In-plane elastic stability of fixed parabolic shallow arches

The nonlinear behavior of fixed parabolic shallow arches subjected to a vertical uniform load is investigated to evaluate the in-plane buckling load.The virtual work principle method is used to establish the non-linear equilibrium and buckling equations.Analytical solutions for the non-linear in-plane symmetric snap-through and antisymmetric bifurcation buckling loads are obtained.Based on the least square method,an approximation for the symmetric buckling load of fixed parabolic arch is proposed to simplif...     

Global view of Hopf bifurcations of a van der Pol oscillator with delayed state feedback

This paper presents both analytical and numerical studies on the global view of Hopf bifurcations of a van der Pol oscillator with delayed state feedback. Based on a detailed analysis of the stability switches of the trivial equilibrium of the system, the stability charts are given in a parameter space consisting of the time delay and the feedback gains. The center manifold reduction and the normal form method are used to study Hopf bifurcations with respect to the time delay. To gain an insight into the pe...     

Net-shape forming of composite packages with high thermal conductivity

The continuing miniaturization of electronic devices in microelectronics and semiconductors drives the development of new packaging materials with enhanced thermal conductivity to dissipate the heat generated in electronic packages.In recent years,several promising composite materials with high thermal conductivity have been developed successfully for high performance electronic equipment to replace the traditional Kovar and Cu/W or Cu/Mo alloys,such as SiCp/Al,SICp/Cu,diamond/Al and diamond/Cu.However,thes...     

Understanding of the influence of process parameters on the heat transfer behavior at the metal/die interface in high pressure die casting process

The current paper focuses on the influence of the process parameters on the peak values of the interfacial heat transfer coefficient(IHTC)at metal/die interface during high pressure die casting(HPDC)process.A"step shape"casting and AM50 alloy were used during the experiment.The IHTC was determined by solving the inverse thermal problem based on the measured temperature inside the die.Results show that the initial die surface temperature(IDST,TDI)has a dominant influence while the casting pressure and fast shot velocity have a secondary influence on the IHTC peak values.By curve fitting,it was found that the IHTC peak value(hmax)changes as a function of the IDST in a manner of hmax=e αTγ DI .Such relationship between the IHTC peak value and the IDST can also be found when the casting alloy is ADC12,indicating that this phenomenon is a common characteristic in the HPDC process.     

Effects of particle size on the mechanical properties of particle-reinforced Sn-Ag composite solder joint

Particulate size has significant influenced on the mechanical properties of particle-reinforced composite solder joints.In this current research,Cu or Ni reinforcement particles were mechanically added to the Sn-3.5Ag eutectic solder,and the effects of the particle size on the mechanical properties of particle-reinforced composite solder joint were systematically studied. This investigation touched on how mechanical properties of the solder joints are affected by particles size.A quantitative formula was se...     

Deep levels,transport and THz emission properties of SiGe/Si quantum-well structures

In coal mines in such countries as China and Russia,most of the coal mine methane(CMM) generated during mining is emitted to the atmosphere without any effective usage,because the methane concentration of CMM is relatively low and not allowed to be used as fuel for safety reasons.Methane is one of the greenhouse gases.Therefore,if it becomes possible to concentrate CMM to an acceptable level for use as fuel,this will greatly contribute to reduction of greenhouse gas emissions.With the aim of gaining approva...     

俄英医学同义术语的类型划分及英俄、汉俄医学词典编纂启示

同义现象是术语学界长期关注的热点问题,也是当代极具现实意义和有争议的问题。术语的同义现象是建立在表达同一个专业概念的不同术语单位基础上的一种语义关系。通过对医学各领域同义术语(主要是俄语和英语)的分析和描写,划分同义术语的类型,确定现代医学术语的特点,进而发现现代医学双语(主要是英俄、汉俄)词典中暂时还缺乏关于在术语系统功能化条件下使用某一同义术语的相关信息。因此,英俄、汉俄医学词典应对同义术语做相关的信息标注,以帮助使用者选取某一具体医学领域最适合的同义术语。     

铁路运输管理中GIS的应用

随着GIS技术的快速发展和铁路现代化的建设,GIS在铁路运输领域广泛应用。阐述了近几年来GIS在铁路运输领域的发展和应用,在列车运营监控、车站信号诊断、铁路货运营销等领域内的应用,并分析了各种GIS应用方式的特点,提出了应用的发展前景。     

有机发光二极管中多种微观机制共存的有机磁效应

为了探究有机发光二极管(OLEDs)中三重态激子参与的多种机制共同作用下磁场效应的变化规律,揭示复杂环境下OLEDs的性能变化规律,本文在具有较高三重态激子能量的磷光材料m CP中掺入单重态与三重态激子能量共振(ES≈2ET)的荧光染料Rubrene,制备了Rubrene掺杂型的OLEDs.实验发现,掺杂器件的电致发光磁场效应(MEL)表现出了复杂变化,且MEL的低场(B≤5 m T)和高场(5 m T≤B≤500 m T)部分随着掺杂浓度的改变都发生了明显的变化.这些MEL曲线可归结为掺杂体系内超精细相互作用、单重态激子裂变和三重态-三重态激子淬灭三种微观过程共同作用的结果;而不直接产生荧光的三重态激子,可以通过一些自旋混合过程,改变单重态激子的比例,从而对器件发光产生重要影响.器件的工作温度和注入电流密度对磁场效应的影响进一步证实了本研究组的观点.