期刊文献+
共找到147,518篇文章
< 1 2 250 >
每页显示 20 50 100
Micromagnetic simulations on demagnetization processes in anisotropic Nd2Fe14B magnets
1
作者 Lei Li Shengzhi Dong +5 位作者 Rui Han Kuikui Song Dong Li Minggang Zhu Wei Li Wei Sun 《中国稀土学报:英文版》 SCIE EI CAS CSCD 2019年第6期628-632,共5页
Individual grains with diverse dimensional parameters were introduced to investigate the magnetization reversals in anisotropic Nd2 Fe14B magnets. The micromagnetic simulations were carried out via Object Oriented Mic... Individual grains with diverse dimensional parameters were introduced to investigate the magnetization reversals in anisotropic Nd2 Fe14B magnets. The micromagnetic simulations were carried out via Object Oriented MicroMagnetic Framework(OOMMF). With the same bottom area and height, analysis results show that the coercive fields for different bottom shapes are of similar values. Designed as a cubic grain,the coercive field presents descending tendency as grain volume ascends. Under constant grain volume,with aspect ratio increasing, the coercive field decreases in the beginning and increases soon. Based on the demagnetization field vector, the effects of bottom shape, grain volume and aspect ratio on the coercive field can be explained. The nucleation point is chosen to discuss. Its synthetic field and reversal field are calculated by parallelogram law and inverse external field equation, respectively. The synthetic field equal to the reversal field is defined as critical field, which always shows the same tendency as the coercive field for all cases of this study. It can be concluded that critical field is qualified to be a reference index to measure the magnitude of coercive field. 展开更多
关键词 MICROMAGNETIC simulation DEMAGNETIZATION FIELD Coercive FIELD SYNTHETIC FIELD CRITICAL FIELD Rare earths
Effects of freeze-thaw cycle and dry-wet alternation on slope stability 预览
2
作者 YaLing Chou LiYuan Sun +1 位作者 BaoAn Li XiaoLi Wang 《寒旱区科学:英文版》 CSCD 2019年第2期159-172,共14页
The typical loess on high slopes along the BaoLan High-speed Rail, China, was selected as the research object. The influence of the freeze-thaw cycle and dry-wet alternation on the shear-strength parameters of the uns... The typical loess on high slopes along the BaoLan High-speed Rail, China, was selected as the research object. The influence of the freeze-thaw cycle and dry-wet alternation on the shear-strength parameters of the unsaturated loess was investigated by laboratory experimental methods. Moreover, the temperature field, seepage field, and stability of slopes with different gradients were simulated under the effect of the freeze-thaw cycle and dry-wet alternation by using the geotechnical analysis software Geo-Studio. The research results showed (1) when the freeze -thaw cycle was repeated on the slope, with the frozen depth increasing, the melted depth did the same;besides, the closed loop of isotherms formed on the slope;(2) under the action of dry-wet circulation, the negative pore-water pressure and volumetric water content showed an upward tendency. However, owing to the different slope gradients, rainfall infiltration was not the same. As time went by, the differences of the negative pore-water pressure and volumetric water content between the slopes of different gradients continued to increase;(3) with the freeze-thaw cycle and dry-wet alternation increasing, the slope-safety factor decreased. Especially in the early period, the slope-safety factor changed remarkably. For slopes undergoing freeze-thaw action, the slope-safety factor was negatively correlated with the gradient. However, with regard to slopes undergoing dry- wet alternation, the result became more complex because the slope-safety factor was related to both seepage strength and slope grade. Accordingly, further research is needed to study the effect of seepage strength and slope grade on the stability of loess slopes. 展开更多
关键词 FREEZE-THAW action dry-wet ALTERNATION temperature FIELD SEEPAGE FIELD slope stability
在线阅读 下载PDF
Causes of geothermal fields and characteristics of ground temperature fields in China 预览
3
作者 MAO Xiao-ping LI Ke-wen WANG Xin-wei 《地下水科学与工程:英文版》 2019年第1期15-28,共14页
