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振动引起的不稳定磁场对核磁共振谱图的影响
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作者 林雁勤 陈希 +2 位作者 林涛 柯恩锋 陈忠 《厦门大学学报(自然科学版)》 CAS CSCD 北大核心 2006年第3期328-332,共5页
在核磁共振实验中,地基振动等外界干扰会引起磁场不稳定,从而影响高分辨核磁谱图的质量.为探讨振动对谱图的影响,本文将外界振动引起的不稳定磁场作为微扰项,通过Bloch方程从理论上分析了其产生振动干扰峰的机理和振动干扰峰在谱图中的... 在核磁共振实验中,地基振动等外界干扰会引起磁场不稳定,从而影响高分辨核磁谱图的质量.为探讨振动对谱图的影响,本文将外界振动引起的不稳定磁场作为微扰项,通过Bloch方程从理论上分析了其产生振动干扰峰的机理和振动干扰峰在谱图中的分布规律,并利用计算机模拟了几种典型的外界振动产生的干扰峰在谱图上的分布,通过差谱实验揭示了外界振动对谱图的影响.研究结果表明:外界振动会使谱图的线形变差、线宽增大和相位扰乱,从而降低谱图的分辨率.实验结果与理论预测和模拟结果相吻合. 展开更多
关键词 核磁共振 振动 不稳定场 计算机模拟 差谱
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不稳定地温场的有限差分模拟 被引量:3
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作者 赵志根 《安徽地质》 2002年第1期59-61,共3页
对矿井地温场的研究具有多方面的意义。本文采用有限差分法对不稳定地温场进行了研究,根据数学模型建立起差分方程,编制了计算程序,并通过一个实例分析了岩床侵入煤系地层时的温度变化规律。
关键词 不稳定地温 数学模型 有限差分法 岩床
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重新认识波状低云(二)波状低云区的位势不稳定功能
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作者 蔡尔诚 《陕西气象》 1998年第2期8-9,共2页
关键词 波状低云区 位势不稳定场 新认识 暴雨落区 中尺度系统 强降水 稳定 中期暴雨预报 上升运动 气流辐合
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核磁共振中分子间多量子相干及其应用 被引量:2
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作者 陈忠 蔡淑惠 +3 位作者 黄玉清 蔡聪波 林雁勤 陈志伟 《厦门大学学报(自然科学版)》 CAS CSCD 北大核心 2011年第2期193-202,共10页
源自核自旋远程偶极相互作用的分子间多量子相干(iMQC)以其独特的性质在核磁共振领域引起了广泛的关注.与常规的单量子相干信号相比,iMQC信号具有下列特性:iMQC信号与实验可控的偶极相关距离为半径的空间区域内的自旋粒子数相关;iMQC信... 源自核自旋远程偶极相互作用的分子间多量子相干(iMQC)以其独特的性质在核磁共振领域引起了广泛的关注.与常规的单量子相干信号相比,iMQC信号具有下列特性:iMQC信号与实验可控的偶极相关距离为半径的空间区域内的自旋粒子数相关;iMQC信号与局域磁场分布或局域磁化率效应相关;iMQC信号具有独特的弛豫和扩散特性.这些性质使iMQC在核磁共振波谱和成像领域得到了广泛的应用.本文简要介绍了iMQC现象的研究历史以及相应的理论解释,对我们小组这10几年来在iMQC领域的研究进行了系统的阐述,包括对iMQC性质的研究及其在不均匀不稳定场中高分辨核磁共振谱和成像方面的应用研究. 展开更多
关键词 核磁共振 磁共振成像 分子间多量子相干 不均匀不稳定场 高分辨
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一种锥束CT中平板探测器输出图像校正方法 被引量:8
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作者 王苦愚 张定华 +1 位作者 黄魁东 李明君 《计算机辅助设计与图形学学报》 EI CSCD 北大核心 2009年第7期954-961,共8页
为了消除平板探测器缺陷在锥束CT重建切片中引起的伪影,提出一种投影图像校正方法.通过对投影图像进行暗场和增益不一致校正,推导了像元增益系数公式;对增益系数以及像元输出的期望和方差进行直方图分析以识别坏像素,根据坏像素分布特... 为了消除平板探测器缺陷在锥束CT重建切片中引起的伪影,提出一种投影图像校正方法.通过对投影图像进行暗场和增益不一致校正,推导了像元增益系数公式;对增益系数以及像元输出的期望和方差进行直方图分析以识别坏像素,根据坏像素分布特征设计相应的插补方案;通过局部屏蔽区域数据统计暗场波动幅度并逐行修正.实验结果表明,该方法使投影图像灰度分布均匀,像元输出波动和切片伪影得到有效抑制. 展开更多
关键词 锥束CT 平板探测器 投影校正 增益系数 不稳定
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异极式永磁偏置径向磁轴承的建模与实验 被引量:6
