Sedimentary environments in the Hangzhou Bay are introduced by a three-subregional landform pattern and a sedimentation map with six major sedimentation types. The geographic setting, sediment transportation and sedim...Sedimentary environments in the Hangzhou Bay are introduced by a three-subregional landform pattern and a sedimentation map with six major sedimentation types. The geographic setting, sediment transportation and sedimentation in different subregions are discussed with sediment grain parameters. Sedimentary basin suffering from effect of plume front can be identified by the fine sediments with median ( Mdφ ) 7φ-8φ, clay content 30% - 40% and silt 60% - 70%. Sediment transportation along the plume front seems not to be a direct effect on sedimentary formation of the shoals fringing the south coast of the Hangzhou Bay.展开更多
It is of some limitations to analyse residual currents by means of the 25 h anchored current measurements. On the basis of the drift tracking and the mooring system data, here, analyses have been done aiming at the st...It is of some limitations to analyse residual currents by means of the 25 h anchored current measurements. On the basis of the drift tracking and the mooring system data, here, analyses have been done aiming at the structural characteristics and the dynamical mechanisms of the frontal residual current field of the Hangzhou Bay. Especially a theoritical model is given focusing on the frontal density-driven currents. The results indicate that there exists obviously the upper-layer front-driven flow along the orientation of the front during neap tides in the research area of the Hangzhou Bay. But the flow is restrained by the strong vortical viscosity during spring tides. In the lower layer, the effect of the front is little and the subtidal movements are dominated by the tide-induced residual currents. In addition, the influences of wind forcing to the residual current field are also suggested to be important.展开更多
A description is given of the distribution , spacial and temporal variation , mixing and transportation processes about the plume front in the Hangzhou Bay. This front is performed as a group of interfaces among, the ...A description is given of the distribution , spacial and temporal variation , mixing and transportation processes about the plume front in the Hangzhou Bay. This front is performed as a group of interfaces among, the water masses situated in the bay. A discussion is also given of the circulation feature in the frontal zone ence of the front.展开更多
Biogeochemical character of dissolved inorganic nitrogen and phosphate at plume front is studied based on the data, which were observed in the Changjiang River Estuary in 1988. The results are as follows: The concentr...Biogeochemical character of dissolved inorganic nitrogen and phosphate at plume front is studied based on the data, which were observed in the Changjiang River Estuary in 1988. The results are as follows: The concentrations of nitrate and phosphate change abruptly -2+4at plume front and halocline. The concentrations of NO and NH are very high at 10~25 -33-4m depth. The vertical circumfluence transports NO and PO , which are released from organisms at the bottom to phytoplankton.展开更多
For the Pearl River plume, the supercritical, distinct plume front appears in downwelling-favorable winds, which is easily observed due to the distinct boundary between the plume water and the ambient water. In this p...For the Pearl River plume, the supercritical, distinct plume front appears in downwelling-favorable winds, which is easily observed due to the distinct boundary between the plume water and the ambient water. In this paper, in situ and satellite observations of a plume front are utilized to explore the Pearl River plume front properties under the downwelling-favorable winds. Field observations clearly show frontal structure, especially the two-layer structure in the plume water and the downward-motion of water in the frontal region. The Advanced Synthetic Aperture Radar(ASAR) images are also analyzed to unveil the plume front: there is a white stripe on the west side out of the river mouth under downwelling-favorable winds, which is identified as a supercritical plume front, and the width of the plume front is about 250 m. The normalized velocity gradient shows the intense velocity convergence in the front region. Also, analyses of ASAR images imply that the river discharge plays an important role in controlling the location and shape of the front.展开更多
The spatiotemporal characterization of plume sedimentation and microorganisms is critical for developing plume ecological monitoring model.To address the limitations of traditional methods in obtaining high-quality se...The spatiotemporal characterization of plume sedimentation and microorganisms is critical for developing plume ecological monitoring model.To address the limitations of traditional methods in obtaining high-quality sediment,a novel sampling system with 6000 m operational capability and three-month endurance was developed.It is equipped with three sediment samplers,a set of formaldehyde preservation solution injection devices.The system is controlled by a low-power,timing-triggered controllers.To investigate low-disturbance rheological mechanisms,gap controlled rheological tests were conducted to optimize the structural design of the sampling and sealing assembly.Stress-controlled shear rheological tests were employed to investigate the mechanisms governing yield stress in sediments under varying temperature conditions and boundary roughness.Additionally,the coupled Eulerian-Lagrangian(CEL)method and sediment rheological constitutive models were employed to simulate tube-soil interaction dynamics and sediment disturbance.The radial heterogeneity of sediment disturbance and friction variation of the sampling tube were revealed.The tube was completely“plugged”at a penetration depth of 261 mm,providing critical data support to the penetration depth parameters.The deep-sea pressure test and South China Sea field trials demonstrated the system’s capability to collect and preserve quantitative time-series sediment samples with high fidelity.展开更多