There are many arguments on energy sources and main controlling factors of geothermal fields, so a systematic study on the distribution of ground temperature fields shall be necessary. In this paper the thermal conduc... There are many arguments on energy sources and main controlling factors of geothermal fields, so a systematic study on the distribution of ground temperature fields shall be necessary. In this paper the thermal conduction forward method of geothermal field is used to simulate cooling rate of abnormal heat sources and heat transfer of the paleo-uplift model. Combined with a large number of geothermal field exploration cases and oil exploration well temperature curves of domestic and foreign, the following conclusions are drawn:(1) According to the magmatic activity time, the magmatism activities are divided into two categories: Magma active areas (activity time < 500 000 years) and weak/magma inactive areas (activity time > 500 000 years). The latter has a fast cooling rate (the cooling time of the magma pocket buried around 10 km is less than 200 000 years) after it has intruded into the shallow layer and it has no direct contribution to modern geothermal fields;(2) China belongs to a weak/magma inactive area such as Tengchong region and Qinghai-Tibet region because the chronological data of these regions show that its magma activity time is more than 500 000 years;(3) The temperature of most geothermal fields can be obviously divided into three segments in the vertical direction: A high geothermal gradient segment (Segment H) at the surface, then a low geothermal gradient segment (Segment L) at a secondary depth, and finally a lower temperature segment (Segment D) at a deeper depth. The temperature isoline presents a mirror reflection relation on the temperature profile, indicating that geothermal field is dominated by heat conduction, rather than having an abnormally high temperature “heat source” to provide heat;(4) Near-surface (0-5 km) materials’ lateral heterogeneity caused by tectonic movement shall probably be the main controlling factor of ground temperature fields. 展开更多
关键词 Ground temperature FIELD BASEMENT HEAT flow GEOTHERMAL FIELD MAGMA pocket Coefficient of HEAT conduction Palaeouplifth MAGNETOTELLURIC
在线阅读 下载PDF
Modeling electric field of power metal-oxide-semiconductor field-effect transistor with dielectric trench based on Schwarz–Christoffel transformation
4
作者 汪志刚 廖涛 王亚南 《中国物理B:英文版》 SCIE EI CAS CSCD 2019年第5期366-373,共8页
A power metal-oxide-semiconductor field-effect transistor (MOSFET) with dielectric trench is investigated to enhance the reversed blocking capability.The dielectric trench with a low permittivity to reduce the electri... A power metal-oxide-semiconductor field-effect transistor (MOSFET) with dielectric trench is investigated to enhance the reversed blocking capability.The dielectric trench with a low permittivity to reduce the electric field at reversed blocking state has been studied.To analyze the electric field,the drift region is segmented into four regions,where the conformal mapping method based on Schwarz–Christoffel transformation has been applied.According to the analysis,the improvement in the electric field for using the low permittivity trench is mainly due to the two electric field peaks generated in the drift region around this dielectric trench.The analytical results of the electric field and the potential models are in good agreement with the simulation results. 展开更多
关键词 CONFORMAL mapping Schwarz–Christoffel TRANSFORMATION electric field TRENCH metal-oxidesemiconductor FIELD-EFFECT transistor (MOSFET) breakdown voltage
Effects of rotation and gravity on an electro-magneto-thermoelastic medium with diffusion and voids by using the Lord-Shulman and dual-phase-lag models 预览
5
作者 S.M.ABO-DAHAB A.M.ABD-ALLA A.A.KILANY 《应用数学和力学:英文版》 SCIE EI CSCD 2019年第8期1135-1154,共20页
The effects of rotation and gravity on an electro-magneto-thermoelastic medium with diffusion and voids in a generalized thermoplastic half-space are studied by using the Lord-Shulman (L-S) model and the dual-phase-la... The effects of rotation and gravity on an electro-magneto-thermoelastic medium with diffusion and voids in a generalized thermoplastic half-space are studied by using the Lord-Shulman (L-S) model and the dual-phase-lag (DPL) model. The analytical solutions for the displacements, stresses, temperature, diffusion concentration, and volume fraction field with different values of the magnetic field, the rotation, the gravity, and the initial stress are obtained and portrayed graphically. The results indicate that the effects of gravity, rotation, voids, diffusion, initial stress, and electromagnetic field are very pronounced on the physical properties of the material. 展开更多
