Through microscopic analyses(e.g.,organic macerals,thin section observation,scanning electron microscope(SEM)imaging of fresh bedding planes via argon ion milling,and energy spectrum tests)combined with Rock-Eval anal...Through microscopic analyses(e.g.,organic macerals,thin section observation,scanning electron microscope(SEM)imaging of fresh bedding planes via argon ion milling,and energy spectrum tests)combined with Rock-Eval analyses,this study systematically investigated the organic matter and pyrites in the continental shales in the 3^(rd)submember of the Chang 7 Member(Chang 7^(3)submember)in the Yanchang Formation,Ordos Basin and determined their types and the formation and evolutionary characteristics.The results are as follows.The organic matter of the continental shales in the Chang 7^(3)submember is dominated by amorphous bituminites and migrabitumens,which have come into being since the early diagenetic stage and middle diagenetic stage A,respectively.The formation and transformation of organic matter is a prerequisite for the formation of pyrites.The Ordos Basin was a continental freshwater lacustrine basin and lacked sulphates in waters during the deposition of the Chang 7 Member.Therefore,the syndiagenetic stage did not witness the formation of large quantities of pyrites.Since the basin entered early diagenetic stage A,large quantities of sulfur ions were released as the primary organic matter got converted into bituminites and,accordingly,pyrites started to form.However,this stage featured poorer fluid and spatial conditions compared with the syndepositional stage due to withdraw of water,the partial formation of bituminites,and a certain degree of compaction.As a result,large quantities of pyrrhotite failed to transition into typical spherical framboidal pyrites but grew into euhedral monocrystal aggregates.In addition,pyrites are still visible in the migrabitumens in both microfractures and inorganic pores of mudstones and shales,indicating that the pyrite formation period can extend until the middle diagenetic stage A.展开更多
Objective The Susong complex zone（SCZ）is a relatively lowgrade metamorphic unit mostly with an epidoteamphibolite facies,located in the southernmost part of the Dabie orogen.However,its rock compositions,ages,
The Oligocene Huagang Formation is the main sandstone reservoir in the Xihu Sag, situated in the east of the East China Sea Shelf Basin. With an integrated approach of thin-section petrography, ultra-violet fluorescen...The Oligocene Huagang Formation is the main sandstone reservoir in the Xihu Sag, situated in the east of the East China Sea Shelf Basin. With an integrated approach of thin-section petrography, ultra-violet fluorescence microscopy, scanning electron microscopy, and isotope geochemistry, the different diagenetic features were identified, the typical diagenetic parasequences were established, and the diagenetic fluids evolution history were reconstructed for the Oligocene Huagang Formation sandstone reservoir in the south of Xihu Sag. The Huagang Formation sandstone reservoir is now in Period B of the mesodiagenesis, which has undergone significant diagenetic alterations such as mechanical compaction, Pore-lining chlorite cement, feldspar dissolution, quartz cementation and dissolution, and carbonate cementation. Three types of carbonate cements（early siderite,medium ferrocalcite and late ankerite） were identified in the Huagang Formation sandstone reservoir. The carbon and oxygen isotopic compositions of carbonate cements show that the early calcite precipitate from alkaline lacustrine environment whereas the late carbonate cements were closely related to the organic acids. To the Huagang Formation sandstone reservoir, it has experienced two main episodes of dissolution during diagenesis.The early dissolution is that unstable components such as feldspar, lithic fragments, and carbonate cement were dissolved by acidic water. The second dissolution is that quartz and other silicate minerals were dissolved under the alkaline condition. Two main phases of hydrocarbon charging occurred in this study area. The first hydrocarbon emplacement was prior to the medium carbonate cementation but posterior to feldspar dissolution and the onset of quartz cementation at the end of the Miocene. The second hydrocarbon charging occurred in the Quaternary period after the late carbonate precipitation.展开更多
The surface morphology, cross-sections, and joint break force（JBF） of joints welded under different electrode forces were studied. The defects, such as electrode sticking, notch, and excessive expulsions, were obser...The surface morphology, cross-sections, and joint break force（JBF） of joints welded under different electrode forces were studied. The defects, such as electrode sticking, notch, and excessive expulsions, were observed in the joints. No desirable joints were achieved with the consideration of weld geometries and joint performances. From the cross-sectional morphology, the joint evolution during the RMW of Pt alloy and 316 LVM SS wires was developed, which involved cold collapse and heat promoted set-down of Pt alloy wire, unbalanced heating at interface, molten phase squeezed out, and defect formation. Finally, the defect formation was also discussed.展开更多
