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Influence of dual retrogression and re-aging temper on microstructure,strength and exfoliation corrosion behavior of Al-Zn-Mg-Cu alloy 被引量:13
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作者 彭国胜 陈康华 +1 位作者 陈送义 方华婵 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2012年第4期803-809,共7页
Influence of dual retrogression and re-aging(dual-RRA) temper on microstructure,strength and exfoliation corrosion(EC) behavior of Al-Zn-Mg-Cu alloy was investigated by hardness measurements,tensile properties tes... Influence of dual retrogression and re-aging(dual-RRA) temper on microstructure,strength and exfoliation corrosion(EC) behavior of Al-Zn-Mg-Cu alloy was investigated by hardness measurements,tensile properties tests,exfoliation corrosion tests,transmission electron microscopy(TEM) and scanning electron microscopy(SEM) observation combined energy dispersive X-ray detector(EDX) analysis.Dual-RRA temper maintains the matrix precipitates(MPs) similar to RRA temper,meanwhile obtains coarser and sparser grain boundary precipitates(GBPs) as well as higher Cu and lower Zn content compared with T76 temper.Therefore,dual-RRA temper not only keeps strength equivalent to the RRA temper but also obtains higher EC resistance than T76 temper. 展开更多
关键词 aluminum alloy retrogression and re-aging MICROSTRUCTURE tensile properties exfoliation corrosion
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Microstructure and mechanical properties of Al-Zn-Cu-Mg-Sc-Zr alloy after retrogression and re-aging treatments 被引量:8
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作者 李文斌 潘清林 +2 位作者 肖艳苹 何运斌 刘晓艳 《Journal of Central South University》 SCIE EI CAS 2011年第2期279-284,共6页
The mechanical properties and stress corrosion cracking (SCC) resistance of an Al-Zn-Cu-Mg-Sc-Zr alloy under different aging conditions were investigated. The dependence of microstrueture and mechanical properties o... The mechanical properties and stress corrosion cracking (SCC) resistance of an Al-Zn-Cu-Mg-Sc-Zr alloy under different aging conditions were investigated. The dependence of microstrueture and mechanical properties on aging parameters was evaluated by tensile test, hardness test and conductivity measurement. The results show that for the alloys with retrogression and re-aging treatment (RRA), the conductivity increases with the retrogression time and temperature, while the tensile strength decreases. The transmission electron microscopy (TEM) results show that the precipitates η(MgZn2) at grain boundary aggregate apparently with retrogression time and the precipitates inside the matrix exhibit the similar distribution to T6 temper, which comprises fine GP zones, large η'(MgZn2)and η(MgZn2) phases. According to the mechanical properties and microstructure observations, the optimal RRA regime is recommended to be 120℃, 24h + 180 ℃, 30 min + 120 ℃, 24 h. The strength level of the alloy after the optimum RRA treatment is similar to that in T6 condition and the SCC resistance is improved obviously in contrast to T6 condition. 展开更多
关键词 Al-Zn-Cu-Mg-Sc-Zr alloy retrogression and re-aging treatment microstructure mechanical properties stress corrosioncracking
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Retrogression and re-aging treatment of Al-9.99%Zn-1.72%Cu-2.5%Mg-0.13%Zr aluminum alloy 被引量:12
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作者 冯春 刘志义 +2 位作者 宁爱林 刘延斌 曾苏民 《中国有色金属学会会刊:英文版》 CSCD 2006年第5期1163-1170,共8页
The effect of retrogression and re-aging(RRA) heat treatment on the microstructure and mechanical properties of a low frequency electromagnetic casting alloy as Al-9.99%Zn-1.72%Cu-2.5%Mg-0.13%Zr was investigated by te... The effect of retrogression and re-aging(RRA) heat treatment on the microstructure and mechanical properties of a low frequency electromagnetic casting alloy as Al-9.99%Zn-1.72%Cu-2.5%Mg-0.13%Zr was investigated by tensile properties test, Vickers hardness, electrical conductivity test, DSC analysis, SEM and TEM observation. The results show that RRA heat treatment can improve the stress corrosion cracking(SCC) properties with retention of the high strength of T6 level. After preaging at 100 ℃ for 24 h, retrogression at 200 ℃ for 7 min, and then re-aging at 100 ℃ for 24 h, the alloy obtains tensile strength up to 795 MPa, yield strength up to 767 MPa, maintains 9.1% elongation, and electric conductivity of 35.6%IACS. TEM observation shows that the re-dissolution of GP zone and η’ phase in the early stage of regression leads to the decrease of hardness, then the increase in the volume fraction of η’ and η phases leads to the increase again in the peak value, and finally the general coarsening of all particles results in a softening of the alloy. Meanwhile it is found that the conventional T6 heat treatment as the preaging and re-aging regime is not the optimum regime to the RRA treatment of the high-zinc content super-high strength aluminum alloy. 展开更多
