Large-scale detachment faults on mid-ocean ridges (MORs) provide a window into the deeper earth. They have megamullion on their corrugated surfaces, with exposed lower crustal and upper mantle rocks, rela- tively hi...Large-scale detachment faults on mid-ocean ridges (MORs) provide a window into the deeper earth. They have megamullion on their corrugated surfaces, with exposed lower crustal and upper mantle rocks, rela- tively high residual Bouguer gravity anomaly and P-wave velocity, and are commonly associated with ocean- ic core complex. According to 30 detachment faults identified on MORs, we found that their distances to the axis mostly range from 5 to 50 km, half-spreading rates range from 6.8 to 17 mm/a, and activity time ranges from recent to 3 Ma. Most of the detachment faults are developed on the slow spreading Mid-Atlantic Ridge (MAR) and ultra-slow spreading Southwest Indian Ridge (SWIRl, with the dominant half-spreading rates of 7-13 mm/a, especially 10-13 mm/a. Furthermore, they mostly occur at the inside corner of one segment end and result in an asymmetric seafloor spreading. The detachment faults on MORs are mainly controlled by the tectonism and influenced by the magmatism. Long-lived detachment faults tend to be formed where the ridge magma supply is at a moderate level, although the tectonism is a first-order controlling factor. At the slow spreading ridges, detachment faults tend to occur where local magma supply is relatively low, whilst at the ultra-slow spreading ridges, they normally occur where local magma supply is relatively high. These faults are accompanied by hydrothermal activities, with their relationships being useful in the study of hydrothermal polymetallic sulfides and their origin.展开更多
We quantified the systematic variations in global transform fault morphology,revealing a first-order dependence on the spreading rate.(1)The average age offset of both the full transform and transform sub-segments dec...We quantified the systematic variations in global transform fault morphology,revealing a first-order dependence on the spreading rate.(1)The average age offset of both the full transform and transform sub-segments decrease with increasing spreading rate.(2)The average depth of both the transform valley and adjacent ridges are smaller in the fast compared to the slow systems,reflecting possibly density anomalies associated with warmer mantle at the fast systems and rifting at the slow ridges.However,the average depth difference between the transform valley and adjacent ridges is relatively constant from the fast to slow systems.(3)The nodal basin at a ridge-transform intersection is deeper and dominant at the ultraslow and slow systems,possibly reflecting a lower magma supply and stronger viscous resistance to mantle upwelling near a colder transform wall.In contrast,the nodal high,is most prominent in the fast,intermediate,and hotspot-influenced systems,where robust axial volcanic ridges extend toward the ridge-transform intersection.(4)Statistically,the average transform valley is wider at a transform system of larger age offset,reflecting thicker deforming plates flanking the transform fault.(5)The maximum magnitude of the transform earthquakes increases with age offset owing to an increase in the seismogenic area.Individual transform faults also exhibit significant anomalies owing to the complex local tectonic and magmatic processes.展开更多
The target of this study is to develop a spreading rate regression model capable of predicting rate of spread of Nigerian crude oil spills on water. The major factors responsible for spreading rate of crude oil on wat...The target of this study is to develop a spreading rate regression model capable of predicting rate of spread of Nigerian crude oil spills on water. The major factors responsible for spreading rate of crude oil on water were considered, namely surface tension, viscosity, and specific gravity/American Petroleum Institute degree (<sup>0</sup>API), all at specified temperature values. The surface tension, viscosity and density parameters were interactively measured under controlled factorial analysis. The spreading rate of each crude oil was determined by artificially spilling them on laboratory calm/stagnant water in a rectangular tank and their averages were also computed. These averages were used to develop a regression model equation for spreading rate. The model developed indicated that an average spreading rate was 3.3528 cm/s at 37.5<span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">°</span>C and the predictive regression model is evaluated with the interactions of specific gravity, viscosity and surface tension. It is convenient to state that the model will predict the spread rate of crude oils which possess imputed physicochemical properties having pour point averaged 15.5<span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">°</span>C on calm seawater.展开更多
It is well-known that the multi-valued CDMA spreading codes can be designed by means of a pair of mirror multi-rate filter banks based on some optimizing criterion. This paper indicates that there exists a theoretical...It is well-known that the multi-valued CDMA spreading codes can be designed by means of a pair of mirror multi-rate filter banks based on some optimizing criterion. This paper indicates that there exists a theoretical bound in the performance of its circulating correlation property, which is given by an explicit expression. Based on this analysis, a criterion of maximizing entropy is proposed to design such codes. Computer simulation result suggests that the resulted codes outperform the conventional binary balanced Gold codes for an asynchronous CDMA system.展开更多
