Mid-ultraviolet and optical photometry of helium stars     

Gopal C. Kilambi  Praveen Nagar  N. Kameswara Rao 《Journal of Astrophysics and Astronomy》1992,13(2):175-194

Mid-ultraviolet and optical photometric analysis of helium stars are presented. A linear relation exists between the effective temperature derived from model atmospheres and (1965-V)₀ index. The effective temperatures derived from (1965-V)₀ index are somewhat higher than that of MK spectral type estimates especially for late B-type helium objects.  相似文献   

Flickering in the Magnetic Cv Star Am Herculis     

Belinda Kalomeni  E. Rennan PekÜnlÜ  Kadri Yakut 《Astrophysics and Space Science》2005,296(1-4):477-480

In this study, we present a photometric study of AM Her, a prototype of a class of magnetic CVs. Optical photometry of AM Her was obtained using the Russian–Turkish 1.5 m telescope at TüBİTAK National Observatory (TUG) in August 2003. The R band light curve of the system shows two maxima and two minima during one orbital cycle. In both observing nights the star showed flickering at a significant level. The measured flickering time scale is about 5 min.  相似文献   

Geo-effectiveness of solar wind extremes     

Hari Om Vats 《Journal of Astrophysics and Astronomy》2006,27(2-3):227-235

Examples of extreme events of solar wind and their effect on geomagnetic conditions are discussed here. It is found that there are two regimes of high speed solar wind streams with a threshold of ∼ 850 km s^-1. Geomagnetic activity enhancement rate (GAER) is defined as an average increase in Ap value per unit average increase in the peak solar wind velocity (Vp) during the stream. GAER was found to be different in the two regimes of high speed streams with +ve and-ve IMF. GAER is 0.73 and 0.53 for solar wind streams with +ve and -ve IMF respectively for the extremely high speed streams (< 850 km s^-1). This indicates that streams above the threshold speed with +ve IMF are 1.4 times more effective in enhancing geomagnetic activity than those with -ve IMF. However, the high speed streams below the threshold with -ve IMF are 1.1 times more effective in enhancing geomagnetic activity than those with +ve IMF. The violent solar activity period (October–November 2003) of cycle 23 presents a very special case during which many severe and strong effects were seen in the environment of the Earth and other planets; however, the z-component of IMF (Bz) is mostly positive during this period. The most severe geomagnetic storm of this cycle occurred when Bz was positive.  相似文献   

Sensitivity analysis of a deterministic water temperature model to forest canopy and soil temperature in Catamaran Brook (New Brunswick,Canada)     

Andr St‐Hilaire  Nassir El‐Jabi  Daniel Caissie  Guy Morin 《水文研究》2003,17(10):2033-2047

A coupled deterministic hydrological and water temperature model, CEQUEAU, was modified to include soil temperature and crown closure in its calculation of local advective terms in the heat budget. The modified model was than tested to verify its sensitivity to these modifications. An analysis of the heat budget of a small forested catchment in eastern Canada revealed that the advective term related to interflow plays a significant role in the daily water heat budget, providing on average 28% of the local advective budget (which also includes advective heat terms from surface runoff and groundwater) and nearly 14% of the total heat budget (which includes all radiative terms at the water surface, convection and evaporation, as well as the local advective terms). Relative sensitivity indices (RSIs) were used to verify the impact of the newly introduced parameters and variables. Among them, parameters related to the forest cover (crown closure and leaf area index) have a maximum RSI of ?0·6; i.e. a 100% increase in value produces a 60% decrease in the local advective term. Parameters with the greatest influence are the volume of water contributing to interflow and the amplitude of the net radiative flux at the soil surface, which, if doubled, would double the contribution of the local interflow advective term to the heat budget. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Modelling the effect of low soil temperatures on transpiration by Scots pine     

Per‐Erik Mellander  Manfred Sthli  David Gustafsson  Kevin Bishop 《水文研究》2006,20(9):1929-1944

