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长大隧道紧坡地段坡度折减系数的选用 预览
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作者 李小伟 《贵州科学》 2019年第2期87-89,共3页
山区铁路因其复杂的地形条件,常会为克服高程障碍而设置较长的紧坡地段。随着设计施工技术的提高,山区铁路中高桥长隧屡见不鲜,并逐渐占有较大比重,因而在长隧紧坡地段,合理选用坡度折减系数具有实际的工程意义。本文结合工程实例,对现... 山区铁路因其复杂的地形条件,常会为克服高程障碍而设置较长的紧坡地段。随着设计施工技术的提高,山区铁路中高桥长隧屡见不鲜,并逐渐占有较大比重,因而在长隧紧坡地段,合理选用坡度折减系数具有实际的工程意义。本文结合工程实例,对现行规范中隧道坡度折减系数的选用进行了初步的探讨。 展开更多
关键词 山区铁路 长大隧道 坡度 折减系数选用
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基于MATLAB的条件极值研究 预览
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作者 唐家德 《楚雄师范学院学报》 2019年第3期10-15,共6页
求解条件极值的基本方法为拉格朗日乘数法,直接从隐函数组出发推导拉格朗日乘数法既繁琐又不易让人理解,但注意到在一定的条件下,二元函数[f(x,y)]的极值点必定出现在该函数的等高线与约束曲线[g(x,y)=0]的切点上,由于等高线和约束曲线... 求解条件极值的基本方法为拉格朗日乘数法,直接从隐函数组出发推导拉格朗日乘数法既繁琐又不易让人理解,但注意到在一定的条件下,二元函数[f(x,y)]的极值点必定出现在该函数的等高线与约束曲线[g(x,y)=0]的切点上,由于等高线和约束曲线上任意一点处的梯度向量[▽,▽g]分别垂直于该等高线和约束曲线,可以得到[▽,▽g]在极值点处相互平行的几何结论,从而容易得出拉格朗日乘数法。 展开更多
关键词 条件极值 梯度 拉格朗日乘数法 MATLAB
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Mobility control of unmanned aerial vehicle as communication relay in airborne multi-user systems
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作者 Gaofeng WU Xiaoguang GAO +2 位作者 Xiaowei Fu Kaifang WAN Ruohai DI 《中国航空学报:英文版》 SCIE EI CAS CSCD 2019年第6期1520-1529,共10页
In this paper, a model-based adaptive mobility control method for an Unmanned Aerial Vehicle(UAV) acting as a communication relay is presented, which is intended to improve the network performance in airborne multi-us... In this paper, a model-based adaptive mobility control method for an Unmanned Aerial Vehicle(UAV) acting as a communication relay is presented, which is intended to improve the network performance in airborne multi-user systems. The mobility control problem is addressed by jointly considering unknown Radio Frequency(RF) channel parameters, unknown multi-user mobility, and non-available Angle of Arrival(AoA) information of the received signal. A Kalman filter and a least-square-based estimation algorithm are used to predict the future user positions and estimate the RF channel parameters between the users and the UAV, respectively. Two different relay application cases are considered: end-to-end and multi-user communications. A line search algorithm is proposed for the former, with its stability given and proven, whereas a simplified gradient-based algorithm is proposed for the latter to provide a target relay position at each decision time step, decreasing the two-dimensional search to a one-dimensional search. Simulation results show that the proposed mobility control algorithms can drive the UAV to reach or track the optimal relay position movement, as well as improving network performance. The proposed method reflects the properties of using different metrics as objective network performance functions. 展开更多
关键词 Channel estimation GRADIENT methods MOTION control Optimization RELAY Unmanned AERIAL vehicle WIRELESS networks
Long-term monitoring revealed fish assemblage zonation in the Three Gorges Reservoir 预览
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作者 LIN Pengcheng GAO Xin +2 位作者 LIU Fei LI Mingzheng LIU Huanzhang 《海洋湖沼学报(英文)》 SCIE CAS CSCD 2019年第4期1258-1267,共10页
Reservoirs are important artificial ecosystems that modify the hydrological and ecological characteristics of a river. Knowledge of the basic characteristics of fish assemblages in reservoirs is a first step toward th... Reservoirs are important artificial ecosystems that modify the hydrological and ecological characteristics of a river. Knowledge of the basic characteristics of fish assemblages in reservoirs is a first step toward the development of effective conservation policies. We used the information collected over a 10-year period (2006-2015) to assess the structure of the fish assemblages in the Three Gorge Reservoir (TGR) in a river-dam gradient. Three fish zones were detected in TGR. Species richness was the highest in the upper zone and lowest in the lower