramolecularly hydrogen-bonded molecular and biological systems.展开更多
基金supported by the Guangdong Basic and Applied Basic Research Foundation(Grant Nos.2025B1515020077 and 2024A15150301-39)the National Natural Science Foundation of China(Grant No.12205138)the Shenzhen Science and Technology Innovation Committee(Grant No.JCYJ2022-0530113206015).
文摘We present a minimal theoretical model for self-sustained oscillations of a thin elastic sheet on a hot plate,induced by thermomechanical coupling.As the plate temperature increases,the sheet’s static deflection becomes unstable via a Hopf bifurcation at a critical temperature TC,giving rise to spontaneous periodic motion.Linear stability analysis yields analytical expressions for the critical oscillation temperature TC and the oscillation period at onset.Numerical simulations of the nonlinear equations confirm the bifurcation and reveal how key parameters(stiffness,thermal softening,thermal coupling,etc.)govern the oscillation amplitude and waveform.Finally,we demonstrate that the self-oscillating sheet can perform mechanical work as a heat engine,and we compare its performance to the Carnot efficiency limit.This work provides design principles for thermally driven selfoscillators with potential applications in soft robotics,adaptive structures,and thermal energy harvesting.
基金supported by NSFC(22271282)the Self-deployment Project Research Program of Haixi Institutes,Chinese Academy of Sciences with the grant number of CXZX-2022-JQ04.
文摘Circularly polarized luminescence(CPL)and two-photon absorption(TPA)materials have garnered considerable attentions due to their minimal energy loss and superior optical penetration[1,2].However,the current challenge lies in the absence of well-developed strategies for designing materials that combine these two exceptional optical properties.
基金The National Natural Science Foundation of China(No.60678042)the Natural Science Foundation of Jiangsu Province(No.BK2006553)the Pre-Research Project of the National Natural Science Foundation supported by Southeast University(No.9207041399)
文摘Carbazole-core multi-branched chromophores 9-ethyl- 3, 6-bis （ 2- { 4- [ 5- （4-tert-butyl-phenyl） - [ 1, 3, 4 ] oxadiazol-2-yl ] - phenyl }-vinyl） -carbazole（3） and 9-ethyl-3-（ 2- {4-[ 5-（4-tert-butyl- phenyl） -[ 1, 3, 4 ] oxadiazol-2-yl ] -phenyl }-vinyl ） -carbazole （ 2 ） are synthesized through Wittig reaction and characterized by nuclear magnetic resonance（NMR）and infrared（IR）. The two- photon absorption properties of chromophores are investigated. These chromophores exhibit large two-photon absorption crosssections and strong blue two-photon excited fluorescence. The cooperative enhancement of two-photon absorption（TPA） in the multi-branched structures is observed. This enhancement is partly attributed to the electronic coupling between the branches. The electronic push-pull structures in the arm and their cooperative effects help the extended charge transfer for TPA.
文摘Vicinal diamines are key motifs widely-found in many pharmaceuticals and biologically active molecules.An appealing approach for synthesizing these molecules is the amination of enamines,but few examples have been explored.With the utilization of nitrogen-centered radicals(NCRs),here we present the development of a dual bio-/photo-catalytic system for achieving enantioselective hydroamination of enamides,which can give easy access to diverse enantioenriched vicinal diamines.These reactions progress efficiently under green light excitation and exhibit excellent enantioselectivities(up to>99%enantiomeric excess).Mechanistic studies uncovered the synergistic effect of the enzyme and the externally added organophotoredox catalyst Rhodamine B(RhB).This work demonstrates the effectiveness of photobiocatalysis to generate and control high-energy radical intermediates,addressing a long-standing challenge in chemical synthesis.
