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71.
72.
Starting with a large number (N=100) of Wind magnetic clouds (MCs) and applying necessary restrictions, we find a proper set of N=29 to investigate the average ecliptic plane projection of the upstream magnetosheath thickness as a function of the longitude
of the solar source of the MCs, for those cases of MCs having upstream shock waves. A few of the obvious restrictions on the
full set of MCs are the need for there to exist a driven upstream shock wave, knowledge of the MC’s solar source, and restriction
to only MCs of low axial latitudes. The analysis required splitting this set into two subsets according to average magnetosheath
speed: slow/average (300 – 500 km s−1) and fast (500 – 1100 km s−1) speeds. Only the fast set gives plausible results, where the estimated magnetosheath thickness (ΔS) goes from 0.042 to 0.079 AU (at 1 AU) over the longitude sector of 0° (adjusted source-center longitude of the average magnetic
cloud) to 40° off center (East or West), based on N=11 appropriate cases. These estimates are well determined with a sigma (σ) for the fit of 0.0055 AU, where σ is effectively the same as
(chi-squared) for the appropriate quadratic fit. The associated linear correlation coefficient for ΔS versus |Longitude| was very good (c.c.=0.93) for the fast range, and ΔS at 60° longitude is extrapolated to be 2.7 times the value at 0°. For the slower speeds we obtain the surprising result that
ΔS is typically more-or-less constant at 0.040±0.013 AU at all longitudes, indicating that the MC as a driver, when moving close
to the normal solar wind speed, has little influence on magnetosheath thickness. In some cases, the correct choice between
two candidate solar-source longitudes for a fast MC might be made by noting the value of the observed ΔS just upstream of the MC. Also, we point out that, for the 29 events, the average sheath speed was well correlated with the
quantity ΔV[=(〈V
MC〉−〈V
UPSTREAM〉)], and also with both 〈V
MC〉 and 〈V
MC,T〉, where 〈V
MC〉 is the first one-hour average of the MC speed, 〈V
MC,T〉 is the average MC speed across the full MC, and 〈V
UPSTREAM〉 is a five-hour average of the solar wind speed just upstream of the shock. 相似文献
73.
J. F. Hansen M. J. Edwards D. H. Froula A. D. Edens G. Gregori T. Ditmire 《Astrophysics and Space Science》2007,307(1-3):219-225
We have previously reported the experimental discovery of a second shock forming ahead of a radiative shock propagating in
Xe. The initial shock is spherical, radiative, with a high Mach number, and it sends a supersonic radiative heat wave far
ahead of itself. The heat wave rapidly slows to a transonic regime and when its Mach number drops to two with respect to the
downstream plasma, the heat wave drives a second shock ahead of itself to satisfy mass and momentum conservation in the heat
wave reference frame. We now show experimental data from a range of mixtures of Xe and N2, gradually changing the properties of the initial shock and the environment into which the shock moves and radiates (the
radiative conductivity and the heat capacity). We have successfully observed second shock formation over the entire range
from 100% Xe mass fraction to 100% N2. The formation radius of the second shock as a function of Xe mass fraction is consistent with an analytical estimate. 相似文献
74.
L. K. Jian C. T. Russell J. G. Luhmann R. M. Skoug J. T. Steinberg 《Solar physics》2008,249(1):85-101
We present comprehensive surveys of 203 stream interaction regions (SIRs) and 124 interplanetary CMEs (ICMEs) during 1979 – 1988
using Pioneer Venus Orbiter (PVO) in situ solar-wind observations at 0.72 AU and examine the solar-cycle variations of the occurrence rate, shock association rate,
duration, width, maximum total perpendicular pressure (P
t), maximum dynamic pressure, maximum magnetic field intensity, and maximum velocity change of these two large-scale solar-wind
structures. The medians, averages, and histogram distributions of these parameters are also reported. Furthermore, we sort
ICMEs into three groups based on the temporal profiles of P
t, and we investigate the variations of the fractional occurrence rate of three groups of ICMEs with solar activity. We find
that the fractional occurrence rate of magnetic-cloud-like ICMEs declined with solar activity, consistent with our former
1-AU results. This study at 0.72 AU provides a point of comparison in the inner heliosphere for examining the radial evolution
of SIRs and ICMEs. The width of SIRs and ICMEs increases by 0.04 and 0.1 AU, respectively, and the maximum P
t decreases to about 1/3 from Venus to Earth orbit. In addition, our work establishes the statistical properties of the solar-wind
conditions at 0.72 AU that control the solar-wind interaction with Venus and its atmosphere loss by related processes.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
75.
