The circulation and zonal wind anomalies in the lower troposphere over the equatorial western Pacific and their roles in the developing and decaying processes of the 1982–1983, 1986 –1987, 1991–1992 and 1997–1998 ...The circulation and zonal wind anomalies in the lower troposphere over the equatorial western Pacific and their roles in the developing and decaying processes of the 1982–1983, 1986 –1987, 1991–1992 and 1997–1998 El Ni?o events and the occurrence of La Ni?a events are analyzed by using the observed data in this paper. The results show that before the developing stage of these El Ni?o events, there were cyclonic circulation anomalies in the lower troposphere over the tropical western Pacific, and the anomalies brought the westerly anomalies over the Indonesia and the tropical western Pacific. However, when the El Ni?o events developed to their mature phase, there were anticyclonic circulation anomalies in the lower troposphere over the tropical western Pacific, and the anomalies made the easterly anomalies appear over the tropical western Pacific. A simple, dynamical model of tropical ocean is used to calculate the response of the equatorial oceanic waves to the observed anomalies of wind stress near the sea surface of the equatorial Pacific during the 1997/98 ENSO cycle, which was the strongest one in the 20th century. It is shown that the zonal wind stress anomalies have an important dynamical effect on the devel-opment and decay of this El Ni?o event and the occurrence of the following La Ni?a event.展开更多
Base isolation can effectively reduce the seismic forces on a superstructure, particularly in lowto medium-rise buildings. However, under strong near-fault ground motions, pounding may occur at the isolation level bet...Base isolation can effectively reduce the seismic forces on a superstructure, particularly in lowto medium-rise buildings. However, under strong near-fault ground motions, pounding may occur at the isolation level between the baseisolated building （BIB） and its surrounding retaining walls. To effectively investigate the behavior of the BIB pounding with adjacent structures, after assessing some commonly used impact models, a modified Kelvin impact model is proposed in this paper. Relevant parameters in the modified Kelvin model are theoretically derived and numerically verified through a simple pounding case. At the same time, inelasticity of the isolated superstructure is introduced in order to accurately evaluate the potential damage to the superstructure caused by the pounding of the BIB with adjacent structures. The reliability of the modified Kelvin impact model is validated through numerical comparisons with other impact models. However, the difference between the numerical results from the various impact analytical models is not significant. Many numerical simulations of BIBs are conducted to investigate the influence of various design parameters and conditions on the peak inter-story drifts and floor accelerations during pounding. It is shown that pounding can substantially increase floor accelerations, especially at the ground floor where impacts occur. Higher modes of vibration are excited during poundings, increasing the inter-story drifts instead of keeping a nearly rigid-body motion of the superstructure. Furthermore, higher ductility demands can be imposed on lower floors of the superstructure. Moreover, impact stiffness seems to play a significant role in the acceleration response at the isolation level and the inter-story drifts of lower floors of the superstructure. Finally, the numerical results show that excessive flexibility of the isolation system used to minimize the floor accelerations may cause the BIB to be more susceptible to pounding under a limited seismic gap.展开更多
The fatigue pre-cracking 304 stainless steel （SS） specimens with lengths of 1.002 mm （L-crack） and 0.575 mm （S-crack） were prepared. Their corrosion behavior was studied by electrochemical noise （EN） in 4 mol/...The fatigue pre-cracking 304 stainless steel （SS） specimens with lengths of 1.002 mm （L-crack） and 0.575 mm （S-crack） were prepared. Their corrosion behavior was studied by electrochemical noise （EN） in 4 mol/L NaC1 ＋ 0.01 mol/L Na2S203 solution under slow-strain-rate-testing （SSRT） conditions. Moreover, the characteristics of L-crack＇s surface morphology and potential distribution with scanning Kelvin probe （SKP） before and after SSRT were also discussed. Compared with S-crack, L-crack is propagated and the features of crack propagation can be obtained. After propagation, the noise amplitudes increase with increasing stress and accelerating corrosion, the white noises at low and high frequencies （WE and WH） of the later stage are one order of magnitude larger than that at early stage in the current power spectral densities （PSDs）. The potential PSDs also increase, but WH disappears. In addition, the crack propagation can be demonstrated according to variation of probability distribution, surface morphology and potential distribution.展开更多
The curved surface of the maximum sea temperature anomaly (MSTA) was created from the JEDAC subsurface sea temperature anomaly data at the tropical Pacific between 1955 and 2000. It is quite similar to the depth distr...The curved surface of the maximum sea temperature anomaly (MSTA) was created from the JEDAC subsurface sea temperature anomaly data at the tropical Pacific between 1955 and 2000. It is quite similar to the depth distribution of the 20℃ isotherm, which is usually the replacement of thermocline. From the distribution and moving trajectory of positive or negative sea temperature anomalies (STA) on the curved surface we analyzed all the El Nino and La Nina events since the later 1960s. Based on the analyses we found that, using the subsurface warm pool as the beginning point, the warm or cold signal propagates initially eastward and upward along the equatorial curved surface of MSTA to the eastern Pacific and stays there several months and then to (urn north, usually moving westward near 10°N to western Pacific and finally propagates southward to return to warm pool to form an off-equator closed circuit. It takes about 2 to 4 years for the temperature anomaly to move around the cycle. If the STA of warm (cold) water is strong enough, there will be two successive El Nino (La Nina) events during the period of 2 to 4 years. Sometime, it becomes weak in motion due to the unsuitable oceanic or atmospheric condition. This kind process may not be considered as an El Nino ( La Nina) event, but the moving trajectory of warm (cold) water can still be recognized. Because of the alternate between warm and cold water around the circuits, the positive (negative) anomaly signal in equatorial western Pacific coexists with negative (positive) anomaly signal near 10°N in eastern Pacific before the outbreak of El Nino (La Nina) event. The signals move in the opposite directions. So it appears as El Nino (La Nina) in equator at 2-4 years intervals. The paper also analyzed several exceptional cases and discussed the effect and importance of oceanic circulation in the evolution of El Nino/ La Nina event.展开更多
