Post-Common-Envelope Binaries with Distorted Secondaries     

Adela Kawka  Stéphane Vennes 《Astrophysics and Space Science》2005,296(1-4):481-484

We will examine the properties of binary systems which have Roche lobe filling secondaries and white dwarf primaries as well as systems where the secondary is only partially filling its Roche lobe. We will also discuss observational properties such as ellipsoidal variations, light reprocessing and radial velocity measurements of the close binary systems BPM 71214, EC 13471-1258 and GD 245. The properties of BPM 71214 and EC 13471-1258 show that these systems may be pre-cataclysmic variables just prior to the onset of mass transfer or they may be hibernating novae. GD 245 is a pre-cataclysmic variable.  相似文献   

Evaluation of Inference Adequacy in Cumulative Logistic Regression Models: An Empirical Validation of ISW Ridge Relationships     

Hsien-Chueh Peter YANG  Alex Kung-Hsiung CHANG  Tsung-Hao CHEN 《海洋工程》2008,(1)

Internal solitary wave propagation over a submarine ridge results in energy dissipation, in which the hydrodynamic interaction between a wave and ridge affects marine environment. This study analyzes the effects of ridge height and potential energy during wave-ridge interaction with a binary and cumulative logistic regression model. In testing the Global Null Hypothesis, all values are p＜0.001, with three statistical methods, such as Likelihood Ratio, Score, and Wald. While comparing with two kinds of models, tests values obtained by cumulative logistic regression models are better than those by binary logistic regression models. Although this study employed cumulative logistic regression model, three probability functions 1, 2 and 3, are utilized for investigating the weighted influence of factors on wave reflection. Deviance and Pearson tests are applied to check the goodness-of-fit of the proposed model. The analytical results demonstrated that both ridge height (X1) and potential energy (X2) significantly impact (p＜0.0001) the amplitude-based reflected rate; the P-values for the deviance and Pearson are all ＞0.05 (0.2839, 0.3438, respectively). That is, the goodness-of-fit between ridge height (X1) and potential energy (X2) can further predict parameters under the scenario of the best parsimonious model.Investigation of 6 predictive powers (R2, Max-rescaled R2, Somers''D, Gamma, Tau-a, and c, respectively) indicate that these predictive estimates of the proposed model have better predictive ability than ridge height alone, and are very similar to the interaction of ridge height and potential energy. It can be concluded that the goodness-of-fit and prediction ability of the cumulative logistic regression model are better than that of the binary logistic regression model.  相似文献   

基于MATLAB的边缘检测算法研究     

田梦娜  徐泮林  丁鹏文 《测绘与空间地理信息》2020,(2):197-199,203,207

边缘检测是处理与剖析图像的主要内容之一,它在文字识别、车牌识别、遥感特征地物的提取等生产和生活领域发挥着非常重要的作用。但是,不同的图像有着不同的特征,到目前为止,没有一种统一的方法对所有的图像及地物的特征进行边缘检测。针对这一不足,本文首先探讨了4种经典的二值化算法和相应的改进二值化算法,并将经典算法与改进后的算法进行对比分析,然后利用Canny算子对二值化处理后的图像进行边缘检测。得出结论,迭代法和改进的迭代法与Canny算子相结合作为边缘检测的方法是一种高效率、高精度的方法。  相似文献   

胜利矿区植被覆盖度时序变化的空间异质性监测   总被引：1，自引：0，他引：1  

王科雯  李晶  王瑞国  付晓 《测绘通报》2020,(11):1-6

通过对胜利矿区的地理位置、气候条件等背景的分析，本文为实现获取时序性植被覆盖度的空间异质性的目的，使用ENVI、GIS、Matlab等软件，基于胜利矿区1985—2017年的Landsat TM/ETM+/OLI遥感数据计算NDVI，利用像元二分模型计算植被覆盖度，得到研究区植被覆盖度均值的时序变化情况。采用转移矩阵法和Sen+Mann-Kendall法对研究区域内不同等级的植被覆盖转移情况及变化趋势情况进行分析。研究表明：胜利矿区植被覆盖度均值波动较大，呈轻微下降趋势。在监测时段内68.36%的高植被覆盖区域植被发生了退化，只有3.2%左右的极低植被覆盖区域得到了良好的改善。此外，研究区植被覆盖度受到结构性因子和随机性因子的影响，空间异质性明显，灌溉区由于人为干涉，植被生长良好，极低植被覆盖面积维持在3%以下，植被覆盖显著下降区域主要集中在露天采坑、排土场等矿业景观区。  相似文献   

