Rigid unit modes in the molecular dynamics simulation of quartz and the incommensurate phase transition     

Frank Stefan Tautz  Volker Heine  Martin T. Dove  Xiaojie Chen 《Physics and Chemistry of Minerals》1991,18(5):326-336

A molecular dynamics simulation of quartz at different temperatures both in the a and in the phase has been conducted. The - phase transition could be observed. A phonon analysis of the -phase confirms and rounds out in a quantitative way the origin of the incommensurate (ic) modulated phase. In particular it traces the optic soft mode at becoming (to a good approximation) a so-called rigid unit mode (RUM) at q0, and elucidates its coupling to the transverse acoustic mode which precipitates the incommensurate transition. This success underpins and illuminates the concept of RUMs and their role in structural phase transitions.  相似文献   

The role of magnetohydrodynamics in heliospheric space plasma physics research     

Murray Dryer  Zdenka Kopal Smith  Shi Tsan Wu 《Astrophysics and Space Science》1988,144(1-2):407-425

Magnetohydrodynamics (MHD) is a fairly recent extension of the field of fluid mechanics. While much remains to be done, it has successfully been applied to the contemporary field of heliospheric space plasma research to evaluate the macroscopic picture of some vital topics via the use of conducting fluid equations and numerical modeling and simulations. Some representative examples from solar and interplanetary physics are described to demonstrate that the continuum approach to global problems (while keeping in mind the assumptions and limitations therein) can be very successful in providing insight and large scale interpretations of otherwise intractable problems in space physics.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988.  相似文献   

A model of the galactic centre with magnetic monopoles     

Wang De-Yu  Peng Qiu-He  Chen Ting-Yang 《Astrophysics and Space Science》1986,118(1-2):379-382

A model of the galactic centre with magnetic monopole has been presented here. The positron can be produced continuously through magnetic monopoles to induce baryon decay (Rubakov catalytic reaction) and a lot of energy can be released as well. The calculation results show that even if the galactic center contains only a few magnetic monopoles (=N _M/N_B10^–24), this massive object can not collapse into a black hole. This model can explain the observed intensities of the annihilation line and higher energy photons ofE >511 keV from the galactic centre.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.  相似文献   

《徐霞客游记》的科学性和时代性——怒江、腾冲地区的实地验证   总被引：2，自引：0，他引：2  

陈述彭 《地理研究》1986,5(4):1-11

作者选取本人身历其境作过工作的怒江、腾冲地区来验证《徐霞客游记》,从徐氏进步的地理概念、游记严谨的逻辑结构、游记作者观察的细致深入等方面论述了徐霞客的献身精神和不朽贡献。  相似文献   

Geochemistry of re and trace elements in ferromanganese nodules and their genesis   总被引：1，自引：0，他引：1  

王贤觉  陈毓蔚  吴明清 《中国海洋湖沼学报》1986,4(3):211-226

Trace and RE element geochemistry and genesis have been studied with respect to ferromanganese nodules from the sediments of the Pacific, Atlantic and Indian oceans.  相似文献   

A possible mechanism of formation of faculae     

Ni Xiang-bin  Jiang Yao-tiao  Chen Zai-zhang  Fang Cheng 《Chinese Astronomy and Astrophysics》1985,9(4):273-277

We propose a new heating mechanism of faculae. We think that the formation of faculae is a result of the Joule dissipation of the Hall current generated by the interaction of the convection field of granules in an active region and the inter-granular magnetic field. For a region to generate effectively Hall current, its characteristic length must be such that the magnetic Reynolds number is less than 1. The equation of energy balance in the facula region is .For five observational models of faculae, we calculated the corresponding velocity fields, and the results are in basic agreement with the observed fields. The present mechanism explains the dependence of the facula brightness on the magnetic and velocity fields, the apparent distribution of the faculae on the solar disk and suggest a possible interpretation of the five structures of faculae.  相似文献   

Evolution of electron and proton temperatures in a flaring loop     

Nagai  F.  Wu  S. T.  Tandberg-Hanssen  E. 《Solar physics》1983,84(1-2):271-283

We have investigated numerically how a temperature difference between electrons and protons is produced in a flaring loop by adopting a one-fluid, two-temperature model instead of a single-temperature model. We have treated a case in which flare energy is released in the form of heating of electrons located in the top part of the loop.In this case, a large temperature difference (T _e/T _p 10) appears in the corona in the energy-input phase of the flare. When the material evaporated from the chromosphere fills the corona, the temperature difference in the loop begins to shrink rapidly from below. Eventually, in the loop apex, the proton temperature exceeds the electron temperature mainly due to cooling of the electrons by conduction down the loop and heating of the protons by compression of the ascending material. In the late phase of the flare (t 15 min from the flare onset), the temperature difference becomes less than 2% of the mean temperature of electrons and protons at every point in the loop.  相似文献   

