On the asphericity of nova remnants caused by rotating white dwarf envelopes

The effect of rotating white dwarf envelopes in determining the structure of nova shells is examined. This is achieved by numerical hydrodynamic simulations of the flows around a binary star system. In previous studies of remnant formation, this rotation has not been included.
It is found that the structures formed in the flow are more consistent with observations of nova shells than the previous theoretical studies. The shells produced by the nova become more prolate with increasing white dwarf envelope rotation. Hence the rotation of white dwarf envelopes must be included in any future discussion of remnant formation.
A possible method of identifying the dominant process by which mixing of accreted and white dwarf matter takes place is suggested.     

Complex absorption and reflection of a multitemperature cyclotron–bremsstrahlung X-ray cooling shock in BY Cam

We re-analyse the ASCA Ginga X-ray data from BY Cam, a slightly asynchronous magnetic accreting white dwarf. The spectra are strongly affected by complex absorption, which we model as a continuous (power-law) distribution of covering fraction and column of neutral material. This absorption causes a smooth hardening of the spectrum below ∼ 3 keV, and is probably produced by material in the pre-shock column which overlies the X-ray emission region. The ASCA data show that the intrinsic emission from the shock is not consistent with a single-temperature plasma. Significant iron L emission coexisting with iron K shell lines from H- and He-like iron clearly shows that there is a wide range of temperatures present, as expected from a cooling shock structure. The Ginga data provide the best constraints on the maximum temperature emission in the shocked plasma, with kT _max = 21⁺¹⁸₋₄ keV. Cyclotron cooling should also be important; it suppresses the highest temperature bremsstrahlung components, so the X-ray data provide only a lower limit on the mass of the white dwarf of M  ≥ 0.5 M⊙. Reflection of the multitemperature bremsstrahlung emission from the white dwarf surface is also significantly detected.   We stress the importance of modelling all these effects in order to gain a physically self-consistent picture of the X-ray spectra from polars in general and BY Cam in particular.     

Erratum: Spiral structure in the accretion disc of the binary IP Pegasi

The paper 'Spiral structure in the accretion disc of the binary IP Pegasi' was published in Mon. Not. R. Astron. Soc. 290 , L28–L32 (1997). Figs 1 and 2 of the paper (grey-scale images) did not reproduce well, and are reprinted here (Fig. 1 overleaf). Colour versions of the images are available on the World Wide Web:http://www-star.st-and.ac.uk/^∼ds10/spirals.html     

关于气象服务产品消费问题的讨论

在人类即将进入知识经济和信息经济的时代,在经济发展需要进入可持续性发展轨道的宏观背景下,研究气象服务产品的消费具有重大理论与实践意义。气象服务产品的消费极具特殊性,风险性等五方面的性质;其消费主体结构与消费客体结构也极为复杂;气象服务产品的消费成本在气象服务产品消费中具有十分重要的地位,决定消费成本有两个经济量,它是制约消费的基本经济变量。     

The discrete Hurst range for skew independent two-valued inflows

A new theoretical interpretation is proposed for Hurst's empirical law which is applicable to discrete-valued inflows and is consistent with the existing interpretation for continuous-valued inflows. This is applied to independent net inflows {X _r} having values +1 and –1 with unequal probabilities. With the aid of a new result on the exchangeability of symmetrically conditioned exchangeable variables, values of the resulting range are obtained and tabulated. It is found that the effect of skewness is very slight for skewness values between (about) 3 and –3, and that Hurst's own approximation, the conditioned range, is remarkably accurate.     

Keplerian expansions in terms of Henrard's practical variables

Formulae for the Keplerian expansions in terms of Henrard's practical variables are given. Two different methods were applied: one using the Bessel functions and one based on the Lie transforms. The former involves less series products, but the latter is more flexible and universal.     

沉积模型和储层随机建模

沉积模型是地层分析的重要工具，可以分为比例尺模型、概念模型和数学模型三大类型，其中数学模型又可分为确定性模型和随机模型。在实际地层分析及模拟工作中，特别是在小尺度问题的研究中，采用随机模型(或称统计学模型)往往更为有利。储层随机建模技术，作为这方面研究的典范，近年来成为储层预测和风险评价的一项较为有效的手段。然而，由于研究目标的复杂性，不同沉积模型之间的嵌套制约关系亦应引起重视。     

主成分-逐步回归在滑坡稳定性分析中的应用

多元回归分析是概率统计理论滑坡稳定性研究中的一种重要应用。然而,一般多元回归方法存在局限性,本文引入主成分-逐步回归模型,既尽可能全面考虑到各影响因素,又能解决因素之间多重相关性可能带来的误差。在理论探讨的基础上,本文结合巴东县赵树岭滑坡研究进行了工程实例分析。     

三维地质建模及其工程应用

本文从三维地质建模的概念出发，探讨了其一般过程，包括地质变量预测、地质特征解译、空间分析等，并介绍了三维地质建模的体视化方法，最后以润扬长江公路大桥工程为例，运用切征级重建方法，建立地质模型，并进行了三维地质的分析。实践表明，三维地质建模技术是认识复杂地质体的空间关系和特征的强有力的工具，具有广阔的应用前景。