关键词 AL-ZN-MG-CU 时效 显微结构 机械性能 应力腐蚀裂纹 铝合金
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Combined use of fly ash and silica to prevent the long-term strength retrogression of oil well cement set and cured at HPHT conditions
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作者 Guo-Dong Cheng Xue-Yu Pang +4 位作者 Jin-Sheng Sun Zheng-Song Qiu Chuang-Chuang Wang Jian-Kun Qin Ning Li 《Petroleum Science》 SCIE EI CAS CSCD 2024年第2期1122-1134,共13页
The long-term strength retrogression of silica-enriched oil well cement poses a significant threat to wellbore integrity in deep and ultra-deep wells, which is a major obstacle for deep petroleum and geothermal energy... The long-term strength retrogression of silica-enriched oil well cement poses a significant threat to wellbore integrity in deep and ultra-deep wells, which is a major obstacle for deep petroleum and geothermal energy development. Previous attempts to address this problem has been unsatisfactory because they can only reduce the strength decline rate. This study presents a new solution to this problem by incorporating fly ash to the traditional silica-cement systems. The influences of fly ash and silica on the strength retrogression behavior of oil well cement systems directly set and cured under the condition of 200°C and 50 MPa are investigated. Test results indicate that the slurries containing only silica or fly ash experience severe strength retrogression from 2 to 30 d curing, while the slurries containing both fly ash and silica experience strength enhancement from 2 to 90 d. The strength test results are corroborated by further evidences from permeability tests as well as microstructure analysis of set cement. Composition of set cement evaluated by quantitative X-ray diffraction analyses with partial or no known crystal structure(PONKCS) method and thermogravimetry analyses revealed that the conversion of amorphous C-(A)-S-H to crystalline phases is the primary cause of long-term strength retrogression.The addition of fly ash can reduce the initial amount of C-(A)-S-H in the set cement, and its combined use with silica can prevent the crystallization of C-(A)-S-H, which is believed to be the working mechanism of this new admixture in improving long-term strength stability of oil well cement systems. 展开更多
关键词 Fly ash Long-term strength retrogression High temperature Quantitative X-ray diffraction(QXRD) Partial or no known crystal structure(PONKCS)
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Various admixtures to mitigate the long-term strength retrogression of Portland cement cured under high pressure and high temperature conditions 被引量:2
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作者 Jiankun Qin Xueyu Pang +2 位作者 Ashok Santra Guodong Cheng Hailong Li 《Journal of Rock Mechanics and Geotechnical Engineering》 SCIE CSCD 2023年第1期191-203,共13页
In order to investigate the problem of long-term strength retrogression in oil well cement systems exposed to high pressure and high temperature(HPHT)curing conditions,various influencing factors,including cement sour... In order to investigate the problem of long-term strength retrogression in oil well cement systems exposed to high pressure and high temperature(HPHT)curing conditions,various influencing factors,including cement sources,particle sizes of silica flour,and additions of silica fume,alumina,colloidal iron oxide and nano-graphene,were investigated.To simulate the environment of cementing geothermal wells and deep wells,cement slurries were directly cured at 50 MPa and 200?C.Mineral compositions(as determined by X-ray diffraction Rietveld refinement),water permeability,compressive strength and Young’s