文章研究了背景为子空间干扰加高斯杂波的距离扩展目标方向检测问题。杂波是均值为零协方差矩阵未知但具有斜对称特性的高斯杂波,目标与干扰分别通过具备斜对称特性的目标子空间和干扰子空间描述。针对方向检测问题,利用上述斜对称性,...文章研究了背景为子空间干扰加高斯杂波的距离扩展目标方向检测问题。杂波是均值为零协方差矩阵未知但具有斜对称特性的高斯杂波,目标与干扰分别通过具备斜对称特性的目标子空间和干扰子空间描述。针对方向检测问题,利用上述斜对称性,根据广义似然比检验(Generalized Likeli-hood Ratio Test,GLRT)准则的一步与两步设计方法,设计了基于GLRT的一步法与两步法的距离扩展目标方向检测器。通过理论推导证明了这2种检测器相对于未知杂波协方差矩阵都具有恒虚警率。对比相同背景下已有检测器,特别是在辅助数据有限的场景下,文章提出的2个检测器表现出了优越的检测性能。展开更多
This study investigates the international spillover effects of US unconventional monetary policy(UMP)-frequently called large-scale asset purchases or quantitative easing(QE)—on advanced and emerging market economies...This study investigates the international spillover effects of US unconventional monetary policy(UMP)-frequently called large-scale asset purchases or quantitative easing(QE)—on advanced and emerging market economies,using structural vector autoregressive models with high-frequency daily data.Blinder(Federal Reserve Bank of St.Louis Rev 92(6):465–479,2010)argued that the QE measures primarily aim to reduce US interest rate spreads,such as term and risk premiums.Considering this argument and recent empirical evidence,we use two spreads as indicators of US UMP:the mortgage and term spreads.Based on data from 20 emerging and 20 advanced countries,our empirical findings reveal that US unconventional monetary policies significantly affect financial conditions in emerging and advanced countries by altering the risktaking behavior of investors.This result suggests that the risk-taking channel plays an important role in transmitting the effects of these policies to the rest of the world.The extent of these effects depends on the type of QE measures.QE measures such as purchases of private sector securities that lower the US mortgage spread exert stronger and more significant spillover effects on international financial markets than those that reduce the US term spread.Furthermore,the estimated financial spillovers vary substantially across countries and between and within the emerging and advanced countries that we examine in this study.展开更多
Chinese tallow tree (Triadica sebifera (L.) Small, Sapium sebiferum (L.) Roxb) is an invasive species that is replacing native ecosystems in areas of eastern Texas. It is imperative that the spatial pattern of the spr...Chinese tallow tree (Triadica sebifera (L.) Small, Sapium sebiferum (L.) Roxb) is an invasive species that is replacing native ecosystems in areas of eastern Texas. It is imperative that the spatial pattern of the spread of this species be identified, as well as causal mechanisms. To that end, we seek to determine factors that contribute to the spread of Chinese tallow using classification and regression tree (CART) and logistic regression. We also attempt to identify current locations and spread rates across eastern Texas using Forest Inventory Analysis (FIA) data within major forest types. Distance to formerly infested plots and roads, slope, and disturbances (natural and anthropogenic) were identified as major (either facilitating or impeding) factors for the spread of Chinese tallow across the landscape. The highest probability of occurrence and spread rate of Chinese tallow were found in the oak/ gum/cypress forest type. Continued disturbance, from harvest events or natural disasters will allow the species to continue to spread throughout the region and could threaten overall forest productivity. We also discuss some implications of the continued spread of Chinese tallow on forest management. Forest managers could benefit from this analysis and use it as a guide for monitoring forest types with the highest risk of invasion.展开更多
AIM:To prospectively investigate the detection rate of laterally spreading tumors(LSTs)of the colorectum by computed tomography(CT)colonography(CTC).METHODS:Patients with LSTs measuring≥20 mm detected during colonosc...AIM:To prospectively investigate the detection rate of laterally spreading tumors(LSTs)of the colorectum by computed tomography(CT)colonography(CTC).METHODS:Patients with LSTs measuring≥20 mm detected during colonoscopy were prospectively enrolled in the study.All patients underwent colonoscopy and subsequent CTC on the same day.CTC was performed using multi-detector CT without contrast in the prone and supine positions.Two radiologists blinded to the existence of LSTs read the virtual endoscopic images as well as 2-D images.LSTs were classified into granular and non-granular types based on colonoscopic appearance.RESULTS:Forty-seven pathologically proven LSTs were evaluated prospectively.Histology included adenomas in 19,mucosal cancers in 19 and T1 cancers in 9.The mean diameter of the LSTs was 35.1 mm.Twenty-eight(60%)LSTs were correctly identified by CTC,and the configuration was similar to the colonoscopic appearance in most cases.Detection rate for the granular type was significantly higher than that for the nongranular type(71%vs 31%,P=0.013).Detection rate of adenomas was significantly lower than mucosal cancers(32%vs 79%,P=0.008)and T1 cancers(32%vs 78%,P=0.042).CONCLUSION:The detection rate of LSTs by CTC,particularly the non-granular type was not acceptable.Practitioners should be aware of the relatively low detection rate when using CTC.展开更多