关键词 electromagnetic field GRAVITY field ROTATION initial stress voids DIFFUSION normal mode analysis Lord-Shulman (L-S) model dual-phase-lag (DPL) model
在线阅读 下载PDF
Optimization of ambipolar current and analog/RF performance for T-shaped tunnel field-effect transistor with gate dielectric spacer
6
作者 韩茹 张海潮 +1 位作者 王党辉 李翠 《中国物理B:英文版》 SCIE EI CAS CSCD 2019年第1期656-662,共7页
A new T-shaped tunnel field-effect transistor(TTFET) with gate dielectric spacer(GDS) structure is proposed in this paper. To further studied the effects of GDS structure on the TTFET, detailed device characteristics ... A new T-shaped tunnel field-effect transistor(TTFET) with gate dielectric spacer(GDS) structure is proposed in this paper. To further studied the effects of GDS structure on the TTFET, detailed device characteristics such as current-voltage relationships, energy band diagrams, band-to-band tunneling(BTBT) rate and the magnitude of the electric field are investigated by using TCAD simulation. It is found that compared with conventional TTFET and TTFET with gate-drain overlap(GDO) structure, GDS-TTFET not only has the minimum ambipolar current but also can suppress the ambipolar current under a more extensive bias range. Furthermore, the analog/RF performances of GDS-TTFET are also investigated in terms of transconductance, gate-source capacitance, gate-drain capacitance, cutoff frequency, and gain bandwidth production. By inserting a low-κ spacer layer between the gate electrode and the gate dielectric, the GDS structure can effectively reduce parasitic capacitances between the gate and the source/drain, which leads to better performance in term of cutoff frequency and gain bandwidth production. Finally, the thickness of the gate dielectric spacer is optimized for better ambipolar current suppression and improved analog/RF performance. 展开更多
关键词 tunneling field effect TRANSISTOR T-SHAPED TUNNEL FIELD-EFFECT TRANSISTOR gate dielectric SPACER ambipolar current analog/RF performance
“场域-惯习”视域下的皖北篾器工艺分析 预览
7
作者 彭心勤 《景德镇学院学报》 2019年第1期94-98,共5页
皖北篾器工艺是皖北地域一项重要的传统手工技艺。皖北篾器原材料的土壤环境、地理及气候对皖北蔑器器型、材料与工艺特征发展起到本源性的制约作用。以实践社会学的“场域-惯习”的理论为方法论,通过对皖北篾器原材料的生长环境分析,... 皖北篾器工艺是皖北地域一项重要的传统手工技艺。皖北篾器原材料的土壤环境、地理及气候对皖北蔑器器型、材料与工艺特征发展起到本源性的制约作用。以实践社会学的“场域-惯习”的理论为方法论,通过对皖北篾器原材料的生长环境分析,疏导出皖北篾器的地理空间特质,依据皖北篾器的场域特征,将这种地理空间和社会空间结合,可以总结出皖北篾器工艺的场域特征。继而以皖北篾器从业手艺人的惯习为媒介,通过场域和惯习的关系分析,以期对皖北篾器工艺的传承性创新场域的建构做出一个揭示。 展开更多
关键词 皖北篾器工艺 “场域” “惯习” 创新场域
在线阅读 下载PDF
Validation and reproducibility of the Heidelberg Edge Perimeter in the detection of glaucomatous visual field defects
8
作者 Qi N. Cui Priyanka Gogt +5 位作者 Jonathan M. Lam Safa Siraj Lisa A. Hark Jonathan S. Myers L. Jay Katz Michael Waisbourd 《国际眼科杂志:英文版》 SCIE CAS 2019年第4期577-581,共5页
AIM: To validate the ability of the Heidelberg Edge Perimeter (HEP) in detecting glaucomatous visual field (VF) defects compared to the Octopus Visual Field (OVF) Analyzer and to determine the test-retest repeatabilit... AIM: To validate the ability of the Heidelberg Edge Perimeter (HEP) in detecting glaucomatous visual field (VF) defects compared to the Octopus Visual Field (OVF) Analyzer and to determine the test-retest repeatability of both modalities. METHODS: This prospective, cross-sectional study was conducted at Wills Eye Hospital, Philadelphia, PA. Glaucoma subjects and unaffected controls underwent VF testing using HEP standard automated perimetry (SAP) III 30-2 Adaptive Staircase Thresholding Algorithm (ASTA) FAST protocol and OVF G-TOP white-on-white strategy. Testing order was randomized. Pearson’s correlation coefficient was calculated for both mean deviation (MD) and pattern standard deviation/square root of loss of variance (PSD/sLV). Receiver operating characteristic (ROC) curves were used to determine the diagnostic abilities of both modalities. Glaucoma subjects returned for repeat testing and intraclass correlation coefficients (ICCs) were calculated to assess test-retest repeatability. RESULTS: Seventy-nine subjects with glaucoma and 36 unaffected controls were enrolled. HEP and OVF were significantly correlated for both MD (r=-0.84;P<0.01) and PSD/sLV (r=0.79;P<0.01). Areas under the ROC curves (AUCs) were also comparable between HEP and OVF for both MD (0.74 and 0.79, respectively;P=0.26) and PSD/sLV (0.74 and 0.82;P=0.08). ICC was high for both HEP (0.96 for MD, 0.95 for PSD/sLV) and OVF (0.82 and 0.88, respectively). Mean test duration (min) was significantly shorter for OVF (2.63) compared to HEP (5.15;P<0.01). CONCLUSION: HEP and OVF show strong correlation for both MD and PSD/sLV, and have similar validity for detecting glaucoma. The test-retest repeatability is high for both HEP and OVF, however the average testing duration of HEP is significantly longer than that of OVF. 展开更多
