Intense plasma waves at and near the solar wind termination shock

Plasma waves are a characteristic feature of shocks in plasmas, and are produced by non-thermal particle distributions that develop in the shock transition layer. The electric fields of these waves have a key role in dissipating energy in the shock and driving the particle distributions back towards thermal equilibrium. Here we report the detection of intense plasma-wave electric fields at the solar wind termination shock. The observations were obtained from the plasma-wave instrument on the Voyager 2 spacecraft. The first evidence of the approach to the shock was the detection of upstream electron plasma oscillations on 1 August 2007 at a heliocentric radial distance of 83.4 au (1 au is the Earth-Sun distance). These narrowband oscillations continued intermittently for about a month until, starting on 31 August 2007 and ending on 1 September 2007, a series of intense bursts of broadband electrostatic waves signalled a series of crossings of the termination shock at a heliocentric radial distance of 83.7 au. The spectrum of these waves is quantitatively similar to those observed at bow shocks upstream of Jupiter, Saturn, Uranus and Neptune.     

Magnetic fields at the solar wind termination shock

A transition between the supersonic solar wind and the subsonic heliosheath was observed by Voyager 1, but the expected termination shock was not seen owing to a gap in the telemetry. Here we report observations of the magnetic field structure and dynamics of the termination shock, made by Voyager 2 on 31 August-1 September 2007 at a distance of 83.7 au from the Sun (1 au is the Earth-Sun distance). A single crossing of the shock was expected, with a boundary that was stable on a timescale of several days. But the data reveal a complex, rippled, quasi-perpendicular supercritical magnetohydrodynamic shock of moderate strength undergoing reformation on a scale of a few hours. The observed structure suggests the importance of ionized interstellar atoms ('pickup protons') at the shock.     

An asymmetric solar wind termination shock

Voyager 2 crossed the solar wind termination shock at 83.7 au in the southern hemisphere, approximately 10 au closer to the Sun than found by Voyager 1 in the north. This asymmetry could indicate an asymmetric pressure from an interstellar magnetic field, from transient-induced shock motion, or from the solar wind dynamic pressure. Here we report that the intensity of 4-5 MeV protons accelerated by the shock near Voyager 2 was three times that observed concurrently by Voyager 1, indicating differences in the shock at the two locations. (Companion papers report on the plasma, magnetic field, plasma-wave and lower energy particle observations at the shock.) Voyager 2 did not find the source of anomalous cosmic rays at the shock, suggesting that the source is elsewhere on the shock or in the heliosheath. The small intensity gradient of Galactic cosmic ray helium indicates that either the gradient is further out in the heliosheath or the local interstellar Galactic cosmic ray intensity is lower than expected.     

Mediation of the solar wind termination shock by non-thermal ions

Broad regions on both sides of the solar wind termination shock are populated by high intensities of non-thermal ions and electrons. The pre-shock particles in the solar wind have been measured by the spacecraft Voyager 1 (refs 1-5) and Voyager 2 (refs 3, 6). The post-shock particles in the heliosheath have also been measured by Voyager 1 (refs 3-5). It was not clear, however, what effect these particles might have on the physics of the shock transition until Voyager 2 crossed the shock on 31 August-1 September 2007 (refs 7-9). Unlike Voyager 1, Voyager 2 is making plasma measurements. Data from the plasma and magnetic field instruments on Voyager 2 indicate that non-thermal ion distributions probably have key roles in mediating dynamical processes at the termination shock and in the heliosheath. Here we report that intensities of low-energy ions measured by Voyager 2 produce non-thermal partial ion pressures in the heliosheath that are comparable to (or exceed) both the thermal plasma pressures and the scalar magnetic field pressures. We conclude that these ions are the >0.028 MeV portion of the non-thermal ion distribution that determines the termination shock structure and the acceleration of which extracts a large fraction of bulk-flow kinetic energy from the incident solar wind.     

Cool heliosheath plasma and deceleration of the upstream solar wind at the termination shock

The solar wind blows outward from the Sun and forms a bubble of solar material in the interstellar medium. The termination shock occurs where the solar wind changes from being supersonic (with respect to the surrounding interstellar medium) to being subsonic. The shock was crossed by Voyager 1 at a heliocentric radius of 94 au (1 au is the Earth-Sun distance) in December 2004 (refs 1-3). The Voyager 2 plasma experiment observed a decrease in solar wind speed commencing on about 9 June 2007, which culminated in several crossings of the termination shock between 30 August and 1 September 2007 (refs 4-7). Since then, Voyager 2 has remained in the heliosheath, the region of shocked solar wind. Here we report observations of plasma at and near the termination shock and in the heliosheath. The heliosphere is asymmetric, pushed inward in the Voyager 2 direction relative to the Voyager 1 direction. The termination shock is a weak, quasi-perpendicular shock that heats the thermal plasma very little. An unexpected finding is that the flow is still supersonic with respect to the thermal ions downstream of the termination shock. Most of the solar wind energy is transferred to the pickup ions or other energetic particles both upstream of and at the termination shock.     