S. Mondal P. Basu S. K. Chakrabarti † 《Monthly notices of the Royal Astronomical Society》2009,396(2):1038-1045
In the present communication of our series of papers dealing with the accretion flows in the pseudo-Kerr geometry, we discuss the effects of viscosity on the accretion flow around a rotating black hole. We find the solution topologies and give special attention to the solutions containing shocks. We draw the parameter space where standing shocks are possible and where the shocks could be oscillating and could produce quasi-periodic oscillations (QPOs) of X-rays observed from black hole candidates. In this model, the extreme locations of the shocks give the upper limits of the QPO frequencies (νQPO ) which could be observed. We show that both the viscosity of the flow and the spin of the black hole a increase the QPO frequency while, as expected, the black hole mass reduces the QPO frequencies. Our major conclusion is that the highest observed frequency gives a strict lower limit of the spin. For instance, a black hole exhibiting νQPO ∼ 400 and 700 Hz must have the spin parameters of a > 0.25 and >0.75 , respectively, provided viscosity of the flow is small. We discuss the implications of our results in the light of observations of QPOs from black hole candidates. 相似文献
76.
KeliZHANG LifangLUO ShuangcaiLI 《国际泥沙研究》2004,19(2):149-153
Hydraulic mechanism of fill formation was studied theoretically and experimentally. It was assumed that the impact of varied boundary on overland flow results in fluctuating of water surface, and shock waves that may contribute to the formation of fills. Both theoretical derivation and laboratory experiments were used to compare the hydraulic characteristics of flows with and without shock waves. Results showed that shock waves can lead to an increase in flow depth, flow velocity, and turbulence intensity. Consequently, flow shear stress or stream energy increase dramatically and fill headcuts may occur where shock waves converge. 相似文献
77.
《Chemie der Erde / Geochemistry》2019,79(4):125542
Space weathering by micrometeoroid bombardment is a cosmic phenomenon on atmosphere-free celestial bodies, a process that is expected to particularly overprint planetesimals and cosmic dust in debris discs. We reproduced micrometeoroid impact craters by femtosecond pulsed laser irradiation on oriented enstatite single crystals (En93Fs7) to investigate the deformation behavior and its orientation dependence. All microcraters show typical bowl shaped morphologies, a glass surface layer with splash like ejecta material and subsurface layering. Although we could reproduce melting and vaporization as typical space weathering effects in the enstatite experiments, there is no formation of agglutinate particles or metallic nanoparticles (npFe0). The shock effects in the deformation layer consist of planar structures like microfractures and cleavages, amorphous lamellae, stacking faults and clinoenstatite lamellae. Their activation and/or orientation depends on the shock direction. In special orientations we observe the activation of glide systems along specific low indexed crystallographic planes. Due to the short timescale and the high strain rates, the most prominent effect is the failure of enstatite by microfracturing along non-rational crystallographic planes. Common deformation mechanisms reported in meteorites like the formation of clinoenstatite lamellae via shearing along [001] (100) occur less frequently. Shear is apparently the dominant mechanism in the formation of the above-mentioned effects and causes also their modification by frictional heating. The wide-spread formation of amorphous lamellae is, for example, interpreted to be the result of this shear heating along planar structures. We interpret this unconventional deformation behavior as a consequence of the small spatial and temporal scale of the experiments, resulting in a short-lived spherical shock wave with high deviatoric stresses in contrast to a long pressure pulse and quasi-hydrostatic compression in large scale impacts that produce typical shock features. 相似文献
78.
H. P. Rossmanith K. Uenishi 《Fragblast: International Journal for Blasting and Fragmentation》2006,10(3):111-162
Spalling is a wave-induced dynamic fracture phenomenon. The waves can be either one: elastic, elasto-plastic, or shock waves. From a continuum mechanics point of view, fracture mechanics and wave propagation form the main ingredients in the formation of spalls. Recently, however, micro-structural effects have become important in the initial stages of spall formation in a variety of engineering materials ranging from metals to rock and concrete. From a structural geology point of view, the rock mass cannot be modelled as a continuum. In this case, a discontinuum approach has to be taken where the individual features of the rock mass such as joints and faults need to be taken into account. From an application point of view, spallation is important where rapid loading by explosives, impact, or energy deposition, occurs. The range of applications stretches from blasting in mining engineering to damage prevention to structures under explosive excitation.
