Consequences of the application of the streamer fluid model to the study of the sprite inception mechanism

We present the results of a streamer-fluid model used to investigate the electrodynamical coupling between the troposphere and upper atmosphere due to the penetration of lightning electric fields into the mesosphere and the lower ionosphere, generating sprites. The model solves the continuity equation for electrons and ions coupled to Poisson equation. The dominant physical response of the atmosphere is the formation of a screening-ionization wave. The wave shields the atmosphere above it from the action of the lightning field and, together with the conductivity reduction below it due to attachment, the wave amplifies the total field below it, allowing for the penetration of intense electric fields in the mesosphere as it propagates downwards into regions of higher density that compress the wave. This is the key physical mechanism for sprite inception. We evaluated the effects of the thundercloud charge geometry, lightning current waveshape, atmospheric conductivity, via different electron density profiles, and the effect of ionization, attachment and electron mobility coefficients in the electrical breakdown process, related to halo production, and sprite streamer initiation. The results showed that electrons with higher mobility are more efficient in shielding the lightning electric field before breakdown, causing delay, and they contribute to the formation of the streamer seed after breakdown, anticipating the sprite streamer inception. Similarly, a higher effective ionization rate, produced by modifications in the attachment and ionization coefficients, anticipates sprite inception. The simulations with 6 different electron density profiles, and therefore conductivities, spanning 4 orders of magnitude, showed that the altitude of breakdown and sprite initiation, as well as their time delays from the lightning discharge are directly related to atmospheric conductivity: higher conductivities produce halo and sprite inception at lower altitudes with longer delays and may hinder sprite formation. We document that variations of 30 times in the lightning current leads to sprite initiation altitudes in the range 66.0–73.5 km, with delays between 1.550 and 34.500 ms, while variations of 4 orders of magnitude in the conductivity profile lead to initiation altitudes 61.0–70.6 km, with delays in the range 3.825–9.825 ms. Consequently, we suggest that lightning characteristics dominate over atmospheric parameters in determining sprites’ initiation altitude and delay. The simulation of a −CG, with a constant current of 30 kA, did not produce a sprite seed, confirming an asymmetry in the response of the atmosphere to positive and negative lightning. This is due to the free electron drift direction that is away from the screening ionization wave, preventing the formation of the streamer seed for the great majority of −CGs. The same does not apply to halos, which depend on the occurrence of breakdown and can be produced by discharges of both polarities.     

飞机系统模拟试验中热电阻及其数字显示仪表的现场校准技术研究

在飞机系统地面模拟试验中．热电阻及其数字显示仪表在液压、飞控等试验系统中广泛使用。针对各试验系统中某些位置的热电阻及其数字显示仪表接线复杂,不便拆卸和传统计量方式的种种弊端等问题,提出了一种由现场计量炉、便携式测温仪和温度校准器等设备组成的现场校准系统。实现对热电阻及其数字显示仪表的现场整体校准,同时亦可实现对热电阻及其数字显示仪表的分部校准,避免了拆卸和安装,提高了工作效率,具有实用价值。     

机务维修系统非例行维修平台的设计研究

非例行维修是航空公司机务维修方案的重要组成部分。由于非例行维修的不确定性,需要调研航空公司的业务流程和运行特点,分析具体的设计需求,开发出有效的现代化非例行维修管理平台。运用Delphi工具及Oracle数据库开发出航空公司非例行机务维修平台,以非单生命周期数据流转为核心,建立起航空公司对于非例行维修的管理平台,并介绍实现平台功能的几项关键技术。实际情况表明平台能够对航空公司的维修管理进行有效的控制,缩短维修时间,降低维修成本。     

卫星通信设备抗直升机旋翼遮挡技术测试验证方法研究

抗旋翼遮挡技术是直升机载卫星通信设备的核心技术.根据直升机载卫星通信系统旋翼遮挡的特点,分析研究了直升机无遮挡通信时间比率与直升机航向和卫星波束入射角的关系,以此分析设计了试飞方案.发现了抗旋翼遮挡技术的重大设计缺陷,并通过试飞中的测试数据对抗旋翼遮挡算法进行了优化改进,有效实现了抗旋翼遮挡技术的有效性验证,达到直升机载卫星通信设备定型试飞的目的,为后续该类型设备的试飞奠定了扎实的理论与实践基础,具有较高的工程应用价值.     

