On the Lyman α and O VI Line Profiles in Streamers and Coronal Holes

The profiles of the Lyα line at 1215.6 Å and of the O VI doublet at 1031.9 Å and 1037.6 Å in the extended solar corona have been analyzed vs. latitude and radial direction, performing observations with the Ultraviolet Coronagraph Spectrometer (UVCS) on board the ESA-NASA solar satellite SOHO (Solar and Heliospheric Observatory). The results show that these lines behave differently with latitude: the H I Ly α line has larger full width at half maximum (FWHM) values in the streamer region and narrower values towards the pole, while the FWHM of O VI lines has a minimum at the center of the streamer and slightly increases towards the polar regions. We briefly discuss the impact of the results on coronal heating theories.     

Constraints on Coronal Outflow Velocities Derived from UVCS Doppler Dimming Measurements and in-Situ Charge State Data

We constrain coronal outflow velocity solutions, resolved along the line-of-sight, by using Doppler dimming models of H I Lyman alpha and O VI 1032/1037 Å emissivities obtained with data from the Ultraviolet Coronagraph Spectrometer (UVCS) on SOHO. The local emissivities, from heliocentric heights of 1.5 to 3.0 solar radii, were determined from 3-D reconstructions of line-of-sight intensities obtained during the first Whole Sun Month Campaign (10 August to 8 September 1996). The models use electron densities derived from polarized brightness measurements made with the visible light coronagraphs on UVCS and LASCO, supplemented with data from Mark III at NCAR/MLSO. Electron temperature profiles are derived from 'freezing-in' temperatures obtained from an analysis of charge state data from SWICS/Ulysses. The work concentrates on neutral hydrogen outflow velocities which depend on modeling the absolute coronal H I Lyα emissivities. We use an iterative method to determine the neutral hydrogen outflow velocity with consistent values for the electron temperatures derived from a freezing-in model.     

Ion Temperatures as Observed in a Solar Coronal Hole

From the widths of the extreme ultraviolet (EUV) lines measured by the SUMER instrument on SOHO, it was found previously (Tu et al. 1998) that the average temperature of Ne⁺⁷, at heights (relative to h₀) above the southern solar limb from 17″ to 64″, ranges between 1.3 and 5 × 10⁶ K and of Ne⁺⁶ between 1 and 4 × 10⁶ K. For mass-per-charge numbers greater than 4 the temperatures of the ions increase slightly with increasing mass-per-charge, while the thermal speed reveals no clear trend. We present a new data set with exposure times much longer than the ones in the previous study. The results obtained from line width analysis of Fe XII (1242 Å), Mg X (1249 Å), Mg VIII (772 Å) Ne VIII (770 Å), and Si VIII (1445 Å) support our previous study. In this case, the trend of increasing temperature begins at a mass-per-charge number of 3. A qualitative explanation based on ion-cyclotron-resonance heating within linear kinetic theory is suggested.     

UVCS Observations of Velocity Shear at Streamer Boundaries in the Corona

Space Science Reviews - Measurements of the intensities of the O?vi 1032and 1037&;nbsp;Å spectral lines in the southern solar hemisphere, from 1.5 to 5&;nbsp;R s, were made with...     

Warm and Hot Gas in the Local ISM

I present a short review of the physical properties and relationships between warm partially ionized and hot and highly ionized gas in the local interstellar-medium (ISM). The majority of the measurements reviewed have been obtained through ultraviolet absorption spectroscopy recorded towards stellar targets located within ～150 pc of the Sun. Many questions still remain to be answered concerning the location, temperature, density and source of ionization of both of these phases of the diffuse interstellar gas. In particular, we focus on absorption observations of the ions of C IV λ 1550 Å and Si IV λ 1394 Å and discuss if highly ionized gas (as traced by the O VI λ 1032 Å ion) has in fact actually been detected within the Local Cavity.     