modulus were used to evaluate the qualities of the set cement.Short-term curing(2e30 d)test results indicated that the adoption of 6 m m ultrafine crystalline silica played the most important role in stabilizing the mechanical properties of oil well cement systems,while the addition of silica fume had a detrimental effect on strength stability.Long-term curing(2e180 d)test results indicated that nano-graphene could stabilize the Young’s modulus of oil well cement systems.However,none of the ad-mixtures studied here can completely prevent the strength retrogression phenomenon due to their inability to stop the conversion of amorphous to crystalline phases. 展开更多
关键词 High pressure and high temperature(HPHT) Strength retrogression Young’s modulus Water permeability Rietveld method
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Effect of non-isothermal retrogression and re-ageing on through-thickness homogeneity of microstructure and properties of Al-8Zn-2Mg-2Cu alloy thick plate 被引量:3
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作者 WU Cai-hong FENG Di +4 位作者 REN Jia-jia ZANG Qian-hao LI Ji-chen LIU Sheng-dan ZHANG Xin-ming 《Journal of Central South University》 SCIE EI CAS CSCD 2022年第3期960-972,共13页
In order to improve the through-thickness homogeneity and properties of aviation aluminum alloy thick plate.The effect of heating-cooling retrogression and re-ageing on the performance of Al-8Zn-2Mg-2Cu alloy thick pl... In order to improve the through-thickness homogeneity and properties of aviation aluminum alloy thick plate.The effect of heating-cooling retrogression and re-ageing on the performance of Al-8Zn-2Mg-2Cu alloy thick plate was investigated by hardness tests, electrical conductivity tests and transmission electron microscopy(TEM) observation.Results revealed that, during retrogression heating, the fine pre-precipitates in surface layer dissolve more and the undissolved η′ or η phases are more coarsened than that of center layer. During slow cooling after retrogression,precipitates continue coarsening but with a lower rate and the secondary precipitation occurs in both layers. Finer precipitates resulting from the secondary precipitation are more in surface. However, the coarsening and secondary precipitation behaviors are restrained in both layers under quick cooling condition. The electrical conductivity and through-thickness homogeneity of precipitates increases while the hardness decreases with cooling rate decreasing. After the optimized non-isothermal retrogression and re-ageing(NRRA) including air-cooling retrogression, the throughthickness homogeneity which is evaluated by integrated retrogression effects has been improved to 94%. The tensile strength, fracture toughness and exfoliation corrosion grade of Al-8Zn-2Mg-2Cu alloy plate is 619 MPa, 24.7 MPa·m^(1/2)and EB, respectively, which indicates that the non-isothermal retrogression and re-aging(NRRA) could improve the mechanical properties and corrosion resistance with higher through-thickness homogeneity. 展开更多
关键词 non-isothermal ageing retrogression and re-ageing Al-8Zn-2Mg-2Cu alloy thick plate HOMOGENEITY
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Effects of retrogression heating rate on microstructures and mechanical properties of aluminum alloy 7050 被引量:13
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作者 李国锋 张新明 +1 位作者 李鹏辉 游江海 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2010年第6期935-941,共7页
The effects of the retrogression heating rate(340℃/min,57℃/min,4.3℃/min)on the microstructures and mechanical properties of aluminum alloy 7050 were investigated by means of hardness measurement,tensile properties ... The effects of the retrogression heating rate(340℃/min,57℃/min,4.3℃/min)on the microstructures and mechanical properties of aluminum alloy 7050 were investigated by means of hardness measurement,tensile properties testing,differential scanning calorimetry(DSC)and transmission electron microscopy(TEM).The results show that the retrogression heating rate significantly affects the microstructures and mechanical properties of the alloys treated by retrogression and re-aging(RRA)process, and it is found that the medium rate(57℃/min)leads to the highest mechanical properties.The strengthening phases in the matrix are mainly the fine dispersed η′precipitates and GP zones,and the grain boundary precipitates are coarse and discontinuous η phases. 展开更多