基金The National Natural Science Foundation of China under contract Nos 91028006 and 41206046the Dayang 115 under contact No.DYXM-115-02-3-01
文摘Large-scale detachment faults on mid-ocean ridges (MORs) provide a window into the deeper earth. They have megamullion on their corrugated surfaces, with exposed lower crustal and upper mantle rocks, rela- tively high residual Bouguer gravity anomaly and P-wave velocity, and are commonly associated with ocean- ic core complex. According to 30 detachment faults identified on MORs, we found that their distances to the axis mostly range from 5 to 50 km, half-spreading rates range from 6.8 to 17 mm/a, and activity time ranges from recent to 3 Ma. Most of the detachment faults are developed on the slow spreading Mid-Atlantic Ridge (MAR) and ultra-slow spreading Southwest Indian Ridge (SWIRl, with the dominant half-spreading rates of 7-13 mm/a, especially 10-13 mm/a. Furthermore, they mostly occur at the inside corner of one segment end and result in an asymmetric seafloor spreading. The detachment faults on MORs are mainly controlled by the tectonism and influenced by the magmatism. Long-lived detachment faults tend to be formed where the ridge magma supply is at a moderate level, although the tectonism is a first-order controlling factor. At the slow spreading ridges, detachment faults tend to occur where local magma supply is relatively low, whilst at the ultra-slow spreading ridges, they normally occur where local magma supply is relatively high. These faults are accompanied by hydrothermal activities, with their relationships being useful in the study of hydrothermal polymetallic sulfides and their origin.
基金The foundation of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)under contract No.GML2019ZD0205the National Natural Science Foundation of China under contract Nos 41976064,41890813,41976066,91958211,and 41706056+4 种基金the scholarship of China Scholarship Councilthe foundations of the Chinese Academy of Sciences under contract Nos Y4SL021001,QYZDY-SSW-DQC005,133244KYSB20180029,and 131551KYSB20200021the National Key Research and Development Program of China under contract Nos 2018YFC0309800 and 2018YFC0310105the Foundation of the China Ocean Mineral Resources Research and Development Association under contract No.DY135-S2-1-04the Guangdong Basic and Applied Basic Research Foundation under contract No.2021A1515012227。
文摘We quantified the systematic variations in global transform fault morphology,revealing a first-order dependence on the spreading rate.(1)The average age offset of both the full transform and transform sub-segments decrease with increasing spreading rate.(2)The average depth of both the transform valley and adjacent ridges are smaller in the fast compared to the slow systems,reflecting possibly density anomalies associated with warmer mantle at the fast systems and rifting at the slow ridges.However,the average depth difference between the transform valley and adjacent ridges is relatively constant from the fast to slow systems.(3)The nodal basin at a ridge-transform intersection is deeper and dominant at the ultraslow and slow systems,possibly reflecting a lower magma supply and stronger viscous resistance to mantle upwelling near a colder transform wall.In contrast,the nodal high,is most prominent in the fast,intermediate,and hotspot-influenced systems,where robust axial volcanic ridges extend toward the ridge-transform intersection.(4)Statistically,the average transform valley is wider at a transform system of larger age offset,reflecting thicker deforming plates flanking the transform fault.(5)The maximum magnitude of the transform earthquakes increases with age offset owing to an increase in the seismogenic area.Individual transform faults also exhibit significant anomalies owing to the complex local tectonic and magmatic processes.
文摘The target of this study is to develop a spreading rate regression model capable of predicting rate of spread of Nigerian crude oil spills on water. The major factors responsible for spreading rate of crude oil on water were considered, namely surface tension, viscosity, and specific gravity/American Petroleum Institute degree (<sup>0</sup>API), all at specified temperature values. The surface tension, viscosity and density parameters were interactively measured under controlled factorial analysis. The spreading rate of each crude oil was determined by artificially spilling them on laboratory calm/stagnant water in a rectangular tank and their averages were also computed. These averages were used to develop a regression model equation for spreading rate. The model developed indicated that an average spreading rate was 3.3528 cm/s at 37.5<span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">°</span>C and the predictive regression model is evaluated with the interactions of specific gravity, viscosity and surface tension. It is convenient to state that the model will predict the spread rate of crude oils which possess imputed physicochemical properties having pour point averaged 15.5<span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">°</span>C on calm seawater.
