The pre-multiplied spanwise energy spectra of streamwise velocity fluctuations are investigated in this paper. Two distinct spectral peaks in the spanwise spectra are observed in low-Reynolds-number wall-bounded turbu...The pre-multiplied spanwise energy spectra of streamwise velocity fluctuations are investigated in this paper. Two distinct spectral peaks in the spanwise spectra are observed in low-Reynolds-number wall-bounded turbulence. The spectra are calculated from direct numerical simulation （DNS） of turbulent channel flows and zero-pressure-gradient boundary layer flows. These two peaks locate in the nearwall and outer regions and are referred to as the inner peak and the outer peak, respectively. This result implies that the streamwise velocity fluctuations can be separated into large and small scales in the spanwise direction even though the friction Reynolds number Rer can be as low as 1000. The properties of the inner and outer peaks in the spanwise spec- tra are analyzed. The locations of the inner peak are invariant over a range of Reynolds numbers. However, the locations of the outer peak are associated with the Reynolds number, which are much higher than those of the outer peak of the pre-multiplied streamwise energy spectra of the streamwise velocity.展开更多
It has been observed for a long time that the high-frequency fall-off constant of source spectra is about 2 for 'large'earthquakes and about 3 for 'small' earthquakes. For earthquakes between 'larg...It has been observed for a long time that the high-frequency fall-off constant of source spectra is about 2 for 'large'earthquakes and about 3 for 'small' earthquakes. For earthquakes between 'large' and 'small', the high-frequencyfall-off constant is not an integer and varies with the size of the earthquake. In this article such a variation is explainedin the perspective of the scaling of stress drop, which proposes a new approach to the study of the scaling of stress dropusing seismic data with lower quality of completeness and high-frequency characteristics. The study on the sourcespectra of the aftershocks of the 1988 Lancang-Gengma, Yunnan, China earthquake shows that the high-frequencyfall-off of source spectra and its variation with the size of earthquake can be well explained by the model that for 'large'earthquakes the stress drop is a constant while for ',small' earthquakes the stress drop increases with the size of theearthquake.展开更多
In order to investigate the anticorrosion performance of the organic coating/metal system, electrochemical impedance spectra （EIS） were measured in the 3.5wt% NaCl solution, the chemical component and the formation ...In order to investigate the anticorrosion performance of the organic coating/metal system, electrochemical impedance spectra （EIS） were measured in the 3.5wt% NaCl solution, the chemical component and the formation of corrosion products scale were analyzed by laser Raman microspectroscopy, and the pattern of the organic coating/metal system was observed by scanning electron microscopy （SEM）. The characteristics and the delamination process of the organic coating/metal system were investigated systematically, and the emphases were on the transportation of the corrosive medium and the changes of the coating/metal interface. The results show that the impedance decreases at the initial immersion, then increases at the middle-immersion, and again decreases at last, which is related to the corrosion products scale. The concentration of Cl in the coating, which destroys the corrosion products scale, increases with the immersion time.展开更多
With the saddle point analysis method for the Bessel function structure and property, the convergence problem and the scaling laws of Thomson backscattering spectra are solved and studied in both cases that are for th...With the saddle point analysis method for the Bessel function structure and property, the convergence problem and the scaling laws of Thomson backscattering spectra are solved and studied in both cases that are for the plane wave laser field without and with applied external constant magnetic field. Some unclear points appeared in previous work are clarified. The extension of the method to a general situation for the laser field with an arbitrary polarization is discussed. We also make a simple analysis and discussion about the optimal spectra dependence of field parameters and its implication to practical applications.展开更多
基金supported by the National Natural Science Foundation of China (Grants 11302238, 11232011, 11572331, and 11490551)the support from the Strategic Priority Research Program (Grant XDB22040104)+1 种基金the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences (Grant QYZDJ-SSW-SYS002)the National Basic Research Program of China (973 Program 2013CB834100 : Nonlinear Science)
文摘The pre-multiplied spanwise energy spectra of streamwise velocity fluctuations are investigated in this paper. Two distinct spectral peaks in the spanwise spectra are observed in low-Reynolds-number wall-bounded turbulence. The spectra are calculated from direct numerical simulation （DNS） of turbulent channel flows and zero-pressure-gradient boundary layer flows. These two peaks locate in the nearwall and outer regions and are referred to as the inner peak and the outer peak, respectively. This result implies that the streamwise velocity fluctuations can be separated into large and small scales in the spanwise direction even though the friction Reynolds number Rer can be as low as 1000. The properties of the inner and outer peaks in the spanwise spec- tra are analyzed. The locations of the inner peak are invariant over a range of Reynolds numbers. However, the locations of the outer peak are associated with the Reynolds number, which are much higher than those of the outer peak of the pre-multiplied streamwise energy spectra of the streamwise velocity.
文摘It has been observed for a long time that the high-frequency fall-off constant of source spectra is about 2 for 'large'earthquakes and about 3 for 'small' earthquakes. For earthquakes between 'large' and 'small', the high-frequencyfall-off constant is not an integer and varies with the size of the earthquake. In this article such a variation is explainedin the perspective of the scaling of stress drop, which proposes a new approach to the study of the scaling of stress dropusing seismic data with lower quality of completeness and high-frequency characteristics. The study on the sourcespectra of the aftershocks of the 1988 Lancang-Gengma, Yunnan, China earthquake shows that the high-frequencyfall-off of source spectra and its variation with the size of earthquake can be well explained by the model that for 'large'earthquakes the stress drop is a constant while for ',small' earthquakes the stress drop increases with the size of theearthquake.
文摘In order to investigate the anticorrosion performance of the organic coating/metal system, electrochemical impedance spectra （EIS） were measured in the 3.5wt% NaCl solution, the chemical component and the formation of corrosion products scale were analyzed by laser Raman microspectroscopy, and the pattern of the organic coating/metal system was observed by scanning electron microscopy （SEM）. The characteristics and the delamination process of the organic coating/metal system were investigated systematically, and the emphases were on the transportation of the corrosive medium and the changes of the coating/metal interface. The results show that the impedance decreases at the initial immersion, then increases at the middle-immersion, and again decreases at last, which is related to the corrosion products scale. The concentration of Cl in the coating, which destroys the corrosion products scale, increases with the immersion time.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11475026 and 11175023)
文摘With the saddle point analysis method for the Bessel function structure and property, the convergence problem and the scaling laws of Thomson backscattering spectra are solved and studied in both cases that are for the plane wave laser field without and with applied external constant magnetic field. Some unclear points appeared in previous work are clarified. The extension of the method to a general situation for the laser field with an arbitrary polarization is discussed. We also make a simple analysis and discussion about the optimal spectra dependence of field parameters and its implication to practical applications.
