The Grain Impact Analyser and Dust Accumulator (GIADA) Experiment for the Rosetta Mission: Design, Performances and First Results

The Grain Impact Analyser and Dust Accumulator (GIADA) onboard the ROSETTA mission to comet 67P/Churyumov–Gerasimenko is devoted to study the cometary dust environment. Thanks to the rendezvous configuration of the mission, GIADA will be plunged in the dust environment of the coma and will be able to explore dust flux evolution and grain dynamic properties with position and time. This will represent a unique opportunity to perform measurements on key parameters that no ground-based observation or fly-by mission is able to obtain and that no tail or coma model elaborated so far has been able to properly simulate. The coma and nucleus properties shall be, then, clarified with consequent improvement of models describing inner and outer coma evolution, but also of models about nucleus emission during different phases of its evolution. GIADA shall be capable to measure mass/size of single particles larger than about 15 μm together with momentum in the range 6.5 × 10⁻¹⁰ ÷ 4.0 × 10⁻⁴ kg m s⁻¹ for velocities up to about 300 m s⁻¹. For micron/submicron particles the cumulative mass shall be detected with sensitivity 10⁻¹⁰ g. These performances are suitable to provide a statistically relevant set of data about dust physical and dynamic properties in the dust environment expected for the target comet 67P/Churyumov–Gerasimenko. Pre-flight measurements and post-launch checkouts demonstrate that GIADA is behaving as expected according to the design specifications. The International GIADA Consortium (I, E, UK, F, D, USA).     

Self-similar solutions to stellar winds with cosmic rays

A two-fluid model is used to study the time evolution of stellar winds including the dynamical effect of cosmic rays. Neglecting the diffusion of cosmic rays, we seek self-similar solutions to spherically symmetric winds with a termination shock. The velocity upstream of the shock is taken to be zero. Physical solutions are those that can connect the shock to the star with the velocity approaching zero at the star. Two parameters govern the behaviour of the solutions, namely, the ratio of the upstream sound speed to the shock speed (in an inertial frame) and the gravitation potential of the central star. In some parameter regimes, no physical solution is possible.     

地磁暴前地面宇宙线强度变化Morlet小波特征分析

用Morlet小波变换对Oulu台站和Apatity台站(主要是Apatity台站)1998-2002年间宇宙线静日和地磁暴前的地面宇宙线强度变化特征进行分析，得到：在宇宙线静日期间普遍存在准24h周期变化特征，并且在当地时间0200，1400左右分别出现最小值和最大值；对12个例子的分析可以看到地面宇宙线强度在地磁暴之前l-2天均出现了不同于宇宙线静日期间变化特征，或有小尺度周期出现，或周期变化完全消失，或有异常24h周期变化，这种变化特征在一定程度上可作为地磁预报的先兆特征之一。     

On a non-primordial origin of the cosmic background radiation and pregalactic density fluctuations

Dusty pregalactic Population III objects may provide a mechanism for an effective thermalization of the star radiation. They may generate the observed microwave background and so the high cosmic photon entropy. Assuming a tepid universe a smaller primordial entropy contribution results in reasonable mass scales and amplification factors of pregalactic density fluctuations.     

First results from the LUCID-Timepix spacecraft payload onboard the TechDemoSat-1 satellite in Low Earth Orbit

The Langton Ultimate Cosmic ray Intensity Detector (LUCID) is a payload onboard the satellite TechDemoSat-1, used to study the radiation environment in Low Earth Orbit ($～$635?km). LUCID operated from 2014 to 2017, collecting over 2.1 million frames of radiation data from its five Timepix detectors on board. LUCID is one of the first uses of the Timepix detector technology in open space, with the data providing useful insight into the performance of this technology in new environments. It provides high-sensitivity imaging measurements of the mixed radiation field, with a wide dynamic range in terms of spectral response, particle type and direction. The data has been analysed using computing resources provided by GridPP, with a new machine learning algorithm that uses the Tensorflow framework. This algorithm provides a new approach to processing Medipix data, using a training set of human labelled tracks, providing greater particle classification accuracy than other algorithms. For managing the LUCID data, we have developed an online platform called Timepix Analysis Platform at School (TAPAS). This provides a swift and simple way for users to analyse data that they collect using Timepix detectors from both LUCID and other experiments. We also present some possible future uses of the LUCID data and Medipix detectors in space.     

