Helium in the terrestrial atmosphere

After a brief historical review of the discovery of helium in the terrestrial atmosphere, the production mechanisms of the isotopes He⁴ and He³ are discussed. Although the radioactive production of He⁴ in the Earth is well understood, some uncertainty still exists for the degassing process leading to an atmospheric influx of (2.5 ±1.5) × 10⁶ atoms cm^–2 s^–1. Different production mechanisms are possible for He³ leading to an influx of (7.5±2.5) atoms cm^–2 s^–1. Observations of helium in the thermosphere show a great variability of this constituent. The different mechanisms proposed to explain the presence of the winter helium bulge are discussed. Since helium ions are present in the topside ionosphere and in the magnetosphere, ionization mechanisms are analyzed. Owing to possible variations and uncertainties in the solar UV flux, the photoionization coefficient is (8±4) × 10^–8 s^–1. Finally, the helium balance between production in the earth and loss into the interplanetary space is discussed with respect to the different processes which can play an effective role.     

The ‘Standard’ Sun Modelling and Helioseismology

The ‘standard’ solar model is based on a number of simplifying assumptions and depends on knowledge of the physical properties of matter in the Sun. Given these assumptions, the constraint that the model have the observed surface luminosity provides an estimate of the initial solar helium abundance. From helioseismic analyses further information can be obtained about the present composition, including a fairly precise measure of the envelope helium abundance and an estimate of the hydrogen profile in the radiative interior. It must be emphasized, however, that these inferences may suffer from systematic error arising from incomplete knowledge about the equation of state and opacity of the solar interior. This revised version was published online in June 2006 with corrections to the Cover Date.     

Double-zone model with diffusive mixing and the mass and helium discrepancies in OB-stars

A model for massive main sequence (MS) stars is proposed that quantitatively accounts for the mass and helium discrepancies in luminous OB stars. The radiative envelope of the model consists of two zones being mixed by rotationally induced turbulent diffusion during the star's evolution on the MS. The rate of the mixing in the outer zone is assumed to be substantially lower than that in the inner zone. Both, the mass and helium discrepancy, are shown to be due to helium enrichment in the envelope produced by turbulent diffusion. Some arguments to support this double-zone stellar model are given.Alexander von Humboldt Fellow     

预冷空气涡轮火箭发动机氦循环系统的参数特性

针对预冷空气涡轮火箭发动机(PATR)方案,建立氦循环系统数学模型,模型考虑组件结构特征、几何尺寸、工质物性等主要因素。数值计算表明:PATR的推力和比冲性能较优,模型可描述发动机氦循环热力过程,其中发动机余气系数是影响发动机推力、比冲的关键参数。提高氦循环系统最高设计压力和降低空气预冷器氦进口温度可有效降低压力损失和氦压气机功率,最高压力每增大1MPa,系统平均压力损失下降1.1%,氦压气机输入功率下降3.2%;空气预冷器氦进口温度每升高1K,系统平均压力损失上升0.086%,氦压气机输入功率升高2.3%。     

Coupling of the coronal he abundance to the solar wind

Models of the transition region — corona — solar wind system are investigated in order to find the coronal helium abundance and to study the role played by coronal helium in controlling the the solar wind proton flux. The thermal force on -particles in the transition region sets the flow of helium into the corona. The frictional coupling between -particles and protons and/or the electric polarization field determines the proton flux in the solar wind as well as the fate of the coronal helium content.     