zone. The riverine zones were dominated by rheophilic species Coreius guichenoti and Pelteobagrus vachelli. The transitional zones were dominated by Coreius heterodon and Rhinogobio cylindricus. The lacustrine zones were dominated by eurytopic species Hypophthalmichthys molitrix, Aristichthys nobilis, Hemiculter bleekeri and Cyprinus carpio. For the functional characteristics, fish assemblages in riverine and transitional zones were dominated by insectivorous species, equilibrium strategists and rheophilic species (e.g., Coreius heterodon and Coreius guichenoti). In lacustrine zones, the fish assemblage was dominated by habitat generalists common to lakes and reservoirs (e.g., Hemiculter bleekeri, Hypophthalmichthys molitrix, Aristichthys nobilis). Moreover, 18 exotic species (e.g., Protosalanx hyalocranius, Ictalurus punctatus, Megalobrama amblycephala, Tilapia) were collected in TGR, most of which only existed in the lacustrine zone. The results highlight the importance of freely flowing riverine reaches for conserving native fish in the upper Changjiang River and adaptive management strategies for fisheries in TGR. 展开更多
关键词 longitudinal GRADIENT IMPOUNDMENT functional GROUPS EXOTIC species dam effects
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从方向导数向量到梯度的直观讲析教学设计 预览
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作者 赵金玲 王萍 +2 位作者 胡筱 储继迅 张志刚 《高师理科学刊》 2019年第5期47-52,共6页
针对理工科学生的特点,设计了从方向导数到梯度的直观讲析教学过程.通过引入偏导数和方向导数的向量解释,辅之以大量的图形和动画演示,深入浅出地向学生直观展示梯度的几何意义,继而利用动图的效果让学生对梯度和方向导数的关系产生直... 针对理工科学生的特点,设计了从方向导数到梯度的直观讲析教学过程.通过引入偏导数和方向导数的向量解释,辅之以大量的图形和动画演示,深入浅出地向学生直观展示梯度的几何意义,继而利用动图的效果让学生对梯度和方向导数的关系产生直观印象,同时利用理论推导对此给出严格数学证明.遵循提出问题——分析问题——解决问题——拓展思考的设计环节,循序渐进地引导学生,训练学生的数学思维,提高了学生分析问题和解决问题的能力. 展开更多
关键词 方向导数 梯度 偏导数 向量 教学设计
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Characteristics of runoff processes and nitrogen loss via surface flow and interflow from weathered granite slopes of Southeast China
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作者 DENG Long-zhou FEI Kai +3 位作者 SUN Tian-yu ZHANG Li-ping FAN Xiao-juan NI Liang 《山地科学学报:英文版》 SCIE CSCD 2019年第5期1048-1064,共17页
Rainfall intensity and slope gradient are two of the most important factors affecting the variations of runoff nitrogen(N).However,the effects of slope gradient and rainfall intensity on N loss via surface flow and in... Rainfall intensity and slope gradient are two of the most important factors affecting the variations of runoff nitrogen(N).However,the effects of slope gradient and rainfall intensity on N loss via surface flow and interflow on weathered granite slopes are poorly understood.In this study,12 artificial rainfalls(three rainfall intensities and four slope gradients)were simulated to investigate the coupling loss characteristics of surface flow–interflow–total nitrogen(TN),nitrate nitrogen(NO3--N)and ammonia nitrogen(NH4+-N)on weathered granite slopes.The results show that slope gradient has a greater impact on the surface flow when the rainfall intensity is relatively large.The effect gradually weakens with the decrement of rainfall intensity.The interflow yield increases firstly with the prolongation of rainfall duration,then tends to be stable and finally decreases.The total surface flow percentage increases with rainfall intensity while it decreases with increasing slope gradient with a range of 10.88%-71.47%.The TN loss concentration of the surface flow continually decreases with rainfall duration while that of the interflow shows different fluctuations.However,the TN loss loads of both surface flow and interflow increase with increasing rainfall intensity and slope gradient.The NO3--N concentration of interflow is much higher than that of the surface flow.The NH4+-N concentration is always less than that of NO3--N with no significant difference between surface flow and interflow.The percentages of the TN,NO3--N,and NH4+-N total loss load and concentration of surface flow and interflow were analyzed.The results show that N loss via both surface flow and interflow occurs mainly in the form of NO3--N.Most of the N loss is caused by interflow which is the preferential path of runoff nutrient loss.These findings provide data support and underlying insights for the control of runoff and N loss on the weathered granite slopes. 展开更多
