De-farming slope farmland has been an effective measure in recent years to improve environment and prevent soil and water loss on the Loess Plateau.There are different views about the defarming method,and also various...De-farming slope farmland has been an effective measure in recent years to improve environment and prevent soil and water loss on the Loess Plateau.There are different views about the defarming method,and also various de-farming patterns have been put into practice.This paper takes the Yangou Watershed in Shaanxi Province of China as a case for studying the comprehensive benefits of transforming slope farmland to terraces.Based on the day-by-day meteorological data of the Yan'an station in 2005 and the data of terrain features,soil and land use data of the Yangou Watershed,the impact of transforming slope farmland on terraces were simulated and analyzed in aspects of yield increase and water-soil conservation under different topographic conditions with the aid of software WIN-YIELD.Furthermore,an empirical analysis was applied to study the effects of transforming slope farmland to terraces in the Yangou Watershed.The results show that:(1) The bigger the topographic gradient is,the more remarkable benefits it has in yield increase and water-soil conservation.(2) Farmland with slope below 5° could be retained,but farmland with slope above 15° should be converted to forest or grassland as soon as possible.(3) Transforming slope farmland to terraces has the same remarkable effects as the current policy of "Relieving and de-farming" in improving agricultural production conditions,safeguarding food security,raising permanent vegetation coverage rate,and preventing soil and water loss.Besides,it is more cost-effective than the policy of "Relieving and de-farming".It's strongly suggested that the policy of transforming slope farmland to terraces be carried out on the Loess Plateau without delay.展开更多
The Shipborne acoustic communication system of the submersible Shenhai Yongshi works in vertical, horizontal and slant channels according to the relative positions. For ease of use, an array combined by a vertical-con...The Shipborne acoustic communication system of the submersible Shenhai Yongshi works in vertical, horizontal and slant channels according to the relative positions. For ease of use, an array combined by a vertical-cone directional transducer and a horizontal-toroid one is installed on the mothership. Improved techniques are proposed to combat adverse channel conditions, such as frequency selectivity, non-stationary ship noise, and Doppler effects of the platform’s nonlinear movement. For coherent modulation, a turbo-coded single-carrier scheme is used. In the receiver, the sparse decision-directed Normalized Least-Mean-Square soft equalizer automatically adjusts the tap pattern and weights according to the multipath structure, the two receivers’ asymmetry, the signal’s frequency selectivity and the noise’s spectrum fluctuation. The use of turbo code in turbo equalization significantly suppresses the error floor and decreases the equalizer’s iteration times, which is verified by both the extrinsic information transfer charts and bit-error-rate performance. For noncoherent modulation, a concatenated error correction scheme of nonbinary convolutional code and Hadamard code is adopted to utilize full frequency diversity. Robust and lowcomplexity synchronization techniques in the time and Doppler domains are proposed. Sea trials with the submersible to a maximum depth of over 4500 m show that the shipborne communication system performs robustly during the adverse conditions. From the ten-thousand communication records in the 28 dives in 2017, the failure rate of the coherent frames and that of the noncoherent packets are both below 10%, where both synchronization errors and decoding errors are taken into account.展开更多
Laparoendoscopic single-site surgery(LESS)is technically challenging;it can reduces instrument triangulation and robust retraction and is associated with a steep learning curve.The instruments of the daVinci surgic...Laparoendoscopic single-site surgery(LESS)is technically challenging;it can reduces instrument triangulation and robust retraction and is associated with a steep learning curve.The instruments of the daVinci surgical system(Intuitive Surgical)are designed with seven degrees of motion mimicing the dexterity of the human hand and wrist.This inherent feature of the robotic arm provides superior ergonomics when performing LESS,especially for complex reconstructive surgery.This review analyzes the evidence supporting current and future application of robotic technology in the field of urologic LESS.展开更多
