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基于角边特征的纸质碎片自动拼接复原算法 预览
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作者 史宝珠 李美安 《计算机应用》 CSCD 北大核心 2019年第2期571-576,共6页
针对人工复原纸质文物碎片存在尝试次数多、拼接速度慢、复原准确性与完成度低等问题,提出一种依据碎片角度与边长特征进行纸质文物碎片自动拼接复原的算法。首先,将碎片图像进行预处理并根据碎片的角度值进行粗匹配,得到角度值相等的... 针对人工复原纸质文物碎片存在尝试次数多、拼接速度慢、复原准确性与完成度低等问题,提出一种依据碎片角度与边长特征进行纸质文物碎片自动拼接复原的算法。首先,将碎片图像进行预处理并根据碎片的角度值进行粗匹配,得到角度值相等的碎片图像;然后,在粗匹配的基础上,利用碎片的角边长进行细匹配减少重叠情况,得到碎片图像的基本匹配结果;最后,利用凹凸函数对方向相对的碎片图像情况进行遗漏弥补,并运用震荡函数对最终匹配图像进行缝隙弥补得到完整拼接结果。理论分析和碎片拼接仿真实验结果表明,与特征点、近似多边形拟合、角序列匹配等碎片自动拼接算法相比,所提算法的拼接准确率、拼接完成度与拼接耗时分别至少提高了12个百分点、11个百分点与10个百分点。所提基于角边特征的碎片拼接算法减少了繁琐的图像计算步骤,精确了碎片匹配结果,使得在实际文物修复等工程中能够实现非规则碎片高效、高精准的匹配。 展开更多
关键词 角度 角边长 凹凸函数 震荡函数 误差弥补 碎片拼接
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Dual Scheimpflug imaging as a screening method for occludable angles-a comparison with gonioscopy
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作者 Natalia Maes Bessa Rebeca de Azevedo Souza +2 位作者 Marcony R. Santhiago Haroldo Vieira Moraes Jr Beatriz Fiuza Gomes 《国际眼科杂志:英文版》 SCIE CAS 2019年第2期241-245,共5页
AIM:To evaluate dual Scheimpflug analyzer(Galilei) as a screening method for the diagnostic of gonioscopically narrow anterior chamber angles(ACA). METHODS:In 40 eyes of 40 patients with different ACA range, the ACA, ... AIM:To evaluate dual Scheimpflug analyzer(Galilei) as a screening method for the diagnostic of gonioscopically narrow anterior chamber angles(ACA). METHODS:In 40 eyes of 40 patients with different ACA range, the ACA, anterior chamber volume(ACV) and anterior chamber depth(ACD) were analyzed using the dual Scheimpflug analyzer(Galilei G6 system). Correspondence between these parameters and Shaffer’s classification based on gonioscopy were studied. Receiving operator characteristic(ROC) curves and partition analysis were used to determine the efficacy of the Galilei system in screening for narrow angles. Agreement(Kappa statistics), sensitivity, and specificity for each eye, according to Galilei measures, were also assessed. RESULTS:Shaffer’s grade(from 0 to 4) were significantly associated with each of the measurements(P<0.001). In screening eyes with narrow angles with the Galilei, the area under the ROC curve was largest(0.90) when ACD was used as the reference, and partition analysis demonstrated that those eyes were most adequately partitioned with an ACD of 2.86 mm with 100% sensitivity and 80% specificity. CONCLUSION:The Galilei is a secure, repeatable and noncontact screening method for narrow angles. However it does not provide sufficient information about the ACA anatomy to be considered a substitute for gonioscopy. 展开更多
关键词 GONIOSCOPY narrow ANTERIOR chamber ANGLE screening diagnostic accuracy ANGLE closure GLAUCOMA GLAUCOMA IMAGING
Effects of hurricane forward speed and approach angle on storm surges:an idealized numerical experiment 预览
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作者 Chenguang Zhang Chunyan Li 《海洋学报:英文版》 SCIE CAS CSCD 2019年第7期48-56,共9页