Accurate measurements of stellar metallicity gradients in the radial and vertical directions of the disk and their temporal variations provide important constraints on the formation and evolution of the Milky Way disk...Accurate measurements of stellar metallicity gradients in the radial and vertical directions of the disk and their temporal variations provide important constraints on the formation and evolution of the Milky Way disk. We use 297 042 main sequence turn-off stars selected from the LAMOST Spectroscopic Survey of the Galactic Anticenter（LSS-GAC） to determine the radial and vertical gradients of stellar metallicity,△[Fe/H]/△R and △[Fe/H]/△｜Z ｜ of the Milky Way disk in the direction of the anticenter. We determine ages of those turn-off stars by isochrone fitting and measure the temporal variations of metallicity gradients. We have carried out a detailed analysis of the selection effects resulting from the selection, observation and data reduction of LSS-GAC targets and the potential biases of a magnitude limited sample on the determinations of metallicity gradients. Our results show that the gradients, both in the radial and vertical directions, exhibit significant spatial and temporal variations. The radial gradients yielded by stars with the oldest ages（ 11 Gyr） are essentially zero at all heights from the disk midplane, while those given by younger stars are always negative. The vertical gradients deduced from stars with the oldest ages（ 11 Gyr）are negative and only show very weak variations with Galactocentric distance in the disk plane, R, while those yielded by younger stars show strong variations with R.After being essentially flat at the earliest epochs of disk formation, the radial gradients steepen as age decreases, reaching a maximum（steepest） at age 7–8 Gyr, and then they flatten again. Similar temporal trends are also found for the vertical gradients. We infer that the assembly of the Milky Way disk may have experienced at least two distinct phases. The earlier phase is probably related to a slow, pressure-supported collapse of gas, when the gas settles down to the disk mainly in the vertical direction. In the later phase, there are significant radial flows of gas in the disk, and the rate of gas inflow near the solar neighborhood reaches a maximum around a lookback time of 7–8 Gyr.The transition between the two phases occurs around a lookback time between 8 and11 Gyr. The two phases may be responsible for the formation of the Milky Way＇s thick and thin disks, respectively. Also, as a consequence, we recommend that stellar age is a natural, physical criterion to distinguish stars from the thin and thick disks. From an epoch earlier than 11 Gyr to one between 8 and 11 Gyr, there is an abrupt, significant change in magnitude of both the radial and vertical metallicity gradients, suggesting that stellar radial migration is unlikely to play an important role in the formation of the thick disk.展开更多
On the basis of the historical profile observations and the recent Kuroshio observations,the yearly formation,development and decay of the high density water found between 50 to 100 m isobath over the middle and south...On the basis of the historical profile observations and the recent Kuroshio observations,the yearly formation,development and decay of the high density water found between 50 to 100 m isobath over the middle and southern East China Sea continental shelf are anyalysed. The formation of this high density water occurs between November and March of the following year. A possible reason for it is that as the mixed water between the coastal water and the outer sea water transports northward by the Taiwan Warm Current, its density increases by surface cooling. It also mixes with the neighbouring lower density water masses. The transportation and decay of the high density water through April to July are also descussed. They can be ascribed to the seasonal surface layer warming and the fast development of Taiwan Warm Current. The high density water disappears in August.展开更多
Rock–soil aggregate landslides(RSALs) are a common geological hazard in deeply incised valleys in southwestern China. Large-scale RSALs are widely distributed in the upper reaches of the Dadu River, Danba County, Sic...Rock–soil aggregate landslides(RSALs) are a common geological hazard in deeply incised valleys in southwestern China. Large-scale RSALs are widely distributed in the upper reaches of the Dadu River, Danba County, Sichuan Province, and are influenced by slope structure, which can be divided into open, lock, strip, and dumbbell types, as well as soil type and meso-structure, which can be classified as layered rock–soil aggregate, block-soil, and grainsoil. In this study, the evolution of four types of structures, such as layered-dumbbell, block-soil lock, banded block-soil, and block-soil open types, were analyzed by field surveys, surface and deep displacement monitoring, and Flac3 D. It was found that the Danba reach of the Dadu River showed incised valley through the evolution from wide to slow valley affected by internal and external geological processes since the Quaternary Glaciation. In the layered-dumbbell rock–soil aggregate, the main sliding pattern is multi-stage sliding at different depths. Circular sliding in the trailing edge and plane sliding along the bedrock in the front edge body occurin the block-soil-lock type aggregate. Large-scale multi-level and circular sliding over long distances occur in the banded block-soil aggregate. The blocksoil open type is stable, with only circular sliding occurring in local and shallow surfaces of the body. The monitoring and numerical simulation results further show that slope structure and regularity have diversified with RSALs. The results provide a basis for analyzing the stability mechanism of RSALs and preventing RSALs in deeply incised valleys.展开更多
In order to control the CaO-Al;O;-SiO;-MgO system inclusions in 50 CrVA spring steel in a lower melting temperature region,high temperature equilibrium experiments between steel and slag were performed in the laborato...In order to control the CaO-Al;O;-SiO;-MgO system inclusions in 50 CrVA spring steel in a lower melting temperature region,high temperature equilibrium experiments between steel and slag were performed in the laboratory,under the conditions of the initial slag basicity within 3-7and the content of Al;O;between 18-35mass%,to investigate the formation and evolution of this type of inclusion.The results indicate that the total oxygen content in the steel decreases with the increase of slag basicity and the decrease of Al;O;content in slags,and CaO-Al;O;-SiO2-MgO inclusions tend to deviate from the low melting point region with the increase of Al;O;content in slags.The most favorable composition for the refining slag is composed of 51-56mass% CaO,9-13mass% SiO;,20-25mass% Al;O;and 6mass% MgO.In this case,the inclusions in 50 CrVA spring steel are mostly in the low melting point regions,in which their plasticities are expected to improve during steel rolling.The MgO-based inclusions were observed in the steel matrix and the formation mechanism was theoretically and schematically revealed.It is also found that adding around 11mass% of MgO into the refining slags is beneficial to reducing the refractory corrosion.Further work should be carried out focusing on the evolution rates of MgO-based inclusions.展开更多