The Upper Ediacaran microbial carbonates of the Tarim Basin are potential reservoir geobodies for future hydrocarbon exploration with rising interest in exploration for deeply-buried reserves.However,little knowledge ...The Upper Ediacaran microbial carbonates of the Tarim Basin are potential reservoir geobodies for future hydrocarbon exploration with rising interest in exploration for deeply-buried reserves.However,little knowledge has been acquired on the types of microbial carbonates that are present,the properties of the reservoir and the pore evolution,hampering predictions of high-quality reservoirs in these carbonates.Integrated with petrography and in-situ U-Pb dating geochronology analyses,this study aims to clarify the types of microbial carbonates present and to reconstruct the pore evolution processes of the potential reservoir rocks.The Upper Ediacaran microbial carbonates of the Tarim Basin can be divided into four types,based on their features in terms of different scales(macro-to micro-):microbial laminite,stromatolite,spongiomicrobialite and microbial-peloidal wackestone/mudstone.Petrophysical properties show that all these microbial carbonates have low porosity and very low permeability with poor connectivity.These carbonates were subject to long-term and complex diagenetic processes,mainly consisting of dissolution,compaction,pervasive dolomitization,cementation and fracturing.The most important reservoir spaces are contributed by vugs and dissolution-enlarged pores,which are likely to have been associated with the widespread uplift of the Aksu area in the terminal Ediacaran.In contrast,the cementation of the fine-to-medium crystalline dolomite greatly reduced the pre-existing pores.Pore types are closely related to different microbial fabrics,which played an important role in the pore evolution of the microbial carbonates.展开更多
There exists many kinds of calculation models of plane and spherical strain fields, but the results of these models are different. The representative models was analyzed, and got some useful conclusions, in which some...There exists many kinds of calculation models of plane and spherical strain fields, but the results of these models are different. The representative models was analyzed, and got some useful conclusions, in which some models are unbiased, some have deviations that can be corrected, some can only be used to compute strain in a uniform medium and can not be extended, and some can be used in the calculation and analysis of continuous strain field as well. Meanwhile, the correction relationship for spherical difference movement （displacement） computed from strain results was given, and the meaning of the non - differential term in spherical strain model was demonstrated.展开更多
采用Halbach单侧聚磁特性,设计出了一种大气隙外笼型转子磁力耦合器(Long Air Gap External-cage Rotor Magnetic Coupler,LAEMC),并分析了其运行特性、调速特性及散热特性,推导出LAEMC电磁转矩解析表达式,据此分析了结构参数对电磁转...采用Halbach单侧聚磁特性,设计出了一种大气隙外笼型转子磁力耦合器(Long Air Gap External-cage Rotor Magnetic Coupler,LAEMC),并分析了其运行特性、调速特性及散热特性,推导出LAEMC电磁转矩解析表达式,据此分析了结构参数对电磁转矩的影响,得出了不同磁化比的Halbach结构对LAEMC电磁转矩的影响规律;根据LAEMC的运行特性,分析了其在离心式负载、恒功率负载及恒转矩负载的调速特性,表明其仅适合离心式负载调速并具有良好的节能效果;在离心式负载转差率为33%处的最大功率损耗点对LAEMC进行热仿真计算,得到永磁体工作温度约为60℃,而通过气隙与之相隔的笼条温度约为360℃,两者温度差达300℃以上,表明所提出的大气隙外笼型转子磁力耦合器———LAEMC在离心式负载上既具有良好的运行特性也具有良好的隔热效果。展开更多
基金the National Natural Science Foundation of China(No.40771086)National Key Technology R&D Program of China (No.2006BAD09B10)Knowledge Innovation Project of Chinese Academy of Sciences (No.KZCX2-XB2-05-01)
文摘De-farming slope farmland has been an effective measure in recent years to improve environment and prevent soil and water loss on the Loess Plateau.There are different views about the defarming method,and also various de-farming patterns have been put into practice.This paper takes the Yangou Watershed in Shaanxi Province of China as a case for studying the comprehensive benefits of transforming slope farmland to terraces.Based on the day-by-day meteorological data of the Yan'an station in 2005 and the data of terrain features,soil and land use data of the Yangou Watershed,the impact of transforming slope farmland on terraces were simulated and analyzed in aspects of yield increase and water-soil conservation under different topographic conditions with the aid of software WIN-YIELD.Furthermore,an empirical analysis was applied to study the effects of transforming slope farmland to terraces in the Yangou Watershed.The results show that:(1) The bigger the topographic gradient is,the more remarkable benefits it has in yield increase and water-soil conservation.(2) Farmland with slope below 5° could be retained,but farmland with slope above 15° should be converted to forest or grassland as soon as possible.(3) Transforming slope farmland to terraces has the same remarkable effects as the current policy of "Relieving and de-farming" in improving agricultural production conditions,safeguarding food security,raising permanent vegetation coverage rate,and preventing soil and water loss.Besides,it is more cost-effective than the policy of "Relieving and de-farming".It's strongly suggested that the policy of transforming slope farmland to terraces be carried out on the Loess Plateau without delay.