关键词 aluminum alloy 7050 retrogression and re-aging treatment MICROSTRUCTURE mechanical properties
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Non-isothermal retrogression kinetics for grain boundary precipitate of 7A55 aluminum alloy 被引量:5
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作者 冯迪 张新明 +2 位作者 刘胜胆 吴泽政 王婷 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2014年第7期2122-2129,共8页
The retrogression kinetics for grain boundary precipitate (GBP) of 7A55 aluminum alloy was investigated by transmission electron microscopy (TEM) observation. The results reveal that the coarsening behavior of GBP... The retrogression kinetics for grain boundary precipitate (GBP) of 7A55 aluminum alloy was investigated by transmission electron microscopy (TEM) observation. The results reveal that the coarsening behavior of GBP obeys “LSW” theory, namely, the cube of GBP average size has a linear dependence relation to retrogression time, and the coarsening rate accelerates at the elevated retrogression temperature. The GBP coarsening activation energy Qo of (115.2±1.3) kJ/mol is obtained subsequently. Taking the retrogression treatment schedule of 190℃, 45 min derived from AA7055 thin plate as reference, the non-isothermal retrogression model for GBP coarsening behavior is established based on “LSW”theory and “iso-kinetics” solution, which includes an Arrhenius form equation. After that, the average size of GBP r(t) is predicted successfully at any non-isothermal process T(t) when the initial size of GBP r0 is given. Finally, the universal characterization method for the microstructure homogeneity along the thickness direction of TA55 aluminum alloy thick plate is also set up. 展开更多
关键词 non-isothermality retrogression kinetic 7A55 aluminum alloy grain boundary precipitate
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Creep aging behavior and performance of Al-Zn-Mg-Cu alloys under different parameters in retrogression aging treatment 被引量:7
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作者 PENG Nan-hui ZHAN Li-hua +4 位作者 MA Bo-lin WANG Qing XU Ling-zhi YUWen-fang SHEN Feng 《Journal of Central South University》 SCIE EI CAS CSCD 2022年第3期986-998,共13页
A study was conducted to better understand how different parameters, namely, regression aging time and regression aging temperature, affect the creep aging properties, i.e., the creep deformation and performance of Al... A study was conducted to better understand how different parameters, namely, regression aging time and regression aging temperature, affect the creep aging properties, i.e., the creep deformation and performance of Al-Zn-MgCu alloy during regressive reaging. The corresponding creep strain and mechanical properties of samples were studied by conducting creep tests and uniaxial tensile tests. The electrical conductivity was measured using an eddy-current conductivity meter. The microstructures were observed by transmission electron microscopy(TEM). With the increase in regression aging time, the steady creep strain first increased and then decreased, and reached the maximum at 45 min.The steady creep strain increased with the increase in regression aging temperature, and reached the maximum at 200 ℃.The level of steady creep strain was determined by precipitation and dislocation recovery. Creep aging strengthens 7B50-RRA treated with regression aging time at 190 ℃ for 10 min, and the difference in the mechanical properties of alloy becomes smaller. The diffusion of solute atoms reduces the scattering of electrons, leading to a significant improvement in electrical conductivity and stress corrosion cracking(SCC) resistance after creep aging. The findings of this study could help in the application of creep aging forming(CAF) technology in Al-Zn-Mg-Cu alloy under RRA treatment. 展开更多
关键词 Al-Zn-Mg-Cu alloy retrogression parameters creep aging behavior performance MICROSTRUCTURE
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Properties of AA7075 aluminum alloy in aging and retrogression and reaging process 被引量:10
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作者 Gokhan OZER Ahmet KARAASLAN 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2017年第11期2357-2362,共6页
