Resonance enhancement has been increasingly employed in the emergent felntosecond stimu- lated Raman spectroscopy （FSRS） to selectively monitor molecular structure and dynamics with improved spectral and temporal re...Resonance enhancement has been increasingly employed in the emergent felntosecond stimu- lated Raman spectroscopy （FSRS） to selectively monitor molecular structure and dynamics with improved spectral and temporal resolutions and signal-to-noise ratios. Such joint eflforts by the technique- and application-oriented scientists and engineers have laid the foundation for exploiting the tunable FSRS methodology to investigate a great variety of photosensitive systems and elucidate the underlying functional mechanisms on molecular time scales. Dur- ing spectral analysis, peak line shapes remain a major concern with an intricate dependence on resonance conditions. Here, we present a comprehensive study of line shapes by tuning the Rarnan pump wavelength from red to blue side of the ground-state absorption band of the fluorescent dye rhodarnine 6G in solution. Distinct line shape patterns in Stokes and anti-Stokes FSRS as well as from the low to high-frequency modes highlight the competition between multiple third-order and higher-order nonlinear pathways, governed by difl^rent res- onance conditions achieved by Raman pump and probe pulses. In particular, the resonance condition of probe wavelength is revealed to play an important role in generating circular line shape changes through oppositely phased dispersion via hot luminescence （HL） pathways. Meanwhile, on-resonance conditions of the Rarnan pump could promote excited-state vibrational modes which are broadened and red-shifted from the coincident ground-state vibrational modes, posing challenges for spectral analysis. Certain strategies in tuning the Raman pump and probe to characteristic regions across an electronic transition band are discussed to improve the FSRS usability and versatility as a powerful structural dynamics toolset to advance chemical, physical, materials, and biological sciences.展开更多
In this work,we simulated 2D infrared spectroscopy(IR)spectroscopy in both transmission geometry and Brewster-angle reflection geometry.Light dispersion and the leakage of s-polarized light are considered in simulatin...In this work,we simulated 2D infrared spectroscopy(IR)spectroscopy in both transmission geometry and Brewster-angle reflection geometry.Light dispersion and the leakage of s-polarized light are considered in simulating the enhancement factor of the reflection mode.Our simulation shows that the dispersion in reflection will only alter the 2D IR lineshape slightly and can be corrected.Leaking spolarized light due to imperfectness of IR polarizers in the reflection geometry may limit the enhancement factor,but such limit is above what a typical experiment can reach.In the current experiment,the enhancement factor is mainly limited by the precision of incident angle,for which ordinary rotation stages are probably not adequate enough.Moreover,traditional energy ratio of pump and probe pulses,which is 9:1,may not be ideal and could be changed to 2:1 in the reflection geometry.Considering all the above factors,the enhancement on the order of 1000 is possible in the current experiment.Nevertheless,near-Brewster angle reflection will enhance both the signal and the noise caused by the signal itself,therefore this method only works if the noise is unrelated to the signal,particularly if the noise is caused by the fluctuation in the probe.It cannot improve the signal to noise ratio when the dominate noise is from the signal itself.The theoretical results here agree reasonably well with published experiment results and pave way for realizing even higher enhancement at nearer-Brewster angle.展开更多
Based on the physical model of capillary pumped loop (CPL) system, the phenomena of pressure oscillation are simplilied and analyzed. From a set of non-linear differential equations, the influence ofsystem parameters ...Based on the physical model of capillary pumped loop (CPL) system, the phenomena of pressure oscillation are simplilied and analyzed. From a set of non-linear differential equations, the influence ofsystem parameters on the performance of the CPL is discussed, including the working temperature(the Set point), loop resistance, vapor volume etc. From the analysis, some measures were taken tohoprove the performance of the loop. Meanwhile, the reason why the deprive of the CPL occurs duringthe operation is given by analyzing the theoretical calculation results.展开更多
A novel dual-loop technique was proposed for single-mode selection in an optoelectronic oscillator （OEO）. It consisted of a pump laser and a feedback circuit including an intensity modulator, a Fabry-Perot （FP） et...A novel dual-loop technique was proposed for single-mode selection in an optoelectronic oscillator （OEO）. It consisted of a pump laser and a feedback circuit including an intensity modulator, a Fabry-Perot （FP） etalon, two optical fiber delay lines, two photodetectors, and an amplifier. By inserting the Fabry-Perot etalon, the proposed dual-loop OEO realized a single mode oscillation ranging from 0 Hz to 20 GHz. The strong oscillation mode was present at 15 GHz, and the side modes suppression ratio （SMSR） exceeded 140dB. More over the length of the two fiber loops were just 5 meters and 36 meters.展开更多