Occurrence features of simultaneous H+- and He+-band EMIC emissions in the outer radiation belt

As an important loss mechanism of radiation belt electrons, electromagnetic ion cyclotron (EMIC) waves show up as three distinct frequency bands below the hydrogen (H⁺), helium (He⁺), and oxygen (O⁺) ion gyrofrequencies. Compared to O⁺-band EMIC waves, H⁺- and He⁺-band emissions generally occur more frequently and result in more efficient scattering removal of <～5?MeV relativistic electrons. Therefore, knowledge about the occurrence of these two bands is important for understanding the evolution of the relativistic electron population. To evaluate the occurrence pattern and wave properties of H⁺- and He⁺-band EMIC waves when they occur concurrently, we investigate 64 events of multi-band EMIC emissions identified from high quality Van Allen Probes wave data. Our quantitative results demonstrate a strong occurrence dependence of the multi-band EMIC emissions on magnetic local time (MLT) and L-shell to mainly concentrate on the dayside region of L?=?～4–6. We also find that the average magnetic field amplitude of H⁺-band waves is larger than that of He⁺-band waves only when L?<?4.5 and AE¹?<?300?nT, and He⁺-band emissions are more intense under all other conditions. In contrast to 5 events that have average H⁺-band amplitude over 2 nT, 19 events exhibit >2 nT He⁺-band amplitude, indicating that the He⁺-band waves can be more easily amplified than the H⁺-band waves under the same circumstances. For simultaneous occurrences of the two EMIC wave bands, their frequencies vary with L-shell and geomagnetic activity: the peak wave frequency of H⁺-band emissions varies between 0.25 and 0.8 f_cp with the average between 0.25 and 0.6 f_cp, while that of He⁺-band emissions varies between 0.03 and 0.23 f_cp with the average between 0.05 and 0.15 f_cp. These newly observed occurrence features of simultaneous H⁺- and He⁺-band EMIC emissions provide improved information to quantify the overall contribution of multi-band EMIC waves to the loss processes of radiation belt electrons.     

Variability of organic material in surface horizons of the hyper-arid Mars-like soils of the Atacama Desert

The objective of this work was to investigate the variability of surface organic carbon within the hyper-arid Yungay region of the Atacama Desert. The fraction of Labile Organic Carbon (LOC) in these samples varied from 2 to 73 μg per gram of soil with a bi-modal distribution with average content of 17 ± 9 μg LOC and 69 ± 3 μg LOC for “low” and “high” samples, respectively. Interestingly, there was no relation between organic levels and geomorphologic shapes. While organics are deposited and distributed in these soils via eolic processes, it is suggested that fog is the dynamic mechanism that is responsible for the variability and peaks in organic carbon throughout the area, where a “high” LOC content sample could be indicative of a biological process. It was determined that there was no significant difference between topological feature or geographical position within the hyper-arid samples and LOC. This very curious result has implications for the investigation of run-off gullies on the planet Mars as our work suggests a need for careful consideration of the expectation of increases in concentrations of organic materials associated with following aqueous altered topology.     

Towards a Unified View of Inhomogeneous Stellar Winds in Isolated Supergiant Stars and Supergiant High Mass X-Ray Binaries

Massive stars, at least \(\sim10\) times more massive than the Sun, have two key properties that make them the main drivers of evolution of star clusters, galaxies, and the Universe as a whole. On the one hand, the outer layers of massive stars are so hot that they produce most of the ionizing ultraviolet radiation of galaxies; in fact, the first massive stars helped to re-ionize the Universe after its Dark Ages. Another important property of massive stars are the strong stellar winds and outflows they produce. This mass loss, and finally the explosion of a massive star as a supernova or a gamma-ray burst, provide a significant input of mechanical and radiative energy into the interstellar space. These two properties together make massive stars one of the most important cosmic engines: they trigger the star formation and enrich the interstellar medium with heavy elements, that ultimately leads to formation of Earth-like rocky planets and the development of complex life. The study of massive star winds is thus a truly multidisciplinary field and has a wide impact on different areas of astronomy.In recent years observational and theoretical evidences have been growing that these winds are not smooth and homogeneous as previously assumed, but rather populated by dense “clumps”. The presence of these structures dramatically affects the mass loss rates derived from the study of stellar winds. Clump properties in isolated stars are nowadays inferred mostly through indirect methods (i.e., spectroscopic observations of line profiles in various wavelength regimes, and their analysis based on tailored, inhomogeneous wind models). The limited characterization of the clump physical properties (mass, size) obtained so far have led to large uncertainties in the mass loss rates from massive stars. Such uncertainties limit our understanding of the role of massive star winds in galactic and cosmic evolution.Supergiant high mass X-ray binaries (SgXBs) are among the brightest X-ray sources in the sky. A large number of them consist of a neutron star accreting from the wind of a massive companion and producing a powerful X-ray source. The characteristics of the stellar wind together with the complex interactions between the compact object and the donor star determine the observed X-ray output from all these systems. Consequently, the use of SgXBs for studies of massive stars is only possible when the physics of the stellar winds, the compact objects, and accretion mechanisms are combined together and confronted with observations.This detailed review summarises the current knowledge on the theory and observations of winds from massive stars, as well as on observations and accretion processes in wind-fed high mass X-ray binaries. The aim is to combine in the near future all available theoretical diagnostics and observational measurements to achieve a unified picture of massive star winds in isolated objects and in binary systems.     