The expansion of river plumes is essential for coastal systems and inner-shelf biogeochemical processes.This investigation employs the Coupled Ocean-Atmosphere-Wave-Sediment Transport(COAWST)modeling system to systema...The expansion of river plumes is essential for coastal systems and inner-shelf biogeochemical processes.This investigation employs the Coupled Ocean-Atmosphere-Wave-Sediment Transport(COAWST)modeling system to systematically analyze the governing mechanisms influencing the Changjiang River plume during winter conditions.Model validation through comparison with the observational datasets demonstrates the system’s capability to accurately reproduce hydrodynamic processes and thermohaline variability.A series of sensitivity experiments was implemented to quantify the relative contributions of distinct forcing mechanisms,including tidal dynamics,wind stress,and waveinduced processes on hydrodynamic patterns and associated temperature-salinity distributions.Numerical simulations reveal that wave-induced vertical mixing generates significant nearshore thermal elevation concurrent with salinity reduction.Tidal residual currents exhibit persistent onshore and northward components,potentially facilitating northward advection of the Changjiang River plume during winter months.Conversely,wind-driven currents impose a constraining effect on plume expansion through the establishment of downwelling-favorable circulation patterns.During extreme wave events,wave-driven current contributions to salinity variance account for 30%−90%,relative to tidal mixing effects.These findings collectively establish wave-current interaction as a critical mechanistic component governing wintertime Changjiang River plume dynamics,with particular relevance to stratification modification and cross-shelf transport processes.展开更多
Mantle plumes and surface erosion and sediment deposition affect the modes of continental lithospheric rupturing in extensional tectonic settings,modulating the evolution of rifting margins.However,their relative cont...Mantle plumes and surface erosion and sediment deposition affect the modes of continental lithospheric rupturing in extensional tectonic settings,modulating the evolution of rifting margins.However,their relative contributions to the overall evolution of rifting margins and possible roles in the formation of microcontinent are still elusive.Here,we use coupled geodynamic and surface processes numerical modeling to assess the extent to which surface processes may determine the formation of microcontinent during lithospheric stretching in presence or absence of a mantle plume underneath.Our modeling results indicate that fast extension rates and hillslope(i.e.,diffusion)erosion promote ridge jump events and therefore the formation of microcontinents.On the contrary,efficient fluvial erosion and far-reaching sediment transport(i.e.,stream power erosion)inhibits ridge jump events and the formation of microcontinents.The ridge jump event and overall evolution in our numerical models is consistent with the shift from the Mascarene Ridge to the Carlsberg Ridge that determined the formation of the Seychelles microcontinent.We therefore speculate that hillslope erosion,rather than fluvial erosion,was predominant during the formation of the Seychelles,a possible indication of overall dry local climate conditions.展开更多
The role of mantle plume in the final stages of rifting of the East Gondwana crustal fragments remains equivocal with only limited evidence so far reported from the southern part of Peninsular India.Here,we report for...The role of mantle plume in the final stages of rifting of the East Gondwana crustal fragments remains equivocal with only limited evidence so far reported from the southern part of Peninsular India.Here,we report for the first time a suite of columnar basalts from the Mesoarchean Coorg Block in the Southern Granulite Terrain(SGT)of India and characterize these rocks through field,petrological,geo-chemical,and isotope geochronological studies.The basalts show porphyritic texture with phenocrysts of pyroxene and plagioclase embedded in fine groundmass.Geochemical data reveal tholeiitic flood basalt affinity with affinities of plume-related magmatism.The zircon U-Pb data of the rocks yield a weighted mean age of 137 Ma,thus corresponding to the Valanginian Age of the Early Cretaceous Period.We suggest the possible geochemical affinity of the studied rocks Kerguelen plume basalts which provide new insights into magmatism associated with the final stages of East Gondwana rifting.展开更多
A wide northeast-trending belt of intraplate alkaline volcanism,exhibiting similar geochemical characteristics,stretches from the Eastern Atlantic Ocean to the Cenozoic rift system in Europe.Its formation is associate...A wide northeast-trending belt of intraplate alkaline volcanism,exhibiting similar geochemical characteristics,stretches from the Eastern Atlantic Ocean to the Cenozoic rift system in Europe.Its formation is associated with both passive and active mechanisms,but it remains a source of ongoing debate among geoscientists.Here,we show that seismic whole-mantle tomography models consistently identify two extensive low-velocity anomalies beneath the Canary Islands(CEAA)and Western-Central Europe(ECRA)at mid-mantle depths,merging near the core-mantle boundary.These low-velocity features are interpreted as two connected broad plumes originating from the top of the African LLSVP,likely feeding diapir-like upwellings in the upper mantle.The CEAA rises vertically,whereas the ECRA is tilted and dissipates at mantle transition zone depths,possibly due to the interaction with the cold Alpine subducted slab,which hinders its continuity at shallower depths.While plate-boundary forces are considered the primary drivers of rifting,the hypothesis that deep mantle plumes play a role in generating volcanic activity provides a compelling explanation for the European rift-related alkaline volcanism,supported by geological,geophysical,and geochemical evidence.展开更多
The existing deep-sea sediment plume tests are mostly under small-scale static water and rarely under large-scale flowing water conditions.In this study,large-scale tank experiments of flowing water were designed and ...The existing deep-sea sediment plume tests are mostly under small-scale static water and rarely under large-scale flowing water conditions.In this study,large-scale tank experiments of flowing water were designed and conducted to investigate the morphological characteristics and concentration evolution of the sediment plumes under different discharge rates(Q)and initial sediment concentrations(c).Viscosity tests,resuspension tests and free settling tests of the sediment solution with different c values were performed to reveal the settling mechanism of the plume diffusion process.The results show that the plume diffusion morphology variation in flowing water has four stages and the plume concentration evolution has three stages.The larger the Q,the smaller the initial incidence angle at the discharge outlet,the larger the diffusion range,the poorer the stability and the more complicated the diffusion morphology.The larger the c,the larger the settling velocity,the faster the formation of high-concentration accumulation zone,the better the stability and the clearer the diffusion boundary.The research results could provide experimental data for assessing the impact of deep-sea mining on the ocean environment.展开更多