基金supported by the Guangxi Natural Science Foundation(Grant No.2024GXNSFDA010014)the National Natural Science Foundation of China(Grant Nos.12364018 and U22A6005)+1 种基金the Guangxi Science and Technology Major Program(Grant No.AA23073019)the Innovation Project of Guangxi Graduate Education(Grant Nos.YCBZ2022049 and YCBZ2023015)。
文摘Exploring advanced techniques capable of probing nanometric acoustic waves in nanostructures is critically important for the development of miniaturized acoustic devices.In this study,we probe the optically-excited acoustic waves in a single silicon nanowire(NW)using the time-resolved(tr-)high-order Laue-zone(HOLZ)lines under convergent-beam electron diffraction(CBED)conditions in an ultrafast transmission electron microscope(UTEM).We devise an experimental scheme to obtain tr-HOLZ lines under off-zone-axis CBED conditions.We also propose a geometric description of HOLZ line formation and use this alternative description to quantitatively evaluate the dynamics of optically-excited silicon NW.Using part of the deformation gradient tensor,our simulations of the dynamics of Si NW reproduce the experimental results.We further discuss the feasibility of a full retrieval of the deformation gradient tensor by using a set of HOLZ lines from three zone axes.Our findings illustrate a strategy for the quantitative access to dynamical acoustic waves optically excited in micro-and nano-structures using UTEM.
文摘Recently, the quantum description of electromagnetic waves in conducting media has been performed. It has been demonstrated that in particular case, the Hamiltonian of the corresponding field can be expressed by Caldirola–Kanai Hamiltonian. In this paper, using the associated annihilation and creation operators of the above-mentioned quantized field, the time-and conductivity-dependent squeezed vacuum and one-photon squeezed states as well as their superpositions, and also the time-and conductivity-dependent excited even and odd coherent states are produced. Also,using a few well-known nonclassicality criteria, the time evolution of nonclassicality features of the above classes of obtained states, in addition to the influence of medium conductivity on them are demonstrated, numerically. It has been shown that the nonclassicality indicators may be adjusted by tuning the conductivity of media.
文摘The electronic structure of methanol/TiO2（ll0） interface has been studied by photoemis- sion spectroscopy. The pronounced resonance which appears at 5.5 eV above the Fermi level in two-photon photoemission spectroscopy （2PPE） is associated with the photocatalyzed dissociation of methanol at fivefold coordinated Ti sites （Ti5c） on TiO2 （110） surface [Chem- ical Science 1, 575 （2010）]. To check whether this resonance signal arises from initial or intermediate states, photon energy dependent 2PPE and comparison between one-photon photoemission spectroscopy and 2PPE have been performed. Both results consistently sug- gest the resonance signal originates from the initially unoccupied intermediate states, i.e., excited states. Dispersion measurements suggest the excited state is localized. Time-resolved studies show the lifetime of the excited state is 24 fs. This work presents comprehensive char- acterization of the excited states on methanol/TiO2（110） interface, and provides elaborate experimental data for the development of theoretical methods in reproducing the excited states on TiO2 surfaces and interfaces.
文摘Objective To observe the clinical efficacy of excitement transfer therapy for insomnia. Methods According to the inclusion criteria, 32 patients, selected from Guoyitang, affiliated Zhongshan Hospital Yanwu Branch of Xiamen University from May to October, 2016, were diagnosed with insomnia and included in this study. All the patients were treated by adopting the excitement transfer therapy, i.e. cluster needling was carried out at the acupoints of wrist and ankle in the manner of penetration needling, and combined with sliding- cupping at governor vessel and bladder meridian on the back. All the subjects were treated for 3 times per week, and treatment for 6 times was considered as I course of treatment. The curative effect was observed after treatment for 2 courses, and follow-up visit was performed for two months after treatment. Efficacy evaluation criteria were established by reference to Guidelines of Clinical Research on Chinese New Herbal Medicine （Trial） Results Cured： 11 cases （34%4 markedly effective： 16 cases （50%）, effective： 4 cases （13%4 ineffective： 1 case. The total effective rate was up to 97%. There was no relapse during two months after the treatment. Conclusion The efficacy of excitement transfer therapy for insomnia was significant, which was worthy of clinical promotion and application.
