专业音响配置中应注意的几个问题

要使专业音响达到优良效果，在配置时应按照建筑声学的要求，计算出音箱电功率，保证音箱与功率放大器匹配，同时要考虑声场带来的影响，做到准确定位，充分发挥出设备的最大功能。     

Modeling Multifractality of the Solar Wind

The question of multifractality is of great importance because it allows us to investigate interplanetary hydromagnetic turbulence. The multifractal spectrum has been investigated with Voyager (magnetic field) data in the outer heliosphere and with Helios (plasma) data in the inner heliosphere. We use the Grassberger and Procaccia method that allows calculation of the generalized dimensions of the solar wind attractor in the phase space directly from the cleaned experimental signal. We analyze time series of plasma parameters of the low-speed streams of the solar wind measured in situ by Helios in the inner heliosphere. The resulting spectrum of dimensions shows a multifractal structure of the solar wind attractor. In order to quantify that multifractality, we use a simple analytical model of the dynamical system. Namely, we consider the generalized self-similar baker’s map with two parameters describing uniform compression and natural invariant measure on the attractor of the system. The action of this map exhibits stretching and folding properties leading to sensitive dependence on initial conditions. The obtained solar wind singularity spectrum is consistent with that for the multifractal measure on the weighted baker’s map.     

Shear Flow Instabilities in Low-Beta Space Plasmas

We study instabilities driven by a sheared plasma flow in the low-frequency domain. Two unstable branches are found: the ion-sound mode and the kinetic Alfvén mode. Both instabilities are aperiodic. The ion-sound instability does not depend on the plasma β (gas/magnetic pressure ratio) and has a maximum growth rate of about 0.1 of the velocity gradient dV ₀/dx. On the other hand, the kinetic Alfvén instability is stronger for larger β and dominates the ion-sound instability for β > 0.05. Possible applications for space plasmas are shortly discussed.     

Complexity,Forced and/or Self-Organized Criticality,and Topological Phase Transitions in Space Plasmas

The first definitive observation that provided convincing evidence indicating certain turbulent space plasma processes are in states of ‘complexity’ was the discovery of the apparent power-law probability distribution of solar flare intensities. Recent statistical studies of complexity in space plasmas came from the AE index, UVI auroral imagery, and in-situ measurements related to the dynamics of the plasma sheet in the Earth's magnetotail and the auroral zone. In this review, we describe a theory of dynamical ‘complexity’ for space plasma systems far from equilibrium. We demonstrate that the sporadic and localized interactions of magnetic coherent structures are the origin of ‘complexity’ in space plasmas. Such interactions generate the anomalous diffusion, transport, acceleration, and evolution of the macroscopic states of the overall dynamical systems. Several illustrative examples are considered. These include: the dynamical multi- and cross-scale interactions of the macro-and kinetic coherent structures in a sheared magnetic field geometry, the preferential acceleration of the bursty bulk flows in the plasma sheet, and the onset of ‘fluctuation induced nonlinear instabilities’ that can lead to magnetic reconfigurations. The technique of dynamical renormalization group is introduced and applied to the study of two-dimensional intermittent MHD fluctuations and an analogous modified forest-fire model exhibiting forced and/or self-organized criticality [FSOC] and other types of topological phase transitions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of q-nonextensive hot electrons on bifurcations of nonlinear and supernonlinear ion-acoustic periodic waves

Nonlinear and supernonlinear ion-acoustic periodic waves are investigated in a three-component unmagnetized plasma which consists of mobile fluid cold ions, Maxwellian cold electrons and q-nonextensive hot electrons employing phase plane analysis. Using the traveling wave transformation, the plasma system is reduced to a planar autonomous dynamical system. Utilizing phase plane analysis of planar dynamical systems, all possible phase portraits including nonlinear homoclinic orbit, nonlinear periodic orbit, supernonlinear homoclinic orbit and supernonlinear periodic orbit are presented depending on physical parameters $q,\alpha ,\sigma$ and V. Using numerical simulations, nonlinear and supernonlinear ion-acoustic periodic waves are shown for different conditions. It is found that the nonextensive parameter q plays a crucial role in the bifurcations of nonlinear and supernonlinear ion-acoustic periodic waves. Our study may be applicable to understand the nonlinear and supernonlinear periodic features in auroral plasma.     