To investigate the formation mechanism of calcium hexaluminate（CaAl_（12）O_（19）, CA_6）, the analytically pure alumina and calcia used as raw materials were mixed in CaO/Al_2O_3 ratio of 12.57：137.43 by mass. The...To investigate the formation mechanism of calcium hexaluminate（CaAl_（12）O_（19）, CA_6）, the analytically pure alumina and calcia used as raw materials were mixed in CaO/Al_2O_3 ratio of 12.57：137.43 by mass. The raw materials were ball-milled and shaped into green specimens, and fired at 1300-1600°C. Then, the phase composition and microstructure evolution of the fired specimen were studied, and a first principle calculation was performed. The results show that in the reaction system of CaO and Al_2O_3, a small amount of CA_6 forms at 1300°C, and greater amounts are formed at 1400°C and higher temperatures. The reaction is as follows： CaO ·2Al_2O_3（CA_2） ＋ 4Al_2O_3 → CA_6. The diffusions of Ca^（2＋） in CA_2 towards Al_2O_3 and Al^（3＋） in Al_2O_3 towards CA_2 change the structures in different degrees of difficulty. Compared with the difficulty of structural change and the corresponding lattice energy change, it is deduced that the main formation mechanism is the diffusion of Ca^（2＋） in CA_2 towards Al_2O_3.展开更多
We compile a new sample of 89 open clusters with ages, distances and metallicities available. We derive a radial iron gradient of about -0.099±0.008 dex kpc^(-1) (unweighted) for the whole sample, which is somewh...We compile a new sample of 89 open clusters with ages, distances and metallicities available. We derive a radial iron gradient of about -0.099±0.008 dex kpc^(-1) (unweighted) for the whole sample, which is somewhat greater than the most recent determination of oxygen gradient from nebulae and young stars. By dividing the clusters into age groups, we show that the iron gradient was steeper in the past and has evolved slowly in time. Current data show a substantial scatter of the cluster metallicities indicating that the Galactic disk has undergone a very rapid, inhomogeneous enrichment. Also, based on a simple, but quite successful model of chemical evolution of the Milky Way disk, we make a detailed calculation of the iron abundance gradient and its time evolution. The predicted current iron gradient is about -0.072 dex kpc^(-1). The model also predicts a steady flattening of the iron gradient with time, which agrees with the result from our open cluster sample.展开更多
Understanding galaxy formation is one of the most pressing issues in cos- mology. We review the current status of galaxy formation from both an observational and a theoretical perspective, and summarize the prospects ...Understanding galaxy formation is one of the most pressing issues in cos- mology. We review the current status of galaxy formation from both an observational and a theoretical perspective, and summarize the prospects for future advances.展开更多
Taking the inter-salt organic-rich shales in the third member of Paleogene Shahejie Formation(Es3)of Dongpu sag in Bohai Bay Basin as an example,the origin of overpressure,development characteristics,formation and evo...Taking the inter-salt organic-rich shales in the third member of Paleogene Shahejie Formation(Es3)of Dongpu sag in Bohai Bay Basin as an example,the origin of overpressure,development characteristics,formation and evolution mechanism,formation stages and geological significance on shale oil and gas of overpressure fractures in the inter-salt shale reservoir were investigated by means of thin section identification,scanning electron microscopy observation,analysis of fluid inclusions,logging data analysis,and formation pressure inversion.The results show that overpressure is universal in the salt-lake basin of Dongpu sag,and under-compaction caused by the sealing of salt-gypsum layer,pressurization due to hydrocarbon generation,transformation and dehydration of clay minerals,and fault sealing are the 4 main factors leading to the occurrence of overpressure.The overpressure fractures are small in scale,with an average length of 356.2μm and an average underground opening of 11.6μm.But they are densely developed,with an average surface density of 0.76 cm/cm2.Moreover,they are often accompanied by oil and gas charging,and thus high in effectiveness.Overpressure fractures were mainly formed during two periods of large-scale oil and gas charging,approximately 25-30 Ma ago and 0-5 Ma ago.Inter-salt overpressure fractures play dual roles as the storage space and migration paths of shale oil and gas.They contribute 22.3%to the porosity of shale reservoir and 51.4%to the permeability.They can connect fracture systems of multiple scales,greatly improving the quality of shale reservoir.During the development of shale oil and gas,inter-salt overpressure fractures can affect the extension and morphology of hydraulic fractures,giving rise to complex and highly permeable volumetric fracture networks,improving hydraulic fracturing effect and enhancing shale oil and gas productivity.展开更多
In this paper,the type,vertical evolution,and distribution pattern of sedimentary facies of the Paleogene Dainan Formation in the Gaoyou Depression of the North Jiangsu Basin are studied in detail.Results show that fa...In this paper,the type,vertical evolution,and distribution pattern of sedimentary facies of the Paleogene Dainan Formation in the Gaoyou Depression of the North Jiangsu Basin are studied in detail.Results show that fan delta,delta,nearshore subaqueous fan,and lacustrine facies developed during the Dainan Formation period and their distribution pattern was mainly controlled by tectonics and paleogeography.The fan delta and nearshore subaqueous fan facies predominantly occur in the southern steep slope region where fault-induced subsidence is thought to have created substantial accommodation,whereas the delta facies are distributed on the northern gentle slope which is thought to have experienced less subsidence.Finally,the lacustrine facies is shown to have developed in the center of the depression,as well as on the flanks of the fan delta,delta,and nearshore subaqueous fan facies.Vertically,the Dainan Formation represents an integrated transgressiveregressive cycle,with the E2d1being the transgressive sequence and the E2d2being the regressive sequence.This distribution model of sedimentary facies plays an important role in predicting favorable reservoir belts for the Dainan Formation in the Gaoyou Depression and similar areas.In the Gaoyou Depression,sandstones of the subaqueous distributary channels in the fan delta and the subaqueous branch channels in the delta are characterized by physical properties favorable for reservoir formation.展开更多