UVCS/SOHO Observations of H I Lyman Alpha Line Profiles in Coronal Holes at Heliocentric Heights Above 3.0 R⊙

The Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO) has been used to measure spectral line profiles for H I Lyα in the south polar coronal hole at projected heliocentric heights from 3.5 to 6.0 R_⊙ during 1998 January 5–11. Observations from 1.5 to 2.5 R_⊙ were made for comparison. The H I Lyα profile is the only one observable with UVCS above 3.5 R_⊙ in coronal holes. Within this region the outflowing coronal plasma becomes nearly collisionless and the ionization balance is believed to become frozen. In this paper, the 1/e half widths of the coronal velocity distributions are provided for the observed heights. The velocity distributions include all motions contributing to the velocities along the line of sight (LOS). The observations have been corrected for instrumental effects and interplanetary H I Lyα. The half widths were found to increase with projected heliographic height from 1.5 to 2.5 R_⊙ and decrease with height from 3.5 to 5 R_⊙. This revised version was published online in June 2006 with corrections to the Cover Date.     

Comparison of Polar and Equatorial Coronal Holes Observed by UVCS/SOHO: Geometry and Physical Properties

We analyzed UVCS/SOHO data and compared the H I Lyα (121.6 nm) and O VI (103.2 nm, 103.7 nm) emission in the polar and equatorial coronal holes. We found that the emission lines have similar characteristics in these two types of coronal holes. Both types show evidence for superradially diverging boundaries. The latitudinal distribution of the O VI line ratio may indicate that the equatorial coronal hole has O⁺⁵ outflow velocities lower than in the polar coronal holes. This revised version was published online in June 2006 with corrections to the Cover Date.     

The Primordial Helium-4 Abundance from Observations of a Large Sample of Blue Compact Dwarf Galaxies

We use a sample of 45 low-metallicity H II regions in blue compact dwarf (BCD) galaxies to determine the primordial helium abundance YP with a precision better than 5%. We have carefully investigated the physical effects which may make the He I line intensities deviate from their recombination values such as collisional and fluorescent enhancements, underlying He I stellar absorption and absorption by Galactic interstellar Na I. By extrapolating the Y vs. O/H and Y vs. N/H linear regressions to O/H = N/H = 0, we obtain YP = 0.244±0.002 and 0.245±0.001, respectively, higher than previous determinations (YP = 0.230 - 0.234). Part of the difference comes from the fact that previous investigators have not taken into account underlying He I stellar absorption, especially in the NW component of the BCD I Zw 18 which, because of its extremely low metallicity plays a key role in the determination of YP. We derive a slope dY/dZ = 2.3±1.0, considerably smaller than those derived before. With this smaller slope and taking into account the errors, chemical evolution models with an outflow of well-mixed material can be built for star-forming dwarf galaxies which satisfy all the observational constraints. Our YP gives _bh ₅₀ ² = 0.058±0.007,f consistent with the lower limit set by dynamical measurements and X-ray observations of clusters of galaxies. It is also consistent, within the framework of standard big bang nucleosynthesis theory, with measurements of primordial 7Li in galactic halo stars and with the D/H abundance measured in absorption systems toward quasars by Burles and Tytler (1997).     

Solar EUV and UV Emission Line Observations Above a Polar Coronal Hole

The roll manoeuvre of SOHO on September 3, 1997 provided the opportunity to study the northern coronal hole with SUMER slits in east-west orientation, so that polar plumes and inter-plume lanes could be observed simultaneously. A preliminary analysis of the observations shows that lines emitted by ions with the lowest formation temperatures (with the exceptions of Ne⁷⁺ and Ar⁷⁺) have the largest ratios of plume to lane radiances at heights between 35 000 km and 70 000 km above the photosphere. All lines have narrower widths inside plumes than outside. Electron densities have been deduced in plumes and lanes from Si VIII and Mg VIII line radiance ratios. The Mg IX pair was used to determine the corresponding electron temperatures. Neon (with a high first-ionization potential) is found to be less abundant relative to magnesium (with low FIP) in a plume compared to an inter-plume lane, but the variation is smaller than previously determined Ne/Mg abundance ratios in a plume relative to the photosphere. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ca对Mg-5Al-8Zn-xCa镁合金显微组织与力学性能的影响

