Towards molecular-level understanding of geochemical processes in mineral exploration     

Joël Brugger  Allan Pring  Frank Reith  Barbara Etschmann  Weihua Liu 《Journal of Geochemical Exploration》2009

  相似文献   

Oblateness effect of Saturn on periodic orbits in the Saturn-Titan restricted three-body problem     

A. Safiya?Beevi  R. K. Sharma 《Astrophysics and Space Science》2012,340(2):245-261

We explore the effect of oblateness of Saturn (more massive primary) on the periodic orbits and the regions of quasi-periodic motion around both the primaries in the Saturn-Titan system in the framework of planar circular restricted three-body problem. First order interior and exterior mean motion resonances are located. The effect of oblateness is studied on the location, nature and size of periodic and quasi-periodic orbits, using the numerical technique of Poincare surface of sections. Some of the periodic orbits change to quasi-periodic orbits due to the effect of oblateness and vice-versa. The stability of the orbits around Saturn, Titan and both varies with the inclusion of oblateness. The centers of the periodic orbits around Titan move towards Saturn, whereas those around Saturn move towards Titan. For the orbit around Titan at C=2.9992, x=0.959494, the apocenter becomes pericenter. By incorporating oblateness effect, the orbit around Titan at C=2.99345, x=0.924938 is captured by Saturn, remains in various trajectories around Saturn, and as time progresses it spirals away around both the primaries.  相似文献   

Suppression of the large‐scale Lorentz force by turbulence     

G. Rüdiger  L.L. Kitchatinov  M. Schultz 《Astronomische Nachrichten》2012,333(1):84-91

The components of the total stress tensor (Reynolds stress plus Maxwell stress) are computed within the quasilinear approximation for a driven turbulence influenced by a large‐scale magnetic background field. The conducting fluid has an arbitrary magnetic Prandtl number and the turbulence without the background field is assumed as homogeneous and isotropic with a free Strouhal number St. The total large‐scale magnetic tension is always reduced by the turbulence with the possibility of a ‘catastrophic quenching’ for large magnetic Reynolds number Rm so that even its sign is reversed. The total magnetic pressure is enhanced by turbulence in the high‐conductivity limit but it is reduced in the low‐conductivity limit. Also in this case the sign of the total pressure may reverse but only for special turbulences with sufficiently large St > 1. The turbulence‐induced terms of the stress tensor are suppressed by strong magnetic fields. For the tension term this quenching grows with the square of the Hartmann number of the magnetic field. For microscopic (i.e. small) diffusivity values the magnetic tension term becomes thus highly quenched even for field amplitudes much smaller than their equipartition value. In the opposite case of large‐eddy simulations the magnetic quenching is only mild but then also the turbulence‐induced Maxwell tensor components for weak fields remain rather small (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

A site evaluation campaign for a ground based atmospheric Cherenkov telescope in Romania     

Aurelian Andrei Radu  Tatiana Angelescu  Valentin Curtef  Florin Delia  Daniel Felea  Ioana Goia  Dumitru Ha?egan  Bogdan Lucaschi  Ancuta Manea  Vlad Popa  Ioan Rali??  Radu V?c?reanu 《Experimental Astronomy》2012,34(1):31-42

Around the world, several scientific projects share the interest of a global network of small Cherenkov telescopes for monitoring observations of the brightest blazars??the DWARF network. A small, ground based, imaging atmospheric Cherenkov telescope of last generation is intended to be installed and operated in Romania as a component of the DWARF network. To prepare the construction of the observatory, two support projects have been initiated. Within the framework of these projects, we have assessed a number of possible sites where to settle the observatory. In this paper we submit a brief report on the general characteristics of the best four sites selected after the local infrastructure, the nearby facilities and the social impact criteria have been applied.  相似文献   

GETEMME—a mission to explore the Martian satellites and the fundamentals of solar system physics     

