NF-3风洞神经网络自适应稳风速控制系统研制

介绍西北工业大学NF-3大型低速直流式翼型风洞改进后的稳风速控制系统的结构、控制原理和性能特点.针对低速直流风洞风速控制系统建模困难,易受外界干扰影响,且自身参数时变不确定,控制难度大的特点,新系统采用了多线程、数字式数据采集方式,带死区控制的PSD神经网络自适应控制算法.通过在NF-3风洞三元试验段和二元试验段的实际应用,与正在使用的模糊控制系统相比较,新系统的适应性和鲁棒性更强,调试时间大为缩短,风速控制精度在风速大于10m/s时从国军标的合格指标0.3%提高到先进指标0.1%,稳定时间减少了10%左右,人机交互也更加友好.     

Pioneer and Voyager observations of large-scale spatial and temporal variations in the solar wind

The Pioneer 10, Pioneer 11, and Voyager 2 spacecraft were launched in 1972, 1974, and 1977, respectively. While these three spacecraft are all at compartively low heliographic latitudes compared with Ulysses, their observation span almost two solar cycles, a range of heliocentric distances from 1 to 57 AU, and provide a unique insight into the long-term variability of the global structure of the solar wind. We examine the spatial and temporal variation of average solar wind parameters and fluxes. Our obsevations suggest that the global structure of the outer heliosphere during the declining phase of the solar cycle at heliographic latitudes up to 17.5°N was charaterized by two competing phenomena: 1) a large-scale increase of solar wind density, temperature, mass flux, dynamic pressure, kinetic energy flux, and thermal enery flux with heliographic latitude, similar to the large-scale latitudinal gradient of velocity seen in IPS observations, 2) a small-scale decrease in velocity and temperature, and increase in density near the heliospheric current sheet, which is associated with a band of low speed, low temperature, and high density solar wind similar to that observed in the inner heliosphere.     

Hard Limiter Performance as a Polarity Detector for Extremely Polluted Signals

A hard limiter is a simple, yet highly efficient, RF signal sensor for VLF and LF navigation receivers. The observation reliability is used as the single quality criterion for the hard limiter if applied as a singlebit analog-to-digital converter (ADC). The effects of noise (Gaussian and atmospheric), nonsynchronous and synchronous interference, and dc offset on the observation reliability are described extensively. The single parameter determination Pobs is adequate for characterizing the polarity detector. This facilitates rank ordering of influences disturbing the signal and is a useful tool in optimizing digital tracking loops. The ?built-in? noise-censoring properties of the hard limiter in the presence of atmospheric noise are excellent. Therefore, three different atmospheric noise models are used in the determination of the observation reliability Pobs. Some ways for coping with other disturbances that potentially threaten the good performance of the hard limiter are suggested.     

Comparison of ≳40 keV Electron Events at High and Low Heliolatitudes: Ulysses/HI-SCALE and ACE/EPAM

We have performed a joint survey of anisotropic ≳40 keV electron events from August 1997 to September 2000 using the matched detectors on the Ulysses (ULS)/HI-SCALE and the ACE/EPAM instruments. A computer algorithm selected events with strong, statistically significant pitch-angle anisotropies. Electron pitch-angle distributions at ACE (∼1 AU) are often ‘beams’ that are strongly collimated along the local interplanetary magnetic field (IMF). These flare-associated impulsive injections can display rapid rise times (∼15 min) and slower decays, or more irregular intensity histories. At ULS, the electron intensities are lower and the time histories smoother, but strong anisotropies are still observable, indicating direct, nearly field-aligned propagation outward from the Sun. We focus on four event periods, selected from the survey, during times when the angle between the footpoints of the IMF lines intersecting ACE and ULS is small. These events span three full years and cover a wide range of distances and heliographic latitudes. We found one reasonably good association between impulsive electron events at ACE and ULS, and two events with small field-aligned gradients. This revised version was published online in August 2006 with corrections to the Cover Date.     