关键词 glaucoma HEIDELBERG EDGE PERIMETER standard automated PERIMETRY Octopus VISUAL FIELD Analyzer VISUAL FIELD
Spontaneous magnetic field multipolar structure in toroidal plasmas based on 2D equilibrium
9
作者 何柳秀 刘明海 赵双云 《等离子体科学与技术:英文版》 SCIE EI CAS CSCD 2019年第4期70-75,共6页
The multipolar magnetic field structure is investigated by the momentum conservation equation with self-c on sistent 3D sheared flows during transition of plasma properties from local paramagnetic to diamagnelic field... The multipolar magnetic field structure is investigated by the momentum conservation equation with self-c on sistent 3D sheared flows during transition of plasma properties from local paramagnetic to diamagnelic fields.Numerical results show that the traditional poloidal magnetic field(Bp)is one part of equilibrium magnetic fields.The non-zero-order quantities are originaled from the higher-order terms of 2D equilibrium treatment based on a Fourier expansion of 0(r,0).The distributions of magnetic field vectors of the order of 1,2,and 3 terms are presented respectively in two.four,and six polar fields with the local vortex structures(spontaneous magnetic conn ection).The excitation mechanisms of the magnetic vortices are the coupling effects of the magnetic fluid structure pattern and the toroidal effects.These results can help us understand the physical mechanism of the in teraction between the external perturbation fields and control tearing modes,as well as the radial plasma flow and magnetic vortices. 展开更多
关键词 magnetic FIELD configuration VORTEX STRUCTURE multipolar FIELD
Design and Application of a New Splitter Plate Pressure Probe for Wind Tunnel Flow Measurements 预览
10
作者 Kasim Biber 《机械工程与自动化:英文版》 2019年第6期188-192,共5页
A new siplitter plate presure probe was developed for flow field measurements on an airfoil with slotted flap in a low speed wind tunnel with 7 by 10 ft test section. Wind tunnel tests were conducted at a Reynolds num... A new siplitter plate presure probe was developed for flow field measurements on an airfoil with slotted flap in a low speed wind tunnel with 7 by 10 ft test section. Wind tunnel tests were conducted at a Reynolds number of 2.2 million and Mach number of 0.13. The splitter plate was made of aluminum and had pressure taps on its one side. The probe can make many measurements in the plane of the plate simultaneously by using these pressure tabs. It was supported by a traversing strut in the wind tunnel and surveyed the flow field on the airfoil upper surface. Measured pressures were presented by isobars of coefficients. These isobars were connected with the pressure coefficients distributed over the airfoil. Results of splitter plate pressure probe compare well with other single-point measuring probes. However, results show that no matter how small the probe, its presence in the flow causes a disturbance, especially in the highly time-dependent separated flow regions. 展开更多
关键词 Splitter plate-pressure probe flow field pressures wind tunnel instrumentation flow field isobars multi-element
在线阅读 下载PDF
Efficient construction of a substitution box based on a Mordell elliptic curve over a finite field
11
作者 Naveed Ahmed AZAM Umar HAYAT Ikram ULLAH 《信息与电子工程前沿:英文版》 SCIE EI CSCD 2019年第10期1378-1389,共12页
Elliptic curve cryptography has been used in many security systems due to its small key size and high security compared with other cryptosystems. In many well-known security systems, a substitution box (S-box) is the ... Elliptic curve cryptography has been used in many security systems due to its small key size and high security compared with other cryptosystems. In many well-known security systems, a substitution box (S-box) is the only non-linear component. Recently, it has been shown that the security of a cryptosystem can be improved using dynamic S-boxes instead of a static S-box. This necessitates the construction of new secure S-boxes. We propose an efficient method to generate S-boxes that are based on a class of Mordell elliptic curves over prime fields and achieved by defining different total orders. The proposed scheme is devel-oped in such a way that for each input it outputs an S-box in linear time and constant space. Due to this property, our method takes less time and space than the existing S-box construction methods over elliptic curves. Computational results show that the pro-posed method is capable of generating cryptographically strong S-boxes with security comparable to some of the existing S-boxes constructed via different mathematical structures. 展开更多