关键词 Simulated RAINFALL Nitrogen loss Surface flow INTERFLOW SLOPE GRADIENT RAINFALL intensity Weathered GRANITE SLOPE
Robust RGB-D Camera and IMU Fusion-based Cooperative and Relative Close-range Localization for Multiple Turtle-inspired Amphibious Spherical Robots
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作者 Huiming Xing Liwei Shi +5 位作者 Kun Tang Shuxiang Guo Xihuan Hou Yu Liu Huikang Liu Yao Hu 《仿生工程学报:英文版》 SCIE EI CSCD 2019年第3期442-454,共13页
In the narrow, submarine, unstructured environment, the present localization approaches, such as GPS measurement, dead?rcckoning, acoustic positioning, artificial landmarks-based method, are hard to be used for multip... In the narrow, submarine, unstructured environment, the present localization approaches, such as GPS measurement, dead?rcckoning, acoustic positioning, artificial landmarks-based method, are hard to be used for multiple small-scale underwater robots. Therefore, this paper proposes a novel RGB-D camera and Inertial Measurement Unit (IMU) fusion-based cooperative and relative close-range localization approach for special environments, such as underwater caves. Owing to the rotation movement with zero-radius, the cooperative localization of Multiple Turtle-inspired Amphibious Spherical Robot (MTASRs) is realized. Firstly, we present an efficient Histogram of Oriented Gradient (HOG) and Color Names (CNs) fusion feature extracted from color images ofTASRs. Then, by training Support Vector Machine (SVM) classifier with this fusion feature, an automatic recognition method of TASRs is developed. Secondly, RGB-D camerabased measurement model is obtained by the depth map In order to realize the cooperative and relative close-range localization of MTASRs, the MTASRs model is established with RGB-D camera and IMU. Finally, the depth measurement in water is corrected and the efficiency of RGB-D camera for underwater application is validated. Then experiments of our proposed localization method with three robots were conducted and the results verified the feasibility of the proposed method for MTASRs. 展开更多
关键词 vision LOCALIZATION bio-inspired robots RGB-D CAMERA histogram of oriented gradient and color names FUSION feature Co operative and RELATIVE LOCALIZATION (CRL)
Electrical, Thermal, and Mechanical Properties of Cu/Ti3AlC2 Functional Gradient Materials Prepared by Low-temperature Spark Plasma Sintering
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作者 陈艳林 PENG Hang +3 位作者 LOU Lang HUANG Kang YAN Ming 吴崇刚 《武汉理工大学学报:材料科学英文版》 SCIE EI CAS 2019年第4期876-882,共7页
Cu/Ti3AlC2 composite and functional-gradient materials with excellent electrical conductivity and thermal conductivity as well as good flexural properties were prepared by low-temperature spark plasma sintering of Cu ... Cu/Ti3AlC2 composite and functional-gradient materials with excellent electrical conductivity and thermal conductivity as well as good flexural properties were prepared by low-temperature spark plasma sintering of Cu and Ti3AlC2 powder mixtures. The phase compositions of the materials were analyzed by X-ray diffraction, and their microstructure was characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. Further, the electrical conductivity, thermal conductivity, and flexural properties of the materials were tested. Results show that, for the composite materials, the resistivity rises from 0.75 × 10^-7 Ω·m only to 1.32 × 10^-7 Ω·m and the thermal diffusivity reduces from 82.5 mm^2/s simply to 39.8 mm^2/s, while the flexural strength improves from 412.9 MPa to 471.3 MPa, as the content of Ti3AlC2 is increased from 5 wt%to 25 wt%. Additionally, the functional-gradient materials sintered without interface between the layers exhibit good designability, and their overall electrical conductivity, thermal conductivity, and flexural strength are all higher than those of the corresponding uniform composite material. 展开更多