Various types of paleo-uplifts with different characteristics are developed in the Tarim Basin.Previously,there were multiple opinions on the pale-uplifts origins and structural evolution,so the oil and gas exploratio...Various types of paleo-uplifts with different characteristics are developed in the Tarim Basin.Previously,there were multiple opinions on the pale-uplifts origins and structural evolution,so the oil and gas exploration ideas and deployment in the Tarim Basin were not developed smoothly.In this paper,regional seismic interpretation and structural analysis were carried out on the deep marine carbonate rocks in this basin based on the new seismic and drilling data.Then combined with the structural denudation results,the paleo-structural frameworks were reconstructed.And finally,the formation stage and main controlling factors of paleo-uplifts were discussed.It is shown that the Middle Ordovician is the key period when regional extension was converted to compression in this basin,so stratigraphic,sedimentary and structural differences occurred.Before the deposition of Yijianfang Fm in late Middle Ordovician,three carbonate paleo-uplifts(i.e.,the Northern,Central and SW Tarim paleo-uplifts)begun to appear,and they were all broad-folded paleo-uplifts of nearly E-W striking and were formed at the same stage.The distribution and development of the Phanerozoic uplifts in this basin are restricted by the Northern and Southern Tarim basement paleuplifts of nearly E-W striking which were developed during the Precambrian.It is indicated that all the three paleo-uplifts are compressional paleo-uplifts originated from the convergence of the southern plate margin based on the basement paleo-uplifts and they are all characterized by similar structural characteristics and inherited formation and evolution.The current differences of paleo-uplifts are controlled by multi-stage intense structural reformation since the Silurian.It is concluded that the oil and gas exploration potential is immense in the carbonate reservoirs of well-preserved deep paleo-structural zones in a larger area.展开更多
Type II and Ib/c supernovae （SNe II and Ib/c） have made major stellar nu- cleosynthetic contributions to the inventories of stable nuclides during chemical evolu- tion of the Galaxy. A case study is performed here w...Type II and Ib/c supernovae （SNe II and Ib/c） have made major stellar nu- cleosynthetic contributions to the inventories of stable nuclides during chemical evolu- tion of the Galaxy. A case study is performed here with the help of recently developed numerical simulations of Galactic chemical evolution in the solar neighborhood to un- derstand the contributions of SNe II and Ib/c by comparing the stellar nucleosynthetic yields obtained by two leading groups in this field. These stellar nucleosynthetic yields differ in terms of their treatment of stellar evolution and nucleosynthesis. The formu- lation describing Galactic chemical evolution is developed with the recently revised solar metallicity of -0.014. Furthermore, the recent nucleosynthetic yields of stellar models based on the revised solar metallicity are also used. The analysis suggests that it could be difficult to explain, in a self-consistent manner, the various features asso- ciated with the elemental evolutionary trends over Galactic timescales by any single adopted stellar nucleosynthetic model that incorporates SNe II and Ib/c.展开更多
Semi-analytic models of galaxy formation are powerful tools to study the evolution of a galaxy population in a cosmological context. However, most models overpredict the number of low- mass galaxies at high redshifts ...Semi-analytic models of galaxy formation are powerful tools to study the evolution of a galaxy population in a cosmological context. However, most models overpredict the number of low- mass galaxies at high redshifts and the colors of model galaxies are not right in the sense that low-mass satellite galaxies are too red and centrals are too blue. The recent version of the L-Galaxies model by Henriques et al. （H15） is a step forward to solve these problems by reproducing the evolution of stellar mass function and the overall fraction of red galaxies. In this paper we compare the two model predictions of L-Galaxies （the other is Guo et al., G13） to SDSS data in detail. We find that in the H15 model the red fraction of central galaxies now agrees with the data due to their implementation of strong AGN feedback, but the stellar mass of centrals in massive halos is now slightly lower than what is indicated by the data. For satellite galaxies, the red fraction of low-mass galaxies （log M./M~ 〈 10） also agrees with the data, but the color of massive satellites （10 〈 logM,/M~ 〈 11） is slightly bluer. The correct color of centrals and the bluer color of massive satellites indicate that quenching in massive satellites is not strong enough. We also find that there are too many red spirals and less bulge-dominated galaxies in both H15 and G13 models. Our results suggest that additional mechanisms, such as more minor mergers or disk instability, are needed to slightly increase the stellar mass of the central galaxy in massive galaxies, mainly in the bulge component, and bulge dominated galaxies will be quenched not only by minor mergers, but also by some other mechanisms.展开更多
基金funded by the subproject of the National Science and Technology Major Project(No.2017ZX05036004).
