Infrared spectrum and structural role of titanium in synthetic Ti-garnets     

P. Tarte  R. Cahay  A. Garcia 《Physics and Chemistry of Minerals》1979,4(1):55-63

Ti-spessartite, Ti-andradite and its indium homolog, Ca₃In₂(Si, Ti)₃O₁₂, have been synthesized and investigated by infrared (ir) spectroscopy. The use of isotopic species (⁴⁶Ti-⁵⁰Ti) gives the unequivocal proof that some of the additional bands observed in the 800–600 cm^?1 region are due to TiO₄ tetrahedra. For Si-Ti replacements up to 10 mol%, the localization of Ti on the available tetrahedral sites depends on the nature of the cations. For the In garnet all (or nearly all) Ti is located on tetrahedral sites; in Ti-andradite Ti is distributed over tetrahedral and octahedral sites, tetrahedral sites being thus occupied, in part by Ti (ir band near 700 cm^?1) and in part by Fe (ir band near 650 cm^?1); and Ti-spessartite the presence of Ti on tetrahedral sites is doubtful, these sites being essentially occupied by Al.  相似文献   

Twist transport in strongly torsioned astrophysical flux tubes     

L. C. Garcia de Andrade 《Astrophysics and Space Science》2007,310(1-2):25-29

Riemannian geometrical effects on the expansion of the electron magnetohydrodynamical (EMH) superconductivity modeled twisted nonplanar thin magnetic flux tubes are considered. A solution is found which represents almost incompressible plasma flows, where the twist of flux tube is computed in terms of the continuous variation of its cross-section. It is shown that the twist increases in regions where twisted flux tube expands as in Parker’s conjecture. From computation of compression along the tube we show that when the torsion is weak a centrifugal or vorticity effect on the longitudinal direction of the tube enhances the screening effect on the “superconductor”. Throughout the paper we consider helical flux tubes where torsion and curvature of the tube are constants. Thus we show that the Parker’s conjecture is valid in a continuos manner for these type II superconducting twisted flux tubes. Throughout the paper we adopt the approximation that the radial component of the magnetic field varies so slowly along the tube axis that it can be approximated to zero along the tube. It is suggested that the models discussed here may also be applied to DNA and nanotubes.  相似文献   

WSO and the winds of massive stars: the gate to the metal-poor Local Universe     

Miriam Garcia  Artemio Herrero  Francisco Najarro 《Astrophysics and Space Science》2011,335(1):91-96

The spectrographs on-board the World Space Observatory (WSO) will provide access to the 1020–1800 Å wavelength range with unprecedented sensitivity. Previous observatories operating in the 1150–2000 Å range (such as IUE and HST-STIS) have proved extremely useful to study the winds of OB type stars, which leave their most prominent imprints in the far ultraviolet range. The addition of the λ < 1200 Å wavelengths is critical as it contains important diagnostic lines for mass loss and shocks in the wind, as found by FUSE-based analyses.WSO will enable quantitative spectroscopic analyses of blue massive stars in the Local Group beyond the Magellanic Clouds. The results will lead to the characterization of their winds as a function of metallicity, and shed new light on current urging questions regarding radiation driven winds.  相似文献   

Geochronology and paleoenvironment of pluvial Harper Lake,Mojave Desert,California, USA     

Anna L. Garcia  Jeffrey R. Knott  Shannon A. Mahan  Jordon Bright 《Quaternary Research》2014

Accurate reconstruction of the paleo-Mojave River and pluvial lake (Harper, Manix, Cronese, and Mojave) system of southern California is critical to understanding paleoclimate and the North American polar jet stream position over the last 500 ka. Previous studies inferred a polar jet stream south of 35°N at 18 ka and at ~ 40°N at 17–14 ka. Highstand sediments of Harper Lake, the upstream-most pluvial lake along the Mojave River, have yielded uncalibrated radiocarbon ages ranging from 24,000 to > 30,000 ¹⁴C yr BP. Based on geologic mapping, radiocarbon and optically stimulated luminescence dating, we infer a ~ 45–40 ka age for the Harper Lake highstand sediments. Combining the Harper Lake highstand with other Great Basin pluvial lake/spring and marine climate records, we infer that the North American polar jet stream was south of 35°N about 45–40 ka, but shifted to 40°N by ~ 35 ka. Ostracodes (Limnocythere ceriotuberosa) from Harper Lake highstand sediments are consistent with an alkaline lake environment that received seasonal inflow from the Mojave River, thus confirming the lake was fed by the Mojave River. The ~ 45–40 ka highstand at Harper Lake coincides with a shallowing interval at downstream Lake Manix.  相似文献   

Optical and X-ray observations of the neutron star soft X-ray transient XTE J1709–267     