面向深空探测的电磁帆推进技术研究进展

电磁帆是一类利用太阳风驱动的无工质或少工质新型推进技术,在需要推力器长时间工作的深空探测任务中具有非常广阔的应用前景。首先介绍了电磁帆的基本概念和主要分类,其次分别介绍了电帆、纯磁帆和磁等离子体帆三类推进方式的系统组成和工作原理,重点介绍了各自的研究现状,并梳理出了相关关键技术,同时介绍了等离子体磁罩技术。最后对电磁帆推进技术研究进展进行了总结,为国内开展此方面研究提供了研究方向和发展思路。     

微等离子体转化二氧化碳发射光谱诊断

火星大气层的主要成分为二氧化碳，如果能够利用低温等离子体方法高效分解二氧化碳，使其转化为氧气和一氧化碳加以利用，可以大幅降低航天员生命保障相关载荷长途运输的成本，进一步提高生命保障能力。低温等离子体放电过程中会产生大量活性组分，可以在数百度温度下实现二氧化碳的高效解离，是具有很大潜力的二氧化碳解离与转化方式。设计了一种尺度在亚毫米级、功率输入为数瓦的直流微槽等离子体反应器，可以在较低气体温度下实现二氧化碳分解。测量了反应器电流、功率等放电参数，采用发射光谱确定了体系中激发态组分，分析了激发态粒子谱线强度随输入电压、稀释气体比例等反应器工作参数变化，利用氮气分子振转谱带测量了等离子体放电区振动温度和气体温度。研究表明，添加氩、氦、氮气均可以增强二氧化碳的分解，添加氦气可以促进二氧化碳的电离过程。稀释气体激发态因具有高能量，可以通过潘宁解离通道增强二氧化碳分解。氦组分激发态的能量高于二氧化碳电离能，可以促进二氧化碳的电离反应。微等离子体内存在强烈的振动 平动非平衡现象：振动温度约为4400~4800K，而气体温度仅为450 ~600K，表明可以通过合理的放电和结构设计，定向将能量注入到振动态，从而进一步促进二氧化碳的振动解离。     

燃烧室头部激励的等离子体强化燃烧特性实验研究

等离子体助燃是一种新型的强化燃烧技术，近年来受到国内外学者的广泛关注。本文开创性地研制了基于旋转滑动弧等离子体的强化燃烧头部，建立了某型航空发动机三头部燃烧室实验件的等离子体助燃实验平台，验证了该等离子体强化燃烧技术应用于型号发动机燃烧室的可行性。实验研究等离子体助燃在不同余气系数和不同输入电压条件下对平均出口温度、燃烧效率、温度分布系数以及熄火边界的影响。实验结果表明，与正常燃烧相比，施加等离子体助燃后的燃烧效率有明显的提高，在输入电压为U0=240V，余气系数为 α=0.8时，等离子体助燃的燃烧效率提高3.24%。实施等离子体助燃后，燃烧室出口温度分布场分布得到明显的改善，在富油工况α=0.8，出口温度分布系数减少39.8%。等离子体助燃输入电压越高熄火边界扩展程度越明显，相比于正常工况条件下，等离子体助燃U0=240V的熄火边界扩宽了7.34%。     

Identification of seismic activity sources on the subsatellite track by ionospheric plasma disturbances detected with the Sich-2 onboard probes

Using a cylindrical Langmuir probe and the authors’ proprietary two-channel pressure transducer, ionospheric plasma parameter distributions along the orbit of the Sich-2 satellite (Ukraine, 2011–2012) were measured. This paper is concerned with identifying the space–time location of ionospheric plasma disturbance sources, including the epicenters of actual earthquakes (before or during the satellite flyover) and incipient earthquakes on the subsatellite track, from the measured distributions of the electron density and temperature and the neutral particle temperature along the satellite orbit. To do this, the measured ionospheric plasma parameter distributions are connected to the coordinates on the subsatellite track.It is shown that local disturbances in the electron density and temperature and neutral particle temperature distributions in the satellite orbit in the ionosphere may serve as indicators of seismic activity on the subsatellite track. The epicenters of incipient earthquakes may be set off from other plasma parameter disturbance sources associated with seismic activity using information provided by special monitoring and survey centers that monitor the current seismic situation.     

Plasma transport process in the equatorial/low-latitude ionosphere

The behaviour of the equatorial/low-latitude ionosphere and the transport processes during magnetic disturbed and quiet periods of a high solar activity year, 2014, in the American sector are investigated. Parameters used include vertical drift (Vz), transport term (W), NmF2, hmF2 and scale-height (H). The F2 plasma variations followed the diurnal local solar pattern, being higher at daytime. The sunset maximum and sunrise minimum peaks of hmF2 were directly opposite to the scale height (H) pattern. The plasma distribution was basically controlled by combined actions of the electrodynamic convection/thermospheric composition, which is geomagnetic activity dependent. The annual, semi-annual and winter-anomalies of the F2 parameters were higher at the dip equator in comparison with the low-latitude. The Vz pre-reversal peak magnitude coincided with hmF2 peak and the effects are more pronounced during geomagnetic disturbed conditions. The transport term pattern was similar to that of the scale height and it is suggested as a proxy parameter for quantifying low-latitude plasma irregularities and distribution of thermospheric composition.