文摘Through microscopic analyses(e.g.,organic macerals,thin section observation,scanning electron microscope(SEM)imaging of fresh bedding planes via argon ion milling,and energy spectrum tests)combined with Rock-Eval analyses,this study systematically investigated the organic matter and pyrites in the continental shales in the 3^(rd)submember of the Chang 7 Member(Chang 7^(3)submember)in the Yanchang Formation,Ordos Basin and determined their types and the formation and evolutionary characteristics.The results are as follows.The organic matter of the continental shales in the Chang 7^(3)submember is dominated by amorphous bituminites and migrabitumens,which have come into being since the early diagenetic stage and middle diagenetic stage A,respectively.The formation and transformation of organic matter is a prerequisite for the formation of pyrites.The Ordos Basin was a continental freshwater lacustrine basin and lacked sulphates in waters during the deposition of the Chang 7 Member.Therefore,the syndiagenetic stage did not witness the formation of large quantities of pyrites.Since the basin entered early diagenetic stage A,large quantities of sulfur ions were released as the primary organic matter got converted into bituminites and,accordingly,pyrites started to form.However,this stage featured poorer fluid and spatial conditions compared with the syndepositional stage due to withdraw of water,the partial formation of bituminites,and a certain degree of compaction.As a result,large quantities of pyrrhotite failed to transition into typical spherical framboidal pyrites but grew into euhedral monocrystal aggregates.In addition,pyrites are still visible in the migrabitumens in both microfractures and inorganic pores of mudstones and shales,indicating that the pyrite formation period can extend until the middle diagenetic stage A.
基金financially supported by the National Basic Research Program of China(grant No.2015CB856104)the National Natural Science Foundation of China(grant No.41773020)
文摘Objective The Susong complex zone（SCZ）is a relatively lowgrade metamorphic unit mostly with an epidoteamphibolite facies,located in the southernmost part of the Dabie orogen.However,its rock compositions,ages,
基金The National Natural Science Foundation under contract Nos 41502142 and 41502110the National Science and Technology Major Project under contract No.2016ZX05026-007-05the Youth Innovation Promotion Association CAS
文摘The Oligocene Huagang Formation is the main sandstone reservoir in the Xihu Sag, situated in the east of the East China Sea Shelf Basin. With an integrated approach of thin-section petrography, ultra-violet fluorescence microscopy, scanning electron microscopy, and isotope geochemistry, the different diagenetic features were identified, the typical diagenetic parasequences were established, and the diagenetic fluids evolution history were reconstructed for the Oligocene Huagang Formation sandstone reservoir in the south of Xihu Sag. The Huagang Formation sandstone reservoir is now in Period B of the mesodiagenesis, which has undergone significant diagenetic alterations such as mechanical compaction, Pore-lining chlorite cement, feldspar dissolution, quartz cementation and dissolution, and carbonate cementation. Three types of carbonate cements（early siderite,medium ferrocalcite and late ankerite） were identified in the Huagang Formation sandstone reservoir. The carbon and oxygen isotopic compositions of carbonate cements show that the early calcite precipitate from alkaline lacustrine environment whereas the late carbonate cements were closely related to the organic acids. To the Huagang Formation sandstone reservoir, it has experienced two main episodes of dissolution during diagenesis.The early dissolution is that unstable components such as feldspar, lithic fragments, and carbonate cement were dissolved by acidic water. The second dissolution is that quartz and other silicate minerals were dissolved under the alkaline condition. Two main phases of hydrocarbon charging occurred in this study area. The first hydrocarbon emplacement was prior to the medium carbonate cementation but posterior to feldspar dissolution and the onset of quartz cementation at the end of the Miocene. The second hydrocarbon charging occurred in the Quaternary period after the late carbonate precipitation.
基金Funded by the National Natural Science Foundation of China(No.51365044)the State Key Laboratory for Mechanical Behavior of Materials(No.20111203)the State Key Laboratory of Advanced Welding and Joining,Harbin Institute of Technology(No.AWJ-M13-09)
文摘The surface morphology, cross-sections, and joint break force（JBF） of joints welded under different electrode forces were studied. The defects, such as electrode sticking, notch, and excessive expulsions, were observed in the joints. No desirable joints were achieved with the consideration of weld geometries and joint performances. From the cross-sectional morphology, the joint evolution during the RMW of Pt alloy and 316 LVM SS wires was developed, which involved cold collapse and heat promoted set-down of Pt alloy wire, unbalanced heating at interface, molten phase squeezed out, and defect formation. Finally, the defect formation was also discussed.