Measurement of the Abundance of Helium-3 in the Sun and in the Local Interstellar Cloud with SWICS on Ulysses

The abundance of 3He in the present day local interstellar cloud (LIC) and in the sun has important implications for the study of galactic evolution and for estimating the production of light nuclei in the early universe. Data from the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses is used to measure the isotopic ratio of helium (3He/4He = ) both in the solar wind and the local interstellar cloud. For the solar wind, the unique high-latitude orbit of Ulysses allows us to study this ratio in the slow and highly dynamic wind in the ecliptic plane as well as the steady high-latitude wind of the polar coronal holes. The 3He+/4He+ ratio in the local cloud is derived from the isotopic ratio of pickup helium measured in the high-speed solar wind. In the LIC the ratio is found to be (2.48 _-0.62 ^+0.68 ) × 10^-4 with the 1- uncertainty resulting almost entirely from statistical error. In the solar wind, is determined with great statistical accuracy but shows systematic differences between fast and slow solar wind streams. The slow wind ratio is variable. Its weighted average value (4.08 ± 0.25) × 10-4 is, within uncertainties, in agreement with the Apollo SWC results. The high wind ratio is less variable but smaller. The average in the fast wind is (3.3 ± 0.3) × 10-4.     

Observation of the interstellar helium cone by the NOZOMI spacecraft

‘The Japanese Mars probe, NOZOMI, is staying in the interplanetary space (1–1.5 AU) until its Mars’ orbit insertion scheduled in early 2004. Every 16 months on this interplanetary orbit the spacecraft crosses around 1 AU the ‘gravitational focusing cone’ of the interstellar helium, which are penetrating into the inner heliosphere under the solar gravity. During the first crossing of the cone in the season of March–May 2000, we observed these helium particles after the solar wind pickup process with an E/q type ion detector aboard NOZOMI. We have estimated the original temperature of the interstellar helium as 11 000 K. This revised version was published online in August 2006 with corrections to the Cover Date.     

The core helium flash

The role of convection in the core helium flash is simulated by two-dimensional eddies interacting with the thermonuclear runaway. These eddies are followed by the explicit solution of the 2D conservation laws with a 2D finite difference hydrodynamics code. Thus, no phenomenological theory of convection such as the local mixing length theory is required.Our core helium flash is violent, producing a deflagration wave. This differs from the detonation wave (and subsequent disruption of the entire star) produced in previous spherically symmetric violent core helium flashes as the second dimension provides a degree of relief which allows the expansion wave to decouple itself from the burning front. Our results predict that a considerable amount of helium in the core will be burned before the horizontal branch is reached and that some envelope mass loss is likely.     

The evolution of the anomalous component of the cosmic rays during the Ulysses mission

We have studied the evolution of the anomalous cosmic ray component at ULYSSES using observations of the quiet time helium fluxes obtained with the COSPIN Low Energy Telescope during the years from launch in October 1990 to the latest data in 1994. Shown are preliminary results of measurements in the energy range from 4.0 to 19 MeV/n. Following the drop in solar activity in late 1991, the low energy cosmic ray helium flux started to increase and continue to rise until the end of 1993, signifying the appearance of the anomalous component at ULYSSES.     

Concentration Measurements in a Transient Helium-Air Mixture Utilizing an Electron Beam

In order to determine the available test time in a helium-driven shock tunnel, an interface detection system has been developed to indicate the arrival of helium driver gas at the test section. This is done by exciting the gas at the test section with a high-energy electron beam and spectroscopically analyzing the resulting fluorescence to determine ine the helium concentration. Relative values of helium and air emission intensities are calculated and compared with experimental data from both static and transient gas mixtures.     

激波与氦气泡相互作用的实验与数值研究

提出了一种在激波管中实现运动激波与球形气一气界面相互作用的研究方案。以肥皂膜作为气体交界面,高压火花为光源,采用阴影法,在马赫数M=1．2的情况下,在矩形激波管中开展了一系列的实验研究,获得了激波作用下球形氦气泡界面发展变化的相关实验结果。还通过求解二维轴对称的Euler方程,结合网格自适应策略,对实验过程进行了数值模拟。通过与实验结果的对比分析,证实了涡量的产生和分布对于界面的变形和发展有着重要意义。     

