Statistical modelling of radio wave propagation under sporadic E-Layer influence

A technique of modelling the one-hop radio wave propagation at middle latitudes in the presence of sporadic E-Layer is presented. The technique is focused on the performance of the long-term forecast of the maximum usable frequency range and on the increase of the radio communication reliability. Examples of calculation for medium-distance paths are shown.     

Propagation of plasma bubbles observed in Brazil from GPS and airglow data

Equatorial spread-F is a common occurrence in the equatorial ionosphere that is associated with large variations in plasma density that often cause scintillation and interference in communication signals. These events are known to result from Rayleigh–Taylor instability, but the day-to-day variability of their occurrence is not well understood. The triggering mechanism of plasma depletions is still a matter of debate, but may be linked to gravity waves that under favorable conditions propagate to the middle atmosphere. Understanding the triggering of ESF was the focus of the SpreadFEx campaign near Brasilia, Brazil in 2005. The campaign provided co-located airglow and GPS observations to study the onset of plasma depletions and their evolution as they traversed the region. Comparisons between the 630.0 nm airglow data and GPS data demonstrate the ability of the compact dual frequency GPS array to detect the plasma bubbles and retrieve reliable propagation characteristics of the depletions. In this case study, a plasma depletion was detected and moved over the array at velocities of 85–110 m/s, slowing as it moved towards the east. Correlation of consecutive airglow images gives consistent estimates of the eastward drift over the same time period. Mapping the airglow data to the GPS line-of-sight geometry allows direct comparison and reveals a resolvable westward tilt of the plasma depletion that may be due to vertical shear. The uniqueness of this study is the ability to resolve locally the characteristics of the plasma depletion without relying on assumptions about the mapping of the depletion along magnetic field lines to large latitudinal distances. It presents new information for understanding ESF development and the development of depletions strong enough to produce scintillation.     

On the importance of total electron content enhancements during the extreme solar minimum

Observations of ionospheric vertical total electron content (vTEC) from European ground-based Global Navigation Satellite Systems (GNSS) receivers during the period January 2008–January 2010 are used to investigate, for the first time, vTEC sensitivity to weak geomagnetic disturbances under extreme solar minimum conditions. This study shows a significant number of events for the period in question, all of which exhibited some form of exceptionally large values of vTEC during small-magnitude geomagnetic disturbances. To illustrate our point on the importance of vTEC enhancements during the extreme solar minimum and its relevance for the current GNSS and future Galileo applications, we present in this paper the results associated with two significant events that both occurred in equinoctial months. The 10–12 October 2009 event of anomalous TEC enhancement at two distant mid-latitude locations HERS (0.3 E; 50.9 N) and NICO (33.4 E, 35.1 N) is discussed in the context of strong vTEC variations during the well established ionospheric storm on 11 October 2008. We conclude with a short summary of the new findings and their consequences on ionospheric monitoring and modelling for operational communication and navigation systems.     

离子束加工中工件吸收热功率分析与建模研究

利用束流修正理论和蒙特卡罗模拟法对离子束加工中某一工艺参数下工件吸收的功率进行理论建模,然后采用测温实验对理论模型进行验证.设计实验时,利用有限元仿真确定了一种合理的轰击靶材铜,简化了实验并且方便了计算.     

Equatorial total electron content (TEC) at low and high solar activity

Total electron content (TEC) derived from ionosonde data recorded at the station of Korhogo (Lat = 9.33°N, Long = 5.43°W, Dip = 0.67°S) are compared to the International Reference Ionosphere (IRI) model predicted TEC for high (1999) and low (1994) solar activity conditions. The results show that the model represents the diurnal variation of the TEC as well as a solar activity and seasonal dependence. This variation is closer to that of the ionosonde-inferred TEC at high solar activity. However, at low solar activity the IRI overestimates the ionosonde-inferred TEC. The relative deviation ΔTEC is more prominent in the equinoctial seasons during nighttime hours where it is as high as 70%. At daytime hours, the relative deviation is estimated to 0–30%.     

Regolith effects in planetary X-ray fluorescence spectroscopy: Laboratory studies at 1.7–6.4 keV

Laboratory measurements are presented to study the effects of the physical properties of regolith on planetary soft X-ray fluorescence spectroscopy. Two laboratory setups are used to independently measure these regolith effects using lunar regolith analog samples with three different particle-size ranges. Discussion is given on the data analysis. Some of the data may be valid only for qualitative conclusions. Analytical modelling is used to separate the effects expected for a plane-parallel and homogeneous medium from those of measured regolith analogs. The surface roughness and porosity of the regolith are observed to induce an enhancement of the higher-energy part of the spectrum as a function of the incidence angle. The enhancement is larger for rougher surfaces. A brief discussion is given on the relevance of this study for future planetary missions carrying soft X-ray spectrometers.     

A study on the quintic nonlinear beam vibrations using asymptotic approximate approaches

This paper intends to promote the application of modern analytical approaches to the governing equation of transversely vibrating quintic nonlinear beams. Four new studied methods are Stiffness analytical approximation method, Homotopy Perturbation Method with an Auxiliary Term, Max–Min Approach (MMA) and Iteration Perturbation Method (IPM). The powerful analytical approaches are used to obtain the nonlinear frequency–amplitude relationship for dynamic behavior of vibrating beams with quintic nonlinearity. It is demonstrated that the first terms in series expansions of all methods are sufficient to obtain a highly accurate solution. Finally, a numerical example is conducted to verify the integrity of the asymptotic methods.     

复合材料桨叶振动特性分析的一种新方法

 本文研究了复合材料桨叶振动特性的分析方法。基于连续介质力学理论,提出了一个新的等参曲梁单元,详细推导了梁上任意一点的形状函数,讨论了复杂翼型剖面的积分技术。算例表明,本文的计算结果与实验结果非常吻合。     

The Effect of Composite Flexures on Aeroelastic Stability of a Hingeless Rotor Blade

The effects of ply orientation angle of composite flexures on stability of hingeless rotor blade system are studied.The composite hingeless rotor blade system is simplified as a hub,a flap flexure and a lag flexure.pitch bearing and main blade.The kinematics formulations are inferred by employing the moderate deflection beam theory.The shear deformation and warping related to torsion are considered.The quasi-steady strip theory with dynamic inflow effects is applied to obtain the aerodynamic loads acting on the blade.Based on these.the set of finite element formulations of a hingeless rotor blade system is worked out.The numerical results show that the ply angle of the composite flexures has great effects on the aeroelastic stability of rotor blade.     

EBPVD法制备NiCrAlY/ZrO2-8Y2O3微层复合板的拉伸力学性能研究

采用电子束物理气相沉积(EBPVD)工艺制备了NiCrAlY／ZrO2—8Y2O3微层复合板，测试了该材料在不同温度下的拉伸力学性能，初步探讨了拉伸强度与延伸率随温度变化而变化的可能机理。结果表明：该材料的屈服极限、强度极限和最大延伸率均随温度的升高而降低，在室温时它是一种脆性材料而在高温时则是延性良好的塑性材料。