关于地磁与空间微物理场及其应用系统研究的思考

本文从地磁对地球科学研究及防灾减灾、资源利用与国民经济建设的影响与需求出发,简要介绍了地磁学、地磁测量仪器与传感器以及地磁在导航、空间天气、大气科学、日地关系等相关学科中应用的研究现状,提出了传感器与基础材料、地磁测量理论与技术、地磁和空间微物理场与地球系统关系、地磁理论在相关领域的研究设想,以及地磁和空间微物理场多要素一体化探测系统与公共信息共享平台建设及应用系统开发的设想,提出了推动地磁科学研究及产品与应用系统开发的几点建议,展示了地磁学研究的发展趋势与应用前景。

地球与空间微物理场研究及其应用系统构建

本文从地球资源利用、自然灾害应对等全球性科学问题的角度阐明了构建公共的地球与空间微物理场探测共享系统、建立地磁定位导航等应用系统以及它们在气象、水文、海洋、地震、生态、环境、医学、工业、农业、交通等相关领域中应用的重要意义。并通过相关领域国内外研究进展和相关科学研究与社会经济发展需求分析,提出了研究设想;预测了地磁研究对我国国民经济建设可能带来的巨大影响和未来发展趋势;最后,提出了积极推进地磁应用的几点建议。

雷暴云中起电活动对动力和微物理过程的影响

本文通过改变三维强风暴动力—电耦合数值模式中电场参量的引入条件,将电场带入积云运动方程及水凝物下落末速中,模拟比较了有无电场影响下模拟云的主要差异。在考虑电场的作用下,由于初期电活动并不剧烈,降水强度与云内风速变化较小;随着云中起电活动的增强,考虑电场影响的模拟云内上升、下沉风速均有所增加,对应时段的降水强度有明显起伏,但累计液态与固态降水量增加微弱;同时,闪电数目增多,闪电发生得更早,持续的时间更长,电场的影响是不可忽视的。模拟发现:雷暴成熟时期,由于电场力的作用,雹粒子瞬时落速变化的极值均超过10 m s^-1,霰粒子瞬时落速变化极值也超过了7 m s^-1。但强电场的区域较小,粒子下落时经过强电场区域的时间较短,所以落速极值变化不大,相比之下电场力对半径较小粒子的下落末速的瞬时改变更显著。电场通过对粒子下落速度的影响,改变了水凝物粒子主要源项的生成率,增加雨滴、冰晶粒子的生成率,减小霰、雹粒子的生成率,调整了三相水凝物粒子的时空分布,使云中水汽总量增加9%,释放潜热增加7%,为云体的进一步发展提供了内能。

Production of super-high strength aluminum alloy billets by low frequency electromagnetic casting

The effects of low frequency electromagnetic field on the macro-physical fields in the semi-continuous casting process of aluminum alloys and the microstructure and crack in the billets were studied and analyzed by the numerical and experimental methods.Comparison of the results for the macro-physical fields in the low frequency electromagnetic casting（LFEC） process with the conventional DC casting process indicates the following characters due to the application of electromagnetic field：an entirely changed direction and remarkably increased velocity of melt flow;a uniform distribution and a decreased gradient of temperature;elevated isothermal lines;a reduced sump depth;decreased stress and plastic deformation.Further,the microstructure of the billets is refined remarkably and the crack in the billets is eliminated in LFEC process because of modification of the macro-physical fields induced by the application of low frequency electromagnetic field.

Micro-FAST中升温速率和烧结温度对零件致密化的影响

采用Gleeble-1500D热模拟机对316L不锈钢粉末进行烧结,制备出尺寸为Φ1.0 mm×1.0 mm的微型零件,并研究了升温速率和烧结温度对微型零件微观组织及性能的影响。结果表明:随着升温速率和烧结温度的提高,烧结试样体系的孔隙数量减少,试样的相对密度增加;在升温速率为50℃/s、烧结温度为900℃时,得到了近全致密的试样,且烧结温度低于传统烧结方法的烧结温度;试样最大轴向尺寸变化出现在快速升温阶段,说明在多物理场活化烧结微成形中升温速率对致密化的贡献比烧结温度更大。

Carburization of ferrochromium metals in chromium ore fines containing coal during voluminal reduction by microwave heating

Chromium ore fines containing coal (COFCC) can be rapidly heated by microwave to conduct the voluminal reduction, which lays a foundation of getting sponge ferrochromium powders with a lower content of C. Under the conditions of COFCC with n(O)-n(C) (molar ratio) as 1.00-0.84 and n(SiO2)-n(CaO) as 1.00-0.39, the samples were heated by 10 kW microwave power to reach the given temperatures and held for different times respectively. The results show that the low-C-Cr ferrochromium metal phase in the reduced materials forms before the high-C-Cr ferrochromium metal phase does. With increasing temperature the C content of ferrochromium metals is in a positive correlation with the content of Cr. The C content of ferrochromium metal in reduced materials is 0-10.07% with an average value of 4.68%. With the increase of holding time the Cr content in ferrochromium metals is in a negative correlation with the content of C, while the content of Fe changes in the contrary way. In the microwave field the kinetic conditions of carburization are closely related with the temperature of microwave heating, holding time and carbon fitting ratio.

Generation of Superpositions of Coherent Interaction States Along a Straight Line via Raman Interaction

We present an alternative scheme for preparing the superpositions of coherent states along a straight line of a cavity field using degenerate atom-cavity field Raman interaction. In the scheme, a collection of A-type three-level atoms is orderly sent through the cavity to interact with the cavity field adjusted by a microwave source connected to it, followed by state-selective measurements. In this way, we can prepare the superpositions of several coherent states along a straight line with arbitrary weighting factors for the cavity field. In the scheme, the coherence of the atom-cavity system may be maintained and the second microwave field is unnecessary, which is prior to the previous scheme.

Multiphysics Simulation of a Novel Concept of MEMS-based Solid Propellant Thruster for Space Propulsion

This work analyzes a novel MEMS-based architecture of submillimeter size thruster for the propulsion of small spacecrafts,addressing its preliminary characterization of performance.The architecture of microthruster comprises a setup of miniaturized channels surrounding the solid-propellant reservoir filled up with a high-energetic polymer.These channels guide the hot gases from the combustion region towards the nozzle entrance located at the opposite side of the thruster.Numerical simulations of the transient response of the combustion gases and wafer heating in thruster firings have been conducted with FLUENT under a multiphysics modelling that fully couples the gas and solid parts involved.The approach includes the gas-wafer and gas-polymer thermal exchange,burnback of the polymer with a simplified non-reacting gas pyrolysis model at its front,and a slip-model inside the nozzle portion to incorporate the effect of gas-surface and rarefaction onto the gas expansion.Besides,accurate characterization of thruster operation requires the inclusion of the receding front of the polymer and heat transfer in the moving gas-solid interfaces.The study stresses the improvement attained in thermal management by the inclusion of lateral micro-channels in the device.In particular,the temperature maps reveal the significant dependence of the thermal loss on the instantaneous surface of the reservoir wall exposed to the heat flux of hot gases.Specifically,the simulations stress the benefit of implementing such a pattern of micro-channels connecting the exit of the combustion reservoir with the nozzle.The results prove that hot gases flowing along the micro-channels exert a sealing action upon the heat flux at the reservoir wall and partly mitigate the overall thermal loss at the inner-wall vicinity during the burnback.The analysis shows that propellant decomposition rate is accelerated due to surface preheating and it suggests that a delay of the flame extinction into the reservoir is possible.The simulated operation of the thruster concept shows encouraging performance.