高温气冷堆核电站主氦风机驱动电机绝缘系统评定技术研究

设计了一套在0.1 MPa氦气和空气环境下测试绝缘系统电气绝缘性能的试验装置,完成了0.1 MPa气压下氦气和空气中主氦风机驱动电机绝缘系统模型的局部放电起始电压(PDIV)、起晕电压、匝间冲击、绝缘电阻和工频击穿电压对比试验。试验结果表明:在0.1 MPa气压下,绝缘系统在氦气环境下的部分绝缘性能较空气中大幅下降,氦气环境下绝缘系统的PDIV值约为空气中的50%,起晕电压值约为空气中的20%~25%, 闪络(击穿)电压约为空气中的50%。     

系统误差条件下的多运动站无源定位性能分析

 系统误差的存在可能对无源定位的性能带来较大影响。针对多运动站得到的含有系统误差的观测量信息,推导了定位误差的克拉美-罗下限(CRLB)。首先根据具体系统误差模型推导测量误差的统计信息,然后根据系统误差导致不同时刻观测量相关的特点,将非对角矩阵的误差协方差矩阵写为分块矩阵的形式,并在此基础上推导其递推计算式,最后以系统误差情况下多运动站只测角无源定位为例进行定位性能的仿真分析。仿真结果表明系统误差的存在对定位误差CRLB影响较大,在定位中需要重点考虑。     

Evolution of the Protosolar Nebula and Formation of the Giant Planets

The formation of planetary systems is intimately tied to the question of the evolution of the gas and solid material in the early nebula. Current models of evolution of circumstellar disks are reviewed here with emphasis on the so-called “alpha models” in which angular momentum is transported outward by turbulent viscosity, parameterized by an dimensionless parameter α. A simple 1D model of protoplanetary disks that includes gas and embedded particles is used to introduce key questions on planetesimal formation. This model includes the aerodynamic properties of solid ice and rock grains to calculate their migration and growth. We show that the evolution of the nebula and migration and growth of its solids proceed on timescales that are generally not much longer than the timescale necessary to fully form the star-disk system from the molecular cloud. Contrary to a widely used approach, planet formation therefore can neither be studied in a static nebula nor in a nebula evolving from an arbitrary initial condition. We propose a simple approach to both account for sedimentation from the molecular cloud onto the disk, disk evolution and migration of solids. Giant planets have key roles in the history of the forming Solar System: they formed relatively early, when a significant amount of hydrogen and helium were still present in the nebula, and have a mass that is a sizable fraction of the disk mass at any given time. Their composition is also of interest because when compared to the solar composition, their enrichment in elements other than hydrogen and helium is a witness of sorting processes that occured in the protosolar nebula. We review likely scenarios capable of explaining both the presence of central dense cores in Jupiter, Saturn, Uranus and Neptune and their global composition. This revised version was published online in August 2006 with corrections to the Cover Date.     

彩色氦气泡在风洞试验中的应用

彩色氦气泡流动显示是一极好的新技术。在风洞中应用彩色氦气泡进行流动显示已于1984年3月在哈尔滨空气动力研究所实现了,获得了丰富多采的彩色迹线,摄制了清晰的彩色录象和彩色照片。不久之后,进行了轿车、面包车、高楼、船舵、鱼鳞波表面、细长体、圆柱体、降落伞和各种飞机模型的试验。 本文描述了彩色氦气泡流动显示技术,介绍了在风洞中进行流动显示的一般装置、基本原理和应用。     

Solar wind helium isotopic composition from SWICS/ULYSSES

This is the first study of the isotopic composition of solar wind helium with the SWICS time-of flight mass spectrometer. Although the design of SWICS is not optimized to measure³He abundances precisely,⁴He/³He flux ratios can be deduced from the data. The long term ratio is 2290±200, which agrees with the results obtained with the ICI magnetic mass spectrometer on ISEE-3 and with the Apollo SWC foil experiments.The ULYSSES spacecraft follows a trajectory which is ideal for the study of different solar wind types. During one year, from mid-1992 to mid-1993, it was in a range of heliographic latitudes where a recurrent fast stream from the southern polar coronal hole was observed every solar rotation. Solar wind bulk velocities ranged from 350 km/s to 950 km/s which would, in principle allow us to identify velocity-correlated compositional variations. Our investigation of solar wind helium, however, shows an isotopic ratio which does not depend on the solar wind speed.     