The effects of hurricane forward speed(V)and approach angle(θ)on storm surge are important and a systematic investigation covering possible and continuous ranges of these parameters has not been done before.Here we p... The effects of hurricane forward speed(V)and approach angle(θ)on storm surge are important and a systematic investigation covering possible and continuous ranges of these parameters has not been done before.Here we present such a study with a numerical experiment using the Finite Volume Community Ocean Model(FVCOM).The hurricane track is simplified as a straight line,such that V andθfully define the motion of the hurricane.The maximum surge is contributed by both free waves and a forced storm surge wave moving with the hurricane.Among the free waves,Kelvin-type waves can only propagate in the down-coast direction.Simulations show that those waves can only have a significant positive storm surge when the hurricane velocity has a down-coast component.The optimal values of V andθthat maximize the storm surge in an idealized semi-circular ocean basin are functions of the bathymetry.For a constant bathymetry,the maximum surge occurs when the hurricane approaches the coast from the normal direction when the free wave generation is minimal;for a stepped bathymetry,the maximum surge occurs at a certain acute approach angle which maximizes the duration of persistent wind forcing;a step-like bathymetry with a sloped shelf is similar to the stepped bathymetry,with the added possibility of landfall resonance when the free and forced waves are moving at about the same velocity.For other cases,the storm surge is smaller,given other parameters(hurricane size,maximum wind speed,etc.)unchanged. 展开更多
关键词 storm SURGE experiments FVCOM HURRICANE forward speed APPROACH ANGLE KELVIN waves forced and free SURGE interactions
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大脑中动脉CTA-MIP后处理参数的优化及初步研究 预览
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作者 陈明山 邢刚 《国际医学放射学杂志》 北大核心 2019年第1期26-31,共6页
目的应用CT血管成像(CTA)最大密度投影(MIP)的多平面重组(MPR)后处理技术分析大脑中动脉(MCA)分段显示与所选层面厚度及角度间的关系,确定MCA分段显示的优化参数。方法回顾性分析2014年6月—2016年6月因疑似MCA缺血行头颅CTA及数字减影... 目的应用CT血管成像(CTA)最大密度投影(MIP)的多平面重组(MPR)后处理技术分析大脑中动脉(MCA)分段显示与所选层面厚度及角度间的关系,确定MCA分段显示的优化参数。方法回顾性分析2014年6月—2016年6月因疑似MCA缺血行头颅CTA及数字减影血管造影(DSA)检查的100例病人(764处节段血管)资料,其中男60例,女40例,平均(64.3±10.7)岁。利用CTA容积再现(VR)平台,分别测量所有病例M1段、M2段、M2-5段的空间跨度及走行角度参数值并进行分组,随后在CTA-MIP-MPR平台,对MPR厚度和偏移角度的不同测试值进行验证,并对各个重组影像进行质量评分,确定各分段最优参数,并将优化CTA-MIP影像与DSA影像进行比较分析,评价其优化效果。多组间比较采用单因素方差分析,应用受试者操作特征(ROC)曲线评价优化CTA-MIP诊断血管狭窄的价值,CTA与DSA检查结果的一致性分析采用Kappa检验。结果在CTA-MIP中,MCA M1段最优化参数为冠状面、层厚15 mm、角度偏移0°,其影像质量评分为3.85±0.51,均高于其他组(均P<0.05);MCA M2段最优化参数为矢状面、层厚25 mm、角度偏移0°,其影像质量评分为3.36±0.53,均高于其他组(均P<0.05);M2-5段最优化参数为①低头冠状面、层厚35 mm、角度偏移35°;②外旋矢状面、层厚35 mm、轴转25°、矢转30°;2组影像质量评分分别为3.41±0.40、3.42±0.33,均高于其他组(均P<0.05)。优化CTA-MIP检查对血管狭窄的诊断敏感度、特异度、阳性预测值、阴性预测值、ROC曲线下面积分别为90.5%、97.7%、87.5%、98.3%、0.941。对于4种不同狭窄程度血管的诊断,优化CTA-MIP检查与DSA检查结果一致率为96.5%(κ=0.783,P<0.05)。结论基于优化的选层厚度及偏移角度,CTA-MIP分段显示能够清晰展示MCA各段管腔大小、走行及分支细节,与DSA有较高的一致性。 展开更多
关键词 大脑中动脉 CT血管成像 最大密度投影 角度 厚度 分段显示 参数优化
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Impacts of Wettability on Immiscible Fluid Flow Pattern-Microfluidic Chip Experiment 预览
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作者 Zheng Xianglei Jang Jaewon 《中国炼油与石油化工:英文版》 SCIE CAS 2019年第1期80-89,共10页
Immiscible fluid flow is frequently found in resource recovery or soil remediation. The flow pattern in the porous media is affected by the wettability of pore surface. In this study, quartz substrates and microfluidi... Immiscible fluid flow is frequently found in resource recovery or soil remediation. The flow pattern in the porous media is affected by the wettability of pore surface. In this study, quartz substrates and microfluidic chips are treated by silica nanoparticles(SNP) and triethoxy(octyl)silane(TES) to