关键词 Substitution box Finite field Mordell elliptic curve Total order Computational complexity
The influence of irregular seafloor topography on the seismic wave field and migration imaging 预览
12
作者 Fuxing Han Kun Wang Jianguo Sun 《海洋学报:英文版》 SCIE CAS CSCD 2019年第3期151-158,共8页
One of the problems experienced in marine geophysical exploration is that the layered features in the migration imaging profile are blurred and the seismic energy reflected is weaker in the middle or lower parts. In t... One of the problems experienced in marine geophysical exploration is that the layered features in the migration imaging profile are blurred and the seismic energy reflected is weaker in the middle or lower parts. In this study we model the seismic wavefield records in the undulating seafloor when there is both a slight change and significant change in seafloor topography to analyze its influence on the seismic reflection data and migration imaging profiles. We compare and analyze the wave field records collected at the same point on the original and modified velocity models, and the cross-bonding resulting migration imaging profiles. The results show that whether the seismic reflection data collection is performed along the direction of the survey line or against the direction of the survey line, slight changes in the seafloor topography have little effect on the wave field records and the migration profile, while significant changes in the seafloor topography have great effect on both the wave field records and migration profile. 展开更多
关键词 SEAFLOOR TOPOGRAPHY SEISMIC wave field SEISMIC REFLECTIONS MIGRATION imaging
在线阅读 下载PDF
Simulated impacts of atmospheric gravity waves on the initiation and optical emissions of sprite halos in the mesosphere
13
作者 Jinbo ZHANG Qilin ZHANG +2 位作者 Xiufeng GUO Wenhao HOU Haiyang GAO 《中国科学:地球科学英文版》 SCIE EI CAS CSCD 2019年第4期631-642,共12页
The correlation between atmospheric gravity waves(GWs) and Transient Luminous Events(TLEs) has been poorly studied using both synchronous observations and numerical simulations. To investigate the modulation effects o... The correlation between atmospheric gravity waves(GWs) and Transient Luminous Events(TLEs) has been poorly studied using both synchronous observations and numerical simulations. To investigate the modulation effects of GWs on TLEs,a troposphere-mesosphere quasi-electrostatic field model is developed in three-dimensional Cartesian coordinates, and the effects of GW perturbations on the initiation and optical emissions of sprite halos are simulated using the model. Simulation results indicate that the atmospheric density at lower ionosphere altitudes becomes inhomogeneous due to GW perturbations, and sprite halos tend to initiate in the GW troughs due to the lower electric breakdown threshold. GW perturbations cause the deformation of sprite halos, strong luminous regions distribute mainly along the GW troughs while optical intensities along the GW peaks is relatively weak. Larger GW perturbations lead to more pronounced deformation of sprite halos, however, stronger lightning discharges in the troposphere result in less optical perturbations of sprite halos. The observed luminous intensities and optical morphology of sprite halos are also affected by the observing orientations and the lightning polarities. 展开更多
关键词 Three-dimensional quasi-electrostatic field model SPRITE HALOS Optical emission Gravity WAVES
Zeeman slowing atoms using the magnetic field from a magneto-optical trap
14
作者 晏文 姚远 +3 位作者 孙雨昕 Hoyt W.Chad 蒋燕义 马龙生 《中国光学快报:英文版》 SCIE EI CAS CSCD 2019年第4期6-9,共4页
We study a Zeeman slower using the magnetic field generated by a pair of coils for a magneto-optical trap. The efficiency of the Zeeman slower is shown to be dependent on the intensity and frequency detuning of the la... We study a Zeeman slower using the magnetic field generated by a pair of coils for a magneto-optical trap. The efficiency of the Zeeman slower is shown to be dependent on the intensity and frequency detuning of the laser light for slowing the atoms. With the help of numerical analysis, optimal experimental parameters are explored.Experimentally, the optimal frequency detuning and intensity of the slowing beam are explored, and 4×10^7 ytterbium atoms are trapped in the magneto-optical trap. 展开更多