基金supported by the National Key Basic Research Program of China (2014CB845700)supported by the National Natural Science Foundation of China (Grant No.11473001)B.Q.C acknowledges partial funding from the China Postdoctoral Science Foundation (2014M560843)
文摘Accurate measurements of stellar metallicity gradients in the radial and vertical directions of the disk and their temporal variations provide important constraints on the formation and evolution of the Milky Way disk. We use 297 042 main sequence turn-off stars selected from the LAMOST Spectroscopic Survey of the Galactic Anticenter（LSS-GAC） to determine the radial and vertical gradients of stellar metallicity,△[Fe/H]/△R and △[Fe/H]/△｜Z ｜ of the Milky Way disk in the direction of the anticenter. We determine ages of those turn-off stars by isochrone fitting and measure the temporal variations of metallicity gradients. We have carried out a detailed analysis of the selection effects resulting from the selection, observation and data reduction of LSS-GAC targets and the potential biases of a magnitude limited sample on the determinations of metallicity gradients. Our results show that the gradients, both in the radial and vertical directions, exhibit significant spatial and temporal variations. The radial gradients yielded by stars with the oldest ages（ 11 Gyr） are essentially zero at all heights from the disk midplane, while those given by younger stars are always negative. The vertical gradients deduced from stars with the oldest ages（ 11 Gyr）are negative and only show very weak variations with Galactocentric distance in the disk plane, R, while those yielded by younger stars show strong variations with R.After being essentially flat at the earliest epochs of disk formation, the radial gradients steepen as age decreases, reaching a maximum（steepest） at age 7–8 Gyr, and then they flatten again. Similar temporal trends are also found for the vertical gradients. We infer that the assembly of the Milky Way disk may have experienced at least two distinct phases. The earlier phase is probably related to a slow, pressure-supported collapse of gas, when the gas settles down to the disk mainly in the vertical direction. In the later phase, there are significant radial flows of gas in the disk, and the rate of gas inflow near the solar neighborhood reaches a maximum around a lookback time of 7–8 Gyr.The transition between the two phases occurs around a lookback time between 8 and11 Gyr. The two phases may be responsible for the formation of the Milky Way＇s thick and thin disks, respectively. Also, as a consequence, we recommend that stellar age is a natural, physical criterion to distinguish stars from the thin and thick disks. From an epoch earlier than 11 Gyr to one between 8 and 11 Gyr, there is an abrupt, significant change in magnitude of both the radial and vertical metallicity gradients, suggesting that stellar radial migration is unlikely to play an important role in the formation of the thick disk.
文摘On the basis of the historical profile observations and the recent Kuroshio observations,the yearly formation,development and decay of the high density water found between 50 to 100 m isobath over the middle and southern East China Sea continental shelf are anyalysed. The formation of this high density water occurs between November and March of the following year. A possible reason for it is that as the mixed water between the coastal water and the outer sea water transports northward by the Taiwan Warm Current, its density increases by surface cooling. It also mixes with the neighbouring lower density water masses. The transportation and decay of the high density water through April to July are also descussed. They can be ascribed to the seasonal surface layer warming and the fast development of Taiwan Warm Current. The high density water disappears in August.
基金funded by the National Science Foundation of China(Grant Nos.41702374,4177020938,2018YFC1505406)China Geological Survey projects(Grant Nos.DD20190640,20190505)
文摘Rock–soil aggregate landslides(RSALs) are a common geological hazard in deeply incised valleys in southwestern China. Large-scale RSALs are widely distributed in the upper reaches of the Dadu River, Danba County, Sichuan Province, and are influenced by slope structure, which can be divided into open, lock, strip, and dumbbell types, as well as soil type and meso-structure, which can be classified as layered rock–soil aggregate, block-soil, and grainsoil. In this study, the evolution of four types of structures, such as layered-dumbbell, block-soil lock, banded block-soil, and block-soil open types, were analyzed by field surveys, surface and deep displacement monitoring, and Flac3 D. It was found that the Danba reach of the Dadu River showed incised valley through the evolution from wide to slow valley affected by internal and external geological processes since the Quaternary Glaciation. In the layered-dumbbell rock–soil aggregate, the main sliding pattern is multi-stage sliding at different depths. Circular sliding in the trailing edge and plane sliding along the bedrock in the front edge body occurin the block-soil-lock type aggregate. Large-scale multi-level and circular sliding over long distances occur in the banded block-soil aggregate. The blocksoil open type is stable, with only circular sliding occurring in local and shallow surfaces of the body. The monitoring and numerical simulation results further show that slope structure and regularity have diversified with RSALs. The results provide a basis for analyzing the stability mechanism of RSALs and preventing RSALs in deeply incised valleys.
基金support of the funds by the National Key Research and Development Program of China(No.2017YFB0304001)
文摘In order to control the CaO-Al;O;-SiO;-MgO system inclusions in 50 CrVA spring steel in a lower melting temperature region,high temperature equilibrium experiments between steel and slag were performed in the laboratory,under the conditions of the initial slag basicity within 3-7and the content of Al;O;between 18-35mass%,to investigate the formation and evolution of this type of inclusion.The results indicate that the total oxygen content in the steel decreases with the increase of slag basicity and the decrease of Al;O;content in slags,and CaO-Al;O;-SiO2-MgO inclusions tend to deviate from the low melting point region with the increase of Al;O;content in slags.The most favorable composition for the refining slag is composed of 51-56mass% CaO,9-13mass% SiO;,20-25mass% Al;O;and 6mass% MgO.In this case,the inclusions in 50 CrVA spring steel are mostly in the low melting point regions,in which their plasticities are expected to improve during steel rolling.The MgO-based inclusions were observed in the steel matrix and the formation mechanism was theoretically and schematically revealed.It is also found that adding around 11mass% of MgO into the refining slags is beneficial to reducing the refractory corrosion.Further work should be carried out focusing on the evolution rates of MgO-based inclusions.
