Self-similar adiabatic flow headed by a magnetogasdynamic cylindrical shock wave in a rotating non-ideal gas     

J. P. Vishwakarma  Anil Kumar Maurya  K. K. Singh 《地球物理与天体物理流体动力学》2013,107(2):155-168

Similarity solutions are obtained for one-dimensional adiabatic flow behind a magnetogasdynamic cylindrical shock wave propagating in a rotating non-ideal gas in presence of an azimuthal magnetic field. The density of the medium ahead of the shock is assumed to be constant. In order to obtain the similarity solutions the angular velocity of the ambient medium is assumed to be obeying a power law and to be decreasing as the distance from the axis increases. It is found that the similarity solutions exist, in both the cases, when the initial magnetic field is constant or obeying a power law. The effects of an increase in the value of the index for variation of angular velocity of the ambient medium, in the value of the parameter of the non-idealness of the gas and in the strength of the initial magnetic field are obtained.  相似文献   

Enhancement of Solar Energetic Particles During a Shock – Magnetic Cloud Interacting Complex Structure     

Chenglong Shen  Yuming Wang  Pinzhong Ye  S. Wang 《Solar physics》2008,252(2):409-418

The behavior of solar energetic particles (SEPs) in a shock – magnetic cloud interacting complex structure observed by the Advanced Composition Explorer (ACE) spacecraft on 5 November 2001 is analyzed. A strong shock causing magnetic field strength and solar wind speed increases of about 41 nT and 300 km s⁻¹, respectively, propagated within a preceding magnetic cloud (MC). It is found that an extraordinary SEP enhancement appeared at the high-energy (≥10 MeV) proton intensities and extended over and only over the entire period of the shock – MC structure passing through the spacecraft. Such SEP behavior is much different from the usual picture that the SEPs are depressed in MCs. The comparison of this event with other top SEP events of solar cycle 23 (2000 Bastille Day and 2003 Halloween events) shows that such an enhancement resulted from the effects of the shock – MC complex structure leading to the highest ≥10 MeV proton intensity of solar cycle 23. Our analysis suggests that the relatively isolated magnetic field configuration of MCs combined with an embedded strong shock could significantly enhance the SEP intensity; SEPs are accelerated by the shock and confined into the MC. Further, we find that the SEP enhancement at lower energies happened not only within the shock – MC structure but also after it, probably owing to the presence of a following MC-like structure. This is consistent with the picture that SEP fluxes could be enhanced in the magnetic topology between two MCs, which was proposed based on numerical simulations by Kallenrode and Cliver (Proc. 27th ICRC 8, 3318, 2001b).  相似文献   

Infrasonic Observations of Meteoroids: Preliminary Results from a Coordinated Optical-radar-infrasound Observing Campaign     

Wayne N. Edwards  Peter G. Brown  Robert J. Weryk  Douglas O. ReVelle 《Earth, Moon, and Planets》2008,102(1-4):221-229

Recent observations using the newly installed Elginfield infrasound array in coordination with the Southern Ontario all-sky meteor camera network and Canadian Meteor Orbit Radar (CMOR) has shown that the number of meteors producing infrasound at the Earth’s surface is more frequent than previously thought. These data show the flux of meteoroids capable of producing infrasound at the ground is at least 1/month and is limited to meteors with peak visual brightness above −2. Comparisons to current meteor infrasound theory show excellent agreement with amplitude and period predictions for weakly non-linear shock waves using a realistic vertically inhomogeneous atmosphere. Similar predictions show isothermal assumptions underestimate the amplitude by orders of magnitude.  相似文献   

The man swimming against the stream knows the strength of it : Hydraulics and social relations in an Argentinean irrigation system     

Maurits W. Ertsen  Ronald van Nooijen 《Physics and Chemistry of the Earth》2009,34(3):200-208

In this paper we discuss hydraulic behavior of irrigation infrastructure within a context of spatially distributed power relations in an Argentinean irrigation system. In the Río Dulce basin, the irrigation area known as the Proyecto Río Dulce (PRD, command area 350,000 hectares) is the main irrigated area. An interesting characteristic of the PRD is that the larger landowners are mainly situated in tail end areas. Despite this potentially disadvantageous position, downstream farmers do not encounter problems in terms of water availability. This should not be regarded as self-evident: the hydraulic properties of the canals induce a need for downstream farmers to take deliberate action to ensure proper water delivery to their farms. When upstream farmers do not irrigate, too much water can flow downstream; when they irrigate too much, or manipulate cross regulators, downstream water scarcity can be the result; when canals are not maintained, extensive plant growth will increase hydraulic resistance and decrease discharges. It is not a coincidence that the downstream farmers invest heavily in canal operation and maintenance. These investments appear to be appropriate, as larger farmers tend to irrigate much more on average, compared to the smaller farmers upstream. The Argentinean case brings up issues on the structuring effects of irrigation systems, which need stronger theoretical understanding.  相似文献   