关键词 Cu/Ti3AlC2 FUNCTIONAL gradient material ELECTRICAL CONDUCTIVITY THERMAL CONDUCTIVITY
Gradient Estimates and Harnack Inequalities for Positive Solutions of ■u =■υ/■t on Self-shrinkers
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作者 Ye Cheng ZHU Qing CHEN 《数学学报:英文版》 SCIE CSCD 2019年第7期1217-1226,共10页
In this paper, we investigate the positive solutions of ■u =■υ/■t on self-shrinkers, then get some gradient estimates and Harnack inequalities for the positive solutions.
关键词 Harnack INEQUALITY self^shrinker ∞-Bakry-Emery RICCI TENSOR gradient ESTIMATE
Analytical solutions for buckling of size-dependent Timoshenko beams 预览
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作者 Xiaojian XU Mulian ZHENG 《应用数学和力学:英文版》 SCIE EI CSCD 2019年第7期953-976,共24页
The inconsistences of the higher-order shear resultant expressed in terms of displacement(s) and the complete boundary value problems of structures modeled by the nonlocal strain gradient theory have not been well add... The inconsistences of the higher-order shear resultant expressed in terms of displacement(s) and the complete boundary value problems of structures modeled by the nonlocal strain gradient theory have not been well addressed. This paper develops a size-dependent Timoshenko beam model that considers both the nonlocal effect and strain gradient effect. The variationally consistent boundary conditions corresponding to the equations of motion of Timoshenko beams are reformulated with the aid of the weighted residual method. The complete boundary value problems of nonlocal strain gradient Timoshenko beams undergoing buckling are solved in closed forms. All the possible higher-order boundary conditions induced by the strain gradient are selectively suggested based on the fact that the buckling loads increase with the increasing aspect ratios of beams from the conventional mechanics point of view. Then, motivated by the expression for beams with simply-supported (SS) boundary conditions, some semiempirical formulae are obtained by curve fitting procedures. 展开更多
关键词 BUCKLING STRAIN GRADIENT theory BOUNDARY condition
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Experimental demonstration of influence of underwater turbulence on ghost imaging
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作者 殷曼倩 王乐 赵生妹 《中国物理B:英文版》 SCIE EI CAS CSCD 2019年第9期180-185,共6页
It is difficult to obtain a clear image in underwater turbulence environment with classical imaging methods due to the absorption, scattering, and underwater turbulence on the propagation beam.However, ghost imaging(G... It is difficult to obtain a clear image in underwater turbulence environment with classical imaging methods due to the absorption, scattering, and underwater turbulence on the propagation beam.However, ghost imaging(GI), a nonlocally imaging technique, has shown the turbulence-free ability in atmospheric turbulence by exploiting the second-order correlation between the signal beam and the reference beam.In this paper, we experimentally investigate the imaging quality of GI affected by the underwater environment, where the underwater environment is simulated by a 1 m×0.4 m×0.4 m tank with distilled water.The water temperature is controlled by a heater inside the tank, and a temperature gradient is obtained by putting the heater at different positions of the tank.The water vibration is produced by a heavy force, and the turbid medium is obtained by dissolving very small specks of CaCO3 in the water.A set of Hadamard speckle pattern pairs are generated and modulated on the incident beam, and then the beam illuminates on an unknown object after passing through the simulated underwater environment.With the second-order correlations, the image is reconstructed under different temperature gradients, water vibration, and turbid medium ratios.The results show that GI has the turbulence-free ability under lower temperature gradient, water vibration, and turbid media.The structural similarity image measurement(SSIM)values of the reconstructed images only start to decrease when the temperature gradient is greater than 4.0℃.The same temperature gradient produced at the different positions has a little effect on the quality of the underwater GI. 展开更多