Hall thrusters with large height-radius ratio,owing to their unique advantages in compactness,lightweight,and high performance,have progressively emerged as a preferred choice for diverse space propulsion applications...Hall thrusters with large height-radius ratio,owing to their unique advantages in compactness,lightweight,and high performance,have progressively emerged as a preferred choice for diverse space propulsion applications in the future.However,the amplification of the annular effect in structures with a large height-radius ratio poses a practical problem of plume over-focusing,which seriously restricts the further improvement of Hall thruster performance and the extension of its life.In this study,the formation mechanism of over-focused plume is deeply investigated,and it is ascertained that an intensified radial electric field directed towards the inner wall within the channel serves as a key contributing factor.This phenomenon is fundamentally attributed to structural characteristics of large height-radius ratio that induce pronounced inward inclination of field lines within strong magnetic field zone.Based on this,the design concept of focused magnetic field is proposed,wherein straight magnetic field lines are established within the strong magnetic field zone to generate a quasi-axial accelerating electric field.Simultaneously,the symmetrical magnetic field inside the channel ensures ionization concentration near the channel center,thereby achieving optimal matching between the ionization zone and accelerating field.Experimental results demonstrate that employing a focused magnetic field significantly reduces the divergence half-angle of the plume and yields an excellently barrel-shaped focusing plume morphology in HEP-1350PM.Consequently,the total efficiency of the thruster surpasses 60%,while erosion belt on the inner wall is shortened by nearly 50%.These advancements effectively enhance thruster performance and prolong its operational lifespan.This study can not only resolve practical problems associated with plume over-focusing,but also provide a fundamental guiding principle for magnetic field design of Hall thrusters.展开更多
The ionic liquid electrospray thruster is a microminiature thruster that can be applied on a micro or nano-satellite,and its highly energy-efficient,compact,modular system can be used for both main propulsion and alti...The ionic liquid electrospray thruster is a microminiature thruster that can be applied on a micro or nano-satellite,and its highly energy-efficient,compact,modular system can be used for both main propulsion and altitude control.In this study,an ionic liquid electrospray thruster with a 100-tip emitter configuration is tested primarily to examine the difference in performance of the thruster at different angles with time-of-flight(TOF)mass spectrometry tests.In the experiment,it was measured that the half-angle of the thruster plume angle emission was in the range of−60 degrees to+65 degrees.Accordingly,the measurement range was set from−50 degrees to+50 degrees,with an interval of 10 degrees.Relative to the results of the 0 degree current curve,the positive mode is relatively homogeneous at all angles of the operating mode.In the negative mode,for n 2 ions,the negative angle region accounts for a larger proportion and the positive angle region accounts for a smaller proportion,which makes a significant difference to the specific impulse of the two regions.The range of the specific impulse at different angles is 3776-4401 s under the typical working condition of+2.5 kV.Under−2.5 kV,the range of the specific impulse at different angles is 3309-4654 s.This research quantifies the angular performance variations of the ionic liquid electrospray thruster,offering valuable data to improve its design and operational reliability for precise propulsion and altitude control in satellite applications.展开更多
Classification of plume and spatter images was studied to evaluate the welding stability. A high-speed camera was used to capture the instantaneous images of plume and spatters during high power disk laser welding. Ch...Classification of plume and spatter images was studied to evaluate the welding stability. A high-speed camera was used to capture the instantaneous images of plume and spatters during high power disk laser welding. Characteristic parameters such as the area and number of spatters, the average grayscale of a spatter image, the entropy of a spatter grayscale image, the coordinate ratio of the plume centroid and the welding point, the polar coordinates of the plume centroid were defined and extracted. Karhunen-Loeve transform method was used to change the seven characteristics into three primary characteristics to reduce the dimensions. Also, K-nearest neighbor method was used to classify the plume and spatter images into two categories such as good and poor welding quality. The results show that plume and spatter have a close relationship with the welding stability, and two categories could be recognized effectively using K-nearest neighbor method based on Karhunen-Loeve transform.展开更多
Aim To investigate the effects of the incident orientation on the microwave attenuation. Methods Attenuation allowing microwave signal transmitting in an oblique or vertical direction through the solid propellant ex...Aim To investigate the effects of the incident orientation on the microwave attenuation. Methods Attenuation allowing microwave signal transmitting in an oblique or vertical direction through the solid propellant exhaust plume was computed, and the experiments were performed utilizing a lab scale solid rocket motor with a fully expanded nozzle. Results The predicted results accord well with the experimental results. Conclusion The microwave attenuation in the oblique path is greater than that in the vertical path.展开更多
An improved near far field divided coupled method was established to investigate the electromagnetic properties of mildly overexpanded and underexpanded rocket exhaust plumes. Firstly, axisymmetric Navier Stokes eq...An improved near far field divided coupled method was established to investigate the electromagnetic properties of mildly overexpanded and underexpanded rocket exhaust plumes. Firstly, axisymmetric Navier Stokes equations incorporated with k ε two equation turbulence models were solved using time dependent approach to calculate the pressure of the near filed. Secondly, parabolized axisymmetric Navier Stokes equations incorporated with finite rate chemical kinetics models were marching on the detailed pressure map of the near field. The termination of the near field would yield the initial line for the far field. In addition, in the far field, the spatial marching method was directly used under the constant pressure condition, but considering more complicated chemically reacting process. Finally, the electromagnetic parameters of the whole plume were calculated with the electron conductive model. The calculated results of the overexpanded and underexpanded rocket exhaust plume were discussed. The predicted microwave attenuation accorded with the experimental results. This improved method is feasible for calculating the microwave attenuation characteristics of mildly non fully expanded rocket exhaust plumes.展开更多