Training the rivers and exploring the coasts. Knowledge evolution in the Netherlands in two engineering fields between 1800 and 1940     

Bert Toussaint 《Physics and Chemistry of the Earth》2009,34(3):132-141

In this paper, the author wants to explore the knowledge development in two crucial fields, river management and coast management in the 19th century and first decades of the 20th century. Were there similar characteristics in this development? Which types of knowledge can be distinguished? Who were the principal actors in these processes? Did the knowledge evolution have a Dutch stamp or a rather international flavour?To structure the analysis, the author uses the concept of technology regime, a set of technical rules which shapes the know-how of engineers, their design rules and research processes. The analysis shows that the knowledge development of river management and coastal management followed different evolution paths between 1800 and 1940. In the field of river management, a substantial amount of mathematical and physical theories had been gradually developed since the end of the 17th century. After 1850, the regularization approach met gradually a widespread support. Empirical data, design rules, theoretical knowledge and engineering pivoted around the regularization approach, and a technology regime around this approach emerged. The regularization regime further developed in the 20th century, and handbooks were increasingly shaped by mathematical and physical reasoning and formulas. On the other hand, coastal management was until the 1880s a rather marginal activity. Coastal engineering was an extremely complex and multidimensional field of knowledge which no engineer was able to grasp.The foundation of a Dutch weather institute was a first important step towards a more theoretical approach. The Zuiderzee works (starting in 1925) gave probably the most important stimuli to scientific coastal research. It was also a main factor in setting up scientific institutes by Rijkswaterstaat. So from the 1920s, Rijkswaterstaat became a major producer of scientific knowledge, not only in tidal modelling but also in coastal research. Due to a multidisciplinary knowledge network, coastal research transformed from a marginal to a first-rank scientific field, and this transformation enabled Rijkswaterstaat to set a much higher level of ambition in coastal management. The 1953 flood and the Deltaworks marked a new era. New design rules for sea dykes and river levees, based on a revolutionary statistical risk approach were determined, and design rules for the Deltaworks estuary closures were developed, being enabled by the development of hydraulic research.  相似文献   

辉长岩在冲击加载下的相变及物态方程          下载免费PDF全文

地力夏提  黄晓葛  陈祖安  刘福生  袁贤昊  白武明 《地球物理学报》2014,57(9):2826-2832

岩石相变关系对限定地球内部物质成分和动力学关系有着重要意义.利用光探针在14~39 GPa压力区间对热压烧结的辉长岩样品进行了冲击波加载实验.从16 GPa开始,D-u线斜率发生明显变化,说明样品内发生了相变.利用原始的Hugoniot曲线结合地震波状态方程（Seismic Equation of State）得到了Birch-Murnaghan型的等熵压缩线和相变能.结合前人的实验结果,得到了辉长岩的Grü neisen参数γ₀,约为2.3.计算得到相变后的矿物集合体在零压下的密度为3.41 g·cm^-3.根据以上参数分析得出,在此压力段辉长岩相变主要由长石的分解反应和石英的高压相变控制.  相似文献   

Crystallization and impact history of a meteoritic sample of early lunar crust(NWA 3163)refined by atom probe geochronology     

L.F.White  D.E.Moser  K.T.Tait  B.Langelier  I.Barker  J.R.Darling 《地学前缘(英文版)》2019,10(5):1841-1848

Granulitic lunar meteorites offer rare insights into the timing and nature of igneous,metamorphic and impact processes in the lunar crust.Accurately dating the different events recorded by these materials is very challenging,however,due to low trace element abundances(e.g.Sm,Nd,Lu,Hf),rare micrometerscale U-Th-bearing accessory minerals,and disturbed Ar-Ar systematics following a multi-stage history of shock and thermal metamorphism.Here we report on micro-baddeleyite grains in granulitic mafic breccia NWA 3163 for the first time and show that targeted microstructural analysis(electron backscatter diffraction)and nanoscale geochronology(atom probe tomography)can overcome these barriers to lunar chronology.A twinned(～90°/401)baddeleyite domain yields a ~(232)Th/~(208)Pb age of 4328 ± 309 Ma,which overlaps with a robust secondary ion mass spectrometry(SIMS)~(207)Pb/~(206)Pb age of 4308 ± 18.6 Ma and is interpreted here as the crystallization age for the igneous protolith of NWA 3163.A second microstructural domain,2μm in width,contains patchy overprinting baddeleyite and yields a Th-Pb age of 2175 ±143 Ma,interpreted as dating the last substantial impact event to affect the sample.This finding demonstrates the potential of combining microstructural characterization with nanoscale geochronology when resolving complex P-T-t histories in planetary materials,here yielding the oldest measured crystallization age for components of lunar granulite NWA 3163 and placing further constraints on the formation and evolution of lunar crust.  相似文献   