基金financially supported by the National Nature Science Foundation of China(No.51172120)
文摘To investigate the formation mechanism of calcium hexaluminate（CaAl_（12）O_（19）, CA_6）, the analytically pure alumina and calcia used as raw materials were mixed in CaO/Al_2O_3 ratio of 12.57：137.43 by mass. The raw materials were ball-milled and shaped into green specimens, and fired at 1300-1600°C. Then, the phase composition and microstructure evolution of the fired specimen were studied, and a first principle calculation was performed. The results show that in the reaction system of CaO and Al_2O_3, a small amount of CA_6 forms at 1300°C, and greater amounts are formed at 1400°C and higher temperatures. The reaction is as follows： CaO ·2Al_2O_3（CA_2） ＋ 4Al_2O_3 → CA_6. The diffusions of Ca^（2＋） in CA_2 towards Al_2O_3 and Al^（3＋） in Al_2O_3 towards CA_2 change the structures in different degrees of difficulty. Compared with the difficulty of structural change and the corresponding lattice energy change, it is deduced that the main formation mechanism is the diffusion of Ca^（2＋） in CA_2 towards Al_2O_3.
基金the National Natural Science Foundation ofChina (No. 19873014) and NKBRSFG19990754, and partly by SRF for ROCS, SEM.
文摘We compile a new sample of 89 open clusters with ages, distances and metallicities available. We derive a radial iron gradient of about -0.099±0.008 dex kpc^(-1) (unweighted) for the whole sample, which is somewhat greater than the most recent determination of oxygen gradient from nebulae and young stars. By dividing the clusters into age groups, we show that the iron gradient was steeper in the past and has evolved slowly in time. Current data show a substantial scatter of the cluster metallicities indicating that the Galactic disk has undergone a very rapid, inhomogeneous enrichment. Also, based on a simple, but quite successful model of chemical evolution of the Milky Way disk, we make a detailed calculation of the iron abundance gradient and its time evolution. The predicted current iron gradient is about -0.072 dex kpc^(-1). The model also predicts a steady flattening of the iron gradient with time, which agrees with the result from our open cluster sample.
文摘Understanding galaxy formation is one of the most pressing issues in cos- mology. We review the current status of galaxy formation from both an observational and a theoretical perspective, and summarize the prospects for future advances.
基金Supported by the China National Science and Technology Major Project(2011ZX05006-004)
文摘Taking the inter-salt organic-rich shales in the third member of Paleogene Shahejie Formation(Es3)of Dongpu sag in Bohai Bay Basin as an example,the origin of overpressure,development characteristics,formation and evolution mechanism,formation stages and geological significance on shale oil and gas of overpressure fractures in the inter-salt shale reservoir were investigated by means of thin section identification,scanning electron microscopy observation,analysis of fluid inclusions,logging data analysis,and formation pressure inversion.The results show that overpressure is universal in the salt-lake basin of Dongpu sag,and under-compaction caused by the sealing of salt-gypsum layer,pressurization due to hydrocarbon generation,transformation and dehydration of clay minerals,and fault sealing are the 4 main factors leading to the occurrence of overpressure.The overpressure fractures are small in scale,with an average length of 356.2μm and an average underground opening of 11.6μm.But they are densely developed,with an average surface density of 0.76 cm/cm2.Moreover,they are often accompanied by oil and gas charging,and thus high in effectiveness.Overpressure fractures were mainly formed during two periods of large-scale oil and gas charging,approximately 25-30 Ma ago and 0-5 Ma ago.Inter-salt overpressure fractures play dual roles as the storage space and migration paths of shale oil and gas.They contribute 22.3%to the porosity of shale reservoir and 51.4%to the permeability.They can connect fracture systems of multiple scales,greatly improving the quality of shale reservoir.During the development of shale oil and gas,inter-salt overpressure fractures can affect the extension and morphology of hydraulic fractures,giving rise to complex and highly permeable volumetric fracture networks,improving hydraulic fracturing effect and enhancing shale oil and gas productivity.
基金financially supported by the National Natural Science Foundation of China (Grants Nos. 41272124 and 41402092)Natural Science Foundation (Youth Science Fund Project) of Jiangsu Province (BK20140604)+1 种基金the Fundamental Research Funds for the Central Universities (20620140386)the State Key Laboratory for Mineral Deposits Research of Nanjing University (Grant No. ZZKT-201321)
文摘In this paper,the type,vertical evolution,and distribution pattern of sedimentary facies of the Paleogene Dainan Formation in the Gaoyou Depression of the North Jiangsu Basin are studied in detail.Results show that fan delta,delta,nearshore subaqueous fan,and lacustrine facies developed during the Dainan Formation period and their distribution pattern was mainly controlled by tectonics and paleogeography.The fan delta and nearshore subaqueous fan facies predominantly occur in the southern steep slope region where fault-induced subsidence is thought to have created substantial accommodation,whereas the delta facies are distributed on the northern gentle slope which is thought to have experienced less subsidence.Finally,the lacustrine facies is shown to have developed in the center of the depression,as well as on the flanks of the fan delta,delta,and nearshore subaqueous fan facies.Vertically,the Dainan Formation represents an integrated transgressiveregressive cycle,with the E2d1being the transgressive sequence and the E2d2being the regressive sequence.This distribution model of sedimentary facies plays an important role in predicting favorable reservoir belts for the Dainan Formation in the Gaoyou Depression and similar areas.In the Gaoyou Depression,sandstones of the subaqueous distributary channels in the fan delta and the subaqueous branch channels in the delta are characterized by physical properties favorable for reservoir formation.