氦气谐振点火器和气氧/煤油火炬点火器研究

为了实现液体推进剂火箭发动机重复多次可靠启动，研究了利用气动谐振热效应形成的高温高能点火源进行气氧／煤油等可贮存推进剂多次点火的方案。为此研制了氦气谐振点火器和气氧／煤油火炬点火器。氦气点火器在较宽的气源温度(-2℃～33℃)变化范围、较大喷嘴入口压力(1．5MPa～3．OMPa)变化范围内均具有好的谐振加热性能。气氧／煤油火炬点火器能够多次可靠地点火并生成稳定的点火火炬。由于不受谐振产生条件的限制，气氧和煤油的流量可以在较大的范围内选择，生成点火火炬的温度范围也很宽，富燃点火炬更具工程应用价值。研究结果表明氦气谐振点火器及其气氧／煤油火炬点火器具有结构简单，可靠性高，无毒无污染等优点，对于重复多次启动的液体火箭发动机有着诱人的应用前景。     

深冷组合发动机吸气模态最大状态控制规律研究

为了研究深冷组合循环发动机吸气模态最大状态控制规律,基于部件法建立了发动机热力学计算模型,依据整机共同工作条件确定了发动机非设计点计算的变量与平衡方程。根据工质间的相互影响关系,提出了以氦压气机转速和氦涡轮前温度为控制变量的双变量控制规律。在考虑发动机机械负荷、气动负荷、热负荷及压气机稳定裕度等限制的条件下,根据制定的最大状态控制规律,完成了高度特性和速度特性的计算。根据限制条件计算得到了发动机的工作包线,并指出了最大状态控制规律的区域划分。最后,将控制规律应用于工作包线内,获得了压气机转速、换算转速及工质流量等参数的分布规律。结果表明：工作包线上下边界分别取决于氦压气机喘振裕度限制和空气压气机换算转速下限,右边界限制取决于换热器1氦气出口温度上限。深冷组合循环发动机最大状态控制规律应划分为2个区域,分界线满足以下条件：空气压气机和氦压气机换算转速同时达到最大值。分界线以上空气压气机达到最大工作状态,分界线以下氦压气机达到最大工作状态。空气压气机进口参数是决定控制规律分界线的主要因素。     

氦气分析检测中不确定度评定

依据JJF1135-2005<化学分析测量不确定度评定>,对氦气分析检测中的不确定度进行了评定,分析了各不确定度分量,并通过建立气相色谱外标法测量结果不确定度的数学模型 ,计算了其测量结果的相对合成标准不确定度和扩展不确定度.     

Signature of coronal holes and streamers in the interplanetary space

The properties of different solar wind streams depend on the large scale structure of the coronal magnetic field. We present average values and distributions of bulk parameters (density, velocity, temperature, mass flux, momentum, and kinetic and thermal energy, ratio of thermal and magnetic pressure, as well as the helium abundance) as observed on board the Prognoz 7 satellite in different types of the solar wind streams. Maximum mass flux is recorded in the streams emanating from the coronal streamers while maximum thermal and kinetic energy fluxes are observed in the streams from the coronal holes. The momentum fluxes are equal in both types of streams. The maximum ratio of thermal and magnetic pressure is observed in heliospheric current sheet. The helium abundance in streams from coronal holes is higher than in streams from streamers, and its dependences on density and mass flux are different in different types of the streams. Also, the dynamics of -particle velocity and temperature relative to protons in streams from coronal holes and streamers is discussed.