fabricate the water-wet and oil-wet surfaces. The wettability of the treated-surface is measured in term of contact angle for several combinations of surrounding fluid and a liquid droplet. The effect of the wettability on the fluid flow pattern is explored by injecting oil and water alternately into the surface-treated microfluidic chips. The results reveal that the SNP-coated quartz substrate shows strong water-wet property and the TES coating makes water-repellent/oil-wet surfaces. In addition, it is found that the maximum and minimum oil and water saturation during alternate injection of oil and water depends on the surface wettability of the microfluidic chips. The characteristics of the pore-scale fluid flow pattern are also described. 展开更多
关键词 WETTABILITY contact angle nanoparticle coating HYDROPHILIC HYDROPHOBIC microfluidic chip
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倾斜底板角度对侧向挑入消力池的岸边溢洪道的影响
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作者 海琴 《水电能源科学》 北大核心 2019年第6期80-83,共4页
针对岸边溢洪道从侧面挑入与之平行布置的已有消力池来消能的布置形式,采用数值模拟方法研究了不同倾斜底板角度及挑坎与消力池间高差的溢洪道水力特性及消力池内的水流流态等。结果表明,随着挑坎底板倾角的逐渐增大,水舌左支流量逐渐减... 针对岸边溢洪道从侧面挑入与之平行布置的已有消力池来消能的布置形式,采用数值模拟方法研究了不同倾斜底板角度及挑坎与消力池间高差的溢洪道水力特性及消力池内的水流流态等。结果表明,随着挑坎底板倾角的逐渐增大,水舌左支流量逐渐减小,右支流量逐渐增大,挑坎所受最大压强与挑坎内最大水深均逐渐减小;消力池底板最大压强逐渐增大,但最大冲击点位置逐渐向消力池右侧及上游区域移动,即消力池左侧边墙与尾坎逐渐不受冲。 展开更多
关键词 岸边溢洪道 消力池 倾斜底板 角度 数值模拟
3D Object Detection Based on Vanishing Point and Prior Orientation
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作者 GAO Yongbin ZHAO Huaqing +2 位作者 FANG Zhijun HUANG Bo ZHONG Cengsi 《武汉大学学报:自然科学英文版》 CAS CSCD 2019年第5期369-375,共7页
3D object detection is one of the most challenging research tasks in computer vision. In order to solve the problem of template information dependency of 3D object proposal in the method of 3D object detection based o... 3D object detection is one of the most challenging research tasks in computer vision. In order to solve the problem of template information dependency of 3D object proposal in the method of 3D object detection based on 2.5D information, we proposed a 3D object detector based on fusion of vanishing point and prior orientation, which estimates an accurate 3D proposal from 2.5D data, and provides an excellent start point for 3D object classification and localization. The algorithm first calculates three mutually orthogonal vanishing points by the Euler angle principle and projects them into the pixel coordinate system. Then, the top edge of the 2D proposal is sampled by the preset sampling pitch, and the first one vertex is taken. Finally, the remaining seven vertices of the 3D proposal are calculated according to the linear relationship between the three vanishing points and the vertices, and the complete information of the 3D proposal is obtained. The experimental results show that this proposed method improves the Mean Average Precision score by 2.7% based on the Amodal3Det method. 展开更多
关键词 image analysis 3D OBJECT DETECTION prior ORIENTATION VANISHING point EULER ANGLE
Analysis on the Equity of Compulsory Education and Higher Education from the Angle of Charging 预览
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作者 Yalun An 《教育理论综述(英文)》 2019年第1期21-25,共5页