The process of charge transfer based on triboelectrification （TE） and contact electrification （CE） has been recently utilized as the basis for a new and promising energy harvesting technology, i.e., triboelectric ...The process of charge transfer based on triboelectrification （TE） and contact electrification （CE） has been recently utilized as the basis for a new and promising energy harvesting technology, i.e., triboelectric nanogenerators, as well as self- powered sensors and systems. The electrostatic charge transfer between two surfaces can occur in both the TE and the CE modes depending on the involvement of relative sliding friction. Does the sliding behavior in TE induce any fundamental difference in the charge transfer from the CE？ Few studies are available on this comparison because of the challenges in ruling out the effect of the contact area using traditional macro-scale characterization methods. This paper provides the first study on the fundamental differences in CE and TE at the nanoscale based on scanning probe microscopic methods. A quantitative comparison of the two processes at equivalent contact time and force is provided, and the results suggest that the charge transfer from TE is much faster than that from CE, but the saturation value of the transferred charge density is the same. The measured frictional energy dissipation of -11 eV when the tip scans over distance of I A sheds light on a potential mechanism： The friction may facilitate the charge transfer process via electronic excitation. These results provide fundamental guidance for the selection of materials and device structures to enable the TE or the CE in different applications; the CE mode is favorable for frequent moderate contact such as vibration energy harvesting and the TE mode is favorable for instant movement such as harvesting of energy from human walking.展开更多
The initial corrosion behavior and mechanism of 7B04 aluminum alloy under acid immersion and salt spray environments(pH=3.5)are studied by Scanning Electron Microscope(SEM),optical microscope,Fourier Transform Infrare...The initial corrosion behavior and mechanism of 7B04 aluminum alloy under acid immersion and salt spray environments(pH=3.5)are studied by Scanning Electron Microscope(SEM),optical microscope,Fourier Transform Infrared Spectroscopy(FT-IR),X-Ray Diffraction(XRD),potentiodynamic polarization,Electrochemical Impedance Spectroscopy(EIS),and Scanning Kelvin Probe(SKP).The results show that pitting corrosion occurs at the initial corrosion stage,and the potential difference between the second phase particles is the main cause of pitting.Pitting pits on different locations gradually expand and coalesce with the proceeding of corrosion.The main components of corrosion products are Al_(2)O_(3),Al(OH)_(3),and AlCl_(3),and the generation rate of the corrosion product layer under the salt spray environment is larger than that under acid immersion environment.Under both environments,the Volta potential distribution first disperses and then concentrates,while the charge transfer resistance first decreases and then increases with the corrosion time.The Volta potential gradually shifts in a positive direction,indicating that corrosion products have an inhibitory effect on corrosion.After the same corrosion time,the corrosion product layer resistance and the expectation of the Volta potential of the salt spray sample are higher than those of the immersion sample.Comparatively,the corrosion current density for the salt spray sample is significantly lower than the immersion sample,which indicates that the thicker the corrosion product layer,the stronger the inhibition of corrosion reaction.展开更多
The 2015/16 El Nio developed from weak warm conditions in late 2014 and NINO3.4 reached 3℃ in November 2015. We describe the characteristics of the evolution of the 2015/16 El Nio using various data sets including ...The 2015/16 El Nio developed from weak warm conditions in late 2014 and NINO3.4 reached 3℃ in November 2015. We describe the characteristics of the evolution of the 2015/16 El Nio using various data sets including SST, surface winds,outgoing longwave radiation and subsurface temperature from an ensemble operational ocean reanalyses, and place this event in the context of historical ENSO events since 1979. One salient feature about the 2015/16 El Nio was a large number of westerly wind bursts and downwelling oceanic Kelvin waves(DWKVs). Four DWKVs were observed in April-November 2015 that initiated and enhanced the eastern-central Pacific warming. Eastward zonal current anomalies associated with DWKVs advected the warm pool water eastward in spring/summer. An upwelling Kelvin wave(UWKV) emerged in early November 2015 leading to a rapid decline of the event. Another outstanding feature was that NINO4 reached a historical high(1.7℃), which was 1℃(0.8℃) higher than that of the 1982/83(1997/98) El Nio . Although NINO3 was comparable to that of the 1982/83 and 1997/98 El Nio , NINO1+2 was much weaker. Consistently, enhanced convection was displaced 20 degree westward, and the maximum D20 anomaly was about 1/3.1/2 of that in 1997 and 1982 near the west coast of South America.展开更多
