潮湿的沙子有助于埃及人建筑金字塔吗?

建筑古埃及金字塔的人可能向沙漠的沙子中注水,以便于拖动巨大的雪橇。德国科学家Christian Wagner和他在荷兰、伊朗及法国的同事们,通过研究不同种类的沙中摩擦力与水的含量之间的关系得到了上述结论。他们发现,埃及沙漠中的沙子在弄湿后变得特别滑溜,这一现象可能被用来搬运建筑金字塔的巨石。     

A comparison of coal supply-demand in China and in the US based on a network model

Through analysis the actual coal supply and demand in the US and China, the properties of the coal supply-demand market in both countries are investigated based on the energy supply-demand network. The validity of our model is verified by comparing numerical results with empirical results. The comparison of empirical results and the comparison of coal network model parameters between in the US and in China reveal the essence of the internal differences and similarities of coal supply and demand in these two countries. The third stage of China＇s coal network was close to that of the US in 1995, indicating that the evolutional situation of China＇s coal market begins to transit to an oligopolistic type. Finally, suggestions for China＇s coal supply-demand strategy are put forward.     

Intercombination transitions of the carbon-like isoelectronic sequence

Energy levels, wavelengths, transition rates, oscillator strengths, and lifetimes between the 2s22p23P1,2s22p23P2,and 2s2p35S2 levels of ions in the carbon-like (C-like) isoelectronic sequence (nuclear charges Z=7-92) are calculated in the valence and core-valence limits using the multiconfiguration Dirac-Fock method. The Breit interaction, quantum electrodynamics (QED), and finite nuclear mass effects are taken into account in subsequent relativistic configuration-interaction calculations. The calculated energies and transition rates are compared with the critically evaluated experimental values and other recent calculated results. Our calculated data are in good agreement with these data.     

非线性随机积分和微分方程组的解*

在本文中我们首先对具有随机定义域的连续随机算子组证明了Darbao型不动点定理。应用此定理我们给出了非线性随机Volterra积分方程组和非线性随机微分方程组的Cauchy问题解的存在性准则。这些随机方程组的极值随机解的存在性和随机比较结果也被获得。我们的定理改进和推广Tyaughn,Lakshmikantham,Lakshmikantham-Leela,DeBlast-Myjak和第一作者的相应结果。     

An Efficient and Accurate Spectral Method for Acoustic Scattering in Elliptic Domains

An efficient and accurate method for solving the two-dimensional Helmhokz equation in domains exterior to elongated obstacles is developed in this paper. The method is based on the so called transformed field expansion (TFE) coupled with a spectral-Galerkin solver for elliptical domain using Mathieu functions. Numerical results are presented to show the accuracy and stability of the proposed method.     

A GENERALIZATION OF GLOBALLY TOPOLOGICAL LINEARIZATION THEOREM

In this paper, the globally topological linearization theorem of a certain system is given which generalizes the known result.     

测量液体密度的二种新方法

本文介绍二种新型液体密度的传感器原理、测量方法、实验结果以及它们在化学实验、化工与医药工业中自动化检测密度方面的应用。     

A One-Dimensional Method for Calculating the Exit Wavefunction

We develop the multi-slice method for calculating wavefunction of a crystal consisting of atomic columns. The new method reduces numerical calculation from two dimensions to one dimension and is much faster than that of the traditional multi-slice method. The calculated result by the one-dimensional method is in agreement with that of the traditional one.