采用重力铸造法制备了Mg-5Al-8Zn-x Ca(x=0,1.75,2.0,2.25,2.5,2.75,3.0,wt%)合金。使用XRD、OM和SEM等研究了Ca含量对合金组织与力学性能的影响。结果表明:铸态Mg-5Al-8Zn-x Ca合金主要由α-Mg基体、β-Mg17Al12相、Mg32(Al,Zn)49相及MgZn2相和Al2Ca相组成。当Ca含量从1.75wt%增加到2.75wt%时,基体晶粒显著细化,β-Mg17Al12相由粗大的连续网状转变为细小的断续网状分布于晶界上,层片状Al2Ca相也显著细化,此时合金的拉伸强度达到最大值138 MPa,较未加Ca时提高了27.8%;Ca含量继续增加至3.0wt%,晶粒又发生粗化,合金拉伸强度发生下降;拉伸断裂形式均为准解理脆性断裂。     

镁基水反应金属燃料与水反应模型及数值分析

为研究宽广温度范围内镁基水金属燃料/水反应特性,在总结国内外研究成果的基础上,建立了包含镁/水和碳/水两个主要反应的镁基水反应金属燃料/水反应模型,其中镁/水反应在不同温度段分别采用动力学和扩散分段控制,镁/水扩散燃烧模型考虑部分氧化镁在镁液滴表面凝聚;碳/水反应为反应动力学控制,反应动力学模型依据阿仑尼乌斯公式。采用数值分析方法,研究了水燃比和镁含量对燃料/水和镁/水反应特性的影响规律。研究结果表明:燃料/水反应特性的计算结果与实验值相符;在保证一定燃料自持燃烧温度的基础上,提高镁含量,选择合适的水燃比,有利于提高燃料/水的反应特性,促进燃料/水反应快速、充分的进行。     

Spectroscopic Measurement of Coronal Compositions

Although the elemental composition in all parts of the solar photosphere appears to be the same this is clearly not the case with the solar upper atmosphere (SUA). Spectroscopic studies show that in the corona elemental composition along solar equatorial regions is usually different from polar regions; composition in quiet Sun regions is often different from coronal hole and active region compositions and the transition region composition is frequently different from the coronal composition along the same line of sight. In the following two issues are discussed. The first involves abundance ratios between the high-FIP O and Ne and the low-FIP Mg and Fe that are important for meaningful comparisons between photospheric and SUA compositions and the second involves a review of composition and time variability of SUA plasmas at heights of 1.0≤h≤1.5R _⊙.     

涡轮叶栅叶尖间隙流实验研究(英文)

This article describes the effects of some factors on the tip clearance flow in axial linear turbine cascades. The measurements of the total pressure loss coefficient are made at the cascade outlets by using a five-hole probe at exit Mach numbers of 0.10, 0.14 and 0.19. At each exit Mach number, experiments are performed at the tip clearance heights of 1.0%, 1.5%, 2.0%, 2.5% and 3.0% of the blade height. The effects of the non-uniform tip clearance height of each blade in the pitchwise direction are also studied. The results show that at a given tip clearance height, generally, total pressure loss rises with exit Mach numbers proportionally. At a fixed exit Mach number, the total pressure loss augments nearly proportionally as the tip clearance height increases. The increased tip clearance heights in the tip regions of two adjacent blades are to be blame for the larger clearance loss of the center blade. Compared to the effects of the tip clearance height, the effects of the exit Mach number and the pitchwise variation of the tip clearance height on the cascade total pressure loss are so less significant to be omitted.     

Rare Atoms,Molecules and Radicals in the Coma of P/Halley

We have searched for rare molecules and radicals in the coma of P/Halley using the ion data obtained by IMS-Giotto. Whereas our established methods were used in the ionosphere, a new model was developed for the interpretation of the ion data in the outer coma. Ne/H₂O < 1.5 × 10^-3 was determined in the coma of the comet. Upper limits for the production of Na were derived from the very low abundance of Na⁺. Methyl cyanide and (probably) ethyl cyanide were identified with abundances of CH₃CN/H₂O = (1.4 ± .6) × 10^-3 and C₂H₅CN/H₂O = (2.8 ± 1.6) × 10^-4. These results and upper limits for other N-bearing species confirm that nitrogen is depleted in the Halley material. C₄H was identified and a point source strength of C₄H/H₂O = (2.3 ± .8) × 10^-3 was derived. Our upper limit for C₃H is lower than the abundance of C₄H. This is in agreement with the enhanced abundances of C_nH species with even numbers of C-atoms found in interstellar molecular clouds, suggesting that the C₄H in Halley was synthesized under molecular cloud conditions. Thus, C₄H and other organics with unpaired electrons may turn out to be indicators for a molecular cloud origin of cometary constituents. This revised version was published online in June 2006 with corrections to the Cover Date.     