Galvanic corrosion on samples of AZ91D magnesium alloy coupled with 2A12 aluminum alloy during neutral salt spray test was investigated.The variations of the surface potential were measured using scanning kelvin probe...Galvanic corrosion on samples of AZ91D magnesium alloy coupled with 2A12 aluminum alloy during neutral salt spray test was investigated.The variations of the surface potential were measured using scanning kelvin probe（SKP）.The results showed that galvanic effect on the corrosion of AZ91D magnesium alloy is closely related to the potential difference between the anodic and cathodic materials.In the initial period,corrosion only occurred in a narrow area at the coupling interface because of the limited distance galvanic current.Then,the corrosion rate of 2A12 aluminum alloy was accelerated due to its poor stability in strong alkali environment,which was attributed to the strong alkalization caused by the corrosion of AZ91D magnesium alloy.With the increase of the potential of 2A12 aluminum alloy as a result of the continuous covering of corrosion products,the potential difference between the two materials was enlarged,which enhanced the galvanic corrosion.展开更多
In this paper, the zonal wind anomalies in the lower troposphere over the tropical Pacific during 1980-1994 are analyzed by using the observed data. The results show that during the formation of the 1982/83, 1986/87 a...In this paper, the zonal wind anomalies in the lower troposphere over the tropical Pacific during 1980-1994 are analyzed by using the observed data. The results show that during the formation of the 1982/83, 1986/87 and 1991/92 ENSO events, there were the larger westerly anomalies in the lower troposphere over the equatorial Pacific. Moreover, it is explained by using the correlation analyses that the westerly anomalies over the equatorial Pacific could cause the warm episodes of the equatorial central and eastern Pacific. A simple air-sea coupled model is used to discuss theoretically the dynamical effect of the observed westerly anomalies of wind stress near the sea surface of the equatorial Pacific on the ENSO cycle occurred in the period of 1981-1983. It is shown by using the theoretical calculations of the equatorial oceanic Kelvin wave and Rossby waves responding to the forcing of the observed anomalies of zonal wind stress near the sea surface of the equatorial Pacific that the westerly anomalies of wind stress near the sea surface of the equatorial Pacific make significant dynamical effect on the ENSO cycles occurred in the period of 1982-1983.展开更多
By elongating the regular Kelvin model in one direction and keeping unchanged in the other two directions,the anisotropic model was constructed.Then,the simplified periodic structural cell was obtained according to th...By elongating the regular Kelvin model in one direction and keeping unchanged in the other two directions,the anisotropic model was constructed.Then,the simplified periodic structural cell was obtained according to the periodicity and symmetry of the model in the whole space.Using the half-strut element and elastic deflection theory to analyze the mechanical behavior as were adopted in the previous studies,this paper obtained the theoretical expressions for the compressive stress and strain as well as the corresponding curves in the rise and transverse directions.In addition,the theoretical results were examined by the finite element simulation.Results indicated that the theoretical analysis was very close to the finite element simulation when the strain was not too high,which confirmed the validity of theoretical analysis.At the same time,the anisotropy was shown to have a significant effect on the mechanical properties of open-cell foams.As the anisotropy ratio increased,the compressive stress was improved in the rise direction but dropped in the transverse direction under the same strain.展开更多
A convenient and universal residue calculus method is proposed to study the stochastic response behaviors of an axially moving viscoelastic beam with random noise excitations and fractional order constitutive relation...A convenient and universal residue calculus method is proposed to study the stochastic response behaviors of an axially moving viscoelastic beam with random noise excitations and fractional order constitutive relationship, where the random excitation can be decomposed as a nonstationary stochastic process, Mittag-Leffler internal noise, and external stationary noise excitation. Then, based on the Laplace transform approach, we derived the mean value function, variance function and covariance function through the Green＇s function technique and the residue calculus method, and obtained theoretical results. In some special case of fractional order derivative α , the Monte Carlo approach and error function results were applied to check the effectiveness of the analytical results, and good agreement was found. Finally in a general-purpose case, we also confirmed the analytical conclusion via the direct Monte Carlo simulation.展开更多
The eastern edge of the western Pacific warm pool （WPWP） in the upper layer （shallower than 50m） exhibits significant zonal displacements on interannual scale. Employing an intermediate ocean model, the dynamic me...The eastern edge of the western Pacific warm pool （WPWP） in the upper layer （shallower than 50m） exhibits significant zonal displacements on interannual scale. Employing an intermediate ocean model, the dynamic mechanism for the interannual zonal displacement of the WPWP eastern edge in the upper layer is investigated by diagnosing the dynamic impacts of zonal current anomalies induced by wind, waves （Kelvin and Rossby waves）, and their boundary reflections. The interannual zonal displacements of the WPWP eastern edge in the upper layer and the zonal current anomaly in the equatorial Pacific west of ll0~W for more than 30 years can be well simulated. The modeling results show that zonal current anomalies in the central and eastern equatorial Pacific are the dominant dynamic mechanism for the zonal displacements of the eastern edge of the upper WPWP warm water. Composite analyses suggest that the zonal current anomalies induced by waves dominate the zonal displacement of the WPWP eastern edge, whereas the role played by zonal wind-driven current anomalies is very small. A sensitivity test proves that the zonal current anomalies associated with reflected waves on the western and eastern Pacific boundaries can act as a restoring force that results in the interannual reciprocating zonal motion of the WPWP eastern edge.展开更多