载能带电粒子在物质中电子阻止本领研究进展

综述了最近几年关于带电粒子在物质中电子阻止本领研究的新进展。分别考虑了固体中电子之间的关联－交换作用、靶原子内壳层电子分布、重离子的有效电荷数、分子离子产生的Ｖｉｃｉａｇｅ效应、表面等离子激发等因素对电子阻止本领的影响，同时也讨论了带电粒子在二维材料及有限温度靶中的电子阻止本领。     

Solar release time of solar energetic particles and associated acceleration source in corona

Solar energetic particles （SEPs） are accelerated in corona at an early phase of solar energetic particle events （SEPE）. The acceleration mechanism of SEPs in corona can only be inferred from an analysis of multi-band observational data, as the observation of SEPs is usually made around 1AU. In this context, people have investigated spectrums, charge state, solar release time （SRT）, and multi-band data of SEPEs, in an attempt to judge the acceleration mechanism of SEPs. The SRT computation of SEPs is an important and commonly used approach to study the acceleration mechanism of SEPs in corona. This paper reviews some important findings concerning the SRT computation of SEPs, and analyzes different merits of each approach for such calculation, based on a range of SEPE case studies. This paper also analyzes and discusses both possible and actual acceleration mechanisms of a number of SEPEs, by calculating the SRT of the SEPEs. Finally, the paper summarizes the possible problems in studying an acceleration mechanism of SEPEs inferred from the SRT of SEP.     

添加TiC对纳米Si3N4陶瓷热震行为的影响

采用热压烧结法制备含不同质量分数TiC的纳米Si3N4陶瓷材料,研究TiC的添加对其力学性能与热震行为的影响.研究发现适量TiC颗粒的添加提高了纳米Si3N4陶瓷的力学性能,最佳添加量为10%;强度和韧性的提高以及裂纹偏转的存在使纳米Si3N4陶瓷的热震临界温差和热震循环疲劳性能得到改善.     

燃煤电厂周边气溶胶单颗粒的微观形貌和化学组分

采集燃煤电厂上风向和下风向PM2.5样品,使用带能谱的透射电镜观察单颗粒的特征。根据颗粒的微观形貌、化学组分及电子束作用下的稳定性,将颗粒物分成9种类型:富Si、富Ca、富S、富K、富Fe、飞灰、有机、烟尘和其他颗粒.研究表明,燃煤电厂排放的球形富Fe颗粒和飞灰颗粒使下风向气溶胶中球形颗粒的数量增加;下风向气溶胶中富S颗粒和富Ca颗粒的相对丰度高于上风向,这可能与电厂控制SO2排放使用石灰石作脱硫剂有关;电厂下风向具有核壳结构颗粒的数量明显多于上风向,其原因是来自燃煤电厂或上风向的颗粒在合适的条件下(如温度高、相对湿度大、SO2与NOx浓度高等),易与其他物质发生化学反应形成具有核壳结构的复杂颗粒。     

SQL Server 2005 下T-SQL增强的研究和应用

SQL Server 2005对T-SQL进行了大量的改进和增强,以帮助程序员更有效地操纵数据,文章围绕具体实例介绍了这些增强功能的原理和应用,分析了其应用场景,比较了其性能.     

SQL Server 2005下T-SQL增强功能的研究和应用

SQL Server2005对T—SQL进行了大量的改进和增强,以帮助程序员更有效地操纵数据,文章围绕具体实例介绍了这些增强功能的原理和应用,分析了其应用场景,比较了其性能。     

空泡溃灭冲击波对流场携带颗粒的作用

讨论了无限大小域中考察液体压缩性影响下空泡溃灭冲击波对固体颗粒的作用，求得了固体颗粒所获得的最大速度，当满足一定条件时，固体颗粒运动速度值之高足以打坏现有水工建筑物所用的混凝土，引起固壁的大面积剥落，形成空蚀，冲击和磨蚀的恶性循环。     

Dust-cloud structures behind a shock wave moving over a deposited layer of fine particles

The present paper investigates dispersed-phase flow structures of a dust cloud induced by a normal shock wave moving at a constant speed over a flat surface deposited with fine particles. In the shock-fitted coordinates, the general equations of dusty-gas boundary layer flows are formulated within the framework of a multi-fluid model and parametric numerical studies of the carrier- and dispersed-phase flow fields are performed. The problem associated with crossing particle trajectories and the formation of local particle accumulation regions are solved by using the full Lagrangian method for the dispersed phase. The basic features of the near-wall two-phase flow under consideration including the role of Saffman force in the particle entrainment and the development of discontinuities or singularities in the particle density profiles are discussed. The effects associated with account of the non-uniformity of particle size and the finiteness of the particle Knudsen numbers are studied in detail.     