This article mainly discusses the fairness of compulsory education and the transformation of higher education between free and charged. Through the development of China’s compulsory education and higher education, we... This article mainly discusses the fairness of compulsory education and the transformation of higher education between free and charged. Through the development of China’s compulsory education and higher education, we expound the deficiencies and the concept of perfection at current stage and then points out strategies of equity in compulsory education and higher education based on the current situation. 展开更多
关键词 The ANGLE of CHARGING Compulsory EDUCATION Higher EDUCATION FAIRNESS
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U形渠道量水平板水力性能试验研究 预览
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作者 王文娥 张维乐 胡笑涛 《农业工程学报》 EI CAS CSCD 北大核心 2019年第13期84-90,共7页
根据北方灌区渠道底坡缓且灌溉水流多泥沙的现状,该文针对U型渠道设计了平板量水装置。为了探索不同尺寸悬垂薄平板在明渠水流冲击作用下的水力学特性,确定流量与平板偏转角度之间的关系。分析水流流态,将渠道运动水流分为3部分,对平板... 根据北方灌区渠道底坡缓且灌溉水流多泥沙的现状,该文针对U型渠道设计了平板量水装置。为了探索不同尺寸悬垂薄平板在明渠水流冲击作用下的水力学特性,确定流量与平板偏转角度之间的关系。分析水流流态,将渠道运动水流分为3部分,对平板部分水流应用闸孔淹没出流公式,建立流量计算模型,得出流量与角度的半经验关系式。对流量系数计算模型中的待定系数进行估计,得到了统一形式的流量公式。U型平板测流范围为9~44L/s,经验证,计算流量与实测流量之间最大相对误差为6.9%,平均相对误差为3.2%,其中收缩比0.547、0.439平板测流相对误差均小于5%,满足灌区量水要求。同一收缩比板型,相对水头损失随着流量增大而减小,不同收缩比板型,相对水头损失随着板型收缩比增大而增大,除收缩比0.715平板在小流量(本试验大约为10L/s)测流时,相对水头损失比在10%以上,其余平板测流时相对水头损失均小于10%,其中收缩比为0.439和0.337平板最大水头损失不超过上游总水头6%。经过综合分析,选择0.547到0.439为平板最佳收缩比测流范围。研究可为灌区量水设施的改进提供依据。 展开更多
关键词 流量 渠道 角度 渠道闸孔出流 流量系数 水头损失
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低雷诺数下团聚体细颗粒阻力修正系数的实验研究
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作者 刘胜佳 张光学 +4 位作者 马振方 王进卿 詹明秀 池作和 刘宇 《实验力学》 CSCD 北大核心 2019年第5期819-823,共5页
对团聚体状细颗粒的阻力修正系数进行落球法实验研究,得到颗粒粒径比、团聚体颗粒与流场夹角、规则团聚体颗粒自身夹角和不规则团聚体的分形维数等参数对阻力修正系数的影响。结果表明,团聚体所含颗粒的粒径之比越大,其阻力修正系数越大... 对团聚体状细颗粒的阻力修正系数进行落球法实验研究,得到颗粒粒径比、团聚体颗粒与流场夹角、规则团聚体颗粒自身夹角和不规则团聚体的分形维数等参数对阻力修正系数的影响。结果表明,团聚体所含颗粒的粒径之比越大,其阻力修正系数越大;团聚体颗粒阻力修正系数随团聚体与流场夹角的增大而增大;团聚体颗粒自身夹角越大,阻力修正系数越大,团聚体颗粒自身夹角越接近0°,其阻力修正系数越接近于1。对于不规则团聚体颗粒,阻力修正系数随分形维数的增大而减小。 展开更多
关键词 细颗粒物 团聚体 阻力修正系数 夹角 分形维数
Mathematical Model of Drag Torque with Surface Tension in Single-Plate Wet Clutch
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作者 Zengxiong Peng Shihua Yuan 《中国机械工程学报:英文版》 SCIE EI CAS CSCD 2019年第2期93-99,共7页
Reduction of drag torque in disengaged wet clutches is essential for transmission research because it is one of the potentials of e ciency improvement. Aeration of oil film between two closely rotating plates promotes... Reduction of drag torque in disengaged wet clutches is essential for transmission research because it is one of the potentials of e ciency improvement. Aeration of oil film between two closely rotating plates promotes the decrease of drag torque at high speed region. The e ects of surface tension and static contact angles during aeration are nonnegligible showed by test results. The traditional lubrication model does not adequately predict the experimental results with di erent surface tension and contact angles during aeration. Hence, in this present paper, contact angles between Aluminum and Teflon materials were firstly measured, and the drag torques under two di erent contact angles were examined experimentally. An improved lubrication model of drag torque based on Navier–Stokes equations at the gas-liquid interface was built. The lubrication boundary condition was modified to introduce the e ects of surface tension and contact angle. The model shows that the e ects at the beginning of aeration of oil film are significant. These e ects almost occur at stationary plate due to low Reynolds number and Weber number. The