A high-resolution customized numerical model is used to analyze the water transport in the three major water passages between the Andaman Sea(AS)and the Bay of Bengal,i.e.,the Preparis Channel(PC),the Ten Degree Chann...A high-resolution customized numerical model is used to analyze the water transport in the three major water passages between the Andaman Sea(AS)and the Bay of Bengal,i.e.,the Preparis Channel(PC),the Ten Degree Channel(TDC),and the Great Channel(GC),based on the daily averaged simulation results ranging from 2010 to 2019.Spectral analysis and Empirical Orthogonal Function(EOF)methods are employed to investigate the spatiotemporal variability of the water exchange and controlling mechanisms.The results of model simulation indicate that the net average transports of the PC and GC,as well as their linear trend,are opposite to that of the TDC.This indicates that the PC and the GC are the main inflow channels of the AS,while the TDC is the main outflow channel of the AS.The transport variability is most pronounced at surface levels and between 100 m and 200 m depth,likely affected by monsoons and circulation.A 182.4-d semiannual variability is consistently seen in all three channels,which is also evident in their second principal components.Based on sea level anomalies and EOF analysis results,this is primarily due to equatorial winds during the monsoon transition period,causing eastward movement of Kelvin waves along the AS coast,thereby affecting the spatiotemporal characteristics of the flow in the AS.The first EOF of the PC flow field section shows a split at 100 m deep,likely due to topography.The first EOF of the TDC flow field section is steady but has potent seasonal oscillations in its time series.Meanwhile,the first EOF of the GC flow field section indicates a stable surface inflow,probably influenced by the equatorial Indian Ocean’s eastward current.展开更多
The common ways to activate a chemical reaction are by heat,electric current,or light.However,mechanochemistry,where the chemical reaction is activated by applied mechanical force,is less common and only poorly unders...The common ways to activate a chemical reaction are by heat,electric current,or light.However,mechanochemistry,where the chemical reaction is activated by applied mechanical force,is less common and only poorly understood at the atomic scale.Here we report a tip-induced activation of chemical reaction of carbon monoxide to dioxide on oxidized rutile TiO_(2)(110)surface.The activation is studied by atomic force microscopy,Kelvin probe force microscopy under ultrahigh-vacuum and liquid nitrogen temperature conditions,and density functional theory(DFT)modeling.The reaction is inferred from hysteretic behavior of frequency shift signal further supported by vector force mapping of vertical and lateral forces needed to trigger the chemical reaction with torque motion of carbon monoxide towards an oxygen adatom.The reaction is found to proceed stochastically at very small tip-sample distances.Furthermore,the local contact potential difference reveals the atomic-scale charge redistribution in the reactants required to unlock the reaction.Our results open up new insights into the mechanochemistry on metal oxide surfaces at the atomic scale.展开更多
This study aims to investigate characteristics of continental shelf wave(CSW)on the northwestern continental shelf of the South China Sea(SCS)induced by winter storms in 2021.Mooring and cruise observations,tidal gaug...This study aims to investigate characteristics of continental shelf wave(CSW)on the northwestern continental shelf of the South China Sea(SCS)induced by winter storms in 2021.Mooring and cruise observations,tidal gauge data at stations Hong Kong,Zhapo and Qinglan and sea surface wind data from January 1 to February 28,2021 are used to examine the relationship between along-shelf wind and sea level fluctuation.Two events of CSWs driven by the along-shelf sea surface wind are detected from wavelet spectra of tidal gauge data.The signals are triply peaked at periods of 56 h,94 h and 180 h,propagating along the coast with phase speed ranging from 6.9 m/s to18.9 m/s.The dispersion relation shows their property of the Kelvin mode of CSW.We develop a simple method to estimate amplitude of sea surface fluctuation by along-shelf wind.The results are comparable with the observation data,suggesting it is effective.The mode 2 CSWs fits very well with the mooring current velocity data.The results from rare current help to understand wave-current interaction in the northwestern SCS.展开更多
The phosphate protective film and micro-galvanic corrosion of biological Mg-3Zn-xNd (x = 0, 0.6, 1.2) alloys were investigated by scanning and transmission electron microscopy, quasi-in-situ observation, scanning Kelv...The phosphate protective film and micro-galvanic corrosion of biological Mg-3Zn-xNd (x = 0, 0.6, 1.2) alloys were investigated by scanning and transmission electron microscopy, quasi-in-situ observation, scanning Kelvin probe force microscopy (SKPFM) and electrochemical tests. The results revealed the Mg-Zn-Nd phases formed in Mg-3Zn alloy contained with Nd. Adding Nd resulted in a significant decline in the cracks of the phosphate protective film and micro-galvanic corrosion of alloys, which were recorded by quasi-in-situ observation. In addition, the Volta potential difference of Mg-Zn-Nd/α-Mg (~ 188 mV) was lower than MgZn/α-Mg (~ 419 mV) and Zn-rich/α-Mg (~ 260 mV), and the corrosion rates of alloys markedly decreased after the addition of 0.6 wt% Nd. The improvement in corrosion resistance of Nd-containing alloys was mainly attributed to the following: (i) the addition of Nd reduced the Volta potential difference (second phases/α-Mg);(ii) the phosphate protective film containing Nd_(2)O_(3) deposited on the surface of the alloys, effectively preventing the penetration of harmful anions.展开更多
基金the National Key Program for Developing Basic Research (Grant No. 1998040900).