关键词 study a ZEEMAN magnetic field GENERATED MAGNETO-OPTICAL TRAP
Oscillation and Migration of Bubbles within Ultrasonic Field
15
作者 吴文华 杨鹏飞 +1 位作者 翟薇 魏炳波 《中国物理快报:英文版》 SCIE CAS CSCD 2019年第8期65-68,共4页
The oscillation and migration of bubbles within an intensive ultrasonic field are important issues concerning acoustic cavitation in liquids.We establish a selection map of bubble oscillation mode related to initial b... The oscillation and migration of bubbles within an intensive ultrasonic field are important issues concerning acoustic cavitation in liquids.We establish a selection map of bubble oscillation mode related to initial bubble radius and driving sound pressure under 20 kHz ultrasound and analyze the individual-bubble migration induced by the combined effects of pressure gradient and acoustic streaming.Our results indicate that the pressure threshold of stable and transient cavitation decreases with the increasing initial bubble radius.At the pressure antinode,the Bjerknes force dominates the bubble migration, resulting in the large bubbles gathering toward antinode center,whereas small bubbles escape from antinode.By contrast,at the pressure node,the bubble migration is primarily controlled by acoustic streaming,which effectively weakens the bubble adhesion on the container walls,thereby enhancing the cavitation effect in the whole liquid. 展开更多
关键词 OSCILLATION MIGRATION ULTRASONIC FIELD
Analysis of typhoon wind hazard in Shenzhen City by Monte-Carlo Simulation 预览
16
作者 GUO Yunxia HOU Yijun QI Peng 《海洋湖沼学报(英文)》 SCIE CAS CSCD 2019年第6期1994-2013,共20页
As one of the most serious natural disasters,many typhoons affect southeastern China every year.Taking Shenzhen,a coastal city in southeast China as an example,we employed a Monte-Carlo simulation to generate a large ... As one of the most serious natural disasters,many typhoons affect southeastern China every year.Taking Shenzhen,a coastal city in southeast China as an example,we employed a Monte-Carlo simulation to generate a large number of virtual typhoons for wind hazard analysis.By analyzing 67-year historical typhoons data from 1949 to 2015 using the Best Track Dataset for Tropical Cyclones over the Western North Pacific recorded by the Shanghai Typhoon Institute,China Meteorological Administration(CMASTI),typhoon characteristic parameters were extracted and optimal statistical distributions established for the parameters in relation to Shenzhen.We employed the Monte-Carlo method to sample each distribution to generate the characteristic parameters of virtual typhoons.In addition,the Yah Meng(YM)wind field model was introduced,and the sensitivity of the YM model to several parameters discussed.Using the YM wind field model,extreme wind speeds were extracted from the virtual typhoons.The extreme wind speeds for different return periods were predicted and compared with the current structural code to provide improved wind load information for wind-resistant structural design. 展开更多
关键词 TYPHOON HAZARD ANALYSIS Monte-Carlo simulation WIND field model EXTREME WIND SPEED
在线阅读 下载PDF
Hydrocarbon generation characteristics and exploration prospects of Proterozoic source rocks in China
17
作者 Wenzhi ZHAO Xiaomei WANG +6 位作者 Suyun HU Shuichang ZHANG Huajian WANG Shuwei GUAN Yuntao YE Rong REN Tongshan WANG 《中国科学:地球科学英文版》 SCIE EI CAS CSCD 2019年第6期909-934,共26页
A large number of primary oil and gas reservoirs have been discovered in Proterozoic strata all over the globe.Proterozoic sequences are widely distributed in China, and the discovery of large Sinian-aged gas reservoi... A large number of primary oil and gas reservoirs have been discovered in Proterozoic strata all over the globe.Proterozoic sequences are widely distributed in China, and the discovery of large Sinian-aged gas reservoirs in the Sichuan Basin and Mesoproterozoic liquid oil seepages in North China shows that attention should be paid to the exploration potential of Proterozoic strata. In this paper, the main controlling factors of Proterozoic source rocks are discussed. Principally, active atmospheric circulation and astronomical cycles may have driven intense upwelling and runoff to provide nutrients;oxygenated oceanic surface waters could have provided suitable environments for the organisms to thrive;volcanic activity and terrestrial weathering caused by continental break-up would have injected large amounts of nutrients into the ocean, leading to persistent blooms of marine organisms;and extensive anoxic deep waters may have created