model shows that an increase in the surface tension promotes aeration, but does not a ect the peak drag torque. Increasing contact angle also promotes the aeration, and accelerates the decrease of drag torque. The larger contact angle is, the smaller the peak drag torque will be. A computational fluid dynamics(CFD) model based on volume of fluid(VOF) method was presented to validate the interface shape when aeration occurs. The model prediction has a good agreement with experimental observations for Aluminum plates and Teflon plates. The modified lubrication model of drag torque gives a convenient description of the e ects of surface tension and contact angel, and lays down a frame to understand the beginning of aeration. 展开更多
关键词 Drag TORQUE WET CLUTCH Surface tension Contact angle
Optimization of Input Parameters of AWJM: Using Three Different Abrasives on MS2062 预览
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作者 Kusnurkar S.V J.S.Sidhu 《非金属材料科学(英文)》 2019年第1期28-38,共11页
The objective of this work is to optimize input parameters of AWJM (Abrasive Water Jet Machining) such as Nozzle Transverse Speed (NTS), Abrasive Flow Rate (AFR) and Stand-off Distance (SOD) using three different abra... The objective of this work is to optimize input parameters of AWJM (Abrasive Water Jet Machining) such as Nozzle Transverse Speed (NTS), Abrasive Flow Rate (AFR) and Stand-off Distance (SOD) using three different abrasives Garnet, Brown Fused Alumina and White Aluminum Oxide on MS2062 and to compare their performance with surface finish, MRR and kerf angle. Experiments were conducted according to Taguchi’s design of experiments. Analysis of variance is conducted to investigate the influence of each parameter on responses Three controllable parameters of three levels are applied for determining the optimal responses The results revealed that NTS is a most significant factor for MRR among three abrasives followed by AFR and SOD, with regards to surface finish and MRR White Aluminum Oxide has emerged as a most strong abrasive followed by Brown Fused Alumina and Garnet. It is recommended, to achieve the better surface finish, less kerf angle and good MRR White Aluminum Oxide be used in place of Garnet which is mostly used by the industry today. 展开更多
关键词 GARNET White aluminum oxide Brown FUSED alumina NOZZLE transverse speed Abrasive flow Rate Standoff distance KERF angle MRR Taguchi ANOVA
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Patterning catalyst via inkjet printing to grow single-walled carbon nanotubes
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作者 Zeyao Zhang Yitan Li +6 位作者 Sheng Zhu Xiyan Liu Xiulan Zhao Meihui Li Haoyu Li Feng Yang Yan Li 《中国化学快报:英文版》 SCIE CAS CSCD 2019年第2期505-508,共4页
Controlled growth of patterned single-walled carbon nanotubes (SWNTs) is an important issue in many applications. Herein, we demonstrated a method to pattern catalyst via inkjet printing for the growth of SWNTs, using... Controlled growth of patterned single-walled carbon nanotubes (SWNTs) is an important issue in many applications. Herein, we demonstrated a method to pattern catalyst via inkjet printing for the growth of SWNTs, using metal salt solutions as the inks and an ordinary office-use printer. We printed water solutions of cobalt acetate on hydrophilic Si substrates and grew high quality SWNT films. The composition of the precursor solutions and the hydrophilicity of the substrates were crucial factors to the patterning. 展开更多