文摘The circulation and zonal wind anomalies in the lower troposphere over the equatorial western Pacific and their roles in the developing and decaying processes of the 1982–1983, 1986 –1987, 1991–1992 and 1997–1998 El Ni?o events and the occurrence of La Ni?a events are analyzed by using the observed data in this paper. The results show that before the developing stage of these El Ni?o events, there were cyclonic circulation anomalies in the lower troposphere over the tropical western Pacific, and the anomalies brought the westerly anomalies over the Indonesia and the tropical western Pacific. However, when the El Ni?o events developed to their mature phase, there were anticyclonic circulation anomalies in the lower troposphere over the tropical western Pacific, and the anomalies made the easterly anomalies appear over the tropical western Pacific. A simple, dynamical model of tropical ocean is used to calculate the response of the equatorial oceanic waves to the observed anomalies of wind stress near the sea surface of the equatorial Pacific during the 1997/98 ENSO cycle, which was the strongest one in the 20th century. It is shown that the zonal wind stress anomalies have an important dynamical effect on the devel-opment and decay of this El Ni?o event and the occurrence of the following La Ni?a event.
基金National Natural Science Foundation of China Under Grant No.50778077 and 50878093
文摘Base isolation can effectively reduce the seismic forces on a superstructure, particularly in lowto medium-rise buildings. However, under strong near-fault ground motions, pounding may occur at the isolation level between the baseisolated building （BIB） and its surrounding retaining walls. To effectively investigate the behavior of the BIB pounding with adjacent structures, after assessing some commonly used impact models, a modified Kelvin impact model is proposed in this paper. Relevant parameters in the modified Kelvin model are theoretically derived and numerically verified through a simple pounding case. At the same time, inelasticity of the isolated superstructure is introduced in order to accurately evaluate the potential damage to the superstructure caused by the pounding of the BIB with adjacent structures. The reliability of the modified Kelvin impact model is validated through numerical comparisons with other impact models. However, the difference between the numerical results from the various impact analytical models is not significant. Many numerical simulations of BIBs are conducted to investigate the influence of various design parameters and conditions on the peak inter-story drifts and floor accelerations during pounding. It is shown that pounding can substantially increase floor accelerations, especially at the ground floor where impacts occur. Higher modes of vibration are excited during poundings, increasing the inter-story drifts instead of keeping a nearly rigid-body motion of the superstructure. Furthermore, higher ductility demands can be imposed on lower floors of the superstructure. Moreover, impact stiffness seems to play a significant role in the acceleration response at the isolation level and the inter-story drifts of lower floors of the superstructure. Finally, the numerical results show that excessive flexibility of the isolation system used to minimize the floor accelerations may cause the BIB to be more susceptible to pounding under a limited seismic gap.
基金Project(2006CB605004) supported by the National Basic Research Program of China
文摘The fatigue pre-cracking 304 stainless steel （SS） specimens with lengths of 1.002 mm （L-crack） and 0.575 mm （S-crack） were prepared. Their corrosion behavior was studied by electrochemical noise （EN） in 4 mol/L NaC1 ＋ 0.01 mol/L Na2S203 solution under slow-strain-rate-testing （SSRT） conditions. Moreover, the characteristics of L-crack＇s surface morphology and potential distribution with scanning Kelvin probe （SKP） before and after SSRT were also discussed. Compared with S-crack, L-crack is propagated and the features of crack propagation can be obtained. After propagation, the noise amplitudes increase with increasing stress and accelerating corrosion, the white noises at low and high frequencies （WE and WH） of the later stage are one order of magnitude larger than that at early stage in the current power spectral densities （PSDs）. The potential PSDs also increase, but WH disappears. In addition, the crack propagation can be demonstrated according to variation of probability distribution, surface morphology and potential distribution.
基金This work was supported by the National Natural Science Foundation of China under Grant No.40126002.
文摘The curved surface of the maximum sea temperature anomaly (MSTA) was created from the JEDAC subsurface sea temperature anomaly data at the tropical Pacific between 1955 and 2000. It is quite similar to the depth distribution of the 20℃ isotherm, which is usually the replacement of thermocline. From the distribution and moving trajectory of positive or negative sea temperature anomalies (STA) on the curved surface we analyzed all the El Nino and La Nina events since the later 1960s. Based on the analyses we found that, using the subsurface warm pool as the beginning point, the warm or cold signal propagates initially eastward and upward along the equatorial curved surface of MSTA to the eastern Pacific and stays there several months and then to (urn north, usually moving westward near 10°N to western Pacific and finally propagates southward to return to warm pool to form an off-equator closed circuit. It takes about 2 to 4 years for the temperature anomaly to move around the cycle. If the STA of warm (cold) water is strong enough, there will be two successive El Nino (La Nina) events during the period of 2 to 4 years. Sometime, it becomes weak in motion due to the unsuitable oceanic or atmospheric condition. This kind process may not be considered as an El Nino ( La Nina) event, but the moving trajectory of warm (cold) water can still be recognized. Because of the alternate between warm and cold water around the circuits, the positive (negative) anomaly signal in equatorial western Pacific coexists with negative (positive) anomaly signal near 10°N in eastern Pacific before the outbreak of El Nino (La Nina) event. The signals move in the opposite directions. So it appears as El Nino (La Nina) in equator at 2-4 years intervals. The paper also analyzed several exceptional cases and discussed the effect and importance of oceanic circulation in the evolution of El Nino/ La Nina event.