A retrogression process was applied to AA7075alloy at180,240and320°C for1,30,50,70,90and120min.After the retrogression,aging treatment was reapplied with T6conditions(120°C,24h).The mechanical properties of ... A retrogression process was applied to AA7075alloy at180,240and320°C for1,30,50,70,90and120min.After the retrogression,aging treatment was reapplied with T6conditions(120°C,24h).The mechanical properties of aged samples were determined by V-Charpy and hardness tests and also,physical properties of samples were determined by electrical conductivity tests.Moreover,microstructural properties were characterized by light microscope and transmission electron microscope.The results show that the effects of the temperature and the duration of the retrogression and reagent on the impact toughness and hardness are related to the precipitates at the grain boundary. 展开更多
关键词 aluminum alloy precipitate behavior retrogression and reaging impact toughness HARDNESS electrical conductivity
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Redistribution and re-precipitation of solute atom during retrogression and reaging of Al-Zn-Mg-Cu alloys 被引量:10
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作者 宁爱林 刘志义 +1 位作者 彭北山 曾苏民 《中国有色金属学会会刊:英文版》 CSCD 2007年第5期1005-1011,共7页
The redistribution and re-precipitation of solute atom during retrogression and reaging of three different Al-Zn-Mg-Cu aluminum alloys were investigated. The results of hardness and tensile strength test indicate that... The redistribution and re-precipitation of solute atom during retrogression and reaging of three different Al-Zn-Mg-Cu aluminum alloys were investigated. The results of hardness and tensile strength test indicate that after pre-aging at 100 ℃ or 120 ℃ and retrogressing at 200 ℃ for various time and re-aging treatment, the hardness and strength of the alloys are all larger than those under pre-aging condition, some of them even exceed the value under peak aging(T6) condition. TEM observation shows that the PFZ formed during retrogressing in short time becomes narrow and even disappears after re-aging treatment. However, the PFZ formed during retrogressing for a long time does not narrow after re-aging treatment. It is suggested that the redistribution and re-precipitation of solute atom during re-aging treatment result in the narrowing and even disappearance of the PFZ formed during retrogression, which reinforces the grain-boundaries and presents the value of tensile strength exceeding peak-aging strength in the RRA condition, while the precipitates in the matrix of the alloys still keep or even exhibit a more dispersed distribution, and a 展开更多
关键词 Al-Zn-Mg-Cu复合物 铝合金 老化现象 金属
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Effect of Pre-Aging, Over-Aging and Re-Aging on Exfoliation Corrosion and Electrochemical Corrosion Behavior of Al-Zn-Mg-Cu Alloys 被引量:1
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作者 Xingzhi Liao Xiaohua Kong +1 位作者 Pengxuan Dong Kanghua Chen 《Journal of Materials Science and Chemical Engineering》 2020年第2期81-88,共8页
By means of TEM, hardness, conductivity, tensile strength test, fracture toughness test, polarization curve and EIS, the Al-Zn-Mg-Cu alloys treated by a new multi-stage aging system, i.e. pre-aging, over-aging and re-... By means of TEM, hardness, conductivity, tensile strength test, fracture toughness test, polarization curve and EIS, the Al-Zn-Mg-Cu alloys treated by a new multi-stage aging system, i.e. pre-aging, over-aging and re-aging (120&#176;C/24h + 160&#176;C/8h + 120&#176;C/24h), were characterized. It is found that compared with the Al-Zn-Mg-Cu alloys treated by T76 (120&#176;C/24h + 160&#176;C/8h), the new multi-stage aging treatment can improve the tensile strength, fracture toughness, hardness and conductivity of the alloys at the same time. This is mainly due to the pre-aging, over-aging and re-aging process of super high strength aluminum alloys. Compared with the two-stage over aging process, the formation of multi-stage multi-phase precipitation structure can improve the strength, toughness and corrosion resistance of the alloys at the same time. The polarization curve is consistent with the conclusion. Therefore, we conducted this study to test how the comprehensive properties of the alloy can be improved. 展开更多