快速凝固Al－Li－Mg－Cu－Zr合金粉末除气过程中的表面反应

研究了未除气及３５０℃／２ｈ,４５０℃／２ｈ,５００℃／２ｈ除气快速凝固（ＲＳ）Ａｌ－Ｌｉ－Ｍｇ－Ｃｕ－Ｚｒ合金粉末表面结构及氧化层厚度和组成,探讨了除气过程中粉末表面的化学反应。结果表明,通常不含Ｌｉ的铝合金粉末除气工艺对ＲＳＡｌ－Ｌｉ合金的效果不明显。     

The Genesis Solar Wind Concentrator: Flight and Post-Flight Conditions and Modeling of Instrumental Fractionation

The Genesis mission Solar Wind Concentrator was built to enhance fluences of solar wind by an average of 20x over the 2.3 years that the mission exposed substrates to the solar wind. The Concentrator targets survived the hard landing upon return to Earth and were used to determine the isotopic composition of solar-wind—and hence solar—oxygen and nitrogen. Here we report on the flight operation of the instrument and on simulations of its performance. Concentration and fractionation patterns obtained from simulations are given for He, Li, N, O, Ne, Mg, Si, S, and Ar in SiC targets, and are compared with measured concentrations and isotope ratios for the noble gases. Carbon is also modeled for a Si target. Predicted differences in instrumental fractionation between elements are discussed. Additionally, as the Concentrator was designed only for ions ≤22 AMU, implications of analyzing elements as heavy as argon are discussed. Post-flight simulations of instrumental fractionation as a function of radial position on the targets incorporate solar-wind velocity and angular distributions measured in flight, and predict fractionation patterns for various elements and isotopes of interest. A tighter angular distribution, mostly due to better spacecraft spin stability than assumed in pre-flight modeling, results in a steeper isotopic fractionation gradient between the center and the perimeter of the targets. Using the distribution of solar-wind velocities encountered during flight, which are higher than those used in pre-flight modeling, results in elemental abundance patterns slightly less peaked at the center. Mean fractionations trend with atomic mass, with differences relative to the measured isotopes of neon of +4.1±0.9 ‰/amu for Li, between ?0.4 and +2.8 ‰/amu for C, +1.9±0.7‰/amu for N, +1.3±0.4 ‰/amu for O, ?7.5±0.4 ‰/amu for Mg, ?8.9±0.6 ‰/amu for Si, and ?22.0±0.7 ‰/amu for S (uncertainties reflect Monte Carlo statistics). The slopes of the fractionation trends depend to first order only on the relative differential mass ratio, Δm/m. This article and a companion paper (Reisenfeld et al. 2012, this issue) provide post-flight information necessary for the analysis of the Genesis solar wind samples, and thus serve to complement the Space Science Review volume, The Genesis Mission (v. 105, 2003).     

主流攻角对双射流孔气膜冷却特性的影响

应用压力敏感漆技术,在平板上测量了不同主流攻角(i=-30°,-20°,-10°,0°,10°,20°,30°)下双射流孔的气膜冷却效率,并利用计算流体动力学(CFD)计算得到的流场对气膜冷却效率的规律进行了解析。所研究的双射流孔结构的孔间无量纲横向距离为0.5,孔间无量纲流向距离为3;射流与主流密度比为1.0,吹风比分别为0.5、1.0、1.5、2.0。结果表明小的主流攻角(i=-10°,0°,10°)下,流场中存在反肾型涡对或挤压作用,气膜层与壁面贴附良好,气膜冷却效率最高;大正值攻角(i=20°,30°)下,虽然气膜覆盖面积大,但反肾型涡对退化,气膜冷却效率下降;大负值攻角(i=-20°,-30°)下,流场中有肾型涡对,且气膜横向覆盖受限,气膜冷却效率最低。     