珠江三角洲台风龙卷的活动特征及环境条件分析     

黄先香  俞小鼎  炎利军  李彩玲  李兆明 《气象》2019,45(6):777-790

利用常规观测、自动气象站、多普勒雷达等资料分析珠江三角洲台风龙卷的活动特征及其产生的环境条件。结果表明:台风龙卷发生在6—10月,时间多为10—20时,出现在台风登陆后1.3～21.3 h的时段内;多数龙卷位于台风中心的东北象限,台风中心在广东湛江一广西东南部或北部湾附近时是珠江三角洲龙卷发生的高风险期。高层辐散、低层辐合及中低空强东南急流在珠江口附近叠加是龙卷产生的有利环流背景。强或弱龙卷环境条件的共同特征为低抬升凝结高度、强深层和低层垂直风切变及较大风暴相对螺旋度(SRH),主要差异是强龙卷的深层和低层垂直风切变与SRH更大;相似台风路径下,有/无龙卷环境条件的明显差异在于0～1 km低层垂直风切变和SRH,两值越大出现超级单体或中气旋的可能性越大,龙卷发生概率也就越高。台风龙卷风暴母体属于低质心的微型超级单体风暴;低层有强或中等强度中气旋,有时强中气旋中心伴有龙卷涡旋特征(TVS);龙卷出现在钩状回波顶端或TVS附近。与西风带超级单体龙卷相比,台风龙卷中气旋的尺度更小、垂直伸展高度更低。  相似文献   

Low mass stellar companions around four giant stars     

《New Astronomy》2015

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The Restricted Three-Body Problem: Comments on the Rotational Effect     

Rodica Roman  Sorin Adrian Roman 《Astrophysics and Space Science》2006,301(1-4):179-184

The synchronization between the orbital motion and axial rotation of the two component stars of a binary system is reviewed. Some previous published papers are mentioned and the general conclusion is outlined: If we shall use a rotating coordinate system synchronous with one of the two stellar axial rotations, it is not possible to obtain a Jacobi integral and the Roche geometry cannot be further analyzed. In addition, a theoretical approach is summarized in order to use the axial rotations of the two component stars, even if the constants of the stellar structure (k₂)₁, (k₂)₂must be taken into consideration. So it is found that if the stellar angular velocities are higher than the corresponding Keplerian angular velocity (ω_i≫ ω_k, i= ), the problem of the rotational effect could be of practical consideration. Finally, a theoretical relationship between the two constants (k₂)₁and (k₂)₂of the stellar structure is established.  相似文献   

一个β中涡对双台风相互作用影响的物理过程     

代刊  罗哲贤  滕代高 《南京气象学院学报》2008,31(4):494-502

利用高分辨率f平面正压拟谱模式,分析一个β中尺度涡对双台风相互作用影响的物理过程。结果表明：β中涡的存在可以使原本排斥的两个DeMaria型台风涡旋合并;β中涡改变双台风相互作用终态的物理机制是：初始时段处于某一台风涡旋正影响区内的β中涡,构成了非对称涡度场,进而在该台风涡旋内部产生指向另一个台风涡旋的气流。该气流如果足够强,则会使两个台风的中心距离在短时间内下降到合并临界距离之内,触发双涡合并过程的发生。  相似文献   

台风登陆前后雨带断裂与非对称降水的成因分析   总被引：5，自引：1，他引：4  

丁治英  王勇  沈新勇  徐海明 《热带气象学报》2009,25(5):513-520

利用美国WRF(Weather Research Forecast)模式对“海棠”台风(0505)登陆前后的雨带变化进行分析和模拟试验。结果显示：台风登陆前后其雨带会产生断裂,这种现象可发生在陆地和海上,使非对称降水更加明显。分析得出雨带断裂不仅与地形有关,而且与高层台风环流和中纬度系统的相互作用有关：台风登陆前后,200 hPa南亚高压和台风外围的辐散气流结合形成在台风西北方向的弱倒槽,台风中心西侧及西北侧的中低层辐散流场稳定维持,使高层气旋性流场加强,与气旋性流场相伴的正涡度一部分随气流逆时针旋转,并逐步平流至台风中心附近的正涡度区形成一个沿22～25 °N的正涡度输送带并延伸至台风中心东部,而中心东部高层的正涡度带中有下沉运动,不利于降水发展而导致雨带断裂是非对称降水的主要原因。高层台风的带状涡度向外围的传播可导致中纬度气旋性环流的进一步加强和正涡度向台风输送的加强,使雨带断裂更加明显。  相似文献   

A comparison of variational formats for porous media subjected to dynamic loading     

B. Lenhof  F. Larsson  K. Runesson 《国际地质力学数值与分析法杂志》2011,35(7):807-823

This paper presents a comparison of two variational formats for fully saturated porous media subjected to dynamic loading, whereby the general situation of relative fluid acceleration is considered: (1) the classical three‐field ( u , p, w )‐format and (2) a novel two‐field ( u , p)‐format, where the seepage velocity w is a spatially ‘local’ field whose treatment resembles that of internal variables in material models. The limited numerical comparison shows that the ( u , p)‐format competes well with the ( u , p, w )‐format. Indeed, it is consistent with the general acceleration modeling in the full range of permeabilities. Moreover, in the low permeability regime (where the magnitude of w is insignificant), the new format reflects the situation pertinent to ‘added‐mass’ and is more efficient than the classical ( u , p, w )‐format. Finally, the ( u , p)‐formatcan conveniently be implemented in existing FE‐codes based on the ‘added mass’ formulation. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献