P. G. Jonker †  D. K. Galloway  J. E. McClintock  M. Buxton  M. Garcia  S. Murray 《Monthly notices of the Royal Astronomical Society》2004,354(3):666-674

  相似文献   

Calculating the long-term displacement rates of a normal fault from the high-resolution stratigraphic record (early Tethyan rifting, French Alps)     

F. Chevalier  M. Guiraud  J.-P. Garcia  J.-L. Dommergues  D. Quesne  P. Allemand  T. Dumont 《地学学报》2003,15(6):410-416

Displacement rates of normal faults deduced from stratigraphic data are often unreliable. Here we calculate the velocity of motion on a normal fault from the variations in accommodation potential on both sides of the fault within a high‐resolution time‐frame established by biostratigraphy and physical stratigraphy. Our example is the Ornon normal fault bounding the Early Jurassic Bourg‐d'Oisans Basin formed during Tethyan rifting. We show that motion on the fault was discontinuous when examined at high resolution and over a long time interval. During a first interval (Hettangian to Sinemurian Arietites bucklandi zone) a low rate of displacement (=202–423 m Myr^?1) coeval with diffused extensional deformation throughout the sedimentary basin is observed. A second interval of localized deformation (Early Sinemurian Caenisites turneri zone) is characterized by higher rates of displacement on the fault (1846 m Myr^?1). Our results concur with recent numerical models identifying the main stages of extensional deformation.  相似文献   

A progress report on the design of the 8 m aperture Optical/Infrared Telescope     

B. Mack  D. Harman  S. Atkinson  C. Garcia 《Astrophysics and Space Science》1989,160(1-2):111-118

Progress of the design study carried out y the Instituto de Astrophysica de Canarias and Royal Greenwich Observatory joint project office for an 8 m aperture Optical/Infrared Telescope. This includes the development of an active pneumatic support system for both the radial and axial supports of an 8 m diameter thin meniscus mirror and the investigations of new technology encoding systems.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.  相似文献   

Changes in magma composition at Arenal volcano,Costa Rica, 1965–1985: Real-time monitoring of open-system differentiation     

Mark K. Reagan  James B. Gill  Eduardo Malavassi  Michael O. Garcia 《Bulletin of Volcanology》1987,49(5):708-708

  相似文献   

A numerical response of the middle atmosphere to the 11-year solar cycle     

Rolando R. Garcia  Susan Solomon  Raymond G. Roble  David W. Rusch 《Planetary and Space Science》1984,32(4):411-423

A two-dimensional numerical model with coupled photochemistry and dynamics has been used to investigate the response of the middle atmosphere (16–116 km) to changes in solar activity over the 11-year solar cycle. Model inputs that vary with solar cycle include solar radiation, cosmic ray and auroral ionization rates and the flux of NO_x at the model's upper boundary.In this study, the results of model runs for solar cycle minimum and maximum conditions are compared. In the stratosphere, using currently accepted estimates of changes in solar radiation at wavelengths longer than 180 nm, only small responses in ozone, temperature and zonal winds are obtained. On the other hand, changes at shorter wavelengths, and the effects of particle precipitation, lead to large variations in the abundances of trace species in the thermosphere and upper mesosphere. In particular, very large abundances of NO_x are produced above 90 km by auroral particle precipitation. Considerable amounts of NO_x are transported subsequently to the stratosphere by the global mean meridional circulation. It is shown that this excess NO_x can lead to significant decreases in ozone concentrations at high latitudes and that it may explain observations of nitrate deposition in Antarctic snow.  相似文献   

Determination of the onset dates of the rainy season in central Amazon with equatorially antisymmetric outgoing longwave radiation     

Sâmia R. Garcia  Mary T. Kayano 《Theoretical and Applied Climatology》2009,97(3-4):361-372

The present work provides a new methodology to determine onset dates of the rainy season (ONR) in central Amazon (CAM) using the antisymmetric in relation to the equator outgoing longwave radiation (OLR) (AOLR) data, for the 1979–2006 period. Spatial averages of the AOLR ( $\overline {AOLR} $ ) over the CAM for the ONR periods are obtained. These periods correspond to 25 pentads centered on the mean pentad for the ONR. The sign changes from positive to negative of the $\overline {AOLR} $ for the ONR periods indicate the transition from dry to wet season. Composites of several variables are done for pentads before and after the ONR dates. These composites show physically consistent features. The potential of the $\overline {AOLR} $ time series as an index for monitoring tasks is analyzed. The results here show that the $\overline {AOLR} $ for the ONR period captures the transition from dry to wet conditions in the CAM area during 2006. The advantages of this method are discussed. The new simple method proposed here seems to be efficient in determining the ONR in the CAM.  相似文献