太阳风离子尺度湍流与太阳风加热

太阳风源自太阳大气,在行星际空间传播过程中被持续加热,然而究竟是何种能量加热了太阳风至今未研究清楚.太阳风普遍处于湍动状态,其湍动能量被认为是加热太阳风的重要能源.然而,太阳风湍流通过何种载体、基于何种微观物理机制加热了太阳风尚不明确,这是相关研究的关键问题.将回顾人类对太阳风加热问题的研究历史,着重介绍近年来我国学者在太阳风离子尺度湍流与加热方面取得的研究进展,展望未来在太阳风加热研究中有待解决的科学问题和可能的研究方向.     

Induced Raman scattering in pulsar magnetospheres

It is shown that induced Raman scattering of electromagnetic waves in the strongly magnetized electron–positron plasma of pulsar magnetospheres may be important for wave propagation and as an effective saturation mechanism for electromagnetic instabilities. The frequencies at which strong Raman scattering occurs in the outer parts of a magnetosphere fall into the observed radio band. The typical threshold intensities for the strong Raman scattering are of the order of the observed intensities, implying that pulsar magnetospheres may be optically thick to Raman scattering of electromagnetic waves.     

Ion‐ion charge exchange and X‐rays from the winds of hot stars

Charge exchange occurs between charged ions with enough energy to overcome Coulomb repulsion, a condition satisfied for collisions at velocities like those of the winds driven from hot stars by radiation pressure. X‐ray line ratios in some hot stars are inconsistent with those expected from thermal plasmas excited by electron impact. Ion‐ion interactions including charge exchange might be responsible instead if high‐velocity collisions between ions are enabled by the presence of a magnetic field in the wind, suggesting a possible alternative mechanism to the widely accepted instability‐driven shock model. The nature of a plasma in charge‐exchange equilibrium is yet to be determined (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Stability of magnetic equilibria in radio bubbles

Current-carrying flows, in the laboratory and in astrophysical jets, can form remarkably stable magnetic structures. Decades of experience show that such flows often build equilibria that reverse field directions, evolving to a magnetohydrodynamic (MHD) Taylor state, which has remarkable stability properties. We model jets and the magnetic bubbles they build as reversed-field pinch equilibria by assuming the driver current to be stiff in the MHD sense. Taking the jet current as rigid and a fixed function of position, we prove a theorem: that the same, simple MHD stability conditions guarantee stability, even after the jet turns off. This means that magnetic structures harbouring a massive inventory of magnetic energy can persist long after the building jet current has died away. These may be the relic radio 'fossils', 'ghost bubbles' or 'magnetic balloons' found in clusters. These equilibria, which are under magnetic tension, will evolve, retaining the stability properties from that state. The remaining fossil is not a disordered ball of magnetic fields, but a stable structure under tension, able to respond to the slings and arrows of outside forces. Typically their Alfvén speeds greatly exceed the cluster sound speed, and so they can keep out hot cluster plasma, leading to X-ray ghosts. Passing shocks cannot easily destroy them, but can energize and light them up anew at radio frequencies. Bubbles can rise in the hot cluster plasma, perhaps detaching from the parent radio galaxy but stable against Rayleigh–Taylor and other modes.     

The example of effective plasma acceleration in a magnetosphere

The problem of effective transform of Poynting flux energy into the kinetic energy of relativistic plasma outflow in a magnetosphere is considered. In this article we present an example of such acceleration. In order to perform it, we use the approach of ideal axisymmetric magnetohydrodynamics (MHD). For highly magnetized plasma outflow we show that a linear growth of Lorentz factor with a cylindrical distance from the rotational axis is a general result for any field configuration in the sub-magnetosonic flow. In the far region the full magnetohydrodynamics problem for one-dimensional flow is considered. It turns out that the effective plasma outflow acceleration is possible in the paraboloidal magnetic field. It is shown that such an acceleration is due to the drift of charged particles in the crossed electric and magnetic field. The clear explanation of the absence of acceleration in the monopole magnetic field if given.      