In this paper,the CFD simulation and new flow unsteadiness analysis for a single-blade centrifugal pump with whole flow passage were carried out.The periodic flow unsteadiness has been quantitatively investigated in d...In this paper,the CFD simulation and new flow unsteadiness analysis for a single-blade centrifugal pump with whole flow passage were carried out.The periodic flow unsteadiness has been quantitatively investigated in detail by defining unsteady intensity and turbulence intensity in both rotor and volute domains under design condition Q=33 L s 1.The results show that the distributions of flow unsteadiness are the functions of impeller rotating angle and have complex unsteady characteristics.The obvious T u fluctuations can be also observed for different impeller positions.In addition,time-averaged unsteady intensity and time-averaged turbulence intensity were calculated by averaging the results of each mesh node for entire impeller revolution period to evaluate the strength distributions of flow unsteadiness directly and comprehensively.The accumulative results of an impeller revolution can directly show the positions and strength of the flow unsteadiness and turbulence intensity in both rotor and stator domains which can be an important aspect to be considered in the single-blade pump optimum design procedure for obtaining more stable inner flow of the pump and decreasing flow-induced vibration and noise.The flow unsteadiness in the side chamber cannot be neglected for an accurate prediction of the inner flow of the pump,and the optimizing design procedure for a single-blade pump impeller will not be accurate using CFD tool if the unsteady flow phenomenon in the side chamber is not considered.展开更多
A series of isometric,radially expanding tubular units,made of dielectric elastomer with compliant electrodes,constitute a soft linear peristaltic pump with distributed actuation for transport of incompressible fluids...A series of isometric,radially expanding tubular units,made of dielectric elastomer with compliant electrodes,constitute a soft linear peristaltic pump with distributed actuation for transport of incompressible fluids.Based on the Gent strain energy model,this paper theoretically analyzes the homogeneous large deformation of the peristaltic unit.We discuss the effects of axial prestretch on the actuation of the actuator.We then predict the maximum actuation strain of this actuator which is limited by dielectric strength of the polymer.The results presented here extend the previous study based on linear elasticity,and can predict the electromechanical behaviors of the novel actuator at large deformations.展开更多
基金supported by the U.S.National Science Foundation CAREER grant(CHE-1455353)the Oregon State University(OSU) Research Equipment Reserve Fund(Spring 2014)to C.Fang(USTC9603)the Wei Family Private Foundation in supporting C.Chen(USTC 0903) during his graduate studies at OSU Chemistry
文摘Resonance enhancement has been increasingly employed in the emergent felntosecond stimu- lated Raman spectroscopy （FSRS） to selectively monitor molecular structure and dynamics with improved spectral and temporal resolutions and signal-to-noise ratios. Such joint eflforts by the technique- and application-oriented scientists and engineers have laid the foundation for exploiting the tunable FSRS methodology to investigate a great variety of photosensitive systems and elucidate the underlying functional mechanisms on molecular time scales. Dur- ing spectral analysis, peak line shapes remain a major concern with an intricate dependence on resonance conditions. Here, we present a comprehensive study of line shapes by tuning the Rarnan pump wavelength from red to blue side of the ground-state absorption band of the fluorescent dye rhodarnine 6G in solution. Distinct line shape patterns in Stokes and anti-Stokes FSRS as well as from the low to high-frequency modes highlight the competition between multiple third-order and higher-order nonlinear pathways, governed by difl^rent res- onance conditions achieved by Raman pump and probe pulses. In particular, the resonance condition of probe wavelength is revealed to play an important role in generating circular line shape changes through oppositely phased dispersion via hot luminescence （HL） pathways. Meanwhile, on-resonance conditions of the Rarnan pump could promote excited-state vibrational modes which are broadened and red-shifted from the coincident ground-state vibrational modes, posing challenges for spectral analysis. Certain strategies in tuning the Raman pump and probe to characteristic regions across an electronic transition band are discussed to improve the FSRS usability and versatility as a powerful structural dynamics toolset to advance chemical, physical, materials, and biological sciences.
