检索结果-南通市图书馆

On the Calculation of Lyapunov Indicators with Post-stabilization in a Weyl Field

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Journal of Astronomy and Astrophysics 2006年第2期6卷 125-140页

作者： Xin Wu Hong Zhang Xiao-sheng wan Department of Physics Nanchang University Nanchang 330047 Department of Astronomy Nanjing University Nanjing 210093

We present details of a work aiming at the overestimation of Lyapunov exponents defined by the geodesic deviation equations in the previous work. The geodesic deviation vector with post-stabilization is used to compute the fast Lyapunov indicator, considered to be a very sensitive tool for discrimination between ordered or weakly chaotic motions. We make a detailed study of the dynamics in the superposed Weyl field between a black hole and shell of octopoles by using the fast Lyapunov indicator with the Poincare surface of section. In particular, we examine the effects on the dynamics around the fixed points, of varying one of the three parameters （specific energy E, specific angular momentum L and octopolar moment 0）, while keeping the other two fixed, and identify the intervals of the varying parameter where the motion is regular or chaotic.

关键词： black hole physics - stars: circumstellar matter - chaos - methods:numerical

Pulse-gated mode of commercial superconducting nanowire single photon detectors

在线全文

学校读者我要写书评

暂无评论

Chinese Physics B 2021年第4期30卷 144-150页

作者： Fan Liu Mu-sheng Jiang Yi-Fei Lu Yang wang wan-Su Bao Henan Key Laboratory of Quantum Information and Cryptography SSF IEUZhengzhou 450001China Synergetic Innovation Centre of Quantum Information and Quantum Physics University of Science and Technology of ChinaHefei 230026China

High detection efficiency and low intrinsic dark count rate are two advantages of superconducting nanowire single photon detectors(SNSPDs).However,the stray photons penetrated into the fiber would cause the extrinsic dark count rate,owing to the free running mode of *** order to improve the performance of SNSPDs in realistic scenarios,stray photons should be investigated and suppression methods should be *** this study,we demonstrate the pulsegated mode,with 500 kHz gating frequency,of a commercial SNSPD system for suppressing the response of stray photons about three orders of magnitude than its free-running counterpart on the extreme test *** we push the gating frequency to 8 MHz,the dark count rate still keeps under 4% of free-running *** experiments,the intrinsic dark count rate is also suppressed to 4.56 × 10^(-2) counts per second with system detection efficiency of 76.4372%.Furthermore,the time-correlated single-photon counting analysis also approves the validity of our mode in suppressing the responses of stray photons.

关键词： quantum detector superconducting nanowire pulse gated dark count rate

Range expansion of the invasive cotton mealybug, Phenacoccus solenopsis Tinsley: An increasing threat to agricultural and horticultural crops in China

在线全文

学校读者我要写书评

暂无评论

Journal of Integrative Agriculture 2020年第3期19卷 881-885页

作者： wang Yu-sheng DAI Tian-mei TIAN Hu wan Fang-hao ZHANG Gui-fen State Key Laboratory for Biology of Plant Diseases and Insect Pests/Key Laboratory of Integrated Pest Management of Crop Ministry of Agriculture and Rural Affairs/Institute of Plant ProtectionChinese Academy of Agricultural SciencesBeijing 100193P.R.China Hunan Provincial Key Laboratory for Control of Forest Diseases and Pests College of ForestryCentral South University of Forestry and TechnologyChangsha 410004P.R.China Caofeidian Customs House Tangshan 063210P.R.China Center for Management of Invasive Alien Species Ministry of Agriculture and Rural AffairsBeijing 100193P.R.China

The globally invasive cotton mealybug Phenacoccus solenopsis Tinsley,has recently invaded several Chinese regions,and continues to expand its *** mealybug is a polyphagous insect pest,with at least 200 host plants from 63 families,including cotton,food crops,fruits,ornamental plants,tobacco,and ***,we describe the first finding of *** in Shandong Province,and investigate the abundances of its natural enemies(predator Coccinella septempunctata *** parasitoid Aenasius bambawalei Hayat).All three species were detected from ornamental and weed species in Linyi,Shandong,in September 2018,and were positively identified using DNA *** analysis revealed significant identity(99.38-100%) between sequences of *** obtained in this study and those published in the *** invasive pest represents a major potential threat to agri-horticulture in Shandong,which is a key province of China for production and export of many vegetables,flowers,fruits,and other *** mealybug species has a wide range of potential distribution in Shandong and is easily dispersed with agricultural and horticultural transport *** monitoring and management strategies are required to limit the spread of this pest species.