关键词 SINGLE-WALLED carbon NANOTUBES INKJET printing PATTERNING Contact angle Chemical vapor deposition
Close up observation and inversion of low-altitude ENA emissions during a substorm event
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作者 Li LU Susan MCKENNA-LAWLOR Jan BALAZ 《中国科学:地球科学英文版》 SCIE EI CAS CSCD 2019年第6期1024-1032,共9页
During a series of substorm events on November 12 2004, the Neutral Atom Detector Unit(NUADU) flying onboard the TC-2 spacecraft observed, close to perigee, bright low-altitude Energetic Neutral Atom(ENA) emissions fr... During a series of substorm events on November 12 2004, the Neutral Atom Detector Unit(NUADU) flying onboard the TC-2 spacecraft observed, close to perigee, bright low-altitude Energetic Neutral Atom(ENA) emissions from both north and south poles. Through utilizing high temporal and spatial resolution data inversion techniques we present here a global view the associated processes of energetic ion deposition and injection at the uniquely high temporal resolution of a few minutes. It is demonstrated that the ENA emissions observed came mainly from the, low-altitude, high magnetic latitude polar region. Since precipitating ions follow magnetic field lines and have more chance to produce ENA emissions through charge exchange there.Therefore, the employment of a low-orbit satellite to record at high temporal and spatial resolution ENA image data is inferred to be the best way to monitor those dynamic ring current variations that occur during geomagnetic activity. 展开更多
关键词 LOW-ALTITUDE ENA EMISSIONS ENA image INVERSION Pitch angle distribution ION injection ION deposition
Classification and Friction Angle from CPT in Gneissic Residual Soil of Brazil 预览
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作者 Fábio K. Silva César S. Godoi Li Fernanda S. Schuch 《地质资源与工程:英文版》 2019年第3期105-111,共7页
The current research presents the results of experiment in situ and laboratory research with the goal of determining the friction angle in residual soil using the CPT (cone penetration test). This experimental researc... The current research presents the results of experiment in situ and laboratory research with the goal of determining the friction angle in residual soil using the CPT (cone penetration test). This experimental research was completed in an area of study, composed of slopes and plateaus, located in the southern region of Brazil, in the Santo Amaro da Imperatriz municipality. An SPT (standard penetration test) and CPT in situ test investigation campaign was conducted and collected from deformed and undeformed samples for physical characterization and triaxial tests. The results made it possible to classify the soils analyzed according to the unified methodology proposed by Robertson that, based on studies provide friction angle values along the hole’s depth, and obtained through the CPT. The friction angle values obtained in the CPT indicated a well-defined trend of high values at the surface, which decrease in the middle of the soil mass and increase again near the healthy rock. The friction angles estimated by the CPT were overestimated when compared to laboratory estimations. This occurrence is explained by the fact that the measured resistance of the field tests is embedded in the cementation and suction plots. 展开更多
关键词 SOIL RESIDUAL in SITU tests FRICTION angle.