The giant impact hypothesis for the Moon's origin has had difficulty explaining the nearly identical isotopic compositions of Moon rocks and rocks from Earth's silicate mantle and crust.These similarities are ...The giant impact hypothesis for the Moon's origin has had difficulty explaining the nearly identical isotopic compositions of Moon rocks and rocks from Earth's silicate mantle and crust.These similarities are instead more compatible with the Darwin-Wise hypothesis that the Moon arose by fission of a rapidly spinning Earth.To overcome problems with the fission model concerning structural stability and angular momentum conservation,some authors suggested that lunar fission was feasible on a more slowly rotating Earth if assisted by a nuclear explosion near the core-mantle boundary.In this light we consider the possible roles of the large low-velocity provinces(LLVPs).These long-lived structures have been implicated in diverse geophysical processes ranging from deep mantle plumes to continental breakup and mass extinction events.While the LLVPs have been seen as possible remnants of the giant imp actor,we propose that one of them was the site of lunar ejection.Internal heating of the liquid core is suggested to have given rise to an equatorial belt just under the core-mantle boundary analogous to the one recently detected by Ma and Tkalcic[Sci Adv 10(35):eadn5562,2024].Upwellings of heat and volatiles from this belt then generated two antipodal,equatorial bulges:the precursors of the Pacific and African LLVPs.Prior to the emergence of plate tectonics,core heat was mainly dissipated by networks of deep mantle plumes extending above the proto-LLVPs.These plume networks represent conduits of weakened mantle through which proto-lunar materials could later rise in a focused ejection.Continuing heat buildup in the core eventually triggered a cataclysmic explosion in the Pacific proto-LLVP,possibly analogous to a planetary-scale kimberlite eruption.This explosion launched LLVP and overlying mantle material into a low Earth orbit,where it coalesced to form the Moon.Some possible sources of additional energy to power the explosion are considered,including nuclear fission,bolide impacts and a hypothetical gravitational decay process culminating in a'A event'.展开更多
Based on the temporal-spatial distribution and geochemical characteristics,the Emeishan basalts can be divided into two types: high-P_2O-TiO_2 basalt (HPT) andlow-P_2O_5-TiO_2 basalt (LPT), which differ distinctly in ...Based on the temporal-spatial distribution and geochemical characteristics,the Emeishan basalts can be divided into two types: high-P_2O-TiO_2 basalt (HPT) andlow-P_2O_5-TiO_2 basalt (LPT), which differ distinctly in geochemistry: the LPTs are characterizedby relatively high abundances of MgO, total FeO and P_2O_5 and compatible elements (Cr, Ni, Sc), andrelatively low contents of moderately compatible elements (V, Y, Yb, Co), LREE and otherincompatible elements compared with the HPT. On the diagrams of trace element ratios, they areplotted on an approximately linear mixing line between depleted and enriched mantle sources,suggesting that these two types of basalts resulted from interactions of varying degrees betweenmantle plume and lithospheric mantle containing such volatile-rich minerals as amphibole andapatite. The source region of the LPT involves a smaller proportion of lithospheric components,while that of the HTP has a larger proportion of lithospheric components. Trachyte is generated bypartial melting of the basic igneous rocks at the base of the lower continental crust. Both the twotypes of magmas underwent certain crystal fractionation and contamination of the lower crest athigh-level magma chambers and en route to the surface.展开更多
Mineral deposits are unevenly distributed in the Earth's crust, which is closely related to the formation and evolution of the Earth. In the early history of the Earth, controlled by the gravitational contraction ...Mineral deposits are unevenly distributed in the Earth's crust, which is closely related to the formation and evolution of the Earth. In the early history of the Earth, controlled by the gravitational contraction and thermal expansion, lighter elements, such as radioactive, halogen-family, rare and rare earth elements and alkali metals, migrated upwards; whereas heavier elements, such as iron-family and platinum-family elements, base metals and noble metals, had a tendency of sinking to the Earth's core, so that the elements iron, nickel, gold and silver are mainly concentrated in the Earth's core. However, during the formation of the stratified structure of the Earth, the existence of temperature, pressure and viscosity differences inside and outside the Earth resulted in vertical material movement manifested mainly by cascaded evolution of mantle plumes in the Earth. The stratifications and vertical movement of the Earth were interdependent and constituted the motive force of the mantle-core movement. The cascaded evolution of mantle plumes opens the passageways for the migration of deep-seated ore-forming material, and thus elements such as gold and silver concentrated in the core and on the core-mantle boundary migrate as the gaseous state together with the hot material flow of mantle plumes against the gravitational force through the passageways to the lithosphere, then migrate as the mixed gas-liquid state to the near-surface level and finally are concentrated in favorable structural expansion zones, forming mineral deposits. This is possibly the important metallogenic mechanism for gold, silver, lead, zinc, copper and other many elements. Take for example the NE-plunging crown of the Fuping mantle-branch structure, the paper analyzes ductile-brittle shear zone-type gold fields (Weijiayu) at the core of the magmatic-metamorphic complex, principal detachment-type gold fields (Shangmingyu) and hanging-wall cover fissure-vein-type lead-zinc polymetallic ore fields (Lianbaling) and further briefly analyzes the source of ore-forming material and constructs an ore-forming and -controlling model.展开更多
基金This work is supported by both Grant-4860244 from the National Natural Science Foundation of China and Grant-188011 from the Zhejiang Provincial Natural Science Foundation
文摘Sedimentary environments in the Hangzhou Bay are introduced by a three-subregional landform pattern and a sedimentation map with six major sedimentation types. The geographic setting, sediment transportation and sedimentation in different subregions are discussed with sediment grain parameters. Sedimentary basin suffering from effect of plume front can be identified by the fine sediments with median ( Mdφ ) 7φ-8φ, clay content 30% - 40% and silt 60% - 70%. Sediment transportation along the plume front seems not to be a direct effect on sedimentary formation of the shoals fringing the south coast of the Hangzhou Bay.