Jürgen Oberst  Valéry Lainey  Christophe Le Poncin-Lafitte  Veronique Dehant  Pascal Rosenblatt  Stephan Ulamec  Jens Biele  J?rn Spurmann  Ralph Kahle  Volker Klein  Ulrich Schreiber  Anja Schlicht  Nicolas Rambaux  Philippe Laurent  Beno?t Noyelles  Bernard Foulon  Alexander Zakharov  Leonid Gurvits  Denis Uchaev  Scott Murchie  Cheryl Reed  Slava G. Turyshev  Jesus Gil  Mariella Graziano  Konrad Willner  Kai Wickhusen  Andreas Pasewaldt  Marita W?hlisch  Harald Hoffmann 《Experimental Astronomy》2012,34(2):243-271

GETEMME (Gravity, Einstein??s Theory, and Exploration of the Martian Moons?? Environment), a mission which is being proposed in ESA??s Cosmic Vision program, shall be launched for Mars on a Soyuz Fregat in 2020. The spacecraft will initially rendezvous with Phobos and Deimos in order to carry out a comprehensive mapping and characterization of the two satellites and to deploy passive Laser retro-reflectors on their surfaces. In the second stage of the mission, the spacecraft will be transferred into a lower 1500-km Mars orbit, to carry out routine Laser range measurements to the reflectors on Phobos and Deimos. Also, asynchronous two-way Laser ranging measurements between the spacecraft and stations of the ILRS (International Laser Ranging Service) on Earth are foreseen. An onboard accelerometer will ensure a high accuracy for the spacecraft orbit determination. The inversion of all range and accelerometer data will allow us to determine or improve dramatically on a host of dynamic parameters of the Martian satellite system. From the complex motion and rotation of Phobos and Deimos we will obtain clues on internal structures and the origins of the satellites. Also, crucial data on the time-varying gravity field of Mars related to climate variation and internal structure will be obtained. Ranging measurements will also be essential to improve on several parameters in fundamental physics, such as the Post-Newtonian parameter ?? as well as time-rate changes of the gravitational constant and the Lense-Thirring effect. Measurements by GETEMME will firmly embed Mars and its satellites into the Solar System reference frame.  相似文献   

The effects of the polytropic coefficient on plasma sheath in two cases isothermal and adiabatic ion thermal flow     

Mansour Khoramabadi  S. Farhad?Masoudi 《Astrophysics and Space Science》2012,341(2):501-505

Recently it has been shown that for finite and small values of the electron Debye length, the ion polytropic coefficient is approached to some constant value in the plasma sheath region by decreasing the plasma density. In this paper, using a plasma multi fluid model, the effect of ion polytropic coefficient γ _i on the plasma sheath structure have been examined. The numerical calculations of the basic equation of the model show that the polytropic coefficient strongly affects on the plasma sheath characteristics. The results show that by transition from an isothermal flow (γ _i =1) to an adiabatic flow (γ _i =3), the net current to the wall and the electric potential distribution increase and the sheath width decreases in a thermal plasma sheath.  相似文献   

Dark energy and the anthropic principle     

Michal K?í?ek 《New Astronomy》2012,17(1):1-7

The Hubble constant is split into two terms H = H₁ + H₂ , where H₁ is a decreasing function due to the Big Bang and the subsequent gravitational interaction that slows the expansion of the Universe and H₂ is an increasing function that corresponds to dark energy which accelerates this expansion. For T = 13.7 Gyr we prove that H₂(T) > 5 m/(yr AU). This is a quite large number and thus the impact of dark energy, which is spread almost everywhere uniformly, should be observable not only on large scales, but also in our Solar system. In particular, we show that Earth, Mars and other planets were closer to the Sun 4.5 Gyr ago. The recession speed ≈5.3 m/yr of the Earth from the Sun seems to be just right for an almost constant influx of solar energy from the origin of life on Earth up to the present over which time the Sun’s luminosity has increased approximately linearly. This presents further support for the Anthropic Principle. Namely, the existence of dark energy guarantees very stable conditions for the development of intelligent life on Earth over a period of 3.5 Gyr.  相似文献   

Photometric observations and orbital period variations of HS 0705 + 6700 and NY Vir     