For ecosystem modelling of the Boreal forest it is important to include processes associated with low soil temperature during spring‐early summer, as these affect the tree water uptake. The COUP model, a physically based SVAT model, was tested with 2 years of soil and snow physical measurements and sap flow measurements in a 70‐year‐old Scots pine stand in the boreal zone of northern Sweden. During the first year the extent and duration of soil frost was manipulated in the field. The model was successful in reproducing the timing of the soil warming after the snowmelt and frost thaw. A delayed soil warming, into the growing season, severely reduced the transpiration. We demonstrated the potential for considerable overestimation of transpiration by the model if the reduction of the trees' capacity to transpire due to low soil temperatures is not taken into account. We also demonstrated that the accumulated effect of aboveground conditions could be included when simulating the relationship between soil temperature and tree water uptake. This improved the estimated transpiration for the control plot and when soil warming was delayed into the growing season. The study illustrates the need of including antecedent conditions on root growth in the model in order to catch these effects on transpiration. The COUP model is a promising tool for predicting transpiration in high‐latitude stands. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Tests and constraints on theories of galaxy formation and evolution     

Rodger I. Thompson 《Astrophysics and Space Science》2003,284(2):353-356

Tests and constraints on current theories of galaxy formation and evolution are presented. They are derived from observations of the Northern Hubble Deep Field with WFPC2 and NICMOS. Photometric redshifts, extinctions and spectral energy distributions are calculated for all objects in the field. The tests and constraints are derived from the output of this analysis. The tests of the predictions from hierarchical and pure luminosity evolution galaxy evolution calculations favor the hierarchical model. Constraints are provided by the current luminosity function and its evolution to a redshift of 6. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

海拉尔盆地乌尔逊凹陷古流体动力场数值模拟   总被引：5，自引：0，他引：5  

杨金侠 《地球科学与环境学报》2003,25(3):41-47

首先对地下水动力场进行数学描述,以水动力为主线,建立适合该地区的数学模型,选择正确的地质模型参数,主要采用数值计算和模拟等手段,在恢复出乌尔逊凹陷主要目的层在不同地质历史时期古水动力的基础上又恢复出古流体势的演化历史。整体上,在乌尔逊凹陷,各主要地质时期的油势演化特征为西部地区大于东部地区,乌南大于乌北,且低势区的发育有较好的继承性。最后,依据油气聚集理论,进行油气运移聚集系统的划分、油气运移方向的分析,从而得出有关研究区油气运移聚集条件的认识,主要从流体动力的角度考虑,指出有利聚集区,认为在乌尔逊凹陷苏4～苏18井区、苏132～苏17～铜2井区及巴1～巴2～巴4井区为有利油气运移聚集区。  相似文献   

RELAXING ASSUMPTIONS OF PERFECT INFORMATION IN PARK VISITATION MODELS*     

Daniel J. Stynes  Daniel M. Spotts  John R. Strunk 《The Professional geographer》1985,37(1):21-28

Variables related to urban park awareness are identified and methods for relaxing assumptions of perfect information in park use models are discussed. Park awareness is related to park characteristics (age and degree of development of the park), population characteristics (race, age, length of residence, recreation participation), and distance. Park attributes are stronger predictors of both park awareness and use than is distance. These findings parallel similar research on the cognitive aspects of shopping decisions.  相似文献   

时空概念中的椭球改正     

夏哲仁 《测绘学报》1991,20(3):190-200

  相似文献   

广西大厂拉么锌铜多金属矿床成岩成矿作用年代学研究   总被引：20，自引：1，他引：19  

李华芹  王登红  梅玉萍  梁婷  陈振宇  郭春丽  应立娟 《地质学报》2008,82(7):912-2008-01-30

本文对广西大厂矿田拉么矿区内出露的酸性侵入岩和矿石进行了精细的年代学研究,分别获得龙箱盖含斑黑云母花岗岩锆石原位SHRIMP UPb和全岩RbSr等时线年龄为94±4Ma（95%可信度）和98.6±1.9Ma（95%可信度）,矽卡岩成矿期锌铜矿石中石英矿物RbSr等时线年龄为98.6±6Ma（95%可信度）。上述测定结果表明,拉么锌铜多金属矿床的成矿年龄与相关岩体的成岩年龄接近,均形成于早白垩世晚期。  相似文献