ideal conditions for the preservation of organic matter. Additionally, the appearance of eukaryotes resulted in diversified hydrocarbon parent material, which effectively improved the generation potential for oil and gas. Through the comparison of Formations across different cratons, seven sets of Proterozoic organic-rich source rocks have been recognized in China, which mainly developed during interglacial periods and are also comparable worldwide. The Hongshuizhuang and Xiamaling Formations in North China have already been identified previously as Mesoproterozoic source rocks. The early Proterozoic Changchengian System is highly promising as a potential source rock in the Ordos Basin. In the Upper Yangtze area, the Neoproterozoic Datangpo and Doushantuo Formations are extensively distributed, and represent the major source rocks for Sinian gas reservoirs in the Sichuan Basin. Moreover, the Nanhuan System may contain abundant shales with high organic matter contents in the Tarim Basin, although this possibility still needs to be verified. Indeed, all three cratons may contain source 展开更多
关键词 PROTEROZOIC Source ROCKS HYDROCARBON generation CHARACTERISTICS Replacement field
Numerical Investigation of Transient Temperature Distribution during Ti-6Al-4V Selective Laser Melting
18
作者 XING Xiaodong ZHOU Qiuyu +2 位作者 WANG Shiyuan WANG Liquan JIANG Fengchun 《热科学学报:英文版》 SCIE EI CAS CSCD 2019年第2期370-377,共8页
The transient temperature field in the powder bed has a crucial effect on the quality of parts fabricated using Selective Laser Melting(SLM). In this study, a finite element model is established regarding the variance... The transient temperature field in the powder bed has a crucial effect on the quality of parts fabricated using Selective Laser Melting(SLM). In this study, a finite element model is established regarding the variance of temperature-dependent thermal properties and transformation latent heat. The temperature distribution and melt pool dimensions of a laser scan track were obtained by varying multiple parameters(layer thickness, laser power and scan speed). The effects of transition of material state and heat source model are also analyzed in this paper. The finite element simulation results show that an increased laser power and/or decreased scan speed results in an elevated maximum temperature of the powder layer and a larger melt pool size. Furthermore, it is found that the maximum temperature is significantly lowered due to the heat diffusion into the previous sintered zone. The heat source model has to be selected properly according to the element size. 展开更多
关键词 Selective Laser MELTING TRANSIENT temperature field process parameters MELT POOL
Axial magnetic field effect in numerical analysis of high power Cherenkov free electron laser
19
作者 F BazoubAND B Maraghechi 《中国物理B:英文版》 SCIE EI CAS CSCD 2019年第6期176-183,共8页
Cherenkov free electron laser(CFEL) is simulated numerically by using the single particle method to optimize the electron beam. The electron beam is assumed to be moving near the surface of a flat dielectric slab alon... Cherenkov free electron laser(CFEL) is simulated numerically by using the single particle method to optimize the electron beam. The electron beam is assumed to be moving near the surface of a flat dielectric slab along a growing radiation. The set of coupled nonlinear differential equations of motion is solved to study the electron dynamics. For three sets of parameters, in high power CFEL, it is found that an axial magnetic field is always necessary to keep the electron beam in the interaction region and its optimal strength is reported for each case. At the injection point, the electron beam’s distance above the dielectric surface is kept at a minimum value so that the electrons neither hit the dielectric nor move away from it to the weaker radiation fields and out of the interaction region. The optimal electron beam radius and current are thereby calculated. This analysis is in agreement with two previous numerical studies for a cylindrical waveguide but is at odds with analytical treatments of a flat dielectric that does not use an axial magnetic field. This is backed by an interesting physical reasoning. 展开更多
关键词 CHERENKOV free ELECTRON laser AXIAL magnetic field flat dielectric SLAB ELECTRON beam
柴胡中药资源研究进展 预览
20
作者 王梦迪 靳光乾 《山东林业科技》 2019年第3期107-110,114共5页
通过查阅有关文献,按柴胡的植物资源、主要产地、化学成分、药理药效和安全性等,进行了概括总结和归纳,为柴胡的研究和开发利用提供有益的参考。
关键词 柴胡 产地 植物资源 化学成分 药理药效 安全性
在线阅读 下载PDF
上一页 1 2 250 下一页 到第
使用帮助 返回顶部 意见反馈