关键词 UNDERWATER GHOST imaging temperature GRADIENT turbid media water VIBRATION
Impurity profile of macitentan in tablet dosage form using a stability-indicating high performance liquid chromatography method and forced degradation study 预览
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作者 Narasimha S LAKKA Chandrasekar KUPPAN Parthasarathy RANGASAMY 《色谱》 CAS CSCD 北大核心 2019年第1期100-110,共11页
Macitentan(MAC)is a pulmonary arterial hypertension(PAH)drug marketed as a tablet and often has stability issues in the final dosage form.Quantitative determination of MAC and its associated impurities in tablet dosag... Macitentan(MAC)is a pulmonary arterial hypertension(PAH)drug marketed as a tablet and often has stability issues in the final dosage form.Quantitative determination of MAC and its associated impurities in tablet dosage form has not been previously reported.This study quantified impurities present in Macitentan tablets using a binary solvent-based gradient elution method using reversed phase-high performance liquid chromatography.The developed method was validated per International Conference on Harmonization(ICH)guidelines and the drug product was subjected to forced degradation studies to evaluate stability.The developed method efficiently separated the drug and impurities(48 min)without interference from solvents,excipients,or other impurities.The developed method met all guidelines in all characteristics with recoveries ranging from 85%-115%,linearity with r^2≥0.996 6,and substantial robustness.The stability-indicating nature of the method was evaluated using stressed conditions(hydrolysis:1 N HCl at 80℃/15min;1 N NaOH at 25℃/45min;humidity stress(90%relative humidity)at 25℃for 24h,oxidation:at 6%(v/v)H2O2,80℃/15min,thermolysis:at 105℃/16h and photolysis:UV light at 200Wh/m^2;Fluorescent light at 1.2 million luxh).Forced degradation experiments showed that the developed method was effective for impurity profiling.All stressed samples were assayed and mass balance was>96%.Forced degradation results indicated that MAC tablets were sensitive to hydrolysis(acid and alkali)and thermal conditions.The developed method is suitable for both assay and impurity determination,which is applicable to the pharmaceutical industry. 展开更多
关键词 reverse phase-high performance liquid chromatography(RP-HPLC) STABILITY-INDICATING METHOD forced degradation STUDY binary solvent gradient ENDOTHELIN receptor antagonist(ERA) pulmonary arterial hypertension(PAH) macitentan(MAC) IMPURITY profiling
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Experimental study on the flow pattern and pressure gradient of air-water two-phase flow in a horizontal circular mini-channel 预览
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作者 Sudaija Aqli Haq +2 位作者 Deendarlianto Indarto Adhika Widyaparaga 《水动力学研究与进展:英文版》 SCIE EI CSCD 2019年第1期102-116,共15页