关键词 AL-ZN-MG-CU-ZR Alloys Pre-aging OVER-AGING and re-aging Exfoliation CORROSION Electrochemical CORROSION
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Effect of Retrogression and Reaging on Stress Corrosion Cracking of Spray Formed Al Alloy 被引量:2
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作者 Ruiming Su Yingdong Qu +2 位作者 Xiang Li Junhua You Rongde Li 《Materials Sciences and Applications》 2016年第1期1-7,共7页
Stress corrosion cracking (SCC) resistance of a spray formed Al-Zn-Mg-Cu alloy underwent retrogression and reaging (RRA) was studied by slow strain rate tests in dry air and 3.5 wt% NaCl solution. The results showed t... Stress corrosion cracking (SCC) resistance of a spray formed Al-Zn-Mg-Cu alloy underwent retrogression and reaging (RRA) was studied by slow strain rate tests in dry air and 3.5 wt% NaCl solution. The results showed that after RRA treatment, interrupted η phases at grain boundaries and slightly wide precipitate free zones could decrease SCC susceptibility of the alloy. Lots of reticular dislocations appeared in deformation process could prevent hydrogen induced cracking, and then SCC. Abundance transgranular dispersive η' phases separated out again promoted tensile strength to 759.4 MPa. The fracture ways of the specimens were dimple fracture in dry air and sub-cleavage fracture in 3.5% NaCl solution. 展开更多
关键词 Spray Forming Al-Zn-Mg-Cu Alloy retrogression and Reaging Stress Corrosion Cracking
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Retrogression characteristics of a novel Al-Cu-Li-X alloy
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作者 Zhi-shan Yuan Zheng Lu +3 位作者 Xiu-liang Wu You-hua Xie Sheng-long Dai Chang-sheng Liu 《International Journal of Minerals,Metallurgy and Materials》 SCIE EI CAS CSCD 2010年第5期624-628,共5页
Retrogression characteristics of a novel Al-Cu-Li-X alloy of 2A97 were studied by hardness testing, transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The retrogression treatments... Retrogression characteristics of a novel Al-Cu-Li-X alloy of 2A97 were studied by hardness testing, transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The retrogression treatments of aging at 155°C for 12 h followed by aging at 220 and 240°C were chosen by determining the peak temperature of δ' precipitation at 230°C by DSC. The retrogression treatment at a lower temperature of 220°C causes the precipitation and coarsening of δ' and θ' phases in the matrix, resulting in an increase in hardness. Retrogression at a higher temperature of 240°C causes the dissolution and coarsening of δ' and θ' precipitates in the matrix and on the grain boundaries, resulting in a decrease in hardness. Microstructural changes upon retrogression including the appearance of equilibrium precipitates such as T1, T2, δ', and θ are confirmed by the selected area electron diffraction and the bright and dark field image analysis. 展开更多
关键词 retrogression artificial aging aluminum-lithium alloy MICROSTRUCTURE
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DIAGNOSTIC STUDY OF INTRASEASONAL ANOMALOUS PROGRESSION & RETROGRESSION OF SUBTROPICAL HIGH OVER WESTERN PACIFIC
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作者 喻世华 杨维武 《Journal of Tropical Meteorology》 SCIE 1997年第1期42-51,共10页
Diagnostic study on two intraseasonal progressive and retrogressive progress of anomalous subtropical high in western Pacific is carried out with the aid of daily 2. 5°×2.5° grid point data of ECMWF inJ... Diagnostic study on two intraseasonal progressive and retrogressive progress of anomalous subtropical high in western Pacific is carried out with the aid of daily 2. 5°×2.5° grid point data of ECMWF inJuly and August of 1980 and 1983. It is revealed that the anomalous progression and retrosression ofthis high is intraseasonally teleconnected with that in the eastern Pacific, shown as low-ftequency wavespropagating westward along a latitudinal wave train across the northern Pacific i the same oscillatory displacement of eastern subtropical high is again triggered off by the variation of convergent sink of uppertropospheric divergent wind field in eastern Pacific, being resulted from anomalous heating from monsoon area in South Asia through trade wind zone in the Pacific Ocean. 展开更多
关键词 SUBTROPICAL high ANOMALOUS PROGRESSION & retrogression TELECONNECTION diagnostic study