Reconnection on open field lines ahead of coronal mass ejections

Plasma and magnetic field signatures from 29 November 1990 indicate that the Ulysses spacecraft passed through a series of interplanetary structures that were most likely formed by magnetic reconnection on open field lines ahead of a coronal mass ejection (CME). This reconnection changed the magnetic topology of the upstream region by converting normal open interplanetary magnetic field into a pair of regions: one magnetically disconnected from the Sun and the other, a tongue, connected back to the Sun at both ends. This process provides a new method for producing both heat flux dropouts and counterstreaming suprathermal electron signatures in interplanetary space. In this paper we expand upon the 29 November case study and argue that reconnection ahead of CMEs should be less common at high heliolatitudes.     

空间高阶差分近似对三维ADI-FDTD数值色散的影响

研究采用空间高阶差分近似的三维交替方向隐式时域有限差分法(ADI-FDTD,Alternating-Direction Implicit Finite-Difference Time-Domain)数值色散问题,首先推导了采用空间高阶差分近似的数值色散迭代公式,分别对最小相速方向和最大相速方向进行二阶、四阶、六阶、十阶空间差分数值色散误差的数值计算和比较,并分析数值色散对空间差分阶数的依赖关系,最后发现在均匀网格中采用四阶空间差分能得到较好的效果.     

Investigation of natural and artificial stimulation of the ionospheric Alfvén resonator at high latitude

A brief review is provided of recent progress in understanding the ionospheric Alfvén resonator (IAR) at high latitude. Firstly, naturally occurring resonances of the IAR as detected by pulsation magnetometers in the auroral zone at Sodankylä and in the polar cap at Barentsburg are considered. The characteristics of the IAR in the two regions are broadly similar, although the effects of solar illumination are less clear at the higher latitudes. Secondly we review recent attempts to stimulate the IAR through high-power radio frequency experiments both in the auroral zone at Tromsø with the European Incoherent SCATter (EISCAT) heater, and within the polar cap at Longyearbyen with the Space Plasma Exploration by Active Radar (SPEAR) facility. In the auroral zone at, Tromsø the stimulated IAR has been observed by ground-based magnetometers, and through electron acceleration observed on the FAST spacecraft. At SPEAR in the polar cap, the stimulated IAR has been investigated, with ground magnetometers, with the first results indicative of a positive detection.     

Harnessing functional food strategies for the health challenges of space travel—Fermented soy for astronaut nutrition

Astronauts face numerous health challenges during long-duration space missions, including diminished immunity, bone loss and increased risk of radiation-induced carcinogenesis. Changes in the intestinal flora of astronauts may contribute to these problems. Soy-based fermented food products could provide a nutritional strategy to help alleviate these challenges by incorporating beneficial lactic acid bacteria, while reaping the benefits of soy isoflavones. We carried out strain selection for the development of soy ferments, selecting strains of lactic acid bacteria showing the most effective growth and fermentation ability in soy milk (Streptococcus thermophilus ST5, Bifidobacterium longum R0175 and Lactobacillus helveticus R0052). Immunomodulatory bioactivity of selected ferments was assessed using an in vitro challenge system with human intestinal epithelial and macrophage cell lines, and selected ferments show the ability to down-regulate production of the pro-inflammatory cytokine interleukin-8 following challenge with tumour necrosis factor-alpha. The impact of fermentation on vitamin B1 and B6 levels and on isoflavone biotransformation to agluconic forms was also assessed, with strain variation-dependent biotransformation ability detected. Overall this suggests that probiotic bacteria can be successfully utilized to develop soy-based fermented products targeted against health problems associated with long-term space travel.     

Fifty Years of Cosmic Radiation Data

Cosmic radiation has been measured by a variety of techniques since 1933. This paper presents the evolution of data acquisition, processing, and availability of cosmic radiation data from the early years to the present time. Information on the worldwide network of neutron monitor stations and the availability of these cosmic radiation records is included. This revised version was published online in August 2006 with corrections to the Cover Date.