Impact cratering: The South American record – Part 1     

《Chemie der Erde / Geochemistry》2019,79(1):1-61

The Earth’s impact record is known to be rather limited in both time and space. There are ca. 190 impact structures currently known on Earth, representing a minor fraction of all the impact events that contributed to the initial formation of our protoplanet, and then to formation and modification of the surface of the planet. Moreover, the distribution of impact structures on Earth is manifestly uneven. One continent that stands out for its relatively small number of confirmed impact structures and impact ejecta occurrences is South America. The limited impact record for this large continent makes a robust case that there is a significant potential for further discoveries. Significant information on the impact record of South America is dispersed in different types of publications (journal articles, books, conferences abstracts, etc.), and in several languages, making it difficult to access and disseminate it among the geoscientific community. We aim to present a summary of the current knowledge of the impact record of this continent, encompassing the existing literature on the subject. It is published in two parts, with the first one covering an up-to-date introduction to impact cratering processes and to the criteria to identify/confirm an impact structure and related deposits. This is followed by a comprehensive analysis of the Brazilian impact structures. The Brazilian impact record accounts for the totality of the large structures of this kind currently confirmed in South America. The second part will examine the impact record of other countries in South America, provide information about a number of proposed impact structures, and review those that already have been discarded as not being formed by impact.  相似文献   

A new extinct genus of Glandulariini with two species from Upper Cretaceous Burmese amber (Coleoptera: Staphylinidae: Scydmaeninae)     

《Cretaceous Research》2017

The Glandulariini (=Cyrtoscydmini) is today the largest, most species-rich and most diverse tribe of Scydmaeninae comprising over 70% of the extant species of this subfamily. Named genera and species of Glandulariini are known mostly from Miocene to Eocene ambers, with only one, recently described Mesozoic taxon. Here we report the second genus of Glandulariini from Upper Cretaceous Burmese amber, Cenomaniola Jałoszyński and Yamamoto, gen. nov., with two species, C. carinata Jałoszyński and Yamamoto, sp. nov. and C. macrophthalma Jałoszyński and Yamamoto, sp. nov. Cenomaniola shows the general body plan typical of the ‘Euconnus complex’ within Glandulariini, with thick bristles on the sides of head and pronotum, a character conserved for nearly a hundred million years. With the previous discovery of Scydmobisetia Jałoszyński and Yamamoto, two major body forms typical of the extant Glandulariini are already proved to have differentiated in or before the Late Cretaceous. This demonstrates early origins and a long conservation of ‘Euconnus-like’ and ‘Sciacharis/Horaeomorphus-like’ body plan in the currently largest group among Scydmaeninae.  相似文献   

A Raman spectroscopic study of shock-wave densification of vitreous silica   总被引：1，自引：0，他引：1  

M. Okuno  B. Reynard  Y. Shimada  Y. Syono  C. Willaime 《Physics and Chemistry of Minerals》1999,26(4):304-311

The densification processes in SiO₂ glass induced by shock-wave compression up to 43.4 GPa are investigated by Raman spectroscopy. At first, densification increases with increasing shock pressure. A maximum densification of 11% is obtained for a shock pressure of 26.3 GPa. This densification is attributed to the reduction of the average Si−O−Si angle, which occurs first by the collapse of the largest ring cavities, then by further reduction of the average ring size. For higher shock pressures, a different structural modification is observed, resulting in decreasing densification with increasing shock pressure. Indeed, the recovered densification becomes very small, with values of 1.8 and 0.5% at 32 and 43.4 GPa, respectively. This is attributed to partial annealing of the samples due to high after shock residual temperatures. The study of the annealing process of the most densified glass by in situ high temperature Raman spectroscopy confirms that relaxation of the Si−O−Si angle starts at a lower temperature (about 800 K) than that of the siloxane rings (about 1000 K), thus explaining the high intensity of the siloxane defect bands in the samples schocked at compressions of 32 and 43.4 GPa. The large intensity of the siloxane bands in the nearly undensified samples shocked by compressions above 30 GPa may be explained by the relaxation during decompression of five- and six-fold coordinated silicon species formed at high pressure and high temperature during the shock event. Received: March 30, 1998 / Revised, accepted: August 21, 1998  相似文献