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作者 吴磊涛 王东 +2 位作者 苏振中 张贤彪 薛滟膑 《电工技术学报》 EI CSCD 北大核心 2018年第5期1051-1057,共7页
为了满足储能飞轮系统、卫星动量轮等对高空间利用率的需求,提出了一种异极式永磁偏置径向磁轴承的拓扑结构。通过在槽口放置平行充磁的永磁体获得紧凑的结构,同时永磁磁路和电励磁磁路耦合距离较短,有利于获取高解耦特性。该文首先采... 为了满足储能飞轮系统、卫星动量轮等对高空间利用率的需求,提出了一种异极式永磁偏置径向磁轴承的拓扑结构。通过在槽口放置平行充磁的永磁体获得紧凑的结构,同时永磁磁路和电励磁磁路耦合距离较短,有利于获取高解耦特性。该文首先采用磁力线法,分别获取考虑齿槽效应、转子偏心的永磁磁场、电励磁磁场的气隙磁通密度分布,建立了磁路模型;然后根据磁路模型求解位移刚度和电流刚度,建立磁轴承的数学模型;与有限元仿真进行对比,证明所建立的磁场模型能够准确计算气隙磁通密度分布。设计、制造一台实验样机并进行相关实验,实验结果验证了磁路模型及有限元仿真的可靠性。 展开更多
关键词 结构 磁路模型 有限元仿真 静态性能
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柳州地区春季严重对流天气预报业务系统
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作者 李家文 韦贵爵 刘泽军 《广西气象》 2000年第4期10-11,14,共3页
通过对柳州地区春季严重对流天气形成的能量场和不稳定场特征的分析 ,在天气学分型的基础上 ,利用T10 6数值预报产品 ,并借助 Micaps平台 ,研制出适合柳州地区运行的业务系统。
关键词 预报 业务系统 严重对流天气 能量 不稳定场
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Analytic computation on the forcible thawing temperature field formed by a single heat transfer pipe with unsteady outer surface temperature 被引量:3
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《Journal of Coal Science & Engineering(China)》 2012年第1期18-24,共7页
A comprehensive and systematic research on the forcible thawing temperature field formed by a single heat transfer pipe with unsteady outer surface temperature was carried out by analytic computation according to the ... A comprehensive and systematic research on the forcible thawing temperature field formed by a single heat transfer pipe with unsteady outer surface temperature was carried out by analytic computation according to the theory of similitude. The distribution law of thawing temperature field, calculation formulas of thawing radius b, heat flux density q and average thawing temperature T were obtained. It theoretically explains that the main influential factors of thawing radius b, heat flux density q and thawing average temperature T are K,f, Lx and co(l), but Lc affects little. Finally, based on the forcible thawing project of Hulusu air shaft lining, the field data indicate that the analytical formulas of this article are comparatively accurate. 展开更多
关键词 analytic computation forcible thawing temperature field theory of similitude artificial ground freezing
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The Causes of Contagion: Rational or Irrational Behavior?