文摘It is of some limitations to analyse residual currents by means of the 25 h anchored current measurements. On the basis of the drift tracking and the mooring system data, here, analyses have been done aiming at the structural characteristics and the dynamical mechanisms of the frontal residual current field of the Hangzhou Bay. Especially a theoritical model is given focusing on the frontal density-driven currents. The results indicate that there exists obviously the upper-layer front-driven flow along the orientation of the front during neap tides in the research area of the Hangzhou Bay. But the flow is restrained by the strong vortical viscosity during spring tides. In the lower layer, the effect of the front is little and the subtidal movements are dominated by the tide-induced residual currents. In addition, the influences of wind forcing to the residual current field are also suggested to be important.
文摘A description is given of the distribution , spacial and temporal variation , mixing and transportation processes about the plume front in the Hangzhou Bay. This front is performed as a group of interfaces among, the water masses situated in the bay. A discussion is also given of the circulation feature in the frontal zone ence of the front.
基金We wish to thank the National Natural Science Foundation of China which has offerd us the financial support for this research (No: 49736220).
文摘Biogeochemical character of dissolved inorganic nitrogen and phosphate at plume front is studied based on the data, which were observed in the Changjiang River Estuary in 1988. The results are as follows: The concentrations of nitrate and phosphate change abruptly -2+4at plume front and halocline. The concentrations of NO and NH are very high at 10~25 -33-4m depth. The vertical circumfluence transports NO and PO , which are released from organisms at the bottom to phytoplankton.
基金supported by the National Natural Science Foundation of China(Grant Nos.41476002 and 41206164)the Natural Science Foundation of Shandong Province(Grant No.ZR2014DQ013)+1 种基金State Key Laboratory of Tropical Oceanography,South China Sea Institute of Oceanology,Chinese Academy of Sciences(Grant No.LTO1409)China Postdoctoral Science Foundation(Grant No.2014M560574)
文摘For the Pearl River plume, the supercritical, distinct plume front appears in downwelling-favorable winds, which is easily observed due to the distinct boundary between the plume water and the ambient water. In this paper, in situ and satellite observations of a plume front are utilized to explore the Pearl River plume front properties under the downwelling-favorable winds. Field observations clearly show frontal structure, especially the two-layer structure in the plume water and the downward-motion of water in the frontal region. The Advanced Synthetic Aperture Radar(ASAR) images are also analyzed to unveil the plume front: there is a white stripe on the west side out of the river mouth under downwelling-favorable winds, which is identified as a supercritical plume front, and the width of the plume front is about 250 m. The normalized velocity gradient shows the intense velocity convergence in the front region. Also, analyses of ASAR images imply that the river discharge plays an important role in controlling the location and shape of the front.
基金supported by the National Key R&D Program of China(No.2022YFC2803900)the National Natural Science Foundation of China(No.42276191)Zhejiang University Students Science and Technology Innovation Activity Plan(New Talent Plan)(No.2024R401185).
文摘The spatiotemporal characterization of plume sedimentation and microorganisms is critical for developing plume ecological monitoring model.To address the limitations of traditional methods in obtaining high-quality sediment,a novel sampling system with 6000 m operational capability and three-month endurance was developed.It is equipped with three sediment samplers,a set of formaldehyde preservation solution injection devices.The system is controlled by a low-power,timing-triggered controllers.To investigate low-disturbance rheological mechanisms,gap controlled rheological tests were conducted to optimize the structural design of the sampling and sealing assembly.Stress-controlled shear rheological tests were employed to investigate the mechanisms governing yield stress in sediments under varying temperature conditions and boundary roughness.Additionally,the coupled Eulerian-Lagrangian(CEL)method and sediment rheological constitutive models were employed to simulate tube-soil interaction dynamics and sediment disturbance.The radial heterogeneity of sediment disturbance and friction variation of the sampling tube were revealed.The tube was completely“plugged”at a penetration depth of 261 mm,providing critical data support to the penetration depth parameters.The deep-sea pressure test and South China Sea field trials demonstrated the system’s capability to collect and preserve quantitative time-series sediment samples with high fidelity.
基金The Strategic Priority Research Program of the Chinese Academy of Sciences under contract No.XDC0190102the National Key Research and Development Program of China under contract No.2022YFC3105005the Guangdong Key Project under contract No.2019BT02H594.
