清煤机运料螺杆的性能和仿真磨损试验分析

为研究清煤机集料装置的运输效率,以某型号清煤机的运料螺杆作为研究对象,利用能量法构建了颗粒和叶片作用的力学模型,得到了受力和转速的数学关系。将螺杆参数赋予三维模型,以Archard磨损理论和离散元素法为基础,利用Edem建立螺杆煤料耦合模型。通过控制变量法对螺杆的运输能力进行分析,研究了不同粒径的煤以及不同的转速对螺杆的的磨损深度的影响。结果表明,在转速控制方面,提高转速能够提升煤的运输效率,但是过高的转速将导致颗粒沿径向飞出,而转速在20 r/min～65 r/min内变化时,螺杆磨损深度是呈现先降低后升高的趋势,若在35 r/min～50 r/min内增大转速,对效率提升效果最为显著,同时螺杆所受扭矩相对较小,综上螺杆转速的最佳区间在35 r/min～50 r/min。此外,相比于小颗粒,运送大颗粒煤块时螺杆磨损较为严重,因此在实际应用中,大块煤炭的运输应在螺杆低速下进行。基于上述结论,以最小驱动转矩为目标建立优化数学模型,得到了清煤机螺杆的最优结构和动力参数,并通过仿真试验验证了优化过程的正确性。为改善清煤机运输效率、降低设备能耗、延长设备寿命提供了理论参考,对螺旋输送机的参数优化提供了研究思路。     

Preparation and characterization of a new long afterglow phosphor CaSnO<Subscript>3</Subscript>: Yb<Superscript>3+</Superscript>

A new phosphor CaSnO₃: Yb³⁺ was synthesized by a traditional solid-state reaction and the luminescent properties were investigated. The phosphors are well crystallized at 1200?°C. The excitation and the emission spectra show the characteristic broad of the Sn²⁺ ion and the X-ray photoelectron spectroscopy demonstrate the existence of Sn²⁺ ions caused by the doping of Yb³⁺ ions. The CaSnO₃: Yb³⁺ phosphor showed a typical afterglow behavior when the UV source was switched off. Thermal simulated luminescence study indicated that the persistent afterglow of CaSnO₃: Yb³⁺ phosphor was generated by the suitable electron or hole traps which were resulted from doping the calcium stannate host with rare-earth ions (Yb³⁺).     

Extraordinary high-temperature mechanical properties in binder-free nanopolycrystalline WC ceramic

From the perspective of high-temperature applications,materials with excellent high-temperature me-chanical properties are always desirable.The present work dem...     

An overview on GNSS carrier-phase time transfer research

Global navigation satellite system(GNSS) carrier phase observations are two orders of higher accuracy than pseudo-range observations, and they are less affected by multipath besides. As a result, the time transfer accuracy can reach 0.1 ns, and the frequency transfer stability can reach 1×10~(-15) with carrier phase(CP) method, therefore CP method is considered the most accurate and promising time transfer technology. The focus of this paper is to present a comprehensive summary of CP method,with specific attention directed toward day-boundary clock jump, ambiguity resolution(AR), multi-system time transfer and real-time time transfer. Day-boundary clock jump is essentially caused by pseudo-range noise. Several approaches were proposed to solve the problem, such as continuously processing strategy, sliding batch and bidirectional filtering methods which were compared in this study. Additionally, researches on AR in CP method were introduced. Many scholars attempted to fix the single-difference ambiguities to improve the time transfer result, however, owing to the uncalibrated phase delay(UPD) was not considered, the current studies on AR in CP method were still immature. Moreover, because four GNSS systems could be used for time-transfer currently, which was helpful to increase the accuracy and reliability, the researches on multi-system time transfer were reviewed. What's more, real-time time transfer attracted more attention nowadays, the preliminary research results were presented.     

超高对比度是如何炼成的你的

在LCD领域中,发展得最快的其实不是液晶显示器屏幕的大小,而是显示器对比度。回顾一年多以前,某款拥有2000：1的动态对比度的产品一出现就被赋予了“机皇”的称号。如今,这样的对比度只能算是入门级别,动辄上万的产品比比皆是,而最近上市的三星T220G的对比度更是达到了40000：1!