This contribution offers a multi-faceted and multi-disciplinary approach to the study of spalling with special attention to analytical and experimental work. The reader is assumed to be somewhat familiar with the basics of continuum mechanics, fracture mechanics, and propagation of elastic, plastic and shock waves. The application to rock and concrete will show the effects of structural geological discontinuities such as open and closed joints - and to some degree also faulting - in rock, as well as the micro-structure of concrete on the (shock) wave field.
Extensive use will be made of time-space diagrams which proved very useful in practical applications to blasting problems [Rossmanith, H.P., 2002, The use of Lagrange diagrams in precise initiation blasting. Part I: two interacting blastholes, Fragblast 6, 104-136]. 相似文献
This contribution offers a multi-faceted and multi-disciplinary approach to the study of spalling with special attention to analytical and experimental work. The reader is assumed to be somewhat familiar with the basics of continuum mechanics, fracture mechanics, and propagation of elastic, plastic and shock waves. The application to rock and concrete will show the effects of structural geological discontinuities such as open and closed joints - and to some degree also faulting - in rock, as well as the micro-structure of concrete on the (shock) wave field.
Extensive use will be made of time-space diagrams which proved very useful in practical applications to blasting problems [Rossmanith, H.P., 2002, The use of Lagrange diagrams in precise initiation blasting. Part I: two interacting blastholes, Fragblast 6, 104-136]. 相似文献
79.
80.
南极月球陨石MIL05035矿物学、岩石学及演化历史 总被引:1,自引:0,他引:1
月球陨石MIL05035岩石类型上属于普通辉石低钛玄武岩,粗粒辉长结构,无角砾化。主要矿物为辉石(60.2%)、斜长石(27.3%)和橄榄石(6.05%),次要矿物为石英(4.36%)、钛铁矿(1.25%)和陨硫铁(0.84%),含极少量富Ti、Fe尖晶石和磷灰石,广泛发育由钙铁辉石+铁橄榄石+石英组成的后成合晶三相集合体。辉石颗粒具有明显的化学成分不均匀性和出溶片晶,核部相对贫铁钙富镁(Fs30.2-60.8Wo14.2-35.0),边部富铁钙贫镁(Fs47.5-64.9Wo22.8-44.3)。熔长石化斜长石具有微弱的成分环带,边部相对富碱金属元素(Ab9.3-12.3,Or0.31-1.03),核部则相反(Ab7.6-10.6,Or0.12-0.36),含有未熔长石化的残留斜长石。橄榄石具有粗晶橄榄石(Fa95.5-96.6)和后成合晶中细粒橄榄石(Fa88.9-93.5)两种产状。石英具有脉状、团块状和蠕虫状等产状:脉状石英大部分转变为二氧化硅玻璃,核部石英具有较宽的拉曼谱特征峰(448~502cm-1),证明其经历了冲击变质与退变质作用;团块状石英分布于粗粒橄榄石颗粒间或橄榄石与斜长石和辉石接触边界上,与斜长石构成充填结构;蠕虫状石英分布于细粒后成合晶中。粗粒辉石边部铁辉石和后成合晶中辉石成分的继承性、结构上的延续性、光学特征上的冲击暗化现象、与冲击熔脉结构上的相关性和后成合晶中发育与粗粒辉石方向几乎一致的解理等方面的证据,认为后成合晶可能由于铁辉石在冲击压力释放与温度降低后的退变质作用下分解形成。根据岩石矿物结构观察、成分分析和MELTS模拟表明该陨石母岩的岩浆演化过程可能为:母岩浆在温度降低后首先产生极少量钛铁尖晶石、其次是普通辉石和钙长石先后结晶;随着温度下降,贫钙铁普通辉石、铁钙铁辉石和铁普通辉石等在普通辉石边部大量结晶,钙长石边部分异结晶少量培长石或拉长石;随着温度继续下降,早期结晶的普通辉石析出易变辉石等出溶片晶,橄榄石在辉石和斜长石边部结晶;其后,钛铁矿和陨硫铁析出,石英沿橄榄石和钙长石等先结晶矿物裂隙充填。出露月表后强烈的冲击变质作用使斜长石几乎全部转变为熔长石、石英大部分转变为二氧化硅玻璃,并具有一系列面状变形,冲击熔脉发育,冲击变质程度至少为S5。本研究为月球的岩浆演化和冲击变质过程提供了重要证据。 相似文献