Properties of Ground Level Enhancement Events and the Associated Solar Eruptions During Solar Cycle 23

Solar cycle 23 witnessed the most complete set of observations of coronal mass ejections (CMEs) associated with the Ground Level Enhancement (GLE) events. We present an overview of the observed properties of the GLEs and those of the two associated phenomena, viz., flares and CMEs, both being potential sources of particle acceleration. Although we do not find a striking correlation between the GLE intensity and the parameters of flares and CMEs, the solar eruptions are very intense involving X-class flares and extreme CME speeds (average ～2000?km/s). An M7.1 flare and a 1200?km/s CME are the weakest events in the list of 16 GLE events. Most (80?%) of the CMEs are full halos with the three non-halos having widths in the range 167 to 212?degrees. The active regions in which the GLE events originate are generally large: 1290?msh (median 1010?msh) compared to 934?msh (median: 790?msh) for SEP-producing active regions. For accurate estimation of the CME height at the time of metric type?II onset and GLE particle release, we estimated the initial acceleration of the CMEs using flare and CME observations. The initial acceleration of GLE-associated CMEs is much larger (by a factor of 2) than that of ordinary CMEs (2.3?km/s² vs. 1?km/s²). We confirmed the initial acceleration for two events for which CME measurements are available in the inner corona. The GLE particle release is delayed with respect to the onset of all electromagnetic signatures of the eruptions: type?II bursts, low frequency type?III bursts, soft X-ray flares and CMEs. The presence of metric type?II radio bursts some 17?min (median: 16?min; range: 3 to 48?min) before the GLE onset indicates shock formation well before the particle release. The release of GLE particles occurs when the CMEs reach an average height of ～3.09?R _s (median: 3.18?R _s ; range: 1.71 to 4.01?R _s ) for well-connected events (source longitude in the range W20–W90). For poorly connected events, the average CME height at GLE particle release is ～66?% larger (mean: 5.18?R _s ; median: 4.61?R _s ; range: 2.75–8.49?R _s ). The longitudinal dependence is consistent with shock accelerations because the shocks from poorly connected events need to expand more to cross the field lines connecting to an Earth observer. On the other hand, the CME height at metric type?II burst onset has no longitudinal dependence because electromagnetic signals do not require magnetic connectivity to the observer. For several events, the GLE particle release is very close to the time of first appearance of the CME in the coronagraphic field of view, so we independently confirmed the CME height at particle release. The CME height at metric type?II burst onset is in the narrow range 1.29 to 1.8?R _s , with mean and median values of 1.53 and 1.47?R _s . The CME heights at metric type?II burst onset and GLE particle release correspond to the minimum and maximum in the Alfvén speed profile. The increase in CME speed between these two heights suggests an increase in Alfvénic Mach number from?2 to?3. The CME heights at GLE particle release are in good agreement with those obtained from the velocity dispersion analysis (Reames in Astrophys. J. 693:812, 2009a; Astrophys. J. 706:844, 2009b) including the source longitude dependence. We also discuss the implications of the delay of GLE particle release with respect to complex type?III bursts by ～18?min (median: 16?in; range: 2 to 44?min) for the flare acceleration mechanism. A?similar analysis is also performed on the delay of particle release relative to the hard X-ray emission.     

支板阻力特性实验

实验在超燃冲压发动机直连式试验台进行,燃烧式加热器出口气流马赫数为2.7,总温为1 337 K.利用推力测量系统对不同结构尺寸支板的冷流阻力和热试阻力进行了研究.比较了高度分别为37.5 mm和71 mm,后掠角分别为0°,30°和45°的支板冷流阻力,结果表明支板的冷流阻力随支板高度的增大而增大,随后掠角的增大而减小;实验还在燃烧模态下对不同当量比时支板的阻力进行了对比,结果表明支板的热试阻力比冷流阻力小,且支板的热试阻力随当量比的增加而减小.