An adaptive filter for cancelling noise contained in the direct absorption spectra is reported. This technique takes advantage of the periodical nature of the repetitively scanned spectral signal, and requires no prio...An adaptive filter for cancelling noise contained in the direct absorption spectra is reported. This technique takes advantage of the periodical nature of the repetitively scanned spectral signal, and requires no prior knowledge of the detailed properties of noises. An experimental system devised for measuring CH4 is used to test the performance of the filter. The measurement results show that the signal-to-noise （S/N） value is improved by a factor of 2. A higher enhancement factor of the S/N value of 5.4 is obtained through open-air measurement owing to higher distortions of the raw data. In addition, the response time of this filter, which characterizes the real-time detection ability of the system, is nine times shorter than that of a conventional signal averaging solution, under the condition that the filter order is 100.展开更多
Based on the frequency-domain multimode theoretical model, detailed investigations on the noise characteristic of the semiconductor ring laser （SRL） are first performed in this paper. The comprehensive nonlinear ter...Based on the frequency-domain multimode theoretical model, detailed investigations on the noise characteristic of the semiconductor ring laser （SRL） are first performed in this paper. The comprehensive nonlinear terms related to the third order nonlinear susceptibility Z3 are included in this model; the Langevin noise sources for electric field and carrier density fluctuations are also taken into account. As the injection current increases, the SRL may present several operation regimes. Remarkable and unusual low frequency noise enhancement in the form of a broad low frequency tail extending all the way to the relaxation oscillation peak is observed in any of the operation regimes of SRLs. The influences of the backscattering coefficient on the relative intensity noise （RIN） spectrum in typical operation regimes are investigated in detail.展开更多
Strain engineering is a useful strategy for modifying the catalytic activity of electrocatalysts.However,in-situ visual characterization of the strain effect on the catalytic activity at nanoscale remains a huge chall...Strain engineering is a useful strategy for modifying the catalytic activity of electrocatalysts.However,in-situ visual characterization of the strain effect on the catalytic activity at nanoscale remains a huge challenge.Herein,we performed in-situ electrochemical scanning tunneling microscopy(EC-STM)imaging measurements at the local strained regions of extruded singlecrystal molybdenum dioxide(MoO_(2))sheets with combination of current noise analysis(n-EC-STM).The intensity-enhanced noise was observed at the local strained region compared to the unstrained regions in the same frame,which reveals the positive effect of compressive strain on the hydrogen evolution reaction(HER)activity of MoO_(2)provided that the intensity of noise is positively correlated with catalytic HER Faradic current.Therefore,we clearly“see”the strain-induced enhancement of HER activity of MoO_(2)at nanoscale by means of noise visualization.This work extends the visual characterization of strain engineering in electrocatalysis and related fields.展开更多
The effects of the correlation time τ between noises on the noise-enhanced stability （NES） phe- nomenon in an asymmetric bistable system driven by cross-correlated noise are investigated. The ex- pressions for the ...The effects of the correlation time τ between noises on the noise-enhanced stability （NES） phe- nomenon in an asymmetric bistable system driven by cross-correlated noise are investigated. The ex- pressions for the average escape time from the left metastable state TL and from the right metastable state TR are derived. The results indicate that： i） The NES effect is suppressed as the correlation time τ increases for two metastable states; ii） The increase in τ speeds up the escape process from the right state for positively correlated noise, whereas its role is reverses for negatively correlated; iii） In the escape process from the left state, the role of τ is opposite to that in escape from the right state.展开更多
Two examples of the use of vortex control to reduce noise and enhance the stable operating range of a centrifugal compressor are presented in this paper.In the case of high-flow operation of a centrifugal compressor w...Two examples of the use of vortex control to reduce noise and enhance the stable operating range of a centrifugal compressor are presented in this paper.In the case of high-flow operation of a centrifugal compressor with a vaned diffuser,a discrete frequency noise induced by interaction between the impeller-discharge flow and the diffuser vane,which appears most notably in the power spectra of the radiated noise,can be reduced using a tapered diffuser vane(TDV) without affecting the performance of the compressor.Twin longitudinal vortices produced by leakage flow passing through the tapered portion of the diffuser vane induce secondary flow in the direction of the blade surface and prevent flow separation from the leading edge of the diffuser.The use of a TDV can effectively reduce both the discrete frequency noise generated by the interaction between the impeller-discharge flow and the diffuser surface and the broadband turbulent noise component.In the case of low-flow operation,a leading-edge vortex(LEV) that forms on the shroud side of the suction surface near the leading edge of the diffuser increases significantly in size and blocks flow in the diffuser passage.The formation of an LEV may adversely affect the performance of the compressor and may cause the diffuser to stall.Using a one-side tapered diffuser vane to suppress the evolution of an LEV,the stable operating range of the compressor can be increased by more than 12 percent,and the pressure-rise characteristics of the compressor can be improved.The results of a supplementary examination of the structure and unsteady behavior of LEVs,conducted by means of detailed numerical simulations,are also presented.展开更多
基金supported by the National Key Scientific Instrument and Equipment Development Project under Grant No.2012YQ22011902
文摘An adaptive filter for cancelling noise contained in the direct absorption spectra is reported. This technique takes advantage of the periodical nature of the repetitively scanned spectral signal, and requires no prior knowledge of the detailed properties of noises. An experimental system devised for measuring CH4 is used to test the performance of the filter. The measurement results show that the signal-to-noise （S/N） value is improved by a factor of 2. A higher enhancement factor of the S/N value of 5.4 is obtained through open-air measurement owing to higher distortions of the raw data. In addition, the response time of this filter, which characterizes the real-time detection ability of the system, is nine times shorter than that of a conventional signal averaging solution, under the condition that the filter order is 100.