Experimental studies on the flow pattern and the pressure gradient of gas-liquid co-current two-phase flow in a mini-channel were conducted.The test section was a transparent circular channel of 1.6 mm inner diameter.... Experimental studies on the flow pattern and the pressure gradient of gas-liquid co-current two-phase flow in a mini-channel were conducted.The test section was a transparent circular channel of 1.6 mm inner diameter.The working fluids were air and water.The superficial velocities of gas and liquid were in the range of 0.025-66.300 m/s and 0.033-4.935 m/s,respectively.In the present work,the flow pattern and the pressure gradient data were obtained by analyzing the flow images captured by a high-speed camera,and by using the pressure transducer,respectively.As a result,it was found that (1) the obtained flow patterns were bubbly,plug,slug-annular,annular,and chum flows,(2) new experimental correlations on the bubble and plug lengths were proposed,whereas the lengths are the function of the homogeneous void fraction,(3) both gas and liquid superficial velocities affect proportionally to the pressure gradient,whereas it increases with the increase both of JG,JL.In addition,the obtained flow patterns are in a good agreement with that of the available flow pattern maps in the open literatures,such as,Triplett et al.(1999) and Chung and Kawaji (2004). 展开更多
关键词 TWO-PHASE FLOW mini channel FLOW pattern pressure GRADIENT plug length
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Discovering unusual structures from exception using big data and machine learning techniques
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作者 Jianshu Jie Zongxiang Hu +9 位作者 Guoyu Qian Mouyi Weng Shunning Li Shucheng Li Mingyu Hu Dong Chen Weiji Xiao Jiaxin Zheng Lin-Wang Wang Feng Pan 《科学通报:英文版》 SCIE EI CSCD 2019年第9期612-616,共5页
Recently, machine learning(ML) has become a widely used technique in materials science study. Most work focuses on predicting the rule and overall trend by building a machine learning model. However,new insights are o... Recently, machine learning(ML) has become a widely used technique in materials science study. Most work focuses on predicting the rule and overall trend by building a machine learning model. However,new insights are often learnt from exceptions against the overall trend. In this work, we demonstrate that how unusual structures are discovered from exceptions when machine learning is used to get the relationship between atomic and electronic structures based on big data from high-throughput calculation database. For example, after training an ML model for the relationship between atomic and electronic structures of crystals, we find AgO2 F, an unusual structure with both Ag3+and O22à, from structures whose band gap deviates much from the prediction made by our model. A further investigation on this structure might shed light into the research on anionic redox in transition metal oxides of Li-ion batteries. 展开更多
关键词 Machine learning GRADIENT BOOSTING decision tree Band gap UNUSUAL STRUCTURES
Research on changes of hydrodynamics and ion-exchange adsorption in Brackish-Water Interface 预览
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作者 MIAO Qing-zhuang ZHOU Xiao-ni +3 位作者 WANG Gui-ling ZHANG Wei LIU Feng XING Lin-xiao 《地下水科学与工程:英文版》 2019年第2期94-105,共12页
In light of multiple field experiments in typical tidal areas with active sea-land interaction, corresponding analysis through hydrodynamic simulation and of ion composition evolution all insist on following conclusio... In light of multiple field experiments in typical tidal areas with active sea-land interaction, corresponding analysis through hydrodynamic simulation and of ion composition evolution all insist on following conclusions. Due to the tide, the groundwater level is basically in line with its level but with a slight lag. Moreover, smaller amplitude of such changes were always accompanied by greater distance from shores. In this paper, two salt-freshwater interfaces were identified, namely, a large wedge-shaped interface and an inverted U-shaped one located at K5 (monitoring point). The critical hydraulic gradient of saltwater intrusion was between 0.0345 and 0.0377. Apart from that, mathematical and physical models were adopted to measure the influence of tides, showing a inverse proportion to the hydraulic gradient In addition, characteristics of ionic components can prove that K^+ was adsorbed and Ca^2+ was displaced during saline intrusion, while a reverse process was witnessed during desalting. In summary, cation exchange adsorption plus other complex physical chemical effects would take place during saltwater intrusion. 展开更多