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汽车天窗加强件辊压工艺设计 预览
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作者 张晶晶 朱傲 殷浩然 《内燃机与配件》 2019年第9期31-33,共3页
辊压成型是一种节材、节能、高效的金属板料成型新工艺、新技术,是通过顺序配置的多道次成型辊轮,把卷材、带材等金属板带不断地进行横向弯曲,以制成特定断面型材的塑性加工工艺。材料根据截面不同,辊轮组对数也不同。文章从实际出发,... 辊压成型是一种节材、节能、高效的金属板料成型新工艺、新技术,是通过顺序配置的多道次成型辊轮,把卷材、带材等金属板带不断地进行横向弯曲,以制成特定断面型材的塑性加工工艺。材料根据截面不同,辊轮组对数也不同。文章从实际出发,联系车间生产,对汽车天窗加强件辊压工艺进行设计,确定截面加工辊花图以及辊轮的设计,主要攻克段数划分,角度分配等难点。 展开更多
关键词 辊压成型 辊花 角度 段数
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U形明渠流量与悬垂平板偏转角关系研究
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作者 张维乐 王文娥 胡笑涛 《水力发电学报》 CSCD 北大核心 2019年第6期69-76,共8页
为确定明渠流量与平板偏转角度的关系,本文研究了悬垂薄平板在明渠水流冲击作用下的动力学特性及平板偏转现象,分析绕轴自由旋转薄平板在水中的受力,将平板所受水流作用力竖直向上的分力假设为静水压力,应用动量定理与力矩平衡原理,推... 为确定明渠流量与平板偏转角度的关系,本文研究了悬垂薄平板在明渠水流冲击作用下的动力学特性及平板偏转现象,分析绕轴自由旋转薄平板在水中的受力,将平板所受水流作用力竖直向上的分力假设为静水压力,应用动量定理与力矩平衡原理,推导了平板偏转角度α与流量Q之间的理论关系式,并在U型渠道上进行试验,验证理论公式的合理性。流量小于10 L/s时计算流量与实测流量的相对误差超过10%,其他均小于10%,流量大于17 L/s时误差均小于5%以内,测流范围在10~44 L/s,当悬垂薄平板与明渠横断面等大时,流量Q与偏转角度α存在单值对应关系,角度α随着流量Q的增大而增大;板前后水位差Δh随着角度α增大有逐渐减小并趋于定值(大概3 cm)的趋势,平板下水流流态随着平板偏转角度的增大由急流过渡为缓流;绕流阻力R随着雷诺数Re的增大而增大,阻力系数Cd随着雷诺数Re的增大而减小,平板偏转角度α与板前后水位差和阻力系数有关。 展开更多
关键词 角度 流量 绕流阻力 阻力系数 受力方向
Remote Sensing Monitoring of Surface Characteristics in the Badain Jaran, Tengger, and Ulan Buh Deserts of China 预览
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作者 LIU Qingsheng LIU Gaohuan +1 位作者 HUANG Chong LI He 《中国地理科学:英文版》 SCIE CSCD 2019年第1期151-165,共15页
Deserts and sandy land in northern China are very susceptible to sandy desertification and are the main source of sand-dust storms of Asian dust. However, because of the complex factors involved, descriptions of the r... Deserts and sandy land in northern China are very susceptible to sandy desertification and are the main source of sand-dust storms of Asian dust. However, because of the complex factors involved, descriptions of the relationship between sandy desertification and surface characteristics in these regions are lacking. We monitored the surface characteristics and their changes in time using information about soil, vegetation, and landforms in the Badain Jaran Desert(BJD), Tengger Desert(TD), and Ulan Buh Desert(UBD) in the northern China. The monitoring was done using tasseled cap angle(TCA), disturbance index(DI), and topsoil grain size index(TGSI) from Moderate Resolution Imaging Spectroradiometer(MODIS) images combined with a decision tree classification. Results showed that the TD had higher topsoil fine sand content, and the ratio of non-vegetated to vegetated areas was similar with that in the UBD. Northeast-southwest coarse sand dunes with thin interdune(NECTI) dominated the BD, fine sand dunes(FSD) dominated the TD, and a combination of northeast-southwest coarse sand dunes with wide interdune(NECWI) and northwest-southeast coarse sand dunes with wide interdune(NWCWI) dominated the UBD. From 2000 to 2015, in the BJD the area of the NECTI, non-sand dune(Non) and potential sand sources(PSS) increased, whereas the area of the NECWI, FSD and NWCWI decreased, indicating a improve process in the BJD. In the TD, the area covered by Non increased, whereas the area covered by PSS, NECWI, NECTI, FSD, and NWCWI decreased from 2000 to 2015. The area covered by the various surface characteristic types fluctuated annually in the UBD from 2000 to 2015. Changes in surface characteristics reflect the combined effects of natural conditions and human activity. The findings of our study will assist scientists and policy makers in proposing different management techniques to combat sandy desertification for the different surface characteristics of these regions. 展开更多
关键词 surface characteristics MODIS DESERT tasseled CAP angle DISTURBANCE INDEX TOPSOIL GRAIN size INDEX