基金Research was supported by U.S. Department of Energy, Office of Basic Energy Sciences （No. DE-FG02- 07ER46394） and the National Science Foundation （No. DMR-1505319）. We also would like to express our sincere appreciation to Dr. Ricardo Garcia for the insightful discussion on modeling and calculation of the dynamic motion of the cantilever in tapping mode AFM.
文摘The process of charge transfer based on triboelectrification （TE） and contact electrification （CE） has been recently utilized as the basis for a new and promising energy harvesting technology, i.e., triboelectric nanogenerators, as well as self- powered sensors and systems. The electrostatic charge transfer between two surfaces can occur in both the TE and the CE modes depending on the involvement of relative sliding friction. Does the sliding behavior in TE induce any fundamental difference in the charge transfer from the CE？ Few studies are available on this comparison because of the challenges in ruling out the effect of the contact area using traditional macro-scale characterization methods. This paper provides the first study on the fundamental differences in CE and TE at the nanoscale based on scanning probe microscopic methods. A quantitative comparison of the two processes at equivalent contact time and force is provided, and the results suggest that the charge transfer from TE is much faster than that from CE, but the saturation value of the transferred charge density is the same. The measured frictional energy dissipation of -11 eV when the tip scans over distance of I A sheds light on a potential mechanism： The friction may facilitate the charge transfer process via electronic excitation. These results provide fundamental guidance for the selection of materials and device structures to enable the TE or the CE in different applications; the CE mode is favorable for frequent moderate contact such as vibration energy harvesting and the TE mode is favorable for instant movement such as harvesting of energy from human walking.
基金co-supported by the China Postdoctoral Science Foundation(No.2019M653929)the Green Innovation Science+1 种基金Technology Plan of CollegesUniversities in Shandong Province,China(No.2020KJA014).
文摘The initial corrosion behavior and mechanism of 7B04 aluminum alloy under acid immersion and salt spray environments(pH=3.5)are studied by Scanning Electron Microscope(SEM),optical microscope,Fourier Transform Infrared Spectroscopy(FT-IR),X-Ray Diffraction(XRD),potentiodynamic polarization,Electrochemical Impedance Spectroscopy(EIS),and Scanning Kelvin Probe(SKP).The results show that pitting corrosion occurs at the initial corrosion stage,and the potential difference between the second phase particles is the main cause of pitting.Pitting pits on different locations gradually expand and coalesce with the proceeding of corrosion.The main components of corrosion products are Al_(2)O_(3),Al(OH)_(3),and AlCl_(3),and the generation rate of the corrosion product layer under the salt spray environment is larger than that under acid immersion environment.Under both environments,the Volta potential distribution first disperses and then concentrates,while the charge transfer resistance first decreases and then increases with the corrosion time.The Volta potential gradually shifts in a positive direction,indicating that corrosion products have an inhibitory effect on corrosion.After the same corrosion time,the corrosion product layer resistance and the expectation of the Volta potential of the salt spray sample are higher than those of the immersion sample.Comparatively,the corrosion current density for the salt spray sample is significantly lower than the immersion sample,which indicates that the thicker the corrosion product layer,the stronger the inhibition of corrosion reaction.
文摘The 2015/16 El Nio developed from weak warm conditions in late 2014 and NINO3.4 reached 3℃ in November 2015. We describe the characteristics of the evolution of the 2015/16 El Nio using various data sets including SST, surface winds,outgoing longwave radiation and subsurface temperature from an ensemble operational ocean reanalyses, and place this event in the context of historical ENSO events since 1979. One salient feature about the 2015/16 El Nio was a large number of westerly wind bursts and downwelling oceanic Kelvin waves(DWKVs). Four DWKVs were observed in April-November 2015 that initiated and enhanced the eastern-central Pacific warming. Eastward zonal current anomalies associated with DWKVs advected the warm pool water eastward in spring/summer. An upwelling Kelvin wave(UWKV) emerged in early November 2015 leading to a rapid decline of the event. Another outstanding feature was that NINO4 reached a historical high(1.7℃), which was 1℃(0.8℃) higher than that of the 1982/83(1997/98) El Nio . Although NINO3 was comparable to that of the 1982/83 and 1997/98 El Nio , NINO1+2 was much weaker. Consistently, enhanced convection was displaced 20 degree westward, and the maximum D20 anomaly was about 1/3.1/2 of that in 1997 and 1982 near the west coast of South America.
基金Funded by the National Natural Science Foundation of China(No.51271032)
文摘Galvanic corrosion on samples of AZ91D magnesium alloy coupled with 2A12 aluminum alloy during neutral salt spray test was investigated.The variations of the surface potential were measured using scanning kelvin probe（SKP）.The results showed that galvanic effect on the corrosion of AZ91D magnesium alloy is closely related to the potential difference between the anodic and cathodic materials.In the initial period,corrosion only occurred in a narrow area at the coupling interface because of the limited distance galvanic current.Then,the corrosion rate of 2A12 aluminum alloy was accelerated due to its poor stability in strong alkali environment,which was attributed to the strong alkalization caused by the corrosion of AZ91D magnesium alloy.With the increase of the potential of 2A12 aluminum alloy as a result of the continuous covering of corrosion products,the potential difference between the two materials was enlarged,which enhanced the galvanic corrosion.