关键词 Seawater-freshwater INTERFACE WEDGE-SHAPED INTERFACE Hydraulic gradient Critical value Ion-exchange ADSORPTION
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氢氧反应容器的热应力模拟计算 预览
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作者 马建 《山东化工》 CAS 2019年第3期152-153,157共3页
本文通过氢氧反应容器的反应热的有限元模拟分析,获得密闭状态下的氢氧反应生热引起的容器的温度场、温度梯度及热应力等参数,以了解密闭反应容器的结构变化情况。
关键词 反应热 温度场 梯度 热应力
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Seasonal response of surface wind to SST perturbation in the Northern Hemisphere 预览
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作者 HE Jingjing HAN Xueshuang LIN Xiaopei 《海洋湖沼学报(英文)》 SCIE CAS CSCD 2019年第4期1165-1175,共11页
The seasonal response of surface wind speed to sea surface temperature (SST) change in the Northern Hemisphere was investigated using 10 years (2002-2011) high-resolution satellite observations and reanalysis data. Th... The seasonal response of surface wind speed to sea surface temperature (SST) change in the Northern Hemisphere was investigated using 10 years (2002-2011) high-resolution satellite observations and reanalysis data. The results showed that correlation between surface wind speed perturbations and SST perturbations exhibits remarkable seasonal variation, with more positive correlation is stronger in the cold seasons than in the warm seasons. This seasonality in a positive correlation between SST and surface wind speed is attributable primarily to seasonal changes of oceanic and atmospheric background conditions in frontal regions. The mean SST gradient and the prevailing surface winds are strong in winter and weak in summer. Additionally, the eddy-induced response of surface wind speed is stronger in winter than in summer, although the locations and numbers of mesoscale eddies do not show obvious seasonal features. The response of surface wind speed is apparently due to stability and mixing within the marine atmospheric boundary layer (MABL), modulated by SST perturbations. In the cold seasons, the stronger positive (negative) SST perturbations are easier to increase (decrease) the MABL height and trigger (suppress) momentum vertical mixing, contributing to the positive correlation between SST and surface wind speed. In comparison, SST perturbations are relatively weak in the warm seasons, resulting in a weak response of surface wind speed to SST changes. This result holds for each individual region with energetic eddy activity in the Northern Hemisphere. 展开更多
关键词 SEASONALITY positive correlation sea surface temperature (SST) gradient marine atmospheric boundary layer (MABL) height MESOSCALE EDDY
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减反膜的梯度化与激光损伤阈值之间的关系研究 预览
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作者 王燕 杭凌侠 《应用光学》 CAS CSCD 北大核心 2019年第1期143-149,共7页
光学减反膜是激光系统的重要组成部分,也是在激光照射下最容易发生损伤的部分,如何提高减反膜的激光损伤阈值是研究的热点之一。在保持目标透射光谱要求和膜系总光学厚度不变的前提下,研究了不同梯度化减反膜与激光损伤阈值之间的关系... 光学减反膜是激光系统的重要组成部分,也是在激光照射下最容易发生损伤的部分,如何提高减反膜的激光损伤阈值是研究的热点之一。在保持目标透射光谱要求和膜系总光学厚度不变的前提下,研究了不同梯度化减反膜与激光损伤阈值之间的关系。首先采用混合渐变膜系设计方法设计了一种渐变减反膜系,G/H 1→H/L/A;其次通过渐变折射率分层等效方法将渐变减反膜系进行不同的梯度化,并利用PECVD技术,在K9玻璃上沉积了满足光学性能指标要求的不同渐变减反膜系(多层梯度渐变膜系和相应的坡度渐变膜系);最后进行了激光损伤阈值(LIDT)测量。研究结果表明:在保持目标透射光谱要求和膜系总光学厚度不变的前提下,渐变减反膜系相比于传统减反膜系,抗激光损伤阈值有明显的提高;随着梯度化层数的增加,渐变减反膜系的激光损伤阈值呈减小的趋势;对于相同膜层的渐变折射率薄膜,采用坡度法制备的样片抗激光损伤阈值均优于采用梯度化制备的样片。 展开更多
关键词 梯度化 减反膜 透过率 电场 激光损伤阈值
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A Liutex based definition and identification of vortex core center lines 预览
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作者 Yi-sheng Gao Jian-ming Liu +1 位作者 Yi-fei Yu Chaoqun Liu 《水动力学研究与进展:英文版》 SCIE EI CSCD 2019年第3期445-454,共10页