基金supported by the Key Program (Grant. No. 50635010)General Program (Grant. No. 50975018) of National Natural Science Foundation of China
文摘Vibration control is an efficient way to minimize a rotating machine’s vibration level so that its vibration fault-free can be realized.While,several factors,such as unbalance,misalignment and instability,contribute to the serious vibration of rotating machines.It is necessary that one apparatus can depress vibration caused by two or more reasons.The fault self-recovery(FSR) mechanism is introduced and investigated.Strategies of vibration control are investigated theoretically using numerical method firstly.Active magneticelectric exciter(AME) are selected as the actuator of a FSR device because it can provide suitable force by varying the control current in the exciters depending upon a proportional and derivative control law.By numerical study,it is indicate that only a small control force is needed to improve stability margins of the compressor and prevent subsynchronous vibration fault efficiently.About synchronous vibration,three control strategies,searching in whole circle,fast optimizing control(FOC),and none mistaking control,are investigated to show which of the control strategy can realize the fault self-recovery in the shortest time.Experimental study is conducted on a test rig with variable rotating speed.Results of the test indicate that the non-mistake control strategy can minimize synchronous vibration in less than three seconds.The proposed research can provide a new insight for subsynchronous and synchronous vibration restraining about centrifugal compressor.
文摘A surface femtosecond two-photon photoemission （2PPE） spectrometer devoted to the study of ultrafast excited electron dynamics and photochemical kinetics on metal and metal oxide surfaces has been constructed. Low energy photoelectrons are measured using a hemispherical electron energy analyzer with an imaging detector that allows us to detect the energy and the angular distributions of the photoelectrons simultaneously. A Mach-Zehnder interferom- eter was built for the time-resolved 2PPE （TR-2PPE） measurement to study ultrafast surface excited electron dynamics, which was demonstrated on the Cu（111） surface. A scheme for measuring time-dependent 2PPE （TD-2PPE） spectra has also been developed for studies of surface photochemistry. This technique has been applied to a preliminary study on the photochemical kinetics on ethanol/TiO2（110）. We have also shown that the ultrafast dynamics of photoinduced surface excited resonances can be investigated in a reliable way by combining the TR-2PPE and TD-2PPE techniques.
基金ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.61137005 and No.10974023）, the Program for Liaoning Excellent Talents in University （No.LJQ2012002）, and the Program for New Century Excellent Talents in University （No.NCET-12-0077）.
文摘The excited state intramolecular proton transfer （ESIPT） coupled charge transfer of baicalein has been investigated using steady-state spectroscopic experiment and quantum chemistry calculations. The absence of the absorption peak from S1 excited state both in the experi-mental and calculated absorption spectra indicates that S1 is a dark state. The dark excited state S1 results in the very weak fluorescence of solid baicalein in the experiment. The fron- tier molecular orbital and the charge difference densities of baicalein show clearly that the S1 state is a charge-transfer state whereas the S2 state is a locally excited state. The only one stationary point on the potential energy profile of excited state suggests that the ESIPT reaction of baicalein is a barrierless process.
文摘Herein we have employed high-level multi-reference CASSCF and MS-CASPT2 electronic structure methods to systematically study the photochemical mechanism of intramolecularly hydrogen-bonded 2-（2＇-hydroxyphenyl）-4-methyloxazole. At the CASSCF level, we have optimized minima, conical intersections, minimum-energy reaction paths relevant to the excited-state intramolecular proton transfer （ESIPT）, rotation, photoisomerization, and the excited-state deactivation pathways. The energies of all structures and paths are refined by the MS-CASPT2 method. On the basis of the present results, we found that the ESIPT process in a conformer with the OH... N hydrogen bond is essentially barrierless process; whereas, the ESIPT process is inhibited in the other conformer with the OH... O hydrogen bond. The central single-bond rotation of the S1 enol species is energetically unfavorable due to a large barrier. In addition, the excited-state deactivation of the S1 keto species, as a result of the ultrafast ESIPT, is very efficient because of the existence of two easily-approached keto S1/S0 conical intersections. In stark contrast to the S1 keto species, the decay of the S1 enol species is almostly blocked. The present theoretical study contributes valuable knowledge to the understanding of photochemistry of similar intramolecularly hydrogen-bonded molecular and biological systems.