基金Project supported by the National Major S&T Project(Grant No.2011ZX05004&2011ZX05003-004)the National Natural Science Fund Project(Grant No.41472103).
文摘Various types of paleo-uplifts with different characteristics are developed in the Tarim Basin.Previously,there were multiple opinions on the pale-uplifts origins and structural evolution,so the oil and gas exploration ideas and deployment in the Tarim Basin were not developed smoothly.In this paper,regional seismic interpretation and structural analysis were carried out on the deep marine carbonate rocks in this basin based on the new seismic and drilling data.Then combined with the structural denudation results,the paleo-structural frameworks were reconstructed.And finally,the formation stage and main controlling factors of paleo-uplifts were discussed.It is shown that the Middle Ordovician is the key period when regional extension was converted to compression in this basin,so stratigraphic,sedimentary and structural differences occurred.Before the deposition of Yijianfang Fm in late Middle Ordovician,three carbonate paleo-uplifts(i.e.,the Northern,Central and SW Tarim paleo-uplifts)begun to appear,and they were all broad-folded paleo-uplifts of nearly E-W striking and were formed at the same stage.The distribution and development of the Phanerozoic uplifts in this basin are restricted by the Northern and Southern Tarim basement paleuplifts of nearly E-W striking which were developed during the Precambrian.It is indicated that all the three paleo-uplifts are compressional paleo-uplifts originated from the convergence of the southern plate margin based on the basement paleo-uplifts and they are all characterized by similar structural characteristics and inherited formation and evolution.The current differences of paleo-uplifts are controlled by multi-stage intense structural reformation since the Silurian.It is concluded that the oil and gas exploration potential is immense in the carbonate reservoirs of well-preserved deep paleo-structural zones in a larger area.
文摘Type II and Ib/c supernovae （SNe II and Ib/c） have made major stellar nu- cleosynthetic contributions to the inventories of stable nuclides during chemical evolu- tion of the Galaxy. A case study is performed here with the help of recently developed numerical simulations of Galactic chemical evolution in the solar neighborhood to un- derstand the contributions of SNe II and Ib/c by comparing the stellar nucleosynthetic yields obtained by two leading groups in this field. These stellar nucleosynthetic yields differ in terms of their treatment of stellar evolution and nucleosynthesis. The formu- lation describing Galactic chemical evolution is developed with the recently revised solar metallicity of -0.014. Furthermore, the recent nucleosynthetic yields of stellar models based on the revised solar metallicity are also used. The analysis suggests that it could be difficult to explain, in a self-consistent manner, the various features asso- ciated with the elemental evolutionary trends over Galactic timescales by any single adopted stellar nucleosynthetic model that incorporates SNe II and Ib/c.
基金supported by the National Basic Research Program of China (2015CB857003 and 2013CB834900)the Natural Science Foundation of Jiangsu Province (No. BK 20140050)+1 种基金the National Natural Science Foundation of China (NSFC, No.11333008)the Strategic Priority Research Program ‘The Emergence of Cosmological Structure’ of CAS (No. XDB09010403)
文摘Semi-analytic models of galaxy formation are powerful tools to study the evolution of a galaxy population in a cosmological context. However, most models overpredict the number of low- mass galaxies at high redshifts and the colors of model galaxies are not right in the sense that low-mass satellite galaxies are too red and centrals are too blue. The recent version of the L-Galaxies model by Henriques et al. （H15） is a step forward to solve these problems by reproducing the evolution of stellar mass function and the overall fraction of red galaxies. In this paper we compare the two model predictions of L-Galaxies （the other is Guo et al., G13） to SDSS data in detail. We find that in the H15 model the red fraction of central galaxies now agrees with the data due to their implementation of strong AGN feedback, but the stellar mass of centrals in massive halos is now slightly lower than what is indicated by the data. For satellite galaxies, the red fraction of low-mass galaxies （log M./M~ 〈 10） also agrees with the data, but the color of massive satellites （10 〈 logM,/M~ 〈 11） is slightly bluer. The correct color of centrals and the bluer color of massive satellites indicate that quenching in massive satellites is not strong enough. We also find that there are too many red spirals and less bulge-dominated galaxies in both H15 and G13 models. Our results suggest that additional mechanisms, such as more minor mergers or disk instability, are needed to slightly increase the stellar mass of the central galaxy in massive galaxies, mainly in the bulge component, and bulge dominated galaxies will be quenched not only by minor mergers, but also by some other mechanisms.