文摘The expansion of river plumes is essential for coastal systems and inner-shelf biogeochemical processes.This investigation employs the Coupled Ocean-Atmosphere-Wave-Sediment Transport(COAWST)modeling system to systematically analyze the governing mechanisms influencing the Changjiang River plume during winter conditions.Model validation through comparison with the observational datasets demonstrates the system’s capability to accurately reproduce hydrodynamic processes and thermohaline variability.A series of sensitivity experiments was implemented to quantify the relative contributions of distinct forcing mechanisms,including tidal dynamics,wind stress,and waveinduced processes on hydrodynamic patterns and associated temperature-salinity distributions.Numerical simulations reveal that wave-induced vertical mixing generates significant nearshore thermal elevation concurrent with salinity reduction.Tidal residual currents exhibit persistent onshore and northward components,potentially facilitating northward advection of the Changjiang River plume during winter months.Conversely,wind-driven currents impose a constraining effect on plume expansion through the establishment of downwelling-favorable circulation patterns.During extreme wave events,wave-driven current contributions to salinity variance account for 30%−90%,relative to tidal mixing effects.These findings collectively establish wave-current interaction as a critical mechanistic component governing wintertime Changjiang River plume dynamics,with particular relevance to stratification modification and cross-shelf transport processes.
基金financially supported by the National Science Foundation of China(No.41920104010)the China Postdoctoral Science Foundation(No.2024M762767)+3 种基金the Fundamental Research Funds for the Central University,CHD(No.300102264104)by the Postdoctoral Fellowship Program of CPSF(No.GZC20241444)supported by Fondazione Cariplo and Fondazione CDP(No.2022-1546_001)by the Italian Ministry of Education,MUR(Project Dipartimenti di Eccellenza,TECLA,Department of Earth and Environmental Sciences,University of Milano-Bicocca)。
文摘Mantle plumes and surface erosion and sediment deposition affect the modes of continental lithospheric rupturing in extensional tectonic settings,modulating the evolution of rifting margins.However,their relative contributions to the overall evolution of rifting margins and possible roles in the formation of microcontinent are still elusive.Here,we use coupled geodynamic and surface processes numerical modeling to assess the extent to which surface processes may determine the formation of microcontinent during lithospheric stretching in presence or absence of a mantle plume underneath.Our modeling results indicate that fast extension rates and hillslope(i.e.,diffusion)erosion promote ridge jump events and therefore the formation of microcontinents.On the contrary,efficient fluvial erosion and far-reaching sediment transport(i.e.,stream power erosion)inhibits ridge jump events and the formation of microcontinents.The ridge jump event and overall evolution in our numerical models is consistent with the shift from the Mascarene Ridge to the Carlsberg Ridge that determined the formation of the Seychelles microcontinent.We therefore speculate that hillslope erosion,rather than fluvial erosion,was predominant during the formation of the Seychelles,a possible indication of overall dry local climate conditions.
基金supported by the“Startup Grant for the University Teachers”of the University of Kerala.
文摘The role of mantle plume in the final stages of rifting of the East Gondwana crustal fragments remains equivocal with only limited evidence so far reported from the southern part of Peninsular India.Here,we report for the first time a suite of columnar basalts from the Mesoarchean Coorg Block in the Southern Granulite Terrain(SGT)of India and characterize these rocks through field,petrological,geo-chemical,and isotope geochronological studies.The basalts show porphyritic texture with phenocrysts of pyroxene and plagioclase embedded in fine groundmass.Geochemical data reveal tholeiitic flood basalt affinity with affinities of plume-related magmatism.The zircon U-Pb data of the rocks yield a weighted mean age of 137 Ma,thus corresponding to the Valanginian Age of the Early Cretaceous Period.We suggest the possible geochemical affinity of the studied rocks Kerguelen plume basalts which provide new insights into magmatism associated with the final stages of East Gondwana rifting.
基金supported by grant D86-RALMI23CIVIE_01 awarded by the Italian Ministry of University and Research under the Program for Young Researchers“Rita Levi Montalcini”.
文摘A wide northeast-trending belt of intraplate alkaline volcanism,exhibiting similar geochemical characteristics,stretches from the Eastern Atlantic Ocean to the Cenozoic rift system in Europe.Its formation is associated with both passive and active mechanisms,but it remains a source of ongoing debate among geoscientists.Here,we show that seismic whole-mantle tomography models consistently identify two extensive low-velocity anomalies beneath the Canary Islands(CEAA)and Western-Central Europe(ECRA)at mid-mantle depths,merging near the core-mantle boundary.These low-velocity features are interpreted as two connected broad plumes originating from the top of the African LLSVP,likely feeding diapir-like upwellings in the upper mantle.The CEAA rises vertically,whereas the ECRA is tilted and dissipates at mantle transition zone depths,possibly due to the interaction with the cold Alpine subducted slab,which hinders its continuity at shallower depths.While plate-boundary forces are considered the primary drivers of rifting,the hypothesis that deep mantle plumes play a role in generating volcanic activity provides a compelling explanation for the European rift-related alkaline volcanism,supported by geological,geophysical,and geochemical evidence.
基金supported by the Major Project of Hunan Natural Science Foundation,China(No.2021JC0010)the National Natural Science Foundation of China(No.51274251)。
文摘The existing deep-sea sediment plume tests are mostly under small-scale static water and rarely under large-scale flowing water conditions.In this study,large-scale tank experiments of flowing water were designed and conducted to investigate the morphological characteristics and concentration evolution of the sediment plumes under different discharge rates(Q)and initial sediment concentrations(c).Viscosity tests,resuspension tests and free settling tests of the sediment solution with different c values were performed to reveal the settling mechanism of the plume diffusion process.The results show that the plume diffusion morphology variation in flowing water has four stages and the plume concentration evolution has three stages.The larger the Q,the smaller the initial incidence angle at the discharge outlet,the larger the diffusion range,the poorer the stability and the more complicated the diffusion morphology.The larger the c,the larger the settling velocity,the faster the formation of high-concentration accumulation zone,the better the stability and the clearer the diffusion boundary.The research results could provide experimental data for assessing the impact of deep-sea mining on the ocean environment.