基金Supported by the National Natural Science Foundation of China(No.69872027)
文摘It is well-known that the multi-valued CDMA spreading codes can be designed by means of a pair of mirror multi-rate filter banks based on some optimizing criterion. This paper indicates that there exists a theoretical bound in the performance of its circulating correlation property, which is given by an explicit expression. Based on this analysis, a criterion of maximizing entropy is proposed to design such codes. Computer simulation result suggests that the resulted codes outperform the conventional binary balanced Gold codes for an asynchronous CDMA system.
文摘文章研究了背景为子空间干扰加高斯杂波的距离扩展目标方向检测问题。杂波是均值为零协方差矩阵未知但具有斜对称特性的高斯杂波,目标与干扰分别通过具备斜对称特性的目标子空间和干扰子空间描述。针对方向检测问题,利用上述斜对称性,根据广义似然比检验(Generalized Likeli-hood Ratio Test,GLRT)准则的一步与两步设计方法,设计了基于GLRT的一步法与两步法的距离扩展目标方向检测器。通过理论推导证明了这2种检测器相对于未知杂波协方差矩阵都具有恒虚警率。对比相同背景下已有检测器,特别是在辅助数据有限的场景下,文章提出的2个检测器表现出了优越的检测性能。
基金Funding was provided by Anadolu University Scientific Research Project Commission(Grant number:1605E282).
文摘This study investigates the international spillover effects of US unconventional monetary policy(UMP)-frequently called large-scale asset purchases or quantitative easing(QE)—on advanced and emerging market economies,using structural vector autoregressive models with high-frequency daily data.Blinder(Federal Reserve Bank of St.Louis Rev 92(6):465–479,2010)argued that the QE measures primarily aim to reduce US interest rate spreads,such as term and risk premiums.Considering this argument and recent empirical evidence,we use two spreads as indicators of US UMP:the mortgage and term spreads.Based on data from 20 emerging and 20 advanced countries,our empirical findings reveal that US unconventional monetary policies significantly affect financial conditions in emerging and advanced countries by altering the risktaking behavior of investors.This result suggests that the risk-taking channel plays an important role in transmitting the effects of these policies to the rest of the world.The extent of these effects depends on the type of QE measures.QE measures such as purchases of private sector securities that lower the US mortgage spread exert stronger and more significant spillover effects on international financial markets than those that reduce the US term spread.Furthermore,the estimated financial spillovers vary substantially across countries and between and within the emerging and advanced countries that we examine in this study.
文摘Chinese tallow tree (Triadica sebifera (L.) Small, Sapium sebiferum (L.) Roxb) is an invasive species that is replacing native ecosystems in areas of eastern Texas. It is imperative that the spatial pattern of the spread of this species be identified, as well as causal mechanisms. To that end, we seek to determine factors that contribute to the spread of Chinese tallow using classification and regression tree (CART) and logistic regression. We also attempt to identify current locations and spread rates across eastern Texas using Forest Inventory Analysis (FIA) data within major forest types. Distance to formerly infested plots and roads, slope, and disturbances (natural and anthropogenic) were identified as major (either facilitating or impeding) factors for the spread of Chinese tallow across the landscape. The highest probability of occurrence and spread rate of Chinese tallow were found in the oak/ gum/cypress forest type. Continued disturbance, from harvest events or natural disasters will allow the species to continue to spread throughout the region and could threaten overall forest productivity. We also discuss some implications of the continued spread of Chinese tallow on forest management. Forest managers could benefit from this analysis and use it as a guide for monitoring forest types with the highest risk of invasion.
文摘AIM:To prospectively investigate the detection rate of laterally spreading tumors(LSTs)of the colorectum by computed tomography(CT)colonography(CTC).METHODS:Patients with LSTs measuring≥20 mm detected during colonoscopy were prospectively enrolled in the study.All patients underwent colonoscopy and subsequent CTC on the same day.CTC was performed using multi-detector CT without contrast in the prone and supine positions.Two radiologists blinded to the existence of LSTs read the virtual endoscopic images as well as 2-D images.LSTs were classified into granular and non-granular types based on colonoscopic appearance.RESULTS:Forty-seven pathologically proven LSTs were evaluated prospectively.Histology included adenomas in 19,mucosal cancers in 19 and T1 cancers in 9.The mean diameter of the LSTs was 35.1 mm.Twenty-eight(60%)LSTs were correctly identified by CTC,and the configuration was similar to the colonoscopic appearance in most cases.Detection rate for the granular type was significantly higher than that for the nongranular type(71%vs 31%,P=0.013).Detection rate of adenomas was significantly lower than mucosal cancers(32%vs 79%,P=0.008)and T1 cancers(32%vs 78%,P=0.042).CONCLUSION:The detection rate of LSTs by CTC,particularly the non-granular type was not acceptable.Practitioners should be aware of the relatively low detection rate when using CTC.