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Detection of short-term urban land use changes by combining SAR time series images and spectral angle mapping
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作者 Zhuokun PAN Yueming HU Guangxing WANG 《地球科学前沿:英文版》 SCIE CAS CSCD 2019年第3期495-509,共15页
Rapid urban sprawl and re-construction of old towns have been leading to great changes of land use in cities of China. To witness short-term urban land use changes, rapid or real time remote sensing images and effecti... Rapid urban sprawl and re-construction of old towns have been leading to great changes of land use in cities of China. To witness short-term urban land use changes, rapid or real time remote sensing images and effective detection methods are required. With the availability of short repeat cycle, relatively high spatial resolution, and weather-independent Synthetic Aperture Radar (SAR) remotely sensed data, detection of short-term urban land use changes becomes possible. This paper adopts newly released Sentinel-1 SAR data for urban change detection in Tianhe District of Guangzhou City in Southern China, where dramatic urban redevelopment practices have been taking place in past years. An integrative method that combines the SAR time series data and a spectral angle mapping (SAM) was developed and applied to detect the short-term land use changes. Linear trend transformations of the SAR time series data were first conducted to reveal patterns of substantial changes. Spectral mixture analysis was then conducted to extract temporal endmembers to reflect the land development patterns based on the SAR backscattering intensities over time. Moreover, SAM was applied to extract the information of significant increase and decrease patterns. The results of validation and method comparison showed a significant capability of both the proposed method and the SAR time series images for detecting the short-term urban land use changes. The method received an overall accuracy of 78%, being more accurate than that using a bi-temporal image change detection method. The results revealed land use conversions due to the removal of old buildings and their replacement by new construction. This implies that SAR time series data reflects the spatiotemporal evolution of urban constructed areas within a short time period and this study provided the potential for detecting changes that requires continuously short-term capability, and could be potential in other landscapes. 展开更多
关键词 Sentinel-1 SAR time series IMAGES urban land use change DETECTION TEMPORAL ENDMEMBER spectral angle mapping
High-Brightness Low-Divergence Tapered Lasers with a Narrow Taper Angle
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作者 陈忠浩 渠红伟 +4 位作者 马晓龙 齐爱谊 周旭彦 王宇飞 郑婉华 《中国物理快报:英文版》 SCIE CAS CSCD 2019年第8期43-46,共4页
High-brightness tapered lasers with photonic crystal structures are designed and fabricated.A narrow taper angle is designed for the tapered section.The device delivers an output power of 3.3 W and a maximum wall-plug... High-brightness tapered lasers with photonic crystal structures are designed and fabricated.A narrow taper angle is designed for the tapered section.The device delivers an output power of 3.3 W and a maximum wall-plug efficiency of 43%.The vertical beam divergence is around 110 at different currents.Nearly diffraction-limited beam qualities for the vertical and lateral directions are obtained.The lateral beam quality factor M2 is below 2.5 and the vertical M2 value is around 1.5 across the whole operating current range.The maximum brightness is 85 MW·cm-2sr-1.When the current is above 3.3 A,the brightness is still above 80 MW·cm-2sr-1. 展开更多
关键词 profile HIGH-BRIGHTNESS NARROW TAPER ANGLE
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