基金financial support from the National Key R&D Program of China(No.2022YFE0204100)the National Natural Science Foundation of China(Nos.U23B20152 and 52402479)。
文摘Hall thrusters with large height-radius ratio,owing to their unique advantages in compactness,lightweight,and high performance,have progressively emerged as a preferred choice for diverse space propulsion applications in the future.However,the amplification of the annular effect in structures with a large height-radius ratio poses a practical problem of plume over-focusing,which seriously restricts the further improvement of Hall thruster performance and the extension of its life.In this study,the formation mechanism of over-focused plume is deeply investigated,and it is ascertained that an intensified radial electric field directed towards the inner wall within the channel serves as a key contributing factor.This phenomenon is fundamentally attributed to structural characteristics of large height-radius ratio that induce pronounced inward inclination of field lines within strong magnetic field zone.Based on this,the design concept of focused magnetic field is proposed,wherein straight magnetic field lines are established within the strong magnetic field zone to generate a quasi-axial accelerating electric field.Simultaneously,the symmetrical magnetic field inside the channel ensures ionization concentration near the channel center,thereby achieving optimal matching between the ionization zone and accelerating field.Experimental results demonstrate that employing a focused magnetic field significantly reduces the divergence half-angle of the plume and yields an excellently barrel-shaped focusing plume morphology in HEP-1350PM.Consequently,the total efficiency of the thruster surpasses 60%,while erosion belt on the inner wall is shortened by nearly 50%.These advancements effectively enhance thruster performance and prolong its operational lifespan.This study can not only resolve practical problems associated with plume over-focusing,but also provide a fundamental guiding principle for magnetic field design of Hall thrusters.
基金supported by the National Key R&D Program of China(Nos.2020YFC2201103 and 2022YFB4601300)National Natural Science Foundation of China(No.U22B20120)+1 种基金the Program of Beijing Engineering Research Center of Efficient and Green Aerospace Propulsion Technology(No.LabASP-2024-09)the Beijing Institute of Technology Research Fund Program for Young Scholars.
文摘The ionic liquid electrospray thruster is a microminiature thruster that can be applied on a micro or nano-satellite,and its highly energy-efficient,compact,modular system can be used for both main propulsion and altitude control.In this study,an ionic liquid electrospray thruster with a 100-tip emitter configuration is tested primarily to examine the difference in performance of the thruster at different angles with time-of-flight(TOF)mass spectrometry tests.In the experiment,it was measured that the half-angle of the thruster plume angle emission was in the range of−60 degrees to+65 degrees.Accordingly,the measurement range was set from−50 degrees to+50 degrees,with an interval of 10 degrees.Relative to the results of the 0 degree current curve,the positive mode is relatively homogeneous at all angles of the operating mode.In the negative mode,for n 2 ions,the negative angle region accounts for a larger proportion and the positive angle region accounts for a smaller proportion,which makes a significant difference to the specific impulse of the two regions.The range of the specific impulse at different angles is 3776-4401 s under the typical working condition of+2.5 kV.Under−2.5 kV,the range of the specific impulse at different angles is 3309-4654 s.This research quantifies the angular performance variations of the ionic liquid electrospray thruster,offering valuable data to improve its design and operational reliability for precise propulsion and altitude control in satellite applications.
基金Project (51175095) supported by the National Natural Science Foundation of ChinaProjects (10251009001000001,9151009001000020) supported by the Natural Science Foundation of Guangdong Province,ChinaProject (20104420110001) supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China
文摘Classification of plume and spatter images was studied to evaluate the welding stability. A high-speed camera was used to capture the instantaneous images of plume and spatters during high power disk laser welding. Characteristic parameters such as the area and number of spatters, the average grayscale of a spatter image, the entropy of a spatter grayscale image, the coordinate ratio of the plume centroid and the welding point, the polar coordinates of the plume centroid were defined and extracted. Karhunen-Loeve transform method was used to change the seven characteristics into three primary characteristics to reduce the dimensions. Also, K-nearest neighbor method was used to classify the plume and spatter images into two categories such as good and poor welding quality. The results show that plume and spatter have a close relationship with the welding stability, and two categories could be recognized effectively using K-nearest neighbor method based on Karhunen-Loeve transform.
文摘Aim To investigate the effects of the incident orientation on the microwave attenuation. Methods Attenuation allowing microwave signal transmitting in an oblique or vertical direction through the solid propellant exhaust plume was computed, and the experiments were performed utilizing a lab scale solid rocket motor with a fully expanded nozzle. Results The predicted results accord well with the experimental results. Conclusion The microwave attenuation in the oblique path is greater than that in the vertical path.