桨尖下反对旋翼BVI噪声特性的抑制分析

基于计算流体力学(Computational fluid dynamics,CFD)方法,分析研究了新型下反桨尖对前飞状态旋翼桨/涡干扰(Blade-vortex interaction,BVI)噪声特性的影响。首先,通过求解Navier-Stokes方程获得准确的噪声声源信息,湍流模型采用一方程S-A模型。采用双时间法进行时间推进,为了提高流场的收敛速度,在伪时间方向上使用高效的隐式LU-SGS格式推进,并采用并行算法进行加速。然后,在获得的可靠声源信息基础上,采用基于FW-H方程的Farassat 1A公式求解噪声。对有试验结果的算例进行了对比计算分析,验证了本文噪声预测方法的有效性。在此基础上,针对具有典型BVI噪声特征的前飞斜下降状态,开展了不同下反角度桨尖新型旋翼噪声辐射特性的计算分析,通过噪声辐射球的对比结果表明,选择适当的下反桨尖,可以有效地降低前飞斜下降状态下旋翼BVI噪声,从而达到较好的旋翼噪声抑制效果。     

数控集成制造执行系统(MES)的构建与实施

"十五"期间,为保障高新工程实施.国家加大了对国防军工企业技术改造的投入,不少航空主机厂增加了大量高档数控机床,或对旧机床进行了数控化改造,数控机床数量越来越多,数控化率越来越高;与此同时,军工企业制造信息化总体进展良好,但发展不平衡,机床设备普遍处于单机运行管理状态,这种状况导致了数控机床的整体效率、数字化车间的综合集成效应得不到有效、充分的发挥,已成为影响国家高新T程及重点型号生产配套能力进一步提升的瓶颈.     

Detection of the quantity of kinesin and microgravity-sensitive kinesin genes in rat bone marrow stromal cells grown in a simulated microgravity environment

Kinesin and kinesin-like proteins (KLPs) constitute a superfamily of microtubule motor proteins found in all eukaryotic organisms. Members of the kinesin superfamily are known to play important roles in many fundamental cellular and developmental processes. To date, few published studies have reported on the effects of microgravity on kinesin expression. In this paper, we describe the expression pattern and microgravity-sensitive genes of kinesin in rat bone marrow stromal cells cultured in a ground-based rotating bioreactor. The quantity of kinesin under the clinorotation condition was examined by immunoblot analysis with anti-kinesin. Furthermore, the distribution of kinesin at various times during clinorotation was determined by dual immunostaining, using anti-kinesin monoclonal antibody or anti-β-tubulin monoclonal antibody. In terms of kinesin quantity, we found that the ratios of the amounts of clinorotated/stationary KLPs decreased from clinorotation day 5 to day 10, although it increased on days 2 and 3. Immunofluorescence analysis revealed that kinesin in the nucleus was the first to be affected by simulated microgravity, following the kinesin at the periphery that was affected at various times during clinorotation. Real-time RT-PCR analysis of kinesin mRNA expression was performed and led to the identification of 3 microgravity-sensitive kinesin genes: KIF9, KIFC1, and KIF21A. Our results suggest that kinesin has a distinct expression pattern, and the identification of microgravity-sensitive kinesin genes offers insight into fundamental cell biology.