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作者 Viorel Cratciuneanu Andreea Pardau Carmen Emilia Pascal 《Journal of Modern Accounting and Auditing》 2013年第11期1507-1518,共12页
The threats concerning financial stability seriously affect the overall functioning of the economy at a local, regional, national, and continental level instead of a global level, and therefore, the emphasis is laid o... The threats concerning financial stability seriously affect the overall functioning of the economy at a local, regional, national, and continental level instead of a global level, and therefore, the emphasis is laid on analyzing the causes and effects of such threats. Financial crises in the current decade, as well as those in the past have shown that a major cause of instability in the global market is the so-called financial contagion. This leads to a natural question: whether similar authorities could specify and mitigate these shocks through efficient calculation followed by stability measures taken by banking networks. To answer this question, an empirical research was conducted by analyzing the degree of contagion induced by markets in Central and Eastern Europe, based on an econometric model, involving over 17 European countries, from January 2006 to January 2013. 展开更多
关键词 financial crisis contagion social protection systemic risk
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Opening up the Economy of Turkey to the Outside World: The Stabilization Decisions of January 24th 1980, Economic Situation in pre and Post January 24th Period
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作者 Karluk Sadik Ridvan Kucuksakarya Sevilay 《Chinese Business Review》 2016年第6期265-281,共17页
As a result of the fact that the stabilization program put into force in 1978 and 1979 in the Economy of Turkey could not be efficiently implemented due to the political instability and weak governments, a need to dra... As a result of the fact that the stabilization program put into force in 1978 and 1979 in the Economy of Turkey could not be efficiently implemented due to the political instability and weak governments, a need to draft a new stabilization program emerged. The stabilization program of January 24th, 1980 was prepared in this environment. This is a program which includes the structural transformations in the long term as well as the aims foreseen to be realized in the short term. The program adopted the implementation of significant changes in the structure of the economy and the price mechanism in the market which becomes the only guide as the basic principle. The difference from the previous programs is an economic development program intending to provide a very permanent and structural change in the economy rather than to realize the short-term goals. With the decisions, a large devaluation was implemented, the exchange rate policy and importation were liberated, foreign capital and exportation were encouraged, the subsidies with the exception of energy, fertilizer, and transportation were removed, restrictions were imposed on the support purchases in agricultural products, and the overseas contracting services were supported. There are two structural objectives desired to be performed in the long term, shrinking the public sector and removing the intervention in the markets. The basic philosophy is to decrease the state intervention to the minimum level in the economy and to bring functionality to the market economy and to validate the price mechanism. In this paper, the stabilization decisions in the economy of Turkey belonging to pre- and early post-January 24th period will be comparatively analysed. 展开更多
关键词 The Decisions of January 24th 1980 Turgut 0zal Siileyman Demirel export-oriented industrializationpolicy the decisions of February 4th and April 5th 1994
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Charge Densities of Unstable Nuclei with Electron Scattering
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作者 褚衍运 任中洲 +1 位作者 王再军 董铁矿 《Communications in Theoretical Physics》 SCIE CAS CSCD 2010年第8期347-354,共8页
Relativistic mean-field theory and phase-shift analysis are combined together to investigate the elasticCoulomb scattering between electrons and unstable nuclei.Electron scattering at several different energies is stu... Relativistic mean-field theory and phase-shift analysis are combined together to investigate the elasticCoulomb scattering between electrons and unstable nuclei.Electron scattering at several different energies is studiedand compared,in order to see the energy dependence of electron-nucleus scattering.It is shown that electron scattering at200 MeV or 300 MeV can be used to reveal electron-nucleus scattering information around the first diffraction minimum-Shiftsin opposite directions are obtained for the first diffraction minima of the electron scattering off the ground andfirst excited states of ^(17)F with ^(16)O as reference,and similar effects are obtained for ^(18)Ne.Besides,some neutron-richN = 8 isotones are also studied.Results show that electron scattering will be very useful and important in studyingboth proton- and neutron-rich nuclei in the future. 展开更多
关键词 electron scattering relativistic mean field theory phase-shift analysis exotic nuclei
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The impact of credit risk transfer on financial stability
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作者 Shoufang Wang 《International English Education Research》 2015年第5期39-41,共3页
The development of credit risk transfer market disperse the credit risk of banks, at the same time, also give a threat to the whole financial system with instability. This paper from the influence factors of financial... The development of credit risk transfer market disperse the credit risk of banks, at the same time, also give a threat to the whole financial system with instability. This paper from the influence factors of financial stability, explores how credit risk affecting the stability of financial system. Research found that the rating risk of credit risk transfer can cause default contagion in the financial markets. 展开更多