基金supported by the National Natural Science Foundation of China(No.21973102,No.21573243,and No.21327802)。
文摘In this work,we simulated 2D infrared spectroscopy(IR)spectroscopy in both transmission geometry and Brewster-angle reflection geometry.Light dispersion and the leakage of s-polarized light are considered in simulating the enhancement factor of the reflection mode.Our simulation shows that the dispersion in reflection will only alter the 2D IR lineshape slightly and can be corrected.Leaking spolarized light due to imperfectness of IR polarizers in the reflection geometry may limit the enhancement factor,but such limit is above what a typical experiment can reach.In the current experiment,the enhancement factor is mainly limited by the precision of incident angle,for which ordinary rotation stages are probably not adequate enough.Moreover,traditional energy ratio of pump and probe pulses,which is 9:1,may not be ideal and could be changed to 2:1 in the reflection geometry.Considering all the above factors,the enhancement on the order of 1000 is possible in the current experiment.Nevertheless,near-Brewster angle reflection will enhance both the signal and the noise caused by the signal itself,therefore this method only works if the noise is unrelated to the signal,particularly if the noise is caused by the fluctuation in the probe.It cannot improve the signal to noise ratio when the dominate noise is from the signal itself.The theoretical results here agree reasonably well with published experiment results and pave way for realizing even higher enhancement at nearer-Brewster angle.
文摘Based on the physical model of capillary pumped loop (CPL) system, the phenomena of pressure oscillation are simplilied and analyzed. From a set of non-linear differential equations, the influence ofsystem parameters on the performance of the CPL is discussed, including the working temperature(the Set point), loop resistance, vapor volume etc. From the analysis, some measures were taken tohoprove the performance of the loop. Meanwhile, the reason why the deprive of the CPL occurs duringthe operation is given by analyzing the theoretical calculation results.
文摘A novel dual-loop technique was proposed for single-mode selection in an optoelectronic oscillator （OEO）. It consisted of a pump laser and a feedback circuit including an intensity modulator, a Fabry-Perot （FP） etalon, two optical fiber delay lines, two photodetectors, and an amplifier. By inserting the Fabry-Perot etalon, the proposed dual-loop OEO realized a single mode oscillation ranging from 0 Hz to 20 GHz. The strong oscillation mode was present at 15 GHz, and the side modes suppression ratio （SMSR） exceeded 140dB. More over the length of the two fiber loops were just 5 meters and 36 meters.
基金supported by the National Outstanding Young Scientists Founds of China (Grant No. 50825902)Jiangsu Provincial Project for Innovative Postgraduates of China (Grant No.CX10B_262Z)
文摘In this paper,the CFD simulation and new flow unsteadiness analysis for a single-blade centrifugal pump with whole flow passage were carried out.The periodic flow unsteadiness has been quantitatively investigated in detail by defining unsteady intensity and turbulence intensity in both rotor and volute domains under design condition Q=33 L s 1.The results show that the distributions of flow unsteadiness are the functions of impeller rotating angle and have complex unsteady characteristics.The obvious T u fluctuations can be also observed for different impeller positions.In addition,time-averaged unsteady intensity and time-averaged turbulence intensity were calculated by averaging the results of each mesh node for entire impeller revolution period to evaluate the strength distributions of flow unsteadiness directly and comprehensively.The accumulative results of an impeller revolution can directly show the positions and strength of the flow unsteadiness and turbulence intensity in both rotor and stator domains which can be an important aspect to be considered in the single-blade pump optimum design procedure for obtaining more stable inner flow of the pump and decreasing flow-induced vibration and noise.The flow unsteadiness in the side chamber cannot be neglected for an accurate prediction of the inner flow of the pump,and the optimizing design procedure for a single-blade pump impeller will not be accurate using CFD tool if the unsteady flow phenomenon in the side chamber is not considered.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11102149,10872157,11072185,and 10972174)
文摘A series of isometric,radially expanding tubular units,made of dielectric elastomer with compliant electrodes,constitute a soft linear peristaltic pump with distributed actuation for transport of incompressible fluids.Based on the Gent strain energy model,this paper theoretically analyzes the homogeneous large deformation of the peristaltic unit.We discuss the effects of axial prestretch on the actuation of the actuator.We then predict the maximum actuation strain of this actuator which is limited by dielectric strength of the polymer.The results presented here extend the previous study based on linear elasticity,and can predict the electromechanical behaviors of the novel actuator at large deformations.