Melting of the subcontinental lithospheric mantle by the Emeishan mantle plume; evidence from the basal alkaline basalts in Dongchuan, Yunnan, Southwestern China   总被引：3，自引：0，他引：3  

Xie-Yan Song  Hua-Wen Qi  Paul T. Robinson  Mei-Fu Zhou  Zhi-Min Cao  Lie-Meng Chen 《Lithos》2008,100(1-4):93-111

The Emeishan continental flood basalt (ECFB) sequence in Dongchuan, SW China comprises a basal tephrite unit overlain by an upper tholeiitic basalt unit. The upper basalts have high TiO₂ contents (3.2–5.2 wt.%), relatively high rare-earth element (REE) concentrations (40 to 60 ppm La, 12.5 to 16.5 ppm Sm, and 3 to 4 ppm Yb), moderate Zr/Nb and Nb/La ratios (9.3–10.2 and 0.6–0.9, respectively) and relatively high _{Nd (t)} values, ranging from − 0.94 to 2.3, and are comparable to the high-Ti ECFB elsewhere. The tephrites have relatively high P₂O₅ (1.3–2.0 wt.%), low REE concentrations (e.g., 17 to 23 ppm La, 4 to 5.3 ppm Sm, and 2 to 3 ppm Yb), high Nb/La (2.0–3.9) ratios, low Zr/Nb ratios (2.3–4.2), and extremely low _{Nd (t)} values (mostly ranging from − 10.6 to − 11.1). The distinct compositional differences between the tephrites and the overlying tholeiitic basalts cannot be explained by either fractional crystallization or crustal contamination of a common parental magma. The tholeiitic basalts formed by partial melting of the Emeishan plume head at a depth where garnet was stable, perhaps > 80 km. We propose that the tephrites were derived from magmas formed when the base of the previously metasomatized, volatile-mineral bearing subcontinental lithospheric mantle was heated by the upwelling mantle plume.  相似文献   

A preliminary stable isotope study on Mogok Ruby, Myanmar     

Tzen-Fu Yui  Khin Zaw  Chao-Ming Wu 《Ore Geology Reviews》2008,34(1-2):192

The primary occurrence of ruby in the Mogok area, northern Myanmar is exclusively found in marble along with spinel–forsterite-bearing marble and phlogopite–graphite marble. These marble units are enclosed within banded biotite–garnet–sillimanite–oligoclase gneisses. Samples of these marbles collected for C–O stable isotope analysis show two trends of δ¹³C–δ¹⁸O variation resulting most likely from fluid–rock interactions. Ruby-bearing marble and phlogopite–graphite marble follow a trend with coupled C–O depletion, whereas spinel–forsterite-bearing marble follows a δ¹⁸O depletion trend with relatively constant δ¹³C values. Ruby formation might have resulted from CO₂-rich fluid–rock interaction, while spinel–forsterite-bearing marble was genetically related to CO₂-poor fluid–rock interaction. Both fluids may have arisen from external sources. Based on graphite Raman spectral thermometry, the estimated temperature for phlogopite–graphite marble, and probably ruby-bearing marble, was lower than 607 °C, and for spinel–forsterite-bearing marble, lower than 710 °C. Contrasting C/O diffusion between graphite/ruby/spinel/forsterite and calcite, local variations of isotopic compositions of newly formed minerals as a result of non-pervasive fluid infiltration, and open-system isotopic disturbance during cooling may have affected C-/O-isotopic fractionations between minerals. The estimated high formation temperatures for ruby and spinel/forsterite imply that the parental fluids may have been related to nearby igneous intrusions and/or metamorphic processes. Whether these two types of fluid were genetically related is unclear based on the present data.  相似文献   

印度共和国主要矿产资源及其地质特征   总被引：2，自引：0，他引：2  

张建华吴良士 《矿床地质》2008,27(4):541-542

印度共和国是南亚地区矿产资源比较丰富的国家,铁矿探明储量175.7亿吨;铝土矿探明储量26.54亿吨;锰矿探明储量1.35亿吨;铬铁矿储量5900万吨;重晶石储量3000万吨。目前,全印度已开发了89种矿产资源,其中有52种非金属矿产,11种金属矿产,22种稀有金属矿产,4种能源矿产。全国生产矿  相似文献