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<i>β</i>-HCG Level as a Predictive Marker of Pregnancy Progression or Retrogression
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作者 George Gborienemi Simeon Marymar Ezejimofor Newton Cleston Odumoson 《Open Journal of Obstetrics and Gynecology》 2021年第6期713-719,共7页
An ordered sequence of biologic events is precursors of the birth of a healthy baby. Hormonal interactions acting as a nexus between the fetus, placenta and mother that controls the establishment and progression of pr... An ordered sequence of biologic events is precursors of the birth of a healthy baby. Hormonal interactions acting as a nexus between the fetus, placenta and mother that controls the establishment and progression of pregnancy and fetal development are very important. We examined the role of Beta-Human Chorionic Gonadotropin (<i><span style="font-family:Verdana;">β</span></i><span style="font-family:Verdana;">-HCG) as a predictive marker. Applying radioimmunoassay that utilizes anti-sera generated from specific </span><i><span style="font-family:Verdana;">β</span></i><span style="font-family:Verdana;">-submit of HCG we evaluated the serum </span><i><span style="font-family:Verdana;">β</span></i><span style="font-family:Verdana;">-HCG level in 60 pregnant women in the three trimesters. Results showed that there was consistent increase in concentration that drops gradually and maintained a plateau only to drop from the 40</span><sup><span style="font-family:Verdana;">th</span></sup><span style="font-family:Verdana;"> week of pregnancy. 3 subjects (5%) that had a sudden sharp drop in </span><i><span style="font-family:Verdana;">β</span></i><span style="font-family:Verdana;">-HCG level resulted in complications. Inclusion of </span><i><span style="font-family:Verdana;">β</span></i><span style="font-family:Verdana;">-HCG level screening and monitoring in pregnancy will raise assurance of progress or retrogression in pregnancy. We provide data that can be used as a reference range for </span><i><span style="font-family:Verdana;">β</span></i><span style="font-family:Verdana;">-HCG using this method.</span> 展开更多
关键词 β-HCG Predictive Marker PREGNANCY PROGRESSION retrogression
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Impact of a retrogressive thaw slump on surrounding vegetation communities in the Fenghuoshan mountains,Qinghai-Tibet Plateau 被引量:1
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作者 Gang Wei LaJia Weisai +5 位作者 ZiJie Zhou XinNing Wu SiRu Gao ZiTeng Fu QingBai Wu GuanLi Jiang 《Research in Cold and Arid Regions》 CSCD 2023年第1期11-17,共7页
Under global warming,permafrost around the world is experiencing degradation which is especially so on the Third Pole,the Qinghai-Tibet Plateau(QTP),China.Retrogressive thaw slump(RTS)is one of the thermokarst feature... Under global warming,permafrost around the world is experiencing degradation which is especially so on the Third Pole,the Qinghai-Tibet Plateau(QTP),China.Retrogressive thaw slump(RTS)is one of the thermokarst features caused by rapid degradation of ice rich permafrost,which transforms landforms and threatens infrastructures,and even affects the terrestrial carbon cycle.In this work,vegetation communities surrounding a RTS in the Fenghuoshan Mountains of the interior portion of the Qinghai-Tibet Plateau have been investigated to examine the impact from RTS.This investigation indicates that the occurrence of RTS influences the vegetation community by altering their habitats,especially the soil water content,which forces the vegetation community to evolve in order to adapt to the alterations.In the interior part of RTS where it has been disturbed tremendously,alterations have produced a wider niche and richer plant species.This favors species of a wet environment in a habitat where it was a relatively dry environment of alpine steppe prior to the occurrence of RTS.This study adds to limited observations regarding the impact of RTS to vegetation community on the QTP and helps us to reach a broader understanding of the effects of permafrost degradation as well as global warming. 展开更多
关键词 retrogressive thaw slump Vegetation community Rapid permafrost degradation Global warming Qinghai-Tibet plateau
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Tumor: Life Retrogression?