关键词 credit risk financial stability credit derivative instrument
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Identification of meta-instable stress state based on experimental study of evolution of the temperature field during stick-slip instability on a 5° bending fault 被引量:31
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作者 MA Jin S I SHERMAN GUO YanShuang 《Science China Earth Sciences》 SCIE EI CAS 2012年第6期869-881,共13页
Identification of the meta-instable stress state and study of its mechanism and evolution of relevant physical fields would be of great significance for determination of potential seismic risks and estimation of criti... Identification of the meta-instable stress state and study of its mechanism and evolution of relevant physical fields would be of great significance for determination of potential seismic risks and estimation of critical times. In laboratory experiments, that the specimen enters the meta-instable is marked by accelerated stress release. Could we use the experimental result to identify the earthquake in natural conditions? Because the observational data from one station can only reflect the stress state beneath this station, the key problem for identification of the meta-instability is how to recognize regional stress state through observational data from many stations. In this work, we choose the evolution of the temperature field over varied deformation stages during a stick-slip event on a 5 bending fault as an example, and attempt to find the response features of the physical quantity when the fault enters the meta-instable state. We discuss the characteristics of stages for the stress build-up, stress-time process deviating from linearity before instability, meta-instability, instability, and post-instability, respectively. The result shows that the fault instability slide is a conversion process from independent activities of each fault segment to synergism activity. The instability implies completion of the synergism. The stage deviating from linearity is the onset of stress release, and it is also the onset of the synergism. At the meta-instability stages, stress release becomes dominant, while the synergism tends to finish. Therefore, the analysis of the regional overall stress state should not start from individual stations, and instead it should begin with the evolution of the whole deformation field. 展开更多
关键词 earthquake risk stress state meta-instable state evolution of the temperature field synergism bending fault
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Supersonic Moist Air Jet Impingements on Flat Surface 被引量:2
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作者 ALAM Miah Md.Ashraful MATSUO Shigeru SETOGUCHI Toshiaki 《Journal of Thermal Science》 SCIE EI CAS CSCD 2010年第1期51-59,共9页
Pronounced aeroacoustic resonances are exhibited in the flow field where a jet emerges from an orifice or a nozzle and impinges on a solid surface. One instance where such resonances are produced is in a high speed je... Pronounced aeroacoustic resonances are exhibited in the flow field where a jet emerges from an orifice or a nozzle and impinges on a solid surface. One instance where such resonances are produced is in a high speed jet impingement, such as in the space launch vehicle systems, jet-engine exhaust impingement, and in the short take-off and vertical landing (STOVE) aircraft, etc. A highly unsteady flowfield leading to a drastic increase of noise level with very high dynamic pressure and thermal loads are noticed on nearby surfaces results dramatic lift loss, severe ground erosion and hot gas ingestion to the inlet in the jet engines. This highly unsteady behavior of the im- pinging jets is due to a feedback loop between the fluid and acoustic fields. In actual jet flow, the working gas may contain condensable gas such as steam or moist air. In these cases, the non-equilibrium condensation may occur at the region between nozzle exit and an object. The jet flow with non-equilibrium condensation may be quite different from that without condensation. Therefore, in this study, the effect of the non-equilibrium condensation of moist air on the axisymmetric under-expanded supersonic impinging jet on a vertical flat plate was investigated numerically. 展开更多
关键词 compressible flow SUPERSONIC IMPINGING non-equilibrium condensation OSCILLATION
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Superradiant Instability of D-Dimensional Reissner–Nordstr?m Black Hole Mirror System
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作者 李然 赵俊坤 张延明 《Communications in Theoretical Physics》 SCIE CAS CSCD 2015年第5期569-574,共6页
We analytically study the superradiant instability of charged massless scalar field in the background of D-dimensional Reissner-Nordstr6m (RN) black hole caused by mirror-like boundary condition. By using the asympt... We analytically study the superradiant instability of charged massless scalar field in the background of D-dimensional Reissner-Nordstr6m (RN) black hole caused by mirror-like boundary condition. By using the asymptotic matching method to solve the Klein-Gordon equation that governs the dynamics of scalar field, we have derived the expressions of complex parts of boxed quasinormal frequencies, and shown they are positive in the regime of superradiance. This indicates the charged scalar field is unstable in D-dimensional Reissner-Nordstr6m (RN) black hole surrounded by mirror. However, the numerical work to calculate the boxed quasinormal frequencies in this system is still required in the future. 展开更多
关键词 Reissner-NordstrSm black hole SUPERRADIANCE INSTABILITY
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