基金Project supported by the Major State Basic Research Development Program of China (Grant No.2010CB328206)
文摘Based on the frequency-domain multimode theoretical model, detailed investigations on the noise characteristic of the semiconductor ring laser （SRL） are first performed in this paper. The comprehensive nonlinear terms related to the third order nonlinear susceptibility Z3 are included in this model; the Langevin noise sources for electric field and carrier density fluctuations are also taken into account. As the injection current increases, the SRL may present several operation regimes. Remarkable and unusual low frequency noise enhancement in the form of a broad low frequency tail extending all the way to the relaxation oscillation peak is observed in any of the operation regimes of SRLs. The influences of the backscattering coefficient on the relative intensity noise （RIN） spectrum in typical operation regimes are investigated in detail.
基金the financial supports from the National Natural Science Foundation of China(No.22072039)the Fundamental Research Fund for the Central Universities(No.HNU-531118010220).
文摘Strain engineering is a useful strategy for modifying the catalytic activity of electrocatalysts.However,in-situ visual characterization of the strain effect on the catalytic activity at nanoscale remains a huge challenge.Herein,we performed in-situ electrochemical scanning tunneling microscopy(EC-STM)imaging measurements at the local strained regions of extruded singlecrystal molybdenum dioxide(MoO_(2))sheets with combination of current noise analysis(n-EC-STM).The intensity-enhanced noise was observed at the local strained region compared to the unstrained regions in the same frame,which reveals the positive effect of compressive strain on the hydrogen evolution reaction(HER)activity of MoO_(2)provided that the intensity of noise is positively correlated with catalytic HER Faradic current.Therefore,we clearly“see”the strain-induced enhancement of HER activity of MoO_(2)at nanoscale by means of noise visualization.This work extends the visual characterization of strain engineering in electrocatalysis and related fields.
基金This work was supported by the National Natural Science Foundation of China （Grant No. 11165016）, the Key Project of Research Fund of Education Department of Yunnan Province （Grant No. 2013Z097） and the Natural Science Founda- tion of Yunnan Province of China （Grant No. 2012FB176）.
文摘The effects of the correlation time τ between noises on the noise-enhanced stability （NES） phe- nomenon in an asymmetric bistable system driven by cross-correlated noise are investigated. The ex- pressions for the average escape time from the left metastable state TL and from the right metastable state TR are derived. The results indicate that： i） The NES effect is suppressed as the correlation time τ increases for two metastable states; ii） The increase in τ speeds up the escape process from the right state for positively correlated noise, whereas its role is reverses for negatively correlated; iii） In the escape process from the left state, the role of τ is opposite to that in escape from the right state.
文摘Two examples of the use of vortex control to reduce noise and enhance the stable operating range of a centrifugal compressor are presented in this paper.In the case of high-flow operation of a centrifugal compressor with a vaned diffuser,a discrete frequency noise induced by interaction between the impeller-discharge flow and the diffuser vane,which appears most notably in the power spectra of the radiated noise,can be reduced using a tapered diffuser vane(TDV) without affecting the performance of the compressor.Twin longitudinal vortices produced by leakage flow passing through the tapered portion of the diffuser vane induce secondary flow in the direction of the blade surface and prevent flow separation from the leading edge of the diffuser.The use of a TDV can effectively reduce both the discrete frequency noise generated by the interaction between the impeller-discharge flow and the diffuser surface and the broadband turbulent noise component.In the case of low-flow operation,a leading-edge vortex(LEV) that forms on the shroud side of the suction surface near the leading edge of the diffuser increases significantly in size and blocks flow in the diffuser passage.The formation of an LEV may adversely affect the performance of the compressor and may cause the diffuser to stall.Using a one-side tapered diffuser vane to suppress the evolution of an LEV,the stable operating range of the compressor can be increased by more than 12 percent,and the pressure-rise characteristics of the compressor can be improved.The results of a supplementary examination of the structure and unsteady behavior of LEVs,conducted by means of detailed numerical simulations,are also presented.