关键词： Aenasius bambawalei Coccinella septempunctata field investigation invasive insect pest molecular identification Phenacoccus solenopsis rapid spreading

在线全文

学校读者我要写书评

暂无评论

经颅多谱勒检测阿尔茨海默病的对照研究

四川精神卫生 2007年第4期20卷 193-195页

作者：万艳琼盛建华王燕盛明王秀华上海市精神卫生中心 200030

目的了解阿尔茨海默病(AD)的颅内各大血管血流速度的改变情况,及其与认知功能改变之间的关系。方法记录60例首次入院的AD患者经颅多谱勒(TCD)颅内血管检测结果,包括两侧大脑中动脉、两侧大脑前动脉、两侧大脑后动脉、基底动脉、两侧椎... 详细信息

目的了解阿尔茨海默病(AD)的颅内各大血管血流速度的改变情况,及其与认知功能改变之间的关系。方法记录60例首次入院的AD患者经颅多谱勒(TCD)颅内血管检测结果,包括两侧大脑中动脉、两侧大脑前动脉、两侧大脑后动脉、基底动脉、两侧椎动脉。同时记录简易智力状态检查(MMSE)结果。对照组为60例血管性痴呆(VD)和60例精神分裂症(S)。结果研究组和对照组自身每一颅内动脉的两侧血流速度无显著差异(P>0.05)。AD组的TCD检测异常率为90.00%,其中以血流速度降低为突出表现,与VD组无显著性差异(P>0.05),但明显低于S组(P<0.01或0.05,两侧椎动脉除外)。AD的颅内各动脉(右侧大脑后动脉除外)血流速度与简易智力状态检查(MMSE)分数呈正相关。结论AD的TCD检测对该病的病因探讨、认知功能评估及治疗有一定意义。

关键词：阿尔茨海默病经颅多谱勒检测认知功能

Effect of tongue clearance on hydraulic performance of double support vortex pump

在线全文

学校读者我要写书评

暂无评论

Defence Technology（防务技术） 2019年第4期15卷 645-654页

作者： Xiang-yang Li wan-qiang Chen sheng-dun Zhao Pump Equipment Engineering Research Center of Shaanxi Province Xi'an Aeronautical University Xi'an 710077 China School of Mechanical Engineering Xi'an Jiaotong University Xi'an 710049 China

In order to study influence of tongue clearance on the hydraulic performance of double support vortex pump,three dimensional flow model with symmetric variable size tongue clearance was established by changing section parameter of tongue clearance,and applied to numerically simulate the steady inner flow in a vortex pump based on fixed working conditions and impeller through ANSYS *** numerical results show the influence of tongue channel with two sections(non-uniform and uniform sections)on flow field characteristics in vortex ***,the variation of tongue channel section changes the vortex structure distribution in circumferential flow *** the spiral forward vortex structure in the circumferential direction shifts to large radius side with increasing tongue ***,the circumferential velocity gradient and axial pressure gradient both diminish with the increase of the tongue section,and the inlet/outlet pressure difference and velocity distribution also reduce with increasing tongue channel ***,for vortex pump with non-uniform section of tongue channel,the head diminishes and the efficiency remains constant approximately with the increase of the tongue width,while the head and the efficiency both diminish for uniform section of tongue channel.

关键词： Vortex pump Tongue clearance Non-uniform flow passage Numerical simulation

Seismological evidence for the convergence of crustal stress orientation before large earthquakes

在线全文

学校读者我要写书评

暂无评论

Earthquake Science 2009年第6期22卷 623-629页

作者： Yongge wan Shuzhong sheng Institute of Disaster Prevention Science and Technology Sanhe 065201 China Institute of Geophysics China Earthquake Administration Beijing 100081 China

Earthquakes are caused by the failure of faults, driven by tectonic stress build-up in the Earth＇s crust. To study the earthquake preparation process and assess regional earthquake potentials, it is vitally important to understand the crustal stress evolution process and identify its change in pattern associated with the seismogenic process. In this study we investigate the focal mechanism orientations of earthquakes in southern California from 1982 to 1999, basing on a focal mechanism catalog from Hauksson. We find that for the two large earthquakes occurred in southern California, the 1992 Mw7.3 Landers and the 1999 Mw7.1 Hector Mine, the orientations of focal mechanisms near the coming earthquake tend to converge to the stress direction promoting the rupture of the coming earthquake and align with its focal mechanism about half-year before its occurrence, suggesting that the tectonic stress field gets more organized in favor of the rupture of the event pre-seismically. The degree of stress convergence is measured by the orientation angle RMS （root mean square） between the preshocks＇ focal mechanisms and the focal mechanism of the large event studied, and its time series recorded the stress convergence process. The degree of anomalies, measured by the F-tests, indicates that the convergence of stress orientations become significant at 90% confidence about half-year prior to both the Landers and Hector Mine quakes, and it becomes even more prominent at 99% confidence right before the occurrences. Our study may be of significance for assessment of regional seismic potentials.