Six core issues for vortex definition and identification concern with (1) the absolute strength,(2) the relative strength,(3) the rotational axis,(4) the vortex core center,(5) the vortex core size, and (6) the vortex... Six core issues for vortex definition and identification concern with (1) the absolute strength,(2) the relative strength,(3) the rotational axis,(4) the vortex core center,(5) the vortex core size, and (6) the vortex boundary (Liu C. 2019). However, most of the currently popular vortex identification methods, including the Q criterion, the criterion and the Acj criterion etc., are Eulerian local region-type vortex identification criteria and can only approximately identify the vortex boundary by somewhat arbitrary threshold. On the other hand, the existing Eulerian local line-type methods, which seek to extract line-type features such as vortex core line, are not entirely satisfactory since most of these methods are based on vorticity or pressure minimum that will fail in many cases. The key issue is the lack of a reasonable mathematical definition for vortex core center. To address this issue, a Liutex (previously named Rortex) based definition of vortex core center is proposed in this paper. The vortex core center, also called vortex rotation axis line here, is defined as a line where the Liutex magnitude gradient vector is aligned with the Liutex vector, which mathematically implies that the cross product of the Liutex magnitude gradient vector and the Liutex vector on the line is equal to zero. Based on this definition, a novel three-step method for extracting vortex rotation axis lines is presented. Two test cases, namely the Burgers vortex and hairpin vortices, are examined to justify the proposed method. The results demonstrate that the proposed method can successfully identify vortex rotation axis lines without any user-specified threshold, so that the proposed method is very straightforward, robust and efficient. 展开更多
关键词 VORTEX DEFINITION VORTEX IDENTIFICATION flow visualization Liutex Liutex MAGNITUDE GRADIENT VORTEX core LINES
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BHONEM:Binary High-Order Network Embedding Methods for Net worked-Guarantee Loans
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作者 Da-Wei Cheng Yi Tu +2 位作者 Zhen-Wei Ma Zhi-Bin Niu Li-Qing Zhang 《计算机科学技术学报:英文版》 SCIE EI CSCD 2019年第3期657-669,共13页
Networked-guarantee loans may cause systemic risk related concern for the government and banks in China.The prediction of the default of enterprise loans is a typical machine learning based classification problem, and... Networked-guarantee loans may cause systemic risk related concern for the government and banks in China.The prediction of the default of enterprise loans is a typical machine learning based classification problem, and the networked guarantee makes this problem very difficult to solve. As we know, a complex network is usually stored and represented by an adjacency matrix. It is a high-dimensional and sparse matrix, whereas machine-learning methods usually need lowdimensional dense feature representations. Therefore, in this paper, we propose a binary higher-order network embedding method to learn the low-dimensional representations of a guarantee network. We first set vertices of this heterogeneous economic network by binary roles (guarantor and guarantee), and then define high-order adjacent measures based on their roles and economic domain knowledge. Afterwards, we design a penalty parameter in the objective function to balance the importance of network structure and adjacency. We optimize it by negative sampling based gradient descent algorithms,which solve the limitation of stochastic gradient descent on weighted edges without compromising efficiency. Finally, we test our proposed method on three real-world network datasets. The result shows that this method outperforms other start-of-the-art algorithms for both classification accuracy and robustness, especially in a guarantee network. 展开更多
关键词 networked-guarantee loan HIGH-ORDER NETWORK embedding representative learning gradient descent
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