科技创新推动河南经济高质量发展研究

科技创新是驱动经济高质量发展的核心引擎.作为国内第五大经济体,河南省经济高质量发展是国家经济高质量发展的重要内容.科技创新推动河南经济高质量发展呈现基础不厚、起点不高、动力不强、活力不足、借力不够等实践特征,建议从完善创新投入体系、强化科技创新载体、优化科技创新机制、深化开放创新、完善创新生态系统等方面提升河南自主创新能力,增强科技创新对经济高质量发展的驱动作用.     

Climate-mediated energetic constraints on the distribution of hibernating mammals

To predict the consequences of human-induced global climate change, we need to understand how climate is linked to biogeography. Energetic constraints are commonly invoked to explain animal distributions, and physiological parameters are known to vary along distributional gradients. But the causal nature of the links between climate and animal biogeography remain largely obscure. Here we develop a bioenergetic model that predicts the feasibility of mammalian hibernation under different climatic conditions. As an example, we use the well-quantified hibernation energetics of the little brown bat (Myotis lucifugus) to parameterize the model. Our model predicts pronounced effects of ambient temperature on total winter energy requirements, and a relatively narrow combination of hibernaculum temperatures and winter lengths permitting successful hibernation. Microhabitat and northern distribution limits of M. lucifugus are consistent with model predictions, suggesting that the thermal dependence of hibernation energetics constrains the biogeography of this species. Integrating projections of climate change into our model predicts a pronounced northward range expansion of hibernating bats within the next 80 years. Bioenergetics can provide the simple link between climate and biogeography needed to predict the consequences of climate change.     

灯具产品中使用端头标记的重要性

本文介绍了标记在传统灯具和新型LED灯具产品的使用,阐述了灯具端头标记的正确应用,避免用户在使用照明灯具时遭遇触电的危险,为广大消费者选择优质产品的提供了参考。     

PCI总线传输的终止方式探析

探讨了PCI总线传输的终止方式。PCI总线的主设备和目标设备都可以终止PCI传输。主设备和目标设备在终止一次传输的同时还以信号的电平组合告知主设备其不同的终止状态。主设备启动的终止有正常终止和主设备失败终止;目标设备启动的终止有重试、解除连接和目标设备失败。     

废弃含能材料的资源化利用

废弃含能材料主要来源于退役武器和超过储存期的弹药,是特殊性质的危险品,传统的处理方法是焚烧法,没有物尽其用,且造成环境污染。几种资源化利用的途径是：再生用于军事、转变为化工原料或产品、作为一般或特殊能源、作为主要组分制成民用炸药。研究结果表明,将其制成民用炸药,能充分利用含能材料特有的燃烧和爆炸性质,具有处理过程安全、处理成本低、操作简单、无三废排放及产品性能好的优点,利于实现工业化,是大规模处理和利用废弃含能材料的较好途径。     

TiO_2粒子对膜吸收过程中近膜壁面处溶质传质行为的影响

采用纯CO2-去离子水为实验体系,在板式膜器中研究了孔隙率对膜吸收过程传质效果的影响,并考察了吸收剂搅拌与否对传质性能的影响。结果表明,吸收剂静止时,孔隙率对传质效果影响很小。当吸收剂处于搅拌状态时,传质得到强化,但由于膜壁面处溶质浓度分布情况不同使得传质效果随孔隙率的增加而增大。为改变近膜壁面处溶质浓度的分布情况,利用固体粒子将动量引入液相边界层内,使膜壁面处溶质浓度分布趋于均匀。固相粒子的加入减小了不同孔隙率膜之间的传质效果差异,同时还强化了传质,传质效果提高40%以上,且孔隙率越小强化效果越大。此外,随固含率的增加,强化效果增强,固含率的继续增大,强化效果的增强变得平缓。随着搅拌转速的增加,强化效果减弱。     

关于非线性规划数值算法停止准则的讨论

本文评述并讨论了几种非线性规划数值算法的停止准则 ,并在此基础上提出了一种较好的停止准则 .