Chemical abundances from B-stars in the Magellanic Clouds     

A. Reitermann  O. Stahl  B. Wolf  B. Baschek 《Astrophysics and Space Science》1989,156(1-2):113-117

We observed near-Main-Sequence B-stars in the Magellanic Clouds with the 3.6 m telescope and CASPEC at La Silla. We obtained spectra of high resolution and high S/N-ratio. The stars are members of the blue globular clusters NGC 1818 (LMC) and NGC 330 (SMC). The spectra are used for differential abundance analyses using HER as galactic reference star. Apart from CNO the metals are underabundant by about a factor of three and four for the LMC and SMC star, respectively. The CNO pattern is interesting since in both stars oxygen is considerably more abundant than carbon.Based on observations collected at ESO, La Silla and on Calar Alto, Spain and on observations made with the International Ultraviolet Explorer.  相似文献   

GPS observations of the ionospheric F2-layer behavior during the 20th November 2003 geomagnetic storm over South Korea   总被引：4，自引：1，他引：3  

Shuanggen Jin  O. F. Luo  P. Park 《Journal of Geodesy》2008,82(12):883-892

The ionospheric F2-layer peak density (NmF2) and its height (hmF2) are of great influence on the shape of the ionospheric electron density profile Ne (h) and may be indicative of other physical processes within the ionosphere, especially those due to geomagnetic storms. Such parameters are often estimated using models such as the semiempirical international reference ionosphere (IRI) models or are measured using moderately priced to expensive instrumentation, such as ionosondes or incoherent scatter radars. Global positioning system (GPS) observations have become a powerful tool for mapping high-resolution ionospheric structures, which can be used to study the ionospheric response to geomagnetic storms. In this paper, we describe how 3-D ionospheric electron density profiles were produced from data of the dense permanent Korean GPS network using the tomography reconstruction technique. These profiles are verified by independent ionosonde data. The responses of GPS-derived parameters at the ionospheric F2-layer to the 20th November 2003 geomagnetic storm over South Korea are investigated. A fairly large increase in the electron density at the F2-layer peak (the NmF2) (positive storm) has been observed during this storm, which is accompanied by a significant uplift in the height of the F2 layer peak (the hmF2). This is confirmed by independent ionosonde observations. We suggest that the F2-layer peak height uplift and NmF2 increase are mainly associated with a strong eastward electric field, and are not associated with the increase of the O/N₂ ratio obtained from the GUVI instruments aboard the TIMED satellite. It is also inferred that the increase in NmF2 is not caused by the changes in neutral composition, but is related to other nonchemical effects, such as dynamical changes of vertical ion motions induced by winds and E × B drifts, tides and waves in the mesosphere/lower thermosphere region, which can be dynamically coupled upward to generate ionospheric perturbations and oscillations.  相似文献   

Spin rate estimation of sounding rockets using GPS wind-up   总被引：2，自引：1，他引：1  

M. García-Fernández  M. Markgraf  O. Montenbruck 《GPS Solutions》2008,12(3):155-161

Carrier phase wind-up is a well-known effect that arises from the relative rotation between a transmitting and receiving antenna. In GPS measurements at L1 frequency, this effect translates into an error of 19.029 cm per full relative rotation of antennas. Since this effect is independent of the satellite elevation for pure rotation about the antenna boresight axis, it is usually absorbed by the clock estimation in navigation algorithms. Therefore, the impact of wind-up is usually neglected for applications that do not require accuracies to the cm level like RTK. However, in receiving platforms with high rotation rate, the accumulated wind-up value can be important and actually be larger than receiver noise or even ionospheric variations. Therefore, in such scenarios, the wind-up contribution can be isolated and used as a source of information to compute the spin rate of such platforms using an appropriate combination of GPS observables. This work shows some results of a coarse, yet simple, approach to monitor the rotation angle and spin-rate of spin stabilized sounding rockets flown by DLR.  相似文献   

老松公路延吉段K64+300～K64+900边坡稳定性评价及治理措施     

佴磊  刘建磊  周能娟  沈世伟  丁黄平 《世界地质》2008,27(4)

对老松公路10标边坡开挖后的稳定性分析表明,地表及地下水是影响其稳定性的重要因素,排水不畅使边坡体饱水处于欠安全状态,稳定性难以保证.针对该边坡体的特点,采用了支撑盲沟和排水盲沟联合作用并结合坡面防护的处治措施,疏干坡体内地表及地下水,增大抗滑力,达到了提高边坡稳定性,保护生态环境,美化公路的目的.  相似文献   

A bootstrap based space–time surveillance model with an application to crime occurrences     

Youngho Kim  Morton O’Kelly 《Journal of Geographical Systems》2008,10(2):141-165

This study proposes a bootstrap-based space–time surveillance model. Designed to find emerging hotspots in near-real time, the bootstrap based model is characterized by its use of past occurrence information and bootstrap permutations. Many existing space–time surveillance methods, using population at risk data to generate expected values, have resulting hotspots bounded by administrative area units and are of limited use for near-real time applications because of the population data needed. However, this study generates expected values for local hotspots from past occurrences rather than population at risk. Also, bootstrap permutations of previous occurrences are used for significant tests. Consequently, the bootstrap-based model, without the requirement of population at risk data, (1) is free from administrative area restriction, (2) enables more frequent surveillance for continuously updated registry database, and (3) is readily applicable to criminology and epidemiology surveillance. The bootstrap-based model performs better for space–time surveillance than the space–time scan statistic. This is shown by means of simulations and an application to residential crime occurrences in Columbus, OH, year 2000.  相似文献   

A Microwave Tomographic Approach for Nondestructive Testing of Dielectric Coated Metallic Surfaces     

Mudanyal  O. Yldz  S. Semerci  O. Yapar  A. Akduman  I. 《Geoscience and Remote Sensing Letters, IEEE》2008,5(2):180-184

A microwave imaging method for nondestructive testing of perfectly conducting surfaces beyond a layered media is presented. The method is an adaptation of the surface reconstruction approach by Yapar et al. to the present problem. It is based on the analytical continuation of the measured data to the surface under test through a special representation of the scattered field in terms of Fourier transform and Taylor expansion. Then the problem is reduced to the solution of a nonlinear equation which is solved iteratively via the Newton method and regularization in the least squares sense. Numerical simulations show that defects as small as lambda/500 can be recovered through the presented algorithm.  相似文献   

Geochemical and Sm-Nd isotopic characteristics of the Neoproterozoic terrigenous rocks of the Tuva-Mongolian Massif     

S. V. Veshcheva  O. M. Turkina  E. F. Letnikova  Yu. L. Ronkin 《Doklady Earth Sciences》2008,418(1):155-160

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Correlation of neoproterozoic volcanism in the southeastern White Sea region and western Urals: New age data on the Solozero basalts (Onega Graben)     

A. A. Nosova  Yu. O. Larionova  N. V. Veretennikov  E. V. Yutkina 《Doklady Earth Sciences》2008,419(2):303-307

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Isotopic parameters of meteoric waters in fractured porous rocks of the Tulukuev ore deposit     

E. O. Dubinina  V. A. Petrov  V. N. Golubev 《Doklady Earth Sciences》2008,421(2):914-918

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Genetic approach to the resolution of gemological problems of quartz and its colored varieties     

O. V. Balitskaya 《Doklady Earth Sciences》2008,421(2):992-994

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