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作者 Xiong-Zhi Wu Hao-Ran Zhang 《TMR Theory and Hypothesis》 2018年第1期2-8,共7页
Cancer emerged in human history for centuries. It seems that while human beings are evolving, tumors are always on their heels. In order to explain and study the mechanism of tumor progression, we proposed a new hypot... Cancer emerged in human history for centuries. It seems that while human beings are evolving, tumors are always on their heels. In order to explain and study the mechanism of tumor progression, we proposed a new hypothesis that the tumor is a retrogression of life evolution, in other word, a resurgence of some past fragments in human development history. Our inference was based on the fact that tumors are not foreign diseases, but use of human inherent developmental genes to achieve self-improvement. Characteristics and biological behavior of tumor cells are similar to human normal stem cell to some degree. Thus, studying the process of human evolution could speculate and analyze the occurrence and development of tumors. The latest research showed that many cancer treatment were also taking advantages of those features about retrogression. Continuous in-depth analysis about tumor environmental characteristics and internal law of human evolution may produce new approaches to promote cancer prevention and treatment. Our hypothesis, for the first time, proposed that taking advantage of the evolution laws to reverse the tumor progression as a path of life retrogression is better than exterminating them completely as outside enemies. Some new studies on tumor induced differentiation had also demonstrated the clinical significance of our hypothesis 展开更多
关键词 TUMOR Life retrogression Development memory EVOLUTION
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High-resolution assessment of retrogressive thaw slump susceptibility in the Qinghai-Tibet Engineering Corridor
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作者 GuoAn Yin Jing Luo +4 位作者 FuJun Niu MingHao Liu ZeYong Gao TianChun Dong WeiHeng Ni 《Research in Cold and Arid Regions》 CSCD 2023年第6期288-294,共7页
Under the rapidly warming climate in the Arctic and high mountain areas,permafrost is thawing,leading to various hazards at a global scale.One common permafrost hazard termed retrogressive thaw slump(RTS)occurs extens... Under the rapidly warming climate in the Arctic and high mountain areas,permafrost is thawing,leading to various hazards at a global scale.One common permafrost hazard termed retrogressive thaw slump(RTS)occurs extensively in ice-rich permafrost areas.Understanding the spatial and temporal distributive features of RTSs in a changing climate is crucial to assessing the damage to infrastructure and decision-making.To this end,we used a machine learning-based model to investigate the environmental factors that could lead to RTS occurrence and create a susceptibility map for RTS along the Qinghai-Tibet Engineering Corridor(QTEC)at a local scale.The results indicate that extreme summer climate events(e.g.,maximum air temperature and rainfall)contributes the most to the RTS occurrence over the flat areas with fine-grained soils.The model predicts that 13%(ca.22,948 km^(2))of the QTEC falls into high to very high susceptibility categories under the current climate over the permafrost areas with mean annual ground temperature at 10 m depth ranging from-3 to-1℃.This study provides insights into the impacts of permafrost thaw on the stability of landscape,carbon stock,and infrastructure,and the results are of value for engineering planning and maintenance. 展开更多
关键词 retrogressive thaw slumps THERMOKARST Permafrost degradation Machine learning
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地下盐岩溶腔储库单井水平溶解建造流体运移研究
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作者 李超 梁卫国 +2 位作者 张胜利 肖宁 李静 《地下空间与工程学报》 CSCD 北大核心 2024年第4期1257-1265,1297,共10页
为提高水平盐穴储库单井后退式溶腔建腔速率,通过相似模型试验与数值计算开展建腔期注水方向对腔内流体运移规律影响研究。数值模拟结果表明:注入淡水接触腔内卤水后浓度会迅速升高,当浓度达到23%左右变为缓慢升高;上下同时入射有利于... 为提高水平盐穴储库单井后退式溶腔建腔速率,通过相似模型试验与数值计算开展建腔期注水方向对腔内流体运移规律影响研究。数值模拟结果表明:注入淡水接触腔内卤水后浓度会迅速升高,当浓度达到23%左右变为缓慢升高;上下同时入射有利于快速溶腔,垂直向下入射有利于建造更大腔体。相似模型试验流体运移规律与数值模拟基本一致,证明了数值模型的正确性。试验发现:腔内流体主要分为羽流区、边界溶解区、对流扩散区和底部饱和区4个区域;改变注水方向使羽流区流体浓度和流速改变,进而影响边界溶解区高度,与水平入射相比,垂直向上入射、上下型入射、四周型入射和垂直向下入射高度增加了22.2%、26.9%、51.1%、135.6%;改变注水方向使淡水初始向下流速改变,进而改变底部饱和区高度,与水平入射相比,垂上、四周、上下、垂下入射高度降低0%、12.9%、29.9%、70.1%。 展开更多
关键词 盐岩水平溶腔 注水方向 流体运移 溶解速率 后退式建腔
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