文摘In this paper, the zonal wind anomalies in the lower troposphere over the tropical Pacific during 1980-1994 are analyzed by using the observed data. The results show that during the formation of the 1982/83, 1986/87 and 1991/92 ENSO events, there were the larger westerly anomalies in the lower troposphere over the equatorial Pacific. Moreover, it is explained by using the correlation analyses that the westerly anomalies over the equatorial Pacific could cause the warm episodes of the equatorial central and eastern Pacific. A simple air-sea coupled model is used to discuss theoretically the dynamical effect of the observed westerly anomalies of wind stress near the sea surface of the equatorial Pacific on the ENSO cycle occurred in the period of 1981-1983. It is shown by using the theoretical calculations of the equatorial oceanic Kelvin wave and Rossby waves responding to the forcing of the observed anomalies of zonal wind stress near the sea surface of the equatorial Pacific that the westerly anomalies of wind stress near the sea surface of the equatorial Pacific make significant dynamical effect on the ENSO cycles occurred in the period of 1982-1983.
基金supported by the National Natural Science Foundation of China (Grant No.10572013,10932001)the Common Construction Project of Education Committee of Beijing (GrantNo.XK100060522)
文摘By elongating the regular Kelvin model in one direction and keeping unchanged in the other two directions,the anisotropic model was constructed.Then,the simplified periodic structural cell was obtained according to the periodicity and symmetry of the model in the whole space.Using the half-strut element and elastic deflection theory to analyze the mechanical behavior as were adopted in the previous studies,this paper obtained the theoretical expressions for the compressive stress and strain as well as the corresponding curves in the rise and transverse directions.In addition,the theoretical results were examined by the finite element simulation.Results indicated that the theoretical analysis was very close to the finite element simulation when the strain was not too high,which confirmed the validity of theoretical analysis.At the same time,the anisotropy was shown to have a significant effect on the mechanical properties of open-cell foams.As the anisotropy ratio increased,the compressive stress was improved in the rise direction but dropped in the transverse direction under the same strain.
基金supported by the National Natural Science Foundation of China (11172233, 10932009 and 10972181)Program for New Century Excellent Talents in University+1 种基金the Shaanxi Project for Young New Star in Science & TechnologyNPU Foundation for Fundamental Research and New Faculties and Research Area Project
文摘A convenient and universal residue calculus method is proposed to study the stochastic response behaviors of an axially moving viscoelastic beam with random noise excitations and fractional order constitutive relationship, where the random excitation can be decomposed as a nonstationary stochastic process, Mittag-Leffler internal noise, and external stationary noise excitation. Then, based on the Laplace transform approach, we derived the mean value function, variance function and covariance function through the Green＇s function technique and the residue calculus method, and obtained theoretical results. In some special case of fractional order derivative α , the Monte Carlo approach and error function results were applied to check the effectiveness of the analytical results, and good agreement was found. Finally in a general-purpose case, we also confirmed the analytical conclusion via the direct Monte Carlo simulation.
基金Supported by the National Basic Research Program of China (No. 2006CB403606)the National Special Project: Chinese Offshore Investigation and Assessment (Nos. 908-02-01-02, 908-ZC-I-13)+1 种基金the Open Fund of State Key Laboratory of Satellite Ocean Environment Dynamics (No. 200601)the Scientific Research Foundation of Third Institute of Oceanography, SOA (No. 2009003)
文摘The eastern edge of the western Pacific warm pool （WPWP） in the upper layer （shallower than 50m） exhibits significant zonal displacements on interannual scale. Employing an intermediate ocean model, the dynamic mechanism for the interannual zonal displacement of the WPWP eastern edge in the upper layer is investigated by diagnosing the dynamic impacts of zonal current anomalies induced by wind, waves （Kelvin and Rossby waves）, and their boundary reflections. The interannual zonal displacements of the WPWP eastern edge in the upper layer and the zonal current anomaly in the equatorial Pacific west of ll0~W for more than 30 years can be well simulated. The modeling results show that zonal current anomalies in the central and eastern equatorial Pacific are the dominant dynamic mechanism for the zonal displacements of the eastern edge of the upper WPWP warm water. Composite analyses suggest that the zonal current anomalies induced by waves dominate the zonal displacement of the WPWP eastern edge, whereas the role played by zonal wind-driven current anomalies is very small. A sensitivity test proves that the zonal current anomalies associated with reflected waves on the western and eastern Pacific boundaries can act as a restoring force that results in the interannual reciprocating zonal motion of the WPWP eastern edge.
基金The Joint Advanced Marine and Ecological Studies(JAMES)in the Bay of Bengal and eastern equatorial Indian Ocean supported by the Global Change and Air-Sea InteractionⅡProgram under contract Nos GASI-01-EIND-STwin and GASI-04-WLHY-03Zhejiang Provincial Ten Thousand Talents Plan under contract No.2020R52038.