文摘An improved near far field divided coupled method was established to investigate the electromagnetic properties of mildly overexpanded and underexpanded rocket exhaust plumes. Firstly, axisymmetric Navier Stokes equations incorporated with k ε two equation turbulence models were solved using time dependent approach to calculate the pressure of the near filed. Secondly, parabolized axisymmetric Navier Stokes equations incorporated with finite rate chemical kinetics models were marching on the detailed pressure map of the near field. The termination of the near field would yield the initial line for the far field. In addition, in the far field, the spatial marching method was directly used under the constant pressure condition, but considering more complicated chemically reacting process. Finally, the electromagnetic parameters of the whole plume were calculated with the electron conductive model. The calculated results of the overexpanded and underexpanded rocket exhaust plume were discussed. The predicted microwave attenuation accorded with the experimental results. This improved method is feasible for calculating the microwave attenuation characteristics of mildly non fully expanded rocket exhaust plumes.
文摘The giant impact hypothesis for the Moon's origin has had difficulty explaining the nearly identical isotopic compositions of Moon rocks and rocks from Earth's silicate mantle and crust.These similarities are instead more compatible with the Darwin-Wise hypothesis that the Moon arose by fission of a rapidly spinning Earth.To overcome problems with the fission model concerning structural stability and angular momentum conservation,some authors suggested that lunar fission was feasible on a more slowly rotating Earth if assisted by a nuclear explosion near the core-mantle boundary.In this light we consider the possible roles of the large low-velocity provinces(LLVPs).These long-lived structures have been implicated in diverse geophysical processes ranging from deep mantle plumes to continental breakup and mass extinction events.While the LLVPs have been seen as possible remnants of the giant imp actor,we propose that one of them was the site of lunar ejection.Internal heating of the liquid core is suggested to have given rise to an equatorial belt just under the core-mantle boundary analogous to the one recently detected by Ma and Tkalcic[Sci Adv 10(35):eadn5562,2024].Upwellings of heat and volatiles from this belt then generated two antipodal,equatorial bulges:the precursors of the Pacific and African LLVPs.Prior to the emergence of plate tectonics,core heat was mainly dissipated by networks of deep mantle plumes extending above the proto-LLVPs.These plume networks represent conduits of weakened mantle through which proto-lunar materials could later rise in a focused ejection.Continuing heat buildup in the core eventually triggered a cataclysmic explosion in the Pacific proto-LLVP,possibly analogous to a planetary-scale kimberlite eruption.This explosion launched LLVP and overlying mantle material into a low Earth orbit,where it coalesced to form the Moon.Some possible sources of additional energy to power the explosion are considered,including nuclear fission,bolide impacts and a hypothetical gravitational decay process culminating in a'A event'.
文摘Based on the temporal-spatial distribution and geochemical characteristics,the Emeishan basalts can be divided into two types: high-P_2O-TiO_2 basalt (HPT) andlow-P_2O_5-TiO_2 basalt (LPT), which differ distinctly in geochemistry: the LPTs are characterizedby relatively high abundances of MgO, total FeO and P_2O_5 and compatible elements (Cr, Ni, Sc), andrelatively low contents of moderately compatible elements (V, Y, Yb, Co), LREE and otherincompatible elements compared with the HPT. On the diagrams of trace element ratios, they areplotted on an approximately linear mixing line between depleted and enriched mantle sources,suggesting that these two types of basalts resulted from interactions of varying degrees betweenmantle plume and lithospheric mantle containing such volatile-rich minerals as amphibole andapatite. The source region of the LPT involves a smaller proportion of lithospheric components,while that of the HTP has a larger proportion of lithospheric components. Trachyte is generated bypartial melting of the basic igneous rocks at the base of the lower continental crust. Both the twotypes of magmas underwent certain crystal fractionation and contamination of the lower crest athigh-level magma chambers and en route to the surface.
基金This research was performed as part of the project supported by the National Natural Science Foundation of China(grant 40272088)Knowledge Innovation Project of the Chinese Academy of Sciences(KZCX1-07)the Program of Financially Aiding Backbone Teachers Working in Colleges and Universities(J-00-25).
文摘Mineral deposits are unevenly distributed in the Earth's crust, which is closely related to the formation and evolution of the Earth. In the early history of the Earth, controlled by the gravitational contraction and thermal expansion, lighter elements, such as radioactive, halogen-family, rare and rare earth elements and alkali metals, migrated upwards; whereas heavier elements, such as iron-family and platinum-family elements, base metals and noble metals, had a tendency of sinking to the Earth's core, so that the elements iron, nickel, gold and silver are mainly concentrated in the Earth's core. However, during the formation of the stratified structure of the Earth, the existence of temperature, pressure and viscosity differences inside and outside the Earth resulted in vertical material movement manifested mainly by cascaded evolution of mantle plumes in the Earth. The stratifications and vertical movement of the Earth were interdependent and constituted the motive force of the mantle-core movement. The cascaded evolution of mantle plumes opens the passageways for the migration of deep-seated ore-forming material, and thus elements such as gold and silver concentrated in the core and on the core-mantle boundary migrate as the gaseous state together with the hot material flow of mantle plumes against the gravitational force through the passageways to the lithosphere, then migrate as the mixed gas-liquid state to the near-surface level and finally are concentrated in favorable structural expansion zones, forming mineral deposits. This is possibly the important metallogenic mechanism for gold, silver, lead, zinc, copper and other many elements. Take for example the NE-plunging crown of the Fuping mantle-branch structure, the paper analyzes ductile-brittle shear zone-type gold fields (Weijiayu) at the core of the magmatic-metamorphic complex, principal detachment-type gold fields (Shangmingyu) and hanging-wall cover fissure-vein-type lead-zinc polymetallic ore fields (Lianbaling) and further briefly analyzes the source of ore-forming material and constructs an ore-forming and -controlling model.