关键词： focal mechanism stress orientation convergence evolution F-test

Upper-rim-modified thioether thiacalix[4]arene used for liquid-liquid extraction of Au(Ⅲ)and Pd(Ⅱ)in hydrochloric acid medium

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Chemical Engineering 2024年第2期66卷 110-118页

作者： sheng wan Rong Xie Jianhong Fan Kewen Tang Department of Chemistry and Chemical Engineering Hunan Institute of Science and TechnologyYueyang 414006China

Gold(Au)and palladium(Pd)play an increasing role in the production and human life;Therefore,it is of great significance to study their recovery.A 5,11,17,23-tetra-ethylthio-25,26,27,28-tetra-hydroxyl thiacalix[4]arene(TCAET)was synthesized specifically for the capture of Au(Ⅲ)and Pd(Ⅱ)from HCl medium by liquid-liquid *** a 0.1 mol·L^(-1)HCl medium,the transfer of Au(Ⅲ)and Pd(Ⅱ)from the aqueous phase to the organic phase was highly efficient,with a transfer ratio of 100%for Au(Ⅲ)and 98%for Pd(Ⅱ).Furthermore,the extraction equilibrium time for Au(Ⅲ)was just 5 ***'s method data demonstrated that TCAET formed complexes with Au(Ⅲ)and Pd(Ⅱ)in a ratio of 2:3 and 1:1,respectively,during the extraction *** showed high selectivity toward Pd(Ⅱ)and Au(Ⅲ)over other competing metal ***,both Au(Ⅲ)and Pd(Ⅱ)could be successfully stripped from the loaded organic phases with a 1.0 mol·L^(-1)thiourea in 0.5 mol·L^(-1)HCl and 0.5 mol·L^(-1)thiourea in 0.5 mol·L^(-1)HCl,*** obtained from five consecutive extraction-stripping cycles showed good reusability of TCAET toward Au(Ⅲ)and Pd(Ⅱ)*** conclusion can provide a certain reference for thiacalixarene in the recovery of precious metal species.

关键词： Thiacalixarene Upper-rim modification Liquid-liquid extraction Precious metal Thioether

Shaped-Beam Pattern Synthesis Through the Construction of Weighted Generalized Rayleigh Quotient

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Electronics 2019年第1期28卷 207-214页

作者： YANG Yin wan Chuan sheng Weixing HAN Yubing MA Xiaofeng School of Electronic and Optical Engineering Nanjing University of Science and Technology

A novel shaped-beam pattern synthesis method of generating an arbitrary footprint pattern under an arbitrary array structure is proposed. The embedded element pattern information is included in the pattern model, and a new cost function composed of three optimization items which are sidelobe levels,mainlobe ripples and mainlobe gains is constructed through the model. During the optimization process,to further enhance the performance of the synthesized pattern, a weight matrix is designed and added to the optimization items, then the generalized Rayleigh quotient approximation method is used to obtain the final array element excitations. To illustrate the good performance of the provided method, several synthesis examples with different arrays and footprints are presented. Compared with other algorithms such as Weighted alternating reverse projection(WARP) method, the proposed method can achieve better results with lower sidelobe levels, smaller mainlobe ripples and less computational load.

关键词： Pattern synthesis Embedded element pattern Mutual coupling Generalized Rayleigh quotient approximation Arbitrary footprint

Modeling of flow and debris ejection in blasting erosion arc machining in end milling mode

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Advances in Manufacturing 2020年第4期8卷 508-518页

作者： Ji-Peng Chen Lin Gu wan-sheng Zhao Mario Guagliano School of Mechanical and Electronic Engineering Nanjing Forestry UniversityNanjing 210037People's Republic of China Department of Mechanical Engineering Polytechnic University of MilanPiazza Leonardo da Vinci32MilanItaly State Key Laboratory of Mechanical System and Vibration School of Mechanical EngineeringShanghai Jiao Tong UniversityShanghai 200240People's Republic of China

Blasting erosion arc machining(BEAM)is a typical arc discharge machining technology that was developed around 2012 to improve the machinability of difficult-to-cut *** milling BEAM has been successfully developed and preliminarily applied in ***,owing to the high complexity of the flow field and the difficulty of observing debris in the discharge gap,studies of the flow and debris in end milling BEAM are *** this study,fluid dynamics simulations and particle tracking are used to investigate the flow characteristics and debris ejection processes in end milling ***,the end milling BEAM m o d e is *** the numerical modeling parameters,geometric models,and simulation methods are presented in ***,the flow distribution and debris ejection are described,analyzed,and *** velocity and pressure distributions of the axial feed and radial feed are observed;the rotation speed and milling depth are found to have almost no effect on the flow velocity ***,debris is ejected more rapidly in the radial feed than in the axial *** particle kinetic energy tends to increase with increasing milling depth,and smaller particles are more easily expelled from the flushing *** study attempts to reveal the flow field properties and debris ejection mechanism of end milling BEAM,which will be helpful in gaining a better understanding of BEAM.

关键词： Modeling Flow Debris ejection Blasting erosion arc machining(BEAM) End milling