文摘A high-resolution customized numerical model is used to analyze the water transport in the three major water passages between the Andaman Sea(AS)and the Bay of Bengal,i.e.,the Preparis Channel(PC),the Ten Degree Channel(TDC),and the Great Channel(GC),based on the daily averaged simulation results ranging from 2010 to 2019.Spectral analysis and Empirical Orthogonal Function(EOF)methods are employed to investigate the spatiotemporal variability of the water exchange and controlling mechanisms.The results of model simulation indicate that the net average transports of the PC and GC,as well as their linear trend,are opposite to that of the TDC.This indicates that the PC and the GC are the main inflow channels of the AS,while the TDC is the main outflow channel of the AS.The transport variability is most pronounced at surface levels and between 100 m and 200 m depth,likely affected by monsoons and circulation.A 182.4-d semiannual variability is consistently seen in all three channels,which is also evident in their second principal components.Based on sea level anomalies and EOF analysis results,this is primarily due to equatorial winds during the monsoon transition period,causing eastward movement of Kelvin waves along the AS coast,thereby affecting the spatiotemporal characteristics of the flow in the AS.The first EOF of the PC flow field section shows a split at 100 m deep,likely due to topography.The first EOF of the TDC flow field section is steady but has potent seasonal oscillations in its time series.Meanwhile,the first EOF of the GC flow field section indicates a stable surface inflow,probably influenced by the equatorial Indian Ocean’s eastward current.
基金supported by a Grant-in-Aid for Scientific Research from Japan Society for the Promotion of Science(JSPS)from the Ministry of Education,Culture,Sports,Science,and Technology of Japan(Nos.JP16H06327,JP17H01061,A21J103560,and JP22H00282)supported by the International Joint Research Promotion Program of Osaka University(Nos.J171013014,J171013007,J181013004,J181013006,Ja1999001,Ja19990011,and A21J103560)+1 种基金JSPSthe National Natural Science Foundation of China(No.J191053055)supported by APVV-21-0272,VEGA-2/0070/21,VEGA-2/0125/20,VEGA-2/0131/23,and H2020 TREX GA No.952165 projects。
文摘The common ways to activate a chemical reaction are by heat,electric current,or light.However,mechanochemistry,where the chemical reaction is activated by applied mechanical force,is less common and only poorly understood at the atomic scale.Here we report a tip-induced activation of chemical reaction of carbon monoxide to dioxide on oxidized rutile TiO_(2)(110)surface.The activation is studied by atomic force microscopy,Kelvin probe force microscopy under ultrahigh-vacuum and liquid nitrogen temperature conditions,and density functional theory(DFT)modeling.The reaction is inferred from hysteretic behavior of frequency shift signal further supported by vector force mapping of vertical and lateral forces needed to trigger the chemical reaction with torque motion of carbon monoxide towards an oxygen adatom.The reaction is found to proceed stochastically at very small tip-sample distances.Furthermore,the local contact potential difference reveals the atomic-scale charge redistribution in the reactants required to unlock the reaction.Our results open up new insights into the mechanochemistry on metal oxide surfaces at the atomic scale.
基金The National Key R&D Program of China under contract No.2022YFC3104805the National Natural Science Foundation of China under contract Nos 42276019,41706025 and 41976200+4 种基金the Innovation Team Plan for Universities in Guangdong Province under contract No.2019KCXTF021the First-class Discipline Plan of Guangdong Province under contract Nos 080503032101and 231420003the Program for Scientific Research Start-up Funds of Guangdong Ocean University under contract No.060302032106the Open Fund Project of Key Laboratory of Marine Environmental Information Technology(2019)Ministry of Natural Resources。
文摘This study aims to investigate characteristics of continental shelf wave(CSW)on the northwestern continental shelf of the South China Sea(SCS)induced by winter storms in 2021.Mooring and cruise observations,tidal gauge data at stations Hong Kong,Zhapo and Qinglan and sea surface wind data from January 1 to February 28,2021 are used to examine the relationship between along-shelf wind and sea level fluctuation.Two events of CSWs driven by the along-shelf sea surface wind are detected from wavelet spectra of tidal gauge data.The signals are triply peaked at periods of 56 h,94 h and 180 h,propagating along the coast with phase speed ranging from 6.9 m/s to18.9 m/s.The dispersion relation shows their property of the Kelvin mode of CSW.We develop a simple method to estimate amplitude of sea surface fluctuation by along-shelf wind.The results are comparable with the observation data,suggesting it is effective.The mode 2 CSWs fits very well with the mooring current velocity data.The results from rare current help to understand wave-current interaction in the northwestern SCS.
基金support by the National Natural Science Foundation of China(No.51961026).
文摘The phosphate protective film and micro-galvanic corrosion of biological Mg-3Zn-xNd (x = 0, 0.6, 1.2) alloys were investigated by scanning and transmission electron microscopy, quasi-in-situ observation, scanning Kelvin probe force microscopy (SKPFM) and electrochemical tests. The results revealed the Mg-Zn-Nd phases formed in Mg-3Zn alloy contained with Nd. Adding Nd resulted in a significant decline in the cracks of the phosphate protective film and micro-galvanic corrosion of alloys, which were recorded by quasi-in-situ observation. In addition, the Volta potential difference of Mg-Zn-Nd/α-Mg (~ 188 mV) was lower than MgZn/α-Mg (~ 419 mV) and Zn-rich/α-Mg (~ 260 mV), and the corrosion rates of alloys markedly decreased after the addition of 0.6 wt% Nd. The improvement in corrosion resistance of Nd-containing alloys was mainly attributed to the following: (i) the addition of Nd reduced the Volta potential difference (second phases/α-Mg);(ii) the phosphate protective film containing Nd_(2)O_(3) deposited on the surface of the alloys, effectively preventing the penetration of harmful anions.