常压室温等离子体技术诱变选育鲅鱼抗氧化肽发酵菌株

鲅鱼(Spanish mackerel)加工后的废弃物富含蛋白质,为了提高蛋白质的利用率并减少环境污染,可以采用微生物发酵的方法酶解这部分蛋白质制取抗氧化活性肽。本实验室已经筛选出一株芽孢杆菌(Bacillus subtilis)Hy-2,以其发酵水产加工废弃物得到了具有较高抗氧化性的产物。为了进一步提高产物的抗氧化性,作者以该株产蛋白酶芽孢杆菌Hy-2为出发菌,采用常压室温等离子体(ARTP)诱变的方法筛选出1株突变菌Hy-23,以鲅鱼加工后的废弃物为原料,接种该突变菌株进行发酵,得到了具有一定抗氧化活性的发酵产物,酶解物总抗氧化活性提高了12.4%。经遗传稳定性测定,该芽孢杆菌突变株在传代8次之后其遗传稳定性仍然良好。     

The impact of correlated noise on SuperWASP detection rates for transiting extrasolar planets

The evolution of the Alfvén turbulence due to three-wave interactions is discussed using kinetic theory for a collisionless, thermal plasma. There are three low-frequency modes, analogous to the three modes of compressible magnetohydrodynamics (MHD). When only Alfvén waves are considered, the known anisotropy of turbulence in incompressible MHD theory is reproduced. Inclusion of a fast mode wave leads to the separation of turbulence into two regimes: small wave numbers where three-wave processes involving a fast mode are dominant, and large wave numbers where the three Alfvén wave process is dominant. Possible application of the anisotropic Alfvén turbulence to the interstellar medium and dissipation of magnetic energy in magnetars are discussed.     

Solar Impulsive Hard X-Ray Emission and Two-Stage Electron Acceleration

Heating and acceleration of electrons in solar impulsive hard X-ray (HXR) flares are studied according to the two-stage acceleration model developed by Zhang for solar 3He-rich events. It is shown that electrostatic H-cyclotron waves can be excited at a parallel phase velocity less than about the electron thermal velocity and thus can significantly heat the electrons (up to 40 MK) through Landau resonance. The preheated electrons with velocities above a threshold are further accelerated to high energies in the flare-acceleration process. The flare-produced electron spectrum is obtained and shown to be thermal at low energies and power law at high energies. In the non-thermal energy range, the spectrum can be double power law if the spectral power index is energy dependent or related. The electron energy spectrum obtained by this study agrees quantitatively with the result derived from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) HXR observations in the flare of 2002 July 23. The total flux and energy flux of electrons accelerated in the solar flare also agree with the measurements.     

Esa Microgravity Research Activities In The Field Of Physical Sciences And Applications

During the eighties, microgravity research focussed predominantly on the investigation of fundamental phenomena, often with limited industrial support. Although this approach led to some rather impressive breakthroughs in terms of new theoretical insights and microgravity experimentation, the need for increased co-ordination and interest from industry became increasingly apparent. In this decade, a user-driven research strategy has been instigated by ESA to promote microgravity research. The objective is to coordinate ESA, national activities and industry into an overall European strategy, which will allow valuable application-oriented microgravity research to be performed aboard the International Space Station (ISS). On this basis, it is expected that scientific progress will evolve even more rapidly due to the easier planning, regular access and longer experiment-durations associated with the ISS. This paper highlights the wealth of microgravity research being co-ordinated by ESA in the field of physical sciences. A number of key areas of research under microgravity conditions are currently being explored such as alloy solidification, crystal growth,measurement of thermophysical properties, combustion mechanisms, fluid flow, cold atom physics and complex plasmas, to name but a few. The following sections will provide background information relating to the various ESA research programmes, as well as emphasising their microgravity relevance. This revised version was published online in July 2006 with corrections to the Cover Date.