C.M. ÇamurdanD. Zengin Çamurdan  C. ?banogˇlu 《New Astronomy》2012,17(3):325-330

We present photometric observations of two post-common-envelope stars, NY Vir (=PG 1336-018) and HS 0705 + 6700. The V band CCD observation of NY Vir was performed by a 40 cm telescope at Ege University Observatory and the R band observations of HS 0705 + 6700 were performed by 100 cm telescope at TÜB?TAK National Observatory. The new light curves were analyzed by the WD code and the physical parameters of stars were determined. We obtained new mid-eclipse timings for HS 0705 + 6700 and combined them with those previously published data. The analysis of the O-C residuals yields a period of about 8.06 ± 0.28 yr and an amplitude of 98.5 s for the system HS 0705 + 6700, which is attributed to the third star physically bounded to the evolved eclipsing pair. A mass function of 1.2 × 10⁻⁴ M_⊙ for the third star is obtained. The existence of a third star is also confirmed by the light curve analysis, indicating light contribution of about 0.043 at phase 0.25 in R-bandpass of the eclipsing pair. Using mass-luminosity relationship of the low mass stars we estimate a mass of 0.12 M_⊙ with an orbital inclination of about 20°. The O-C residuals obtained for the system NY Vir were represented by a downward parabola which indicates orbital period decrease in the system. Using the coefficient of quadratic term we calculate a rate of orbital period decrease of about dP/dt = −4.09 × 10⁻⁸days yr⁻¹. The period decrease we have measured in NY Vir may be explained by angular momentum loss from the binary system.  相似文献   

Presolar silicate and oxide abundances and compositions in the ungrouped carbonaceous chondrite Adelaide and the K chondrite Kakangari: The effects of secondary processing     

Christine FLOSS  Frank J. STADERMANN 《Meteoritics & planetary science》2012,47(6):992-1009

Abstract– Although it has been suggested that the ungrouped carbonaceous chondrite Adelaide and the K chondrite Kakangari could be considered highly primitive, our study of their presolar grain abundances shows that both have experienced more secondary processing than other primitive chondrites with high presolar grain abundances. Presolar grains are rare in Kakangari and are present in reduced abundances in Adelaide (approximately 70 ppm for O‐anomalous grains). Thermal annealing has led to widespread crystallization of their fine‐grained matrices, and accounts for the partial to complete destruction of presolar grains. In addition, presolar silicates in Adelaide show elevated Fe abundances and Fe‐rich rims indicative of infiltration of Fe into the grains from the surrounding matrix. This process probably also took place during annealing, most likely in the solar nebula, in a region with an enhanced dust‐to‐gas ratio. The most primitive meteorites, with the highest presolar grain abundances, appear to be those whose matrices contain abundant amorphous material that has escaped any significant thermal or aqueous alteration.  相似文献   

Heliospheric Observations of STEREO-Directed Coronal Mass Ejections in 2008?–?2010: Lessons for Future Observations of Earth-Directed CMEs     

N. Lugaz  P. Kintner  C. M?stl  L. K. Jian  C. J. Davis  C. J. Farrugia 《Solar physics》2012,279(2):497-515

We present a study of coronal mass ejections (CMEs) which impacted one of the STEREO spacecraft between January 2008 and early 2010. We focus our study on 20 CMEs which were observed remotely by the Heliospheric Imagers (HIs) onboard the other STEREO spacecraft up to large heliocentric distances. We compare the predictions of the Fixed-?? and Harmonic Mean (HM) fitting methods, which only differ by the assumed geometry of the CME. It is possible to use these techniques to determine from remote-sensing observations the CME direction of propagation, arrival time and final speed which are compared to in-situ measurements. We find evidence that for large viewing angles, the HM fitting method predicts the CME direction better. However, this may be due to the fact that only wide CMEs can be successfully observed when the CME propagates more than 100^° from the observing spacecraft. Overall eight CMEs, originating from behind the limb as seen by one of the STEREO spacecraft can be tracked and their arrival time at the other STEREO spacecraft can be successfully predicted. This includes CMEs, such as the events on 4 December 2009 and 9 April 2010, which were viewed 130^° away from their direction of propagation. Therefore, we predict that some Earth-directed CMEs will be observed by the HIs until early 2013, when the separation between Earth and one of the STEREO spacecraft will be similar to the separation of the two STEREO spacecraft in 2009??C?2010.  相似文献