基金financially supported by the National Natural Science Foundation of China(Grant No.61471351)the National Key Research and Development Program of China(Grant Nos.2016YFC0300300 and 2016YFC0300605)the National High Technology Research and Development Program of China(863 Program,Grant No.2009AA093301)
文摘The Shipborne acoustic communication system of the submersible Shenhai Yongshi works in vertical, horizontal and slant channels according to the relative positions. For ease of use, an array combined by a vertical-cone directional transducer and a horizontal-toroid one is installed on the mothership. Improved techniques are proposed to combat adverse channel conditions, such as frequency selectivity, non-stationary ship noise, and Doppler effects of the platform’s nonlinear movement. For coherent modulation, a turbo-coded single-carrier scheme is used. In the receiver, the sparse decision-directed Normalized Least-Mean-Square soft equalizer automatically adjusts the tap pattern and weights according to the multipath structure, the two receivers’ asymmetry, the signal’s frequency selectivity and the noise’s spectrum fluctuation. The use of turbo code in turbo equalization significantly suppresses the error floor and decreases the equalizer’s iteration times, which is verified by both the extrinsic information transfer charts and bit-error-rate performance. For noncoherent modulation, a concatenated error correction scheme of nonbinary convolutional code and Hadamard code is adopted to utilize full frequency diversity. Robust and lowcomplexity synchronization techniques in the time and Doppler domains are proposed. Sea trials with the submersible to a maximum depth of over 4500 m show that the shipborne communication system performs robustly during the adverse conditions. From the ten-thousand communication records in the 28 dives in 2017, the failure rate of the coherent frames and that of the noncoherent packets are both below 10%, where both synchronization errors and decoding errors are taken into account.
文摘Laparoendoscopic single-site surgery(LESS)is technically challenging;it can reduces instrument triangulation and robust retraction and is associated with a steep learning curve.The instruments of the daVinci surgical system(Intuitive Surgical)are designed with seven degrees of motion mimicing the dexterity of the human hand and wrist.This inherent feature of the robotic arm provides superior ergonomics when performing LESS,especially for complex reconstructive surgery.This review analyzes the evidence supporting current and future application of robotic technology in the field of urologic LESS.
基金financially supported by the National Key Research and Development(R&D)Program of China(2017YFC0603103)the National Natural Science Foundation of China(U19B6003)。
文摘The Upper Ediacaran microbial carbonates of the Tarim Basin are potential reservoir geobodies for future hydrocarbon exploration with rising interest in exploration for deeply-buried reserves.However,little knowledge has been acquired on the types of microbial carbonates that are present,the properties of the reservoir and the pore evolution,hampering predictions of high-quality reservoirs in these carbonates.Integrated with petrography and in-situ U-Pb dating geochronology analyses,this study aims to clarify the types of microbial carbonates present and to reconstruct the pore evolution processes of the potential reservoir rocks.The Upper Ediacaran microbial carbonates of the Tarim Basin can be divided into four types,based on their features in terms of different scales(macro-to micro-):microbial laminite,stromatolite,spongiomicrobialite and microbial-peloidal wackestone/mudstone.Petrophysical properties show that all these microbial carbonates have low porosity and very low permeability with poor connectivity.These carbonates were subject to long-term and complex diagenetic processes,mainly consisting of dissolution,compaction,pervasive dolomitization,cementation and fracturing.The most important reservoir spaces are contributed by vugs and dissolution-enlarged pores,which are likely to have been associated with the widespread uplift of the Aksu area in the terminal Ediacaran.In contrast,the cementation of the fine-to-medium crystalline dolomite greatly reduced the pre-existing pores.Pore types are closely related to different microbial fabrics,which played an important role in the pore evolution of the microbial carbonates.
基金supported by the Natural Eleventh Five Years Scientific and Technolosical Plan( 2006BACOLB03-01-01)
文摘There exists many kinds of calculation models of plane and spherical strain fields, but the results of these models are different. The representative models was analyzed, and got some useful conclusions, in which some models are unbiased, some have deviations that can be corrected, some can only be used to compute strain in a uniform medium and can not be extended, and some can be used in the calculation and analysis of continuous strain field as well. Meanwhile, the correction relationship for spherical difference movement （displacement） computed from strain results was given, and the meaning of the non - differential term in spherical strain model was demonstrated.
文摘采用Halbach单侧聚磁特性,设计出了一种大气隙外笼型转子磁力耦合器(Long Air Gap External-cage Rotor Magnetic Coupler,LAEMC),并分析了其运行特性、调速特性及散热特性,推导出LAEMC电磁转矩解析表达式,据此分析了结构参数对电磁转矩的影响,得出了不同磁化比的Halbach结构对LAEMC电磁转矩的影响规律;根据LAEMC的运行特性,分析了其在离心式负载、恒功率负载及恒转矩负载的调速特性,表明其仅适合离心式负载调速并具有良好的节能效果;在离心式负载转差率为33%处的最大功率损耗点对LAEMC进行热仿真计算,得到永磁体工作温度约为60℃,而通过气隙与之相隔的笼条温度约为360℃,两者温度差达300℃以上,表明所提出的大气隙外笼型转子磁力耦合器———LAEMC在离心式负载上既具有良好的运行特性也具有良好的隔热效果。