Atmospheric pressure variations at extratropical latitudes associated with Forbush decreases of galactic cosmic rays

Changes of troposphere pressure associated with short-time variations of galactic cosmic rays (GCRs) taking place in the Northern hemisphere’s cold months (October–March) were analyzed for the period 1980–2006, NCEP/NCAR reanalysis data being used. Noticeable pressure variations during Forbush decreases of GCRs were revealed at extratropical latitudes of both hemispheres. The maxima of pressure increase were observed on the 3rd–4th days after the event onsets over Northern Europe and the European part of Russia in the Northern hemisphere, as well as on the 4th–5th days over the eastern part of the South Atlantic opposite Queen Maud Land and over the d’Urville Sea in the Southern Ocean. According to the weather chart analysis, the observed pressure growth, as a rule, results from the weakening of cyclones and intensification of anticyclone development in these areas. The presented results suggest that cosmic ray variations may influence the evolution of extratropical baric systems and play an important role in solar-terrestrial relationships.     

微尘沉积形貌对冲击气膜冷却结构换热特性影响的数值研究

带有微尘的空气进入航空发动机,极易在涡轮叶片内冷通道发生沉积。为探究微尘沉积形貌对涡轮叶片内冷通道换热特性的影响,选取冲击气膜冷却结构,基于微尘沉积实验结果,构造微尘沉积形貌,由锥状突起和环状突起组成,通过数值模拟获得不同射流雷诺数下冲击靶面努塞尔数Nu。研究结果表明,冲击靶面微尘沉积层的出现,将大幅降低浸润面积平均努塞尔数Nuwetted,而对映射面积平均努塞尔数Nuavg影响较小;冲击驻点周围的高换热区范围减少;相邻冲击孔中点附近的高换热区努塞尔数Nu增大;此外,射流雷诺数的增大整体上提高了冲击靶面的换热强度。由于锥状突起和环状突起的扰动作用, 壁面附近回流涡增多, 使得冲击靶面大部分区域温度边界层厚度增加,因此换热性能降低。     

宇宙噪声的电离层闪烁与电离层不规则结构的结构参数

利用宇宙噪声是均匀的。各向同性的背景电磁辐射的假设,对电子密度涨落空间分布波数谱为负幂律函数的电离层不规则结构,用射线光学方法导出了闪烁功率谱的表示式。与射电星和轨道人造卫星信标的电离层闪烁相比,减少了因相对运动弓队的变量。用数值计算方法研究了电离层不规则结构的结构参量L_y、l_y、p、η对功率谱的影响。与实测资料比较,发现电离层吸收事件期间且Riometer记录的闪烁资料中,60%以上相应的不规则结构有L_y>103,η>η₀(0.2<η₀<0.5).      

天基微小空间碎片探测研究

随着空间碎片数量的不断增多,天基微小空间碎片探测已经成为一个热点．首先介绍了空间碎片在低地球轨道上的分布情况以及它对于航天器的危害,然后介绍了国外微小碎片探测器的基本情况,并在这些探测结果的基础上提出了一个探测器方案．这种探测器的传感器采用了新型的压电材料聚偏二氟乙稀(PVDF),使用了飞行时间法(TOF)准确测定空间碎片的飞行速度,以及快脉冲分析系统分析碎片的质量．     

铝颗粒云燃烧研究进展

为探究铝颗粒云燃烧特性,把握其研究进展,并为后续研究工作提供参考,本文首先简述了铝颗粒点火、燃烧过程,总结了铝颗粒燃烧机理;其次,综述了铝颗粒云燃烧的实验、理论和模拟研究进展,从不同维度分析了影响颗粒云火焰速度的关键参数,并提出颗粒云燃烧的研究方向,包括提升颗粒云燃烧实验颗粒分散均匀性与表征精度、降低火焰传播速度等实验结果散差、改善颗粒云燃烧理论预测模型精度及构建实用的颗粒云燃烧模拟CFD模型。